mm/page-writeback.c

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