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 * Sleep at most 200ms at a time in balance_dirty_pages().
  41 */
  42#define MAX_PAUSE               max(HZ/5, 1)
  43
  44/*
  45 * Estimate write bandwidth at 200ms intervals.
  46 */
  47#define BANDWIDTH_INTERVAL      max(HZ/5, 1)
  48
  49/*
  50 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
  51 * will look to see if it needs to force writeback or throttling.
  52 */
  53static long ratelimit_pages = 32;
  54
  55/*
  56 * When balance_dirty_pages decides that the caller needs to perform some
  57 * non-background writeback, this is how many pages it will attempt to write.
  58 * It should be somewhat larger than dirtied pages to ensure that reasonably
  59 * large amounts of I/O are submitted.
  60 */
  61static inline long sync_writeback_pages(unsigned long dirtied)
  62{
  63        if (dirtied < ratelimit_pages)
  64                dirtied = ratelimit_pages;
  65
  66        return dirtied + dirtied / 2;
  67}
  68
  69/* The following parameters are exported via /proc/sys/vm */
  70
  71/*
  72 * Start background writeback (via writeback threads) at this percentage
  73 */
  74int dirty_background_ratio = 10;
  75
  76/*
  77 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
  78 * dirty_background_ratio * the amount of dirtyable memory
  79 */
  80unsigned long dirty_background_bytes;
  81
  82/*
  83 * free highmem will not be subtracted from the total free memory
  84 * for calculating free ratios if vm_highmem_is_dirtyable is true
  85 */
  86int vm_highmem_is_dirtyable;
  87
  88/*
  89 * The generator of dirty data starts writeback at this percentage
  90 */
  91int vm_dirty_ratio = 20;
  92
  93/*
  94 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
  95 * vm_dirty_ratio * the amount of dirtyable memory
  96 */
  97unsigned long vm_dirty_bytes;
  98
  99/*
 100 * The interval between `kupdate'-style writebacks
 101 */
 102unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
 103
 104/*
 105 * The longest time for which data is allowed to remain dirty
 106 */
 107unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
 108
 109/*
 110 * Flag that makes the machine dump writes/reads and block dirtyings.
 111 */
 112int block_dump;
 113
 114/*
 115 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
 116 * a full sync is triggered after this time elapses without any disk activity.
 117 */
 118int laptop_mode;
 119
 120EXPORT_SYMBOL(laptop_mode);
 121
 122/* End of sysctl-exported parameters */
 123
 124unsigned long global_dirty_limit;
 125
 126/*
 127 * Scale the writeback cache size proportional to the relative writeout speeds.
 128 *
 129 * We do this by keeping a floating proportion between BDIs, based on page
 130 * writeback completions [end_page_writeback()]. Those devices that write out
 131 * pages fastest will get the larger share, while the slower will get a smaller
 132 * share.
 133 *
 134 * We use page writeout completions because we are interested in getting rid of
 135 * dirty pages. Having them written out is the primary goal.
 136 *
 137 * We introduce a concept of time, a period over which we measure these events,
 138 * because demand can/will vary over time. The length of this period itself is
 139 * measured in page writeback completions.
 140 *
 141 */
 142static struct prop_descriptor vm_completions;
 143static struct prop_descriptor vm_dirties;
 144
 145/*
 146 * couple the period to the dirty_ratio:
 147 *
 148 *   period/2 ~ roundup_pow_of_two(dirty limit)
 149 */
 150static int calc_period_shift(void)
 151{
 152        unsigned long dirty_total;
 153
 154        if (vm_dirty_bytes)
 155                dirty_total = vm_dirty_bytes / PAGE_SIZE;
 156        else
 157                dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
 158                                100;
 159        return 2 + ilog2(dirty_total - 1);
 160}
 161
 162/*
 163 * update the period when the dirty threshold changes.
 164 */
 165static void update_completion_period(void)
 166{
 167        int shift = calc_period_shift();
 168        prop_change_shift(&vm_completions, shift);
 169        prop_change_shift(&vm_dirties, shift);
 170}
 171
 172int dirty_background_ratio_handler(struct ctl_table *table, int write,
 173                void __user *buffer, size_t *lenp,
 174                loff_t *ppos)
 175{
 176        int ret;
 177
 178        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 179        if (ret == 0 && write)
 180                dirty_background_bytes = 0;
 181        return ret;
 182}
 183
 184int dirty_background_bytes_handler(struct ctl_table *table, int write,
 185                void __user *buffer, size_t *lenp,
 186                loff_t *ppos)
 187{
 188        int ret;
 189
 190        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 191        if (ret == 0 && write)
 192                dirty_background_ratio = 0;
 193        return ret;
 194}
 195
 196int dirty_ratio_handler(struct ctl_table *table, int write,
 197                void __user *buffer, size_t *lenp,
 198                loff_t *ppos)
 199{
 200        int old_ratio = vm_dirty_ratio;
 201        int ret;
 202
 203        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 204        if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
 205                update_completion_period();
 206                vm_dirty_bytes = 0;
 207        }
 208        return ret;
 209}
 210
 211
 212int dirty_bytes_handler(struct ctl_table *table, int write,
 213                void __user *buffer, size_t *lenp,
 214                loff_t *ppos)
 215{
 216        unsigned long old_bytes = vm_dirty_bytes;
 217        int ret;
 218
 219        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 220        if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
 221                update_completion_period();
 222                vm_dirty_ratio = 0;
 223        }
 224        return ret;
 225}
 226
 227/*
 228 * Increment the BDI's writeout completion count and the global writeout
 229 * completion count. Called from test_clear_page_writeback().
 230 */
 231static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
 232{
 233        __inc_bdi_stat(bdi, BDI_WRITTEN);
 234        __prop_inc_percpu_max(&vm_completions, &bdi->completions,
 235                              bdi->max_prop_frac);
 236}
 237
 238void bdi_writeout_inc(struct backing_dev_info *bdi)
 239{
 240        unsigned long flags;
 241
 242        local_irq_save(flags);
 243        __bdi_writeout_inc(bdi);
 244        local_irq_restore(flags);
 245}
 246EXPORT_SYMBOL_GPL(bdi_writeout_inc);
 247
 248void task_dirty_inc(struct task_struct *tsk)
 249{
 250        prop_inc_single(&vm_dirties, &tsk->dirties);
 251}
 252
 253/*
 254 * Obtain an accurate fraction of the BDI's portion.
 255 */
 256static void bdi_writeout_fraction(struct backing_dev_info *bdi,
 257                long *numerator, long *denominator)
 258{
 259        prop_fraction_percpu(&vm_completions, &bdi->completions,
 260                                numerator, denominator);
 261}
 262
 263static inline void task_dirties_fraction(struct task_struct *tsk,
 264                long *numerator, long *denominator)
 265{
 266        prop_fraction_single(&vm_dirties, &tsk->dirties,
 267                                numerator, denominator);
 268}
 269
 270/*
 271 * task_dirty_limit - scale down dirty throttling threshold for one task
 272 *
 273 * task specific dirty limit:
 274 *
 275 *   dirty -= (dirty/8) * p_{t}
 276 *
 277 * To protect light/slow dirtying tasks from heavier/fast ones, we start
 278 * throttling individual tasks before reaching the bdi dirty limit.
 279 * Relatively low thresholds will be allocated to heavy dirtiers. So when
 280 * dirty pages grow large, heavy dirtiers will be throttled first, which will
 281 * effectively curb the growth of dirty pages. Light dirtiers with high enough
 282 * dirty threshold may never get throttled.
 283 */
 284#define TASK_LIMIT_FRACTION 8
 285static unsigned long task_dirty_limit(struct task_struct *tsk,
 286                                       unsigned long bdi_dirty)
 287{
 288        long numerator, denominator;
 289        unsigned long dirty = bdi_dirty;
 290        u64 inv = dirty / TASK_LIMIT_FRACTION;
 291
 292        task_dirties_fraction(tsk, &numerator, &denominator);
 293        inv *= numerator;
 294        do_div(inv, denominator);
 295
 296        dirty -= inv;
 297
 298        return max(dirty, bdi_dirty/2);
 299}
 300
 301/* Minimum limit for any task */
 302static unsigned long task_min_dirty_limit(unsigned long bdi_dirty)
 303{
 304        return bdi_dirty - bdi_dirty / TASK_LIMIT_FRACTION;
 305}
 306
 307/*
 308 *
 309 */
 310static unsigned int bdi_min_ratio;
 311
 312int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 313{
 314        int ret = 0;
 315
 316        spin_lock_bh(&bdi_lock);
 317        if (min_ratio > bdi->max_ratio) {
 318                ret = -EINVAL;
 319        } else {
 320                min_ratio -= bdi->min_ratio;
 321                if (bdi_min_ratio + min_ratio < 100) {
 322                        bdi_min_ratio += min_ratio;
 323                        bdi->min_ratio += min_ratio;
 324                } else {
 325                        ret = -EINVAL;
 326                }
 327        }
 328        spin_unlock_bh(&bdi_lock);
 329
 330        return ret;
 331}
 332
 333int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 334{
 335        int ret = 0;
 336
 337        if (max_ratio > 100)
 338                return -EINVAL;
 339
 340        spin_lock_bh(&bdi_lock);
 341        if (bdi->min_ratio > max_ratio) {
 342                ret = -EINVAL;
 343        } else {
 344                bdi->max_ratio = max_ratio;
 345                bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
 346        }
 347        spin_unlock_bh(&bdi_lock);
 348
 349        return ret;
 350}
 351EXPORT_SYMBOL(bdi_set_max_ratio);
 352
 353/*
 354 * Work out the current dirty-memory clamping and background writeout
 355 * thresholds.
 356 *
 357 * The main aim here is to lower them aggressively if there is a lot of mapped
 358 * memory around.  To avoid stressing page reclaim with lots of unreclaimable
 359 * pages.  It is better to clamp down on writers than to start swapping, and
 360 * performing lots of scanning.
 361 *
 362 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
 363 *
 364 * We don't permit the clamping level to fall below 5% - that is getting rather
 365 * excessive.
 366 *
 367 * We make sure that the background writeout level is below the adjusted
 368 * clamping level.
 369 */
 370
 371static unsigned long highmem_dirtyable_memory(unsigned long total)
 372{
 373#ifdef CONFIG_HIGHMEM
 374        int node;
 375        unsigned long x = 0;
 376
 377        for_each_node_state(node, N_HIGH_MEMORY) {
 378                struct zone *z =
 379                        &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
 380
 381                x += zone_page_state(z, NR_FREE_PAGES) +
 382                     zone_reclaimable_pages(z);
 383        }
 384        /*
 385         * Make sure that the number of highmem pages is never larger
 386         * than the number of the total dirtyable memory. This can only
 387         * occur in very strange VM situations but we want to make sure
 388         * that this does not occur.
 389         */
 390        return min(x, total);
 391#else
 392        return 0;
 393#endif
 394}
 395
 396/**
 397 * determine_dirtyable_memory - amount of memory that may be used
 398 *
 399 * Returns the numebr of pages that can currently be freed and used
 400 * by the kernel for direct mappings.
 401 */
 402unsigned long determine_dirtyable_memory(void)
 403{
 404        unsigned long x;
 405
 406        x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
 407
 408        if (!vm_highmem_is_dirtyable)
 409                x -= highmem_dirtyable_memory(x);
 410
 411        return x + 1;   /* Ensure that we never return 0 */
 412}
 413
 414static unsigned long hard_dirty_limit(unsigned long thresh)
 415{
 416        return max(thresh, global_dirty_limit);
 417}
 418
 419/*
 420 * global_dirty_limits - background-writeback and dirty-throttling thresholds
 421 *
 422 * Calculate the dirty thresholds based on sysctl parameters
 423 * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
 424 * - vm.dirty_ratio             or  vm.dirty_bytes
 425 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
 426 * real-time tasks.
 427 */
 428void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
 429{
 430        unsigned long background;
 431        unsigned long dirty;
 432        unsigned long uninitialized_var(available_memory);
 433        struct task_struct *tsk;
 434
 435        if (!vm_dirty_bytes || !dirty_background_bytes)
 436                available_memory = determine_dirtyable_memory();
 437
 438        if (vm_dirty_bytes)
 439                dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
 440        else
 441                dirty = (vm_dirty_ratio * available_memory) / 100;
 442
 443        if (dirty_background_bytes)
 444                background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
 445        else
 446                background = (dirty_background_ratio * available_memory) / 100;
 447
 448        if (background >= dirty)
 449                background = dirty / 2;
 450        tsk = current;
 451        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
 452                background += background / 4;
 453                dirty += dirty / 4;
 454        }
 455        *pbackground = background;
 456        *pdirty = dirty;
 457        trace_global_dirty_state(background, dirty);
 458}
 459
 460/**
 461 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
 462 * @bdi: the backing_dev_info to query
 463 * @dirty: global dirty limit in pages
 464 *
 465 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
 466 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
 467 * And the "limit" in the name is not seriously taken as hard limit in
 468 * balance_dirty_pages().
 469 *
 470 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
 471 * - starving fast devices
 472 * - piling up dirty pages (that will take long time to sync) on slow devices
 473 *
 474 * The bdi's share of dirty limit will be adapting to its throughput and
 475 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
 476 */
 477unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
 478{
 479        u64 bdi_dirty;
 480        long numerator, denominator;
 481
 482        /*
 483         * Calculate this BDI's share of the dirty ratio.
 484         */
 485        bdi_writeout_fraction(bdi, &numerator, &denominator);
 486
 487        bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
 488        bdi_dirty *= numerator;
 489        do_div(bdi_dirty, denominator);
 490
 491        bdi_dirty += (dirty * bdi->min_ratio) / 100;
 492        if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
 493                bdi_dirty = dirty * bdi->max_ratio / 100;
 494
 495        return bdi_dirty;
 496}
 497
 498static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
 499                                       unsigned long elapsed,
 500                                       unsigned long written)
 501{
 502        const unsigned long period = roundup_pow_of_two(3 * HZ);
 503        unsigned long avg = bdi->avg_write_bandwidth;
 504        unsigned long old = bdi->write_bandwidth;
 505        u64 bw;
 506
 507        /*
 508         * bw = written * HZ / elapsed
 509         *
 510         *                   bw * elapsed + write_bandwidth * (period - elapsed)
 511         * write_bandwidth = ---------------------------------------------------
 512         *                                          period
 513         */
 514        bw = written - bdi->written_stamp;
 515        bw *= HZ;
 516        if (unlikely(elapsed > period)) {
 517                do_div(bw, elapsed);
 518                avg = bw;
 519                goto out;
 520        }
 521        bw += (u64)bdi->write_bandwidth * (period - elapsed);
 522        bw >>= ilog2(period);
 523
 524        /*
 525         * one more level of smoothing, for filtering out sudden spikes
 526         */
 527        if (avg > old && old >= (unsigned long)bw)
 528                avg -= (avg - old) >> 3;
 529
 530        if (avg < old && old <= (unsigned long)bw)
 531                avg += (old - avg) >> 3;
 532
 533out:
 534        bdi->write_bandwidth = bw;
 535        bdi->avg_write_bandwidth = avg;
 536}
 537
 538/*
 539 * The global dirtyable memory and dirty threshold could be suddenly knocked
 540 * down by a large amount (eg. on the startup of KVM in a swapless system).
 541 * This may throw the system into deep dirty exceeded state and throttle
 542 * heavy/light dirtiers alike. To retain good responsiveness, maintain
 543 * global_dirty_limit for tracking slowly down to the knocked down dirty
 544 * threshold.
 545 */
 546static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
 547{
 548        unsigned long limit = global_dirty_limit;
 549
 550        /*
 551         * Follow up in one step.
 552         */
 553        if (limit < thresh) {
 554                limit = thresh;
 555                goto update;
 556        }
 557
 558        /*
 559         * Follow down slowly. Use the higher one as the target, because thresh
 560         * may drop below dirty. This is exactly the reason to introduce
 561         * global_dirty_limit which is guaranteed to lie above the dirty pages.
 562         */
 563        thresh = max(thresh, dirty);
 564        if (limit > thresh) {
 565                limit -= (limit - thresh) >> 5;
 566                goto update;
 567        }
 568        return;
 569update:
 570        global_dirty_limit = limit;
 571}
 572
 573static void global_update_bandwidth(unsigned long thresh,
 574                                    unsigned long dirty,
 575                                    unsigned long now)
 576{
 577        static DEFINE_SPINLOCK(dirty_lock);
 578        static unsigned long update_time;
 579
 580        /*
 581         * check locklessly first to optimize away locking for the most time
 582         */
 583        if (time_before(now, update_time + BANDWIDTH_INTERVAL))
 584                return;
 585
 586        spin_lock(&dirty_lock);
 587        if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
 588                update_dirty_limit(thresh, dirty);
 589                update_time = now;
 590        }
 591        spin_unlock(&dirty_lock);
 592}
 593
 594void __bdi_update_bandwidth(struct backing_dev_info *bdi,
 595                            unsigned long thresh,
 596                            unsigned long dirty,
 597                            unsigned long bdi_thresh,
 598                            unsigned long bdi_dirty,
 599                            unsigned long start_time)
 600{
 601        unsigned long now = jiffies;
 602        unsigned long elapsed = now - bdi->bw_time_stamp;
 603        unsigned long written;
 604
 605        /*
 606         * rate-limit, only update once every 200ms.
 607         */
 608        if (elapsed < BANDWIDTH_INTERVAL)
 609                return;
 610
 611        written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
 612
 613        /*
 614         * Skip quiet periods when disk bandwidth is under-utilized.
 615         * (at least 1s idle time between two flusher runs)
 616         */
 617        if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
 618                goto snapshot;
 619
 620        if (thresh)
 621                global_update_bandwidth(thresh, dirty, now);
 622
 623        bdi_update_write_bandwidth(bdi, elapsed, written);
 624
 625snapshot:
 626        bdi->written_stamp = written;
 627        bdi->bw_time_stamp = now;
 628}
 629
 630static void bdi_update_bandwidth(struct backing_dev_info *bdi,
 631                                 unsigned long thresh,
 632                                 unsigned long dirty,
 633                                 unsigned long bdi_thresh,
 634                                 unsigned long bdi_dirty,
 635                                 unsigned long start_time)
 636{
 637        if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
 638                return;
 639        spin_lock(&bdi->wb.list_lock);
 640        __bdi_update_bandwidth(bdi, thresh, dirty, bdi_thresh, bdi_dirty,
 641                               start_time);
 642        spin_unlock(&bdi->wb.list_lock);
 643}
 644
 645/*
 646 * balance_dirty_pages() must be called by processes which are generating dirty
 647 * data.  It looks at the number of dirty pages in the machine and will force
 648 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
 649 * If we're over `background_thresh' then the writeback threads are woken to
 650 * perform some writeout.
 651 */
 652static void balance_dirty_pages(struct address_space *mapping,
 653                                unsigned long write_chunk)
 654{
 655        unsigned long nr_reclaimable, bdi_nr_reclaimable;
 656        unsigned long nr_dirty;  /* = file_dirty + writeback + unstable_nfs */
 657        unsigned long bdi_dirty;
 658        unsigned long background_thresh;
 659        unsigned long dirty_thresh;
 660        unsigned long bdi_thresh;
 661        unsigned long task_bdi_thresh;
 662        unsigned long min_task_bdi_thresh;
 663        unsigned long pages_written = 0;
 664        unsigned long pause = 1;
 665        bool dirty_exceeded = false;
 666        bool clear_dirty_exceeded = true;
 667        struct backing_dev_info *bdi = mapping->backing_dev_info;
 668        unsigned long start_time = jiffies;
 669
 670        for (;;) {
 671                nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
 672                                        global_page_state(NR_UNSTABLE_NFS);
 673                nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
 674
 675                global_dirty_limits(&background_thresh, &dirty_thresh);
 676
 677                /*
 678                 * Throttle it only when the background writeback cannot
 679                 * catch-up. This avoids (excessively) small writeouts
 680                 * when the bdi limits are ramping up.
 681                 */
 682                if (nr_dirty <= (background_thresh + dirty_thresh) / 2)
 683                        break;
 684
 685                bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
 686                min_task_bdi_thresh = task_min_dirty_limit(bdi_thresh);
 687                task_bdi_thresh = task_dirty_limit(current, bdi_thresh);
 688
 689                /*
 690                 * In order to avoid the stacked BDI deadlock we need
 691                 * to ensure we accurately count the 'dirty' pages when
 692                 * the threshold is low.
 693                 *
 694                 * Otherwise it would be possible to get thresh+n pages
 695                 * reported dirty, even though there are thresh-m pages
 696                 * actually dirty; with m+n sitting in the percpu
 697                 * deltas.
 698                 */
 699                if (task_bdi_thresh < 2 * bdi_stat_error(bdi)) {
 700                        bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
 701                        bdi_dirty = bdi_nr_reclaimable +
 702                                    bdi_stat_sum(bdi, BDI_WRITEBACK);
 703                } else {
 704                        bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
 705                        bdi_dirty = bdi_nr_reclaimable +
 706                                    bdi_stat(bdi, BDI_WRITEBACK);
 707                }
 708
 709                /*
 710                 * The bdi thresh is somehow "soft" limit derived from the
 711                 * global "hard" limit. The former helps to prevent heavy IO
 712                 * bdi or process from holding back light ones; The latter is
 713                 * the last resort safeguard.
 714                 */
 715                dirty_exceeded = (bdi_dirty > task_bdi_thresh) ||
 716                                  (nr_dirty > dirty_thresh);
 717                clear_dirty_exceeded = (bdi_dirty <= min_task_bdi_thresh) &&
 718                                        (nr_dirty <= dirty_thresh);
 719
 720                if (!dirty_exceeded)
 721                        break;
 722
 723                if (!bdi->dirty_exceeded)
 724                        bdi->dirty_exceeded = 1;
 725
 726                bdi_update_bandwidth(bdi, dirty_thresh, nr_dirty,
 727                                     bdi_thresh, bdi_dirty, start_time);
 728
 729                /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
 730                 * Unstable writes are a feature of certain networked
 731                 * filesystems (i.e. NFS) in which data may have been
 732                 * written to the server's write cache, but has not yet
 733                 * been flushed to permanent storage.
 734                 * Only move pages to writeback if this bdi is over its
 735                 * threshold otherwise wait until the disk writes catch
 736                 * up.
 737                 */
 738                trace_balance_dirty_start(bdi);
 739                if (bdi_nr_reclaimable > task_bdi_thresh) {
 740                        pages_written += writeback_inodes_wb(&bdi->wb,
 741                                                             write_chunk);
 742                        trace_balance_dirty_written(bdi, pages_written);
 743                        if (pages_written >= write_chunk)
 744                                break;          /* We've done our duty */
 745                }
 746                __set_current_state(TASK_UNINTERRUPTIBLE);
 747                io_schedule_timeout(pause);
 748                trace_balance_dirty_wait(bdi);
 749
 750                dirty_thresh = hard_dirty_limit(dirty_thresh);
 751                /*
 752                 * max-pause area. If dirty exceeded but still within this
 753                 * area, no need to sleep for more than 200ms: (a) 8 pages per
 754                 * 200ms is typically more than enough to curb heavy dirtiers;
 755                 * (b) the pause time limit makes the dirtiers more responsive.
 756                 */
 757                if (nr_dirty < dirty_thresh &&
 758                    bdi_dirty < (task_bdi_thresh + bdi_thresh) / 2 &&
 759                    time_after(jiffies, start_time + MAX_PAUSE))
 760                        break;
 761
 762                /*
 763                 * Increase the delay for each loop, up to our previous
 764                 * default of taking a 100ms nap.
 765                 */
 766                pause <<= 1;
 767                if (pause > HZ / 10)
 768                        pause = HZ / 10;
 769        }
 770
 771        /* Clear dirty_exceeded flag only when no task can exceed the limit */
 772        if (clear_dirty_exceeded && bdi->dirty_exceeded)
 773                bdi->dirty_exceeded = 0;
 774
 775        if (writeback_in_progress(bdi))
 776                return;
 777
 778        /*
 779         * In laptop mode, we wait until hitting the higher threshold before
 780         * starting background writeout, and then write out all the way down
 781         * to the lower threshold.  So slow writers cause minimal disk activity.
 782         *
 783         * In normal mode, we start background writeout at the lower
 784         * background_thresh, to keep the amount of dirty memory low.
 785         */
 786        if ((laptop_mode && pages_written) ||
 787            (!laptop_mode && (nr_reclaimable > background_thresh)))
 788                bdi_start_background_writeback(bdi);
 789}
 790
 791void set_page_dirty_balance(struct page *page, int page_mkwrite)
 792{
 793        if (set_page_dirty(page) || page_mkwrite) {
 794                struct address_space *mapping = page_mapping(page);
 795
 796                if (mapping)
 797                        balance_dirty_pages_ratelimited(mapping);
 798        }
 799}
 800
 801static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
 802
 803/**
 804 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
 805 * @mapping: address_space which was dirtied
 806 * @nr_pages_dirtied: number of pages which the caller has just dirtied
 807 *
 808 * Processes which are dirtying memory should call in here once for each page
 809 * which was newly dirtied.  The function will periodically check the system's
 810 * dirty state and will initiate writeback if needed.
 811 *
 812 * On really big machines, get_writeback_state is expensive, so try to avoid
 813 * calling it too often (ratelimiting).  But once we're over the dirty memory
 814 * limit we decrease the ratelimiting by a lot, to prevent individual processes
 815 * from overshooting the limit by (ratelimit_pages) each.
 816 */
 817void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
 818                                        unsigned long nr_pages_dirtied)
 819{
 820        struct backing_dev_info *bdi = mapping->backing_dev_info;
 821        unsigned long ratelimit;
 822        unsigned long *p;
 823
 824        if (!bdi_cap_account_dirty(bdi))
 825                return;
 826
 827        ratelimit = ratelimit_pages;
 828        if (mapping->backing_dev_info->dirty_exceeded)
 829                ratelimit = 8;
 830
 831        /*
 832         * Check the rate limiting. Also, we do not want to throttle real-time
 833         * tasks in balance_dirty_pages(). Period.
 834         */
 835        preempt_disable();
 836        p =  &__get_cpu_var(bdp_ratelimits);
 837        *p += nr_pages_dirtied;
 838        if (unlikely(*p >= ratelimit)) {
 839                ratelimit = sync_writeback_pages(*p);
 840                *p = 0;
 841                preempt_enable();
 842                balance_dirty_pages(mapping, ratelimit);
 843                return;
 844        }
 845        preempt_enable();
 846}
 847EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
 848
 849void throttle_vm_writeout(gfp_t gfp_mask)
 850{
 851        unsigned long background_thresh;
 852        unsigned long dirty_thresh;
 853
 854        for ( ; ; ) {
 855                global_dirty_limits(&background_thresh, &dirty_thresh);
 856
 857                /*
 858                 * Boost the allowable dirty threshold a bit for page
 859                 * allocators so they don't get DoS'ed by heavy writers
 860                 */
 861                dirty_thresh += dirty_thresh / 10;      /* wheeee... */
 862
 863                if (global_page_state(NR_UNSTABLE_NFS) +
 864                        global_page_state(NR_WRITEBACK) <= dirty_thresh)
 865                                break;
 866                congestion_wait(BLK_RW_ASYNC, HZ/10);
 867
 868                /*
 869                 * The caller might hold locks which can prevent IO completion
 870                 * or progress in the filesystem.  So we cannot just sit here
 871                 * waiting for IO to complete.
 872                 */
 873                if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
 874                        break;
 875        }
 876}
 877
 878/*
 879 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
 880 */
 881int dirty_writeback_centisecs_handler(ctl_table *table, int write,
 882        void __user *buffer, size_t *length, loff_t *ppos)
 883{
 884        proc_dointvec(table, write, buffer, length, ppos);
 885        bdi_arm_supers_timer();
 886        return 0;
 887}
 888
 889#ifdef CONFIG_BLOCK
 890void laptop_mode_timer_fn(unsigned long data)
 891{
 892        struct request_queue *q = (struct request_queue *)data;
 893        int nr_pages = global_page_state(NR_FILE_DIRTY) +
 894                global_page_state(NR_UNSTABLE_NFS);
 895
 896        /*
 897         * We want to write everything out, not just down to the dirty
 898         * threshold
 899         */
 900        if (bdi_has_dirty_io(&q->backing_dev_info))
 901                bdi_start_writeback(&q->backing_dev_info, nr_pages);
 902}
 903
 904/*
 905 * We've spun up the disk and we're in laptop mode: schedule writeback
 906 * of all dirty data a few seconds from now.  If the flush is already scheduled
 907 * then push it back - the user is still using the disk.
 908 */
 909void laptop_io_completion(struct backing_dev_info *info)
 910{
 911        mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
 912}
 913
 914/*
 915 * We're in laptop mode and we've just synced. The sync's writes will have
 916 * caused another writeback to be scheduled by laptop_io_completion.
 917 * Nothing needs to be written back anymore, so we unschedule the writeback.
 918 */
 919void laptop_sync_completion(void)
 920{
 921        struct backing_dev_info *bdi;
 922
 923        rcu_read_lock();
 924
 925        list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
 926                del_timer(&bdi->laptop_mode_wb_timer);
 927
 928        rcu_read_unlock();
 929}
 930#endif
 931
 932/*
 933 * If ratelimit_pages is too high then we can get into dirty-data overload
 934 * if a large number of processes all perform writes at the same time.
 935 * If it is too low then SMP machines will call the (expensive)
 936 * get_writeback_state too often.
 937 *
 938 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
 939 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
 940 * thresholds before writeback cuts in.
 941 *
 942 * But the limit should not be set too high.  Because it also controls the
 943 * amount of memory which the balance_dirty_pages() caller has to write back.
 944 * If this is too large then the caller will block on the IO queue all the
 945 * time.  So limit it to four megabytes - the balance_dirty_pages() caller
 946 * will write six megabyte chunks, max.
 947 */
 948
 949void writeback_set_ratelimit(void)
 950{
 951        ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
 952        if (ratelimit_pages < 16)
 953                ratelimit_pages = 16;
 954        if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
 955                ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
 956}
 957
 958static int __cpuinit
 959ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
 960{
 961        writeback_set_ratelimit();
 962        return NOTIFY_DONE;
 963}
 964
 965static struct notifier_block __cpuinitdata ratelimit_nb = {
 966        .notifier_call  = ratelimit_handler,
 967        .next           = NULL,
 968};
 969
 970/*
 971 * Called early on to tune the page writeback dirty limits.
 972 *
 973 * We used to scale dirty pages according to how total memory
 974 * related to pages that could be allocated for buffers (by
 975 * comparing nr_free_buffer_pages() to vm_total_pages.
 976 *
 977 * However, that was when we used "dirty_ratio" to scale with
 978 * all memory, and we don't do that any more. "dirty_ratio"
 979 * is now applied to total non-HIGHPAGE memory (by subtracting
 980 * totalhigh_pages from vm_total_pages), and as such we can't
 981 * get into the old insane situation any more where we had
 982 * large amounts of dirty pages compared to a small amount of
 983 * non-HIGHMEM memory.
 984 *
 985 * But we might still want to scale the dirty_ratio by how
 986 * much memory the box has..
 987 */
 988void __init page_writeback_init(void)
 989{
 990        int shift;
 991
 992        writeback_set_ratelimit();
 993        register_cpu_notifier(&ratelimit_nb);
 994
 995        shift = calc_period_shift();
 996        prop_descriptor_init(&vm_completions, shift);
 997        prop_descriptor_init(&vm_dirties, shift);
 998}
 999
1000/**
1001 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1002 * @mapping: address space structure to write
1003 * @start: starting page index
1004 * @end: ending page index (inclusive)
1005 *
1006 * This function scans the page range from @start to @end (inclusive) and tags
1007 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1008 * that write_cache_pages (or whoever calls this function) will then use
1009 * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
1010 * used to avoid livelocking of writeback by a process steadily creating new
1011 * dirty pages in the file (thus it is important for this function to be quick
1012 * so that it can tag pages faster than a dirtying process can create them).
1013 */
1014/*
1015 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1016 */
1017void tag_pages_for_writeback(struct address_space *mapping,
1018                             pgoff_t start, pgoff_t end)
1019{
1020#define WRITEBACK_TAG_BATCH 4096
1021        unsigned long tagged;
1022
1023        do {
1024                spin_lock_irq(&mapping->tree_lock);
1025                tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1026                                &start, end, WRITEBACK_TAG_BATCH,
1027                                PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1028                spin_unlock_irq(&mapping->tree_lock);
1029                WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1030                cond_resched();
1031                /* We check 'start' to handle wrapping when end == ~0UL */
1032        } while (tagged >= WRITEBACK_TAG_BATCH && start);
1033}
1034EXPORT_SYMBOL(tag_pages_for_writeback);
1035
1036/**
1037 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1038 * @mapping: address space structure to write
1039 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1040 * @writepage: function called for each page
1041 * @data: data passed to writepage function
1042 *
1043 * If a page is already under I/O, write_cache_pages() skips it, even
1044 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
1045 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
1046 * and msync() need to guarantee that all the data which was dirty at the time
1047 * the call was made get new I/O started against them.  If wbc->sync_mode is
1048 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1049 * existing IO to complete.
1050 *
1051 * To avoid livelocks (when other process dirties new pages), we first tag
1052 * pages which should be written back with TOWRITE tag and only then start
1053 * writing them. For data-integrity sync we have to be careful so that we do
1054 * not miss some pages (e.g., because some other process has cleared TOWRITE
1055 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1056 * by the process clearing the DIRTY tag (and submitting the page for IO).
1057 */
1058int write_cache_pages(struct address_space *mapping,
1059                      struct writeback_control *wbc, writepage_t writepage,
1060                      void *data)
1061{
1062        int ret = 0;
1063        int done = 0;
1064        struct pagevec pvec;
1065        int nr_pages;
1066        pgoff_t uninitialized_var(writeback_index);
1067        pgoff_t index;
1068        pgoff_t end;            /* Inclusive */
1069        pgoff_t done_index;
1070        int cycled;
1071        int range_whole = 0;
1072        int tag;
1073
1074        pagevec_init(&pvec, 0);
1075        if (wbc->range_cyclic) {
1076                writeback_index = mapping->writeback_index; /* prev offset */
1077                index = writeback_index;
1078                if (index == 0)
1079                        cycled = 1;
1080                else
1081                        cycled = 0;
1082                end = -1;
1083        } else {
1084                index = wbc->range_start >> PAGE_CACHE_SHIFT;
1085                end = wbc->range_end >> PAGE_CACHE_SHIFT;
1086                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1087                        range_whole = 1;
1088                cycled = 1; /* ignore range_cyclic tests */
1089        }
1090        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1091                tag = PAGECACHE_TAG_TOWRITE;
1092        else
1093                tag = PAGECACHE_TAG_DIRTY;
1094retry:
1095        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1096                tag_pages_for_writeback(mapping, index, end);
1097        done_index = index;
1098        while (!done && (index <= end)) {
1099                int i;
1100
1101                nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1102                              min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1103                if (nr_pages == 0)
1104                        break;
1105
1106                for (i = 0; i < nr_pages; i++) {
1107                        struct page *page = pvec.pages[i];
1108
1109                        /*
1110                         * At this point, the page may be truncated or
1111                         * invalidated (changing page->mapping to NULL), or
1112                         * even swizzled back from swapper_space to tmpfs file
1113                         * mapping. However, page->index will not change
1114                         * because we have a reference on the page.
1115                         */
1116                        if (page->index > end) {
1117                                /*
1118                                 * can't be range_cyclic (1st pass) because
1119                                 * end == -1 in that case.
1120                                 */
1121                                done = 1;
1122                                break;
1123                        }
1124
1125                        done_index = page->index;
1126
1127                        lock_page(page);
1128
1129                        /*
1130                         * Page truncated or invalidated. We can freely skip it
1131                         * then, even for data integrity operations: the page
1132                         * has disappeared concurrently, so there could be no
1133                         * real expectation of this data interity operation
1134                         * even if there is now a new, dirty page at the same
1135                         * pagecache address.
1136                         */
1137                        if (unlikely(page->mapping != mapping)) {
1138continue_unlock:
1139                                unlock_page(page);
1140                                continue;
1141                        }
1142
1143                        if (!PageDirty(page)) {
1144                                /* someone wrote it for us */
1145                                goto continue_unlock;
1146                        }
1147
1148                        if (PageWriteback(page)) {
1149                                if (wbc->sync_mode != WB_SYNC_NONE)
1150                                        wait_on_page_writeback(page);
1151                                else
1152                                        goto continue_unlock;
1153                        }
1154
1155                        BUG_ON(PageWriteback(page));
1156                        if (!clear_page_dirty_for_io(page))
1157                                goto continue_unlock;
1158
1159                        trace_wbc_writepage(wbc, mapping->backing_dev_info);
1160                        ret = (*writepage)(page, wbc, data);
1161                        if (unlikely(ret)) {
1162                                if (ret == AOP_WRITEPAGE_ACTIVATE) {
1163                                        unlock_page(page);
1164                                        ret = 0;
1165                                } else {
1166                                        /*
1167                                         * done_index is set past this page,
1168                                         * so media errors will not choke
1169                                         * background writeout for the entire
1170                                         * file. This has consequences for
1171                                         * range_cyclic semantics (ie. it may
1172                                         * not be suitable for data integrity
1173                                         * writeout).
1174                                         */
1175                                        done_index = page->index + 1;
1176                                        done = 1;
1177                                        break;
1178                                }
1179                        }
1180
1181                        /*
1182                         * We stop writing back only if we are not doing
1183                         * integrity sync. In case of integrity sync we have to
1184                         * keep going until we have written all the pages
1185                         * we tagged for writeback prior to entering this loop.
1186                         */
1187                        if (--wbc->nr_to_write <= 0 &&
1188                            wbc->sync_mode == WB_SYNC_NONE) {
1189                                done = 1;
1190                                break;
1191                        }
1192                }
1193                pagevec_release(&pvec);
1194                cond_resched();
1195        }
1196        if (!cycled && !done) {
1197                /*
1198                 * range_cyclic:
1199                 * We hit the last page and there is more work to be done: wrap
1200                 * back to the start of the file
1201                 */
1202                cycled = 1;
1203                index = 0;
1204                end = writeback_index - 1;
1205                goto retry;
1206        }
1207        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1208                mapping->writeback_index = done_index;
1209
1210        return ret;
1211}
1212EXPORT_SYMBOL(write_cache_pages);
1213
1214/*
1215 * Function used by generic_writepages to call the real writepage
1216 * function and set the mapping flags on error
1217 */
1218static int __writepage(struct page *page, struct writeback_control *wbc,
1219                       void *data)
1220{
1221        struct address_space *mapping = data;
1222        int ret = mapping->a_ops->writepage(page, wbc);
1223        mapping_set_error(mapping, ret);
1224        return ret;
1225}
1226
1227/**
1228 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1229 * @mapping: address space structure to write
1230 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1231 *
1232 * This is a library function, which implements the writepages()
1233 * address_space_operation.
1234 */
1235int generic_writepages(struct address_space *mapping,
1236                       struct writeback_control *wbc)
1237{
1238        struct blk_plug plug;
1239        int ret;
1240
1241        /* deal with chardevs and other special file */
1242        if (!mapping->a_ops->writepage)
1243                return 0;
1244
1245        blk_start_plug(&plug);
1246        ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1247        blk_finish_plug(&plug);
1248        return ret;
1249}
1250
1251EXPORT_SYMBOL(generic_writepages);
1252
1253int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1254{
1255        int ret;
1256
1257        if (wbc->nr_to_write <= 0)
1258                return 0;
1259        if (mapping->a_ops->writepages)
1260                ret = mapping->a_ops->writepages(mapping, wbc);
1261        else
1262                ret = generic_writepages(mapping, wbc);
1263        return ret;
1264}
1265
1266/**
1267 * write_one_page - write out a single page and optionally wait on I/O
1268 * @page: the page to write
1269 * @wait: if true, wait on writeout
1270 *
1271 * The page must be locked by the caller and will be unlocked upon return.
1272 *
1273 * write_one_page() returns a negative error code if I/O failed.
1274 */
1275int write_one_page(struct page *page, int wait)
1276{
1277        struct address_space *mapping = page->mapping;
1278        int ret = 0;
1279        struct writeback_control wbc = {
1280                .sync_mode = WB_SYNC_ALL,
1281                .nr_to_write = 1,
1282        };
1283
1284        BUG_ON(!PageLocked(page));
1285
1286        if (wait)
1287                wait_on_page_writeback(page);
1288
1289        if (clear_page_dirty_for_io(page)) {
1290                page_cache_get(page);
1291                ret = mapping->a_ops->writepage(page, &wbc);
1292                if (ret == 0 && wait) {
1293                        wait_on_page_writeback(page);
1294                        if (PageError(page))
1295                                ret = -EIO;
1296                }
1297                page_cache_release(page);
1298        } else {
1299                unlock_page(page);
1300        }
1301        return ret;
1302}
1303EXPORT_SYMBOL(write_one_page);
1304
1305/*
1306 * For address_spaces which do not use buffers nor write back.
1307 */
1308int __set_page_dirty_no_writeback(struct page *page)
1309{
1310        if (!PageDirty(page))
1311                return !TestSetPageDirty(page);
1312        return 0;
1313}
1314
1315/*
1316 * Helper function for set_page_dirty family.
1317 * NOTE: This relies on being atomic wrt interrupts.
1318 */
1319void account_page_dirtied(struct page *page, struct address_space *mapping)
1320{
1321        if (mapping_cap_account_dirty(mapping)) {
1322                __inc_zone_page_state(page, NR_FILE_DIRTY);
1323                __inc_zone_page_state(page, NR_DIRTIED);
1324                __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1325                task_dirty_inc(current);
1326                task_io_account_write(PAGE_CACHE_SIZE);
1327        }
1328}
1329EXPORT_SYMBOL(account_page_dirtied);
1330
1331/*
1332 * Helper function for set_page_writeback family.
1333 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1334 * wrt interrupts.
1335 */
1336void account_page_writeback(struct page *page)
1337{
1338        inc_zone_page_state(page, NR_WRITEBACK);
1339}
1340EXPORT_SYMBOL(account_page_writeback);
1341
1342/*
1343 * For address_spaces which do not use buffers.  Just tag the page as dirty in
1344 * its radix tree.
1345 *
1346 * This is also used when a single buffer is being dirtied: we want to set the
1347 * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1348 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1349 *
1350 * Most callers have locked the page, which pins the address_space in memory.
1351 * But zap_pte_range() does not lock the page, however in that case the
1352 * mapping is pinned by the vma's ->vm_file reference.
1353 *
1354 * We take care to handle the case where the page was truncated from the
1355 * mapping by re-checking page_mapping() inside tree_lock.
1356 */
1357int __set_page_dirty_nobuffers(struct page *page)
1358{
1359        if (!TestSetPageDirty(page)) {
1360                struct address_space *mapping = page_mapping(page);
1361                struct address_space *mapping2;
1362
1363                if (!mapping)
1364                        return 1;
1365
1366                spin_lock_irq(&mapping->tree_lock);
1367                mapping2 = page_mapping(page);
1368                if (mapping2) { /* Race with truncate? */
1369                        BUG_ON(mapping2 != mapping);
1370                        WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1371                        account_page_dirtied(page, mapping);
1372                        radix_tree_tag_set(&mapping->page_tree,
1373                                page_index(page), PAGECACHE_TAG_DIRTY);
1374                }
1375                spin_unlock_irq(&mapping->tree_lock);
1376                if (mapping->host) {
1377                        /* !PageAnon && !swapper_space */
1378                        __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1379                }
1380                return 1;
1381        }
1382        return 0;
1383}
1384EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1385
1386/*
1387 * When a writepage implementation decides that it doesn't want to write this
1388 * page for some reason, it should redirty the locked page via
1389 * redirty_page_for_writepage() and it should then unlock the page and return 0
1390 */
1391int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1392{
1393        wbc->pages_skipped++;
1394        return __set_page_dirty_nobuffers(page);
1395}
1396EXPORT_SYMBOL(redirty_page_for_writepage);
1397
1398/*
1399 * Dirty a page.
1400 *
1401 * For pages with a mapping this should be done under the page lock
1402 * for the benefit of asynchronous memory errors who prefer a consistent
1403 * dirty state. This rule can be broken in some special cases,
1404 * but should be better not to.
1405 *
1406 * If the mapping doesn't provide a set_page_dirty a_op, then
1407 * just fall through and assume that it wants buffer_heads.
1408 */
1409int set_page_dirty(struct page *page)
1410{
1411        struct address_space *mapping = page_mapping(page);
1412
1413        if (likely(mapping)) {
1414                int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1415                /*
1416                 * readahead/lru_deactivate_page could remain
1417                 * PG_readahead/PG_reclaim due to race with end_page_writeback
1418                 * About readahead, if the page is written, the flags would be
1419                 * reset. So no problem.
1420                 * About lru_deactivate_page, if the page is redirty, the flag
1421                 * will be reset. So no problem. but if the page is used by readahead
1422                 * it will confuse readahead and make it restart the size rampup
1423                 * process. But it's a trivial problem.
1424                 */
1425                ClearPageReclaim(page);
1426#ifdef CONFIG_BLOCK
1427                if (!spd)
1428                        spd = __set_page_dirty_buffers;
1429#endif
1430                return (*spd)(page);
1431        }
1432        if (!PageDirty(page)) {
1433                if (!TestSetPageDirty(page))
1434                        return 1;
1435        }
1436        return 0;
1437}
1438EXPORT_SYMBOL(set_page_dirty);
1439
1440/*
1441 * set_page_dirty() is racy if the caller has no reference against
1442 * page->mapping->host, and if the page is unlocked.  This is because another
1443 * CPU could truncate the page off the mapping and then free the mapping.
1444 *
1445 * Usually, the page _is_ locked, or the caller is a user-space process which
1446 * holds a reference on the inode by having an open file.
1447 *
1448 * In other cases, the page should be locked before running set_page_dirty().
1449 */
1450int set_page_dirty_lock(struct page *page)
1451{
1452        int ret;
1453
1454        lock_page(page);
1455        ret = set_page_dirty(page);
1456        unlock_page(page);
1457        return ret;
1458}
1459EXPORT_SYMBOL(set_page_dirty_lock);
1460
1461/*
1462 * Clear a page's dirty flag, while caring for dirty memory accounting.
1463 * Returns true if the page was previously dirty.
1464 *
1465 * This is for preparing to put the page under writeout.  We leave the page
1466 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1467 * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1468 * implementation will run either set_page_writeback() or set_page_dirty(),
1469 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1470 * back into sync.
1471 *
1472 * This incoherency between the page's dirty flag and radix-tree tag is
1473 * unfortunate, but it only exists while the page is locked.
1474 */
1475int clear_page_dirty_for_io(struct page *page)
1476{
1477        struct address_space *mapping = page_mapping(page);
1478
1479        BUG_ON(!PageLocked(page));
1480
1481        if (mapping && mapping_cap_account_dirty(mapping)) {
1482                /*
1483                 * Yes, Virginia, this is indeed insane.
1484                 *
1485                 * We use this sequence to make sure that
1486                 *  (a) we account for dirty stats properly
1487                 *  (b) we tell the low-level filesystem to
1488                 *      mark the whole page dirty if it was
1489                 *      dirty in a pagetable. Only to then
1490                 *  (c) clean the page again and return 1 to
1491                 *      cause the writeback.
1492                 *
1493                 * This way we avoid all nasty races with the
1494                 * dirty bit in multiple places and clearing
1495                 * them concurrently from different threads.
1496                 *
1497                 * Note! Normally the "set_page_dirty(page)"
1498                 * has no effect on the actual dirty bit - since
1499                 * that will already usually be set. But we
1500                 * need the side effects, and it can help us
1501                 * avoid races.
1502                 *
1503                 * We basically use the page "master dirty bit"
1504                 * as a serialization point for all the different
1505                 * threads doing their things.
1506                 */
1507                if (page_mkclean(page))
1508                        set_page_dirty(page);
1509                /*
1510                 * We carefully synchronise fault handlers against
1511                 * installing a dirty pte and marking the page dirty
1512                 * at this point. We do this by having them hold the
1513                 * page lock at some point after installing their
1514                 * pte, but before marking the page dirty.
1515                 * Pages are always locked coming in here, so we get
1516                 * the desired exclusion. See mm/memory.c:do_wp_page()
1517                 * for more comments.
1518                 */
1519                if (TestClearPageDirty(page)) {
1520                        dec_zone_page_state(page, NR_FILE_DIRTY);
1521                        dec_bdi_stat(mapping->backing_dev_info,
1522                                        BDI_RECLAIMABLE);
1523                        return 1;
1524                }
1525                return 0;
1526        }
1527        return TestClearPageDirty(page);
1528}
1529EXPORT_SYMBOL(clear_page_dirty_for_io);
1530
1531int test_clear_page_writeback(struct page *page)
1532{
1533        struct address_space *mapping = page_mapping(page);
1534        int ret;
1535
1536        if (mapping) {
1537                struct backing_dev_info *bdi = mapping->backing_dev_info;
1538                unsigned long flags;
1539
1540                spin_lock_irqsave(&mapping->tree_lock, flags);
1541                ret = TestClearPageWriteback(page);
1542                if (ret) {
1543                        radix_tree_tag_clear(&mapping->page_tree,
1544                                                page_index(page),
1545                                                PAGECACHE_TAG_WRITEBACK);
1546                        if (bdi_cap_account_writeback(bdi)) {
1547                                __dec_bdi_stat(bdi, BDI_WRITEBACK);
1548                                __bdi_writeout_inc(bdi);
1549                        }
1550                }
1551                spin_unlock_irqrestore(&mapping->tree_lock, flags);
1552        } else {
1553                ret = TestClearPageWriteback(page);
1554        }
1555        if (ret) {
1556                dec_zone_page_state(page, NR_WRITEBACK);
1557                inc_zone_page_state(page, NR_WRITTEN);
1558        }
1559        return ret;
1560}
1561
1562int test_set_page_writeback(struct page *page)
1563{
1564        struct address_space *mapping = page_mapping(page);
1565        int ret;
1566
1567        if (mapping) {
1568                struct backing_dev_info *bdi = mapping->backing_dev_info;
1569                unsigned long flags;
1570
1571                spin_lock_irqsave(&mapping->tree_lock, flags);
1572                ret = TestSetPageWriteback(page);
1573                if (!ret) {
1574                        radix_tree_tag_set(&mapping->page_tree,
1575                                                page_index(page),
1576                                                PAGECACHE_TAG_WRITEBACK);
1577                        if (bdi_cap_account_writeback(bdi))
1578                                __inc_bdi_stat(bdi, BDI_WRITEBACK);
1579                }
1580                if (!PageDirty(page))
1581                        radix_tree_tag_clear(&mapping->page_tree,
1582                                                page_index(page),
1583                                                PAGECACHE_TAG_DIRTY);
1584                radix_tree_tag_clear(&mapping->page_tree,
1585                                     page_index(page),
1586                                     PAGECACHE_TAG_TOWRITE);
1587                spin_unlock_irqrestore(&mapping->tree_lock, flags);
1588        } else {
1589                ret = TestSetPageWriteback(page);
1590        }
1591        if (!ret)
1592                account_page_writeback(page);
1593        return ret;
1594
1595}
1596EXPORT_SYMBOL(test_set_page_writeback);
1597
1598/*
1599 * Return true if any of the pages in the mapping are marked with the
1600 * passed tag.
1601 */
1602int mapping_tagged(struct address_space *mapping, int tag)
1603{
1604        return radix_tree_tagged(&mapping->page_tree, tag);
1605}
1606EXPORT_SYMBOL(mapping_tagged);
1607
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