swap_info: swap_map of chars not shorts

Halve the vmalloc'ed swap_map array from unsigned shorts to unsigned
chars: it's still very unusual to reach a swap count of 126, and the
next patch allows it to be extended indefinitely.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index c9d8870892b89d7cf8839ca40ae135a949f7e25e..f733deb107480c7d6a65c8f8446fad098733fe3c 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -151,9 +151,9 @@ enum {
 
 #define SWAP_CLUSTER_MAX 32
 
-#define SWAP_MAP_MAX   0x7ffe
-#define SWAP_MAP_BAD   0x7fff
-#define SWAP_HAS_CACHE  0x8000         /* There is a swap cache of entry. */
+#define SWAP_MAP_MAX   0x7e
+#define SWAP_MAP_BAD   0x7f
+#define SWAP_HAS_CACHE 0x80            /* There is a swap cache of entry. */
 
 /*
  * The in-memory structure used to track swap areas.
@@ -167,7 +167,7 @@ struct swap_info_struct {
        struct block_device *bdev;
        struct swap_extent first_swap_extent;
        struct swap_extent *curr_swap_extent;
-       unsigned short *swap_map;
+       unsigned char *swap_map;
        unsigned int lowest_bit;
        unsigned int highest_bit;
        unsigned int lowest_alloc;      /* while preparing discard cluster */

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 52497490a7ca8de933feebddd44d57249244c78d..c0d7b9ed0c16507ca598a20f146b44fcbc802a5f 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -53,7 +53,7 @@ static struct swap_info_struct *swap_info[MAX_SWAPFILES];
 
 static DEFINE_MUTEX(swapon_mutex);
 
-static inline int swap_count(unsigned short ent)
+static inline unsigned char swap_count(unsigned char ent)
 {
        return ent & ~SWAP_HAS_CACHE;
 }
@@ -203,7 +203,7 @@ static int wait_for_discard(void *word)
 #define LATENCY_LIMIT          256
 
 static inline unsigned long scan_swap_map(struct swap_info_struct *si,
-                                         unsigned short usage)
+                                         unsigned char usage)
 {
        unsigned long offset;
        unsigned long scan_base;
@@ -531,12 +531,12 @@ out:
        return NULL;
 }
 
-static unsigned short swap_entry_free(struct swap_info_struct *p,
-                          swp_entry_t entry, unsigned short usage)
+static unsigned char swap_entry_free(struct swap_info_struct *p,
+                                    swp_entry_t entry, unsigned char usage)
 {
        unsigned long offset = swp_offset(entry);
-       unsigned short count;
-       unsigned short has_cache;
+       unsigned char count;
+       unsigned char has_cache;
 
        count = p->swap_map[offset];
        has_cache = count & SWAP_HAS_CACHE;
@@ -591,7 +591,7 @@ void swap_free(swp_entry_t entry)
 void swapcache_free(swp_entry_t entry, struct page *page)
 {
        struct swap_info_struct *p;
-       unsigned short count;
+       unsigned char count;
 
        p = swap_info_get(entry);
        if (p) {
@@ -975,7 +975,7 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
 {
        unsigned int max = si->max;
        unsigned int i = prev;
-       int count;
+       unsigned char count;
 
        /*
         * No need for swap_lock here: we're just looking
@@ -1013,8 +1013,8 @@ static int try_to_unuse(unsigned int type)
 {
        struct swap_info_struct *si = swap_info[type];
        struct mm_struct *start_mm;
-       unsigned short *swap_map;
-       unsigned short swcount;
+       unsigned char *swap_map;
+       unsigned char swcount;
        struct page *page;
        swp_entry_t entry;
        unsigned int i = 0;
@@ -1174,6 +1174,12 @@ static int try_to_unuse(unsigned int type)
                 * If that's wrong, then we should worry more about
                 * exit_mmap() and do_munmap() cases described above:
                 * we might be resetting SWAP_MAP_MAX too early here.
+                *
+                * Yes, that's wrong: though very unlikely, swap count 0x7ffe
+                * could surely occur if pid_max raised from PID_MAX_DEFAULT;
+                * and we are now lowering SWAP_MAP_MAX to 0x7e, making it
+                * much easier to reach.  But the next patch will fix that.
+                *
                 * We know "Undead"s can happen, they're okay, so don't
                 * report them; but do report if we reset SWAP_MAP_MAX.
                 */
@@ -1492,7 +1498,7 @@ bad_bmap:
 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 {
        struct swap_info_struct *p = NULL;
-       unsigned short *swap_map;
+       unsigned char *swap_map;
        struct file *swap_file, *victim;
        struct address_space *mapping;
        struct inode *inode;
@@ -1762,7 +1768,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
        sector_t span;
        unsigned long maxpages = 1;
        unsigned long swapfilepages;
-       unsigned short *swap_map = NULL;
+       unsigned char *swap_map = NULL;
        struct page *page = NULL;
        struct inode *inode = NULL;
        int did_down = 0;
@@ -1938,13 +1944,13 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
                goto bad_swap;
 
        /* OK, set up the swap map and apply the bad block list */
-       swap_map = vmalloc(maxpages * sizeof(short));
+       swap_map = vmalloc(maxpages);
        if (!swap_map) {
                error = -ENOMEM;
                goto bad_swap;
        }
 
-       memset(swap_map, 0, maxpages * sizeof(short));
+       memset(swap_map, 0, maxpages);
        for (i = 0; i < swap_header->info.nr_badpages; i++) {
                int page_nr = swap_header->info.badpages[i];
                if (page_nr <= 0 || page_nr >= swap_header->info.last_page) {
@@ -2082,12 +2088,12 @@ void si_swapinfo(struct sysinfo *val)
  * - swap-cache reference is requested but there is already one. -> EEXIST
  * - swap-cache reference is requested but the entry is not used. -> ENOENT
  */
-static int __swap_duplicate(swp_entry_t entry, unsigned short usage)
+static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 {
        struct swap_info_struct *p;
        unsigned long offset, type;
-       unsigned short count;
-       unsigned short has_cache;
+       unsigned char count;
+       unsigned char has_cache;
        int err = -EINVAL;
 
        if (non_swap_entry(entry))