mm/page-writeback.c

   1 /*
   2  * mm/page-writeback.c.
   3  *
   4  * Copyright (C) 2002, Linus Torvalds.
   5  *
   6  * Contains functions related to writing back dirty pages at the
   7  * address_space level.
   8  *
   9  * 10Apr2002    akpm@zip.com.au
  10  *              Initial version
  11  */
  12
  13 #include <linux/kernel.h>
  14 #include <linux/module.h>
  15 #include <linux/spinlock.h>
  16 #include <linux/fs.h>
  17 #include <linux/mm.h>
  18 #include <linux/swap.h>
  19 #include <linux/slab.h>
  20 #include <linux/pagemap.h>
  21 #include <linux/writeback.h>
  22 #include <linux/init.h>
  23 #include <linux/backing-dev.h>
  24 #include <linux/blkdev.h>
  25 #include <linux/mpage.h>
  26 #include <linux/percpu.h>
  27 #include <linux/notifier.h>
  28 #include <linux/smp.h>
  29 #include <linux/sysctl.h>
  30 #include <linux/cpu.h>
  31 #include <linux/syscalls.h>
  32
  33 /*
  34  * The maximum number of pages to writeout in a single bdflush/kupdate
  35  * operation.  We do this so we don't hold I_LOCK against an inode for
  36  * enormous amounts of time, which would block a userspace task which has
  37  * been forced to throttle against that inode.  Also, the code reevaluates
  38  * the dirty each time it has written this many pages.
  39  */
  40 #define MAX_WRITEBACK_PAGES     1024
  41
  42 /*
  43  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
  44  * will look to see if it needs to force writeback or throttling.
  45  */
  46 static long ratelimit_pages = 32;
  47
  48 static long total_pages;        /* The total number of pages in the machine. */
  49 static int dirty_exceeded __cacheline_aligned_in_smp;   /* Dirty mem may be over limit */
  50
  51 /*
  52  * When balance_dirty_pages decides that the caller needs to perform some
  53  * non-background writeback, this is how many pages it will attempt to write.
  54  * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
  55  * large amounts of I/O are submitted.
  56  */
  57 static inline long sync_writeback_pages(void)
  58 {
  59         return ratelimit_pages + ratelimit_pages / 2;
  60 }
  61
  62 /* The following parameters are exported via /proc/sys/vm */
  63
  64 /*
  65  * Start background writeback (via pdflush) at this percentage
  66  */
  67 int dirty_background_ratio = 10;
  68
  69 /*
  70  * The generator of dirty data starts writeback at this percentage
  71  */
  72 int vm_dirty_ratio = 40;
  73
  74 /*
  75  * The interval between `kupdate'-style writebacks, in jiffies
  76  */
  77 int dirty_writeback_interval = 5 * HZ;
  78
  79 /*
  80  * The longest number of jiffies for which data is allowed to remain dirty
  81  */
  82 int dirty_expire_interval = 30 * HZ;
  83
  84 /*
  85  * Flag that makes the machine dump writes/reads and block dirtyings.
  86  */
  87 int block_dump;
  88
  89 /*
  90  * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
  91  * a full sync is triggered after this time elapses without any disk activity.
  92  */
  93 int laptop_mode;
  94
  95 EXPORT_SYMBOL(laptop_mode);
  96
  97 /* End of sysctl-exported parameters */
  98
  99
 100 static void background_writeout(unsigned long _min_pages);
 101
 102 struct writeback_state
 103 {
 104         unsigned long nr_dirty;
 105         unsigned long nr_unstable;
 106         unsigned long nr_mapped;
 107         unsigned long nr_writeback;
 108 };
 109
 110 static void get_writeback_state(struct writeback_state *wbs)
 111 {
 112         wbs->nr_dirty = read_page_state(nr_dirty);
 113         wbs->nr_unstable = read_page_state(nr_unstable);
 114         wbs->nr_mapped = read_page_state(nr_mapped);
 115         wbs->nr_writeback = read_page_state(nr_writeback);
 116 }
 117
 118 /*
 119  * Work out the current dirty-memory clamping and background writeout
 120  * thresholds.
 121  *
 122  * The main aim here is to lower them aggressively if there is a lot of mapped
 123  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
 124  * pages.  It is better to clamp down on writers than to start swapping, and
 125  * performing lots of scanning.
 126  *
 127  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
 128  *
 129  * We don't permit the clamping level to fall below 5% - that is getting rather
 130  * excessive.
 131  *
 132  * We make sure that the background writeout level is below the adjusted
 133  * clamping level.
 134  */
 135 static void
 136 get_dirty_limits(struct writeback_state *wbs, long *pbackground, long *pdirty,
 137                 struct address_space *mapping)
 138 {
 139         int background_ratio;           /* Percentages */
 140         int dirty_ratio;
 141         int unmapped_ratio;
 142         long background;
 143         long dirty;
 144         unsigned long available_memory = total_pages;
 145         struct task_struct *tsk;
 146
 147         get_writeback_state(wbs);
 148
 149 #ifdef CONFIG_HIGHMEM
 150         /*
 151          * If this mapping can only allocate from low memory,
 152          * we exclude high memory from our count.
 153          */
 154         if (mapping && !(mapping_gfp_mask(mapping) & __GFP_HIGHMEM))
 155                 available_memory -= totalhigh_pages;
 156 #endif
 157
 158
 159         unmapped_ratio = 100 - (wbs->nr_mapped * 100) / total_pages;
 160
 161         dirty_ratio = vm_dirty_ratio;
 162         if (dirty_ratio > unmapped_ratio / 2)
 163                 dirty_ratio = unmapped_ratio / 2;
 164
 165         if (dirty_ratio < 5)
 166                 dirty_ratio = 5;
 167
 168         background_ratio = dirty_background_ratio;
 169         if (background_ratio >= dirty_ratio)
 170                 background_ratio = dirty_ratio / 2;
 171
 172         background = (background_ratio * available_memory) / 100;
 173         dirty = (dirty_ratio * available_memory) / 100;
 174         tsk = current;
 175         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
 176                 background += background / 4;
 177                 dirty += dirty / 4;
 178         }
 179         *pbackground = background;
 180         *pdirty = dirty;
 181 }
 182
 183 /*
 184  * balance_dirty_pages() must be called by processes which are generating dirty
 185  * data.  It looks at the number of dirty pages in the machine and will force
 186  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
 187  * If we're over `background_thresh' then pdflush is woken to perform some
 188  * writeout.
 189  */
 190 static void balance_dirty_pages(struct address_space *mapping)
 191 {
 192         struct writeback_state wbs;
 193         long nr_reclaimable;
 194         long background_thresh;
 195         long dirty_thresh;
 196         unsigned long pages_written = 0;
 197         unsigned long write_chunk = sync_writeback_pages();
 198
 199         struct backing_dev_info *bdi = mapping->backing_dev_info;
 200
 201         for (;;) {
 202                 struct writeback_control wbc = {
 203                         .bdi            = bdi,
 204                         .sync_mode      = WB_SYNC_NONE,
 205                         .older_than_this = NULL,
 206                         .nr_to_write    = write_chunk,
 207                 };
 208
 209                 get_dirty_limits(&wbs, &background_thresh,
 210                                         &dirty_thresh, mapping);
 211                 nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
 212                 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
 213                         break;
 214
 215                 if (!dirty_exceeded)
 216                         dirty_exceeded = 1;
 217
 218                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
 219                  * Unstable writes are a feature of certain networked
 220                  * filesystems (i.e. NFS) in which data may have been
 221                  * written to the server's write cache, but has not yet
 222                  * been flushed to permanent storage.
 223                  */
 224                 if (nr_reclaimable) {
 225                         writeback_inodes(&wbc);
 226                         get_dirty_limits(&wbs, &background_thresh,
 227                                         &dirty_thresh, mapping);
 228                         nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
 229                         if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
 230                                 break;
 231                         pages_written += write_chunk - wbc.nr_to_write;
 232                         if (pages_written >= write_chunk)
 233                                 break;          /* We've done our duty */
 234                 }
 235                 blk_congestion_wait(WRITE, HZ/10);
 236         }
 237
 238         if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh && dirty_exceeded)
 239                 dirty_exceeded = 0;
 240
 241         if (writeback_in_progress(bdi))
 242                 return;         /* pdflush is already working this queue */
 243
 244         /*
 245          * In laptop mode, we wait until hitting the higher threshold before
 246          * starting background writeout, and then write out all the way down
 247          * to the lower threshold.  So slow writers cause minimal disk activity.
 248          *
 249          * In normal mode, we start background writeout at the lower
 250          * background_thresh, to keep the amount of dirty memory low.
 251          */
 252         if ((laptop_mode && pages_written) ||
 253              (!laptop_mode && (nr_reclaimable > background_thresh)))
 254                 pdflush_operation(background_writeout, 0);
 255 }
 256
 257 /**
 258  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
 259  * @mapping: address_space which was dirtied
 260  * @nr_pages_dirtied: number of pages which the caller has just dirtied
 261  *
 262  * Processes which are dirtying memory should call in here once for each page
 263  * which was newly dirtied.  The function will periodically check the system's
 264  * dirty state and will initiate writeback if needed.
 265  *
 266  * On really big machines, get_writeback_state is expensive, so try to avoid
 267  * calling it too often (ratelimiting).  But once we're over the dirty memory
 268  * limit we decrease the ratelimiting by a lot, to prevent individual processes
 269  * from overshooting the limit by (ratelimit_pages) each.
 270  */
 271 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
 272                                         unsigned long nr_pages_dirtied)
 273 {
 274         static DEFINE_PER_CPU(unsigned long, ratelimits) = 0;
 275         unsigned long ratelimit;
 276         unsigned long *p;
 277
 278         ratelimit = ratelimit_pages;
 279         if (dirty_exceeded)
 280                 ratelimit = 8;
 281
 282         /*
 283          * Check the rate limiting. Also, we do not want to throttle real-time
 284          * tasks in balance_dirty_pages(). Period.
 285          */
 286         preempt_disable();
 287         p =  &__get_cpu_var(ratelimits);
 288         *p += nr_pages_dirtied;
 289         if (unlikely(*p >= ratelimit)) {
 290                 *p = 0;
 291                 preempt_enable();
 292                 balance_dirty_pages(mapping);
 293                 return;
 294         }
 295         preempt_enable();
 296 }
 297 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
 298
 299 void throttle_vm_writeout(void)
 300 {
 301         struct writeback_state wbs;
 302         long background_thresh;
 303         long dirty_thresh;
 304
 305         for ( ; ; ) {
 306                 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
 307
 308                 /*
 309                  * Boost the allowable dirty threshold a bit for page
 310                  * allocators so they don't get DoS'ed by heavy writers
 311                  */
 312                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
 313
 314                 if (wbs.nr_unstable + wbs.nr_writeback <= dirty_thresh)
 315                         break;
 316                 blk_congestion_wait(WRITE, HZ/10);
 317         }
 318 }
 319
 320
 321 /*
 322  * writeback at least _min_pages, and keep writing until the amount of dirty
 323  * memory is less than the background threshold, or until we're all clean.
 324  */
 325 static void background_writeout(unsigned long _min_pages)
 326 {
 327         long min_pages = _min_pages;
 328         struct writeback_control wbc = {
 329                 .bdi            = NULL,
 330                 .sync_mode      = WB_SYNC_NONE,
 331                 .older_than_this = NULL,
 332                 .nr_to_write    = 0,
 333                 .nonblocking    = 1,
 334         };
 335
 336         for ( ; ; ) {
 337                 struct writeback_state wbs;
 338                 long background_thresh;
 339                 long dirty_thresh;
 340
 341                 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
 342                 if (wbs.nr_dirty + wbs.nr_unstable < background_thresh
 343                                 && min_pages <= 0)
 344                         break;
 345                 wbc.encountered_congestion = 0;
 346                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 347                 wbc.pages_skipped = 0;
 348                 writeback_inodes(&wbc);
 349                 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 350                 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
 351                         /* Wrote less than expected */
 352                         blk_congestion_wait(WRITE, HZ/10);
 353                         if (!wbc.encountered_congestion)
 354                                 break;
 355                 }
 356         }
 357 }
 358
 359 /*
 360  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
 361  * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
 362  * -1 if all pdflush threads were busy.
 363  */
 364 int wakeup_pdflush(long nr_pages)
 365 {
 366         if (nr_pages == 0) {
 367                 struct writeback_state wbs;
 368
 369                 get_writeback_state(&wbs);
 370                 nr_pages = wbs.nr_dirty + wbs.nr_unstable;
 371         }
 372         return pdflush_operation(background_writeout, nr_pages);
 373 }
 374
 375 static void wb_timer_fn(unsigned long unused);
 376 static void laptop_timer_fn(unsigned long unused);
 377
 378 static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
 379 static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
 380
 381 /*
 382  * Periodic writeback of "old" data.
 383  *
 384  * Define "old": the first time one of an inode's pages is dirtied, we mark the
 385  * dirtying-time in the inode's address_space.  So this periodic writeback code
 386  * just walks the superblock inode list, writing back any inodes which are
 387  * older than a specific point in time.
 388  *
 389  * Try to run once per dirty_writeback_interval.  But if a writeback event
 390  * takes longer than a dirty_writeback_interval interval, then leave a
 391  * one-second gap.
 392  *
 393  * older_than_this takes precedence over nr_to_write.  So we'll only write back
 394  * all dirty pages if they are all attached to "old" mappings.
 395  */
 396 static void wb_kupdate(unsigned long arg)
 397 {
 398         unsigned long oldest_jif;
 399         unsigned long start_jif;
 400         unsigned long next_jif;
 401         long nr_to_write;
 402         struct writeback_state wbs;
 403         struct writeback_control wbc = {
 404                 .bdi            = NULL,
 405                 .sync_mode      = WB_SYNC_NONE,
 406                 .older_than_this = &oldest_jif,
 407                 .nr_to_write    = 0,
 408                 .nonblocking    = 1,
 409                 .for_kupdate    = 1,
 410         };
 411
 412         sync_supers();
 413
 414         get_writeback_state(&wbs);
 415         oldest_jif = jiffies - dirty_expire_interval;
 416         start_jif = jiffies;
 417         next_jif = start_jif + dirty_writeback_interval;
 418         nr_to_write = wbs.nr_dirty + wbs.nr_unstable +
 419                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
 420         while (nr_to_write > 0) {
 421                 wbc.encountered_congestion = 0;
 422                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 423                 writeback_inodes(&wbc);
 424                 if (wbc.nr_to_write > 0) {
 425                         if (wbc.encountered_congestion)
 426                                 blk_congestion_wait(WRITE, HZ/10);
 427                         else
 428                                 break;  /* All the old data is written */
 429                 }
 430                 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 431         }
 432         if (time_before(next_jif, jiffies + HZ))
 433                 next_jif = jiffies + HZ;
 434         if (dirty_writeback_interval)
 435                 mod_timer(&wb_timer, next_jif);
 436 }
 437
 438 /*
 439  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
 440  */
 441 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
 442                 struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
 443 {
 444         proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
 445         if (dirty_writeback_interval) {
 446                 mod_timer(&wb_timer,
 447                         jiffies + dirty_writeback_interval);
 448                 } else {
 449                 del_timer(&wb_timer);
 450         }
 451         return 0;
 452 }
 453
 454 static void wb_timer_fn(unsigned long unused)
 455 {
 456         if (pdflush_operation(wb_kupdate, 0) < 0)
 457                 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
 458 }
 459
 460 static void laptop_flush(unsigned long unused)
 461 {
 462         sys_sync();
 463 }
 464
 465 static void laptop_timer_fn(unsigned long unused)
 466 {
 467         pdflush_operation(laptop_flush, 0);
 468 }
 469
 470 /*
 471  * We've spun up the disk and we're in laptop mode: schedule writeback
 472  * of all dirty data a few seconds from now.  If the flush is already scheduled
 473  * then push it back - the user is still using the disk.
 474  */
 475 void laptop_io_completion(void)
 476 {
 477         mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
 478 }
 479
 480 /*
 481  * We're in laptop mode and we've just synced. The sync's writes will have
 482  * caused another writeback to be scheduled by laptop_io_completion.
 483  * Nothing needs to be written back anymore, so we unschedule the writeback.
 484  */
 485 void laptop_sync_completion(void)
 486 {
 487         del_timer(&laptop_mode_wb_timer);
 488 }
 489
 490 /*
 491  * If ratelimit_pages is too high then we can get into dirty-data overload
 492  * if a large number of processes all perform writes at the same time.
 493  * If it is too low then SMP machines will call the (expensive)
 494  * get_writeback_state too often.
 495  *
 496  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
 497  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
 498  * thresholds before writeback cuts in.
 499  *
 500  * But the limit should not be set too high.  Because it also controls the
 501  * amount of memory which the balance_dirty_pages() caller has to write back.
 502  * If this is too large then the caller will block on the IO queue all the
 503  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
 504  * will write six megabyte chunks, max.
 505  */
 506
 507 static void set_ratelimit(void)
 508 {
 509         ratelimit_pages = total_pages / (num_online_cpus() * 32);
 510         if (ratelimit_pages < 16)
 511                 ratelimit_pages = 16;
 512         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
 513                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
 514 }
 515
 516 static int
 517 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
 518 {
 519         set_ratelimit();
 520         return 0;
 521 }
 522
 523 static struct notifier_block ratelimit_nb = {
 524         .notifier_call  = ratelimit_handler,
 525         .next           = NULL,
 526 };
 527
 528 /*
 529  * If the machine has a large highmem:lowmem ratio then scale back the default
 530  * dirty memory thresholds: allowing too much dirty highmem pins an excessive
 531  * number of buffer_heads.
 532  */
 533 void __init page_writeback_init(void)
 534 {
 535         long buffer_pages = nr_free_buffer_pages();
 536         long correction;
 537
 538         total_pages = nr_free_pagecache_pages();
 539
 540         correction = (100 * 4 * buffer_pages) / total_pages;
 541
 542         if (correction < 100) {
 543                 dirty_background_ratio *= correction;
 544                 dirty_background_ratio /= 100;
 545                 vm_dirty_ratio *= correction;
 546                 vm_dirty_ratio /= 100;
 547
 548                 if (dirty_background_ratio <= 0)
 549                         dirty_background_ratio = 1;
 550                 if (vm_dirty_ratio <= 0)
 551                         vm_dirty_ratio = 1;
 552         }
 553         mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
 554         set_ratelimit();
 555         register_cpu_notifier(&ratelimit_nb);
 556 }
 557
 558 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
 559 {
 560         int ret;
 561
 562         if (wbc->nr_to_write <= 0)
 563                 return 0;
 564         wbc->for_writepages = 1;
 565         if (mapping->a_ops->writepages)
 566                 ret =  mapping->a_ops->writepages(mapping, wbc);
 567         else
 568                 ret = generic_writepages(mapping, wbc);
 569         wbc->for_writepages = 0;
 570         return ret;
 571 }
 572
 573 /**
 574  * write_one_page - write out a single page and optionally wait on I/O
 575  *
 576  * @page: the page to write
 577  * @wait: if true, wait on writeout
 578  *
 579  * The page must be locked by the caller and will be unlocked upon return.
 580  *
 581  * write_one_page() returns a negative error code if I/O failed.
 582  */
 583 int write_one_page(struct page *page, int wait)
 584 {
 585         struct address_space *mapping = page->mapping;
 586         int ret = 0;
 587         struct writeback_control wbc = {
 588                 .sync_mode = WB_SYNC_ALL,
 589                 .nr_to_write = 1,
 590         };
 591
 592         BUG_ON(!PageLocked(page));
 593
 594         if (wait)
 595                 wait_on_page_writeback(page);
 596
 597         if (clear_page_dirty_for_io(page)) {
 598                 page_cache_get(page);
 599                 ret = mapping->a_ops->writepage(page, &wbc);
 600                 if (ret == 0 && wait) {
 601                         wait_on_page_writeback(page);
 602                         if (PageError(page))
 603                                 ret = -EIO;
 604                 }
 605                 page_cache_release(page);
 606         } else {
 607                 unlock_page(page);
 608         }
 609         return ret;
 610 }
 611 EXPORT_SYMBOL(write_one_page);
 612
 613 /*
 614  * For address_spaces which do not use buffers.  Just tag the page as dirty in
 615  * its radix tree.
 616  *
 617  * This is also used when a single buffer is being dirtied: we want to set the
 618  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
 619  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
 620  *
 621  * Most callers have locked the page, which pins the address_space in memory.
 622  * But zap_pte_range() does not lock the page, however in that case the
 623  * mapping is pinned by the vma's ->vm_file reference.
 624  *
 625  * We take care to handle the case where the page was truncated from the
 626  * mapping by re-checking page_mapping() insode tree_lock.
 627  */
 628 int __set_page_dirty_nobuffers(struct page *page)
 629 {
 630         if (!TestSetPageDirty(page)) {
 631                 struct address_space *mapping = page_mapping(page);
 632                 struct address_space *mapping2;
 633
 634                 if (mapping) {
 635                         write_lock_irq(&mapping->tree_lock);
 636                         mapping2 = page_mapping(page);
 637                         if (mapping2) { /* Race with truncate? */
 638                                 BUG_ON(mapping2 != mapping);
 639                                 if (mapping_cap_account_dirty(mapping))
 640                                         inc_page_state(nr_dirty);
 641                                 radix_tree_tag_set(&mapping->page_tree,
 642                                         page_index(page), PAGECACHE_TAG_DIRTY);
 643                         }
 644                         write_unlock_irq(&mapping->tree_lock);
 645                         if (mapping->host) {
 646                                 /* !PageAnon && !swapper_space */
 647                                 __mark_inode_dirty(mapping->host,
 648                                                         I_DIRTY_PAGES);
 649                         }
 650                 }
 651                 return 1;
 652         }
 653         return 0;
 654 }
 655 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
 656
 657 /*
 658  * When a writepage implementation decides that it doesn't want to write this
 659  * page for some reason, it should redirty the locked page via
 660  * redirty_page_for_writepage() and it should then unlock the page and return 0
 661  */
 662 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
 663 {
 664         wbc->pages_skipped++;
 665         return __set_page_dirty_nobuffers(page);
 666 }
 667 EXPORT_SYMBOL(redirty_page_for_writepage);
 668
 669 /*
 670  * If the mapping doesn't provide a set_page_dirty a_op, then
 671  * just fall through and assume that it wants buffer_heads.
 672  */
 673 int fastcall set_page_dirty(struct page *page)
 674 {
 675         struct address_space *mapping = page_mapping(page);
 676
 677         if (likely(mapping)) {
 678                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
 679                 if (spd)
 680                         return (*spd)(page);
 681                 return __set_page_dirty_buffers(page);
 682         }
 683         if (!PageDirty(page)) {
 684                 if (!TestSetPageDirty(page))
 685                         return 1;
 686         }
 687         return 0;
 688 }
 689 EXPORT_SYMBOL(set_page_dirty);
 690
 691 /*
 692  * set_page_dirty() is racy if the caller has no reference against
 693  * page->mapping->host, and if the page is unlocked.  This is because another
 694  * CPU could truncate the page off the mapping and then free the mapping.
 695  *
 696  * Usually, the page _is_ locked, or the caller is a user-space process which
 697  * holds a reference on the inode by having an open file.
 698  *
 699  * In other cases, the page should be locked before running set_page_dirty().
 700  */
 701 int set_page_dirty_lock(struct page *page)
 702 {
 703         int ret;
 704
 705         lock_page(page);
 706         ret = set_page_dirty(page);
 707         unlock_page(page);
 708         return ret;
 709 }
 710 EXPORT_SYMBOL(set_page_dirty_lock);
 711
 712 /*
 713  * Clear a page's dirty flag, while caring for dirty memory accounting.
 714  * Returns true if the page was previously dirty.
 715  */
 716 int test_clear_page_dirty(struct page *page)
 717 {
 718         struct address_space *mapping = page_mapping(page);
 719         unsigned long flags;
 720
 721         if (mapping) {
 722                 write_lock_irqsave(&mapping->tree_lock, flags);
 723                 if (TestClearPageDirty(page)) {
 724                         radix_tree_tag_clear(&mapping->page_tree,
 725                                                 page_index(page),
 726                                                 PAGECACHE_TAG_DIRTY);
 727                         write_unlock_irqrestore(&mapping->tree_lock, flags);
 728                         if (mapping_cap_account_dirty(mapping))
 729                                 dec_page_state(nr_dirty);
 730                         return 1;
 731                 }
 732                 write_unlock_irqrestore(&mapping->tree_lock, flags);
 733                 return 0;
 734         }
 735         return TestClearPageDirty(page);
 736 }
 737 EXPORT_SYMBOL(test_clear_page_dirty);
 738
 739 /*
 740  * Clear a page's dirty flag, while caring for dirty memory accounting.
 741  * Returns true if the page was previously dirty.
 742  *
 743  * This is for preparing to put the page under writeout.  We leave the page
 744  * tagged as dirty in the radix tree so that a concurrent write-for-sync
 745  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
 746  * implementation will run either set_page_writeback() or set_page_dirty(),
 747  * at which stage we bring the page's dirty flag and radix-tree dirty tag
 748  * back into sync.
 749  *
 750  * This incoherency between the page's dirty flag and radix-tree tag is
 751  * unfortunate, but it only exists while the page is locked.
 752  */
 753 int clear_page_dirty_for_io(struct page *page)
 754 {
 755         struct address_space *mapping = page_mapping(page);
 756
 757         if (mapping) {
 758                 if (TestClearPageDirty(page)) {
 759                         if (mapping_cap_account_dirty(mapping))
 760                                 dec_page_state(nr_dirty);
 761                         return 1;
 762                 }
 763                 return 0;
 764         }
 765         return TestClearPageDirty(page);
 766 }
 767 EXPORT_SYMBOL(clear_page_dirty_for_io);
 768
 769 int test_clear_page_writeback(struct page *page)
 770 {
 771         struct address_space *mapping = page_mapping(page);
 772         int ret;
 773
 774         if (mapping) {
 775                 unsigned long flags;
 776
 777                 write_lock_irqsave(&mapping->tree_lock, flags);
 778                 ret = TestClearPageWriteback(page);
 779                 if (ret)
 780                         radix_tree_tag_clear(&mapping->page_tree,
 781                                                 page_index(page),
 782                                                 PAGECACHE_TAG_WRITEBACK);
 783                 write_unlock_irqrestore(&mapping->tree_lock, flags);
 784         } else {
 785                 ret = TestClearPageWriteback(page);
 786         }
 787         return ret;
 788 }
 789
 790 int test_set_page_writeback(struct page *page)
 791 {
 792         struct address_space *mapping = page_mapping(page);
 793         int ret;
 794
 795         if (mapping) {
 796                 unsigned long flags;
 797
 798                 write_lock_irqsave(&mapping->tree_lock, flags);
 799                 ret = TestSetPageWriteback(page);
 800                 if (!ret)
 801                         radix_tree_tag_set(&mapping->page_tree,
 802                                                 page_index(page),
 803                                                 PAGECACHE_TAG_WRITEBACK);
 804                 if (!PageDirty(page))
 805                         radix_tree_tag_clear(&mapping->page_tree,
 806                                                 page_index(page),
 807                                                 PAGECACHE_TAG_DIRTY);
 808                 write_unlock_irqrestore(&mapping->tree_lock, flags);
 809         } else {
 810                 ret = TestSetPageWriteback(page);
 811         }
 812         return ret;
 813
 814 }
 815 EXPORT_SYMBOL(test_set_page_writeback);
 816
 817 /*
 818  * Return true if any of the pages in the mapping are marged with the
 819  * passed tag.
 820  */
 821 int mapping_tagged(struct address_space *mapping, int tag)
 822 {
 823         unsigned long flags;
 824         int ret;
 825
 826         read_lock_irqsave(&mapping->tree_lock, flags);
 827         ret = radix_tree_tagged(&mapping->page_tree, tag);
 828         read_unlock_irqrestore(&mapping->tree_lock, flags);
 829         return ret;
 830 }
 831 EXPORT_SYMBOL(mapping_tagged);