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