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 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(struct page_state *ps, long *pbackground, long *pdirty)
 121 {
 122         int background_ratio;           /* Percentages */
 123         int dirty_ratio;
 124         int unmapped_ratio;
 125         long background;
 126         long dirty;
 127         struct task_struct *tsk;
 128
 129         get_page_state(ps);
 130
 131         unmapped_ratio = 100 - (ps->nr_mapped * 100) / total_pages;
 132
 133         dirty_ratio = vm_dirty_ratio;
 134         if (dirty_ratio > unmapped_ratio / 2)
 135                 dirty_ratio = unmapped_ratio / 2;
 136
 137         if (dirty_ratio < 5)
 138                 dirty_ratio = 5;
 139
 140         background_ratio = dirty_background_ratio;
 141         if (background_ratio >= dirty_ratio)
 142                 background_ratio = dirty_ratio / 2;
 143
 144         background = (background_ratio * total_pages) / 100;
 145         dirty = (dirty_ratio * total_pages) / 100;
 146         tsk = current;
 147         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
 148                 background += background / 4;
 149                 dirty += dirty / 4;
 150         }
 151         *pbackground = background;
 152         *pdirty = dirty;
 153 }
 154
 155 /*
 156  * balance_dirty_pages() must be called by processes which are generating dirty
 157  * data.  It looks at the number of dirty pages in the machine and will force
 158  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
 159  * If we're over `background_thresh' then pdflush is woken to perform some
 160  * writeout.
 161  */
 162 static void balance_dirty_pages(struct address_space *mapping)
 163 {
 164         struct page_state ps;
 165         long nr_reclaimable;
 166         long background_thresh;
 167         long dirty_thresh;
 168         unsigned long pages_written = 0;
 169         unsigned long write_chunk = sync_writeback_pages();
 170
 171         struct backing_dev_info *bdi = mapping->backing_dev_info;
 172
 173         for (;;) {
 174                 struct writeback_control wbc = {
 175                         .bdi            = bdi,
 176                         .sync_mode      = WB_SYNC_NONE,
 177                         .older_than_this = NULL,
 178                         .nr_to_write    = write_chunk,
 179                 };
 180
 181                 get_dirty_limits(&ps, &background_thresh, &dirty_thresh);
 182                 nr_reclaimable = ps.nr_dirty + ps.nr_unstable;
 183                 if (nr_reclaimable + ps.nr_writeback <= dirty_thresh)
 184                         break;
 185
 186                 dirty_exceeded = 1;
 187
 188                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
 189                  * Unstable writes are a feature of certain networked
 190                  * filesystems (i.e. NFS) in which data may have been
 191                  * written to the server's write cache, but has not yet
 192                  * been flushed to permanent storage.
 193                  */
 194                 if (nr_reclaimable) {
 195                         writeback_inodes(&wbc);
 196                         get_dirty_limits(&ps, &background_thresh,
 197                                         &dirty_thresh);
 198                         nr_reclaimable = ps.nr_dirty + ps.nr_unstable;
 199                         if (nr_reclaimable + ps.nr_writeback <= dirty_thresh)
 200                                 break;
 201                         pages_written += write_chunk - wbc.nr_to_write;
 202                         if (pages_written >= write_chunk)
 203                                 break;          /* We've done our duty */
 204                 }
 205                 blk_congestion_wait(WRITE, HZ/10);
 206         }
 207
 208         if (nr_reclaimable + ps.nr_writeback <= dirty_thresh)
 209                 dirty_exceeded = 0;
 210
 211         if (writeback_in_progress(bdi))
 212                 return;         /* pdflush is already working this queue */
 213
 214         /*
 215          * In laptop mode, we wait until hitting the higher threshold before
 216          * starting background writeout, and then write out all the way down
 217          * to the lower threshold.  So slow writers cause minimal disk activity.
 218          *
 219          * In normal mode, we start background writeout at the lower
 220          * background_thresh, to keep the amount of dirty memory low.
 221          */
 222         if ((laptop_mode && pages_written) ||
 223              (!laptop_mode && (nr_reclaimable > background_thresh)))
 224                 pdflush_operation(background_writeout, 0);
 225 }
 226
 227 /**
 228  * balance_dirty_pages_ratelimited - balance dirty memory state
 229  * @mapping - address_space which was dirtied
 230  *
 231  * Processes which are dirtying memory should call in here once for each page
 232  * which was newly dirtied.  The function will periodically check the system's
 233  * dirty state and will initiate writeback if needed.
 234  *
 235  * On really big machines, get_page_state is expensive, so try to avoid calling
 236  * it too often (ratelimiting).  But once we're over the dirty memory limit we
 237  * decrease the ratelimiting by a lot, to prevent individual processes from
 238  * overshooting the limit by (ratelimit_pages) each.
 239  */
 240 void balance_dirty_pages_ratelimited(struct address_space *mapping)
 241 {
 242         static DEFINE_PER_CPU(int, ratelimits) = 0;
 243         long ratelimit;
 244
 245         ratelimit = ratelimit_pages;
 246         if (dirty_exceeded)
 247                 ratelimit = 8;
 248
 249         /*
 250          * Check the rate limiting. Also, we do not want to throttle real-time
 251          * tasks in balance_dirty_pages(). Period.
 252          */
 253         if (get_cpu_var(ratelimits)++ >= ratelimit) {
 254                 __get_cpu_var(ratelimits) = 0;
 255                 put_cpu_var(ratelimits);
 256                 balance_dirty_pages(mapping);
 257                 return;
 258         }
 259         put_cpu_var(ratelimits);
 260 }
 261 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
 262
 263 /*
 264  * writeback at least _min_pages, and keep writing until the amount of dirty
 265  * memory is less than the background threshold, or until we're all clean.
 266  */
 267 static void background_writeout(unsigned long _min_pages)
 268 {
 269         long min_pages = _min_pages;
 270         struct writeback_control wbc = {
 271                 .bdi            = NULL,
 272                 .sync_mode      = WB_SYNC_NONE,
 273                 .older_than_this = NULL,
 274                 .nr_to_write    = 0,
 275                 .nonblocking    = 1,
 276         };
 277
 278         for ( ; ; ) {
 279                 struct page_state ps;
 280                 long background_thresh;
 281                 long dirty_thresh;
 282
 283                 get_dirty_limits(&ps, &background_thresh, &dirty_thresh);
 284                 if (ps.nr_dirty + ps.nr_unstable < background_thresh
 285                                 && min_pages <= 0)
 286                         break;
 287                 wbc.encountered_congestion = 0;
 288                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 289                 wbc.pages_skipped = 0;
 290                 writeback_inodes(&wbc);
 291                 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 292                 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
 293                         /* Wrote less than expected */
 294                         blk_congestion_wait(WRITE, HZ/10);
 295                         if (!wbc.encountered_congestion)
 296                                 break;
 297                 }
 298         }
 299 }
 300
 301 /*
 302  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
 303  * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
 304  * -1 if all pdflush threads were busy.
 305  */
 306 int wakeup_bdflush(long nr_pages)
 307 {
 308         if (nr_pages == 0) {
 309                 struct page_state ps;
 310
 311                 get_page_state(&ps);
 312                 nr_pages = ps.nr_dirty + ps.nr_unstable;
 313         }
 314         return pdflush_operation(background_writeout, nr_pages);
 315 }
 316
 317 static void wb_timer_fn(unsigned long unused);
 318 static void laptop_timer_fn(unsigned long unused);
 319
 320 static struct timer_list wb_timer =
 321                         TIMER_INITIALIZER(wb_timer_fn, 0, 0);
 322 static struct timer_list laptop_mode_wb_timer =
 323                         TIMER_INITIALIZER(laptop_timer_fn, 0, 0);
 324
 325 /*
 326  * Periodic writeback of "old" data.
 327  *
 328  * Define "old": the first time one of an inode's pages is dirtied, we mark the
 329  * dirtying-time in the inode's address_space.  So this periodic writeback code
 330  * just walks the superblock inode list, writing back any inodes which are
 331  * older than a specific point in time.
 332  *
 333  * Try to run once per dirty_writeback_centisecs.  But if a writeback event
 334  * takes longer than a dirty_writeback_centisecs interval, then leave a
 335  * one-second gap.
 336  *
 337  * older_than_this takes precedence over nr_to_write.  So we'll only write back
 338  * all dirty pages if they are all attached to "old" mappings.
 339  */
 340 static void wb_kupdate(unsigned long arg)
 341 {
 342         unsigned long oldest_jif;
 343         unsigned long start_jif;
 344         unsigned long next_jif;
 345         long nr_to_write;
 346         struct page_state ps;
 347         struct writeback_control wbc = {
 348                 .bdi            = NULL,
 349                 .sync_mode      = WB_SYNC_NONE,
 350                 .older_than_this = &oldest_jif,
 351                 .nr_to_write    = 0,
 352                 .nonblocking    = 1,
 353                 .for_kupdate    = 1,
 354         };
 355
 356         sync_supers();
 357
 358         get_page_state(&ps);
 359         oldest_jif = jiffies - (dirty_expire_centisecs * HZ) / 100;
 360         start_jif = jiffies;
 361         next_jif = start_jif + (dirty_writeback_centisecs * HZ) / 100;
 362         nr_to_write = ps.nr_dirty + ps.nr_unstable +
 363                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
 364         while (nr_to_write > 0) {
 365                 wbc.encountered_congestion = 0;
 366                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 367                 writeback_inodes(&wbc);
 368                 if (wbc.nr_to_write > 0) {
 369                         if (wbc.encountered_congestion)
 370                                 blk_congestion_wait(WRITE, HZ/10);
 371                         else
 372                                 break;  /* All the old data is written */
 373                 }
 374                 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 375         }
 376         if (time_before(next_jif, jiffies + HZ))
 377                 next_jif = jiffies + HZ;
 378         if (dirty_writeback_centisecs)
 379                 mod_timer(&wb_timer, next_jif);
 380 }
 381
 382 /*
 383  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
 384  */
 385 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
 386                 struct file *file, void __user *buffer, size_t *length)
 387 {
 388         proc_dointvec(table, write, file, buffer, length);
 389         if (dirty_writeback_centisecs) {
 390                 mod_timer(&wb_timer,
 391                         jiffies + (dirty_writeback_centisecs * HZ) / 100);
 392         } else {
 393                 del_timer(&wb_timer);
 394         }
 395         return 0;
 396 }
 397
 398 static void wb_timer_fn(unsigned long unused)
 399 {
 400         if (pdflush_operation(wb_kupdate, 0) < 0)
 401                 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
 402 }
 403
 404 static void laptop_flush(unsigned long unused)
 405 {
 406         sys_sync();
 407 }
 408
 409 static void laptop_timer_fn(unsigned long unused)
 410 {
 411         pdflush_operation(laptop_flush, 0);
 412 }
 413
 414 /*
 415  * We've spun up the disk and we're in laptop mode: schedule writeback
 416  * of all dirty data a few seconds from now.  If the flush is already scheduled
 417  * then push it back - the user is still using the disk.
 418  */
 419 void laptop_io_completion(void)
 420 {
 421         mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode * HZ);
 422 }
 423
 424 /*
 425  * We're in laptop mode and we've just synced. The sync's writes will have
 426  * caused another writeback to be scheduled by laptop_io_completion.
 427  * Nothing needs to be written back anymore, so we unschedule the writeback.
 428  */
 429 void laptop_sync_completion(void)
 430 {
 431         del_timer(&laptop_mode_wb_timer);
 432 }
 433
 434 /*
 435  * If ratelimit_pages is too high then we can get into dirty-data overload
 436  * if a large number of processes all perform writes at the same time.
 437  * If it is too low then SMP machines will call the (expensive) get_page_state
 438  * too often.
 439  *
 440  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
 441  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
 442  * thresholds before writeback cuts in.
 443  *
 444  * But the limit should not be set too high.  Because it also controls the
 445  * amount of memory which the balance_dirty_pages() caller has to write back.
 446  * If this is too large then the caller will block on the IO queue all the
 447  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
 448  * will write six megabyte chunks, max.
 449  */
 450
 451 static void set_ratelimit(void)
 452 {
 453         ratelimit_pages = total_pages / (num_online_cpus() * 32);
 454         if (ratelimit_pages < 16)
 455                 ratelimit_pages = 16;
 456         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
 457                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
 458 }
 459
 460 static int
 461 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
 462 {
 463         set_ratelimit();
 464         return 0;
 465 }
 466
 467 static struct notifier_block ratelimit_nb = {
 468         .notifier_call  = ratelimit_handler,
 469         .next           = NULL,
 470 };
 471
 472 /*
 473  * If the machine has a large highmem:lowmem ratio then scale back the default
 474  * dirty memory thresholds: allowing too much dirty highmem pins an excessive
 475  * number of buffer_heads.
 476  */
 477 void __init page_writeback_init(void)
 478 {
 479         long buffer_pages = nr_free_buffer_pages();
 480         long correction;
 481
 482         total_pages = nr_free_pagecache_pages();
 483
 484         correction = (100 * 4 * buffer_pages) / total_pages;
 485
 486         if (correction < 100) {
 487                 dirty_background_ratio *= correction;
 488                 dirty_background_ratio /= 100;
 489                 vm_dirty_ratio *= correction;
 490                 vm_dirty_ratio /= 100;
 491         }
 492         mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100);
 493         set_ratelimit();
 494         register_cpu_notifier(&ratelimit_nb);
 495 }
 496
 497 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
 498 {
 499         if (wbc->nr_to_write <= 0)
 500                 return 0;
 501         if (mapping->a_ops->writepages)
 502                 return mapping->a_ops->writepages(mapping, wbc);
 503         return generic_writepages(mapping, wbc);
 504 }
 505
 506 /**
 507  * write_one_page - write out a single page and optionally wait on I/O
 508  *
 509  * @page - the page to write
 510  * @wait - if true, wait on writeout
 511  *
 512  * The page must be locked by the caller and will be unlocked upon return.
 513  *
 514  * write_one_page() returns a negative error code if I/O failed.
 515  */
 516 int write_one_page(struct page *page, int wait)
 517 {
 518         struct address_space *mapping = page->mapping;
 519         int ret = 0;
 520         struct writeback_control wbc = {
 521                 .sync_mode = WB_SYNC_ALL,
 522                 .nr_to_write = 1,
 523         };
 524
 525         BUG_ON(!PageLocked(page));
 526
 527         if (wait)
 528                 wait_on_page_writeback(page);
 529
 530         if (clear_page_dirty_for_io(page)) {
 531                 page_cache_get(page);
 532                 ret = mapping->a_ops->writepage(page, &wbc);
 533                 if (ret == 0 && wait) {
 534                         wait_on_page_writeback(page);
 535                         if (PageError(page))
 536                                 ret = -EIO;
 537                 }
 538                 page_cache_release(page);
 539         } else {
 540                 unlock_page(page);
 541         }
 542         return ret;
 543 }
 544 EXPORT_SYMBOL(write_one_page);
 545
 546 /*
 547  * For address_spaces which do not use buffers.  Just tag the page as dirty in
 548  * its radix tree.
 549  *
 550  * This is also used when a single buffer is being dirtied: we want to set the
 551  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
 552  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
 553  *
 554  * Most callers have locked the page, which pins the address_space in memory.
 555  * But zap_pte_range() does not lock the page, however in that case the
 556  * mapping is pinned by the vma's ->vm_file reference.
 557  *
 558  * We take care to handle the case where the page was truncated from the
 559  * mapping by re-checking page_mapping() insode tree_lock.
 560  */
 561 int __set_page_dirty_nobuffers(struct page *page)
 562 {
 563         int ret = 0;
 564
 565         if (!TestSetPageDirty(page)) {
 566                 struct address_space *mapping = page_mapping(page);
 567
 568                 if (mapping) {
 569                         spin_lock_irq(&mapping->tree_lock);
 570                         mapping = page_mapping(page);
 571                         if (page_mapping(page)) { /* Race with truncate? */
 572                                 BUG_ON(page_mapping(page) != mapping);
 573                                 if (!mapping->backing_dev_info->memory_backed)
 574                                         inc_page_state(nr_dirty);
 575                                 radix_tree_tag_set(&mapping->page_tree,
 576                                         page_index(page), PAGECACHE_TAG_DIRTY);
 577                         }
 578                         spin_unlock_irq(&mapping->tree_lock);
 579                         if (mapping->host) {
 580                                 /* !PageAnon && !swapper_space */
 581                                 __mark_inode_dirty(mapping->host,
 582                                                         I_DIRTY_PAGES);
 583                         }
 584                 }
 585         }
 586         return ret;
 587 }
 588 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
 589
 590 /*
 591  * When a writepage implementation decides that it doesn't want to write this
 592  * page for some reason, it should redirty the locked page via
 593  * redirty_page_for_writepage() and it should then unlock the page and return 0
 594  */
 595 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
 596 {
 597         wbc->pages_skipped++;
 598         return __set_page_dirty_nobuffers(page);
 599 }
 600 EXPORT_SYMBOL(redirty_page_for_writepage);
 601
 602 /*
 603  * If the mapping doesn't provide a set_page_dirty a_op, then
 604  * just fall through and assume that it wants buffer_heads.
 605  */
 606 int fastcall set_page_dirty(struct page *page)
 607 {
 608         struct address_space *mapping = page_mapping(page);
 609
 610         if (likely(mapping)) {
 611                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
 612                 if (spd)
 613                         return (*spd)(page);
 614                 return __set_page_dirty_buffers(page);
 615         }
 616         if (!PageDirty(page))
 617                 SetPageDirty(page);
 618         return 0;
 619 }
 620 EXPORT_SYMBOL(set_page_dirty);
 621
 622 /*
 623  * set_page_dirty() is racy if the caller has no reference against
 624  * page->mapping->host, and if the page is unlocked.  This is because another
 625  * CPU could truncate the page off the mapping and then free the mapping.
 626  *
 627  * Usually, the page _is_ locked, or the caller is a user-space process which
 628  * holds a reference on the inode by having an open file.
 629  *
 630  * In other cases, the page should be locked before running set_page_dirty().
 631  */
 632 int set_page_dirty_lock(struct page *page)
 633 {
 634         int ret;
 635
 636         lock_page(page);
 637         ret = set_page_dirty(page);
 638         unlock_page(page);
 639         return ret;
 640 }
 641 EXPORT_SYMBOL(set_page_dirty_lock);
 642
 643 /*
 644  * Clear a page's dirty flag, while caring for dirty memory accounting.
 645  * Returns true if the page was previously dirty.
 646  */
 647 int test_clear_page_dirty(struct page *page)
 648 {
 649         struct address_space *mapping = page_mapping(page);
 650         unsigned long flags;
 651
 652         if (mapping) {
 653                 spin_lock_irqsave(&mapping->tree_lock, flags);
 654                 if (TestClearPageDirty(page)) {
 655                         radix_tree_tag_clear(&mapping->page_tree,
 656                                                 page_index(page),
 657                                                 PAGECACHE_TAG_DIRTY);
 658                         spin_unlock_irqrestore(&mapping->tree_lock, flags);
 659                         if (!mapping->backing_dev_info->memory_backed)
 660                                 dec_page_state(nr_dirty);
 661                         return 1;
 662                 }
 663                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
 664                 return 0;
 665         }
 666         return TestClearPageDirty(page);
 667 }
 668 EXPORT_SYMBOL(test_clear_page_dirty);
 669
 670 /*
 671  * Clear a page's dirty flag, while caring for dirty memory accounting.
 672  * Returns true if the page was previously dirty.
 673  *
 674  * This is for preparing to put the page under writeout.  We leave the page
 675  * tagged as dirty in the radix tree so that a concurrent write-for-sync
 676  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
 677  * implementation will run either set_page_writeback() or set_page_dirty(),
 678  * at which stage we bring the page's dirty flag and radix-tree dirty tag
 679  * back into sync.
 680  *
 681  * This incoherency between the page's dirty flag and radix-tree tag is
 682  * unfortunate, but it only exists while the page is locked.
 683  */
 684 int clear_page_dirty_for_io(struct page *page)
 685 {
 686         struct address_space *mapping = page_mapping(page);
 687
 688         if (mapping) {
 689                 if (TestClearPageDirty(page)) {
 690                         if (!mapping->backing_dev_info->memory_backed)
 691                                 dec_page_state(nr_dirty);
 692                         return 1;
 693                 }
 694                 return 0;
 695         }
 696         return TestClearPageDirty(page);
 697 }
 698 EXPORT_SYMBOL(clear_page_dirty_for_io);
 699
 700 /*
 701  * Clear a page's dirty flag while ignoring dirty memory accounting
 702  */
 703 int __clear_page_dirty(struct page *page)
 704 {
 705         struct address_space *mapping = page_mapping(page);
 706
 707         if (mapping) {
 708                 unsigned long flags;
 709
 710                 spin_lock_irqsave(&mapping->tree_lock, flags);
 711                 if (TestClearPageDirty(page)) {
 712                         radix_tree_tag_clear(&mapping->page_tree,
 713                                                 page_index(page),
 714                                                 PAGECACHE_TAG_DIRTY);
 715                         spin_unlock_irqrestore(&mapping->tree_lock, flags);
 716                         return 1;
 717                 }
 718                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
 719                 return 0;
 720         }
 721         return TestClearPageDirty(page);
 722 }
 723
 724 int test_clear_page_writeback(struct page *page)
 725 {
 726         struct address_space *mapping = page_mapping(page);
 727         int ret;
 728
 729         if (mapping) {
 730                 unsigned long flags;
 731
 732                 spin_lock_irqsave(&mapping->tree_lock, flags);
 733                 ret = TestClearPageWriteback(page);
 734                 if (ret)
 735                         radix_tree_tag_clear(&mapping->page_tree,
 736                                                 page_index(page),
 737                                                 PAGECACHE_TAG_WRITEBACK);
 738                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
 739         } else {
 740                 ret = TestClearPageWriteback(page);
 741         }
 742         return ret;
 743 }
 744
 745 int test_set_page_writeback(struct page *page)
 746 {
 747         struct address_space *mapping = page_mapping(page);
 748         int ret;
 749
 750         if (mapping) {
 751                 unsigned long flags;
 752
 753                 spin_lock_irqsave(&mapping->tree_lock, flags);
 754                 ret = TestSetPageWriteback(page);
 755                 if (!ret)
 756                         radix_tree_tag_set(&mapping->page_tree,
 757                                                 page_index(page),
 758                                                 PAGECACHE_TAG_WRITEBACK);
 759                 if (!PageDirty(page))
 760                         radix_tree_tag_clear(&mapping->page_tree,
 761                                                 page_index(page),
 762                                                 PAGECACHE_TAG_DIRTY);
 763                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
 764         } else {
 765                 ret = TestSetPageWriteback(page);
 766         }
 767         return ret;
 768
 769 }
 770 EXPORT_SYMBOL(test_set_page_writeback);
 771
 772 /*
 773  * Return true if any of the pages in the mapping are marged with the
 774  * passed tag.
 775  */
 776 int mapping_tagged(struct address_space *mapping, int tag)
 777 {
 778         unsigned long flags;
 779         int ret;
 780
 781         spin_lock_irqsave(&mapping->tree_lock, flags);
 782         ret = radix_tree_tagged(&mapping->page_tree, tag);
 783         spin_unlock_irqrestore(&mapping->tree_lock, flags);
 784         return ret;
 785 }
 786 EXPORT_SYMBOL(mapping_tagged);