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/rmap.h>
  27 #include <linux/percpu.h>
  28 #include <linux/notifier.h>
  29 #include <linux/smp.h>
  30 #include <linux/sysctl.h>
  31 #include <linux/cpu.h>
  32 #include <linux/syscalls.h>
  33
  34 /*
  35  * The maximum number of pages to writeout in a single bdflush/kupdate
  36  * operation.  We do this so we don't hold I_LOCK against an inode for
  37  * enormous amounts of time, which would block a userspace task which has
  38  * been forced to throttle against that inode.  Also, the code reevaluates
  39  * the dirty each time it has written this many pages.
  40  */
  41 #define MAX_WRITEBACK_PAGES     1024
  42
  43 /*
  44  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
  45  * will look to see if it needs to force writeback or throttling.
  46  */
  47 static long ratelimit_pages = 32;
  48
  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 /*
 103  * Work out the current dirty-memory clamping and background writeout
 104  * thresholds.
 105  *
 106  * The main aim here is to lower them aggressively if there is a lot of mapped
 107  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
 108  * pages.  It is better to clamp down on writers than to start swapping, and
 109  * performing lots of scanning.
 110  *
 111  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
 112  *
 113  * We don't permit the clamping level to fall below 5% - that is getting rather
 114  * excessive.
 115  *
 116  * We make sure that the background writeout level is below the adjusted
 117  * clamping level.
 118  */
 119 static void
 120 get_dirty_limits(long *pbackground, long *pdirty,
 121                                         struct address_space *mapping)
 122 {
 123         int background_ratio;           /* Percentages */
 124         int dirty_ratio;
 125         int unmapped_ratio;
 126         long background;
 127         long dirty;
 128         unsigned long available_memory = vm_total_pages;
 129         struct task_struct *tsk;
 130
 131 #ifdef CONFIG_HIGHMEM
 132         /*
 133          * If this mapping can only allocate from low memory,
 134          * we exclude high memory from our count.
 135          */
 136         if (mapping && !(mapping_gfp_mask(mapping) & __GFP_HIGHMEM))
 137                 available_memory -= totalhigh_pages;
 138 #endif
 139
 140
 141         unmapped_ratio = 100 - ((global_page_state(NR_FILE_MAPPED) +
 142                                 global_page_state(NR_ANON_PAGES)) * 100) /
 143                                         vm_total_pages;
 144
 145         dirty_ratio = vm_dirty_ratio;
 146         if (dirty_ratio > unmapped_ratio / 2)
 147                 dirty_ratio = unmapped_ratio / 2;
 148
 149         if (dirty_ratio < 5)
 150                 dirty_ratio = 5;
 151
 152         background_ratio = dirty_background_ratio;
 153         if (background_ratio >= dirty_ratio)
 154                 background_ratio = dirty_ratio / 2;
 155
 156         background = (background_ratio * available_memory) / 100;
 157         dirty = (dirty_ratio * available_memory) / 100;
 158         tsk = current;
 159         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
 160                 background += background / 4;
 161                 dirty += dirty / 4;
 162         }
 163         *pbackground = background;
 164         *pdirty = dirty;
 165 }
 166
 167 /*
 168  * balance_dirty_pages() must be called by processes which are generating dirty
 169  * data.  It looks at the number of dirty pages in the machine and will force
 170  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
 171  * If we're over `background_thresh' then pdflush is woken to perform some
 172  * writeout.
 173  */
 174 static void balance_dirty_pages(struct address_space *mapping)
 175 {
 176         long nr_reclaimable;
 177         long background_thresh;
 178         long dirty_thresh;
 179         unsigned long pages_written = 0;
 180         unsigned long write_chunk = sync_writeback_pages();
 181
 182         struct backing_dev_info *bdi = mapping->backing_dev_info;
 183
 184         for (;;) {
 185                 struct writeback_control wbc = {
 186                         .bdi            = bdi,
 187                         .sync_mode      = WB_SYNC_NONE,
 188                         .older_than_this = NULL,
 189                         .nr_to_write    = write_chunk,
 190                         .range_cyclic   = 1,
 191                 };
 192
 193                 get_dirty_limits(&background_thresh, &dirty_thresh, mapping);
 194                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
 195                                         global_page_state(NR_UNSTABLE_NFS);
 196                 if (nr_reclaimable + global_page_state(NR_WRITEBACK) <=
 197                         dirty_thresh)
 198                                 break;
 199
 200                 if (!dirty_exceeded)
 201                         dirty_exceeded = 1;
 202
 203                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
 204                  * Unstable writes are a feature of certain networked
 205                  * filesystems (i.e. NFS) in which data may have been
 206                  * written to the server's write cache, but has not yet
 207                  * been flushed to permanent storage.
 208                  */
 209                 if (nr_reclaimable) {
 210                         writeback_inodes(&wbc);
 211                         get_dirty_limits(&background_thresh,
 212                                                 &dirty_thresh, mapping);
 213                         nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
 214                                         global_page_state(NR_UNSTABLE_NFS);
 215                         if (nr_reclaimable +
 216                                 global_page_state(NR_WRITEBACK)
 217                                         <= dirty_thresh)
 218                                                 break;
 219                         pages_written += write_chunk - wbc.nr_to_write;
 220                         if (pages_written >= write_chunk)
 221                                 break;          /* We've done our duty */
 222                 }
 223                 blk_congestion_wait(WRITE, HZ/10);
 224         }
 225
 226         if (nr_reclaimable + global_page_state(NR_WRITEBACK)
 227                 <= dirty_thresh && dirty_exceeded)
 228                         dirty_exceeded = 0;
 229
 230         if (writeback_in_progress(bdi))
 231                 return;         /* pdflush is already working this queue */
 232
 233         /*
 234          * In laptop mode, we wait until hitting the higher threshold before
 235          * starting background writeout, and then write out all the way down
 236          * to the lower threshold.  So slow writers cause minimal disk activity.
 237          *
 238          * In normal mode, we start background writeout at the lower
 239          * background_thresh, to keep the amount of dirty memory low.
 240          */
 241         if ((laptop_mode && pages_written) ||
 242              (!laptop_mode && (nr_reclaimable > background_thresh)))
 243                 pdflush_operation(background_writeout, 0);
 244 }
 245
 246 void set_page_dirty_balance(struct page *page)
 247 {
 248         if (set_page_dirty(page)) {
 249                 struct address_space *mapping = page_mapping(page);
 250
 251                 if (mapping)
 252                         balance_dirty_pages_ratelimited(mapping);
 253         }
 254 }
 255
 256 /**
 257  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
 258  * @mapping: address_space which was dirtied
 259  * @nr_pages_dirtied: number of pages which the caller has just dirtied
 260  *
 261  * Processes which are dirtying memory should call in here once for each page
 262  * which was newly dirtied.  The function will periodically check the system's
 263  * dirty state and will initiate writeback if needed.
 264  *
 265  * On really big machines, get_writeback_state is expensive, so try to avoid
 266  * calling it too often (ratelimiting).  But once we're over the dirty memory
 267  * limit we decrease the ratelimiting by a lot, to prevent individual processes
 268  * from overshooting the limit by (ratelimit_pages) each.
 269  */
 270 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
 271                                         unsigned long nr_pages_dirtied)
 272 {
 273         static DEFINE_PER_CPU(unsigned long, ratelimits) = 0;
 274         unsigned long ratelimit;
 275         unsigned long *p;
 276
 277         ratelimit = ratelimit_pages;
 278         if (dirty_exceeded)
 279                 ratelimit = 8;
 280
 281         /*
 282          * Check the rate limiting. Also, we do not want to throttle real-time
 283          * tasks in balance_dirty_pages(). Period.
 284          */
 285         preempt_disable();
 286         p =  &__get_cpu_var(ratelimits);
 287         *p += nr_pages_dirtied;
 288         if (unlikely(*p >= ratelimit)) {
 289                 *p = 0;
 290                 preempt_enable();
 291                 balance_dirty_pages(mapping);
 292                 return;
 293         }
 294         preempt_enable();
 295 }
 296 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
 297
 298 void throttle_vm_writeout(void)
 299 {
 300         long background_thresh;
 301         long dirty_thresh;
 302
 303         for ( ; ; ) {
 304                 get_dirty_limits(&background_thresh, &dirty_thresh, NULL);
 305
 306                 /*
 307                  * Boost the allowable dirty threshold a bit for page
 308                  * allocators so they don't get DoS'ed by heavy writers
 309                  */
 310                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
 311
 312                 if (global_page_state(NR_UNSTABLE_NFS) +
 313                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
 314                                 break;
 315                 blk_congestion_wait(WRITE, HZ/10);
 316         }
 317 }
 318
 319
 320 /*
 321  * writeback at least _min_pages, and keep writing until the amount of dirty
 322  * memory is less than the background threshold, or until we're all clean.
 323  */
 324 static void background_writeout(unsigned long _min_pages)
 325 {
 326         long min_pages = _min_pages;
 327         struct writeback_control wbc = {
 328                 .bdi            = NULL,
 329                 .sync_mode      = WB_SYNC_NONE,
 330                 .older_than_this = NULL,
 331                 .nr_to_write    = 0,
 332                 .nonblocking    = 1,
 333                 .range_cyclic   = 1,
 334         };
 335
 336         for ( ; ; ) {
 337                 long background_thresh;
 338                 long dirty_thresh;
 339
 340                 get_dirty_limits(&background_thresh, &dirty_thresh, NULL);
 341                 if (global_page_state(NR_FILE_DIRTY) +
 342                         global_page_state(NR_UNSTABLE_NFS) < 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                 nr_pages = global_page_state(NR_FILE_DIRTY) +
 368                                 global_page_state(NR_UNSTABLE_NFS);
 369         return pdflush_operation(background_writeout, nr_pages);
 370 }
 371
 372 static void wb_timer_fn(unsigned long unused);
 373 static void laptop_timer_fn(unsigned long unused);
 374
 375 static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
 376 static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
 377
 378 /*
 379  * Periodic writeback of "old" data.
 380  *
 381  * Define "old": the first time one of an inode's pages is dirtied, we mark the
 382  * dirtying-time in the inode's address_space.  So this periodic writeback code
 383  * just walks the superblock inode list, writing back any inodes which are
 384  * older than a specific point in time.
 385  *
 386  * Try to run once per dirty_writeback_interval.  But if a writeback event
 387  * takes longer than a dirty_writeback_interval interval, then leave a
 388  * one-second gap.
 389  *
 390  * older_than_this takes precedence over nr_to_write.  So we'll only write back
 391  * all dirty pages if they are all attached to "old" mappings.
 392  */
 393 static void wb_kupdate(unsigned long arg)
 394 {
 395         unsigned long oldest_jif;
 396         unsigned long start_jif;
 397         unsigned long next_jif;
 398         long nr_to_write;
 399         struct writeback_control wbc = {
 400                 .bdi            = NULL,
 401                 .sync_mode      = WB_SYNC_NONE,
 402                 .older_than_this = &oldest_jif,
 403                 .nr_to_write    = 0,
 404                 .nonblocking    = 1,
 405                 .for_kupdate    = 1,
 406                 .range_cyclic   = 1,
 407         };
 408
 409         sync_supers();
 410
 411         oldest_jif = jiffies - dirty_expire_interval;
 412         start_jif = jiffies;
 413         next_jif = start_jif + dirty_writeback_interval;
 414         nr_to_write = global_page_state(NR_FILE_DIRTY) +
 415                         global_page_state(NR_UNSTABLE_NFS) +
 416                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
 417         while (nr_to_write > 0) {
 418                 wbc.encountered_congestion = 0;
 419                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 420                 writeback_inodes(&wbc);
 421                 if (wbc.nr_to_write > 0) {
 422                         if (wbc.encountered_congestion)
 423                                 blk_congestion_wait(WRITE, HZ/10);
 424                         else
 425                                 break;  /* All the old data is written */
 426                 }
 427                 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 428         }
 429         if (time_before(next_jif, jiffies + HZ))
 430                 next_jif = jiffies + HZ;
 431         if (dirty_writeback_interval)
 432                 mod_timer(&wb_timer, next_jif);
 433 }
 434
 435 /*
 436  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
 437  */
 438 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
 439                 struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
 440 {
 441         proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
 442         if (dirty_writeback_interval) {
 443                 mod_timer(&wb_timer,
 444                         jiffies + dirty_writeback_interval);
 445                 } else {
 446                 del_timer(&wb_timer);
 447         }
 448         return 0;
 449 }
 450
 451 static void wb_timer_fn(unsigned long unused)
 452 {
 453         if (pdflush_operation(wb_kupdate, 0) < 0)
 454                 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
 455 }
 456
 457 static void laptop_flush(unsigned long unused)
 458 {
 459         sys_sync();
 460 }
 461
 462 static void laptop_timer_fn(unsigned long unused)
 463 {
 464         pdflush_operation(laptop_flush, 0);
 465 }
 466
 467 /*
 468  * We've spun up the disk and we're in laptop mode: schedule writeback
 469  * of all dirty data a few seconds from now.  If the flush is already scheduled
 470  * then push it back - the user is still using the disk.
 471  */
 472 void laptop_io_completion(void)
 473 {
 474         mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
 475 }
 476
 477 /*
 478  * We're in laptop mode and we've just synced. The sync's writes will have
 479  * caused another writeback to be scheduled by laptop_io_completion.
 480  * Nothing needs to be written back anymore, so we unschedule the writeback.
 481  */
 482 void laptop_sync_completion(void)
 483 {
 484         del_timer(&laptop_mode_wb_timer);
 485 }
 486
 487 /*
 488  * If ratelimit_pages is too high then we can get into dirty-data overload
 489  * if a large number of processes all perform writes at the same time.
 490  * If it is too low then SMP machines will call the (expensive)
 491  * get_writeback_state too often.
 492  *
 493  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
 494  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
 495  * thresholds before writeback cuts in.
 496  *
 497  * But the limit should not be set too high.  Because it also controls the
 498  * amount of memory which the balance_dirty_pages() caller has to write back.
 499  * If this is too large then the caller will block on the IO queue all the
 500  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
 501  * will write six megabyte chunks, max.
 502  */
 503
 504 void writeback_set_ratelimit(void)
 505 {
 506         ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
 507         if (ratelimit_pages < 16)
 508                 ratelimit_pages = 16;
 509         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
 510                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
 511 }
 512
 513 static int __cpuinit
 514 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
 515 {
 516         writeback_set_ratelimit();
 517         return 0;
 518 }
 519
 520 static struct notifier_block __cpuinitdata ratelimit_nb = {
 521         .notifier_call  = ratelimit_handler,
 522         .next           = NULL,
 523 };
 524
 525 /*
 526  * If the machine has a large highmem:lowmem ratio then scale back the default
 527  * dirty memory thresholds: allowing too much dirty highmem pins an excessive
 528  * number of buffer_heads.
 529  */
 530 void __init page_writeback_init(void)
 531 {
 532         long buffer_pages = nr_free_buffer_pages();
 533         long correction;
 534
 535         correction = (100 * 4 * buffer_pages) / vm_total_pages;
 536
 537         if (correction < 100) {
 538                 dirty_background_ratio *= correction;
 539                 dirty_background_ratio /= 100;
 540                 vm_dirty_ratio *= correction;
 541                 vm_dirty_ratio /= 100;
 542
 543                 if (dirty_background_ratio <= 0)
 544                         dirty_background_ratio = 1;
 545                 if (vm_dirty_ratio <= 0)
 546                         vm_dirty_ratio = 1;
 547         }
 548         mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
 549         writeback_set_ratelimit();
 550         register_cpu_notifier(&ratelimit_nb);
 551 }
 552
 553 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
 554 {
 555         int ret;
 556
 557         if (wbc->nr_to_write <= 0)
 558                 return 0;
 559         wbc->for_writepages = 1;
 560         if (mapping->a_ops->writepages)
 561                 ret = mapping->a_ops->writepages(mapping, wbc);
 562         else
 563                 ret = generic_writepages(mapping, wbc);
 564         wbc->for_writepages = 0;
 565         return ret;
 566 }
 567
 568 /**
 569  * write_one_page - write out a single page and optionally wait on I/O
 570  *
 571  * @page: the page to write
 572  * @wait: if true, wait on writeout
 573  *
 574  * The page must be locked by the caller and will be unlocked upon return.
 575  *
 576  * write_one_page() returns a negative error code if I/O failed.
 577  */
 578 int write_one_page(struct page *page, int wait)
 579 {
 580         struct address_space *mapping = page->mapping;
 581         int ret = 0;
 582         struct writeback_control wbc = {
 583                 .sync_mode = WB_SYNC_ALL,
 584                 .nr_to_write = 1,
 585         };
 586
 587         BUG_ON(!PageLocked(page));
 588
 589         if (wait)
 590                 wait_on_page_writeback(page);
 591
 592         if (clear_page_dirty_for_io(page)) {
 593                 page_cache_get(page);
 594                 ret = mapping->a_ops->writepage(page, &wbc);
 595                 if (ret == 0 && wait) {
 596                         wait_on_page_writeback(page);
 597                         if (PageError(page))
 598                                 ret = -EIO;
 599                 }
 600                 page_cache_release(page);
 601         } else {
 602                 unlock_page(page);
 603         }
 604         return ret;
 605 }
 606 EXPORT_SYMBOL(write_one_page);
 607
 608 /*
 609  * For address_spaces which do not use buffers.  Just tag the page as dirty in
 610  * its radix tree.
 611  *
 612  * This is also used when a single buffer is being dirtied: we want to set the
 613  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
 614  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
 615  *
 616  * Most callers have locked the page, which pins the address_space in memory.
 617  * But zap_pte_range() does not lock the page, however in that case the
 618  * mapping is pinned by the vma's ->vm_file reference.
 619  *
 620  * We take care to handle the case where the page was truncated from the
 621  * mapping by re-checking page_mapping() insode tree_lock.
 622  */
 623 int __set_page_dirty_nobuffers(struct page *page)
 624 {
 625         if (!TestSetPageDirty(page)) {
 626                 struct address_space *mapping = page_mapping(page);
 627                 struct address_space *mapping2;
 628
 629                 if (mapping) {
 630                         write_lock_irq(&mapping->tree_lock);
 631                         mapping2 = page_mapping(page);
 632                         if (mapping2) { /* Race with truncate? */
 633                                 BUG_ON(mapping2 != mapping);
 634                                 if (mapping_cap_account_dirty(mapping))
 635                                         __inc_zone_page_state(page,
 636                                                                 NR_FILE_DIRTY);
 637                                 radix_tree_tag_set(&mapping->page_tree,
 638                                         page_index(page), PAGECACHE_TAG_DIRTY);
 639                         }
 640                         write_unlock_irq(&mapping->tree_lock);
 641                         if (mapping->host) {
 642                                 /* !PageAnon && !swapper_space */
 643                                 __mark_inode_dirty(mapping->host,
 644                                                         I_DIRTY_PAGES);
 645                         }
 646                 }
 647                 return 1;
 648         }
 649         return 0;
 650 }
 651 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
 652
 653 /*
 654  * When a writepage implementation decides that it doesn't want to write this
 655  * page for some reason, it should redirty the locked page via
 656  * redirty_page_for_writepage() and it should then unlock the page and return 0
 657  */
 658 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
 659 {
 660         wbc->pages_skipped++;
 661         return __set_page_dirty_nobuffers(page);
 662 }
 663 EXPORT_SYMBOL(redirty_page_for_writepage);
 664
 665 /*
 666  * If the mapping doesn't provide a set_page_dirty a_op, then
 667  * just fall through and assume that it wants buffer_heads.
 668  */
 669 int fastcall set_page_dirty(struct page *page)
 670 {
 671         struct address_space *mapping = page_mapping(page);
 672
 673         if (likely(mapping)) {
 674                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
 675                 if (spd)
 676                         return (*spd)(page);
 677                 return __set_page_dirty_buffers(page);
 678         }
 679         if (!PageDirty(page)) {
 680                 if (!TestSetPageDirty(page))
 681                         return 1;
 682         }
 683         return 0;
 684 }
 685 EXPORT_SYMBOL(set_page_dirty);
 686
 687 /*
 688  * set_page_dirty() is racy if the caller has no reference against
 689  * page->mapping->host, and if the page is unlocked.  This is because another
 690  * CPU could truncate the page off the mapping and then free the mapping.
 691  *
 692  * Usually, the page _is_ locked, or the caller is a user-space process which
 693  * holds a reference on the inode by having an open file.
 694  *
 695  * In other cases, the page should be locked before running set_page_dirty().
 696  */
 697 int set_page_dirty_lock(struct page *page)
 698 {
 699         int ret;
 700
 701         lock_page_nosync(page);
 702         ret = set_page_dirty(page);
 703         unlock_page(page);
 704         return ret;
 705 }
 706 EXPORT_SYMBOL(set_page_dirty_lock);
 707
 708 /*
 709  * Clear a page's dirty flag, while caring for dirty memory accounting.
 710  * Returns true if the page was previously dirty.
 711  */
 712 int test_clear_page_dirty(struct page *page)
 713 {
 714         struct address_space *mapping = page_mapping(page);
 715         unsigned long flags;
 716
 717         if (mapping) {
 718                 write_lock_irqsave(&mapping->tree_lock, flags);
 719                 if (TestClearPageDirty(page)) {
 720                         radix_tree_tag_clear(&mapping->page_tree,
 721                                                 page_index(page),
 722                                                 PAGECACHE_TAG_DIRTY);
 723                         write_unlock_irqrestore(&mapping->tree_lock, flags);
 724                         /*
 725                          * We can continue to use `mapping' here because the
 726                          * page is locked, which pins the address_space
 727                          */
 728                         if (mapping_cap_account_dirty(mapping)) {
 729                                 page_mkclean(page);
 730                                 dec_zone_page_state(page, NR_FILE_DIRTY);
 731                         }
 732                         return 1;
 733                 }
 734                 write_unlock_irqrestore(&mapping->tree_lock, flags);
 735                 return 0;
 736         }
 737         return TestClearPageDirty(page);
 738 }
 739 EXPORT_SYMBOL(test_clear_page_dirty);
 740
 741 /*
 742  * Clear a page's dirty flag, while caring for dirty memory accounting.
 743  * Returns true if the page was previously dirty.
 744  *
 745  * This is for preparing to put the page under writeout.  We leave the page
 746  * tagged as dirty in the radix tree so that a concurrent write-for-sync
 747  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
 748  * implementation will run either set_page_writeback() or set_page_dirty(),
 749  * at which stage we bring the page's dirty flag and radix-tree dirty tag
 750  * back into sync.
 751  *
 752  * This incoherency between the page's dirty flag and radix-tree tag is
 753  * unfortunate, but it only exists while the page is locked.
 754  */
 755 int clear_page_dirty_for_io(struct page *page)
 756 {
 757         struct address_space *mapping = page_mapping(page);
 758
 759         if (mapping) {
 760                 if (TestClearPageDirty(page)) {
 761                         if (mapping_cap_account_dirty(mapping)) {
 762                                 page_mkclean(page);
 763                                 dec_zone_page_state(page, NR_FILE_DIRTY);
 764                         }
 765                         return 1;
 766                 }
 767                 return 0;
 768         }
 769         return TestClearPageDirty(page);
 770 }
 771 EXPORT_SYMBOL(clear_page_dirty_for_io);
 772
 773 int test_clear_page_writeback(struct page *page)
 774 {
 775         struct address_space *mapping = page_mapping(page);
 776         int ret;
 777
 778         if (mapping) {
 779                 unsigned long flags;
 780
 781                 write_lock_irqsave(&mapping->tree_lock, flags);
 782                 ret = TestClearPageWriteback(page);
 783                 if (ret)
 784                         radix_tree_tag_clear(&mapping->page_tree,
 785                                                 page_index(page),
 786                                                 PAGECACHE_TAG_WRITEBACK);
 787                 write_unlock_irqrestore(&mapping->tree_lock, flags);
 788         } else {
 789                 ret = TestClearPageWriteback(page);
 790         }
 791         return ret;
 792 }
 793
 794 int test_set_page_writeback(struct page *page)
 795 {
 796         struct address_space *mapping = page_mapping(page);
 797         int ret;
 798
 799         if (mapping) {
 800                 unsigned long flags;
 801
 802                 write_lock_irqsave(&mapping->tree_lock, flags);
 803                 ret = TestSetPageWriteback(page);
 804                 if (!ret)
 805                         radix_tree_tag_set(&mapping->page_tree,
 806                                                 page_index(page),
 807                                                 PAGECACHE_TAG_WRITEBACK);
 808                 if (!PageDirty(page))
 809                         radix_tree_tag_clear(&mapping->page_tree,
 810                                                 page_index(page),
 811                                                 PAGECACHE_TAG_DIRTY);
 812                 write_unlock_irqrestore(&mapping->tree_lock, flags);
 813         } else {
 814                 ret = TestSetPageWriteback(page);
 815         }
 816         return ret;
 817
 818 }
 819 EXPORT_SYMBOL(test_set_page_writeback);
 820
 821 /*
 822  * Wakes up tasks that are being throttled due to writeback congestion
 823  */
 824 void writeback_congestion_end(void)
 825 {
 826         blk_congestion_end(WRITE);
 827 }
 828 EXPORT_SYMBOL(writeback_congestion_end);
 829
 830 /*
 831  * Return true if any of the pages in the mapping are marged with the
 832  * passed tag.
 833  */
 834 int mapping_tagged(struct address_space *mapping, int tag)
 835 {
 836         unsigned long flags;
 837         int ret;
 838
 839         read_lock_irqsave(&mapping->tree_lock, flags);
 840         ret = radix_tree_tagged(&mapping->page_tree, tag);
 841         read_unlock_irqrestore(&mapping->tree_lock, flags);
 842         return ret;
 843 }
 844 EXPORT_SYMBOL(mapping_tagged);