mm/page-writeback.c

   1 /*
   2  * mm/page-writeback.c.
   3  *
   4  * Copyright (C) 2002, Linus Torvalds.
   5  *
   6  * Contains functions related to writing back dirty pages at the
   7  * address_space level.
   8  *
   9  * 10Apr2002    akpm@zip.com.au
  10  *              Initial version
  11  */
  12
  13 #include <linux/kernel.h>
  14 #include <linux/module.h>
  15 #include <linux/spinlock.h>
  16 #include <linux/fs.h>
  17 #include <linux/mm.h>
  18 #include <linux/swap.h>
  19 #include <linux/slab.h>
  20 #include <linux/pagemap.h>
  21 #include <linux/writeback.h>
  22 #include <linux/init.h>
  23 #include <linux/backing-dev.h>
  24 #include <linux/blkdev.h>
  25 #include <linux/mpage.h>
  26 #include <linux/rmap.h>
  27 #include <linux/percpu.h>
  28 #include <linux/notifier.h>
  29 #include <linux/smp.h>
  30 #include <linux/sysctl.h>
  31 #include <linux/cpu.h>
  32 #include <linux/syscalls.h>
  33 #include <linux/buffer_head.h>
  34 #include <linux/pagevec.h>
  35
  36 /*
  37  * The maximum number of pages to writeout in a single bdflush/kupdate
  38  * operation.  We do this so we don't hold I_LOCK against an inode for
  39  * enormous amounts of time, which would block a userspace task which has
  40  * been forced to throttle against that inode.  Also, the code reevaluates
  41  * the dirty each time it has written this many pages.
  42  */
  43 #define MAX_WRITEBACK_PAGES     1024
  44
  45 /*
  46  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
  47  * will look to see if it needs to force writeback or throttling.
  48  */
  49 static long ratelimit_pages = 32;
  50
  51 static int dirty_exceeded __cacheline_aligned_in_smp;   /* Dirty mem may be over limit */
  52
  53 /*
  54  * When balance_dirty_pages decides that the caller needs to perform some
  55  * non-background writeback, this is how many pages it will attempt to write.
  56  * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
  57  * large amounts of I/O are submitted.
  58  */
  59 static inline long sync_writeback_pages(void)
  60 {
  61         return ratelimit_pages + ratelimit_pages / 2;
  62 }
  63
  64 /* The following parameters are exported via /proc/sys/vm */
  65
  66 /*
  67  * Start background writeback (via pdflush) at this percentage
  68  */
  69 int dirty_background_ratio = 10;
  70
  71 /*
  72  * The generator of dirty data starts writeback at this percentage
  73  */
  74 int vm_dirty_ratio = 40;
  75
  76 /*
  77  * The interval between `kupdate'-style writebacks, in jiffies
  78  */
  79 int dirty_writeback_interval = 5 * HZ;
  80
  81 /*
  82  * The longest number of jiffies for which data is allowed to remain dirty
  83  */
  84 int dirty_expire_interval = 30 * HZ;
  85
  86 /*
  87  * Flag that makes the machine dump writes/reads and block dirtyings.
  88  */
  89 int block_dump;
  90
  91 /*
  92  * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
  93  * a full sync is triggered after this time elapses without any disk activity.
  94  */
  95 int laptop_mode;
  96
  97 EXPORT_SYMBOL(laptop_mode);
  98
  99 /* End of sysctl-exported parameters */
 100
 101
 102 static void background_writeout(unsigned long _min_pages);
 103
 104 /*
 105  * Work out the current dirty-memory clamping and background writeout
 106  * thresholds.
 107  *
 108  * The main aim here is to lower them aggressively if there is a lot of mapped
 109  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
 110  * pages.  It is better to clamp down on writers than to start swapping, and
 111  * performing lots of scanning.
 112  *
 113  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
 114  *
 115  * We don't permit the clamping level to fall below 5% - that is getting rather
 116  * excessive.
 117  *
 118  * We make sure that the background writeout level is below the adjusted
 119  * clamping level.
 120  */
 121 static void
 122 get_dirty_limits(long *pbackground, long *pdirty,
 123                                         struct address_space *mapping)
 124 {
 125         int background_ratio;           /* Percentages */
 126         int dirty_ratio;
 127         int unmapped_ratio;
 128         long background;
 129         long dirty;
 130         unsigned long available_memory = vm_total_pages;
 131         struct task_struct *tsk;
 132
 133 #ifdef CONFIG_HIGHMEM
 134         /*
 135          * If this mapping can only allocate from low memory,
 136          * we exclude high memory from our count.
 137          */
 138         if (mapping && !(mapping_gfp_mask(mapping) & __GFP_HIGHMEM))
 139                 available_memory -= totalhigh_pages;
 140 #endif
 141
 142
 143         unmapped_ratio = 100 - ((global_page_state(NR_FILE_MAPPED) +
 144                                 global_page_state(NR_ANON_PAGES)) * 100) /
 145                                         vm_total_pages;
 146
 147         dirty_ratio = vm_dirty_ratio;
 148         if (dirty_ratio > unmapped_ratio / 2)
 149                 dirty_ratio = unmapped_ratio / 2;
 150
 151         if (dirty_ratio < 5)
 152                 dirty_ratio = 5;
 153
 154         background_ratio = dirty_background_ratio;
 155         if (background_ratio >= dirty_ratio)
 156                 background_ratio = dirty_ratio / 2;
 157
 158         background = (background_ratio * available_memory) / 100;
 159         dirty = (dirty_ratio * available_memory) / 100;
 160         tsk = current;
 161         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
 162                 background += background / 4;
 163                 dirty += dirty / 4;
 164         }
 165         *pbackground = background;
 166         *pdirty = dirty;
 167 }
 168
 169 /*
 170  * balance_dirty_pages() must be called by processes which are generating dirty
 171  * data.  It looks at the number of dirty pages in the machine and will force
 172  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
 173  * If we're over `background_thresh' then pdflush is woken to perform some
 174  * writeout.
 175  */
 176 static void balance_dirty_pages(struct address_space *mapping)
 177 {
 178         long nr_reclaimable;
 179         long background_thresh;
 180         long dirty_thresh;
 181         unsigned long pages_written = 0;
 182         unsigned long write_chunk = sync_writeback_pages();
 183
 184         struct backing_dev_info *bdi = mapping->backing_dev_info;
 185
 186         for (;;) {
 187                 struct writeback_control wbc = {
 188                         .bdi            = bdi,
 189                         .sync_mode      = WB_SYNC_NONE,
 190                         .older_than_this = NULL,
 191                         .nr_to_write    = write_chunk,
 192                         .range_cyclic   = 1,
 193                 };
 194
 195                 get_dirty_limits(&background_thresh, &dirty_thresh, mapping);
 196                 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
 197                                         global_page_state(NR_UNSTABLE_NFS);
 198                 if (nr_reclaimable + global_page_state(NR_WRITEBACK) <=
 199                         dirty_thresh)
 200                                 break;
 201
 202                 if (!dirty_exceeded)
 203                         dirty_exceeded = 1;
 204
 205                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
 206                  * Unstable writes are a feature of certain networked
 207                  * filesystems (i.e. NFS) in which data may have been
 208                  * written to the server's write cache, but has not yet
 209                  * been flushed to permanent storage.
 210                  */
 211                 if (nr_reclaimable) {
 212                         writeback_inodes(&wbc);
 213                         get_dirty_limits(&background_thresh,
 214                                                 &dirty_thresh, mapping);
 215                         nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
 216                                         global_page_state(NR_UNSTABLE_NFS);
 217                         if (nr_reclaimable +
 218                                 global_page_state(NR_WRITEBACK)
 219                                         <= dirty_thresh)
 220                                                 break;
 221                         pages_written += write_chunk - wbc.nr_to_write;
 222                         if (pages_written >= write_chunk)
 223                                 break;          /* We've done our duty */
 224                 }
 225                 blk_congestion_wait(WRITE, HZ/10);
 226         }
 227
 228         if (nr_reclaimable + global_page_state(NR_WRITEBACK)
 229                 <= dirty_thresh && dirty_exceeded)
 230                         dirty_exceeded = 0;
 231
 232         if (writeback_in_progress(bdi))
 233                 return;         /* pdflush is already working this queue */
 234
 235         /*
 236          * In laptop mode, we wait until hitting the higher threshold before
 237          * starting background writeout, and then write out all the way down
 238          * to the lower threshold.  So slow writers cause minimal disk activity.
 239          *
 240          * In normal mode, we start background writeout at the lower
 241          * background_thresh, to keep the amount of dirty memory low.
 242          */
 243         if ((laptop_mode && pages_written) ||
 244              (!laptop_mode && (nr_reclaimable > background_thresh)))
 245                 pdflush_operation(background_writeout, 0);
 246 }
 247
 248 void set_page_dirty_balance(struct page *page)
 249 {
 250         if (set_page_dirty(page)) {
 251                 struct address_space *mapping = page_mapping(page);
 252
 253                 if (mapping)
 254                         balance_dirty_pages_ratelimited(mapping);
 255         }
 256 }
 257
 258 /**
 259  * balance_dirty_pages_ratelimited_nr - balance dirty memory state
 260  * @mapping: address_space which was dirtied
 261  * @nr_pages_dirtied: number of pages which the caller has just dirtied
 262  *
 263  * Processes which are dirtying memory should call in here once for each page
 264  * which was newly dirtied.  The function will periodically check the system's
 265  * dirty state and will initiate writeback if needed.
 266  *
 267  * On really big machines, get_writeback_state is expensive, so try to avoid
 268  * calling it too often (ratelimiting).  But once we're over the dirty memory
 269  * limit we decrease the ratelimiting by a lot, to prevent individual processes
 270  * from overshooting the limit by (ratelimit_pages) each.
 271  */
 272 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
 273                                         unsigned long nr_pages_dirtied)
 274 {
 275         static DEFINE_PER_CPU(unsigned long, ratelimits) = 0;
 276         unsigned long ratelimit;
 277         unsigned long *p;
 278
 279         ratelimit = ratelimit_pages;
 280         if (dirty_exceeded)
 281                 ratelimit = 8;
 282
 283         /*
 284          * Check the rate limiting. Also, we do not want to throttle real-time
 285          * tasks in balance_dirty_pages(). Period.
 286          */
 287         preempt_disable();
 288         p =  &__get_cpu_var(ratelimits);
 289         *p += nr_pages_dirtied;
 290         if (unlikely(*p >= ratelimit)) {
 291                 *p = 0;
 292                 preempt_enable();
 293                 balance_dirty_pages(mapping);
 294                 return;
 295         }
 296         preempt_enable();
 297 }
 298 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
 299
 300 void throttle_vm_writeout(void)
 301 {
 302         long background_thresh;
 303         long dirty_thresh;
 304
 305         for ( ; ; ) {
 306                 get_dirty_limits(&background_thresh, &dirty_thresh, NULL);
 307
 308                 /*
 309                  * Boost the allowable dirty threshold a bit for page
 310                  * allocators so they don't get DoS'ed by heavy writers
 311                  */
 312                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
 313
 314                 if (global_page_state(NR_UNSTABLE_NFS) +
 315                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
 316                                 break;
 317                 blk_congestion_wait(WRITE, HZ/10);
 318         }
 319 }
 320
 321
 322 /*
 323  * writeback at least _min_pages, and keep writing until the amount of dirty
 324  * memory is less than the background threshold, or until we're all clean.
 325  */
 326 static void background_writeout(unsigned long _min_pages)
 327 {
 328         long min_pages = _min_pages;
 329         struct writeback_control wbc = {
 330                 .bdi            = NULL,
 331                 .sync_mode      = WB_SYNC_NONE,
 332                 .older_than_this = NULL,
 333                 .nr_to_write    = 0,
 334                 .nonblocking    = 1,
 335                 .range_cyclic   = 1,
 336         };
 337
 338         for ( ; ; ) {
 339                 long background_thresh;
 340                 long dirty_thresh;
 341
 342                 get_dirty_limits(&background_thresh, &dirty_thresh, NULL);
 343                 if (global_page_state(NR_FILE_DIRTY) +
 344                         global_page_state(NR_UNSTABLE_NFS) < background_thresh
 345                                 && min_pages <= 0)
 346                         break;
 347                 wbc.encountered_congestion = 0;
 348                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 349                 wbc.pages_skipped = 0;
 350                 writeback_inodes(&wbc);
 351                 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 352                 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
 353                         /* Wrote less than expected */
 354                         blk_congestion_wait(WRITE, HZ/10);
 355                         if (!wbc.encountered_congestion)
 356                                 break;
 357                 }
 358         }
 359 }
 360
 361 /*
 362  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
 363  * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
 364  * -1 if all pdflush threads were busy.
 365  */
 366 int wakeup_pdflush(long nr_pages)
 367 {
 368         if (nr_pages == 0)
 369                 nr_pages = global_page_state(NR_FILE_DIRTY) +
 370                                 global_page_state(NR_UNSTABLE_NFS);
 371         return pdflush_operation(background_writeout, nr_pages);
 372 }
 373
 374 static void wb_timer_fn(unsigned long unused);
 375 static void laptop_timer_fn(unsigned long unused);
 376
 377 static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
 378 static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
 379
 380 /*
 381  * Periodic writeback of "old" data.
 382  *
 383  * Define "old": the first time one of an inode's pages is dirtied, we mark the
 384  * dirtying-time in the inode's address_space.  So this periodic writeback code
 385  * just walks the superblock inode list, writing back any inodes which are
 386  * older than a specific point in time.
 387  *
 388  * Try to run once per dirty_writeback_interval.  But if a writeback event
 389  * takes longer than a dirty_writeback_interval interval, then leave a
 390  * one-second gap.
 391  *
 392  * older_than_this takes precedence over nr_to_write.  So we'll only write back
 393  * all dirty pages if they are all attached to "old" mappings.
 394  */
 395 static void wb_kupdate(unsigned long arg)
 396 {
 397         unsigned long oldest_jif;
 398         unsigned long start_jif;
 399         unsigned long next_jif;
 400         long nr_to_write;
 401         struct writeback_control wbc = {
 402                 .bdi            = NULL,
 403                 .sync_mode      = WB_SYNC_NONE,
 404                 .older_than_this = &oldest_jif,
 405                 .nr_to_write    = 0,
 406                 .nonblocking    = 1,
 407                 .for_kupdate    = 1,
 408                 .range_cyclic   = 1,
 409         };
 410
 411         sync_supers();
 412
 413         oldest_jif = jiffies - dirty_expire_interval;
 414         start_jif = jiffies;
 415         next_jif = start_jif + dirty_writeback_interval;
 416         nr_to_write = global_page_state(NR_FILE_DIRTY) +
 417                         global_page_state(NR_UNSTABLE_NFS) +
 418                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
 419         while (nr_to_write > 0) {
 420                 wbc.encountered_congestion = 0;
 421                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 422                 writeback_inodes(&wbc);
 423                 if (wbc.nr_to_write > 0) {
 424                         if (wbc.encountered_congestion)
 425                                 blk_congestion_wait(WRITE, HZ/10);
 426                         else
 427                                 break;  /* All the old data is written */
 428                 }
 429                 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 430         }
 431         if (time_before(next_jif, jiffies + HZ))
 432                 next_jif = jiffies + HZ;
 433         if (dirty_writeback_interval)
 434                 mod_timer(&wb_timer, next_jif);
 435 }
 436
 437 /*
 438  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
 439  */
 440 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
 441                 struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
 442 {
 443         proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
 444         if (dirty_writeback_interval) {
 445                 mod_timer(&wb_timer,
 446                         jiffies + dirty_writeback_interval);
 447                 } else {
 448                 del_timer(&wb_timer);
 449         }
 450         return 0;
 451 }
 452
 453 static void wb_timer_fn(unsigned long unused)
 454 {
 455         if (pdflush_operation(wb_kupdate, 0) < 0)
 456                 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
 457 }
 458
 459 static void laptop_flush(unsigned long unused)
 460 {
 461         sys_sync();
 462 }
 463
 464 static void laptop_timer_fn(unsigned long unused)
 465 {
 466         pdflush_operation(laptop_flush, 0);
 467 }
 468
 469 /*
 470  * We've spun up the disk and we're in laptop mode: schedule writeback
 471  * of all dirty data a few seconds from now.  If the flush is already scheduled
 472  * then push it back - the user is still using the disk.
 473  */
 474 void laptop_io_completion(void)
 475 {
 476         mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
 477 }
 478
 479 /*
 480  * We're in laptop mode and we've just synced. The sync's writes will have
 481  * caused another writeback to be scheduled by laptop_io_completion.
 482  * Nothing needs to be written back anymore, so we unschedule the writeback.
 483  */
 484 void laptop_sync_completion(void)
 485 {
 486         del_timer(&laptop_mode_wb_timer);
 487 }
 488
 489 /*
 490  * If ratelimit_pages is too high then we can get into dirty-data overload
 491  * if a large number of processes all perform writes at the same time.
 492  * If it is too low then SMP machines will call the (expensive)
 493  * get_writeback_state too often.
 494  *
 495  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
 496  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
 497  * thresholds before writeback cuts in.
 498  *
 499  * But the limit should not be set too high.  Because it also controls the
 500  * amount of memory which the balance_dirty_pages() caller has to write back.
 501  * If this is too large then the caller will block on the IO queue all the
 502  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
 503  * will write six megabyte chunks, max.
 504  */
 505
 506 void writeback_set_ratelimit(void)
 507 {
 508         ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
 509         if (ratelimit_pages < 16)
 510                 ratelimit_pages = 16;
 511         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
 512                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
 513 }
 514
 515 static int __cpuinit
 516 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
 517 {
 518         writeback_set_ratelimit();
 519         return 0;
 520 }
 521
 522 static struct notifier_block __cpuinitdata ratelimit_nb = {
 523         .notifier_call  = ratelimit_handler,
 524         .next           = NULL,
 525 };
 526
 527 /*
 528  * If the machine has a large highmem:lowmem ratio then scale back the default
 529  * dirty memory thresholds: allowing too much dirty highmem pins an excessive
 530  * number of buffer_heads.
 531  */
 532 void __init page_writeback_init(void)
 533 {
 534         long buffer_pages = nr_free_buffer_pages();
 535         long correction;
 536
 537         correction = (100 * 4 * buffer_pages) / vm_total_pages;
 538
 539         if (correction < 100) {
 540                 dirty_background_ratio *= correction;
 541                 dirty_background_ratio /= 100;
 542                 vm_dirty_ratio *= correction;
 543                 vm_dirty_ratio /= 100;
 544
 545                 if (dirty_background_ratio <= 0)
 546                         dirty_background_ratio = 1;
 547                 if (vm_dirty_ratio <= 0)
 548                         vm_dirty_ratio = 1;
 549         }
 550         mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
 551         writeback_set_ratelimit();
 552         register_cpu_notifier(&ratelimit_nb);
 553 }
 554
 555 /**
 556  * generic_writepages - walk the list of dirty pages of the given
 557  *                      address space and writepage() all of them.
 558  *
 559  * @mapping: address space structure to write
 560  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 561  *
 562  * This is a library function, which implements the writepages()
 563  * address_space_operation.
 564  *
 565  * If a page is already under I/O, generic_writepages() skips it, even
 566  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 567  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 568  * and msync() need to guarantee that all the data which was dirty at the time
 569  * the call was made get new I/O started against them.  If wbc->sync_mode is
 570  * WB_SYNC_ALL then we were called for data integrity and we must wait for
 571  * existing IO to complete.
 572  *
 573  * Derived from mpage_writepages() - if you fix this you should check that
 574  * also!
 575  */
 576 int generic_writepages(struct address_space *mapping,
 577                        struct writeback_control *wbc)
 578 {
 579         struct backing_dev_info *bdi = mapping->backing_dev_info;
 580         int ret = 0;
 581         int done = 0;
 582         int (*writepage)(struct page *page, struct writeback_control *wbc);
 583         struct pagevec pvec;
 584         int nr_pages;
 585         pgoff_t index;
 586         pgoff_t end;            /* Inclusive */
 587         int scanned = 0;
 588         int range_whole = 0;
 589
 590         if (wbc->nonblocking && bdi_write_congested(bdi)) {
 591                 wbc->encountered_congestion = 1;
 592                 return 0;
 593         }
 594
 595         writepage = mapping->a_ops->writepage;
 596
 597         /* deal with chardevs and other special file */
 598         if (!writepage)
 599                 return 0;
 600
 601         pagevec_init(&pvec, 0);
 602         if (wbc->range_cyclic) {
 603                 index = mapping->writeback_index; /* Start from prev offset */
 604                 end = -1;
 605         } else {
 606                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
 607                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
 608                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
 609                         range_whole = 1;
 610                 scanned = 1;
 611         }
 612 retry:
 613         while (!done && (index <= end) &&
 614                (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
 615                                               PAGECACHE_TAG_DIRTY,
 616                                               min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
 617                 unsigned i;
 618
 619                 scanned = 1;
 620                 for (i = 0; i < nr_pages; i++) {
 621                         struct page *page = pvec.pages[i];
 622
 623                         /*
 624                          * At this point we hold neither mapping->tree_lock nor
 625                          * lock on the page itself: the page may be truncated or
 626                          * invalidated (changing page->mapping to NULL), or even
 627                          * swizzled back from swapper_space to tmpfs file
 628                          * mapping
 629                          */
 630                         lock_page(page);
 631
 632                         if (unlikely(page->mapping != mapping)) {
 633                                 unlock_page(page);
 634                                 continue;
 635                         }
 636
 637                         if (!wbc->range_cyclic && page->index > end) {
 638                                 done = 1;
 639                                 unlock_page(page);
 640                                 continue;
 641                         }
 642
 643                         if (wbc->sync_mode != WB_SYNC_NONE)
 644                                 wait_on_page_writeback(page);
 645
 646                         if (PageWriteback(page) ||
 647                             !clear_page_dirty_for_io(page)) {
 648                                 unlock_page(page);
 649                                 continue;
 650                         }
 651
 652                         ret = (*writepage)(page, wbc);
 653                         if (ret) {
 654                                 if (ret == -ENOSPC)
 655                                         set_bit(AS_ENOSPC, &mapping->flags);
 656                                 else
 657                                         set_bit(AS_EIO, &mapping->flags);
 658                         }
 659
 660                         if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE))
 661                                 unlock_page(page);
 662                         if (ret || (--(wbc->nr_to_write) <= 0))
 663                                 done = 1;
 664                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
 665                                 wbc->encountered_congestion = 1;
 666                                 done = 1;
 667                         }
 668                 }
 669                 pagevec_release(&pvec);
 670                 cond_resched();
 671         }
 672         if (!scanned && !done) {
 673                 /*
 674                  * We hit the last page and there is more work to be done: wrap
 675                  * back to the start of the file
 676                  */
 677                 scanned = 1;
 678                 index = 0;
 679                 goto retry;
 680         }
 681         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
 682                 mapping->writeback_index = index;
 683         return ret;
 684 }
 685
 686 EXPORT_SYMBOL(generic_writepages);
 687
 688 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
 689 {
 690         int ret;
 691
 692         if (wbc->nr_to_write <= 0)
 693                 return 0;
 694         wbc->for_writepages = 1;
 695         if (mapping->a_ops->writepages)
 696                 ret = mapping->a_ops->writepages(mapping, wbc);
 697         else
 698                 ret = generic_writepages(mapping, wbc);
 699         wbc->for_writepages = 0;
 700         return ret;
 701 }
 702
 703 /**
 704  * write_one_page - write out a single page and optionally wait on I/O
 705  *
 706  * @page: the page to write
 707  * @wait: if true, wait on writeout
 708  *
 709  * The page must be locked by the caller and will be unlocked upon return.
 710  *
 711  * write_one_page() returns a negative error code if I/O failed.
 712  */
 713 int write_one_page(struct page *page, int wait)
 714 {
 715         struct address_space *mapping = page->mapping;
 716         int ret = 0;
 717         struct writeback_control wbc = {
 718                 .sync_mode = WB_SYNC_ALL,
 719                 .nr_to_write = 1,
 720         };
 721
 722         BUG_ON(!PageLocked(page));
 723
 724         if (wait)
 725                 wait_on_page_writeback(page);
 726
 727         if (clear_page_dirty_for_io(page)) {
 728                 page_cache_get(page);
 729                 ret = mapping->a_ops->writepage(page, &wbc);
 730                 if (ret == 0 && wait) {
 731                         wait_on_page_writeback(page);
 732                         if (PageError(page))
 733                                 ret = -EIO;
 734                 }
 735                 page_cache_release(page);
 736         } else {
 737                 unlock_page(page);
 738         }
 739         return ret;
 740 }
 741 EXPORT_SYMBOL(write_one_page);
 742
 743 /*
 744  * For address_spaces which do not use buffers.  Just tag the page as dirty in
 745  * its radix tree.
 746  *
 747  * This is also used when a single buffer is being dirtied: we want to set the
 748  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
 749  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
 750  *
 751  * Most callers have locked the page, which pins the address_space in memory.
 752  * But zap_pte_range() does not lock the page, however in that case the
 753  * mapping is pinned by the vma's ->vm_file reference.
 754  *
 755  * We take care to handle the case where the page was truncated from the
 756  * mapping by re-checking page_mapping() insode tree_lock.
 757  */
 758 int __set_page_dirty_nobuffers(struct page *page)
 759 {
 760         if (!TestSetPageDirty(page)) {
 761                 struct address_space *mapping = page_mapping(page);
 762                 struct address_space *mapping2;
 763
 764                 if (mapping) {
 765                         write_lock_irq(&mapping->tree_lock);
 766                         mapping2 = page_mapping(page);
 767                         if (mapping2) { /* Race with truncate? */
 768                                 BUG_ON(mapping2 != mapping);
 769                                 if (mapping_cap_account_dirty(mapping))
 770                                         __inc_zone_page_state(page,
 771                                                                 NR_FILE_DIRTY);
 772                                 radix_tree_tag_set(&mapping->page_tree,
 773                                         page_index(page), PAGECACHE_TAG_DIRTY);
 774                         }
 775                         write_unlock_irq(&mapping->tree_lock);
 776                         if (mapping->host) {
 777                                 /* !PageAnon && !swapper_space */
 778                                 __mark_inode_dirty(mapping->host,
 779                                                         I_DIRTY_PAGES);
 780                         }
 781                 }
 782                 return 1;
 783         }
 784         return 0;
 785 }
 786 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
 787
 788 /*
 789  * When a writepage implementation decides that it doesn't want to write this
 790  * page for some reason, it should redirty the locked page via
 791  * redirty_page_for_writepage() and it should then unlock the page and return 0
 792  */
 793 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
 794 {
 795         wbc->pages_skipped++;
 796         return __set_page_dirty_nobuffers(page);
 797 }
 798 EXPORT_SYMBOL(redirty_page_for_writepage);
 799
 800 /*
 801  * If the mapping doesn't provide a set_page_dirty a_op, then
 802  * just fall through and assume that it wants buffer_heads.
 803  */
 804 int fastcall set_page_dirty(struct page *page)
 805 {
 806         struct address_space *mapping = page_mapping(page);
 807
 808         if (likely(mapping)) {
 809                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
 810 #ifdef CONFIG_BLOCK
 811                 if (!spd)
 812                         spd = __set_page_dirty_buffers;
 813 #endif
 814                 return (*spd)(page);
 815         }
 816         if (!PageDirty(page)) {
 817                 if (!TestSetPageDirty(page))
 818                         return 1;
 819         }
 820         return 0;
 821 }
 822 EXPORT_SYMBOL(set_page_dirty);
 823
 824 /*
 825  * set_page_dirty() is racy if the caller has no reference against
 826  * page->mapping->host, and if the page is unlocked.  This is because another
 827  * CPU could truncate the page off the mapping and then free the mapping.
 828  *
 829  * Usually, the page _is_ locked, or the caller is a user-space process which
 830  * holds a reference on the inode by having an open file.
 831  *
 832  * In other cases, the page should be locked before running set_page_dirty().
 833  */
 834 int set_page_dirty_lock(struct page *page)
 835 {
 836         int ret;
 837
 838         lock_page_nosync(page);
 839         ret = set_page_dirty(page);
 840         unlock_page(page);
 841         return ret;
 842 }
 843 EXPORT_SYMBOL(set_page_dirty_lock);
 844
 845 /*
 846  * Clear a page's dirty flag, while caring for dirty memory accounting.
 847  * Returns true if the page was previously dirty.
 848  */
 849 int test_clear_page_dirty(struct page *page)
 850 {
 851         struct address_space *mapping = page_mapping(page);
 852         unsigned long flags;
 853
 854         if (mapping) {
 855                 write_lock_irqsave(&mapping->tree_lock, flags);
 856                 if (TestClearPageDirty(page)) {
 857                         radix_tree_tag_clear(&mapping->page_tree,
 858                                                 page_index(page),
 859                                                 PAGECACHE_TAG_DIRTY);
 860                         write_unlock_irqrestore(&mapping->tree_lock, flags);
 861                         /*
 862                          * We can continue to use `mapping' here because the
 863                          * page is locked, which pins the address_space
 864                          */
 865                         if (mapping_cap_account_dirty(mapping)) {
 866                                 page_mkclean(page);
 867                                 dec_zone_page_state(page, NR_FILE_DIRTY);
 868                         }
 869                         return 1;
 870                 }
 871                 write_unlock_irqrestore(&mapping->tree_lock, flags);
 872                 return 0;
 873         }
 874         return TestClearPageDirty(page);
 875 }
 876 EXPORT_SYMBOL(test_clear_page_dirty);
 877
 878 /*
 879  * Clear a page's dirty flag, while caring for dirty memory accounting.
 880  * Returns true if the page was previously dirty.
 881  *
 882  * This is for preparing to put the page under writeout.  We leave the page
 883  * tagged as dirty in the radix tree so that a concurrent write-for-sync
 884  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
 885  * implementation will run either set_page_writeback() or set_page_dirty(),
 886  * at which stage we bring the page's dirty flag and radix-tree dirty tag
 887  * back into sync.
 888  *
 889  * This incoherency between the page's dirty flag and radix-tree tag is
 890  * unfortunate, but it only exists while the page is locked.
 891  */
 892 int clear_page_dirty_for_io(struct page *page)
 893 {
 894         struct address_space *mapping = page_mapping(page);
 895
 896         if (mapping) {
 897                 if (TestClearPageDirty(page)) {
 898                         if (mapping_cap_account_dirty(mapping)) {
 899                                 page_mkclean(page);
 900                                 dec_zone_page_state(page, NR_FILE_DIRTY);
 901                         }
 902                         return 1;
 903                 }
 904                 return 0;
 905         }
 906         return TestClearPageDirty(page);
 907 }
 908 EXPORT_SYMBOL(clear_page_dirty_for_io);
 909
 910 int test_clear_page_writeback(struct page *page)
 911 {
 912         struct address_space *mapping = page_mapping(page);
 913         int ret;
 914
 915         if (mapping) {
 916                 unsigned long flags;
 917
 918                 write_lock_irqsave(&mapping->tree_lock, flags);
 919                 ret = TestClearPageWriteback(page);
 920                 if (ret)
 921                         radix_tree_tag_clear(&mapping->page_tree,
 922                                                 page_index(page),
 923                                                 PAGECACHE_TAG_WRITEBACK);
 924                 write_unlock_irqrestore(&mapping->tree_lock, flags);
 925         } else {
 926                 ret = TestClearPageWriteback(page);
 927         }
 928         return ret;
 929 }
 930
 931 int test_set_page_writeback(struct page *page)
 932 {
 933         struct address_space *mapping = page_mapping(page);
 934         int ret;
 935
 936         if (mapping) {
 937                 unsigned long flags;
 938
 939                 write_lock_irqsave(&mapping->tree_lock, flags);
 940                 ret = TestSetPageWriteback(page);
 941                 if (!ret)
 942                         radix_tree_tag_set(&mapping->page_tree,
 943                                                 page_index(page),
 944                                                 PAGECACHE_TAG_WRITEBACK);
 945                 if (!PageDirty(page))
 946                         radix_tree_tag_clear(&mapping->page_tree,
 947                                                 page_index(page),
 948                                                 PAGECACHE_TAG_DIRTY);
 949                 write_unlock_irqrestore(&mapping->tree_lock, flags);
 950         } else {
 951                 ret = TestSetPageWriteback(page);
 952         }
 953         return ret;
 954
 955 }
 956 EXPORT_SYMBOL(test_set_page_writeback);
 957
 958 /*
 959  * Wakes up tasks that are being throttled due to writeback congestion
 960  */
 961 void writeback_congestion_end(void)
 962 {
 963         blk_congestion_end(WRITE);
 964 }
 965 EXPORT_SYMBOL(writeback_congestion_end);
 966
 967 /*
 968  * Return true if any of the pages in the mapping are marged with the
 969  * passed tag.
 970  */
 971 int mapping_tagged(struct address_space *mapping, int tag)
 972 {
 973         unsigned long flags;
 974         int ret;
 975
 976         read_lock_irqsave(&mapping->tree_lock, flags);
 977         ret = radix_tree_tagged(&mapping->page_tree, tag);
 978         read_unlock_irqrestore(&mapping->tree_lock, flags);
 979         return ret;
 980 }
 981 EXPORT_SYMBOL(mapping_tagged);