Merge branch 'for-linus' of git://git.o-hand.com/linux-rpurdie-backlight

[sfrench/cifs-2.6.git] / fs / ext4 / mballoc.c

/*
 * Copyright (c) 2003-2006, Cluster File Systems, Inc, info@clusterfs.com
 * Written by Alex Tomas <alex@clusterfs.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public Licens
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-
 */


/*
 * mballoc.c contains the multiblocks allocation routines
 */

#include "mballoc.h"
#include <linux/debugfs.h>
#include <linux/slab.h>
#include <trace/events/ext4.h>

/*
 * MUSTDO:
 *   - test ext4_ext_search_left() and ext4_ext_search_right()
 *   - search for metadata in few groups
 *
 * TODO v4:
 *   - normalization should take into account whether file is still open
 *   - discard preallocations if no free space left (policy?)
 *   - don't normalize tails
 *   - quota
 *   - reservation for superuser
 *
 * TODO v3:
 *   - bitmap read-ahead (proposed by Oleg Drokin aka green)
 *   - track min/max extents in each group for better group selection
 *   - mb_mark_used() may allocate chunk right after splitting buddy
 *   - tree of groups sorted by number of free blocks
 *   - error handling
 */

/*
 * The allocation request involve request for multiple number of blocks
 * near to the goal(block) value specified.
 *
 * During initialization phase of the allocator we decide to use the
 * group preallocation or inode preallocation depending on the size of
 * the file. The size of the file could be the resulting file size we
 * would have after allocation, or the current file size, which ever
 * is larger. If the size is less than sbi->s_mb_stream_request we
 * select to use the group preallocation. The default value of
 * s_mb_stream_request is 16 blocks. This can also be tuned via
 * /sys/fs/ext4/<partition>/mb_stream_req. The value is represented in
 * terms of number of blocks.
 *
 * The main motivation for having small file use group preallocation is to
 * ensure that we have small files closer together on the disk.
 *
 * First stage the allocator looks at the inode prealloc list,
 * ext4_inode_info->i_prealloc_list, which contains list of prealloc
 * spaces for this particular inode. The inode prealloc space is
 * represented as:
 *
 * pa_lstart -> the logical start block for this prealloc space
 * pa_pstart -> the physical start block for this prealloc space
 * pa_len    -> length for this prealloc space
 * pa_free   ->  free space available in this prealloc space
 *
 * The inode preallocation space is used looking at the _logical_ start
 * block. If only the logical file block falls within the range of prealloc
 * space we will consume the particular prealloc space. This make sure that
 * that the we have contiguous physical blocks representing the file blocks
 *
 * The important thing to be noted in case of inode prealloc space is that
 * we don't modify the values associated to inode prealloc space except
 * pa_free.
 *
 * If we are not able to find blocks in the inode prealloc space and if we
 * have the group allocation flag set then we look at the locality group
 * prealloc space. These are per CPU prealloc list repreasented as
 *
 * ext4_sb_info.s_locality_groups[smp_processor_id()]
 *
 * The reason for having a per cpu locality group is to reduce the contention
 * between CPUs. It is possible to get scheduled at this point.
 *
 * The locality group prealloc space is used looking at whether we have
 * enough free space (pa_free) withing the prealloc space.
 *
 * If we can't allocate blocks via inode prealloc or/and locality group
 * prealloc then we look at the buddy cache. The buddy cache is represented
 * by ext4_sb_info.s_buddy_cache (struct inode) whose file offset gets
 * mapped to the buddy and bitmap information regarding different
 * groups. The buddy information is attached to buddy cache inode so that
 * we can access them through the page cache. The information regarding
 * each group is loaded via ext4_mb_load_buddy.  The information involve
 * block bitmap and buddy information. The information are stored in the
 * inode as:
 *
 *  {                        page                        }
 *  [ group 0 bitmap][ group 0 buddy] [group 1][ group 1]...
 *
 *
 * one block each for bitmap and buddy information.  So for each group we
 * take up 2 blocks. A page can contain blocks_per_page (PAGE_CACHE_SIZE /
 * blocksize) blocks.  So it can have information regarding groups_per_page
 * which is blocks_per_page/2
 *
 * The buddy cache inode is not stored on disk. The inode is thrown
 * away when the filesystem is unmounted.
 *
 * We look for count number of blocks in the buddy cache. If we were able
 * to locate that many free blocks we return with additional information
 * regarding rest of the contiguous physical block available
 *
 * Before allocating blocks via buddy cache we normalize the request
 * blocks. This ensure we ask for more blocks that we needed. The extra
 * blocks that we get after allocation is added to the respective prealloc
 * list. In case of inode preallocation we follow a list of heuristics
 * based on file size. This can be found in ext4_mb_normalize_request. If
 * we are doing a group prealloc we try to normalize the request to
 * sbi->s_mb_group_prealloc. Default value of s_mb_group_prealloc is
 * 512 blocks. This can be tuned via
 * /sys/fs/ext4/<partition/mb_group_prealloc. The value is represented in
 * terms of number of blocks. If we have mounted the file system with -O
 * stripe=<value> option the group prealloc request is normalized to the
 * stripe value (sbi->s_stripe)
 *
 * The regular allocator(using the buddy cache) supports few tunables.
 *
 * /sys/fs/ext4/<partition>/mb_min_to_scan
 * /sys/fs/ext4/<partition>/mb_max_to_scan
 * /sys/fs/ext4/<partition>/mb_order2_req
 *
 * The regular allocator uses buddy scan only if the request len is power of
 * 2 blocks and the order of allocation is >= sbi->s_mb_order2_reqs. The
 * value of s_mb_order2_reqs can be tuned via
 * /sys/fs/ext4/<partition>/mb_order2_req.  If the request len is equal to
 * stripe size (sbi->s_stripe), we try to search for contiguous block in
 * stripe size. This should result in better allocation on RAID setups. If
 * not, we search in the specific group using bitmap for best extents. The
 * tunable min_to_scan and max_to_scan control the behaviour here.
 * min_to_scan indicate how long the mballoc __must__ look for a best
 * extent and max_to_scan indicates how long the mballoc __can__ look for a
 * best extent in the found extents. Searching for the blocks starts with
 * the group specified as the goal value in allocation context via
 * ac_g_ex. Each group is first checked based on the criteria whether it
 * can used for allocation. ext4_mb_good_group explains how the groups are
 * checked.
 *
 * Both the prealloc space are getting populated as above. So for the first
 * request we will hit the buddy cache which will result in this prealloc
 * space getting filled. The prealloc space is then later used for the
 * subsequent request.
 */

/*
 * mballoc operates on the following data:
 *  - on-disk bitmap
 *  - in-core buddy (actually includes buddy and bitmap)
 *  - preallocation descriptors (PAs)
 *
 * there are two types of preallocations:
 *  - inode
 *    assiged to specific inode and can be used for this inode only.
 *    it describes part of inode's space preallocated to specific
 *    physical blocks. any block from that preallocated can be used
 *    independent. the descriptor just tracks number of blocks left
 *    unused. so, before taking some block from descriptor, one must
 *    make sure corresponded logical block isn't allocated yet. this
 *    also means that freeing any block within descriptor's range
 *    must discard all preallocated blocks.
 *  - locality group
 *    assigned to specific locality group which does not translate to
 *    permanent set of inodes: inode can join and leave group. space
 *    from this type of preallocation can be used for any inode. thus
 *    it's consumed from the beginning to the end.
 *
 * relation between them can be expressed as:
 *    in-core buddy = on-disk bitmap + preallocation descriptors
 *
 * this mean blocks mballoc considers used are:
 *  - allocated blocks (persistent)
 *  - preallocated blocks (non-persistent)
 *
 * consistency in mballoc world means that at any time a block is either
 * free or used in ALL structures. notice: "any time" should not be read
 * literally -- time is discrete and delimited by locks.
 *
 *  to keep it simple, we don't use block numbers, instead we count number of
 *  blocks: how many blocks marked used/free in on-disk bitmap, buddy and PA.
 *
 * all operations can be expressed as:
 *  - init buddy:                       buddy = on-disk + PAs
 *  - new PA:                           buddy += N; PA = N
 *  - use inode PA:                     on-disk += N; PA -= N
 *  - discard inode PA                  buddy -= on-disk - PA; PA = 0
 *  - use locality group PA             on-disk += N; PA -= N
 *  - discard locality group PA         buddy -= PA; PA = 0
 *  note: 'buddy -= on-disk - PA' is used to show that on-disk bitmap
 *        is used in real operation because we can't know actual used
 *        bits from PA, only from on-disk bitmap
 *
 * if we follow this strict logic, then all operations above should be atomic.
 * given some of them can block, we'd have to use something like semaphores
 * killing performance on high-end SMP hardware. let's try to relax it using
 * the following knowledge:
 *  1) if buddy is referenced, it's already initialized
 *  2) while block is used in buddy and the buddy is referenced,
 *     nobody can re-allocate that block
 *  3) we work on bitmaps and '+' actually means 'set bits'. if on-disk has
 *     bit set and PA claims same block, it's OK. IOW, one can set bit in
 *     on-disk bitmap if buddy has same bit set or/and PA covers corresponded
 *     block
 *
 * so, now we're building a concurrency table:
 *  - init buddy vs.
 *    - new PA
 *      blocks for PA are allocated in the buddy, buddy must be referenced
 *      until PA is linked to allocation group to avoid concurrent buddy init
 *    - use inode PA
 *      we need to make sure that either on-disk bitmap or PA has uptodate data
 *      given (3) we care that PA-=N operation doesn't interfere with init
 *    - discard inode PA
 *      the simplest way would be to have buddy initialized by the discard
 *    - use locality group PA
 *      again PA-=N must be serialized with init
 *    - discard locality group PA
 *      the simplest way would be to have buddy initialized by the discard
 *  - new PA vs.
 *    - use inode PA
 *      i_data_sem serializes them
 *    - discard inode PA
 *      discard process must wait until PA isn't used by another process
 *    - use locality group PA
 *      some mutex should serialize them
 *    - discard locality group PA
 *      discard process must wait until PA isn't used by another process
 *  - use inode PA
 *    - use inode PA
 *      i_data_sem or another mutex should serializes them
 *    - discard inode PA
 *      discard process must wait until PA isn't used by another process
 *    - use locality group PA
 *      nothing wrong here -- they're different PAs covering different blocks
 *    - discard locality group PA
 *      discard process must wait until PA isn't used by another process
 *
 * now we're ready to make few consequences:
 *  - PA is referenced and while it is no discard is possible
 *  - PA is referenced until block isn't marked in on-disk bitmap
 *  - PA changes only after on-disk bitmap
 *  - discard must not compete with init. either init is done before
 *    any discard or they're serialized somehow
 *  - buddy init as sum of on-disk bitmap and PAs is done atomically
 *
 * a special case when we've used PA to emptiness. no need to modify buddy
 * in this case, but we should care about concurrent init
 *
 */

 /*
 * Logic in few words:
 *
 *  - allocation:
 *    load group
 *    find blocks
 *    mark bits in on-disk bitmap
 *    release group
 *
 *  - use preallocation:
 *    find proper PA (per-inode or group)
 *    load group
 *    mark bits in on-disk bitmap
 *    release group
 *    release PA
 *
 *  - free:
 *    load group
 *    mark bits in on-disk bitmap
 *    release group
 *
 *  - discard preallocations in group:
 *    mark PAs deleted
 *    move them onto local list
 *    load on-disk bitmap
 *    load group
 *    remove PA from object (inode or locality group)
 *    mark free blocks in-core
 *
 *  - discard inode's preallocations:
 */

/*
 * Locking rules
 *
 * Locks:
 *  - bitlock on a group        (group)
 *  - object (inode/locality)   (object)
 *  - per-pa lock               (pa)
 *
 * Paths:
 *  - new pa
 *    object
 *    group
 *
 *  - find and use pa:
 *    pa
 *
 *  - release consumed pa:
 *    pa
 *    group
 *    object
 *
 *  - generate in-core bitmap:
 *    group
 *        pa
 *
 *  - discard all for given object (inode, locality group):
 *    object
 *        pa
 *    group
 *
 *  - discard all for given group:
 *    group
 *        pa
 *    group
 *        object
 *
 */
static struct kmem_cache *ext4_pspace_cachep;
static struct kmem_cache *ext4_ac_cachep;
static struct kmem_cache *ext4_free_ext_cachep;
static void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
                                        ext4_group_t group);
static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
                                                ext4_group_t group);
static void release_blocks_on_commit(journal_t *journal, transaction_t *txn);

static inline void *mb_correct_addr_and_bit(int *bit, void *addr)
{
#if BITS_PER_LONG == 64
        *bit += ((unsigned long) addr & 7UL) << 3;
        addr = (void *) ((unsigned long) addr & ~7UL);
#elif BITS_PER_LONG == 32
        *bit += ((unsigned long) addr & 3UL) << 3;
        addr = (void *) ((unsigned long) addr & ~3UL);
#else
#error "how many bits you are?!"
#endif
        return addr;
}

static inline int mb_test_bit(int bit, void *addr)
{
        /*
         * ext4_test_bit on architecture like powerpc
         * needs unsigned long aligned address
         */
        addr = mb_correct_addr_and_bit(&bit, addr);
        return ext4_test_bit(bit, addr);
}

static inline void mb_set_bit(int bit, void *addr)
{
        addr = mb_correct_addr_and_bit(&bit, addr);
        ext4_set_bit(bit, addr);
}

static inline void mb_clear_bit(int bit, void *addr)
{
        addr = mb_correct_addr_and_bit(&bit, addr);
        ext4_clear_bit(bit, addr);
}

static inline int mb_find_next_zero_bit(void *addr, int max, int start)
{
        int fix = 0, ret, tmpmax;
        addr = mb_correct_addr_and_bit(&fix, addr);
        tmpmax = max + fix;
        start += fix;

        ret = ext4_find_next_zero_bit(addr, tmpmax, start) - fix;
        if (ret > max)
                return max;
        return ret;
}

static inline int mb_find_next_bit(void *addr, int max, int start)
{
        int fix = 0, ret, tmpmax;
        addr = mb_correct_addr_and_bit(&fix, addr);
        tmpmax = max + fix;
        start += fix;

        ret = ext4_find_next_bit(addr, tmpmax, start) - fix;
        if (ret > max)
                return max;
        return ret;
}

static void *mb_find_buddy(struct ext4_buddy *e4b, int order, int *max)
{
        char *bb;

        BUG_ON(EXT4_MB_BITMAP(e4b) == EXT4_MB_BUDDY(e4b));
        BUG_ON(max == NULL);

        if (order > e4b->bd_blkbits + 1) {
                *max = 0;
                return NULL;
        }

        /* at order 0 we see each particular block */
        *max = 1 << (e4b->bd_blkbits + 3);
        if (order == 0)
                return EXT4_MB_BITMAP(e4b);

        bb = EXT4_MB_BUDDY(e4b) + EXT4_SB(e4b->bd_sb)->s_mb_offsets[order];
        *max = EXT4_SB(e4b->bd_sb)->s_mb_maxs[order];

        return bb;
}

#ifdef DOUBLE_CHECK
static void mb_free_blocks_double(struct inode *inode, struct ext4_buddy *e4b,
                           int first, int count)
{
        int i;
        struct super_block *sb = e4b->bd_sb;

        if (unlikely(e4b->bd_info->bb_bitmap == NULL))
                return;
        assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));
        for (i = 0; i < count; i++) {
                if (!mb_test_bit(first + i, e4b->bd_info->bb_bitmap)) {
                        ext4_fsblk_t blocknr;

                        blocknr = ext4_group_first_block_no(sb, e4b->bd_group);
                        blocknr += first + i;
                        ext4_grp_locked_error(sb, e4b->bd_group,
                                   __func__, "double-free of inode"
                                   " %lu's block %llu(bit %u in group %u)",
                                   inode ? inode->i_ino : 0, blocknr,
                                   first + i, e4b->bd_group);
                }
                mb_clear_bit(first + i, e4b->bd_info->bb_bitmap);
        }
}

static void mb_mark_used_double(struct ext4_buddy *e4b, int first, int count)
{
        int i;

        if (unlikely(e4b->bd_info->bb_bitmap == NULL))
                return;
        assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
        for (i = 0; i < count; i++) {
                BUG_ON(mb_test_bit(first + i, e4b->bd_info->bb_bitmap));
                mb_set_bit(first + i, e4b->bd_info->bb_bitmap);
        }
}

static void mb_cmp_bitmaps(struct ext4_buddy *e4b, void *bitmap)
{
        if (memcmp(e4b->bd_info->bb_bitmap, bitmap, e4b->bd_sb->s_blocksize)) {
                unsigned char *b1, *b2;
                int i;
                b1 = (unsigned char *) e4b->bd_info->bb_bitmap;
                b2 = (unsigned char *) bitmap;
                for (i = 0; i < e4b->bd_sb->s_blocksize; i++) {
                        if (b1[i] != b2[i]) {
                                printk(KERN_ERR "corruption in group %u "
                                       "at byte %u(%u): %x in copy != %x "
                                       "on disk/prealloc\n",
                                       e4b->bd_group, i, i * 8, b1[i], b2[i]);
                                BUG();
                        }
                }
        }
}

#else
static inline void mb_free_blocks_double(struct inode *inode,
                                struct ext4_buddy *e4b, int first, int count)
{
        return;
}
static inline void mb_mark_used_double(struct ext4_buddy *e4b,
                                                int first, int count)
{
        return;
}
static inline void mb_cmp_bitmaps(struct ext4_buddy *e4b, void *bitmap)
{
        return;
}
#endif

#ifdef AGGRESSIVE_CHECK

#define MB_CHECK_ASSERT(assert)                                         \
do {                                                                    \
        if (!(assert)) {                                                \
                printk(KERN_EMERG                                       \
                        "Assertion failure in %s() at %s:%d: \"%s\"\n", \
                        function, file, line, # assert);                \
                BUG();                                                  \
        }                                                               \
} while (0)

static int __mb_check_buddy(struct ext4_buddy *e4b, char *file,
                                const char *function, int line)
{
        struct super_block *sb = e4b->bd_sb;
        int order = e4b->bd_blkbits + 1;
        int max;
        int max2;
        int i;
        int j;
        int k;
        int count;
        struct ext4_group_info *grp;
        int fragments = 0;
        int fstart;
        struct list_head *cur;
        void *buddy;
        void *buddy2;

        {
                static int mb_check_counter;
                if (mb_check_counter++ % 100 != 0)
                        return 0;
        }

        while (order > 1) {
                buddy = mb_find_buddy(e4b, order, &max);
                MB_CHECK_ASSERT(buddy);
                buddy2 = mb_find_buddy(e4b, order - 1, &max2);
                MB_CHECK_ASSERT(buddy2);
                MB_CHECK_ASSERT(buddy != buddy2);
                MB_CHECK_ASSERT(max * 2 == max2);

                count = 0;
                for (i = 0; i < max; i++) {

                        if (mb_test_bit(i, buddy)) {
                                /* only single bit in buddy2 may be 1 */
                                if (!mb_test_bit(i << 1, buddy2)) {
                                        MB_CHECK_ASSERT(
                                                mb_test_bit((i<<1)+1, buddy2));
                                } else if (!mb_test_bit((i << 1) + 1, buddy2)) {
                                        MB_CHECK_ASSERT(
                                                mb_test_bit(i << 1, buddy2));
                                }
                                continue;
                        }

                        /* both bits in buddy2 must be 0 */
                        MB_CHECK_ASSERT(mb_test_bit(i << 1, buddy2));
                        MB_CHECK_ASSERT(mb_test_bit((i << 1) + 1, buddy2));

                        for (j = 0; j < (1 << order); j++) {
                                k = (i * (1 << order)) + j;
                                MB_CHECK_ASSERT(
                                        !mb_test_bit(k, EXT4_MB_BITMAP(e4b)));
                        }
                        count++;
                }
                MB_CHECK_ASSERT(e4b->bd_info->bb_counters[order] == count);
                order--;
        }

        fstart = -1;
        buddy = mb_find_buddy(e4b, 0, &max);
        for (i = 0; i < max; i++) {
                if (!mb_test_bit(i, buddy)) {
                        MB_CHECK_ASSERT(i >= e4b->bd_info->bb_first_free);
                        if (fstart == -1) {
                                fragments++;
                                fstart = i;
                        }
                        continue;
                }
                fstart = -1;
                /* check used bits only */
                for (j = 0; j < e4b->bd_blkbits + 1; j++) {
                        buddy2 = mb_find_buddy(e4b, j, &max2);
                        k = i >> j;
                        MB_CHECK_ASSERT(k < max2);
                        MB_CHECK_ASSERT(mb_test_bit(k, buddy2));
                }
        }
        MB_CHECK_ASSERT(!EXT4_MB_GRP_NEED_INIT(e4b->bd_info));
        MB_CHECK_ASSERT(e4b->bd_info->bb_fragments == fragments);

        grp = ext4_get_group_info(sb, e4b->bd_group);
        buddy = mb_find_buddy(e4b, 0, &max);
        list_for_each(cur, &grp->bb_prealloc_list) {
                ext4_group_t groupnr;
                struct ext4_prealloc_space *pa;
                pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
                ext4_get_group_no_and_offset(sb, pa->pa_pstart, &groupnr, &k);
                MB_CHECK_ASSERT(groupnr == e4b->bd_group);
                for (i = 0; i < pa->pa_len; i++)
                        MB_CHECK_ASSERT(mb_test_bit(k + i, buddy));
        }
        return 0;
}
#undef MB_CHECK_ASSERT
#define mb_check_buddy(e4b) __mb_check_buddy(e4b,       \
                                        __FILE__, __func__, __LINE__)
#else
#define mb_check_buddy(e4b)
#endif

/* FIXME!! need more doc */
static void ext4_mb_mark_free_simple(struct super_block *sb,
                                void *buddy, ext4_grpblk_t first, ext4_grpblk_t len,
                                        struct ext4_group_info *grp)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        ext4_grpblk_t min;
        ext4_grpblk_t max;
        ext4_grpblk_t chunk;
        unsigned short border;

        BUG_ON(len > EXT4_BLOCKS_PER_GROUP(sb));

        border = 2 << sb->s_blocksize_bits;

        while (len > 0) {
                /* find how many blocks can be covered since this position */
                max = ffs(first | border) - 1;

                /* find how many blocks of power 2 we need to mark */
                min = fls(len) - 1;

                if (max < min)
                        min = max;
                chunk = 1 << min;

                /* mark multiblock chunks only */
                grp->bb_counters[min]++;
                if (min > 0)
                        mb_clear_bit(first >> min,
                                     buddy + sbi->s_mb_offsets[min]);

                len -= chunk;
                first += chunk;
        }
}

/*
 * Cache the order of the largest free extent we have available in this block
 * group.
 */
static void
mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
{
        int i;
        int bits;

        grp->bb_largest_free_order = -1; /* uninit */

        bits = sb->s_blocksize_bits + 1;
        for (i = bits; i >= 0; i--) {
                if (grp->bb_counters[i] > 0) {
                        grp->bb_largest_free_order = i;
                        break;
                }
        }
}

static noinline_for_stack
void ext4_mb_generate_buddy(struct super_block *sb,
                                void *buddy, void *bitmap, ext4_group_t group)
{
        struct ext4_group_info *grp = ext4_get_group_info(sb, group);
        ext4_grpblk_t max = EXT4_BLOCKS_PER_GROUP(sb);
        ext4_grpblk_t i = 0;
        ext4_grpblk_t first;
        ext4_grpblk_t len;
        unsigned free = 0;
        unsigned fragments = 0;
        unsigned long long period = get_cycles();

        /* initialize buddy from bitmap which is aggregation
         * of on-disk bitmap and preallocations */
        i = mb_find_next_zero_bit(bitmap, max, 0);
        grp->bb_first_free = i;
        while (i < max) {
                fragments++;
                first = i;
                i = mb_find_next_bit(bitmap, max, i);
                len = i - first;
                free += len;
                if (len > 1)
                        ext4_mb_mark_free_simple(sb, buddy, first, len, grp);
                else
                        grp->bb_counters[0]++;
                if (i < max)
                        i = mb_find_next_zero_bit(bitmap, max, i);
        }
        grp->bb_fragments = fragments;

        if (free != grp->bb_free) {
                ext4_grp_locked_error(sb, group,  __func__,
                        "EXT4-fs: group %u: %u blocks in bitmap, %u in gd",
                        group, free, grp->bb_free);
                /*
                 * If we intent to continue, we consider group descritor
                 * corrupt and update bb_free using bitmap value
                 */
                grp->bb_free = free;
        }
        mb_set_largest_free_order(sb, grp);

        clear_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &(grp->bb_state));

        period = get_cycles() - period;
        spin_lock(&EXT4_SB(sb)->s_bal_lock);
        EXT4_SB(sb)->s_mb_buddies_generated++;
        EXT4_SB(sb)->s_mb_generation_time += period;
        spin_unlock(&EXT4_SB(sb)->s_bal_lock);
}

/* The buddy information is attached the buddy cache inode
 * for convenience. The information regarding each group
 * is loaded via ext4_mb_load_buddy. The information involve
 * block bitmap and buddy information. The information are
 * stored in the inode as
 *
 * {                        page                        }
 * [ group 0 bitmap][ group 0 buddy] [group 1][ group 1]...
 *
 *
 * one block each for bitmap and buddy information.
 * So for each group we take up 2 blocks. A page can
 * contain blocks_per_page (PAGE_CACHE_SIZE / blocksize)  blocks.
 * So it can have information regarding groups_per_page which
 * is blocks_per_page/2
 *
 * Locking note:  This routine takes the block group lock of all groups
 * for this page; do not hold this lock when calling this routine!
 */

static int ext4_mb_init_cache(struct page *page, char *incore)
{
        ext4_group_t ngroups;
        int blocksize;
        int blocks_per_page;
        int groups_per_page;
        int err = 0;
        int i;
        ext4_group_t first_group;
        int first_block;
        struct super_block *sb;
        struct buffer_head *bhs;
        struct buffer_head **bh;
        struct inode *inode;
        char *data;
        char *bitmap;

        mb_debug(1, "init page %lu\n", page->index);

        inode = page->mapping->host;
        sb = inode->i_sb;
        ngroups = ext4_get_groups_count(sb);
        blocksize = 1 << inode->i_blkbits;
        blocks_per_page = PAGE_CACHE_SIZE / blocksize;

        groups_per_page = blocks_per_page >> 1;
        if (groups_per_page == 0)
                groups_per_page = 1;

        /* allocate buffer_heads to read bitmaps */
        if (groups_per_page > 1) {
                err = -ENOMEM;
                i = sizeof(struct buffer_head *) * groups_per_page;
                bh = kzalloc(i, GFP_NOFS);
                if (bh == NULL)
                        goto out;
        } else
                bh = &bhs;

        first_group = page->index * blocks_per_page / 2;

        /* read all groups the page covers into the cache */
        for (i = 0; i < groups_per_page; i++) {
                struct ext4_group_desc *desc;

                if (first_group + i >= ngroups)
                        break;

                err = -EIO;
                desc = ext4_get_group_desc(sb, first_group + i, NULL);
                if (desc == NULL)
                        goto out;

                err = -ENOMEM;
                bh[i] = sb_getblk(sb, ext4_block_bitmap(sb, desc));
                if (bh[i] == NULL)
                        goto out;

                if (bitmap_uptodate(bh[i]))
                        continue;

                lock_buffer(bh[i]);
                if (bitmap_uptodate(bh[i])) {
                        unlock_buffer(bh[i]);
                        continue;
                }
                ext4_lock_group(sb, first_group + i);
                if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
                        ext4_init_block_bitmap(sb, bh[i],
                                                first_group + i, desc);
                        set_bitmap_uptodate(bh[i]);
                        set_buffer_uptodate(bh[i]);
                        ext4_unlock_group(sb, first_group + i);
                        unlock_buffer(bh[i]);
                        continue;
                }
                ext4_unlock_group(sb, first_group + i);
                if (buffer_uptodate(bh[i])) {
                        /*
                         * if not uninit if bh is uptodate,
                         * bitmap is also uptodate
                         */
                        set_bitmap_uptodate(bh[i]);
                        unlock_buffer(bh[i]);
                        continue;
                }
                get_bh(bh[i]);
                /*
                 * submit the buffer_head for read. We can
                 * safely mark the bitmap as uptodate now.
                 * We do it here so the bitmap uptodate bit
                 * get set with buffer lock held.
                 */
                set_bitmap_uptodate(bh[i]);
                bh[i]->b_end_io = end_buffer_read_sync;
                submit_bh(READ, bh[i]);
                mb_debug(1, "read bitmap for group %u\n", first_group + i);
        }

        /* wait for I/O completion */
        for (i = 0; i < groups_per_page && bh[i]; i++)
                wait_on_buffer(bh[i]);

        err = -EIO;
        for (i = 0; i < groups_per_page && bh[i]; i++)
                if (!buffer_uptodate(bh[i]))
                        goto out;

        err = 0;
        first_block = page->index * blocks_per_page;
        /* init the page  */
        memset(page_address(page), 0xff, PAGE_CACHE_SIZE);
        for (i = 0; i < blocks_per_page; i++) {
                int group;
                struct ext4_group_info *grinfo;

                group = (first_block + i) >> 1;
                if (group >= ngroups)
                        break;

                /*
                 * data carry information regarding this
                 * particular group in the format specified
                 * above
                 *
                 */
                data = page_address(page) + (i * blocksize);
                bitmap = bh[group - first_group]->b_data;

                /*
                 * We place the buddy block and bitmap block
                 * close together
                 */
                if ((first_block + i) & 1) {
                        /* this is block of buddy */
                        BUG_ON(incore == NULL);
                        mb_debug(1, "put buddy for group %u in page %lu/%x\n",
                                group, page->index, i * blocksize);
                        trace_ext4_mb_buddy_bitmap_load(sb, group);
                        grinfo = ext4_get_group_info(sb, group);
                        grinfo->bb_fragments = 0;
                        memset(grinfo->bb_counters, 0,
                               sizeof(*grinfo->bb_counters) *
                                (sb->s_blocksize_bits+2));
                        /*
                         * incore got set to the group block bitmap below
                         */
                        ext4_lock_group(sb, group);
                        ext4_mb_generate_buddy(sb, data, incore, group);
                        ext4_unlock_group(sb, group);
                        incore = NULL;
                } else {
                        /* this is block of bitmap */
                        BUG_ON(incore != NULL);
                        mb_debug(1, "put bitmap for group %u in page %lu/%x\n",
                                group, page->index, i * blocksize);
                        trace_ext4_mb_bitmap_load(sb, group);

                        /* see comments in ext4_mb_put_pa() */
                        ext4_lock_group(sb, group);
                        memcpy(data, bitmap, blocksize);

                        /* mark all preallocated blks used in in-core bitmap */
                        ext4_mb_generate_from_pa(sb, data, group);
                        ext4_mb_generate_from_freelist(sb, data, group);
                        ext4_unlock_group(sb, group);

                        /* set incore so that the buddy information can be
                         * generated using this
                         */
                        incore = data;
                }
        }
        SetPageUptodate(page);

out:
        if (bh) {
                for (i = 0; i < groups_per_page && bh[i]; i++)
                        brelse(bh[i]);
                if (bh != &bhs)
                        kfree(bh);
        }
        return err;
}

/*
 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the
 * block group lock of all groups for this page; do not hold the BG lock when
 * calling this routine!
 */
static noinline_for_stack
int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)
{

        int ret = 0;
        void *bitmap;
        int blocks_per_page;
        int block, pnum, poff;
        int num_grp_locked = 0;
        struct ext4_group_info *this_grp;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct inode *inode = sbi->s_buddy_cache;
        struct page *page = NULL, *bitmap_page = NULL;

        mb_debug(1, "init group %u\n", group);
        blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;
        this_grp = ext4_get_group_info(sb, group);
        /*
         * This ensures that we don't reinit the buddy cache
         * page which map to the group from which we are already
         * allocating. If we are looking at the buddy cache we would
         * have taken a reference using ext4_mb_load_buddy and that
         * would have taken the alloc_sem lock.
         */
        num_grp_locked =  ext4_mb_get_buddy_cache_lock(sb, group);
        if (!EXT4_MB_GRP_NEED_INIT(this_grp)) {
                /*
                 * somebody initialized the group
                 * return without doing anything
                 */
                ret = 0;
                goto err;
        }
        /*
         * the buddy cache inode stores the block bitmap
         * and buddy information in consecutive blocks.
         * So for each group we need two blocks.
         */
        block = group * 2;
        pnum = block / blocks_per_page;
        poff = block % blocks_per_page;
        page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);
        if (page) {
                BUG_ON(page->mapping != inode->i_mapping);
                ret = ext4_mb_init_cache(page, NULL);
                if (ret) {
                        unlock_page(page);
                        goto err;
                }
                unlock_page(page);
        }
        if (page == NULL || !PageUptodate(page)) {
                ret = -EIO;
                goto err;
        }
        mark_page_accessed(page);
        bitmap_page = page;
        bitmap = page_address(page) + (poff * sb->s_blocksize);

        /* init buddy cache */
        block++;
        pnum = block / blocks_per_page;
        poff = block % blocks_per_page;
        page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);
        if (page == bitmap_page) {
                /*
                 * If both the bitmap and buddy are in
                 * the same page we don't need to force
                 * init the buddy
                 */
                unlock_page(page);
        } else if (page) {
                BUG_ON(page->mapping != inode->i_mapping);
                ret = ext4_mb_init_cache(page, bitmap);
                if (ret) {
                        unlock_page(page);
                        goto err;
                }
                unlock_page(page);
        }
        if (page == NULL || !PageUptodate(page)) {
                ret = -EIO;
                goto err;
        }
        mark_page_accessed(page);
err:
        ext4_mb_put_buddy_cache_lock(sb, group, num_grp_locked);
        if (bitmap_page)
                page_cache_release(bitmap_page);
        if (page)
                page_cache_release(page);
        return ret;
}

/*
 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the
 * block group lock of all groups for this page; do not hold the BG lock when
 * calling this routine!
 */
static noinline_for_stack int
ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,
                                        struct ext4_buddy *e4b)
{
        int blocks_per_page;
        int block;
        int pnum;
        int poff;
        struct page *page;
        int ret;
        struct ext4_group_info *grp;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct inode *inode = sbi->s_buddy_cache;

        mb_debug(1, "load group %u\n", group);

        blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;
        grp = ext4_get_group_info(sb, group);

        e4b->bd_blkbits = sb->s_blocksize_bits;
        e4b->bd_info = ext4_get_group_info(sb, group);
        e4b->bd_sb = sb;
        e4b->bd_group = group;
        e4b->bd_buddy_page = NULL;
        e4b->bd_bitmap_page = NULL;
        e4b->alloc_semp = &grp->alloc_sem;

        /* Take the read lock on the group alloc
         * sem. This would make sure a parallel
         * ext4_mb_init_group happening on other
         * groups mapped by the page is blocked
         * till we are done with allocation
         */
repeat_load_buddy:
        down_read(e4b->alloc_semp);

        if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
                /* we need to check for group need init flag
                 * with alloc_semp held so that we can be sure
                 * that new blocks didn't get added to the group
                 * when we are loading the buddy cache
                 */
                up_read(e4b->alloc_semp);
                /*
                 * we need full data about the group
                 * to make a good selection
                 */
                ret = ext4_mb_init_group(sb, group);
                if (ret)
                        return ret;
                goto repeat_load_buddy;
        }

        /*
         * the buddy cache inode stores the block bitmap
         * and buddy information in consecutive blocks.
         * So for each group we need two blocks.
         */
        block = group * 2;
        pnum = block / blocks_per_page;
        poff = block % blocks_per_page;

        /* we could use find_or_create_page(), but it locks page
         * what we'd like to avoid in fast path ... */
        page = find_get_page(inode->i_mapping, pnum);
        if (page == NULL || !PageUptodate(page)) {
                if (page)
                        /*
                         * drop the page reference and try
                         * to get the page with lock. If we
                         * are not uptodate that implies
                         * somebody just created the page but
                         * is yet to initialize the same. So
                         * wait for it to initialize.
                         */
                        page_cache_release(page);
                page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);
                if (page) {
                        BUG_ON(page->mapping != inode->i_mapping);
                        if (!PageUptodate(page)) {
                                ret = ext4_mb_init_cache(page, NULL);
                                if (ret) {
                                        unlock_page(page);
                                        goto err;
                                }
                                mb_cmp_bitmaps(e4b, page_address(page) +
                                               (poff * sb->s_blocksize));
                        }
                        unlock_page(page);
                }
        }
        if (page == NULL || !PageUptodate(page)) {
                ret = -EIO;
                goto err;
        }
        e4b->bd_bitmap_page = page;
        e4b->bd_bitmap = page_address(page) + (poff * sb->s_blocksize);
        mark_page_accessed(page);

        block++;
        pnum = block / blocks_per_page;
        poff = block % blocks_per_page;

        page = find_get_page(inode->i_mapping, pnum);
        if (page == NULL || !PageUptodate(page)) {
                if (page)
                        page_cache_release(page);
                page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);
                if (page) {
                        BUG_ON(page->mapping != inode->i_mapping);
                        if (!PageUptodate(page)) {
                                ret = ext4_mb_init_cache(page, e4b->bd_bitmap);
                                if (ret) {
                                        unlock_page(page);
                                        goto err;
                                }
                        }
                        unlock_page(page);
                }
        }
        if (page == NULL || !PageUptodate(page)) {
                ret = -EIO;
                goto err;
        }
        e4b->bd_buddy_page = page;
        e4b->bd_buddy = page_address(page) + (poff * sb->s_blocksize);
        mark_page_accessed(page);

        BUG_ON(e4b->bd_bitmap_page == NULL);
        BUG_ON(e4b->bd_buddy_page == NULL);

        return 0;

err:
        if (e4b->bd_bitmap_page)
                page_cache_release(e4b->bd_bitmap_page);
        if (e4b->bd_buddy_page)
                page_cache_release(e4b->bd_buddy_page);
        e4b->bd_buddy = NULL;
        e4b->bd_bitmap = NULL;

        /* Done with the buddy cache */
        up_read(e4b->alloc_semp);
        return ret;
}

static void ext4_mb_unload_buddy(struct ext4_buddy *e4b)
{
        if (e4b->bd_bitmap_page)
                page_cache_release(e4b->bd_bitmap_page);
        if (e4b->bd_buddy_page)
                page_cache_release(e4b->bd_buddy_page);
        /* Done with the buddy cache */
        if (e4b->alloc_semp)
                up_read(e4b->alloc_semp);
}


static int mb_find_order_for_block(struct ext4_buddy *e4b, int block)
{
        int order = 1;
        void *bb;

        BUG_ON(EXT4_MB_BITMAP(e4b) == EXT4_MB_BUDDY(e4b));
        BUG_ON(block >= (1 << (e4b->bd_blkbits + 3)));

        bb = EXT4_MB_BUDDY(e4b);
        while (order <= e4b->bd_blkbits + 1) {
                block = block >> 1;
                if (!mb_test_bit(block, bb)) {
                        /* this block is part of buddy of order 'order' */
                        return order;
                }
                bb += 1 << (e4b->bd_blkbits - order);
                order++;
        }
        return 0;
}

static void mb_clear_bits(void *bm, int cur, int len)
{
        __u32 *addr;

        len = cur + len;
        while (cur < len) {
                if ((cur & 31) == 0 && (len - cur) >= 32) {
                        /* fast path: clear whole word at once */
                        addr = bm + (cur >> 3);
                        *addr = 0;
                        cur += 32;
                        continue;
                }
                mb_clear_bit(cur, bm);
                cur++;
        }
}

static void mb_set_bits(void *bm, int cur, int len)
{
        __u32 *addr;

        len = cur + len;
        while (cur < len) {
                if ((cur & 31) == 0 && (len - cur) >= 32) {
                        /* fast path: set whole word at once */
                        addr = bm + (cur >> 3);
                        *addr = 0xffffffff;
                        cur += 32;
                        continue;
                }
                mb_set_bit(cur, bm);
                cur++;
        }
}

static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
                          int first, int count)
{
        int block = 0;
        int max = 0;
        int order;
        void *buddy;
        void *buddy2;
        struct super_block *sb = e4b->bd_sb;

        BUG_ON(first + count > (sb->s_blocksize << 3));
        assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));
        mb_check_buddy(e4b);
        mb_free_blocks_double(inode, e4b, first, count);

        e4b->bd_info->bb_free += count;
        if (first < e4b->bd_info->bb_first_free)
                e4b->bd_info->bb_first_free = first;

        /* let's maintain fragments counter */
        if (first != 0)
                block = !mb_test_bit(first - 1, EXT4_MB_BITMAP(e4b));
        if (first + count < EXT4_SB(sb)->s_mb_maxs[0])
                max = !mb_test_bit(first + count, EXT4_MB_BITMAP(e4b));
        if (block && max)
                e4b->bd_info->bb_fragments--;
        else if (!block && !max)
                e4b->bd_info->bb_fragments++;

        /* let's maintain buddy itself */
        while (count-- > 0) {
                block = first++;
                order = 0;

                if (!mb_test_bit(block, EXT4_MB_BITMAP(e4b))) {
                        ext4_fsblk_t blocknr;

                        blocknr = ext4_group_first_block_no(sb, e4b->bd_group);
                        blocknr += block;
                        ext4_grp_locked_error(sb, e4b->bd_group,
                                   __func__, "double-free of inode"
                                   " %lu's block %llu(bit %u in group %u)",
                                   inode ? inode->i_ino : 0, blocknr, block,
                                   e4b->bd_group);
                }
                mb_clear_bit(block, EXT4_MB_BITMAP(e4b));
                e4b->bd_info->bb_counters[order]++;

                /* start of the buddy */
                buddy = mb_find_buddy(e4b, order, &max);

                do {
                        block &= ~1UL;
                        if (mb_test_bit(block, buddy) ||
                                        mb_test_bit(block + 1, buddy))
                                break;

                        /* both the buddies are free, try to coalesce them */
                        buddy2 = mb_find_buddy(e4b, order + 1, &max);

                        if (!buddy2)
                                break;

                        if (order > 0) {
                                /* for special purposes, we don't set
                                 * free bits in bitmap */
                                mb_set_bit(block, buddy);
                                mb_set_bit(block + 1, buddy);
                        }
                        e4b->bd_info->bb_counters[order]--;
                        e4b->bd_info->bb_counters[order]--;

                        block = block >> 1;
                        order++;
                        e4b->bd_info->bb_counters[order]++;

                        mb_clear_bit(block, buddy2);
                        buddy = buddy2;
                } while (1);
        }
        mb_set_largest_free_order(sb, e4b->bd_info);
        mb_check_buddy(e4b);
}

static int mb_find_extent(struct ext4_buddy *e4b, int order, int block,
                                int needed, struct ext4_free_extent *ex)
{
        int next = block;
        int max;
        int ord;
        void *buddy;

        assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
        BUG_ON(ex == NULL);

        buddy = mb_find_buddy(e4b, order, &max);
        BUG_ON(buddy == NULL);
        BUG_ON(block >= max);
        if (mb_test_bit(block, buddy)) {
                ex->fe_len = 0;
                ex->fe_start = 0;
                ex->fe_group = 0;
                return 0;
        }

        /* FIXME dorp order completely ? */
        if (likely(order == 0)) {
                /* find actual order */
                order = mb_find_order_for_block(e4b, block);
                block = block >> order;
        }

        ex->fe_len = 1 << order;
        ex->fe_start = block << order;
        ex->fe_group = e4b->bd_group;

        /* calc difference from given start */
        next = next - ex->fe_start;
        ex->fe_len -= next;
        ex->fe_start += next;

        while (needed > ex->fe_len &&
               (buddy = mb_find_buddy(e4b, order, &max))) {

                if (block + 1 >= max)
                        break;

                next = (block + 1) * (1 << order);
                if (mb_test_bit(next, EXT4_MB_BITMAP(e4b)))
                        break;

                ord = mb_find_order_for_block(e4b, next);

                order = ord;
                block = next >> order;
                ex->fe_len += 1 << order;
        }

        BUG_ON(ex->fe_start + ex->fe_len > (1 << (e4b->bd_blkbits + 3)));
        return ex->fe_len;
}

static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
{
        int ord;
        int mlen = 0;
        int max = 0;
        int cur;
        int start = ex->fe_start;
        int len = ex->fe_len;
        unsigned ret = 0;
        int len0 = len;
        void *buddy;

        BUG_ON(start + len > (e4b->bd_sb->s_blocksize << 3));
        BUG_ON(e4b->bd_group != ex->fe_group);
        assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
        mb_check_buddy(e4b);
        mb_mark_used_double(e4b, start, len);

        e4b->bd_info->bb_free -= len;
        if (e4b->bd_info->bb_first_free == start)
                e4b->bd_info->bb_first_free += len;

        /* let's maintain fragments counter */
        if (start != 0)
                mlen = !mb_test_bit(start - 1, EXT4_MB_BITMAP(e4b));
        if (start + len < EXT4_SB(e4b->bd_sb)->s_mb_maxs[0])
                max = !mb_test_bit(start + len, EXT4_MB_BITMAP(e4b));
        if (mlen && max)
                e4b->bd_info->bb_fragments++;
        else if (!mlen && !max)
                e4b->bd_info->bb_fragments--;

        /* let's maintain buddy itself */
        while (len) {
                ord = mb_find_order_for_block(e4b, start);

                if (((start >> ord) << ord) == start && len >= (1 << ord)) {
                        /* the whole chunk may be allocated at once! */
                        mlen = 1 << ord;
                        buddy = mb_find_buddy(e4b, ord, &max);
                        BUG_ON((start >> ord) >= max);
                        mb_set_bit(start >> ord, buddy);
                        e4b->bd_info->bb_counters[ord]--;
                        start += mlen;
                        len -= mlen;
                        BUG_ON(len < 0);
                        continue;
                }

                /* store for history */
                if (ret == 0)
                        ret = len | (ord << 16);

                /* we have to split large buddy */
                BUG_ON(ord <= 0);
                buddy = mb_find_buddy(e4b, ord, &max);
                mb_set_bit(start >> ord, buddy);
                e4b->bd_info->bb_counters[ord]--;

                ord--;
                cur = (start >> ord) & ~1U;
                buddy = mb_find_buddy(e4b, ord, &max);
                mb_clear_bit(cur, buddy);
                mb_clear_bit(cur + 1, buddy);
                e4b->bd_info->bb_counters[ord]++;
                e4b->bd_info->bb_counters[ord]++;
        }
        mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);

        mb_set_bits(EXT4_MB_BITMAP(e4b), ex->fe_start, len0);
        mb_check_buddy(e4b);

        return ret;
}

/*
 * Must be called under group lock!
 */
static void ext4_mb_use_best_found(struct ext4_allocation_context *ac,
                                        struct ext4_buddy *e4b)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        int ret;

        BUG_ON(ac->ac_b_ex.fe_group != e4b->bd_group);
        BUG_ON(ac->ac_status == AC_STATUS_FOUND);

        ac->ac_b_ex.fe_len = min(ac->ac_b_ex.fe_len, ac->ac_g_ex.fe_len);
        ac->ac_b_ex.fe_logical = ac->ac_g_ex.fe_logical;
        ret = mb_mark_used(e4b, &ac->ac_b_ex);

        /* preallocation can change ac_b_ex, thus we store actually
         * allocated blocks for history */
        ac->ac_f_ex = ac->ac_b_ex;

        ac->ac_status = AC_STATUS_FOUND;
        ac->ac_tail = ret & 0xffff;
        ac->ac_buddy = ret >> 16;

        /*
         * take the page reference. We want the page to be pinned
         * so that we don't get a ext4_mb_init_cache_call for this
         * group until we update the bitmap. That would mean we
         * double allocate blocks. The reference is dropped
         * in ext4_mb_release_context
         */
        ac->ac_bitmap_page = e4b->bd_bitmap_page;
        get_page(ac->ac_bitmap_page);
        ac->ac_buddy_page = e4b->bd_buddy_page;
        get_page(ac->ac_buddy_page);
        /* on allocation we use ac to track the held semaphore */
        ac->alloc_semp =  e4b->alloc_semp;
        e4b->alloc_semp = NULL;
        /* store last allocated for subsequent stream allocation */
        if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
                spin_lock(&sbi->s_md_lock);
                sbi->s_mb_last_group = ac->ac_f_ex.fe_group;
                sbi->s_mb_last_start = ac->ac_f_ex.fe_start;
                spin_unlock(&sbi->s_md_lock);
        }
}

/*
 * regular allocator, for general purposes allocation
 */

static void ext4_mb_check_limits(struct ext4_allocation_context *ac,
                                        struct ext4_buddy *e4b,
                                        int finish_group)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_free_extent *bex = &ac->ac_b_ex;
        struct ext4_free_extent *gex = &ac->ac_g_ex;
        struct ext4_free_extent ex;
        int max;

        if (ac->ac_status == AC_STATUS_FOUND)
                return;
        /*
         * We don't want to scan for a whole year
         */
        if (ac->ac_found > sbi->s_mb_max_to_scan &&
                        !(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
                ac->ac_status = AC_STATUS_BREAK;
                return;
        }

        /*
         * Haven't found good chunk so far, let's continue
         */
        if (bex->fe_len < gex->fe_len)
                return;

        if ((finish_group || ac->ac_found > sbi->s_mb_min_to_scan)
                        && bex->fe_group == e4b->bd_group) {
                /* recheck chunk's availability - we don't know
                 * when it was found (within this lock-unlock
                 * period or not) */
                max = mb_find_extent(e4b, 0, bex->fe_start, gex->fe_len, &ex);
                if (max >= gex->fe_len) {
                        ext4_mb_use_best_found(ac, e4b);
                        return;
                }
        }
}

/*
 * The routine checks whether found extent is good enough. If it is,
 * then the extent gets marked used and flag is set to the context
 * to stop scanning. Otherwise, the extent is compared with the
 * previous found extent and if new one is better, then it's stored
 * in the context. Later, the best found extent will be used, if
 * mballoc can't find good enough extent.
 *
 * FIXME: real allocation policy is to be designed yet!
 */
static void ext4_mb_measure_extent(struct ext4_allocation_context *ac,
                                        struct ext4_free_extent *ex,
                                        struct ext4_buddy *e4b)
{
        struct ext4_free_extent *bex = &ac->ac_b_ex;
        struct ext4_free_extent *gex = &ac->ac_g_ex;

        BUG_ON(ex->fe_len <= 0);
        BUG_ON(ex->fe_len > EXT4_BLOCKS_PER_GROUP(ac->ac_sb));
        BUG_ON(ex->fe_start >= EXT4_BLOCKS_PER_GROUP(ac->ac_sb));
        BUG_ON(ac->ac_status != AC_STATUS_CONTINUE);

        ac->ac_found++;

        /*
         * The special case - take what you catch first
         */
        if (unlikely(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
                *bex = *ex;
                ext4_mb_use_best_found(ac, e4b);
                return;
        }

        /*
         * Let's check whether the chuck is good enough
         */
        if (ex->fe_len == gex->fe_len) {
                *bex = *ex;
                ext4_mb_use_best_found(ac, e4b);
                return;
        }

        /*
         * If this is first found extent, just store it in the context
         */
        if (bex->fe_len == 0) {
                *bex = *ex;
                return;
        }

        /*
         * If new found extent is better, store it in the context
         */
        if (bex->fe_len < gex->fe_len) {
                /* if the request isn't satisfied, any found extent
                 * larger than previous best one is better */
                if (ex->fe_len > bex->fe_len)
                        *bex = *ex;
        } else if (ex->fe_len > gex->fe_len) {
                /* if the request is satisfied, then we try to find
                 * an extent that still satisfy the request, but is
                 * smaller than previous one */
                if (ex->fe_len < bex->fe_len)
                        *bex = *ex;
        }

        ext4_mb_check_limits(ac, e4b, 0);
}

static noinline_for_stack
int ext4_mb_try_best_found(struct ext4_allocation_context *ac,
                                        struct ext4_buddy *e4b)
{
        struct ext4_free_extent ex = ac->ac_b_ex;
        ext4_group_t group = ex.fe_group;
        int max;
        int err;

        BUG_ON(ex.fe_len <= 0);
        err = ext4_mb_load_buddy(ac->ac_sb, group, e4b);
        if (err)
                return err;

        ext4_lock_group(ac->ac_sb, group);
        max = mb_find_extent(e4b, 0, ex.fe_start, ex.fe_len, &ex);

        if (max > 0) {
                ac->ac_b_ex = ex;
                ext4_mb_use_best_found(ac, e4b);
        }

        ext4_unlock_group(ac->ac_sb, group);
        ext4_mb_unload_buddy(e4b);

        return 0;
}

static noinline_for_stack
int ext4_mb_find_by_goal(struct ext4_allocation_context *ac,
                                struct ext4_buddy *e4b)
{
        ext4_group_t group = ac->ac_g_ex.fe_group;
        int max;
        int err;
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_free_extent ex;

        if (!(ac->ac_flags & EXT4_MB_HINT_TRY_GOAL))
                return 0;

        err = ext4_mb_load_buddy(ac->ac_sb, group, e4b);
        if (err)
                return err;

        ext4_lock_group(ac->ac_sb, group);
        max = mb_find_extent(e4b, 0, ac->ac_g_ex.fe_start,
                             ac->ac_g_ex.fe_len, &ex);

        if (max >= ac->ac_g_ex.fe_len && ac->ac_g_ex.fe_len == sbi->s_stripe) {
                ext4_fsblk_t start;

                start = ext4_group_first_block_no(ac->ac_sb, e4b->bd_group) +
                        ex.fe_start;
                /* use do_div to get remainder (would be 64-bit modulo) */
                if (do_div(start, sbi->s_stripe) == 0) {
                        ac->ac_found++;
                        ac->ac_b_ex = ex;
                        ext4_mb_use_best_found(ac, e4b);
                }
        } else if (max >= ac->ac_g_ex.fe_len) {
                BUG_ON(ex.fe_len <= 0);
                BUG_ON(ex.fe_group != ac->ac_g_ex.fe_group);
                BUG_ON(ex.fe_start != ac->ac_g_ex.fe_start);
                ac->ac_found++;
                ac->ac_b_ex = ex;
                ext4_mb_use_best_found(ac, e4b);
        } else if (max > 0 && (ac->ac_flags & EXT4_MB_HINT_MERGE)) {
                /* Sometimes, caller may want to merge even small
                 * number of blocks to an existing extent */
                BUG_ON(ex.fe_len <= 0);
                BUG_ON(ex.fe_group != ac->ac_g_ex.fe_group);
                BUG_ON(ex.fe_start != ac->ac_g_ex.fe_start);
                ac->ac_found++;
                ac->ac_b_ex = ex;
                ext4_mb_use_best_found(ac, e4b);
        }
        ext4_unlock_group(ac->ac_sb, group);
        ext4_mb_unload_buddy(e4b);

        return 0;
}

/*
 * The routine scans buddy structures (not bitmap!) from given order
 * to max order and tries to find big enough chunk to satisfy the req
 */
static noinline_for_stack
void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
                                        struct ext4_buddy *e4b)
{
        struct super_block *sb = ac->ac_sb;
        struct ext4_group_info *grp = e4b->bd_info;
        void *buddy;
        int i;
        int k;
        int max;

        BUG_ON(ac->ac_2order <= 0);
        for (i = ac->ac_2order; i <= sb->s_blocksize_bits + 1; i++) {
                if (grp->bb_counters[i] == 0)
                        continue;

                buddy = mb_find_buddy(e4b, i, &max);
                BUG_ON(buddy == NULL);

                k = mb_find_next_zero_bit(buddy, max, 0);
                BUG_ON(k >= max);

                ac->ac_found++;

                ac->ac_b_ex.fe_len = 1 << i;
                ac->ac_b_ex.fe_start = k << i;
                ac->ac_b_ex.fe_group = e4b->bd_group;

                ext4_mb_use_best_found(ac, e4b);

                BUG_ON(ac->ac_b_ex.fe_len != ac->ac_g_ex.fe_len);

                if (EXT4_SB(sb)->s_mb_stats)
                        atomic_inc(&EXT4_SB(sb)->s_bal_2orders);

                break;
        }
}

/*
 * The routine scans the group and measures all found extents.
 * In order to optimize scanning, caller must pass number of
 * free blocks in the group, so the routine can know upper limit.
 */
static noinline_for_stack
void ext4_mb_complex_scan_group(struct ext4_allocation_context *ac,
                                        struct ext4_buddy *e4b)
{
        struct super_block *sb = ac->ac_sb;
        void *bitmap = EXT4_MB_BITMAP(e4b);
        struct ext4_free_extent ex;
        int i;
        int free;

        free = e4b->bd_info->bb_free;
        BUG_ON(free <= 0);

        i = e4b->bd_info->bb_first_free;

        while (free && ac->ac_status == AC_STATUS_CONTINUE) {
                i = mb_find_next_zero_bit(bitmap,
                                                EXT4_BLOCKS_PER_GROUP(sb), i);
                if (i >= EXT4_BLOCKS_PER_GROUP(sb)) {
                        /*
                         * IF we have corrupt bitmap, we won't find any
                         * free blocks even though group info says we
                         * we have free blocks
                         */
                        ext4_grp_locked_error(sb, e4b->bd_group,
                                        __func__, "%d free blocks as per "
                                        "group info. But bitmap says 0",
                                        free);
                        break;
                }

                mb_find_extent(e4b, 0, i, ac->ac_g_ex.fe_len, &ex);
                BUG_ON(ex.fe_len <= 0);
                if (free < ex.fe_len) {
                        ext4_grp_locked_error(sb, e4b->bd_group,
                                        __func__, "%d free blocks as per "
                                        "group info. But got %d blocks",
                                        free, ex.fe_len);
                        /*
                         * The number of free blocks differs. This mostly
                         * indicate that the bitmap is corrupt. So exit
                         * without claiming the space.
                         */
                        break;
                }

                ext4_mb_measure_extent(ac, &ex, e4b);

                i += ex.fe_len;
                free -= ex.fe_len;
        }

        ext4_mb_check_limits(ac, e4b, 1);
}

/*
 * This is a special case for storages like raid5
 * we try to find stripe-aligned chunks for stripe-size requests
 * XXX should do so at least for multiples of stripe size as well
 */
static noinline_for_stack
void ext4_mb_scan_aligned(struct ext4_allocation_context *ac,
                                 struct ext4_buddy *e4b)
{
        struct super_block *sb = ac->ac_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        void *bitmap = EXT4_MB_BITMAP(e4b);
        struct ext4_free_extent ex;
        ext4_fsblk_t first_group_block;
        ext4_fsblk_t a;
        ext4_grpblk_t i;
        int max;

        BUG_ON(sbi->s_stripe == 0);

        /* find first stripe-aligned block in group */
        first_group_block = ext4_group_first_block_no(sb, e4b->bd_group);

        a = first_group_block + sbi->s_stripe - 1;
        do_div(a, sbi->s_stripe);
        i = (a * sbi->s_stripe) - first_group_block;

        while (i < EXT4_BLOCKS_PER_GROUP(sb)) {
                if (!mb_test_bit(i, bitmap)) {
                        max = mb_find_extent(e4b, 0, i, sbi->s_stripe, &ex);
                        if (max >= sbi->s_stripe) {
                                ac->ac_found++;
                                ac->ac_b_ex = ex;
                                ext4_mb_use_best_found(ac, e4b);
                                break;
                        }
                }
                i += sbi->s_stripe;
        }
}

/* This is now called BEFORE we load the buddy bitmap. */
static int ext4_mb_good_group(struct ext4_allocation_context *ac,
                                ext4_group_t group, int cr)
{
        unsigned free, fragments;
        int flex_size = ext4_flex_bg_size(EXT4_SB(ac->ac_sb));
        struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);

        BUG_ON(cr < 0 || cr >= 4);

        /* We only do this if the grp has never been initialized */
        if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
                int ret = ext4_mb_init_group(ac->ac_sb, group);
                if (ret)
                        return 0;
        }

        free = grp->bb_free;
        fragments = grp->bb_fragments;
        if (free == 0)
                return 0;
        if (fragments == 0)
                return 0;

        switch (cr) {
        case 0:
                BUG_ON(ac->ac_2order == 0);

                if (grp->bb_largest_free_order < ac->ac_2order)
                        return 0;

                /* Avoid using the first bg of a flexgroup for data files */
                if ((ac->ac_flags & EXT4_MB_HINT_DATA) &&
                    (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) &&
                    ((group % flex_size) == 0))
                        return 0;

                return 1;
        case 1:
                if ((free / fragments) >= ac->ac_g_ex.fe_len)
                        return 1;
                break;
        case 2:
                if (free >= ac->ac_g_ex.fe_len)
                        return 1;
                break;
        case 3:
                return 1;
        default:
                BUG();
        }

        return 0;
}

/*
 * lock the group_info alloc_sem of all the groups
 * belonging to the same buddy cache page. This
 * make sure other parallel operation on the buddy
 * cache doesn't happen  whild holding the buddy cache
 * lock
 */
int ext4_mb_get_buddy_cache_lock(struct super_block *sb, ext4_group_t group)
{
        int i;
        int block, pnum;
        int blocks_per_page;
        int groups_per_page;
        ext4_group_t ngroups = ext4_get_groups_count(sb);
        ext4_group_t first_group;
        struct ext4_group_info *grp;

        blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;
        /*
         * the buddy cache inode stores the block bitmap
         * and buddy information in consecutive blocks.
         * So for each group we need two blocks.
         */
        block = group * 2;
        pnum = block / blocks_per_page;
        first_group = pnum * blocks_per_page / 2;

        groups_per_page = blocks_per_page >> 1;
        if (groups_per_page == 0)
                groups_per_page = 1;
        /* read all groups the page covers into the cache */
        for (i = 0; i < groups_per_page; i++) {

                if ((first_group + i) >= ngroups)
                        break;
                grp = ext4_get_group_info(sb, first_group + i);
                /* take all groups write allocation
                 * semaphore. This make sure there is
                 * no block allocation going on in any
                 * of that groups
                 */
                down_write_nested(&grp->alloc_sem, i);
        }
        return i;
}

void ext4_mb_put_buddy_cache_lock(struct super_block *sb,
                                        ext4_group_t group, int locked_group)
{
        int i;
        int block, pnum;
        int blocks_per_page;
        ext4_group_t first_group;
        struct ext4_group_info *grp;

        blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;
        /*
         * the buddy cache inode stores the block bitmap
         * and buddy information in consecutive blocks.
         * So for each group we need two blocks.
         */
        block = group * 2;
        pnum = block / blocks_per_page;
        first_group = pnum * blocks_per_page / 2;
        /* release locks on all the groups */
        for (i = 0; i < locked_group; i++) {

                grp = ext4_get_group_info(sb, first_group + i);
                /* take all groups write allocation
                 * semaphore. This make sure there is
                 * no block allocation going on in any
                 * of that groups
                 */
                up_write(&grp->alloc_sem);
        }

}

static noinline_for_stack int
ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
{
        ext4_group_t ngroups, group, i;
        int cr;
        int err = 0;
        int bsbits;
        struct ext4_sb_info *sbi;
        struct super_block *sb;
        struct ext4_buddy e4b;

        sb = ac->ac_sb;
        sbi = EXT4_SB(sb);
        ngroups = ext4_get_groups_count(sb);
        /* non-extent files are limited to low blocks/groups */
        if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)))
                ngroups = sbi->s_blockfile_groups;

        BUG_ON(ac->ac_status == AC_STATUS_FOUND);

        /* first, try the goal */
        err = ext4_mb_find_by_goal(ac, &e4b);
        if (err || ac->ac_status == AC_STATUS_FOUND)
                goto out;

        if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
                goto out;

        /*
         * ac->ac2_order is set only if the fe_len is a power of 2
         * if ac2_order is set we also set criteria to 0 so that we
         * try exact allocation using buddy.
         */
        i = fls(ac->ac_g_ex.fe_len);
        ac->ac_2order = 0;
        /*
         * We search using buddy data only if the order of the request
         * is greater than equal to the sbi_s_mb_order2_reqs
         * You can tune it via /sys/fs/ext4/<partition>/mb_order2_req
         */
        if (i >= sbi->s_mb_order2_reqs) {
                /*
                 * This should tell if fe_len is exactly power of 2
                 */
                if ((ac->ac_g_ex.fe_len & (~(1 << (i - 1)))) == 0)
                        ac->ac_2order = i - 1;
        }

        bsbits = ac->ac_sb->s_blocksize_bits;

        /* if stream allocation is enabled, use global goal */
        if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
                /* TBD: may be hot point */
                spin_lock(&sbi->s_md_lock);
                ac->ac_g_ex.fe_group = sbi->s_mb_last_group;
                ac->ac_g_ex.fe_start = sbi->s_mb_last_start;
                spin_unlock(&sbi->s_md_lock);
        }

        /* Let's just scan groups to find more-less suitable blocks */
        cr = ac->ac_2order ? 0 : 1;
        /*
         * cr == 0 try to get exact allocation,
         * cr == 3  try to get anything
         */
repeat:
        for (; cr < 4 && ac->ac_status == AC_STATUS_CONTINUE; cr++) {
                ac->ac_criteria = cr;
                /*
                 * searching for the right group start
                 * from the goal value specified
                 */
                group = ac->ac_g_ex.fe_group;

                for (i = 0; i < ngroups; group++, i++) {
                        if (group == ngroups)
                                group = 0;

                        /* This now checks without needing the buddy page */
                        if (!ext4_mb_good_group(ac, group, cr))
                                continue;

                        err = ext4_mb_load_buddy(sb, group, &e4b);
                        if (err)
                                goto out;

                        ext4_lock_group(sb, group);

                        /*
                         * We need to check again after locking the
                         * block group
                         */
                        if (!ext4_mb_good_group(ac, group, cr)) {
                                ext4_unlock_group(sb, group);
                                ext4_mb_unload_buddy(&e4b);
                                continue;
                        }

                        ac->ac_groups_scanned++;
                        if (cr == 0)
                                ext4_mb_simple_scan_group(ac, &e4b);
                        else if (cr == 1 &&
                                        ac->ac_g_ex.fe_len == sbi->s_stripe)
                                ext4_mb_scan_aligned(ac, &e4b);
                        else
                                ext4_mb_complex_scan_group(ac, &e4b);

                        ext4_unlock_group(sb, group);
                        ext4_mb_unload_buddy(&e4b);

                        if (ac->ac_status != AC_STATUS_CONTINUE)
                                break;
                }
        }

        if (ac->ac_b_ex.fe_len > 0 && ac->ac_status != AC_STATUS_FOUND &&
            !(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
                /*
                 * We've been searching too long. Let's try to allocate
                 * the best chunk we've found so far
                 */

                ext4_mb_try_best_found(ac, &e4b);
                if (ac->ac_status != AC_STATUS_FOUND) {
                        /*
                         * Someone more lucky has already allocated it.
                         * The only thing we can do is just take first
                         * found block(s)
                        printk(KERN_DEBUG "EXT4-fs: someone won our chunk\n");
                         */
                        ac->ac_b_ex.fe_group = 0;
                        ac->ac_b_ex.fe_start = 0;
                        ac->ac_b_ex.fe_len = 0;
                        ac->ac_status = AC_STATUS_CONTINUE;
                        ac->ac_flags |= EXT4_MB_HINT_FIRST;
                        cr = 3;
                        atomic_inc(&sbi->s_mb_lost_chunks);
                        goto repeat;
                }
        }
out:
        return err;
}

static void *ext4_mb_seq_groups_start(struct seq_file *seq, loff_t *pos)
{
        struct super_block *sb = seq->private;
        ext4_group_t group;

        if (*pos < 0 || *pos >= ext4_get_groups_count(sb))
                return NULL;
        group = *pos + 1;
        return (void *) ((unsigned long) group);
}

static void *ext4_mb_seq_groups_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct super_block *sb = seq->private;
        ext4_group_t group;

        ++*pos;
        if (*pos < 0 || *pos >= ext4_get_groups_count(sb))
                return NULL;
        group = *pos + 1;
        return (void *) ((unsigned long) group);
}

static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
{
        struct super_block *sb = seq->private;
        ext4_group_t group = (ext4_group_t) ((unsigned long) v);
        int i;
        int err;
        struct ext4_buddy e4b;
        struct sg {
                struct ext4_group_info info;
                ext4_grpblk_t counters[16];
        } sg;

        group--;
        if (group == 0)
                seq_printf(seq, "#%-5s: %-5s %-5s %-5s "
                                "[ %-5s %-5s %-5s %-5s %-5s %-5s %-5s "
                                  "%-5s %-5s %-5s %-5s %-5s %-5s %-5s ]\n",
                           "group", "free", "frags", "first",
                           "2^0", "2^1", "2^2", "2^3", "2^4", "2^5", "2^6",
                           "2^7", "2^8", "2^9", "2^10", "2^11", "2^12", "2^13");

        i = (sb->s_blocksize_bits + 2) * sizeof(sg.info.bb_counters[0]) +
                sizeof(struct ext4_group_info);
        err = ext4_mb_load_buddy(sb, group, &e4b);
        if (err) {
                seq_printf(seq, "#%-5u: I/O error\n", group);
                return 0;
        }
        ext4_lock_group(sb, group);
        memcpy(&sg, ext4_get_group_info(sb, group), i);
        ext4_unlock_group(sb, group);
        ext4_mb_unload_buddy(&e4b);

        seq_printf(seq, "#%-5u: %-5u %-5u %-5u [", group, sg.info.bb_free,
                        sg.info.bb_fragments, sg.info.bb_first_free);
        for (i = 0; i <= 13; i++)
                seq_printf(seq, " %-5u", i <= sb->s_blocksize_bits + 1 ?
                                sg.info.bb_counters[i] : 0);
        seq_printf(seq, " ]\n");

        return 0;
}

static void ext4_mb_seq_groups_stop(struct seq_file *seq, void *v)
{
}

static const struct seq_operations ext4_mb_seq_groups_ops = {
        .start  = ext4_mb_seq_groups_start,
        .next   = ext4_mb_seq_groups_next,
        .stop   = ext4_mb_seq_groups_stop,
        .show   = ext4_mb_seq_groups_show,
};

static int ext4_mb_seq_groups_open(struct inode *inode, struct file *file)
{
        struct super_block *sb = PDE(inode)->data;
        int rc;

        rc = seq_open(file, &ext4_mb_seq_groups_ops);
        if (rc == 0) {
                struct seq_file *m = (struct seq_file *)file->private_data;
                m->private = sb;
        }
        return rc;

}

static const struct file_operations ext4_mb_seq_groups_fops = {
        .owner          = THIS_MODULE,
        .open           = ext4_mb_seq_groups_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};


/* Create and initialize ext4_group_info data for the given group. */
int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
                          struct ext4_group_desc *desc)
{
        int i, len;
        int metalen = 0;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_group_info **meta_group_info;

        /*
         * First check if this group is the first of a reserved block.
         * If it's true, we have to allocate a new table of pointers
         * to ext4_group_info structures
         */
        if (group % EXT4_DESC_PER_BLOCK(sb) == 0) {
                metalen = sizeof(*meta_group_info) <<
                        EXT4_DESC_PER_BLOCK_BITS(sb);
                meta_group_info = kmalloc(metalen, GFP_KERNEL);
                if (meta_group_info == NULL) {
                        printk(KERN_ERR "EXT4-fs: can't allocate mem for a "
                               "buddy group\n");
                        goto exit_meta_group_info;
                }
                sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)] =
                        meta_group_info;
        }

        /*
         * calculate needed size. if change bb_counters size,
         * don't forget about ext4_mb_generate_buddy()
         */
        len = offsetof(typeof(**meta_group_info),
                       bb_counters[sb->s_blocksize_bits + 2]);

        meta_group_info =
                sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)];
        i = group & (EXT4_DESC_PER_BLOCK(sb) - 1);

        meta_group_info[i] = kzalloc(len, GFP_KERNEL);
        if (meta_group_info[i] == NULL) {
                printk(KERN_ERR "EXT4-fs: can't allocate buddy mem\n");
                goto exit_group_info;
        }
        set_bit(EXT4_GROUP_INFO_NEED_INIT_BIT,
                &(meta_group_info[i]->bb_state));

        /*
         * initialize bb_free to be able to skip
         * empty groups without initialization
         */
        if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
                meta_group_info[i]->bb_free =
                        ext4_free_blocks_after_init(sb, group, desc);
        } else {
                meta_group_info[i]->bb_free =
                        ext4_free_blks_count(sb, desc);
        }

        INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);
        init_rwsem(&meta_group_info[i]->alloc_sem);
        meta_group_info[i]->bb_free_root = RB_ROOT;
        meta_group_info[i]->bb_largest_free_order = -1;  /* uninit */

#ifdef DOUBLE_CHECK
        {
                struct buffer_head *bh;
                meta_group_info[i]->bb_bitmap =
                        kmalloc(sb->s_blocksize, GFP_KERNEL);
                BUG_ON(meta_group_info[i]->bb_bitmap == NULL);
                bh = ext4_read_block_bitmap(sb, group);
                BUG_ON(bh == NULL);
                memcpy(meta_group_info[i]->bb_bitmap, bh->b_data,
                        sb->s_blocksize);
                put_bh(bh);
        }
#endif

        return 0;

exit_group_info:
        /* If a meta_group_info table has been allocated, release it now */
        if (group % EXT4_DESC_PER_BLOCK(sb) == 0)
                kfree(sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)]);
exit_meta_group_info:
        return -ENOMEM;
} /* ext4_mb_add_groupinfo */

static int ext4_mb_init_backend(struct super_block *sb)
{
        ext4_group_t ngroups = ext4_get_groups_count(sb);
        ext4_group_t i;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_super_block *es = sbi->s_es;
        int num_meta_group_infos;
        int num_meta_group_infos_max;
        int array_size;
        struct ext4_group_desc *desc;

        /* This is the number of blocks used by GDT */
        num_meta_group_infos = (ngroups + EXT4_DESC_PER_BLOCK(sb) -
                                1) >> EXT4_DESC_PER_BLOCK_BITS(sb);

        /*
         * This is the total number of blocks used by GDT including
         * the number of reserved blocks for GDT.
         * The s_group_info array is allocated with this value
         * to allow a clean online resize without a complex
         * manipulation of pointer.
         * The drawback is the unused memory when no resize
         * occurs but it's very low in terms of pages
         * (see comments below)
         * Need to handle this properly when META_BG resizing is allowed
         */
        num_meta_group_infos_max = num_meta_group_infos +
                                le16_to_cpu(es->s_reserved_gdt_blocks);

        /*
         * array_size is the size of s_group_info array. We round it
         * to the next power of two because this approximation is done
         * internally by kmalloc so we can have some more memory
         * for free here (e.g. may be used for META_BG resize).
         */
        array_size = 1;
        while (array_size < sizeof(*sbi->s_group_info) *
               num_meta_group_infos_max)
                array_size = array_size << 1;
        /* An 8TB filesystem with 64-bit pointers requires a 4096 byte
         * kmalloc. A 128kb malloc should suffice for a 256TB filesystem.
         * So a two level scheme suffices for now. */
        sbi->s_group_info = kmalloc(array_size, GFP_KERNEL);
        if (sbi->s_group_info == NULL) {
                printk(KERN_ERR "EXT4-fs: can't allocate buddy meta group\n");
                return -ENOMEM;
        }
        sbi->s_buddy_cache = new_inode(sb);
        if (sbi->s_buddy_cache == NULL) {
                printk(KERN_ERR "EXT4-fs: can't get new inode\n");
                goto err_freesgi;
        }
        EXT4_I(sbi->s_buddy_cache)->i_disksize = 0;
        for (i = 0; i < ngroups; i++) {
                desc = ext4_get_group_desc(sb, i, NULL);
                if (desc == NULL) {
                        printk(KERN_ERR
                                "EXT4-fs: can't read descriptor %u\n", i);
                        goto err_freebuddy;
                }
                if (ext4_mb_add_groupinfo(sb, i, desc) != 0)
                        goto err_freebuddy;
        }

        return 0;

err_freebuddy:
        while (i-- > 0)
                kfree(ext4_get_group_info(sb, i));
        i = num_meta_group_infos;
        while (i-- > 0)
                kfree(sbi->s_group_info[i]);
        iput(sbi->s_buddy_cache);
err_freesgi:
        kfree(sbi->s_group_info);
        return -ENOMEM;
}

int ext4_mb_init(struct super_block *sb, int needs_recovery)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        unsigned i, j;
        unsigned offset;
        unsigned max;
        int ret;

        i = (sb->s_blocksize_bits + 2) * sizeof(*sbi->s_mb_offsets);

        sbi->s_mb_offsets = kmalloc(i, GFP_KERNEL);
        if (sbi->s_mb_offsets == NULL) {
                return -ENOMEM;
        }

        i = (sb->s_blocksize_bits + 2) * sizeof(*sbi->s_mb_maxs);
        sbi->s_mb_maxs = kmalloc(i, GFP_KERNEL);
        if (sbi->s_mb_maxs == NULL) {
                kfree(sbi->s_mb_offsets);
                return -ENOMEM;
        }

        /* order 0 is regular bitmap */
        sbi->s_mb_maxs[0] = sb->s_blocksize << 3;
        sbi->s_mb_offsets[0] = 0;

        i = 1;
        offset = 0;
        max = sb->s_blocksize << 2;
        do {
                sbi->s_mb_offsets[i] = offset;
                sbi->s_mb_maxs[i] = max;
                offset += 1 << (sb->s_blocksize_bits - i);
                max = max >> 1;
                i++;
        } while (i <= sb->s_blocksize_bits + 1);

        /* init file for buddy data */
        ret = ext4_mb_init_backend(sb);
        if (ret != 0) {
                kfree(sbi->s_mb_offsets);
                kfree(sbi->s_mb_maxs);
                return ret;
        }

        spin_lock_init(&sbi->s_md_lock);
        spin_lock_init(&sbi->s_bal_lock);

        sbi->s_mb_max_to_scan = MB_DEFAULT_MAX_TO_SCAN;
        sbi->s_mb_min_to_scan = MB_DEFAULT_MIN_TO_SCAN;
        sbi->s_mb_stats = MB_DEFAULT_STATS;
        sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;
        sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;
        sbi->s_mb_group_prealloc = MB_DEFAULT_GROUP_PREALLOC;

        sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
        if (sbi->s_locality_groups == NULL) {
                kfree(sbi->s_mb_offsets);
                kfree(sbi->s_mb_maxs);
                return -ENOMEM;
        }
        for_each_possible_cpu(i) {
                struct ext4_locality_group *lg;
                lg = per_cpu_ptr(sbi->s_locality_groups, i);
                mutex_init(&lg->lg_mutex);
                for (j = 0; j < PREALLOC_TB_SIZE; j++)
                        INIT_LIST_HEAD(&lg->lg_prealloc_list[j]);
                spin_lock_init(&lg->lg_prealloc_lock);
        }

        if (sbi->s_proc)
                proc_create_data("mb_groups", S_IRUGO, sbi->s_proc,
                                 &ext4_mb_seq_groups_fops, sb);

        if (sbi->s_journal)
                sbi->s_journal->j_commit_callback = release_blocks_on_commit;
        return 0;
}

/* need to called with the ext4 group lock held */
static void ext4_mb_cleanup_pa(struct ext4_group_info *grp)
{
        struct ext4_prealloc_space *pa;
        struct list_head *cur, *tmp;
        int count = 0;

        list_for_each_safe(cur, tmp, &grp->bb_prealloc_list) {
                pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
                list_del(&pa->pa_group_list);
                count++;
                kmem_cache_free(ext4_pspace_cachep, pa);
        }
        if (count)
                mb_debug(1, "mballoc: %u PAs left\n", count);

}

int ext4_mb_release(struct super_block *sb)
{
        ext4_group_t ngroups = ext4_get_groups_count(sb);
        ext4_group_t i;
        int num_meta_group_infos;
        struct ext4_group_info *grinfo;
        struct ext4_sb_info *sbi = EXT4_SB(sb);

        if (sbi->s_group_info) {
                for (i = 0; i < ngroups; i++) {
                        grinfo = ext4_get_group_info(sb, i);
#ifdef DOUBLE_CHECK
                        kfree(grinfo->bb_bitmap);
#endif
                        ext4_lock_group(sb, i);
                        ext4_mb_cleanup_pa(grinfo);
                        ext4_unlock_group(sb, i);
                        kfree(grinfo);
                }
                num_meta_group_infos = (ngroups +
                                EXT4_DESC_PER_BLOCK(sb) - 1) >>
                        EXT4_DESC_PER_BLOCK_BITS(sb);
                for (i = 0; i < num_meta_group_infos; i++)
                        kfree(sbi->s_group_info[i]);
                kfree(sbi->s_group_info);
        }
        kfree(sbi->s_mb_offsets);
        kfree(sbi->s_mb_maxs);
        if (sbi->s_buddy_cache)
                iput(sbi->s_buddy_cache);
        if (sbi->s_mb_stats) {
                printk(KERN_INFO
                       "EXT4-fs: mballoc: %u blocks %u reqs (%u success)\n",
                                atomic_read(&sbi->s_bal_allocated),
                                atomic_read(&sbi->s_bal_reqs),
                                atomic_read(&sbi->s_bal_success));
                printk(KERN_INFO
                      "EXT4-fs: mballoc: %u extents scanned, %u goal hits, "
                                "%u 2^N hits, %u breaks, %u lost\n",
                                atomic_read(&sbi->s_bal_ex_scanned),
                                atomic_read(&sbi->s_bal_goals),
                                atomic_read(&sbi->s_bal_2orders),
                                atomic_read(&sbi->s_bal_breaks),
                                atomic_read(&sbi->s_mb_lost_chunks));
                printk(KERN_INFO
                       "EXT4-fs: mballoc: %lu generated and it took %Lu\n",
                                sbi->s_mb_buddies_generated++,
                                sbi->s_mb_generation_time);
                printk(KERN_INFO
                       "EXT4-fs: mballoc: %u preallocated, %u discarded\n",
                                atomic_read(&sbi->s_mb_preallocated),
                                atomic_read(&sbi->s_mb_discarded));
        }

        free_percpu(sbi->s_locality_groups);
        if (sbi->s_proc)
                remove_proc_entry("mb_groups", sbi->s_proc);

        return 0;
}

/*
 * This function is called by the jbd2 layer once the commit has finished,
 * so we know we can free the blocks that were released with that commit.
 */
static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
{
        struct super_block *sb = journal->j_private;
        struct ext4_buddy e4b;
        struct ext4_group_info *db;
        int err, count = 0, count2 = 0;
        struct ext4_free_data *entry;
        struct list_head *l, *ltmp;

        list_for_each_safe(l, ltmp, &txn->t_private_list) {
                entry = list_entry(l, struct ext4_free_data, list);

                mb_debug(1, "gonna free %u blocks in group %u (0x%p):",
                         entry->count, entry->group, entry);

                if (test_opt(sb, DISCARD)) {
                        int ret;
                        ext4_fsblk_t discard_block;

                        discard_block = entry->start_blk +
                                ext4_group_first_block_no(sb, entry->group);
                        trace_ext4_discard_blocks(sb,
                                        (unsigned long long)discard_block,
                                        entry->count);
                        ret = sb_issue_discard(sb, discard_block, entry->count);
                        if (ret == EOPNOTSUPP) {
                                ext4_warning(sb,
                                        "discard not supported, disabling");
                                clear_opt(EXT4_SB(sb)->s_mount_opt, DISCARD);
                        }
                }

                err = ext4_mb_load_buddy(sb, entry->group, &e4b);
                /* we expect to find existing buddy because it's pinned */
                BUG_ON(err != 0);

                db = e4b.bd_info;
                /* there are blocks to put in buddy to make them really free */
                count += entry->count;
                count2++;
                ext4_lock_group(sb, entry->group);
                /* Take it out of per group rb tree */
                rb_erase(&entry->node, &(db->bb_free_root));
                mb_free_blocks(NULL, &e4b, entry->start_blk, entry->count);

                if (!db->bb_free_root.rb_node) {
                        /* No more items in the per group rb tree
                         * balance refcounts from ext4_mb_free_metadata()
                         */
                        page_cache_release(e4b.bd_buddy_page);
                        page_cache_release(e4b.bd_bitmap_page);
                }
                ext4_unlock_group(sb, entry->group);
                kmem_cache_free(ext4_free_ext_cachep, entry);
                ext4_mb_unload_buddy(&e4b);
        }

        mb_debug(1, "freed %u blocks in %u structures\n", count, count2);
}

#ifdef CONFIG_EXT4_DEBUG
u8 mb_enable_debug __read_mostly;

static struct dentry *debugfs_dir;
static struct dentry *debugfs_debug;

static void __init ext4_create_debugfs_entry(void)
{
        debugfs_dir = debugfs_create_dir("ext4", NULL);
        if (debugfs_dir)
                debugfs_debug = debugfs_create_u8("mballoc-debug",
                                                  S_IRUGO | S_IWUSR,
                                                  debugfs_dir,
                                                  &mb_enable_debug);
}

static void ext4_remove_debugfs_entry(void)
{
        debugfs_remove(debugfs_debug);
        debugfs_remove(debugfs_dir);
}

#else

static void __init ext4_create_debugfs_entry(void)
{
}

static void ext4_remove_debugfs_entry(void)
{
}

#endif

int __init init_ext4_mballoc(void)
{
        ext4_pspace_cachep =
                kmem_cache_create("ext4_prealloc_space",
                                     sizeof(struct ext4_prealloc_space),
                                     0, SLAB_RECLAIM_ACCOUNT, NULL);
        if (ext4_pspace_cachep == NULL)
                return -ENOMEM;

        ext4_ac_cachep =
                kmem_cache_create("ext4_alloc_context",
                                     sizeof(struct ext4_allocation_context),
                                     0, SLAB_RECLAIM_ACCOUNT, NULL);
        if (ext4_ac_cachep == NULL) {
                kmem_cache_destroy(ext4_pspace_cachep);
                return -ENOMEM;
        }

        ext4_free_ext_cachep =
                kmem_cache_create("ext4_free_block_extents",
                                     sizeof(struct ext4_free_data),
                                     0, SLAB_RECLAIM_ACCOUNT, NULL);
        if (ext4_free_ext_cachep == NULL) {
                kmem_cache_destroy(ext4_pspace_cachep);
                kmem_cache_destroy(ext4_ac_cachep);
                return -ENOMEM;
        }
        ext4_create_debugfs_entry();
        return 0;
}

void exit_ext4_mballoc(void)
{
        /*
         * Wait for completion of call_rcu()'s on ext4_pspace_cachep
         * before destroying the slab cache.
         */
        rcu_barrier();
        kmem_cache_destroy(ext4_pspace_cachep);
        kmem_cache_destroy(ext4_ac_cachep);
        kmem_cache_destroy(ext4_free_ext_cachep);
        ext4_remove_debugfs_entry();
}


/*
 * Check quota and mark choosed space (ac->ac_b_ex) non-free in bitmaps
 * Returns 0 if success or error code
 */
static noinline_for_stack int
ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
                                handle_t *handle, unsigned int reserv_blks)
{
        struct buffer_head *bitmap_bh = NULL;
        struct ext4_super_block *es;
        struct ext4_group_desc *gdp;
        struct buffer_head *gdp_bh;
        struct ext4_sb_info *sbi;
        struct super_block *sb;
        ext4_fsblk_t block;
        int err, len;

        BUG_ON(ac->ac_status != AC_STATUS_FOUND);
        BUG_ON(ac->ac_b_ex.fe_len <= 0);

        sb = ac->ac_sb;
        sbi = EXT4_SB(sb);
        es = sbi->s_es;


        err = -EIO;
        bitmap_bh = ext4_read_block_bitmap(sb, ac->ac_b_ex.fe_group);
        if (!bitmap_bh)
                goto out_err;

        err = ext4_journal_get_write_access(handle, bitmap_bh);
        if (err)
                goto out_err;

        err = -EIO;
        gdp = ext4_get_group_desc(sb, ac->ac_b_ex.fe_group, &gdp_bh);
        if (!gdp)
                goto out_err;

        ext4_debug("using block group %u(%d)\n", ac->ac_b_ex.fe_group,
                        ext4_free_blks_count(sb, gdp));

        err = ext4_journal_get_write_access(handle, gdp_bh);
        if (err)
                goto out_err;

        block = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);

        len = ac->ac_b_ex.fe_len;
        if (!ext4_data_block_valid(sbi, block, len)) {
                ext4_error(sb, "Allocating blocks %llu-%llu which overlap "
                           "fs metadata\n", block, block+len);
                /* File system mounted not to panic on error
                 * Fix the bitmap and repeat the block allocation
                 * We leak some of the blocks here.
                 */
                ext4_lock_group(sb, ac->ac_b_ex.fe_group);
                mb_set_bits(bitmap_bh->b_data, ac->ac_b_ex.fe_start,
                            ac->ac_b_ex.fe_len);
                ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
                err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
                if (!err)
                        err = -EAGAIN;
                goto out_err;
        }

        ext4_lock_group(sb, ac->ac_b_ex.fe_group);
#ifdef AGGRESSIVE_CHECK
        {
                int i;
                for (i = 0; i < ac->ac_b_ex.fe_len; i++) {
                        BUG_ON(mb_test_bit(ac->ac_b_ex.fe_start + i,
                                                bitmap_bh->b_data));
                }
        }
#endif
        mb_set_bits(bitmap_bh->b_data, ac->ac_b_ex.fe_start,ac->ac_b_ex.fe_len);
        if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
                gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
                ext4_free_blks_set(sb, gdp,
                                        ext4_free_blocks_after_init(sb,
                                        ac->ac_b_ex.fe_group, gdp));
        }
        len = ext4_free_blks_count(sb, gdp) - ac->ac_b_ex.fe_len;
        ext4_free_blks_set(sb, gdp, len);
        gdp->bg_checksum = ext4_group_desc_csum(sbi, ac->ac_b_ex.fe_group, gdp);

        ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
        percpu_counter_sub(&sbi->s_freeblocks_counter, ac->ac_b_ex.fe_len);
        /*
         * Now reduce the dirty block count also. Should not go negative
         */
        if (!(ac->ac_flags & EXT4_MB_DELALLOC_RESERVED))
                /* release all the reserved blocks if non delalloc */
                percpu_counter_sub(&sbi->s_dirtyblocks_counter, reserv_blks);

        if (sbi->s_log_groups_per_flex) {
                ext4_group_t flex_group = ext4_flex_group(sbi,
                                                          ac->ac_b_ex.fe_group);
                atomic_sub(ac->ac_b_ex.fe_len,
                           &sbi->s_flex_groups[flex_group].free_blocks);
        }

        err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
        if (err)
                goto out_err;
        err = ext4_handle_dirty_metadata(handle, NULL, gdp_bh);

out_err:
        sb->s_dirt = 1;
        brelse(bitmap_bh);
        return err;
}

/*
 * here we normalize request for locality group
 * Group request are normalized to s_strip size if we set the same via mount
 * option. If not we set it to s_mb_group_prealloc which can be configured via
 * /sys/fs/ext4/<partition>/mb_group_prealloc
 *
 * XXX: should we try to preallocate more than the group has now?
 */
static void ext4_mb_normalize_group_request(struct ext4_allocation_context *ac)
{
        struct super_block *sb = ac->ac_sb;
        struct ext4_locality_group *lg = ac->ac_lg;

        BUG_ON(lg == NULL);
        if (EXT4_SB(sb)->s_stripe)
                ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_stripe;
        else
                ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc;
        mb_debug(1, "#%u: goal %u blocks for locality group\n",
                current->pid, ac->ac_g_ex.fe_len);
}

/*
 * Normalization means making request better in terms of
 * size and alignment
 */
static noinline_for_stack void
ext4_mb_normalize_request(struct ext4_allocation_context *ac,
                                struct ext4_allocation_request *ar)
{
        int bsbits, max;
        ext4_lblk_t end;
        loff_t size, orig_size, start_off;
        ext4_lblk_t start, orig_start;
        struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
        struct ext4_prealloc_space *pa;

        /* do normalize only data requests, metadata requests
           do not need preallocation */
        if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
                return;

        /* sometime caller may want exact blocks */
        if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
                return;

        /* caller may indicate that preallocation isn't
         * required (it's a tail, for example) */
        if (ac->ac_flags & EXT4_MB_HINT_NOPREALLOC)
                return;

        if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC) {
                ext4_mb_normalize_group_request(ac);
                return ;
        }

        bsbits = ac->ac_sb->s_blocksize_bits;

        /* first, let's learn actual file size
         * given current request is allocated */
        size = ac->ac_o_ex.fe_logical + ac->ac_o_ex.fe_len;
        size = size << bsbits;
        if (size < i_size_read(ac->ac_inode))
                size = i_size_read(ac->ac_inode);

        /* max size of free chunks */
        max = 2 << bsbits;

#define NRL_CHECK_SIZE(req, size, max, chunk_size)      \
                (req <= (size) || max <= (chunk_size))

        /* first, try to predict filesize */
        /* XXX: should this table be tunable? */
        start_off = 0;
        if (size <= 16 * 1024) {
                size = 16 * 1024;
        } else if (size <= 32 * 1024) {
                size = 32 * 1024;
        } else if (size <= 64 * 1024) {
                size = 64 * 1024;
        } else if (size <= 128 * 1024) {
                size = 128 * 1024;
        } else if (size <= 256 * 1024) {
                size = 256 * 1024;
        } else if (size <= 512 * 1024) {
                size = 512 * 1024;
        } else if (size <= 1024 * 1024) {
                size = 1024 * 1024;
        } else if (NRL_CHECK_SIZE(size, 4 * 1024 * 1024, max, 2 * 1024)) {
                start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
                                                (21 - bsbits)) << 21;
                size = 2 * 1024 * 1024;
        } else if (NRL_CHECK_SIZE(size, 8 * 1024 * 1024, max, 4 * 1024)) {
                start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
                                                        (22 - bsbits)) << 22;
                size = 4 * 1024 * 1024;
        } else if (NRL_CHECK_SIZE(ac->ac_o_ex.fe_len,
                                        (8<<20)>>bsbits, max, 8 * 1024)) {
                start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
                                                        (23 - bsbits)) << 23;
                size = 8 * 1024 * 1024;
        } else {
                start_off = (loff_t)ac->ac_o_ex.fe_logical << bsbits;
                size      = ac->ac_o_ex.fe_len << bsbits;
        }
        orig_size = size = size >> bsbits;
        orig_start = start = start_off >> bsbits;

        /* don't cover already allocated blocks in selected range */
        if (ar->pleft && start <= ar->lleft) {
                size -= ar->lleft + 1 - start;
                start = ar->lleft + 1;
        }
        if (ar->pright && start + size - 1 >= ar->lright)
                size -= start + size - ar->lright;

        end = start + size;

        /* check we don't cross already preallocated blocks */
        rcu_read_lock();
        list_for_each_entry_rcu(pa, &ei->i_prealloc_list, pa_inode_list) {
                ext4_lblk_t pa_end;

                if (pa->pa_deleted)
                        continue;
                spin_lock(&pa->pa_lock);
                if (pa->pa_deleted) {
                        spin_unlock(&pa->pa_lock);
                        continue;
                }

                pa_end = pa->pa_lstart + pa->pa_len;

                /* PA must not overlap original request */
                BUG_ON(!(ac->ac_o_ex.fe_logical >= pa_end ||
                        ac->ac_o_ex.fe_logical < pa->pa_lstart));

                /* skip PAs this normalized request doesn't overlap with */
                if (pa->pa_lstart >= end || pa_end <= start) {
                        spin_unlock(&pa->pa_lock);
                        continue;
                }
                BUG_ON(pa->pa_lstart <= start && pa_end >= end);

                /* adjust start or end to be adjacent to this pa */
                if (pa_end <= ac->ac_o_ex.fe_logical) {
                        BUG_ON(pa_end < start);
                        start = pa_end;
                } else if (pa->pa_lstart > ac->ac_o_ex.fe_logical) {
                        BUG_ON(pa->pa_lstart > end);
                        end = pa->pa_lstart;
                }
                spin_unlock(&pa->pa_lock);
        }
        rcu_read_unlock();
        size = end - start;

        /* XXX: extra loop to check we really don't overlap preallocations */
        rcu_read_lock();
        list_for_each_entry_rcu(pa, &ei->i_prealloc_list, pa_inode_list) {
                ext4_lblk_t pa_end;
                spin_lock(&pa->pa_lock);
                if (pa->pa_deleted == 0) {
                        pa_end = pa->pa_lstart + pa->pa_len;
                        BUG_ON(!(start >= pa_end || end <= pa->pa_lstart));
                }
                spin_unlock(&pa->pa_lock);
        }
        rcu_read_unlock();

        if (start + size <= ac->ac_o_ex.fe_logical &&
                        start > ac->ac_o_ex.fe_logical) {
                printk(KERN_ERR "start %lu, size %lu, fe_logical %lu\n",
                        (unsigned long) start, (unsigned long) size,
                        (unsigned long) ac->ac_o_ex.fe_logical);
        }
        BUG_ON(start + size <= ac->ac_o_ex.fe_logical &&
                        start > ac->ac_o_ex.fe_logical);
        BUG_ON(size <= 0 || size > EXT4_BLOCKS_PER_GROUP(ac->ac_sb));

        /* now prepare goal request */

        /* XXX: is it better to align blocks WRT to logical
         * placement or satisfy big request as is */
        ac->ac_g_ex.fe_logical = start;
        ac->ac_g_ex.fe_len = size;

        /* define goal start in order to merge */
        if (ar->pright && (ar->lright == (start + size))) {
                /* merge to the right */
                ext4_get_group_no_and_offset(ac->ac_sb, ar->pright - size,
                                                &ac->ac_f_ex.fe_group,
                                                &ac->ac_f_ex.fe_start);
                ac->ac_flags |= EXT4_MB_HINT_TRY_GOAL;
        }
        if (ar->pleft && (ar->lleft + 1 == start)) {
                /* merge to the left */
                ext4_get_group_no_and_offset(ac->ac_sb, ar->pleft + 1,
                                                &ac->ac_f_ex.fe_group,
                                                &ac->ac_f_ex.fe_start);
                ac->ac_flags |= EXT4_MB_HINT_TRY_GOAL;
        }

        mb_debug(1, "goal: %u(was %u) blocks at %u\n", (unsigned) size,
                (unsigned) orig_size, (unsigned) start);
}

static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);

        if (sbi->s_mb_stats && ac->ac_g_ex.fe_len > 1) {
                atomic_inc(&sbi->s_bal_reqs);
                atomic_add(ac->ac_b_ex.fe_len, &sbi->s_bal_allocated);
                if (ac->ac_b_ex.fe_len >= ac->ac_o_ex.fe_len)
                        atomic_inc(&sbi->s_bal_success);
                atomic_add(ac->ac_found, &sbi->s_bal_ex_scanned);
                if (ac->ac_g_ex.fe_start == ac->ac_b_ex.fe_start &&
                                ac->ac_g_ex.fe_group == ac->ac_b_ex.fe_group)
                        atomic_inc(&sbi->s_bal_goals);
                if (ac->ac_found > sbi->s_mb_max_to_scan)
                        atomic_inc(&sbi->s_bal_breaks);
        }

        if (ac->ac_op == EXT4_MB_HISTORY_ALLOC)
                trace_ext4_mballoc_alloc(ac);
        else
                trace_ext4_mballoc_prealloc(ac);
}

/*
 * Called on failure; free up any blocks from the inode PA for this
 * context.  We don't need this for MB_GROUP_PA because we only change
 * pa_free in ext4_mb_release_context(), but on failure, we've already
 * zeroed out ac->ac_b_ex.fe_len, so group_pa->pa_free is not changed.
 */
static void ext4_discard_allocated_blocks(struct ext4_allocation_context *ac)
{
        struct ext4_prealloc_space *pa = ac->ac_pa;
        int len;

        if (pa && pa->pa_type == MB_INODE_PA) {
                len = ac->ac_b_ex.fe_len;
                pa->pa_free += len;
        }

}

/*
 * use blocks preallocated to inode
 */
static void ext4_mb_use_inode_pa(struct ext4_allocation_context *ac,
                                struct ext4_prealloc_space *pa)
{
        ext4_fsblk_t start;
        ext4_fsblk_t end;
        int len;

        /* found preallocated blocks, use them */
        start = pa->pa_pstart + (ac->ac_o_ex.fe_logical - pa->pa_lstart);
        end = min(pa->pa_pstart + pa->pa_len, start + ac->ac_o_ex.fe_len);
        len = end - start;
        ext4_get_group_no_and_offset(ac->ac_sb, start, &ac->ac_b_ex.fe_group,
                                        &ac->ac_b_ex.fe_start);
        ac->ac_b_ex.fe_len = len;
        ac->ac_status = AC_STATUS_FOUND;
        ac->ac_pa = pa;

        BUG_ON(start < pa->pa_pstart);
        BUG_ON(start + len > pa->pa_pstart + pa->pa_len);
        BUG_ON(pa->pa_free < len);
        pa->pa_free -= len;

        mb_debug(1, "use %llu/%u from inode pa %p\n", start, len, pa);
}

/*
 * use blocks preallocated to locality group
 */
static void ext4_mb_use_group_pa(struct ext4_allocation_context *ac,
                                struct ext4_prealloc_space *pa)
{
        unsigned int len = ac->ac_o_ex.fe_len;

        ext4_get_group_no_and_offset(ac->ac_sb, pa->pa_pstart,
                                        &ac->ac_b_ex.fe_group,
                                        &ac->ac_b_ex.fe_start);
        ac->ac_b_ex.fe_len = len;
        ac->ac_status = AC_STATUS_FOUND;
        ac->ac_pa = pa;

        /* we don't correct pa_pstart or pa_plen here to avoid
         * possible race when the group is being loaded concurrently
         * instead we correct pa later, after blocks are marked
         * in on-disk bitmap -- see ext4_mb_release_context()
         * Other CPUs are prevented from allocating from this pa by lg_mutex
         */
        mb_debug(1, "use %u/%u from group pa %p\n", pa->pa_lstart-len, len, pa);
}

/*
 * Return the prealloc space that have minimal distance
 * from the goal block. @cpa is the prealloc
 * space that is having currently known minimal distance
 * from the goal block.
 */
static struct ext4_prealloc_space *
ext4_mb_check_group_pa(ext4_fsblk_t goal_block,
                        struct ext4_prealloc_space *pa,
                        struct ext4_prealloc_space *cpa)
{
        ext4_fsblk_t cur_distance, new_distance;

        if (cpa == NULL) {
                atomic_inc(&pa->pa_count);
                return pa;
        }
        cur_distance = abs(goal_block - cpa->pa_pstart);
        new_distance = abs(goal_block - pa->pa_pstart);

        if (cur_distance < new_distance)
                return cpa;

        /* drop the previous reference */
        atomic_dec(&cpa->pa_count);
        atomic_inc(&pa->pa_count);
        return pa;
}

/*
 * search goal blocks in preallocated space
 */
static noinline_for_stack int
ext4_mb_use_preallocated(struct ext4_allocation_context *ac)
{
        int order, i;
        struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
        struct ext4_locality_group *lg;
        struct ext4_prealloc_space *pa, *cpa = NULL;
        ext4_fsblk_t goal_block;

        /* only data can be preallocated */
        if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
                return 0;

        /* first, try per-file preallocation */
        rcu_read_lock();
        list_for_each_entry_rcu(pa, &ei->i_prealloc_list, pa_inode_list) {

                /* all fields in this condition don't change,
                 * so we can skip locking for them */
                if (ac->ac_o_ex.fe_logical < pa->pa_lstart ||
                        ac->ac_o_ex.fe_logical >= pa->pa_lstart + pa->pa_len)
                        continue;

                /* non-extent files can't have physical blocks past 2^32 */
                if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)) &&
                        pa->pa_pstart + pa->pa_len > EXT4_MAX_BLOCK_FILE_PHYS)
                        continue;

                /* found preallocated blocks, use them */
                spin_lock(&pa->pa_lock);
                if (pa->pa_deleted == 0 && pa->pa_free) {
                        atomic_inc(&pa->pa_count);
                        ext4_mb_use_inode_pa(ac, pa);
                        spin_unlock(&pa->pa_lock);
                        ac->ac_criteria = 10;
                        rcu_read_unlock();
                        return 1;
                }
                spin_unlock(&pa->pa_lock);
        }
        rcu_read_unlock();

        /* can we use group allocation? */
        if (!(ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC))
                return 0;

        /* inode may have no locality group for some reason */
        lg = ac->ac_lg;
        if (lg == NULL)
                return 0;
        order  = fls(ac->ac_o_ex.fe_len) - 1;
        if (order > PREALLOC_TB_SIZE - 1)
                /* The max size of hash table is PREALLOC_TB_SIZE */
                order = PREALLOC_TB_SIZE - 1;

        goal_block = ext4_grp_offs_to_block(ac->ac_sb, &ac->ac_g_ex);
        /*
         * search for the prealloc space that is having
         * minimal distance from the goal block.
         */
        for (i = order; i < PREALLOC_TB_SIZE; i++) {
                rcu_read_lock();
                list_for_each_entry_rcu(pa, &lg->lg_prealloc_list[i],
                                        pa_inode_list) {
                        spin_lock(&pa->pa_lock);
                        if (pa->pa_deleted == 0 &&
                                        pa->pa_free >= ac->ac_o_ex.fe_len) {

                                cpa = ext4_mb_check_group_pa(goal_block,
                                                                pa, cpa);
                        }
                        spin_unlock(&pa->pa_lock);
                }
                rcu_read_unlock();
        }
        if (cpa) {
                ext4_mb_use_group_pa(ac, cpa);
                ac->ac_criteria = 20;
                return 1;
        }
        return 0;
}

/*
 * the function goes through all block freed in the group
 * but not yet committed and marks them used in in-core bitmap.
 * buddy must be generated from this bitmap
 * Need to be called with the ext4 group lock held
 */
static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
                                                ext4_group_t group)
{
        struct rb_node *n;
        struct ext4_group_info *grp;
        struct ext4_free_data *entry;

        grp = ext4_get_group_info(sb, group);
        n = rb_first(&(grp->bb_free_root));

        while (n) {
                entry = rb_entry(n, struct ext4_free_data, node);
                mb_set_bits(bitmap, entry->start_blk, entry->count);
                n = rb_next(n);
        }
        return;
}

/*
 * the function goes through all preallocation in this group and marks them
 * used in in-core bitmap. buddy must be generated from this bitmap
 * Need to be called with ext4 group lock held
 */
static noinline_for_stack
void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
                                        ext4_group_t group)
{
        struct ext4_group_info *grp = ext4_get_group_info(sb, group);
        struct ext4_prealloc_space *pa;
        struct list_head *cur;
        ext4_group_t groupnr;
        ext4_grpblk_t start;
        int preallocated = 0;
        int count = 0;
        int len;

        /* all form of preallocation discards first load group,
         * so the only competing code is preallocation use.
         * we don't need any locking here
         * notice we do NOT ignore preallocations with pa_deleted
         * otherwise we could leave used blocks available for
         * allocation in buddy when concurrent ext4_mb_put_pa()
         * is dropping preallocation
         */
        list_for_each(cur, &grp->bb_prealloc_list) {
                pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
                spin_lock(&pa->pa_lock);
                ext4_get_group_no_and_offset(sb, pa->pa_pstart,
                                             &groupnr, &start);
                len = pa->pa_len;
                spin_unlock(&pa->pa_lock);
                if (unlikely(len == 0))
                        continue;
                BUG_ON(groupnr != group);
                mb_set_bits(bitmap, start, len);
                preallocated += len;
                count++;
        }
        mb_debug(1, "prellocated %u for group %u\n", preallocated, group);
}

static void ext4_mb_pa_callback(struct rcu_head *head)
{
        struct ext4_prealloc_space *pa;
        pa = container_of(head, struct ext4_prealloc_space, u.pa_rcu);
        kmem_cache_free(ext4_pspace_cachep, pa);
}

/*
 * drops a reference to preallocated space descriptor
 * if this was the last reference and the space is consumed
 */
static void ext4_mb_put_pa(struct ext4_allocation_context *ac,
                        struct super_block *sb, struct ext4_prealloc_space *pa)
{
        ext4_group_t grp;
        ext4_fsblk_t grp_blk;

        if (!atomic_dec_and_test(&pa->pa_count) || pa->pa_free != 0)
                return;

        /* in this short window concurrent discard can set pa_deleted */
        spin_lock(&pa->pa_lock);
        if (pa->pa_deleted == 1) {
                spin_unlock(&pa->pa_lock);
                return;
        }

        pa->pa_deleted = 1;
        spin_unlock(&pa->pa_lock);

        grp_blk = pa->pa_pstart;
        /*
         * If doing group-based preallocation, pa_pstart may be in the
         * next group when pa is used up
         */
        if (pa->pa_type == MB_GROUP_PA)
                grp_blk--;

        ext4_get_group_no_and_offset(sb, grp_blk, &grp, NULL);

        /*
         * possible race:
         *
         *  P1 (buddy init)                     P2 (regular allocation)
         *                                      find block B in PA
         *  copy on-disk bitmap to buddy
         *                                      mark B in on-disk bitmap
         *                                      drop PA from group
         *  mark all PAs in buddy
         *
         * thus, P1 initializes buddy with B available. to prevent this
         * we make "copy" and "mark all PAs" atomic and serialize "drop PA"
         * against that pair
         */
        ext4_lock_group(sb, grp);
        list_del(&pa->pa_group_list);
        ext4_unlock_group(sb, grp);

        spin_lock(pa->pa_obj_lock);
        list_del_rcu(&pa->pa_inode_list);
        spin_unlock(pa->pa_obj_lock);

        call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
}

/*
 * creates new preallocated space for given inode
 */
static noinline_for_stack int
ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
{
        struct super_block *sb = ac->ac_sb;
        struct ext4_prealloc_space *pa;
        struct ext4_group_info *grp;
        struct ext4_inode_info *ei;

        /* preallocate only when found space is larger then requested */
        BUG_ON(ac->ac_o_ex.fe_len >= ac->ac_b_ex.fe_len);
        BUG_ON(ac->ac_status != AC_STATUS_FOUND);
        BUG_ON(!S_ISREG(ac->ac_inode->i_mode));

        pa = kmem_cache_alloc(ext4_pspace_cachep, GFP_NOFS);
        if (pa == NULL)
                return -ENOMEM;

        if (ac->ac_b_ex.fe_len < ac->ac_g_ex.fe_len) {
                int winl;
                int wins;
                int win;
                int offs;

                /* we can't allocate as much as normalizer wants.
                 * so, found space must get proper lstart
                 * to cover original request */
                BUG_ON(ac->ac_g_ex.fe_logical > ac->ac_o_ex.fe_logical);
                BUG_ON(ac->ac_g_ex.fe_len < ac->ac_o_ex.fe_len);

                /* we're limited by original request in that
                 * logical block must be covered any way
                 * winl is window we can move our chunk within */
                winl = ac->ac_o_ex.fe_logical - ac->ac_g_ex.fe_logical;

                /* also, we should cover whole original request */
                wins = ac->ac_b_ex.fe_len - ac->ac_o_ex.fe_len;

                /* the smallest one defines real window */
                win = min(winl, wins);

                offs = ac->ac_o_ex.fe_logical % ac->ac_b_ex.fe_len;
                if (offs && offs < win)
                        win = offs;

                ac->ac_b_ex.fe_logical = ac->ac_o_ex.fe_logical - win;
                BUG_ON(ac->ac_o_ex.fe_logical < ac->ac_b_ex.fe_logical);
                BUG_ON(ac->ac_o_ex.fe_len > ac->ac_b_ex.fe_len);
        }

        /* preallocation can change ac_b_ex, thus we store actually
         * allocated blocks for history */
        ac->ac_f_ex = ac->ac_b_ex;

        pa->pa_lstart = ac->ac_b_ex.fe_logical;
        pa->pa_pstart = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
        pa->pa_len = ac->ac_b_ex.fe_len;
        pa->pa_free = pa->pa_len;
        atomic_set(&pa->pa_count, 1);
        spin_lock_init(&pa->pa_lock);
        INIT_LIST_HEAD(&pa->pa_inode_list);
        INIT_LIST_HEAD(&pa->pa_group_list);
        pa->pa_deleted = 0;
        pa->pa_type = MB_INODE_PA;

        mb_debug(1, "new inode pa %p: %llu/%u for %u\n", pa,
                        pa->pa_pstart, pa->pa_len, pa->pa_lstart);
        trace_ext4_mb_new_inode_pa(ac, pa);

        ext4_mb_use_inode_pa(ac, pa);
        atomic_add(pa->pa_free, &EXT4_SB(sb)->s_mb_preallocated);

        ei = EXT4_I(ac->ac_inode);
        grp = ext4_get_group_info(sb, ac->ac_b_ex.fe_group);

        pa->pa_obj_lock = &ei->i_prealloc_lock;
        pa->pa_inode = ac->ac_inode;

        ext4_lock_group(sb, ac->ac_b_ex.fe_group);
        list_add(&pa->pa_group_list, &grp->bb_prealloc_list);
        ext4_unlock_group(sb, ac->ac_b_ex.fe_group);

        spin_lock(pa->pa_obj_lock);
        list_add_rcu(&pa->pa_inode_list, &ei->i_prealloc_list);
        spin_unlock(pa->pa_obj_lock);

        return 0;
}

/*
 * creates new preallocated space for locality group inodes belongs to
 */
static noinline_for_stack int
ext4_mb_new_group_pa(struct ext4_allocation_context *ac)
{
        struct super_block *sb = ac->ac_sb;
        struct ext4_locality_group *lg;
        struct ext4_prealloc_space *pa;
        struct ext4_group_info *grp;

        /* preallocate only when found space is larger then requested */
        BUG_ON(ac->ac_o_ex.fe_len >= ac->ac_b_ex.fe_len);
        BUG_ON(ac->ac_status != AC_STATUS_FOUND);
        BUG_ON(!S_ISREG(ac->ac_inode->i_mode));

        BUG_ON(ext4_pspace_cachep == NULL);
        pa = kmem_cache_alloc(ext4_pspace_cachep, GFP_NOFS);
        if (pa == NULL)
                return -ENOMEM;

        /* preallocation can change ac_b_ex, thus we store actually
         * allocated blocks for history */
        ac->ac_f_ex = ac->ac_b_ex;

        pa->pa_pstart = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
        pa->pa_lstart = pa->pa_pstart;
        pa->pa_len = ac->ac_b_ex.fe_len;
        pa->pa_free = pa->pa_len;
        atomic_set(&pa->pa_count, 1);
        spin_lock_init(&pa->pa_lock);
        INIT_LIST_HEAD(&pa->pa_inode_list);
        INIT_LIST_HEAD(&pa->pa_group_list);
        pa->pa_deleted = 0;
        pa->pa_type = MB_GROUP_PA;

        mb_debug(1, "new group pa %p: %llu/%u for %u\n", pa,
                        pa->pa_pstart, pa->pa_len, pa->pa_lstart);
        trace_ext4_mb_new_group_pa(ac, pa);

        ext4_mb_use_group_pa(ac, pa);
        atomic_add(pa->pa_free, &EXT4_SB(sb)->s_mb_preallocated);

        grp = ext4_get_group_info(sb, ac->ac_b_ex.fe_group);
        lg = ac->ac_lg;
        BUG_ON(lg == NULL);

        pa->pa_obj_lock = &lg->lg_prealloc_lock;
        pa->pa_inode = NULL;

        ext4_lock_group(sb, ac->ac_b_ex.fe_group);
        list_add(&pa->pa_group_list, &grp->bb_prealloc_list);
        ext4_unlock_group(sb, ac->ac_b_ex.fe_group);

        /*
         * We will later add the new pa to the right bucket
         * after updating the pa_free in ext4_mb_release_context
         */
        return 0;
}

static int ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
{
        int err;

        if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
                err = ext4_mb_new_group_pa(ac);
        else
                err = ext4_mb_new_inode_pa(ac);
        return err;
}

/*
 * finds all unused blocks in on-disk bitmap, frees them in
 * in-core bitmap and buddy.
 * @pa must be unlinked from inode and group lists, so that
 * nobody else can find/use it.
 * the caller MUST hold group/inode locks.
 * TODO: optimize the case when there are no in-core structures yet
 */
static noinline_for_stack int
ext4_mb_release_inode_pa(struct ext4_buddy *e4b, struct buffer_head *bitmap_bh,
                        struct ext4_prealloc_space *pa,
                        struct ext4_allocation_context *ac)
{
        struct super_block *sb = e4b->bd_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        unsigned int end;
        unsigned int next;
        ext4_group_t group;
        ext4_grpblk_t bit;
        unsigned long long grp_blk_start;
        sector_t start;
        int err = 0;
        int free = 0;

        BUG_ON(pa->pa_deleted == 0);
        ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, &bit);
        grp_blk_start = pa->pa_pstart - bit;
        BUG_ON(group != e4b->bd_group && pa->pa_len != 0);
        end = bit + pa->pa_len;

        if (ac) {
                ac->ac_sb = sb;
                ac->ac_inode = pa->pa_inode;
        }

        while (bit < end) {
                bit = mb_find_next_zero_bit(bitmap_bh->b_data, end, bit);
                if (bit >= end)
                        break;
                next = mb_find_next_bit(bitmap_bh->b_data, end, bit);
                start = ext4_group_first_block_no(sb, group) + bit;
                mb_debug(1, "    free preallocated %u/%u in group %u\n",
                                (unsigned) start, (unsigned) next - bit,
                                (unsigned) group);
                free += next - bit;

                if (ac) {
                        ac->ac_b_ex.fe_group = group;
                        ac->ac_b_ex.fe_start = bit;
                        ac->ac_b_ex.fe_len = next - bit;
                        ac->ac_b_ex.fe_logical = 0;
                        trace_ext4_mballoc_discard(ac);
                }

                trace_ext4_mb_release_inode_pa(ac, pa, grp_blk_start + bit,
                                               next - bit);
                mb_free_blocks(pa->pa_inode, e4b, bit, next - bit);
                bit = next + 1;
        }
        if (free != pa->pa_free) {
                printk(KERN_CRIT "pa %p: logic %lu, phys. %lu, len %lu\n",
                        pa, (unsigned long) pa->pa_lstart,
                        (unsigned long) pa->pa_pstart,
                        (unsigned long) pa->pa_len);
                ext4_grp_locked_error(sb, group,
                                        __func__, "free %u, pa_free %u",
                                        free, pa->pa_free);
                /*
                 * pa is already deleted so we use the value obtained
                 * from the bitmap and continue.
                 */
        }
        atomic_add(free, &sbi->s_mb_discarded);

        return err;
}

static noinline_for_stack int
ext4_mb_release_group_pa(struct ext4_buddy *e4b,
                                struct ext4_prealloc_space *pa,
                                struct ext4_allocation_context *ac)
{
        struct super_block *sb = e4b->bd_sb;
        ext4_group_t group;
        ext4_grpblk_t bit;

        trace_ext4_mb_release_group_pa(ac, pa);
        BUG_ON(pa->pa_deleted == 0);
        ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, &bit);
        BUG_ON(group != e4b->bd_group && pa->pa_len != 0);
        mb_free_blocks(pa->pa_inode, e4b, bit, pa->pa_len);
        atomic_add(pa->pa_len, &EXT4_SB(sb)->s_mb_discarded);

        if (ac) {
                ac->ac_sb = sb;
                ac->ac_inode = NULL;
                ac->ac_b_ex.fe_group = group;
                ac->ac_b_ex.fe_start = bit;
                ac->ac_b_ex.fe_len = pa->pa_len;
                ac->ac_b_ex.fe_logical = 0;
                trace_ext4_mballoc_discard(ac);
        }

        return 0;
}

/*
 * releases all preallocations in given group
 *
 * first, we need to decide discard policy:
 * - when do we discard
 *   1) ENOSPC
 * - how many do we discard
 *   1) how many requested
 */
static noinline_for_stack int
ext4_mb_discard_group_preallocations(struct super_block *sb,
                                        ext4_group_t group, int needed)
{
        struct ext4_group_info *grp = ext4_get_group_info(sb, group);
        struct buffer_head *bitmap_bh = NULL;
        struct ext4_prealloc_space *pa, *tmp;
        struct ext4_allocation_context *ac;
        struct list_head list;
        struct ext4_buddy e4b;
        int err;
        int busy = 0;
        int free = 0;

        mb_debug(1, "discard preallocation for group %u\n", group);

        if (list_empty(&grp->bb_prealloc_list))
                return 0;

        bitmap_bh = ext4_read_block_bitmap(sb, group);
        if (bitmap_bh == NULL) {
                ext4_error(sb, "Error reading block bitmap for %u", group);
                return 0;
        }

        err = ext4_mb_load_buddy(sb, group, &e4b);
        if (err) {
                ext4_error(sb, "Error loading buddy information for %u", group);
                put_bh(bitmap_bh);
                return 0;
        }

        if (needed == 0)
                needed = EXT4_BLOCKS_PER_GROUP(sb) + 1;

        INIT_LIST_HEAD(&list);
        ac = kmem_cache_alloc(ext4_ac_cachep, GFP_NOFS);
        if (ac)
                ac->ac_sb = sb;
repeat:
        ext4_lock_group(sb, group);
        list_for_each_entry_safe(pa, tmp,
                                &grp->bb_prealloc_list, pa_group_list) {
                spin_lock(&pa->pa_lock);
                if (atomic_read(&pa->pa_count)) {
                        spin_unlock(&pa->pa_lock);
                        busy = 1;
                        continue;
                }
                if (pa->pa_deleted) {
                        spin_unlock(&pa->pa_lock);
                        continue;
                }

                /* seems this one can be freed ... */
                pa->pa_deleted = 1;

                /* we can trust pa_free ... */
                free += pa->pa_free;

                spin_unlock(&pa->pa_lock);

                list_del(&pa->pa_group_list);
                list_add(&pa->u.pa_tmp_list, &list);
        }

        /* if we still need more blocks and some PAs were used, try again */
        if (free < needed && busy) {
                busy = 0;
                ext4_unlock_group(sb, group);
                /*
                 * Yield the CPU here so that we don't get soft lockup
                 * in non preempt case.
                 */
                yield();
                goto repeat;
        }

        /* found anything to free? */
        if (list_empty(&list)) {
                BUG_ON(free != 0);
                goto out;
        }

        /* now free all selected PAs */
        list_for_each_entry_safe(pa, tmp, &list, u.pa_tmp_list) {

                /* remove from object (inode or locality group) */
                spin_lock(pa->pa_obj_lock);
                list_del_rcu(&pa->pa_inode_list);
                spin_unlock(pa->pa_obj_lock);

                if (pa->pa_type == MB_GROUP_PA)
                        ext4_mb_release_group_pa(&e4b, pa, ac);
                else
                        ext4_mb_release_inode_pa(&e4b, bitmap_bh, pa, ac);

                list_del(&pa->u.pa_tmp_list);
                call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
        }

out:
        ext4_unlock_group(sb, group);
        if (ac)
                kmem_cache_free(ext4_ac_cachep, ac);
        ext4_mb_unload_buddy(&e4b);
        put_bh(bitmap_bh);
        return free;
}

/*
 * releases all non-used preallocated blocks for given inode
 *
 * It's important to discard preallocations under i_data_sem
 * We don't want another block to be served from the prealloc
 * space when we are discarding the inode prealloc space.
 *
 * FIXME!! Make sure it is valid at all the call sites
 */
void ext4_discard_preallocations(struct inode *inode)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        struct super_block *sb = inode->i_sb;
        struct buffer_head *bitmap_bh = NULL;
        struct ext4_prealloc_space *pa, *tmp;
        struct ext4_allocation_context *ac;
        ext4_group_t group = 0;
        struct list_head list;
        struct ext4_buddy e4b;
        int err;

        if (!S_ISREG(inode->i_mode)) {
                /*BUG_ON(!list_empty(&ei->i_prealloc_list));*/
                return;
        }

        mb_debug(1, "discard preallocation for inode %lu\n", inode->i_ino);
        trace_ext4_discard_preallocations(inode);

        INIT_LIST_HEAD(&list);

        ac = kmem_cache_alloc(ext4_ac_cachep, GFP_NOFS);
        if (ac) {
                ac->ac_sb = sb;
                ac->ac_inode = inode;
        }
repeat:
        /* first, collect all pa's in the inode */
        spin_lock(&ei->i_prealloc_lock);
        while (!list_empty(&ei->i_prealloc_list)) {
                pa = list_entry(ei->i_prealloc_list.next,
                                struct ext4_prealloc_space, pa_inode_list);
                BUG_ON(pa->pa_obj_lock != &ei->i_prealloc_lock);
                spin_lock(&pa->pa_lock);
                if (atomic_read(&pa->pa_count)) {
                        /* this shouldn't happen often - nobody should
                         * use preallocation while we're discarding it */
                        spin_unlock(&pa->pa_lock);
                        spin_unlock(&ei->i_prealloc_lock);
                        printk(KERN_ERR "uh-oh! used pa while discarding\n");
                        WARN_ON(1);
                        schedule_timeout_uninterruptible(HZ);
                        goto repeat;

                }
                if (pa->pa_deleted == 0) {
                        pa->pa_deleted = 1;
                        spin_unlock(&pa->pa_lock);
                        list_del_rcu(&pa->pa_inode_list);
                        list_add(&pa->u.pa_tmp_list, &list);
                        continue;
                }

                /* someone is deleting pa right now */
                spin_unlock(&pa->pa_lock);
                spin_unlock(&ei->i_prealloc_lock);

                /* we have to wait here because pa_deleted
                 * doesn't mean pa is already unlinked from
                 * the list. as we might be called from
                 * ->clear_inode() the inode will get freed
                 * and concurrent thread which is unlinking
                 * pa from inode's list may access already
                 * freed memory, bad-bad-bad */

                /* XXX: if this happens too often, we can
                 * add a flag to force wait only in case
                 * of ->clear_inode(), but not in case of
                 * regular truncate */
                schedule_timeout_uninterruptible(HZ);
                goto repeat;
        }
        spin_unlock(&ei->i_prealloc_lock);

        list_for_each_entry_safe(pa, tmp, &list, u.pa_tmp_list) {
                BUG_ON(pa->pa_type != MB_INODE_PA);
                ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, NULL);

                err = ext4_mb_load_buddy(sb, group, &e4b);
                if (err) {
                        ext4_error(sb, "Error loading buddy information for %u",
                                        group);
                        continue;
                }

                bitmap_bh = ext4_read_block_bitmap(sb, group);
                if (bitmap_bh == NULL) {
                        ext4_error(sb, "Error reading block bitmap for %u",
                                        group);
                        ext4_mb_unload_buddy(&e4b);
                        continue;
                }

                ext4_lock_group(sb, group);
                list_del(&pa->pa_group_list);
                ext4_mb_release_inode_pa(&e4b, bitmap_bh, pa, ac);
                ext4_unlock_group(sb, group);

                ext4_mb_unload_buddy(&e4b);
                put_bh(bitmap_bh);

                list_del(&pa->u.pa_tmp_list);
                call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
        }
        if (ac)
                kmem_cache_free(ext4_ac_cachep, ac);
}

/*
 * finds all preallocated spaces and return blocks being freed to them
 * if preallocated space becomes full (no block is used from the space)
 * then the function frees space in buddy
 * XXX: at the moment, truncate (which is the only way to free blocks)
 * discards all preallocations
 */
static void ext4_mb_return_to_preallocation(struct inode *inode,
                                        struct ext4_buddy *e4b,
                                        sector_t block, int count)
{
        BUG_ON(!list_empty(&EXT4_I(inode)->i_prealloc_list));
}
#ifdef CONFIG_EXT4_DEBUG
static void ext4_mb_show_ac(struct ext4_allocation_context *ac)
{
        struct super_block *sb = ac->ac_sb;
        ext4_group_t ngroups, i;

        printk(KERN_ERR "EXT4-fs: Can't allocate:"
                        " Allocation context details:\n");
        printk(KERN_ERR "EXT4-fs: status %d flags %d\n",
                        ac->ac_status, ac->ac_flags);
        printk(KERN_ERR "EXT4-fs: orig %lu/%lu/%lu@%lu, goal %lu/%lu/%lu@%lu, "
                        "best %lu/%lu/%lu@%lu cr %d\n",
                        (unsigned long)ac->ac_o_ex.fe_group,
                        (unsigned long)ac->ac_o_ex.fe_start,
                        (unsigned long)ac->ac_o_ex.fe_len,
                        (unsigned long)ac->ac_o_ex.fe_logical,
                        (unsigned long)ac->ac_g_ex.fe_group,
                        (unsigned long)ac->ac_g_ex.fe_start,
                        (unsigned long)ac->ac_g_ex.fe_len,
                        (unsigned long)ac->ac_g_ex.fe_logical,
                        (unsigned long)ac->ac_b_ex.fe_group,
                        (unsigned long)ac->ac_b_ex.fe_start,
                        (unsigned long)ac->ac_b_ex.fe_len,
                        (unsigned long)ac->ac_b_ex.fe_logical,
                        (int)ac->ac_criteria);
        printk(KERN_ERR "EXT4-fs: %lu scanned, %d found\n", ac->ac_ex_scanned,
                ac->ac_found);
        printk(KERN_ERR "EXT4-fs: groups: \n");
        ngroups = ext4_get_groups_count(sb);
        for (i = 0; i < ngroups; i++) {
                struct ext4_group_info *grp = ext4_get_group_info(sb, i);
                struct ext4_prealloc_space *pa;
                ext4_grpblk_t start;
                struct list_head *cur;
                ext4_lock_group(sb, i);
                list_for_each(cur, &grp->bb_prealloc_list) {
                        pa = list_entry(cur, struct ext4_prealloc_space,
                                        pa_group_list);
                        spin_lock(&pa->pa_lock);
                        ext4_get_group_no_and_offset(sb, pa->pa_pstart,
                                                     NULL, &start);
                        spin_unlock(&pa->pa_lock);
                        printk(KERN_ERR "PA:%u:%d:%u \n", i,
                               start, pa->pa_len);
                }
                ext4_unlock_group(sb, i);

                if (grp->bb_free == 0)
                        continue;
                printk(KERN_ERR "%u: %d/%d \n",
                       i, grp->bb_free, grp->bb_fragments);
        }
        printk(KERN_ERR "\n");
}
#else
static inline void ext4_mb_show_ac(struct ext4_allocation_context *ac)
{
        return;
}
#endif

/*
 * We use locality group preallocation for small size file. The size of the
 * file is determined by the current size or the resulting size after
 * allocation which ever is larger
 *
 * One can tune this size via /sys/fs/ext4/<partition>/mb_stream_req
 */
static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        int bsbits = ac->ac_sb->s_blocksize_bits;
        loff_t size, isize;

        if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
                return;

        if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
                return;

        size = ac->ac_o_ex.fe_logical + ac->ac_o_ex.fe_len;
        isize = (i_size_read(ac->ac_inode) + ac->ac_sb->s_blocksize - 1)
                >> bsbits;

        if ((size == isize) &&
            !ext4_fs_is_busy(sbi) &&
            (atomic_read(&ac->ac_inode->i_writecount) == 0)) {
                ac->ac_flags |= EXT4_MB_HINT_NOPREALLOC;
                return;
        }

        /* don't use group allocation for large files */
        size = max(size, isize);
        if (size > sbi->s_mb_stream_request) {
                ac->ac_flags |= EXT4_MB_STREAM_ALLOC;
                return;
        }

        BUG_ON(ac->ac_lg != NULL);
        /*
         * locality group prealloc space are per cpu. The reason for having
         * per cpu locality group is to reduce the contention between block
         * request from multiple CPUs.
         */
        ac->ac_lg = __this_cpu_ptr(sbi->s_locality_groups);

        /* we're going to use group allocation */
        ac->ac_flags |= EXT4_MB_HINT_GROUP_ALLOC;

        /* serialize all allocations in the group */
        mutex_lock(&ac->ac_lg->lg_mutex);
}

static noinline_for_stack int
ext4_mb_initialize_context(struct ext4_allocation_context *ac,
                                struct ext4_allocation_request *ar)
{
        struct super_block *sb = ar->inode->i_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_super_block *es = sbi->s_es;
        ext4_group_t group;
        unsigned int len;
        ext4_fsblk_t goal;
        ext4_grpblk_t block;

        /* we can't allocate > group size */
        len = ar->len;

        /* just a dirty hack to filter too big requests  */
        if (len >= EXT4_BLOCKS_PER_GROUP(sb) - 10)
                len = EXT4_BLOCKS_PER_GROUP(sb) - 10;

        /* start searching from the goal */
        goal = ar->goal;
        if (goal < le32_to_cpu(es->s_first_data_block) ||
                        goal >= ext4_blocks_count(es))
                goal = le32_to_cpu(es->s_first_data_block);
        ext4_get_group_no_and_offset(sb, goal, &group, &block);

        /* set up allocation goals */
        memset(ac, 0, sizeof(struct ext4_allocation_context));
        ac->ac_b_ex.fe_logical = ar->logical;
        ac->ac_status = AC_STATUS_CONTINUE;
        ac->ac_sb = sb;
        ac->ac_inode = ar->inode;
        ac->ac_o_ex.fe_logical = ar->logical;
        ac->ac_o_ex.fe_group = group;
        ac->ac_o_ex.fe_start = block;
        ac->ac_o_ex.fe_len = len;
        ac->ac_g_ex.fe_logical = ar->logical;
        ac->ac_g_ex.fe_group = group;
        ac->ac_g_ex.fe_start = block;
        ac->ac_g_ex.fe_len = len;
        ac->ac_flags = ar->flags;

        /* we have to define context: we'll we work with a file or
         * locality group. this is a policy, actually */
        ext4_mb_group_or_file(ac);

        mb_debug(1, "init ac: %u blocks @ %u, goal %u, flags %x, 2^%d, "
                        "left: %u/%u, right %u/%u to %swritable\n",
                        (unsigned) ar->len, (unsigned) ar->logical,
                        (unsigned) ar->goal, ac->ac_flags, ac->ac_2order,
                        (unsigned) ar->lleft, (unsigned) ar->pleft,
                        (unsigned) ar->lright, (unsigned) ar->pright,
                        atomic_read(&ar->inode->i_writecount) ? "" : "non-");
        return 0;

}

static noinline_for_stack void
ext4_mb_discard_lg_preallocations(struct super_block *sb,
                                        struct ext4_locality_group *lg,
                                        int order, int total_entries)
{
        ext4_group_t group = 0;
        struct ext4_buddy e4b;
        struct list_head discard_list;
        struct ext4_prealloc_space *pa, *tmp;
        struct ext4_allocation_context *ac;

        mb_debug(1, "discard locality group preallocation\n");

        INIT_LIST_HEAD(&discard_list);
        ac = kmem_cache_alloc(ext4_ac_cachep, GFP_NOFS);
        if (ac)
                ac->ac_sb = sb;

        spin_lock(&lg->lg_prealloc_lock);
        list_for_each_entry_rcu(pa, &lg->lg_prealloc_list[order],
                                                pa_inode_list) {
                spin_lock(&pa->pa_lock);
                if (atomic_read(&pa->pa_count)) {
                        /*
                         * This is the pa that we just used
                         * for block allocation. So don't
                         * free that
                         */
                        spin_unlock(&pa->pa_lock);
                        continue;
                }
                if (pa->pa_deleted) {
                        spin_unlock(&pa->pa_lock);
                        continue;
                }
                /* only lg prealloc space */
                BUG_ON(pa->pa_type != MB_GROUP_PA);

                /* seems this one can be freed ... */
                pa->pa_deleted = 1;
                spin_unlock(&pa->pa_lock);

                list_del_rcu(&pa->pa_inode_list);
                list_add(&pa->u.pa_tmp_list, &discard_list);

                total_entries--;
                if (total_entries <= 5) {
                        /*
                         * we want to keep only 5 entries
                         * allowing it to grow to 8. This
                         * mak sure we don't call discard
                         * soon for this list.
                         */
                        break;
                }
        }
        spin_unlock(&lg->lg_prealloc_lock);

        list_for_each_entry_safe(pa, tmp, &discard_list, u.pa_tmp_list) {

                ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, NULL);
                if (ext4_mb_load_buddy(sb, group, &e4b)) {
                        ext4_error(sb, "Error loading buddy information for %u",
                                        group);
                        continue;
                }
                ext4_lock_group(sb, group);
                list_del(&pa->pa_group_list);
                ext4_mb_release_group_pa(&e4b, pa, ac);
                ext4_unlock_group(sb, group);

                ext4_mb_unload_buddy(&e4b);
                list_del(&pa->u.pa_tmp_list);
                call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
        }
        if (ac)
                kmem_cache_free(ext4_ac_cachep, ac);
}

/*
 * We have incremented pa_count. So it cannot be freed at this
 * point. Also we hold lg_mutex. So no parallel allocation is
 * possible from this lg. That means pa_free cannot be updated.
 *
 * A parallel ext4_mb_discard_group_preallocations is possible.
 * which can cause the lg_prealloc_list to be updated.
 */

static void ext4_mb_add_n_trim(struct ext4_allocation_context *ac)
{
        int order, added = 0, lg_prealloc_count = 1;
        struct super_block *sb = ac->ac_sb;
        struct ext4_locality_group *lg = ac->ac_lg;
        struct ext4_prealloc_space *tmp_pa, *pa = ac->ac_pa;

        order = fls(pa->pa_free) - 1;
        if (order > PREALLOC_TB_SIZE - 1)
                /* The max size of hash table is PREALLOC_TB_SIZE */
                order = PREALLOC_TB_SIZE - 1;
        /* Add the prealloc space to lg */
        rcu_read_lock();
        list_for_each_entry_rcu(tmp_pa, &lg->lg_prealloc_list[order],
                                                pa_inode_list) {
                spin_lock(&tmp_pa->pa_lock);
                if (tmp_pa->pa_deleted) {
                        spin_unlock(&tmp_pa->pa_lock);
                        continue;
                }
                if (!added && pa->pa_free < tmp_pa->pa_free) {
                        /* Add to the tail of the previous entry */
                        list_add_tail_rcu(&pa->pa_inode_list,
                                                &tmp_pa->pa_inode_list);
                        added = 1;
                        /*
                         * we want to count the total
                         * number of entries in the list
                         */
                }
                spin_unlock(&tmp_pa->pa_lock);
                lg_prealloc_count++;
        }
        if (!added)
                list_add_tail_rcu(&pa->pa_inode_list,
                                        &lg->lg_prealloc_list[order]);
        rcu_read_unlock();

        /* Now trim the list to be not more than 8 elements */
        if (lg_prealloc_count > 8) {
                ext4_mb_discard_lg_preallocations(sb, lg,
                                                order, lg_prealloc_count);
                return;
        }
        return ;
}

/*
 * release all resource we used in allocation
 */
static int ext4_mb_release_context(struct ext4_allocation_context *ac)
{
        struct ext4_prealloc_space *pa = ac->ac_pa;
        if (pa) {
                if (pa->pa_type == MB_GROUP_PA) {
                        /* see comment in ext4_mb_use_group_pa() */
                        spin_lock(&pa->pa_lock);
                        pa->pa_pstart += ac->ac_b_ex.fe_len;
                        pa->pa_lstart += ac->ac_b_ex.fe_len;
                        pa->pa_free -= ac->ac_b_ex.fe_len;
                        pa->pa_len -= ac->ac_b_ex.fe_len;
                        spin_unlock(&pa->pa_lock);
                }
        }
        if (ac->alloc_semp)
                up_read(ac->alloc_semp);
        if (pa) {
                /*
                 * We want to add the pa to the right bucket.
                 * Remove it from the list and while adding
                 * make sure the list to which we are adding
                 * doesn't grow big.  We need to release
                 * alloc_semp before calling ext4_mb_add_n_trim()
                 */
                if ((pa->pa_type == MB_GROUP_PA) && likely(pa->pa_free)) {
                        spin_lock(pa->pa_obj_lock);
                        list_del_rcu(&pa->pa_inode_list);
                        spin_unlock(pa->pa_obj_lock);
                        ext4_mb_add_n_trim(ac);
                }
                ext4_mb_put_pa(ac, ac->ac_sb, pa);
        }
        if (ac->ac_bitmap_page)
                page_cache_release(ac->ac_bitmap_page);
        if (ac->ac_buddy_page)
                page_cache_release(ac->ac_buddy_page);
        if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
                mutex_unlock(&ac->ac_lg->lg_mutex);
        ext4_mb_collect_stats(ac);
        return 0;
}

static int ext4_mb_discard_preallocations(struct super_block *sb, int needed)
{
        ext4_group_t i, ngroups = ext4_get_groups_count(sb);
        int ret;
        int freed = 0;

        trace_ext4_mb_discard_preallocations(sb, needed);
        for (i = 0; i < ngroups && needed > 0; i++) {
                ret = ext4_mb_discard_group_preallocations(sb, i, needed);
                freed += ret;
                needed -= ret;
        }

        return freed;
}

/*
 * Main entry point into mballoc to allocate blocks
 * it tries to use preallocation first, then falls back
 * to usual allocation
 */
ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
                                 struct ext4_allocation_request *ar, int *errp)
{
        int freed;
        struct ext4_allocation_context *ac = NULL;
        struct ext4_sb_info *sbi;
        struct super_block *sb;
        ext4_fsblk_t block = 0;
        unsigned int inquota = 0;
        unsigned int reserv_blks = 0;

        sb = ar->inode->i_sb;
        sbi = EXT4_SB(sb);

        trace_ext4_request_blocks(ar);

        /*
         * For delayed allocation, we could skip the ENOSPC and
         * EDQUOT check, as blocks and quotas have been already
         * reserved when data being copied into pagecache.
         */
        if (EXT4_I(ar->inode)->i_delalloc_reserved_flag)
                ar->flags |= EXT4_MB_DELALLOC_RESERVED;
        else {
                /* Without delayed allocation we need to verify
                 * there is enough free blocks to do block allocation
                 * and verify allocation doesn't exceed the quota limits.
                 */
                while (ar->len && ext4_claim_free_blocks(sbi, ar->len)) {
                        /* let others to free the space */
                        yield();
                        ar->len = ar->len >> 1;
                }
                if (!ar->len) {
                        *errp = -ENOSPC;
                        return 0;
                }
                reserv_blks = ar->len;
                while (ar->len && dquot_alloc_block(ar->inode, ar->len)) {
                        ar->flags |= EXT4_MB_HINT_NOPREALLOC;
                        ar->len--;
                }
                inquota = ar->len;
                if (ar->len == 0) {
                        *errp = -EDQUOT;
                        goto out3;
                }
        }

        ac = kmem_cache_alloc(ext4_ac_cachep, GFP_NOFS);
        if (!ac) {
                ar->len = 0;
                *errp = -ENOMEM;
                goto out1;
        }

        *errp = ext4_mb_initialize_context(ac, ar);
        if (*errp) {
                ar->len = 0;
                goto out2;
        }

        ac->ac_op = EXT4_MB_HISTORY_PREALLOC;
        if (!ext4_mb_use_preallocated(ac)) {
                ac->ac_op = EXT4_MB_HISTORY_ALLOC;
                ext4_mb_normalize_request(ac, ar);
repeat:
                /* allocate space in core */
                ext4_mb_regular_allocator(ac);

                /* as we've just preallocated more space than
                 * user requested orinally, we store allocated
                 * space in a special descriptor */
                if (ac->ac_status == AC_STATUS_FOUND &&
                                ac->ac_o_ex.fe_len < ac->ac_b_ex.fe_len)
                        ext4_mb_new_preallocation(ac);
        }
        if (likely(ac->ac_status == AC_STATUS_FOUND)) {
                *errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_blks);
                if (*errp ==  -EAGAIN) {
                        /*
                         * drop the reference that we took
                         * in ext4_mb_use_best_found
                         */
                        ext4_mb_release_context(ac);
                        ac->ac_b_ex.fe_group = 0;
                        ac->ac_b_ex.fe_start = 0;
                        ac->ac_b_ex.fe_len = 0;
                        ac->ac_status = AC_STATUS_CONTINUE;
                        goto repeat;
                } else if (*errp) {
                        ext4_discard_allocated_blocks(ac);
                        ac->ac_b_ex.fe_len = 0;
                        ar->len = 0;
                        ext4_mb_show_ac(ac);
                } else {
                        block = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
                        ar->len = ac->ac_b_ex.fe_len;
                }
        } else {
                freed  = ext4_mb_discard_preallocations(sb, ac->ac_o_ex.fe_len);
                if (freed)
                        goto repeat;
                *errp = -ENOSPC;
                ac->ac_b_ex.fe_len = 0;
                ar->len = 0;
                ext4_mb_show_ac(ac);
        }

        ext4_mb_release_context(ac);

out2:
        kmem_cache_free(ext4_ac_cachep, ac);
out1:
        if (inquota && ar->len < inquota)
                dquot_free_block(ar->inode, inquota - ar->len);
out3:
        if (!ar->len) {
                if (!EXT4_I(ar->inode)->i_delalloc_reserved_flag)
                        /* release all the reserved blocks if non delalloc */
                        percpu_counter_sub(&sbi->s_dirtyblocks_counter,
                                                reserv_blks);
        }

        trace_ext4_allocate_blocks(ar, (unsigned long long)block);

        return block;
}

/*
 * We can merge two free data extents only if the physical blocks
 * are contiguous, AND the extents were freed by the same transaction,
 * AND the blocks are associated with the same group.
 */
static int can_merge(struct ext4_free_data *entry1,
                        struct ext4_free_data *entry2)
{
        if ((entry1->t_tid == entry2->t_tid) &&
            (entry1->group == entry2->group) &&
            ((entry1->start_blk + entry1->count) == entry2->start_blk))
                return 1;
        return 0;
}

static noinline_for_stack int
ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
                      struct ext4_free_data *new_entry)
{
        ext4_grpblk_t block;
        struct ext4_free_data *entry;
        struct ext4_group_info *db = e4b->bd_info;
        struct super_block *sb = e4b->bd_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct rb_node **n = &db->bb_free_root.rb_node, *node;
        struct rb_node *parent = NULL, *new_node;

        BUG_ON(!ext4_handle_valid(handle));
        BUG_ON(e4b->bd_bitmap_page == NULL);
        BUG_ON(e4b->bd_buddy_page == NULL);

        new_node = &new_entry->node;
        block = new_entry->start_blk;

        if (!*n) {
                /* first free block exent. We need to
                   protect buddy cache from being freed,
                 * otherwise we'll refresh it from
                 * on-disk bitmap and lose not-yet-available
                 * blocks */
                page_cache_get(e4b->bd_buddy_page);
                page_cache_get(e4b->bd_bitmap_page);
        }
        while (*n) {
                parent = *n;
                entry = rb_entry(parent, struct ext4_free_data, node);
                if (block < entry->start_blk)
                        n = &(*n)->rb_left;
                else if (block >= (entry->start_blk + entry->count))
                        n = &(*n)->rb_right;
                else {
                        ext4_grp_locked_error(sb, e4b->bd_group, __func__,
                                        "Double free of blocks %d (%d %d)",
                                        block, entry->start_blk, entry->count);
                        return 0;
                }
        }

        rb_link_node(new_node, parent, n);
        rb_insert_color(new_node, &db->bb_free_root);

        /* Now try to see the extent can be merged to left and right */
        node = rb_prev(new_node);
        if (node) {
                entry = rb_entry(node, struct ext4_free_data, node);
                if (can_merge(entry, new_entry)) {
                        new_entry->start_blk = entry->start_blk;
                        new_entry->count += entry->count;
                        rb_erase(node, &(db->bb_free_root));
                        spin_lock(&sbi->s_md_lock);
                        list_del(&entry->list);
                        spin_unlock(&sbi->s_md_lock);
                        kmem_cache_free(ext4_free_ext_cachep, entry);
                }
        }

        node = rb_next(new_node);
        if (node) {
                entry = rb_entry(node, struct ext4_free_data, node);
                if (can_merge(new_entry, entry)) {
                        new_entry->count += entry->count;
                        rb_erase(node, &(db->bb_free_root));
                        spin_lock(&sbi->s_md_lock);
                        list_del(&entry->list);
                        spin_unlock(&sbi->s_md_lock);
                        kmem_cache_free(ext4_free_ext_cachep, entry);
                }
        }
        /* Add the extent to transaction's private list */
        spin_lock(&sbi->s_md_lock);
        list_add(&new_entry->list, &handle->h_transaction->t_private_list);
        spin_unlock(&sbi->s_md_lock);
        return 0;
}

/**
 * ext4_free_blocks() -- Free given blocks and update quota
 * @handle:             handle for this transaction
 * @inode:              inode
 * @block:              start physical block to free
 * @count:              number of blocks to count
 * @metadata:           Are these metadata blocks
 */
void ext4_free_blocks(handle_t *handle, struct inode *inode,
                      struct buffer_head *bh, ext4_fsblk_t block,
                      unsigned long count, int flags)
{
        struct buffer_head *bitmap_bh = NULL;
        struct super_block *sb = inode->i_sb;
        struct ext4_allocation_context *ac = NULL;
        struct ext4_group_desc *gdp;
        struct ext4_super_block *es;
        unsigned long freed = 0;
        unsigned int overflow;
        ext4_grpblk_t bit;
        struct buffer_head *gd_bh;
        ext4_group_t block_group;
        struct ext4_sb_info *sbi;
        struct ext4_buddy e4b;
        int err = 0;
        int ret;

        if (bh) {
                if (block)
                        BUG_ON(block != bh->b_blocknr);
                else
                        block = bh->b_blocknr;
        }

        sbi = EXT4_SB(sb);
        es = EXT4_SB(sb)->s_es;
        if (!(flags & EXT4_FREE_BLOCKS_VALIDATED) &&
            !ext4_data_block_valid(sbi, block, count)) {
                ext4_error(sb, "Freeing blocks not in datazone - "
                           "block = %llu, count = %lu", block, count);
                goto error_return;
        }

        ext4_debug("freeing block %llu\n", block);
        trace_ext4_free_blocks(inode, block, count, flags);

        if (flags & EXT4_FREE_BLOCKS_FORGET) {
                struct buffer_head *tbh = bh;
                int i;

                BUG_ON(bh && (count > 1));

                for (i = 0; i < count; i++) {
                        if (!bh)
                                tbh = sb_find_get_block(inode->i_sb,
                                                        block + i);
                        ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
                                    inode, tbh, block + i);
                }
        }

        /*
         * We need to make sure we don't reuse the freed block until
         * after the transaction is committed, which we can do by
         * treating the block as metadata, below.  We make an
         * exception if the inode is to be written in writeback mode
         * since writeback mode has weak data consistency guarantees.
         */
        if (!ext4_should_writeback_data(inode))
                flags |= EXT4_FREE_BLOCKS_METADATA;

        ac = kmem_cache_alloc(ext4_ac_cachep, GFP_NOFS);
        if (ac) {
                ac->ac_inode = inode;
                ac->ac_sb = sb;
        }

do_more:
        overflow = 0;
        ext4_get_group_no_and_offset(sb, block, &block_group, &bit);

        /*
         * Check to see if we are freeing blocks across a group
         * boundary.
         */
        if (bit + count > EXT4_BLOCKS_PER_GROUP(sb)) {
                overflow = bit + count - EXT4_BLOCKS_PER_GROUP(sb);
                count -= overflow;
        }
        bitmap_bh = ext4_read_block_bitmap(sb, block_group);
        if (!bitmap_bh) {
                err = -EIO;
                goto error_return;
        }
        gdp = ext4_get_group_desc(sb, block_group, &gd_bh);
        if (!gdp) {
                err = -EIO;
                goto error_return;
        }

        if (in_range(ext4_block_bitmap(sb, gdp), block, count) ||
            in_range(ext4_inode_bitmap(sb, gdp), block, count) ||
            in_range(block, ext4_inode_table(sb, gdp),
                      EXT4_SB(sb)->s_itb_per_group) ||
            in_range(block + count - 1, ext4_inode_table(sb, gdp),
                      EXT4_SB(sb)->s_itb_per_group)) {

                ext4_error(sb, "Freeing blocks in system zone - "
                           "Block = %llu, count = %lu", block, count);
                /* err = 0. ext4_std_error should be a no op */
                goto error_return;
        }

        BUFFER_TRACE(bitmap_bh, "getting write access");
        err = ext4_journal_get_write_access(handle, bitmap_bh);
        if (err)
                goto error_return;

        /*
         * We are about to modify some metadata.  Call the journal APIs
         * to unshare ->b_data if a currently-committing transaction is
         * using it
         */
        BUFFER_TRACE(gd_bh, "get_write_access");
        err = ext4_journal_get_write_access(handle, gd_bh);
        if (err)
                goto error_return;
#ifdef AGGRESSIVE_CHECK
        {
                int i;
                for (i = 0; i < count; i++)
                        BUG_ON(!mb_test_bit(bit + i, bitmap_bh->b_data));
        }
#endif
        if (ac) {
                ac->ac_b_ex.fe_group = block_group;
                ac->ac_b_ex.fe_start = bit;
                ac->ac_b_ex.fe_len = count;
                trace_ext4_mballoc_free(ac);
        }

        err = ext4_mb_load_buddy(sb, block_group, &e4b);
        if (err)
                goto error_return;

        if ((flags & EXT4_FREE_BLOCKS_METADATA) && ext4_handle_valid(handle)) {
                struct ext4_free_data *new_entry;
                /*
                 * blocks being freed are metadata. these blocks shouldn't
                 * be used until this transaction is committed
                 */
                new_entry  = kmem_cache_alloc(ext4_free_ext_cachep, GFP_NOFS);
                new_entry->start_blk = bit;
                new_entry->group  = block_group;
                new_entry->count = count;
                new_entry->t_tid = handle->h_transaction->t_tid;

                ext4_lock_group(sb, block_group);
                mb_clear_bits(bitmap_bh->b_data, bit, count);
                ext4_mb_free_metadata(handle, &e4b, new_entry);
        } else {
                /* need to update group_info->bb_free and bitmap
                 * with group lock held. generate_buddy look at
                 * them with group lock_held
                 */
                ext4_lock_group(sb, block_group);
                mb_clear_bits(bitmap_bh->b_data, bit, count);
                mb_free_blocks(inode, &e4b, bit, count);
                ext4_mb_return_to_preallocation(inode, &e4b, block, count);
        }

        ret = ext4_free_blks_count(sb, gdp) + count;
        ext4_free_blks_set(sb, gdp, ret);
        gdp->bg_checksum = ext4_group_desc_csum(sbi, block_group, gdp);
        ext4_unlock_group(sb, block_group);
        percpu_counter_add(&sbi->s_freeblocks_counter, count);

        if (sbi->s_log_groups_per_flex) {
                ext4_group_t flex_group = ext4_flex_group(sbi, block_group);
                atomic_add(count, &sbi->s_flex_groups[flex_group].free_blocks);
        }

        ext4_mb_unload_buddy(&e4b);

        freed += count;

        /* We dirtied the bitmap block */
        BUFFER_TRACE(bitmap_bh, "dirtied bitmap block");
        err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);

        /* And the group descriptor block */
        BUFFER_TRACE(gd_bh, "dirtied group descriptor block");
        ret = ext4_handle_dirty_metadata(handle, NULL, gd_bh);
        if (!err)
                err = ret;

        if (overflow && !err) {
                block += count;
                count = overflow;
                put_bh(bitmap_bh);
                goto do_more;
        }
        sb->s_dirt = 1;
error_return:
        if (freed)
                dquot_free_block(inode, freed);
        brelse(bitmap_bh);
        ext4_std_error(sb, err);
        if (ac)
                kmem_cache_free(ext4_ac_cachep, ac);
        return;
}