linux/mm/page-writeback.c
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   1/*
   2 * mm/page-writeback.c
   3 *
   4 * Copyright (C) 2002, Linus Torvalds.
   5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
   6 *
   7 * Contains functions related to writing back dirty pages at the
   8 * address_space level.
   9 *
  10 * 10Apr2002    Andrew Morton
  11 *              Initial version
  12 */
  13
  14#include <linux/kernel.h>
  15#include <linux/module.h>
  16#include <linux/spinlock.h>
  17#include <linux/fs.h>
  18#include <linux/mm.h>
  19#include <linux/swap.h>
  20#include <linux/slab.h>
  21#include <linux/pagemap.h>
  22#include <linux/writeback.h>
  23#include <linux/init.h>
  24#include <linux/backing-dev.h>
  25#include <linux/task_io_accounting_ops.h>
  26#include <linux/blkdev.h>
  27#include <linux/mpage.h>
  28#include <linux/rmap.h>
  29#include <linux/percpu.h>
  30#include <linux/notifier.h>
  31#include <linux/smp.h>
  32#include <linux/sysctl.h>
  33#include <linux/cpu.h>
  34#include <linux/syscalls.h>
  35#include <linux/buffer_head.h>
  36#include <linux/pagevec.h>
  37#include <trace/events/writeback.h>
  38
  39/*
  40 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
  41 * will look to see if it needs to force writeback or throttling.
  42 */
  43static long ratelimit_pages = 32;
  44
  45/*
  46 * When balance_dirty_pages decides that the caller needs to perform some
  47 * non-background writeback, this is how many pages it will attempt to write.
  48 * It should be somewhat larger than dirtied pages to ensure that reasonably
  49 * large amounts of I/O are submitted.
  50 */
  51static inline long sync_writeback_pages(unsigned long dirtied)
  52{
  53        if (dirtied < ratelimit_pages)
  54                dirtied = ratelimit_pages;
  55
  56        return dirtied + dirtied / 2;
  57}
  58
  59/* The following parameters are exported via /proc/sys/vm */
  60
  61/*
  62 * Start background writeback (via writeback threads) at this percentage
  63 */
  64int dirty_background_ratio = 10;
  65
  66/*
  67 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
  68 * dirty_background_ratio * the amount of dirtyable memory
  69 */
  70unsigned long dirty_background_bytes;
  71
  72/*
  73 * free highmem will not be subtracted from the total free memory
  74 * for calculating free ratios if vm_highmem_is_dirtyable is true
  75 */
  76int vm_highmem_is_dirtyable;
  77
  78/*
  79 * The generator of dirty data starts writeback at this percentage
  80 */
  81int vm_dirty_ratio = 20;
  82
  83/*
  84 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
  85 * vm_dirty_ratio * the amount of dirtyable memory
  86 */
  87unsigned long vm_dirty_bytes;
  88
  89/*
  90 * The interval between `kupdate'-style writebacks
  91 */
  92unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
  93
  94/*
  95 * The longest time for which data is allowed to remain dirty
  96 */
  97unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
  98
  99/*
 100 * Flag that makes the machine dump writes/reads and block dirtyings.
 101 */
 102int block_dump;
 103
 104/*
 105 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
 106 * a full sync is triggered after this time elapses without any disk activity.
 107 */
 108int laptop_mode;
 109
 110EXPORT_SYMBOL(laptop_mode);
 111
 112/* End of sysctl-exported parameters */
 113
 114
 115/*
 116 * Scale the writeback cache size proportional to the relative writeout speeds.
 117 *
 118 * We do this by keeping a floating proportion between BDIs, based on page
 119 * writeback completions [end_page_writeback()]. Those devices that write out
 120 * pages fastest will get the larger share, while the slower will get a smaller
 121 * share.
 122 *
 123 * We use page writeout completions because we are interested in getting rid of
 124 * dirty pages. Having them written out is the primary goal.
 125 *
 126 * We introduce a concept of time, a period over which we measure these events,
 127 * because demand can/will vary over time. The length of this period itself is
 128 * measured in page writeback completions.
 129 *
 130 */
 131static struct prop_descriptor vm_completions;
 132static struct prop_descriptor vm_dirties;
 133
 134/*
 135 * couple the period to the dirty_ratio:
 136 *
 137 *   period/2 ~ roundup_pow_of_two(dirty limit)
 138 */
 139static int calc_period_shift(void)
 140{
 141        unsigned long dirty_total;
 142
 143        if (vm_dirty_bytes)
 144                dirty_total = vm_dirty_bytes / PAGE_SIZE;
 145        else
 146                dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
 147                                100;
 148        return 2 + ilog2(dirty_total - 1);
 149}
 150
 151/*
 152 * update the period when the dirty threshold changes.
 153 */
 154static void update_completion_period(void)
 155{
 156        int shift = calc_period_shift();
 157        prop_change_shift(&vm_completions, shift);
 158        prop_change_shift(&vm_dirties, shift);
 159}
 160
 161int dirty_background_ratio_handler(struct ctl_table *table, int write,
 162                void __user *buffer, size_t *lenp,
 163                loff_t *ppos)
 164{
 165        int ret;
 166
 167        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 168        if (ret == 0 && write)
 169                dirty_background_bytes = 0;
 170        return ret;
 171}
 172
 173int dirty_background_bytes_handler(struct ctl_table *table, int write,
 174                void __user *buffer, size_t *lenp,
 175                loff_t *ppos)
 176{
 177        int ret;
 178
 179        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 180        if (ret == 0 && write)
 181                dirty_background_ratio = 0;
 182        return ret;
 183}
 184
 185int dirty_ratio_handler(struct ctl_table *table, int write,
 186                void __user *buffer, size_t *lenp,
 187                loff_t *ppos)
 188{
 189        int old_ratio = vm_dirty_ratio;
 190        int ret;
 191
 192        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 193        if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
 194                update_completion_period();
 195                vm_dirty_bytes = 0;
 196        }
 197        return ret;
 198}
 199
 200
 201int dirty_bytes_handler(struct ctl_table *table, int write,
 202                void __user *buffer, size_t *lenp,
 203                loff_t *ppos)
 204{
 205        unsigned long old_bytes = vm_dirty_bytes;
 206        int ret;
 207
 208        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 209        if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
 210                update_completion_period();
 211                vm_dirty_ratio = 0;
 212        }
 213        return ret;
 214}
 215
 216/*
 217 * Increment the BDI's writeout completion count and the global writeout
 218 * completion count. Called from test_clear_page_writeback().
 219 */
 220static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
 221{
 222        __prop_inc_percpu_max(&vm_completions, &bdi->completions,
 223                              bdi->max_prop_frac);
 224}
 225
 226void bdi_writeout_inc(struct backing_dev_info *bdi)
 227{
 228        unsigned long flags;
 229
 230        local_irq_save(flags);
 231        __bdi_writeout_inc(bdi);
 232        local_irq_restore(flags);
 233}
 234EXPORT_SYMBOL_GPL(bdi_writeout_inc);
 235
 236void task_dirty_inc(struct task_struct *tsk)
 237{
 238        prop_inc_single(&vm_dirties, &tsk->dirties);
 239}
 240
 241/*
 242 * Obtain an accurate fraction of the BDI's portion.
 243 */
 244static void bdi_writeout_fraction(struct backing_dev_info *bdi,
 245                long *numerator, long *denominator)
 246{
 247        if (bdi_cap_writeback_dirty(bdi)) {
 248                prop_fraction_percpu(&vm_completions, &bdi->completions,
 249                                numerator, denominator);
 250        } else {
 251                *numerator = 0;
 252                *denominator = 1;
 253        }
 254}
 255
 256static inline void task_dirties_fraction(struct task_struct *tsk,
 257                long *numerator, long *denominator)
 258{
 259        prop_fraction_single(&vm_dirties, &tsk->dirties,
 260                                numerator, denominator);
 261}
 262
 263/*
 264 * task_dirty_limit - scale down dirty throttling threshold for one task
 265 *
 266 * task specific dirty limit:
 267 *
 268 *   dirty -= (dirty/8) * p_{t}
 269 *
 270 * To protect light/slow dirtying tasks from heavier/fast ones, we start
 271 * throttling individual tasks before reaching the bdi dirty limit.
 272 * Relatively low thresholds will be allocated to heavy dirtiers. So when
 273 * dirty pages grow large, heavy dirtiers will be throttled first, which will
 274 * effectively curb the growth of dirty pages. Light dirtiers with high enough
 275 * dirty threshold may never get throttled.
 276 */
 277static unsigned long task_dirty_limit(struct task_struct *tsk,
 278                                       unsigned long bdi_dirty)
 279{
 280        long numerator, denominator;
 281        unsigned long dirty = bdi_dirty;
 282        u64 inv = dirty >> 3;
 283
 284        task_dirties_fraction(tsk, &numerator, &denominator);
 285        inv *= numerator;
 286        do_div(inv, denominator);
 287
 288        dirty -= inv;
 289
 290        return max(dirty, bdi_dirty/2);
 291}
 292
 293/*
 294 *
 295 */
 296static unsigned int bdi_min_ratio;
 297
 298int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 299{
 300        int ret = 0;
 301
 302        spin_lock_bh(&bdi_lock);
 303        if (min_ratio > bdi->max_ratio) {
 304                ret = -EINVAL;
 305        } else {
 306                min_ratio -= bdi->min_ratio;
 307                if (bdi_min_ratio + min_ratio < 100) {
 308                        bdi_min_ratio += min_ratio;
 309                        bdi->min_ratio += min_ratio;
 310                } else {
 311                        ret = -EINVAL;
 312                }
 313        }
 314        spin_unlock_bh(&bdi_lock);
 315
 316        return ret;
 317}
 318
 319int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 320{
 321        int ret = 0;
 322
 323        if (max_ratio > 100)
 324                return -EINVAL;
 325
 326        spin_lock_bh(&bdi_lock);
 327        if (bdi->min_ratio > max_ratio) {
 328                ret = -EINVAL;
 329        } else {
 330                bdi->max_ratio = max_ratio;
 331                bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
 332        }
 333        spin_unlock_bh(&bdi_lock);
 334
 335        return ret;
 336}
 337EXPORT_SYMBOL(bdi_set_max_ratio);
 338
 339/*
 340 * Work out the current dirty-memory clamping and background writeout
 341 * thresholds.
 342 *
 343 * The main aim here is to lower them aggressively if there is a lot of mapped
 344 * memory around.  To avoid stressing page reclaim with lots of unreclaimable
 345 * pages.  It is better to clamp down on writers than to start swapping, and
 346 * performing lots of scanning.
 347 *
 348 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
 349 *
 350 * We don't permit the clamping level to fall below 5% - that is getting rather
 351 * excessive.
 352 *
 353 * We make sure that the background writeout level is below the adjusted
 354 * clamping level.
 355 */
 356
 357static unsigned long highmem_dirtyable_memory(unsigned long total)
 358{
 359#ifdef CONFIG_HIGHMEM
 360        int node;
 361        unsigned long x = 0;
 362
 363        for_each_node_state(node, N_HIGH_MEMORY) {
 364                struct zone *z =
 365                        &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
 366
 367                x += zone_page_state(z, NR_FREE_PAGES) +
 368                     zone_reclaimable_pages(z);
 369        }
 370        /*
 371         * Make sure that the number of highmem pages is never larger
 372         * than the number of the total dirtyable memory. This can only
 373         * occur in very strange VM situations but we want to make sure
 374         * that this does not occur.
 375         */
 376        return min(x, total);
 377#else
 378        return 0;
 379#endif
 380}
 381
 382/**
 383 * determine_dirtyable_memory - amount of memory that may be used
 384 *
 385 * Returns the numebr of pages that can currently be freed and used
 386 * by the kernel for direct mappings.
 387 */
 388unsigned long determine_dirtyable_memory(void)
 389{
 390        unsigned long x;
 391
 392        x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
 393
 394        if (!vm_highmem_is_dirtyable)
 395                x -= highmem_dirtyable_memory(x);
 396
 397        return x + 1;   /* Ensure that we never return 0 */
 398}
 399
 400/*
 401 * global_dirty_limits - background-writeback and dirty-throttling thresholds
 402 *
 403 * Calculate the dirty thresholds based on sysctl parameters
 404 * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
 405 * - vm.dirty_ratio             or  vm.dirty_bytes
 406 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
 407 * real-time tasks.
 408 */
 409void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
 410{
 411        unsigned long background;
 412        unsigned long dirty;
 413        unsigned long uninitialized_var(available_memory);
 414        struct task_struct *tsk;
 415
 416        if (!vm_dirty_bytes || !dirty_background_bytes)
 417                available_memory = determine_dirtyable_memory();
 418
 419        if (vm_dirty_bytes)
 420                dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
 421        else
 422                dirty = (vm_dirty_ratio * available_memory) / 100;
 423
 424        if (dirty_background_bytes)
 425                background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
 426        else
 427                background = (dirty_background_ratio * available_memory) / 100;
 428
 429        if (background >= dirty)
 430                background = dirty / 2;
 431        tsk = current;
 432        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
 433                background += background / 4;
 434                dirty += dirty / 4;
 435        }
 436        *pbackground = background;
 437        *pdirty = dirty;
 438}
 439
 440/*
 441 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
 442 *
 443 * Allocate high/low dirty limits to fast/slow devices, in order to prevent
 444 * - starving fast devices
 445 * - piling up dirty pages (that will take long time to sync) on slow devices
 446 *
 447 * The bdi's share of dirty limit will be adapting to its throughput and
 448 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
 449 */
 450unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
 451{
 452        u64 bdi_dirty;
 453        long numerator, denominator;
 454
 455        /*
 456         * Calculate this BDI's share of the dirty ratio.
 457         */
 458        bdi_writeout_fraction(bdi, &numerator, &denominator);
 459
 460        bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
 461        bdi_dirty *= numerator;
 462        do_div(bdi_dirty, denominator);
 463
 464        bdi_dirty += (dirty * bdi->min_ratio) / 100;
 465        if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
 466                bdi_dirty = dirty * bdi->max_ratio / 100;
 467
 468        return bdi_dirty;
 469}
 470
 471/*
 472 * balance_dirty_pages() must be called by processes which are generating dirty
 473 * data.  It looks at the number of dirty pages in the machine and will force
 474 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
 475 * If we're over `background_thresh' then the writeback threads are woken to
 476 * perform some writeout.
 477 */
 478static void balance_dirty_pages(struct address_space *mapping,
 479                                unsigned long write_chunk)
 480{
 481        long nr_reclaimable, bdi_nr_reclaimable;
 482        long nr_writeback, bdi_nr_writeback;
 483        unsigned long background_thresh;
 484        unsigned long dirty_thresh;
 485        unsigned long bdi_thresh;
 486        unsigned long pages_written = 0;
 487        unsigned long pause = 1;
 488        bool dirty_exceeded = false;
 489        struct backing_dev_info *bdi = mapping->backing_dev_info;
 490
 491        for (;;) {
 492                struct writeback_control wbc = {
 493                        .sync_mode      = WB_SYNC_NONE,
 494                        .older_than_this = NULL,
 495                        .nr_to_write    = write_chunk,
 496                        .range_cyclic   = 1,
 497                };
 498
 499                nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
 500                                        global_page_state(NR_UNSTABLE_NFS);
 501                nr_writeback = global_page_state(NR_WRITEBACK);
 502
 503                global_dirty_limits(&background_thresh, &dirty_thresh);
 504
 505                /*
 506                 * Throttle it only when the background writeback cannot
 507                 * catch-up. This avoids (excessively) small writeouts
 508                 * when the bdi limits are ramping up.
 509                 */
 510                if (nr_reclaimable + nr_writeback <=
 511                                (background_thresh + dirty_thresh) / 2)
 512                        break;
 513
 514                bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
 515                bdi_thresh = task_dirty_limit(current, bdi_thresh);
 516
 517                /*
 518                 * In order to avoid the stacked BDI deadlock we need
 519                 * to ensure we accurately count the 'dirty' pages when
 520                 * the threshold is low.
 521                 *
 522                 * Otherwise it would be possible to get thresh+n pages
 523                 * reported dirty, even though there are thresh-m pages
 524                 * actually dirty; with m+n sitting in the percpu
 525                 * deltas.
 526                 */
 527                if (bdi_thresh < 2*bdi_stat_error(bdi)) {
 528                        bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
 529                        bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
 530                } else {
 531                        bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
 532                        bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
 533                }
 534
 535                /*
 536                 * The bdi thresh is somehow "soft" limit derived from the
 537                 * global "hard" limit. The former helps to prevent heavy IO
 538                 * bdi or process from holding back light ones; The latter is
 539                 * the last resort safeguard.
 540                 */
 541                dirty_exceeded =
 542                        (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh)
 543                        || (nr_reclaimable + nr_writeback > dirty_thresh);
 544
 545                if (!dirty_exceeded)
 546                        break;
 547
 548                if (!bdi->dirty_exceeded)
 549                        bdi->dirty_exceeded = 1;
 550
 551                /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
 552                 * Unstable writes are a feature of certain networked
 553                 * filesystems (i.e. NFS) in which data may have been
 554                 * written to the server's write cache, but has not yet
 555                 * been flushed to permanent storage.
 556                 * Only move pages to writeback if this bdi is over its
 557                 * threshold otherwise wait until the disk writes catch
 558                 * up.
 559                 */
 560                trace_wbc_balance_dirty_start(&wbc, bdi);
 561                if (bdi_nr_reclaimable > bdi_thresh) {
 562                        writeback_inodes_wb(&bdi->wb, &wbc);
 563                        pages_written += write_chunk - wbc.nr_to_write;
 564                        trace_wbc_balance_dirty_written(&wbc, bdi);
 565                        if (pages_written >= write_chunk)
 566                                break;          /* We've done our duty */
 567                }
 568                trace_wbc_balance_dirty_wait(&wbc, bdi);
 569                __set_current_state(TASK_UNINTERRUPTIBLE);
 570                io_schedule_timeout(pause);
 571
 572                /*
 573                 * Increase the delay for each loop, up to our previous
 574                 * default of taking a 100ms nap.
 575                 */
 576                pause <<= 1;
 577                if (pause > HZ / 10)
 578                        pause = HZ / 10;
 579        }
 580
 581        if (!dirty_exceeded && bdi->dirty_exceeded)
 582                bdi->dirty_exceeded = 0;
 583
 584        if (writeback_in_progress(bdi))
 585                return;
 586
 587        /*
 588         * In laptop mode, we wait until hitting the higher threshold before
 589         * starting background writeout, and then write out all the way down
 590         * to the lower threshold.  So slow writers cause minimal disk activity.
 591         *
 592         * In normal mode, we start background writeout at the lower
 593         * background_thresh, to keep the amount of dirty memory low.
 594         */
 595        if ((laptop_mode && pages_written) ||
 596            (!laptop_mode && (nr_reclaimable > background_thresh)))
 597                bdi_start_background_writeback(bdi);
 598}
 599
 600void set_page_dirty_balance(struct page *page, int page_mkwrite)
 601{
 602        if (set_page_dirty(page) || page_mkwrite) {
 603                struct address_space *mapping = page_mapping(page);
 604
 605                if (mapping)
 606                        balance_dirty_pages_ratelimited(mapping);
 607        }
 608}
 609
 610static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
 611
 612/**
 613 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
 614 * @mapping: address_space which was dirtied
 615 * @nr_pages_dirtied: number of pages which the caller has just dirtied
 616 *
 617 * Processes which are dirtying memory should call in here once for each page
 618 * which was newly dirtied.  The function will periodically check the system's
 619 * dirty state and will initiate writeback if needed.
 620 *
 621 * On really big machines, get_writeback_state is expensive, so try to avoid
 622 * calling it too often (ratelimiting).  But once we're over the dirty memory
 623 * limit we decrease the ratelimiting by a lot, to prevent individual processes
 624 * from overshooting the limit by (ratelimit_pages) each.
 625 */
 626void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
 627                                        unsigned long nr_pages_dirtied)
 628{
 629        unsigned long ratelimit;
 630        unsigned long *p;
 631
 632        ratelimit = ratelimit_pages;
 633        if (mapping->backing_dev_info->dirty_exceeded)
 634                ratelimit = 8;
 635
 636        /*
 637         * Check the rate limiting. Also, we do not want to throttle real-time
 638         * tasks in balance_dirty_pages(). Period.
 639         */
 640        preempt_disable();
 641        p =  &__get_cpu_var(bdp_ratelimits);
 642        *p += nr_pages_dirtied;
 643        if (unlikely(*p >= ratelimit)) {
 644                ratelimit = sync_writeback_pages(*p);
 645                *p = 0;
 646                preempt_enable();
 647                balance_dirty_pages(mapping, ratelimit);
 648                return;
 649        }
 650        preempt_enable();
 651}
 652EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
 653
 654void throttle_vm_writeout(gfp_t gfp_mask)
 655{
 656        unsigned long background_thresh;
 657        unsigned long dirty_thresh;
 658
 659        for ( ; ; ) {
 660                global_dirty_limits(&background_thresh, &dirty_thresh);
 661
 662                /*
 663                 * Boost the allowable dirty threshold a bit for page
 664                 * allocators so they don't get DoS'ed by heavy writers
 665                 */
 666                dirty_thresh += dirty_thresh / 10;      /* wheeee... */
 667
 668                if (global_page_state(NR_UNSTABLE_NFS) +
 669                        global_page_state(NR_WRITEBACK) <= dirty_thresh)
 670                                break;
 671                congestion_wait(BLK_RW_ASYNC, HZ/10);
 672
 673                /*
 674                 * The caller might hold locks which can prevent IO completion
 675                 * or progress in the filesystem.  So we cannot just sit here
 676                 * waiting for IO to complete.
 677                 */
 678                if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
 679                        break;
 680        }
 681}
 682
 683/*
 684 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
 685 */
 686int dirty_writeback_centisecs_handler(ctl_table *table, int write,
 687        void __user *buffer, size_t *length, loff_t *ppos)
 688{
 689        proc_dointvec(table, write, buffer, length, ppos);
 690        bdi_arm_supers_timer();
 691        return 0;
 692}
 693
 694#ifdef CONFIG_BLOCK
 695void laptop_mode_timer_fn(unsigned long data)
 696{
 697        struct request_queue *q = (struct request_queue *)data;
 698        int nr_pages = global_page_state(NR_FILE_DIRTY) +
 699                global_page_state(NR_UNSTABLE_NFS);
 700
 701        /*
 702         * We want to write everything out, not just down to the dirty
 703         * threshold
 704         */
 705        if (bdi_has_dirty_io(&q->backing_dev_info))
 706                bdi_start_writeback(&q->backing_dev_info, nr_pages);
 707}
 708
 709/*
 710 * We've spun up the disk and we're in laptop mode: schedule writeback
 711 * of all dirty data a few seconds from now.  If the flush is already scheduled
 712 * then push it back - the user is still using the disk.
 713 */
 714void laptop_io_completion(struct backing_dev_info *info)
 715{
 716        mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
 717}
 718
 719/*
 720 * We're in laptop mode and we've just synced. The sync's writes will have
 721 * caused another writeback to be scheduled by laptop_io_completion.
 722 * Nothing needs to be written back anymore, so we unschedule the writeback.
 723 */
 724void laptop_sync_completion(void)
 725{
 726        struct backing_dev_info *bdi;
 727
 728        rcu_read_lock();
 729
 730        list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
 731                del_timer(&bdi->laptop_mode_wb_timer);
 732
 733        rcu_read_unlock();
 734}
 735#endif
 736
 737/*
 738 * If ratelimit_pages is too high then we can get into dirty-data overload
 739 * if a large number of processes all perform writes at the same time.
 740 * If it is too low then SMP machines will call the (expensive)
 741 * get_writeback_state too often.
 742 *
 743 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
 744 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
 745 * thresholds before writeback cuts in.
 746 *
 747 * But the limit should not be set too high.  Because it also controls the
 748 * amount of memory which the balance_dirty_pages() caller has to write back.
 749 * If this is too large then the caller will block on the IO queue all the
 750 * time.  So limit it to four megabytes - the balance_dirty_pages() caller
 751 * will write six megabyte chunks, max.
 752 */
 753
 754void writeback_set_ratelimit(void)
 755{
 756        ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
 757        if (ratelimit_pages < 16)
 758                ratelimit_pages = 16;
 759        if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
 760                ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
 761}
 762
 763static int __cpuinit
 764ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
 765{
 766        writeback_set_ratelimit();
 767        return NOTIFY_DONE;
 768}
 769
 770static struct notifier_block __cpuinitdata ratelimit_nb = {
 771        .notifier_call  = ratelimit_handler,
 772        .next           = NULL,
 773};
 774
 775/*
 776 * Called early on to tune the page writeback dirty limits.
 777 *
 778 * We used to scale dirty pages according to how total memory
 779 * related to pages that could be allocated for buffers (by
 780 * comparing nr_free_buffer_pages() to vm_total_pages.
 781 *
 782 * However, that was when we used "dirty_ratio" to scale with
 783 * all memory, and we don't do that any more. "dirty_ratio"
 784 * is now applied to total non-HIGHPAGE memory (by subtracting
 785 * totalhigh_pages from vm_total_pages), and as such we can't
 786 * get into the old insane situation any more where we had
 787 * large amounts of dirty pages compared to a small amount of
 788 * non-HIGHMEM memory.
 789 *
 790 * But we might still want to scale the dirty_ratio by how
 791 * much memory the box has..
 792 */
 793void __init page_writeback_init(void)
 794{
 795        int shift;
 796
 797        writeback_set_ratelimit();
 798        register_cpu_notifier(&ratelimit_nb);
 799
 800        shift = calc_period_shift();
 801        prop_descriptor_init(&vm_completions, shift);
 802        prop_descriptor_init(&vm_dirties, shift);
 803}
 804
 805/**
 806 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
 807 * @mapping: address space structure to write
 808 * @start: starting page index
 809 * @end: ending page index (inclusive)
 810 *
 811 * This function scans the page range from @start to @end (inclusive) and tags
 812 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
 813 * that write_cache_pages (or whoever calls this function) will then use
 814 * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
 815 * used to avoid livelocking of writeback by a process steadily creating new
 816 * dirty pages in the file (thus it is important for this function to be quick
 817 * so that it can tag pages faster than a dirtying process can create them).
 818 */
 819/*
 820 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
 821 */
 822void tag_pages_for_writeback(struct address_space *mapping,
 823                             pgoff_t start, pgoff_t end)
 824{
 825#define WRITEBACK_TAG_BATCH 4096
 826        unsigned long tagged;
 827
 828        do {
 829                spin_lock_irq(&mapping->tree_lock);
 830                tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
 831                                &start, end, WRITEBACK_TAG_BATCH,
 832                                PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
 833                spin_unlock_irq(&mapping->tree_lock);
 834                WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
 835                cond_resched();
 836                /* We check 'start' to handle wrapping when end == ~0UL */
 837        } while (tagged >= WRITEBACK_TAG_BATCH && start);
 838}
 839EXPORT_SYMBOL(tag_pages_for_writeback);
 840
 841/**
 842 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
 843 * @mapping: address space structure to write
 844 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 845 * @writepage: function called for each page
 846 * @data: data passed to writepage function
 847 *
 848 * If a page is already under I/O, write_cache_pages() skips it, even
 849 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 850 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 851 * and msync() need to guarantee that all the data which was dirty at the time
 852 * the call was made get new I/O started against them.  If wbc->sync_mode is
 853 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 854 * existing IO to complete.
 855 *
 856 * To avoid livelocks (when other process dirties new pages), we first tag
 857 * pages which should be written back with TOWRITE tag and only then start
 858 * writing them. For data-integrity sync we have to be careful so that we do
 859 * not miss some pages (e.g., because some other process has cleared TOWRITE
 860 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
 861 * by the process clearing the DIRTY tag (and submitting the page for IO).
 862 */
 863int write_cache_pages(struct address_space *mapping,
 864                      struct writeback_control *wbc, writepage_t writepage,
 865                      void *data)
 866{
 867        int ret = 0;
 868        int done = 0;
 869        struct pagevec pvec;
 870        int nr_pages;
 871        pgoff_t uninitialized_var(writeback_index);
 872        pgoff_t index;
 873        pgoff_t end;            /* Inclusive */
 874        pgoff_t done_index;
 875        int cycled;
 876        int range_whole = 0;
 877        int tag;
 878
 879        pagevec_init(&pvec, 0);
 880        if (wbc->range_cyclic) {
 881                writeback_index = mapping->writeback_index; /* prev offset */
 882                index = writeback_index;
 883                if (index == 0)
 884                        cycled = 1;
 885                else
 886                        cycled = 0;
 887                end = -1;
 888        } else {
 889                index = wbc->range_start >> PAGE_CACHE_SHIFT;
 890                end = wbc->range_end >> PAGE_CACHE_SHIFT;
 891                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
 892                        range_whole = 1;
 893                cycled = 1; /* ignore range_cyclic tests */
 894        }
 895        if (wbc->sync_mode == WB_SYNC_ALL)
 896                tag = PAGECACHE_TAG_TOWRITE;
 897        else
 898                tag = PAGECACHE_TAG_DIRTY;
 899retry:
 900        if (wbc->sync_mode == WB_SYNC_ALL)
 901                tag_pages_for_writeback(mapping, index, end);
 902        done_index = index;
 903        while (!done && (index <= end)) {
 904                int i;
 905
 906                nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
 907                              min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
 908                if (nr_pages == 0)
 909                        break;
 910
 911                for (i = 0; i < nr_pages; i++) {
 912                        struct page *page = pvec.pages[i];
 913
 914                        /*
 915                         * At this point, the page may be truncated or
 916                         * invalidated (changing page->mapping to NULL), or
 917                         * even swizzled back from swapper_space to tmpfs file
 918                         * mapping. However, page->index will not change
 919                         * because we have a reference on the page.
 920                         */
 921                        if (page->index > end) {
 922                                /*
 923                                 * can't be range_cyclic (1st pass) because
 924                                 * end == -1 in that case.
 925                                 */
 926                                done = 1;
 927                                break;
 928                        }
 929
 930                        done_index = page->index;
 931
 932                        lock_page(page);
 933
 934                        /*
 935                         * Page truncated or invalidated. We can freely skip it
 936                         * then, even for data integrity operations: the page
 937                         * has disappeared concurrently, so there could be no
 938                         * real expectation of this data interity operation
 939                         * even if there is now a new, dirty page at the same
 940                         * pagecache address.
 941                         */
 942                        if (unlikely(page->mapping != mapping)) {
 943continue_unlock:
 944                                unlock_page(page);
 945                                continue;
 946                        }
 947
 948                        if (!PageDirty(page)) {
 949                                /* someone wrote it for us */
 950                                goto continue_unlock;
 951                        }
 952
 953                        if (PageWriteback(page)) {
 954                                if (wbc->sync_mode != WB_SYNC_NONE)
 955                                        wait_on_page_writeback(page);
 956                                else
 957                                        goto continue_unlock;
 958                        }
 959
 960                        BUG_ON(PageWriteback(page));
 961                        if (!clear_page_dirty_for_io(page))
 962                                goto continue_unlock;
 963
 964                        trace_wbc_writepage(wbc, mapping->backing_dev_info);
 965                        ret = (*writepage)(page, wbc, data);
 966                        if (unlikely(ret)) {
 967                                if (ret == AOP_WRITEPAGE_ACTIVATE) {
 968                                        unlock_page(page);
 969                                        ret = 0;
 970                                } else {
 971                                        /*
 972                                         * done_index is set past this page,
 973                                         * so media errors will not choke
 974                                         * background writeout for the entire
 975                                         * file. This has consequences for
 976                                         * range_cyclic semantics (ie. it may
 977                                         * not be suitable for data integrity
 978                                         * writeout).
 979                                         */
 980                                        done_index = page->index + 1;
 981                                        done = 1;
 982                                        break;
 983                                }
 984                        }
 985
 986                        /*
 987                         * We stop writing back only if we are not doing
 988                         * integrity sync. In case of integrity sync we have to
 989                         * keep going until we have written all the pages
 990                         * we tagged for writeback prior to entering this loop.
 991                         */
 992                        if (--wbc->nr_to_write <= 0 &&
 993                            wbc->sync_mode == WB_SYNC_NONE) {
 994                                done = 1;
 995                                break;
 996                        }
 997                }
 998                pagevec_release(&pvec);
 999                cond_resched();
1000        }
1001        if (!cycled && !done) {
1002                /*
1003                 * range_cyclic:
1004                 * We hit the last page and there is more work to be done: wrap
1005                 * back to the start of the file
1006                 */
1007                cycled = 1;
1008                index = 0;
1009                end = writeback_index - 1;
1010                goto retry;
1011        }
1012        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1013                mapping->writeback_index = done_index;
1014
1015        return ret;
1016}
1017EXPORT_SYMBOL(write_cache_pages);
1018
1019/*
1020 * Function used by generic_writepages to call the real writepage
1021 * function and set the mapping flags on error
1022 */
1023static int __writepage(struct page *page, struct writeback_control *wbc,
1024                       void *data)
1025{
1026        struct address_space *mapping = data;
1027        int ret = mapping->a_ops->writepage(page, wbc);
1028        mapping_set_error(mapping, ret);
1029        return ret;
1030}
1031
1032/**
1033 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1034 * @mapping: address space structure to write
1035 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1036 *
1037 * This is a library function, which implements the writepages()
1038 * address_space_operation.
1039 */
1040int generic_writepages(struct address_space *mapping,
1041                       struct writeback_control *wbc)
1042{
1043        struct blk_plug plug;
1044        int ret;
1045
1046        /* deal with chardevs and other special file */
1047        if (!mapping->a_ops->writepage)
1048                return 0;
1049
1050        blk_start_plug(&plug);
1051        ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1052        blk_finish_plug(&plug);
1053        return ret;
1054}
1055
1056EXPORT_SYMBOL(generic_writepages);
1057
1058int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1059{
1060        int ret;
1061
1062        if (wbc->nr_to_write <= 0)
1063                return 0;
1064        if (mapping->a_ops->writepages)
1065                ret = mapping->a_ops->writepages(mapping, wbc);
1066        else
1067                ret = generic_writepages(mapping, wbc);
1068        return ret;
1069}
1070
1071/**
1072 * write_one_page - write out a single page and optionally wait on I/O
1073 * @page: the page to write
1074 * @wait: if true, wait on writeout
1075 *
1076 * The page must be locked by the caller and will be unlocked upon return.
1077 *
1078 * write_one_page() returns a negative error code if I/O failed.
1079 */
1080int write_one_page(struct page *page, int wait)
1081{
1082        struct address_space *mapping = page->mapping;
1083        int ret = 0;
1084        struct writeback_control wbc = {
1085                .sync_mode = WB_SYNC_ALL,
1086                .nr_to_write = 1,
1087        };
1088
1089        BUG_ON(!PageLocked(page));
1090
1091        if (wait)
1092                wait_on_page_writeback(page);
1093
1094        if (clear_page_dirty_for_io(page)) {
1095                page_cache_get(page);
1096                ret = mapping->a_ops->writepage(page, &wbc);
1097                if (ret == 0 && wait) {
1098                        wait_on_page_writeback(page);
1099                        if (PageError(page))
1100                                ret = -EIO;
1101                }
1102                page_cache_release(page);
1103        } else {
1104                unlock_page(page);
1105        }
1106        return ret;
1107}
1108EXPORT_SYMBOL(write_one_page);
1109
1110/*
1111 * For address_spaces which do not use buffers nor write back.
1112 */
1113int __set_page_dirty_no_writeback(struct page *page)
1114{
1115        if (!PageDirty(page))
1116                return !TestSetPageDirty(page);
1117        return 0;
1118}
1119
1120/*
1121 * Helper function for set_page_dirty family.
1122 * NOTE: This relies on being atomic wrt interrupts.
1123 */
1124void account_page_dirtied(struct page *page, struct address_space *mapping)
1125{
1126        if (mapping_cap_account_dirty(mapping)) {
1127                __inc_zone_page_state(page, NR_FILE_DIRTY);
1128                __inc_zone_page_state(page, NR_DIRTIED);
1129                __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1130                task_dirty_inc(current);
1131                task_io_account_write(PAGE_CACHE_SIZE);
1132        }
1133}
1134EXPORT_SYMBOL(account_page_dirtied);
1135
1136/*
1137 * Helper function for set_page_writeback family.
1138 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1139 * wrt interrupts.
1140 */
1141void account_page_writeback(struct page *page)
1142{
1143        inc_zone_page_state(page, NR_WRITEBACK);
1144        inc_zone_page_state(page, NR_WRITTEN);
1145}
1146EXPORT_SYMBOL(account_page_writeback);
1147
1148/*
1149 * For address_spaces which do not use buffers.  Just tag the page as dirty in
1150 * its radix tree.
1151 *
1152 * This is also used when a single buffer is being dirtied: we want to set the
1153 * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1154 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1155 *
1156 * Most callers have locked the page, which pins the address_space in memory.
1157 * But zap_pte_range() does not lock the page, however in that case the
1158 * mapping is pinned by the vma's ->vm_file reference.
1159 *
1160 * We take care to handle the case where the page was truncated from the
1161 * mapping by re-checking page_mapping() inside tree_lock.
1162 */
1163int __set_page_dirty_nobuffers(struct page *page)
1164{
1165        if (!TestSetPageDirty(page)) {
1166                struct address_space *mapping = page_mapping(page);
1167                struct address_space *mapping2;
1168
1169                if (!mapping)
1170                        return 1;
1171
1172                spin_lock_irq(&mapping->tree_lock);
1173                mapping2 = page_mapping(page);
1174                if (mapping2) { /* Race with truncate? */
1175                        BUG_ON(mapping2 != mapping);
1176                        WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1177                        account_page_dirtied(page, mapping);
1178                        radix_tree_tag_set(&mapping->page_tree,
1179                                page_index(page), PAGECACHE_TAG_DIRTY);
1180                }
1181                spin_unlock_irq(&mapping->tree_lock);
1182                if (mapping->host) {
1183                        /* !PageAnon && !swapper_space */
1184                        __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1185                }
1186                return 1;
1187        }
1188        return 0;
1189}
1190EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1191
1192/*
1193 * When a writepage implementation decides that it doesn't want to write this
1194 * page for some reason, it should redirty the locked page via
1195 * redirty_page_for_writepage() and it should then unlock the page and return 0
1196 */
1197int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1198{
1199        wbc->pages_skipped++;
1200        return __set_page_dirty_nobuffers(page);
1201}
1202EXPORT_SYMBOL(redirty_page_for_writepage);
1203
1204/*
1205 * Dirty a page.
1206 *
1207 * For pages with a mapping this should be done under the page lock
1208 * for the benefit of asynchronous memory errors who prefer a consistent
1209 * dirty state. This rule can be broken in some special cases,
1210 * but should be better not to.
1211 *
1212 * If the mapping doesn't provide a set_page_dirty a_op, then
1213 * just fall through and assume that it wants buffer_heads.
1214 */
1215int set_page_dirty(struct page *page)
1216{
1217        struct address_space *mapping = page_mapping(page);
1218
1219        if (likely(mapping)) {
1220                int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1221                /*
1222                 * readahead/lru_deactivate_page could remain
1223                 * PG_readahead/PG_reclaim due to race with end_page_writeback
1224                 * About readahead, if the page is written, the flags would be
1225                 * reset. So no problem.
1226                 * About lru_deactivate_page, if the page is redirty, the flag
1227                 * will be reset. So no problem. but if the page is used by readahead
1228                 * it will confuse readahead and make it restart the size rampup
1229                 * process. But it's a trivial problem.
1230                 */
1231                ClearPageReclaim(page);
1232#ifdef CONFIG_BLOCK
1233                if (!spd)
1234                        spd = __set_page_dirty_buffers;
1235#endif
1236                return (*spd)(page);
1237        }
1238        if (!PageDirty(page)) {
1239                if (!TestSetPageDirty(page))
1240                        return 1;
1241        }
1242        return 0;
1243}
1244EXPORT_SYMBOL(set_page_dirty);
1245
1246/*
1247 * set_page_dirty() is racy if the caller has no reference against
1248 * page->mapping->host, and if the page is unlocked.  This is because another
1249 * CPU could truncate the page off the mapping and then free the mapping.
1250 *
1251 * Usually, the page _is_ locked, or the caller is a user-space process which
1252 * holds a reference on the inode by having an open file.
1253 *
1254 * In other cases, the page should be locked before running set_page_dirty().
1255 */
1256int set_page_dirty_lock(struct page *page)
1257{
1258        int ret;
1259
1260        lock_page(page);
1261        ret = set_page_dirty(page);
1262        unlock_page(page);
1263        return ret;
1264}
1265EXPORT_SYMBOL(set_page_dirty_lock);
1266
1267/*
1268 * Clear a page's dirty flag, while caring for dirty memory accounting.
1269 * Returns true if the page was previously dirty.
1270 *
1271 * This is for preparing to put the page under writeout.  We leave the page
1272 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1273 * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1274 * implementation will run either set_page_writeback() or set_page_dirty(),
1275 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1276 * back into sync.
1277 *
1278 * This incoherency between the page's dirty flag and radix-tree tag is
1279 * unfortunate, but it only exists while the page is locked.
1280 */
1281int clear_page_dirty_for_io(struct page *page)
1282{
1283        struct address_space *mapping = page_mapping(page);
1284
1285        BUG_ON(!PageLocked(page));
1286
1287        if (mapping && mapping_cap_account_dirty(mapping)) {
1288                /*
1289                 * Yes, Virginia, this is indeed insane.
1290                 *
1291                 * We use this sequence to make sure that
1292                 *  (a) we account for dirty stats properly
1293                 *  (b) we tell the low-level filesystem to
1294                 *      mark the whole page dirty if it was
1295                 *      dirty in a pagetable. Only to then
1296                 *  (c) clean the page again and return 1 to
1297                 *      cause the writeback.
1298                 *
1299                 * This way we avoid all nasty races with the
1300                 * dirty bit in multiple places and clearing
1301                 * them concurrently from different threads.
1302                 *
1303                 * Note! Normally the "set_page_dirty(page)"
1304                 * has no effect on the actual dirty bit - since
1305                 * that will already usually be set. But we
1306                 * need the side effects, and it can help us
1307                 * avoid races.
1308                 *
1309                 * We basically use the page "master dirty bit"
1310                 * as a serialization point for all the different
1311                 * threads doing their things.
1312                 */
1313                if (page_mkclean(page))
1314                        set_page_dirty(page);
1315                /*
1316                 * We carefully synchronise fault handlers against
1317                 * installing a dirty pte and marking the page dirty
1318                 * at this point. We do this by having them hold the
1319                 * page lock at some point after installing their
1320                 * pte, but before marking the page dirty.
1321                 * Pages are always locked coming in here, so we get
1322                 * the desired exclusion. See mm/memory.c:do_wp_page()
1323                 * for more comments.
1324                 */
1325                if (TestClearPageDirty(page)) {
1326                        dec_zone_page_state(page, NR_FILE_DIRTY);
1327                        dec_bdi_stat(mapping->backing_dev_info,
1328                                        BDI_RECLAIMABLE);
1329                        return 1;
1330                }
1331                return 0;
1332        }
1333        return TestClearPageDirty(page);
1334}
1335EXPORT_SYMBOL(clear_page_dirty_for_io);
1336
1337int test_clear_page_writeback(struct page *page)
1338{
1339        struct address_space *mapping = page_mapping(page);
1340        int ret;
1341
1342        if (mapping) {
1343                struct backing_dev_info *bdi = mapping->backing_dev_info;
1344                unsigned long flags;
1345
1346                spin_lock_irqsave(&mapping->tree_lock, flags);
1347                ret = TestClearPageWriteback(page);
1348                if (ret) {
1349                        radix_tree_tag_clear(&mapping->page_tree,
1350                                                page_index(page),
1351                                                PAGECACHE_TAG_WRITEBACK);
1352                        if (bdi_cap_account_writeback(bdi)) {
1353                                __dec_bdi_stat(bdi, BDI_WRITEBACK);
1354                                __bdi_writeout_inc(bdi);
1355                        }
1356                }
1357                spin_unlock_irqrestore(&mapping->tree_lock, flags);
1358        } else {
1359                ret = TestClearPageWriteback(page);
1360        }
1361        if (ret)
1362                dec_zone_page_state(page, NR_WRITEBACK);
1363        return ret;
1364}
1365
1366int test_set_page_writeback(struct page *page)
1367{
1368        struct address_space *mapping = page_mapping(page);
1369        int ret;
1370
1371        if (mapping) {
1372                struct backing_dev_info *bdi = mapping->backing_dev_info;
1373                unsigned long flags;
1374
1375                spin_lock_irqsave(&mapping->tree_lock, flags);
1376                ret = TestSetPageWriteback(page);
1377                if (!ret) {
1378                        radix_tree_tag_set(&mapping->page_tree,
1379                                                page_index(page),
1380                                                PAGECACHE_TAG_WRITEBACK);
1381                        if (bdi_cap_account_writeback(bdi))
1382                                __inc_bdi_stat(bdi, BDI_WRITEBACK);
1383                }
1384                if (!PageDirty(page))
1385                        radix_tree_tag_clear(&mapping->page_tree,
1386                                                page_index(page),
1387                                                PAGECACHE_TAG_DIRTY);
1388                radix_tree_tag_clear(&mapping->page_tree,
1389                                     page_index(page),
1390                                     PAGECACHE_TAG_TOWRITE);
1391                spin_unlock_irqrestore(&mapping->tree_lock, flags);
1392        } else {
1393                ret = TestSetPageWriteback(page);
1394        }
1395        if (!ret)
1396                account_page_writeback(page);
1397        return ret;
1398
1399}
1400EXPORT_SYMBOL(test_set_page_writeback);
1401
1402/*
1403 * Return true if any of the pages in the mapping are marked with the
1404 * passed tag.
1405 */
1406int mapping_tagged(struct address_space *mapping, int tag)
1407{
1408        int ret;
1409        rcu_read_lock();
1410        ret = radix_tree_tagged(&mapping->page_tree, tag);
1411        rcu_read_unlock();
1412        return ret;
1413}
1414EXPORT_SYMBOL(mapping_tagged);
1415