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/export.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> /* __set_page_dirty_buffers */
  36#include <linux/pagevec.h>
  37#include <linux/timer.h>
  38#include <linux/sched/rt.h>
  39#include <trace/events/writeback.h>
  40
  41/*
  42 * Sleep at most 200ms at a time in balance_dirty_pages().
  43 */
  44#define MAX_PAUSE               max(HZ/5, 1)
  45
  46/*
  47 * Try to keep balance_dirty_pages() call intervals higher than this many pages
  48 * by raising pause time to max_pause when falls below it.
  49 */
  50#define DIRTY_POLL_THRESH       (128 >> (PAGE_SHIFT - 10))
  51
  52/*
  53 * Estimate write bandwidth at 200ms intervals.
  54 */
  55#define BANDWIDTH_INTERVAL      max(HZ/5, 1)
  56
  57#define RATELIMIT_CALC_SHIFT    10
  58
  59/*
  60 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
  61 * will look to see if it needs to force writeback or throttling.
  62 */
  63static long ratelimit_pages = 32;
  64
  65/* The following parameters are exported via /proc/sys/vm */
  66
  67/*
  68 * Start background writeback (via writeback threads) at this percentage
  69 */
  70int dirty_background_ratio = 10;
  71
  72/*
  73 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
  74 * dirty_background_ratio * the amount of dirtyable memory
  75 */
  76unsigned long dirty_background_bytes;
  77
  78/*
  79 * free highmem will not be subtracted from the total free memory
  80 * for calculating free ratios if vm_highmem_is_dirtyable is true
  81 */
  82int vm_highmem_is_dirtyable;
  83
  84/*
  85 * The generator of dirty data starts writeback at this percentage
  86 */
  87int vm_dirty_ratio = 20;
  88
  89/*
  90 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
  91 * vm_dirty_ratio * the amount of dirtyable memory
  92 */
  93unsigned long vm_dirty_bytes;
  94
  95/*
  96 * The interval between `kupdate'-style writebacks
  97 */
  98unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
  99
 100EXPORT_SYMBOL_GPL(dirty_writeback_interval);
 101
 102/*
 103 * The longest time for which data is allowed to remain dirty
 104 */
 105unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
 106
 107/*
 108 * Flag that makes the machine dump writes/reads and block dirtyings.
 109 */
 110int block_dump;
 111
 112/*
 113 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
 114 * a full sync is triggered after this time elapses without any disk activity.
 115 */
 116int laptop_mode;
 117
 118EXPORT_SYMBOL(laptop_mode);
 119
 120/* End of sysctl-exported parameters */
 121
 122unsigned long global_dirty_limit;
 123
 124/*
 125 * Scale the writeback cache size proportional to the relative writeout speeds.
 126 *
 127 * We do this by keeping a floating proportion between BDIs, based on page
 128 * writeback completions [end_page_writeback()]. Those devices that write out
 129 * pages fastest will get the larger share, while the slower will get a smaller
 130 * share.
 131 *
 132 * We use page writeout completions because we are interested in getting rid of
 133 * dirty pages. Having them written out is the primary goal.
 134 *
 135 * We introduce a concept of time, a period over which we measure these events,
 136 * because demand can/will vary over time. The length of this period itself is
 137 * measured in page writeback completions.
 138 *
 139 */
 140static struct fprop_global writeout_completions;
 141
 142static void writeout_period(unsigned long t);
 143/* Timer for aging of writeout_completions */
 144static struct timer_list writeout_period_timer =
 145                TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0);
 146static unsigned long writeout_period_time = 0;
 147
 148/*
 149 * Length of period for aging writeout fractions of bdis. This is an
 150 * arbitrarily chosen number. The longer the period, the slower fractions will
 151 * reflect changes in current writeout rate.
 152 */
 153#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
 154
 155/*
 156 * Work out the current dirty-memory clamping and background writeout
 157 * thresholds.
 158 *
 159 * The main aim here is to lower them aggressively if there is a lot of mapped
 160 * memory around.  To avoid stressing page reclaim with lots of unreclaimable
 161 * pages.  It is better to clamp down on writers than to start swapping, and
 162 * performing lots of scanning.
 163 *
 164 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
 165 *
 166 * We don't permit the clamping level to fall below 5% - that is getting rather
 167 * excessive.
 168 *
 169 * We make sure that the background writeout level is below the adjusted
 170 * clamping level.
 171 */
 172
 173/*
 174 * In a memory zone, there is a certain amount of pages we consider
 175 * available for the page cache, which is essentially the number of
 176 * free and reclaimable pages, minus some zone reserves to protect
 177 * lowmem and the ability to uphold the zone's watermarks without
 178 * requiring writeback.
 179 *
 180 * This number of dirtyable pages is the base value of which the
 181 * user-configurable dirty ratio is the effictive number of pages that
 182 * are allowed to be actually dirtied.  Per individual zone, or
 183 * globally by using the sum of dirtyable pages over all zones.
 184 *
 185 * Because the user is allowed to specify the dirty limit globally as
 186 * absolute number of bytes, calculating the per-zone dirty limit can
 187 * require translating the configured limit into a percentage of
 188 * global dirtyable memory first.
 189 */
 190
 191static unsigned long highmem_dirtyable_memory(unsigned long total)
 192{
 193#ifdef CONFIG_HIGHMEM
 194        int node;
 195        unsigned long x = 0;
 196
 197        for_each_node_state(node, N_HIGH_MEMORY) {
 198                struct zone *z =
 199                        &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
 200
 201                x += zone_page_state(z, NR_FREE_PAGES) +
 202                     zone_reclaimable_pages(z) - z->dirty_balance_reserve;
 203        }
 204        /*
 205         * Unreclaimable memory (kernel memory or anonymous memory
 206         * without swap) can bring down the dirtyable pages below
 207         * the zone's dirty balance reserve and the above calculation
 208         * will underflow.  However we still want to add in nodes
 209         * which are below threshold (negative values) to get a more
 210         * accurate calculation but make sure that the total never
 211         * underflows.
 212         */
 213        if ((long)x < 0)
 214                x = 0;
 215
 216        /*
 217         * Make sure that the number of highmem pages is never larger
 218         * than the number of the total dirtyable memory. This can only
 219         * occur in very strange VM situations but we want to make sure
 220         * that this does not occur.
 221         */
 222        return min(x, total);
 223#else
 224        return 0;
 225#endif
 226}
 227
 228/**
 229 * global_dirtyable_memory - number of globally dirtyable pages
 230 *
 231 * Returns the global number of pages potentially available for dirty
 232 * page cache.  This is the base value for the global dirty limits.
 233 */
 234static unsigned long global_dirtyable_memory(void)
 235{
 236        unsigned long x;
 237
 238        x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
 239        x -= min(x, dirty_balance_reserve);
 240
 241        if (!vm_highmem_is_dirtyable)
 242                x -= highmem_dirtyable_memory(x);
 243
 244        /* Subtract min_free_kbytes */
 245        x -= min_t(unsigned long, x, min_free_kbytes >> (PAGE_SHIFT - 10));
 246
 247        return x + 1;   /* Ensure that we never return 0 */
 248}
 249
 250/*
 251 * global_dirty_limits - background-writeback and dirty-throttling thresholds
 252 *
 253 * Calculate the dirty thresholds based on sysctl parameters
 254 * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
 255 * - vm.dirty_ratio             or  vm.dirty_bytes
 256 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
 257 * real-time tasks.
 258 */
 259void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
 260{
 261        unsigned long background;
 262        unsigned long dirty;
 263        unsigned long uninitialized_var(available_memory);
 264        struct task_struct *tsk;
 265
 266        if (!vm_dirty_bytes || !dirty_background_bytes)
 267                available_memory = global_dirtyable_memory();
 268
 269        if (vm_dirty_bytes)
 270                dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
 271        else
 272                dirty = (vm_dirty_ratio * available_memory) / 100;
 273
 274        if (dirty_background_bytes)
 275                background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
 276        else
 277                background = (dirty_background_ratio * available_memory) / 100;
 278
 279        if (background >= dirty)
 280                background = dirty / 2;
 281        tsk = current;
 282        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
 283                background += background / 4;
 284                dirty += dirty / 4;
 285        }
 286        *pbackground = background;
 287        *pdirty = dirty;
 288        trace_global_dirty_state(background, dirty);
 289}
 290
 291/**
 292 * zone_dirtyable_memory - number of dirtyable pages in a zone
 293 * @zone: the zone
 294 *
 295 * Returns the zone's number of pages potentially available for dirty
 296 * page cache.  This is the base value for the per-zone dirty limits.
 297 */
 298static unsigned long zone_dirtyable_memory(struct zone *zone)
 299{
 300        /*
 301         * The effective global number of dirtyable pages may exclude
 302         * highmem as a big-picture measure to keep the ratio between
 303         * dirty memory and lowmem reasonable.
 304         *
 305         * But this function is purely about the individual zone and a
 306         * highmem zone can hold its share of dirty pages, so we don't
 307         * care about vm_highmem_is_dirtyable here.
 308         */
 309        unsigned long nr_pages = zone_page_state(zone, NR_FREE_PAGES) +
 310                zone_reclaimable_pages(zone);
 311
 312        /* don't allow this to underflow */
 313        nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
 314        return nr_pages;
 315}
 316
 317/**
 318 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
 319 * @zone: the zone
 320 *
 321 * Returns the maximum number of dirty pages allowed in a zone, based
 322 * on the zone's dirtyable memory.
 323 */
 324static unsigned long zone_dirty_limit(struct zone *zone)
 325{
 326        unsigned long zone_memory = zone_dirtyable_memory(zone);
 327        struct task_struct *tsk = current;
 328        unsigned long dirty;
 329
 330        if (vm_dirty_bytes)
 331                dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
 332                        zone_memory / global_dirtyable_memory();
 333        else
 334                dirty = vm_dirty_ratio * zone_memory / 100;
 335
 336        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
 337                dirty += dirty / 4;
 338
 339        return dirty;
 340}
 341
 342/**
 343 * zone_dirty_ok - tells whether a zone is within its dirty limits
 344 * @zone: the zone to check
 345 *
 346 * Returns %true when the dirty pages in @zone are within the zone's
 347 * dirty limit, %false if the limit is exceeded.
 348 */
 349bool zone_dirty_ok(struct zone *zone)
 350{
 351        unsigned long limit = zone_dirty_limit(zone);
 352
 353        return zone_page_state(zone, NR_FILE_DIRTY) +
 354               zone_page_state(zone, NR_UNSTABLE_NFS) +
 355               zone_page_state(zone, NR_WRITEBACK) <= limit;
 356}
 357
 358int dirty_background_ratio_handler(struct ctl_table *table, int write,
 359                void __user *buffer, size_t *lenp,
 360                loff_t *ppos)
 361{
 362        int ret;
 363
 364        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 365        if (ret == 0 && write)
 366                dirty_background_bytes = 0;
 367        return ret;
 368}
 369
 370int dirty_background_bytes_handler(struct ctl_table *table, int write,
 371                void __user *buffer, size_t *lenp,
 372                loff_t *ppos)
 373{
 374        int ret;
 375
 376        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 377        if (ret == 0 && write)
 378                dirty_background_ratio = 0;
 379        return ret;
 380}
 381
 382int dirty_ratio_handler(struct ctl_table *table, int write,
 383                void __user *buffer, size_t *lenp,
 384                loff_t *ppos)
 385{
 386        int old_ratio = vm_dirty_ratio;
 387        int ret;
 388
 389        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 390        if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
 391                writeback_set_ratelimit();
 392                vm_dirty_bytes = 0;
 393        }
 394        return ret;
 395}
 396
 397int dirty_bytes_handler(struct ctl_table *table, int write,
 398                void __user *buffer, size_t *lenp,
 399                loff_t *ppos)
 400{
 401        unsigned long old_bytes = vm_dirty_bytes;
 402        int ret;
 403
 404        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 405        if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
 406                writeback_set_ratelimit();
 407                vm_dirty_ratio = 0;
 408        }
 409        return ret;
 410}
 411
 412static unsigned long wp_next_time(unsigned long cur_time)
 413{
 414        cur_time += VM_COMPLETIONS_PERIOD_LEN;
 415        /* 0 has a special meaning... */
 416        if (!cur_time)
 417                return 1;
 418        return cur_time;
 419}
 420
 421/*
 422 * Increment the BDI's writeout completion count and the global writeout
 423 * completion count. Called from test_clear_page_writeback().
 424 */
 425static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
 426{
 427        __inc_bdi_stat(bdi, BDI_WRITTEN);
 428        __fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
 429                               bdi->max_prop_frac);
 430        /* First event after period switching was turned off? */
 431        if (!unlikely(writeout_period_time)) {
 432                /*
 433                 * We can race with other __bdi_writeout_inc calls here but
 434                 * it does not cause any harm since the resulting time when
 435                 * timer will fire and what is in writeout_period_time will be
 436                 * roughly the same.
 437                 */
 438                writeout_period_time = wp_next_time(jiffies);
 439                mod_timer(&writeout_period_timer, writeout_period_time);
 440        }
 441}
 442
 443void bdi_writeout_inc(struct backing_dev_info *bdi)
 444{
 445        unsigned long flags;
 446
 447        local_irq_save(flags);
 448        __bdi_writeout_inc(bdi);
 449        local_irq_restore(flags);
 450}
 451EXPORT_SYMBOL_GPL(bdi_writeout_inc);
 452
 453/*
 454 * Obtain an accurate fraction of the BDI's portion.
 455 */
 456static void bdi_writeout_fraction(struct backing_dev_info *bdi,
 457                long *numerator, long *denominator)
 458{
 459        fprop_fraction_percpu(&writeout_completions, &bdi->completions,
 460                                numerator, denominator);
 461}
 462
 463/*
 464 * On idle system, we can be called long after we scheduled because we use
 465 * deferred timers so count with missed periods.
 466 */
 467static void writeout_period(unsigned long t)
 468{
 469        int miss_periods = (jiffies - writeout_period_time) /
 470                                                 VM_COMPLETIONS_PERIOD_LEN;
 471
 472        if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
 473                writeout_period_time = wp_next_time(writeout_period_time +
 474                                miss_periods * VM_COMPLETIONS_PERIOD_LEN);
 475                mod_timer(&writeout_period_timer, writeout_period_time);
 476        } else {
 477                /*
 478                 * Aging has zeroed all fractions. Stop wasting CPU on period
 479                 * updates.
 480                 */
 481                writeout_period_time = 0;
 482        }
 483}
 484
 485/*
 486 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
 487 * registered backing devices, which, for obvious reasons, can not
 488 * exceed 100%.
 489 */
 490static unsigned int bdi_min_ratio;
 491
 492int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 493{
 494        int ret = 0;
 495
 496        spin_lock_bh(&bdi_lock);
 497        if (min_ratio > bdi->max_ratio) {
 498                ret = -EINVAL;
 499        } else {
 500                min_ratio -= bdi->min_ratio;
 501                if (bdi_min_ratio + min_ratio < 100) {
 502                        bdi_min_ratio += min_ratio;
 503                        bdi->min_ratio += min_ratio;
 504                } else {
 505                        ret = -EINVAL;
 506                }
 507        }
 508        spin_unlock_bh(&bdi_lock);
 509
 510        return ret;
 511}
 512
 513int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 514{
 515        int ret = 0;
 516
 517        if (max_ratio > 100)
 518                return -EINVAL;
 519
 520        spin_lock_bh(&bdi_lock);
 521        if (bdi->min_ratio > max_ratio) {
 522                ret = -EINVAL;
 523        } else {
 524                bdi->max_ratio = max_ratio;
 525                bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
 526        }
 527        spin_unlock_bh(&bdi_lock);
 528
 529        return ret;
 530}
 531EXPORT_SYMBOL(bdi_set_max_ratio);
 532
 533static unsigned long dirty_freerun_ceiling(unsigned long thresh,
 534                                           unsigned long bg_thresh)
 535{
 536        return (thresh + bg_thresh) / 2;
 537}
 538
 539static unsigned long hard_dirty_limit(unsigned long thresh)
 540{
 541        return max(thresh, global_dirty_limit);
 542}
 543
 544/**
 545 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
 546 * @bdi: the backing_dev_info to query
 547 * @dirty: global dirty limit in pages
 548 *
 549 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
 550 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
 551 *
 552 * Note that balance_dirty_pages() will only seriously take it as a hard limit
 553 * when sleeping max_pause per page is not enough to keep the dirty pages under
 554 * control. For example, when the device is completely stalled due to some error
 555 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
 556 * In the other normal situations, it acts more gently by throttling the tasks
 557 * more (rather than completely block them) when the bdi dirty pages go high.
 558 *
 559 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
 560 * - starving fast devices
 561 * - piling up dirty pages (that will take long time to sync) on slow devices
 562 *
 563 * The bdi's share of dirty limit will be adapting to its throughput and
 564 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
 565 */
 566unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
 567{
 568        u64 bdi_dirty;
 569        long numerator, denominator;
 570
 571        /*
 572         * Calculate this BDI's share of the dirty ratio.
 573         */
 574        bdi_writeout_fraction(bdi, &numerator, &denominator);
 575
 576        bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
 577        bdi_dirty *= numerator;
 578        do_div(bdi_dirty, denominator);
 579
 580        bdi_dirty += (dirty * bdi->min_ratio) / 100;
 581        if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
 582                bdi_dirty = dirty * bdi->max_ratio / 100;
 583
 584        return bdi_dirty;
 585}
 586
 587/*
 588 * Dirty position control.
 589 *
 590 * (o) global/bdi setpoints
 591 *
 592 * We want the dirty pages be balanced around the global/bdi setpoints.
 593 * When the number of dirty pages is higher/lower than the setpoint, the
 594 * dirty position control ratio (and hence task dirty ratelimit) will be
 595 * decreased/increased to bring the dirty pages back to the setpoint.
 596 *
 597 *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
 598 *
 599 *     if (dirty < setpoint) scale up   pos_ratio
 600 *     if (dirty > setpoint) scale down pos_ratio
 601 *
 602 *     if (bdi_dirty < bdi_setpoint) scale up   pos_ratio
 603 *     if (bdi_dirty > bdi_setpoint) scale down pos_ratio
 604 *
 605 *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
 606 *
 607 * (o) global control line
 608 *
 609 *     ^ pos_ratio
 610 *     |
 611 *     |            |<===== global dirty control scope ======>|
 612 * 2.0 .............*
 613 *     |            .*
 614 *     |            . *
 615 *     |            .   *
 616 *     |            .     *
 617 *     |            .        *
 618 *     |            .            *
 619 * 1.0 ................................*
 620 *     |            .                  .     *
 621 *     |            .                  .          *
 622 *     |            .                  .              *
 623 *     |            .                  .                 *
 624 *     |            .                  .                    *
 625 *   0 +------------.------------------.----------------------*------------->
 626 *           freerun^          setpoint^                 limit^   dirty pages
 627 *
 628 * (o) bdi control line
 629 *
 630 *     ^ pos_ratio
 631 *     |
 632 *     |            *
 633 *     |              *
 634 *     |                *
 635 *     |                  *
 636 *     |                    * |<=========== span ============>|
 637 * 1.0 .......................*
 638 *     |                      . *
 639 *     |                      .   *
 640 *     |                      .     *
 641 *     |                      .       *
 642 *     |                      .         *
 643 *     |                      .           *
 644 *     |                      .             *
 645 *     |                      .               *
 646 *     |                      .                 *
 647 *     |                      .                   *
 648 *     |                      .                     *
 649 * 1/4 ...............................................* * * * * * * * * * * *
 650 *     |                      .                         .
 651 *     |                      .                           .
 652 *     |                      .                             .
 653 *   0 +----------------------.-------------------------------.------------->
 654 *                bdi_setpoint^                    x_intercept^
 655 *
 656 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
 657 * be smoothly throttled down to normal if it starts high in situations like
 658 * - start writing to a slow SD card and a fast disk at the same time. The SD
 659 *   card's bdi_dirty may rush to many times higher than bdi_setpoint.
 660 * - the bdi dirty thresh drops quickly due to change of JBOD workload
 661 */
 662static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
 663                                        unsigned long thresh,
 664                                        unsigned long bg_thresh,
 665                                        unsigned long dirty,
 666                                        unsigned long bdi_thresh,
 667                                        unsigned long bdi_dirty)
 668{
 669        unsigned long write_bw = bdi->avg_write_bandwidth;
 670        unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
 671        unsigned long limit = hard_dirty_limit(thresh);
 672        unsigned long x_intercept;
 673        unsigned long setpoint;         /* dirty pages' target balance point */
 674        unsigned long bdi_setpoint;
 675        unsigned long span;
 676        long long pos_ratio;            /* for scaling up/down the rate limit */
 677        long x;
 678
 679        if (unlikely(dirty >= limit))
 680                return 0;
 681
 682        /*
 683         * global setpoint
 684         *
 685         *                           setpoint - dirty 3
 686         *        f(dirty) := 1.0 + (----------------)
 687         *                           limit - setpoint
 688         *
 689         * it's a 3rd order polynomial that subjects to
 690         *
 691         * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
 692         * (2) f(setpoint) = 1.0 => the balance point
 693         * (3) f(limit)    = 0   => the hard limit
 694         * (4) df/dx      <= 0   => negative feedback control
 695         * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
 696         *     => fast response on large errors; small oscillation near setpoint
 697         */
 698        setpoint = (freerun + limit) / 2;
 699        x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
 700                    limit - setpoint + 1);
 701        pos_ratio = x;
 702        pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
 703        pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
 704        pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
 705
 706        /*
 707         * We have computed basic pos_ratio above based on global situation. If
 708         * the bdi is over/under its share of dirty pages, we want to scale
 709         * pos_ratio further down/up. That is done by the following mechanism.
 710         */
 711
 712        /*
 713         * bdi setpoint
 714         *
 715         *        f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
 716         *
 717         *                        x_intercept - bdi_dirty
 718         *                     := --------------------------
 719         *                        x_intercept - bdi_setpoint
 720         *
 721         * The main bdi control line is a linear function that subjects to
 722         *
 723         * (1) f(bdi_setpoint) = 1.0
 724         * (2) k = - 1 / (8 * write_bw)  (in single bdi case)
 725         *     or equally: x_intercept = bdi_setpoint + 8 * write_bw
 726         *
 727         * For single bdi case, the dirty pages are observed to fluctuate
 728         * regularly within range
 729         *        [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
 730         * for various filesystems, where (2) can yield in a reasonable 12.5%
 731         * fluctuation range for pos_ratio.
 732         *
 733         * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
 734         * own size, so move the slope over accordingly and choose a slope that
 735         * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
 736         */
 737        if (unlikely(bdi_thresh > thresh))
 738                bdi_thresh = thresh;
 739        /*
 740         * It's very possible that bdi_thresh is close to 0 not because the
 741         * device is slow, but that it has remained inactive for long time.
 742         * Honour such devices a reasonable good (hopefully IO efficient)
 743         * threshold, so that the occasional writes won't be blocked and active
 744         * writes can rampup the threshold quickly.
 745         */
 746        bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
 747        /*
 748         * scale global setpoint to bdi's:
 749         *      bdi_setpoint = setpoint * bdi_thresh / thresh
 750         */
 751        x = div_u64((u64)bdi_thresh << 16, thresh + 1);
 752        bdi_setpoint = setpoint * (u64)x >> 16;
 753        /*
 754         * Use span=(8*write_bw) in single bdi case as indicated by
 755         * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
 756         *
 757         *        bdi_thresh                    thresh - bdi_thresh
 758         * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
 759         *          thresh                            thresh
 760         */
 761        span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
 762        x_intercept = bdi_setpoint + span;
 763
 764        if (bdi_dirty < x_intercept - span / 4) {
 765                pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
 766                                    x_intercept - bdi_setpoint + 1);
 767        } else
 768                pos_ratio /= 4;
 769
 770        /*
 771         * bdi reserve area, safeguard against dirty pool underrun and disk idle
 772         * It may push the desired control point of global dirty pages higher
 773         * than setpoint.
 774         */
 775        x_intercept = bdi_thresh / 2;
 776        if (bdi_dirty < x_intercept) {
 777                if (bdi_dirty > x_intercept / 8)
 778                        pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
 779                else
 780                        pos_ratio *= 8;
 781        }
 782
 783        return pos_ratio;
 784}
 785
 786static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
 787                                       unsigned long elapsed,
 788                                       unsigned long written)
 789{
 790        const unsigned long period = roundup_pow_of_two(3 * HZ);
 791        unsigned long avg = bdi->avg_write_bandwidth;
 792        unsigned long old = bdi->write_bandwidth;
 793        u64 bw;
 794
 795        /*
 796         * bw = written * HZ / elapsed
 797         *
 798         *                   bw * elapsed + write_bandwidth * (period - elapsed)
 799         * write_bandwidth = ---------------------------------------------------
 800         *                                          period
 801         */
 802        bw = written - bdi->written_stamp;
 803        bw *= HZ;
 804        if (unlikely(elapsed > period)) {
 805                do_div(bw, elapsed);
 806                avg = bw;
 807                goto out;
 808        }
 809        bw += (u64)bdi->write_bandwidth * (period - elapsed);
 810        bw >>= ilog2(period);
 811
 812        /*
 813         * one more level of smoothing, for filtering out sudden spikes
 814         */
 815        if (avg > old && old >= (unsigned long)bw)
 816                avg -= (avg - old) >> 3;
 817
 818        if (avg < old && old <= (unsigned long)bw)
 819                avg += (old - avg) >> 3;
 820
 821out:
 822        bdi->write_bandwidth = bw;
 823        bdi->avg_write_bandwidth = avg;
 824}
 825
 826/*
 827 * The global dirtyable memory and dirty threshold could be suddenly knocked
 828 * down by a large amount (eg. on the startup of KVM in a swapless system).
 829 * This may throw the system into deep dirty exceeded state and throttle
 830 * heavy/light dirtiers alike. To retain good responsiveness, maintain
 831 * global_dirty_limit for tracking slowly down to the knocked down dirty
 832 * threshold.
 833 */
 834static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
 835{
 836        unsigned long limit = global_dirty_limit;
 837
 838        /*
 839         * Follow up in one step.
 840         */
 841        if (limit < thresh) {
 842                limit = thresh;
 843                goto update;
 844        }
 845
 846        /*
 847         * Follow down slowly. Use the higher one as the target, because thresh
 848         * may drop below dirty. This is exactly the reason to introduce
 849         * global_dirty_limit which is guaranteed to lie above the dirty pages.
 850         */
 851        thresh = max(thresh, dirty);
 852        if (limit > thresh) {
 853                limit -= (limit - thresh) >> 5;
 854                goto update;
 855        }
 856        return;
 857update:
 858        global_dirty_limit = limit;
 859}
 860
 861static void global_update_bandwidth(unsigned long thresh,
 862                                    unsigned long dirty,
 863                                    unsigned long now)
 864{
 865        static DEFINE_SPINLOCK(dirty_lock);
 866        static unsigned long update_time;
 867
 868        /*
 869         * check locklessly first to optimize away locking for the most time
 870         */
 871        if (time_before(now, update_time + BANDWIDTH_INTERVAL))
 872                return;
 873
 874        spin_lock(&dirty_lock);
 875        if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
 876                update_dirty_limit(thresh, dirty);
 877                update_time = now;
 878        }
 879        spin_unlock(&dirty_lock);
 880}
 881
 882/*
 883 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
 884 *
 885 * Normal bdi tasks will be curbed at or below it in long term.
 886 * Obviously it should be around (write_bw / N) when there are N dd tasks.
 887 */
 888static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
 889                                       unsigned long thresh,
 890                                       unsigned long bg_thresh,
 891                                       unsigned long dirty,
 892                                       unsigned long bdi_thresh,
 893                                       unsigned long bdi_dirty,
 894                                       unsigned long dirtied,
 895                                       unsigned long elapsed)
 896{
 897        unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
 898        unsigned long limit = hard_dirty_limit(thresh);
 899        unsigned long setpoint = (freerun + limit) / 2;
 900        unsigned long write_bw = bdi->avg_write_bandwidth;
 901        unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
 902        unsigned long dirty_rate;
 903        unsigned long task_ratelimit;
 904        unsigned long balanced_dirty_ratelimit;
 905        unsigned long pos_ratio;
 906        unsigned long step;
 907        unsigned long x;
 908
 909        /*
 910         * The dirty rate will match the writeout rate in long term, except
 911         * when dirty pages are truncated by userspace or re-dirtied by FS.
 912         */
 913        dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
 914
 915        pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
 916                                       bdi_thresh, bdi_dirty);
 917        /*
 918         * task_ratelimit reflects each dd's dirty rate for the past 200ms.
 919         */
 920        task_ratelimit = (u64)dirty_ratelimit *
 921                                        pos_ratio >> RATELIMIT_CALC_SHIFT;
 922        task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
 923
 924        /*
 925         * A linear estimation of the "balanced" throttle rate. The theory is,
 926         * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
 927         * dirty_rate will be measured to be (N * task_ratelimit). So the below
 928         * formula will yield the balanced rate limit (write_bw / N).
 929         *
 930         * Note that the expanded form is not a pure rate feedback:
 931         *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate)              (1)
 932         * but also takes pos_ratio into account:
 933         *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
 934         *
 935         * (1) is not realistic because pos_ratio also takes part in balancing
 936         * the dirty rate.  Consider the state
 937         *      pos_ratio = 0.5                                              (3)
 938         *      rate = 2 * (write_bw / N)                                    (4)
 939         * If (1) is used, it will stuck in that state! Because each dd will
 940         * be throttled at
 941         *      task_ratelimit = pos_ratio * rate = (write_bw / N)           (5)
 942         * yielding
 943         *      dirty_rate = N * task_ratelimit = write_bw                   (6)
 944         * put (6) into (1) we get
 945         *      rate_(i+1) = rate_(i)                                        (7)
 946         *
 947         * So we end up using (2) to always keep
 948         *      rate_(i+1) ~= (write_bw / N)                                 (8)
 949         * regardless of the value of pos_ratio. As long as (8) is satisfied,
 950         * pos_ratio is able to drive itself to 1.0, which is not only where
 951         * the dirty count meet the setpoint, but also where the slope of
 952         * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
 953         */
 954        balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
 955                                           dirty_rate | 1);
 956        /*
 957         * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
 958         */
 959        if (unlikely(balanced_dirty_ratelimit > write_bw))
 960                balanced_dirty_ratelimit = write_bw;
 961
 962        /*
 963         * We could safely do this and return immediately:
 964         *
 965         *      bdi->dirty_ratelimit = balanced_dirty_ratelimit;
 966         *
 967         * However to get a more stable dirty_ratelimit, the below elaborated
 968         * code makes use of task_ratelimit to filter out singular points and
 969         * limit the step size.
 970         *
 971         * The below code essentially only uses the relative value of
 972         *
 973         *      task_ratelimit - dirty_ratelimit
 974         *      = (pos_ratio - 1) * dirty_ratelimit
 975         *
 976         * which reflects the direction and size of dirty position error.
 977         */
 978
 979        /*
 980         * dirty_ratelimit will follow balanced_dirty_ratelimit iff
 981         * task_ratelimit is on the same side of dirty_ratelimit, too.
 982         * For example, when
 983         * - dirty_ratelimit > balanced_dirty_ratelimit
 984         * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
 985         * lowering dirty_ratelimit will help meet both the position and rate
 986         * control targets. Otherwise, don't update dirty_ratelimit if it will
 987         * only help meet the rate target. After all, what the users ultimately
 988         * feel and care are stable dirty rate and small position error.
 989         *
 990         * |task_ratelimit - dirty_ratelimit| is used to limit the step size
 991         * and filter out the singular points of balanced_dirty_ratelimit. Which
 992         * keeps jumping around randomly and can even leap far away at times
 993         * due to the small 200ms estimation period of dirty_rate (we want to
 994         * keep that period small to reduce time lags).
 995         */
 996        step = 0;
 997        if (dirty < setpoint) {
 998                x = min(bdi->balanced_dirty_ratelimit,
 999                         min(balanced_dirty_ratelimit, task_ratelimit));
1000                if (dirty_ratelimit < x)
1001                        step = x - dirty_ratelimit;
1002        } else {
1003                x = max(bdi->balanced_dirty_ratelimit,
1004                         max(balanced_dirty_ratelimit, task_ratelimit));
1005                if (dirty_ratelimit > x)
1006                        step = dirty_ratelimit - x;
1007        }
1008
1009        /*
1010         * Don't pursue 100% rate matching. It's impossible since the balanced
1011         * rate itself is constantly fluctuating. So decrease the track speed
1012         * when it gets close to the target. Helps eliminate pointless tremors.
1013         */
1014        step >>= dirty_ratelimit / (2 * step + 1);
1015        /*
1016         * Limit the tracking speed to avoid overshooting.
1017         */
1018        step = (step + 7) / 8;
1019
1020        if (dirty_ratelimit < balanced_dirty_ratelimit)
1021                dirty_ratelimit += step;
1022        else
1023                dirty_ratelimit -= step;
1024
1025        bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1026        bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1027
1028        trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
1029}
1030
1031void __bdi_update_bandwidth(struct backing_dev_info *bdi,
1032                            unsigned long thresh,
1033                            unsigned long bg_thresh,
1034                            unsigned long dirty,
1035                            unsigned long bdi_thresh,
1036                            unsigned long bdi_dirty,
1037                            unsigned long start_time)
1038{
1039        unsigned long now = jiffies;
1040        unsigned long elapsed = now - bdi->bw_time_stamp;
1041        unsigned long dirtied;
1042        unsigned long written;
1043
1044        /*
1045         * rate-limit, only update once every 200ms.
1046         */
1047        if (elapsed < BANDWIDTH_INTERVAL)
1048                return;
1049
1050        dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
1051        written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1052
1053        /*
1054         * Skip quiet periods when disk bandwidth is under-utilized.
1055         * (at least 1s idle time between two flusher runs)
1056         */
1057        if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1058                goto snapshot;
1059
1060        if (thresh) {
1061                global_update_bandwidth(thresh, dirty, now);
1062                bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1063                                           bdi_thresh, bdi_dirty,
1064                                           dirtied, elapsed);
1065        }
1066        bdi_update_write_bandwidth(bdi, elapsed, written);
1067
1068snapshot:
1069        bdi->dirtied_stamp = dirtied;
1070        bdi->written_stamp = written;
1071        bdi->bw_time_stamp = now;
1072}
1073
1074static void bdi_update_bandwidth(struct backing_dev_info *bdi,
1075                                 unsigned long thresh,
1076                                 unsigned long bg_thresh,
1077                                 unsigned long dirty,
1078                                 unsigned long bdi_thresh,
1079                                 unsigned long bdi_dirty,
1080                                 unsigned long start_time)
1081{
1082        if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1083                return;
1084        spin_lock(&bdi->wb.list_lock);
1085        __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1086                               bdi_thresh, bdi_dirty, start_time);
1087        spin_unlock(&bdi->wb.list_lock);
1088}
1089
1090/*
1091 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1092 * will look to see if it needs to start dirty throttling.
1093 *
1094 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1095 * global_page_state() too often. So scale it near-sqrt to the safety margin
1096 * (the number of pages we may dirty without exceeding the dirty limits).
1097 */
1098static unsigned long dirty_poll_interval(unsigned long dirty,
1099                                         unsigned long thresh)
1100{
1101        if (thresh > dirty)
1102                return 1UL << (ilog2(thresh - dirty) >> 1);
1103
1104        return 1;
1105}
1106
1107static long bdi_max_pause(struct backing_dev_info *bdi,
1108                          unsigned long bdi_dirty)
1109{
1110        long bw = bdi->avg_write_bandwidth;
1111        long t;
1112
1113        /*
1114         * Limit pause time for small memory systems. If sleeping for too long
1115         * time, a small pool of dirty/writeback pages may go empty and disk go
1116         * idle.
1117         *
1118         * 8 serves as the safety ratio.
1119         */
1120        t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1121        t++;
1122
1123        return min_t(long, t, MAX_PAUSE);
1124}
1125
1126static long bdi_min_pause(struct backing_dev_info *bdi,
1127                          long max_pause,
1128                          unsigned long task_ratelimit,
1129                          unsigned long dirty_ratelimit,
1130                          int *nr_dirtied_pause)
1131{
1132        long hi = ilog2(bdi->avg_write_bandwidth);
1133        long lo = ilog2(bdi->dirty_ratelimit);
1134        long t;         /* target pause */
1135        long pause;     /* estimated next pause */
1136        int pages;      /* target nr_dirtied_pause */
1137
1138        /* target for 10ms pause on 1-dd case */
1139        t = max(1, HZ / 100);
1140
1141        /*
1142         * Scale up pause time for concurrent dirtiers in order to reduce CPU
1143         * overheads.
1144         *
1145         * (N * 10ms) on 2^N concurrent tasks.
1146         */
1147        if (hi > lo)
1148                t += (hi - lo) * (10 * HZ) / 1024;
1149
1150        /*
1151         * This is a bit convoluted. We try to base the next nr_dirtied_pause
1152         * on the much more stable dirty_ratelimit. However the next pause time
1153         * will be computed based on task_ratelimit and the two rate limits may
1154         * depart considerably at some time. Especially if task_ratelimit goes
1155         * below dirty_ratelimit/2 and the target pause is max_pause, the next
1156         * pause time will be max_pause*2 _trimmed down_ to max_pause.  As a
1157         * result task_ratelimit won't be executed faithfully, which could
1158         * eventually bring down dirty_ratelimit.
1159         *
1160         * We apply two rules to fix it up:
1161         * 1) try to estimate the next pause time and if necessary, use a lower
1162         *    nr_dirtied_pause so as not to exceed max_pause. When this happens,
1163         *    nr_dirtied_pause will be "dancing" with task_ratelimit.
1164         * 2) limit the target pause time to max_pause/2, so that the normal
1165         *    small fluctuations of task_ratelimit won't trigger rule (1) and
1166         *    nr_dirtied_pause will remain as stable as dirty_ratelimit.
1167         */
1168        t = min(t, 1 + max_pause / 2);
1169        pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1170
1171        /*
1172         * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1173         * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1174         * When the 16 consecutive reads are often interrupted by some dirty
1175         * throttling pause during the async writes, cfq will go into idles
1176         * (deadline is fine). So push nr_dirtied_pause as high as possible
1177         * until reaches DIRTY_POLL_THRESH=32 pages.
1178         */
1179        if (pages < DIRTY_POLL_THRESH) {
1180                t = max_pause;
1181                pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1182                if (pages > DIRTY_POLL_THRESH) {
1183                        pages = DIRTY_POLL_THRESH;
1184                        t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1185                }
1186        }
1187
1188        pause = HZ * pages / (task_ratelimit + 1);
1189        if (pause > max_pause) {
1190                t = max_pause;
1191                pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1192        }
1193
1194        *nr_dirtied_pause = pages;
1195        /*
1196         * The minimal pause time will normally be half the target pause time.
1197         */
1198        return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1199}
1200
1201/*
1202 * balance_dirty_pages() must be called by processes which are generating dirty
1203 * data.  It looks at the number of dirty pages in the machine and will force
1204 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1205 * If we're over `background_thresh' then the writeback threads are woken to
1206 * perform some writeout.
1207 */
1208static void balance_dirty_pages(struct address_space *mapping,
1209                                unsigned long pages_dirtied)
1210{
1211        unsigned long nr_reclaimable;   /* = file_dirty + unstable_nfs */
1212        unsigned long bdi_reclaimable;
1213        unsigned long nr_dirty;  /* = file_dirty + writeback + unstable_nfs */
1214        unsigned long bdi_dirty;
1215        unsigned long freerun;
1216        unsigned long background_thresh;
1217        unsigned long dirty_thresh;
1218        unsigned long bdi_thresh;
1219        long period;
1220        long pause;
1221        long max_pause;
1222        long min_pause;
1223        int nr_dirtied_pause;
1224        bool dirty_exceeded = false;
1225        unsigned long task_ratelimit;
1226        unsigned long dirty_ratelimit;
1227        unsigned long pos_ratio;
1228        struct backing_dev_info *bdi = mapping->backing_dev_info;
1229        unsigned long start_time = jiffies;
1230
1231        for (;;) {
1232                unsigned long now = jiffies;
1233
1234                /*
1235                 * Unstable writes are a feature of certain networked
1236                 * filesystems (i.e. NFS) in which data may have been
1237                 * written to the server's write cache, but has not yet
1238                 * been flushed to permanent storage.
1239                 */
1240                nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1241                                        global_page_state(NR_UNSTABLE_NFS);
1242                nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1243
1244                global_dirty_limits(&background_thresh, &dirty_thresh);
1245
1246                /*
1247                 * Throttle it only when the background writeback cannot
1248                 * catch-up. This avoids (excessively) small writeouts
1249                 * when the bdi limits are ramping up.
1250                 */
1251                freerun = dirty_freerun_ceiling(dirty_thresh,
1252                                                background_thresh);
1253                if (nr_dirty <= freerun) {
1254                        current->dirty_paused_when = now;
1255                        current->nr_dirtied = 0;
1256                        current->nr_dirtied_pause =
1257                                dirty_poll_interval(nr_dirty, dirty_thresh);
1258                        break;
1259                }
1260
1261                if (unlikely(!writeback_in_progress(bdi)))
1262                        bdi_start_background_writeback(bdi);
1263
1264                /*
1265                 * bdi_thresh is not treated as some limiting factor as
1266                 * dirty_thresh, due to reasons
1267                 * - in JBOD setup, bdi_thresh can fluctuate a lot
1268                 * - in a system with HDD and USB key, the USB key may somehow
1269                 *   go into state (bdi_dirty >> bdi_thresh) either because
1270                 *   bdi_dirty starts high, or because bdi_thresh drops low.
1271                 *   In this case we don't want to hard throttle the USB key
1272                 *   dirtiers for 100 seconds until bdi_dirty drops under
1273                 *   bdi_thresh. Instead the auxiliary bdi control line in
1274                 *   bdi_position_ratio() will let the dirtier task progress
1275                 *   at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1276                 */
1277                bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1278
1279                /*
1280                 * In order to avoid the stacked BDI deadlock we need
1281                 * to ensure we accurately count the 'dirty' pages when
1282                 * the threshold is low.
1283                 *
1284                 * Otherwise it would be possible to get thresh+n pages
1285                 * reported dirty, even though there are thresh-m pages
1286                 * actually dirty; with m+n sitting in the percpu
1287                 * deltas.
1288                 */
1289                if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1290                        bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1291                        bdi_dirty = bdi_reclaimable +
1292                                    bdi_stat_sum(bdi, BDI_WRITEBACK);
1293                } else {
1294                        bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1295                        bdi_dirty = bdi_reclaimable +
1296                                    bdi_stat(bdi, BDI_WRITEBACK);
1297                }
1298
1299                dirty_exceeded = (bdi_dirty > bdi_thresh) &&
1300                                  (nr_dirty > dirty_thresh);
1301                if (dirty_exceeded && !bdi->dirty_exceeded)
1302                        bdi->dirty_exceeded = 1;
1303
1304                bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1305                                     nr_dirty, bdi_thresh, bdi_dirty,
1306                                     start_time);
1307
1308                dirty_ratelimit = bdi->dirty_ratelimit;
1309                pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1310                                               background_thresh, nr_dirty,
1311                                               bdi_thresh, bdi_dirty);
1312                task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1313                                                        RATELIMIT_CALC_SHIFT;
1314                max_pause = bdi_max_pause(bdi, bdi_dirty);
1315                min_pause = bdi_min_pause(bdi, max_pause,
1316                                          task_ratelimit, dirty_ratelimit,
1317                                          &nr_dirtied_pause);
1318
1319                if (unlikely(task_ratelimit == 0)) {
1320                        period = max_pause;
1321                        pause = max_pause;
1322                        goto pause;
1323                }
1324                period = HZ * pages_dirtied / task_ratelimit;
1325                pause = period;
1326                if (current->dirty_paused_when)
1327                        pause -= now - current->dirty_paused_when;
1328                /*
1329                 * For less than 1s think time (ext3/4 may block the dirtier
1330                 * for up to 800ms from time to time on 1-HDD; so does xfs,
1331                 * however at much less frequency), try to compensate it in
1332                 * future periods by updating the virtual time; otherwise just
1333                 * do a reset, as it may be a light dirtier.
1334                 */
1335                if (pause < min_pause) {
1336                        trace_balance_dirty_pages(bdi,
1337                                                  dirty_thresh,
1338                                                  background_thresh,
1339                                                  nr_dirty,
1340                                                  bdi_thresh,
1341                                                  bdi_dirty,
1342                                                  dirty_ratelimit,
1343                                                  task_ratelimit,
1344                                                  pages_dirtied,
1345                                                  period,
1346                                                  min(pause, 0L),
1347                                                  start_time);
1348                        if (pause < -HZ) {
1349                                current->dirty_paused_when = now;
1350                                current->nr_dirtied = 0;
1351                        } else if (period) {
1352                                current->dirty_paused_when += period;
1353                                current->nr_dirtied = 0;
1354                        } else if (current->nr_dirtied_pause <= pages_dirtied)
1355                                current->nr_dirtied_pause += pages_dirtied;
1356                        break;
1357                }
1358                if (unlikely(pause > max_pause)) {
1359                        /* for occasional dropped task_ratelimit */
1360                        now += min(pause - max_pause, max_pause);
1361                        pause = max_pause;
1362                }
1363
1364pause:
1365                trace_balance_dirty_pages(bdi,
1366                                          dirty_thresh,
1367                                          background_thresh,
1368                                          nr_dirty,
1369                                          bdi_thresh,
1370                                          bdi_dirty,
1371                                          dirty_ratelimit,
1372                                          task_ratelimit,
1373                                          pages_dirtied,
1374                                          period,
1375                                          pause,
1376                                          start_time);
1377                __set_current_state(TASK_KILLABLE);
1378                io_schedule_timeout(pause);
1379
1380                current->dirty_paused_when = now + pause;
1381                current->nr_dirtied = 0;
1382                current->nr_dirtied_pause = nr_dirtied_pause;
1383
1384                /*
1385                 * This is typically equal to (nr_dirty < dirty_thresh) and can
1386                 * also keep "1000+ dd on a slow USB stick" under control.
1387                 */
1388                if (task_ratelimit)
1389                        break;
1390
1391                /*
1392                 * In the case of an unresponding NFS server and the NFS dirty
1393                 * pages exceeds dirty_thresh, give the other good bdi's a pipe
1394                 * to go through, so that tasks on them still remain responsive.
1395                 *
1396                 * In theory 1 page is enough to keep the comsumer-producer
1397                 * pipe going: the flusher cleans 1 page => the task dirties 1
1398                 * more page. However bdi_dirty has accounting errors.  So use
1399                 * the larger and more IO friendly bdi_stat_error.
1400                 */
1401                if (bdi_dirty <= bdi_stat_error(bdi))
1402                        break;
1403
1404                if (fatal_signal_pending(current))
1405                        break;
1406        }
1407
1408        if (!dirty_exceeded && bdi->dirty_exceeded)
1409                bdi->dirty_exceeded = 0;
1410
1411        if (writeback_in_progress(bdi))
1412                return;
1413
1414        /*
1415         * In laptop mode, we wait until hitting the higher threshold before
1416         * starting background writeout, and then write out all the way down
1417         * to the lower threshold.  So slow writers cause minimal disk activity.
1418         *
1419         * In normal mode, we start background writeout at the lower
1420         * background_thresh, to keep the amount of dirty memory low.
1421         */
1422        if (laptop_mode)
1423                return;
1424
1425        if (nr_reclaimable > background_thresh)
1426                bdi_start_background_writeback(bdi);
1427}
1428
1429void set_page_dirty_balance(struct page *page, int page_mkwrite)
1430{
1431        if (set_page_dirty(page) || page_mkwrite) {
1432                struct address_space *mapping = page_mapping(page);
1433
1434                if (mapping)
1435                        balance_dirty_pages_ratelimited(mapping);
1436        }
1437}
1438
1439static DEFINE_PER_CPU(int, bdp_ratelimits);
1440
1441/*
1442 * Normal tasks are throttled by
1443 *      loop {
1444 *              dirty tsk->nr_dirtied_pause pages;
1445 *              take a snap in balance_dirty_pages();
1446 *      }
1447 * However there is a worst case. If every task exit immediately when dirtied
1448 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1449 * called to throttle the page dirties. The solution is to save the not yet
1450 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1451 * randomly into the running tasks. This works well for the above worst case,
1452 * as the new task will pick up and accumulate the old task's leaked dirty
1453 * count and eventually get throttled.
1454 */
1455DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1456
1457/**
1458 * balance_dirty_pages_ratelimited - balance dirty memory state
1459 * @mapping: address_space which was dirtied
1460 *
1461 * Processes which are dirtying memory should call in here once for each page
1462 * which was newly dirtied.  The function will periodically check the system's
1463 * dirty state and will initiate writeback if needed.
1464 *
1465 * On really big machines, get_writeback_state is expensive, so try to avoid
1466 * calling it too often (ratelimiting).  But once we're over the dirty memory
1467 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1468 * from overshooting the limit by (ratelimit_pages) each.
1469 */
1470void balance_dirty_pages_ratelimited(struct address_space *mapping)
1471{
1472        struct backing_dev_info *bdi = mapping->backing_dev_info;
1473        int ratelimit;
1474        int *p;
1475
1476        if (!bdi_cap_account_dirty(bdi))
1477                return;
1478
1479        ratelimit = current->nr_dirtied_pause;
1480        if (bdi->dirty_exceeded)
1481                ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1482
1483        preempt_disable();
1484        /*
1485         * This prevents one CPU to accumulate too many dirtied pages without
1486         * calling into balance_dirty_pages(), which can happen when there are
1487         * 1000+ tasks, all of them start dirtying pages at exactly the same
1488         * time, hence all honoured too large initial task->nr_dirtied_pause.
1489         */
1490        p =  &__get_cpu_var(bdp_ratelimits);
1491        if (unlikely(current->nr_dirtied >= ratelimit))
1492                *p = 0;
1493        else if (unlikely(*p >= ratelimit_pages)) {
1494                *p = 0;
1495                ratelimit = 0;
1496        }
1497        /*
1498         * Pick up the dirtied pages by the exited tasks. This avoids lots of
1499         * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1500         * the dirty throttling and livelock other long-run dirtiers.
1501         */
1502        p = &__get_cpu_var(dirty_throttle_leaks);
1503        if (*p > 0 && current->nr_dirtied < ratelimit) {
1504                unsigned long nr_pages_dirtied;
1505                nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1506                *p -= nr_pages_dirtied;
1507                current->nr_dirtied += nr_pages_dirtied;
1508        }
1509        preempt_enable();
1510
1511        if (unlikely(current->nr_dirtied >= ratelimit))
1512                balance_dirty_pages(mapping, current->nr_dirtied);
1513}
1514EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1515
1516void throttle_vm_writeout(gfp_t gfp_mask)
1517{
1518        unsigned long background_thresh;
1519        unsigned long dirty_thresh;
1520
1521        for ( ; ; ) {
1522                global_dirty_limits(&background_thresh, &dirty_thresh);
1523                dirty_thresh = hard_dirty_limit(dirty_thresh);
1524
1525                /*
1526                 * Boost the allowable dirty threshold a bit for page
1527                 * allocators so they don't get DoS'ed by heavy writers
1528                 */
1529                dirty_thresh += dirty_thresh / 10;      /* wheeee... */
1530
1531                if (global_page_state(NR_UNSTABLE_NFS) +
1532                        global_page_state(NR_WRITEBACK) <= dirty_thresh)
1533                                break;
1534                congestion_wait(BLK_RW_ASYNC, HZ/10);
1535
1536                /*
1537                 * The caller might hold locks which can prevent IO completion
1538                 * or progress in the filesystem.  So we cannot just sit here
1539                 * waiting for IO to complete.
1540                 */
1541                if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1542                        break;
1543        }
1544}
1545
1546/*
1547 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1548 */
1549int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1550        void __user *buffer, size_t *length, loff_t *ppos)
1551{
1552        proc_dointvec(table, write, buffer, length, ppos);
1553        return 0;
1554}
1555
1556#ifdef CONFIG_BLOCK
1557void laptop_mode_timer_fn(unsigned long data)
1558{
1559        struct request_queue *q = (struct request_queue *)data;
1560        int nr_pages = global_page_state(NR_FILE_DIRTY) +
1561                global_page_state(NR_UNSTABLE_NFS);
1562
1563        /*
1564         * We want to write everything out, not just down to the dirty
1565         * threshold
1566         */
1567        if (bdi_has_dirty_io(&q->backing_dev_info))
1568                bdi_start_writeback(&q->backing_dev_info, nr_pages,
1569                                        WB_REASON_LAPTOP_TIMER);
1570}
1571
1572/*
1573 * We've spun up the disk and we're in laptop mode: schedule writeback
1574 * of all dirty data a few seconds from now.  If the flush is already scheduled
1575 * then push it back - the user is still using the disk.
1576 */
1577void laptop_io_completion(struct backing_dev_info *info)
1578{
1579        mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1580}
1581
1582/*
1583 * We're in laptop mode and we've just synced. The sync's writes will have
1584 * caused another writeback to be scheduled by laptop_io_completion.
1585 * Nothing needs to be written back anymore, so we unschedule the writeback.
1586 */
1587void laptop_sync_completion(void)
1588{
1589        struct backing_dev_info *bdi;
1590
1591        rcu_read_lock();
1592
1593        list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1594                del_timer(&bdi->laptop_mode_wb_timer);
1595
1596        rcu_read_unlock();
1597}
1598#endif
1599
1600/*
1601 * If ratelimit_pages is too high then we can get into dirty-data overload
1602 * if a large number of processes all perform writes at the same time.
1603 * If it is too low then SMP machines will call the (expensive)
1604 * get_writeback_state too often.
1605 *
1606 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1607 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1608 * thresholds.
1609 */
1610
1611void writeback_set_ratelimit(void)
1612{
1613        unsigned long background_thresh;
1614        unsigned long dirty_thresh;
1615        global_dirty_limits(&background_thresh, &dirty_thresh);
1616        global_dirty_limit = dirty_thresh;
1617        ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1618        if (ratelimit_pages < 16)
1619                ratelimit_pages = 16;
1620}
1621
1622static int
1623ratelimit_handler(struct notifier_block *self, unsigned long action,
1624                  void *hcpu)
1625{
1626
1627        switch (action & ~CPU_TASKS_FROZEN) {
1628        case CPU_ONLINE:
1629        case CPU_DEAD:
1630                writeback_set_ratelimit();
1631                return NOTIFY_OK;
1632        default:
1633                return NOTIFY_DONE;
1634        }
1635}
1636
1637static struct notifier_block ratelimit_nb = {
1638        .notifier_call  = ratelimit_handler,
1639        .next           = NULL,
1640};
1641
1642/*
1643 * Called early on to tune the page writeback dirty limits.
1644 *
1645 * We used to scale dirty pages according to how total memory
1646 * related to pages that could be allocated for buffers (by
1647 * comparing nr_free_buffer_pages() to vm_total_pages.
1648 *
1649 * However, that was when we used "dirty_ratio" to scale with
1650 * all memory, and we don't do that any more. "dirty_ratio"
1651 * is now applied to total non-HIGHPAGE memory (by subtracting
1652 * totalhigh_pages from vm_total_pages), and as such we can't
1653 * get into the old insane situation any more where we had
1654 * large amounts of dirty pages compared to a small amount of
1655 * non-HIGHMEM memory.
1656 *
1657 * But we might still want to scale the dirty_ratio by how
1658 * much memory the box has..
1659 */
1660void __init page_writeback_init(void)
1661{
1662        writeback_set_ratelimit();
1663        register_cpu_notifier(&ratelimit_nb);
1664
1665        fprop_global_init(&writeout_completions);
1666}
1667
1668/**
1669 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1670 * @mapping: address space structure to write
1671 * @start: starting page index
1672 * @end: ending page index (inclusive)
1673 *
1674 * This function scans the page range from @start to @end (inclusive) and tags
1675 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1676 * that write_cache_pages (or whoever calls this function) will then use
1677 * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
1678 * used to avoid livelocking of writeback by a process steadily creating new
1679 * dirty pages in the file (thus it is important for this function to be quick
1680 * so that it can tag pages faster than a dirtying process can create them).
1681 */
1682/*
1683 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1684 */
1685void tag_pages_for_writeback(struct address_space *mapping,
1686                             pgoff_t start, pgoff_t end)
1687{
1688#define WRITEBACK_TAG_BATCH 4096
1689        unsigned long tagged;
1690
1691        do {
1692                spin_lock_irq(&mapping->tree_lock);
1693                tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1694                                &start, end, WRITEBACK_TAG_BATCH,
1695                                PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1696                spin_unlock_irq(&mapping->tree_lock);
1697                WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1698                cond_resched();
1699                /* We check 'start' to handle wrapping when end == ~0UL */
1700        } while (tagged >= WRITEBACK_TAG_BATCH && start);
1701}
1702EXPORT_SYMBOL(tag_pages_for_writeback);
1703
1704/**
1705 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1706 * @mapping: address space structure to write
1707 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1708 * @writepage: function called for each page
1709 * @data: data passed to writepage function
1710 *
1711 * If a page is already under I/O, write_cache_pages() skips it, even
1712 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
1713 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
1714 * and msync() need to guarantee that all the data which was dirty at the time
1715 * the call was made get new I/O started against them.  If wbc->sync_mode is
1716 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1717 * existing IO to complete.
1718 *
1719 * To avoid livelocks (when other process dirties new pages), we first tag
1720 * pages which should be written back with TOWRITE tag and only then start
1721 * writing them. For data-integrity sync we have to be careful so that we do
1722 * not miss some pages (e.g., because some other process has cleared TOWRITE
1723 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1724 * by the process clearing the DIRTY tag (and submitting the page for IO).
1725 */
1726int write_cache_pages(struct address_space *mapping,
1727                      struct writeback_control *wbc, writepage_t writepage,
1728                      void *data)
1729{
1730        int ret = 0;
1731        int done = 0;
1732        struct pagevec pvec;
1733        int nr_pages;
1734        pgoff_t uninitialized_var(writeback_index);
1735        pgoff_t index;
1736        pgoff_t end;            /* Inclusive */
1737        pgoff_t done_index;
1738        int cycled;
1739        int range_whole = 0;
1740        int tag;
1741
1742        pagevec_init(&pvec, 0);
1743        if (wbc->range_cyclic) {
1744                writeback_index = mapping->writeback_index; /* prev offset */
1745                index = writeback_index;
1746                if (index == 0)
1747                        cycled = 1;
1748                else
1749                        cycled = 0;
1750                end = -1;
1751        } else {
1752                index = wbc->range_start >> PAGE_CACHE_SHIFT;
1753                end = wbc->range_end >> PAGE_CACHE_SHIFT;
1754                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1755                        range_whole = 1;
1756                cycled = 1; /* ignore range_cyclic tests */
1757        }
1758        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1759                tag = PAGECACHE_TAG_TOWRITE;
1760        else
1761                tag = PAGECACHE_TAG_DIRTY;
1762retry:
1763        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1764                tag_pages_for_writeback(mapping, index, end);
1765        done_index = index;
1766        while (!done && (index <= end)) {
1767                int i;
1768
1769                nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1770                              min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1771                if (nr_pages == 0)
1772                        break;
1773
1774                for (i = 0; i < nr_pages; i++) {
1775                        struct page *page = pvec.pages[i];
1776
1777                        /*
1778                         * At this point, the page may be truncated or
1779                         * invalidated (changing page->mapping to NULL), or
1780                         * even swizzled back from swapper_space to tmpfs file
1781                         * mapping. However, page->index will not change
1782                         * because we have a reference on the page.
1783                         */
1784                        if (page->index > end) {
1785                                /*
1786                                 * can't be range_cyclic (1st pass) because
1787                                 * end == -1 in that case.
1788                                 */
1789                                done = 1;
1790                                break;
1791                        }
1792
1793                        done_index = page->index;
1794
1795                        lock_page(page);
1796
1797                        /*
1798                         * Page truncated or invalidated. We can freely skip it
1799                         * then, even for data integrity operations: the page
1800                         * has disappeared concurrently, so there could be no
1801                         * real expectation of this data interity operation
1802                         * even if there is now a new, dirty page at the same
1803                         * pagecache address.
1804                         */
1805                        if (unlikely(page->mapping != mapping)) {
1806continue_unlock:
1807                                unlock_page(page);
1808                                continue;
1809                        }
1810
1811                        if (!PageDirty(page)) {
1812                                /* someone wrote it for us */
1813                                goto continue_unlock;
1814                        }
1815
1816                        if (PageWriteback(page)) {
1817                                if (wbc->sync_mode != WB_SYNC_NONE)
1818                                        wait_on_page_writeback(page);
1819                                else
1820                                        goto continue_unlock;
1821                        }
1822
1823                        BUG_ON(PageWriteback(page));
1824                        if (!clear_page_dirty_for_io(page))
1825                                goto continue_unlock;
1826
1827                        trace_wbc_writepage(wbc, mapping->backing_dev_info);
1828                        ret = (*writepage)(page, wbc, data);
1829                        if (unlikely(ret)) {
1830                                if (ret == AOP_WRITEPAGE_ACTIVATE) {
1831                                        unlock_page(page);
1832                                        ret = 0;
1833                                } else {
1834                                        /*
1835                                         * done_index is set past this page,
1836                                         * so media errors will not choke
1837                                         * background writeout for the entire
1838                                         * file. This has consequences for
1839                                         * range_cyclic semantics (ie. it may
1840                                         * not be suitable for data integrity
1841                                         * writeout).
1842                                         */
1843                                        done_index = page->index + 1;
1844                                        done = 1;
1845                                        break;
1846                                }
1847                        }
1848
1849                        /*
1850                         * We stop writing back only if we are not doing
1851                         * integrity sync. In case of integrity sync we have to
1852                         * keep going until we have written all the pages
1853                         * we tagged for writeback prior to entering this loop.
1854                         */
1855                        if (--wbc->nr_to_write <= 0 &&
1856                            wbc->sync_mode == WB_SYNC_NONE) {
1857                                done = 1;
1858                                break;
1859                        }
1860                }
1861                pagevec_release(&pvec);
1862                cond_resched();
1863        }
1864        if (!cycled && !done) {
1865                /*
1866                 * range_cyclic:
1867                 * We hit the last page and there is more work to be done: wrap
1868                 * back to the start of the file
1869                 */
1870                cycled = 1;
1871                index = 0;
1872                end = writeback_index - 1;
1873                goto retry;
1874        }
1875        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1876                mapping->writeback_index = done_index;
1877
1878        return ret;
1879}
1880EXPORT_SYMBOL(write_cache_pages);
1881
1882/*
1883 * Function used by generic_writepages to call the real writepage
1884 * function and set the mapping flags on error
1885 */
1886static int __writepage(struct page *page, struct writeback_control *wbc,
1887                       void *data)
1888{
1889        struct address_space *mapping = data;
1890        int ret = mapping->a_ops->writepage(page, wbc);
1891        mapping_set_error(mapping, ret);
1892        return ret;
1893}
1894
1895/**
1896 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1897 * @mapping: address space structure to write
1898 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1899 *
1900 * This is a library function, which implements the writepages()
1901 * address_space_operation.
1902 */
1903int generic_writepages(struct address_space *mapping,
1904                       struct writeback_control *wbc)
1905{
1906        struct blk_plug plug;
1907        int ret;
1908
1909        /* deal with chardevs and other special file */
1910        if (!mapping->a_ops->writepage)
1911                return 0;
1912
1913        blk_start_plug(&plug);
1914        ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1915        blk_finish_plug(&plug);
1916        return ret;
1917}
1918
1919EXPORT_SYMBOL(generic_writepages);
1920
1921int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1922{
1923        int ret;
1924
1925        if (wbc->nr_to_write <= 0)
1926                return 0;
1927        if (mapping->a_ops->writepages)
1928                ret = mapping->a_ops->writepages(mapping, wbc);
1929        else
1930                ret = generic_writepages(mapping, wbc);
1931        return ret;
1932}
1933
1934/**
1935 * write_one_page - write out a single page and optionally wait on I/O
1936 * @page: the page to write
1937 * @wait: if true, wait on writeout
1938 *
1939 * The page must be locked by the caller and will be unlocked upon return.
1940 *
1941 * write_one_page() returns a negative error code if I/O failed.
1942 */
1943int write_one_page(struct page *page, int wait)
1944{
1945        struct address_space *mapping = page->mapping;
1946        int ret = 0;
1947        struct writeback_control wbc = {
1948                .sync_mode = WB_SYNC_ALL,
1949                .nr_to_write = 1,
1950        };
1951
1952        BUG_ON(!PageLocked(page));
1953
1954        if (wait)
1955                wait_on_page_writeback(page);
1956
1957        if (clear_page_dirty_for_io(page)) {
1958                page_cache_get(page);
1959                ret = mapping->a_ops->writepage(page, &wbc);
1960                if (ret == 0 && wait) {
1961                        wait_on_page_writeback(page);
1962                        if (PageError(page))
1963                                ret = -EIO;
1964                }
1965                page_cache_release(page);
1966        } else {
1967                unlock_page(page);
1968        }
1969        return ret;
1970}
1971EXPORT_SYMBOL(write_one_page);
1972
1973/*
1974 * For address_spaces which do not use buffers nor write back.
1975 */
1976int __set_page_dirty_no_writeback(struct page *page)
1977{
1978        if (!PageDirty(page))
1979                return !TestSetPageDirty(page);
1980        return 0;
1981}
1982
1983/*
1984 * Helper function for set_page_dirty family.
1985 * NOTE: This relies on being atomic wrt interrupts.
1986 */
1987void account_page_dirtied(struct page *page, struct address_space *mapping)
1988{
1989        trace_writeback_dirty_page(page, mapping);
1990
1991        if (mapping_cap_account_dirty(mapping)) {
1992                __inc_zone_page_state(page, NR_FILE_DIRTY);
1993                __inc_zone_page_state(page, NR_DIRTIED);
1994                __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1995                __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
1996                task_io_account_write(PAGE_CACHE_SIZE);
1997                current->nr_dirtied++;
1998                this_cpu_inc(bdp_ratelimits);
1999        }
2000}
2001EXPORT_SYMBOL(account_page_dirtied);
2002
2003/*
2004 * Helper function for set_page_writeback family.
2005 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
2006 * wrt interrupts.
2007 */
2008void account_page_writeback(struct page *page)
2009{
2010        inc_zone_page_state(page, NR_WRITEBACK);
2011}
2012EXPORT_SYMBOL(account_page_writeback);
2013
2014/*
2015 * For address_spaces which do not use buffers.  Just tag the page as dirty in
2016 * its radix tree.
2017 *
2018 * This is also used when a single buffer is being dirtied: we want to set the
2019 * page dirty in that case, but not all the buffers.  This is a "bottom-up"
2020 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2021 *
2022 * Most callers have locked the page, which pins the address_space in memory.
2023 * But zap_pte_range() does not lock the page, however in that case the
2024 * mapping is pinned by the vma's ->vm_file reference.
2025 *
2026 * We take care to handle the case where the page was truncated from the
2027 * mapping by re-checking page_mapping() inside tree_lock.
2028 */
2029int __set_page_dirty_nobuffers(struct page *page)
2030{
2031        if (!TestSetPageDirty(page)) {
2032                struct address_space *mapping = page_mapping(page);
2033                struct address_space *mapping2;
2034
2035                if (!mapping)
2036                        return 1;
2037
2038                spin_lock_irq(&mapping->tree_lock);
2039                mapping2 = page_mapping(page);
2040                if (mapping2) { /* Race with truncate? */
2041                        BUG_ON(mapping2 != mapping);
2042                        WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2043                        account_page_dirtied(page, mapping);
2044                        radix_tree_tag_set(&mapping->page_tree,
2045                                page_index(page), PAGECACHE_TAG_DIRTY);
2046                }
2047                spin_unlock_irq(&mapping->tree_lock);
2048                if (mapping->host) {
2049                        /* !PageAnon && !swapper_space */
2050                        __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2051                }
2052                return 1;
2053        }
2054        return 0;
2055}
2056EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2057
2058/*
2059 * Call this whenever redirtying a page, to de-account the dirty counters
2060 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2061 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2062 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2063 * control.
2064 */
2065void account_page_redirty(struct page *page)
2066{
2067        struct address_space *mapping = page->mapping;
2068        if (mapping && mapping_cap_account_dirty(mapping)) {
2069                current->nr_dirtied--;
2070                dec_zone_page_state(page, NR_DIRTIED);
2071                dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2072        }
2073}
2074EXPORT_SYMBOL(account_page_redirty);
2075
2076/*
2077 * When a writepage implementation decides that it doesn't want to write this
2078 * page for some reason, it should redirty the locked page via
2079 * redirty_page_for_writepage() and it should then unlock the page and return 0
2080 */
2081int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2082{
2083        wbc->pages_skipped++;
2084        account_page_redirty(page);
2085        return __set_page_dirty_nobuffers(page);
2086}
2087EXPORT_SYMBOL(redirty_page_for_writepage);
2088
2089/*
2090 * Dirty a page.
2091 *
2092 * For pages with a mapping this should be done under the page lock
2093 * for the benefit of asynchronous memory errors who prefer a consistent
2094 * dirty state. This rule can be broken in some special cases,
2095 * but should be better not to.
2096 *
2097 * If the mapping doesn't provide a set_page_dirty a_op, then
2098 * just fall through and assume that it wants buffer_heads.
2099 */
2100int set_page_dirty(struct page *page)
2101{
2102        struct address_space *mapping = page_mapping(page);
2103
2104        if (likely(mapping)) {
2105                int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2106                /*
2107                 * readahead/lru_deactivate_page could remain
2108                 * PG_readahead/PG_reclaim due to race with end_page_writeback
2109                 * About readahead, if the page is written, the flags would be
2110                 * reset. So no problem.
2111                 * About lru_deactivate_page, if the page is redirty, the flag
2112                 * will be reset. So no problem. but if the page is used by readahead
2113                 * it will confuse readahead and make it restart the size rampup
2114                 * process. But it's a trivial problem.
2115                 */
2116                ClearPageReclaim(page);
2117#ifdef CONFIG_BLOCK
2118                if (!spd)
2119                        spd = __set_page_dirty_buffers;
2120#endif
2121                return (*spd)(page);
2122        }
2123        if (!PageDirty(page)) {
2124                if (!TestSetPageDirty(page))
2125                        return 1;
2126        }
2127        return 0;
2128}
2129EXPORT_SYMBOL(set_page_dirty);
2130
2131/*
2132 * set_page_dirty() is racy if the caller has no reference against
2133 * page->mapping->host, and if the page is unlocked.  This is because another
2134 * CPU could truncate the page off the mapping and then free the mapping.
2135 *
2136 * Usually, the page _is_ locked, or the caller is a user-space process which
2137 * holds a reference on the inode by having an open file.
2138 *
2139 * In other cases, the page should be locked before running set_page_dirty().
2140 */
2141int set_page_dirty_lock(struct page *page)
2142{
2143        int ret;
2144
2145        lock_page(page);
2146        ret = set_page_dirty(page);
2147        unlock_page(page);
2148        return ret;
2149}
2150EXPORT_SYMBOL(set_page_dirty_lock);
2151
2152/*
2153 * Clear a page's dirty flag, while caring for dirty memory accounting.
2154 * Returns true if the page was previously dirty.
2155 *
2156 * This is for preparing to put the page under writeout.  We leave the page
2157 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2158 * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
2159 * implementation will run either set_page_writeback() or set_page_dirty(),
2160 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2161 * back into sync.
2162 *
2163 * This incoherency between the page's dirty flag and radix-tree tag is
2164 * unfortunate, but it only exists while the page is locked.
2165 */
2166int clear_page_dirty_for_io(struct page *page)
2167{
2168        struct address_space *mapping = page_mapping(page);
2169
2170        BUG_ON(!PageLocked(page));
2171
2172        if (mapping && mapping_cap_account_dirty(mapping)) {
2173                /*
2174                 * Yes, Virginia, this is indeed insane.
2175                 *
2176                 * We use this sequence to make sure that
2177                 *  (a) we account for dirty stats properly
2178                 *  (b) we tell the low-level filesystem to
2179                 *      mark the whole page dirty if it was
2180                 *      dirty in a pagetable. Only to then
2181                 *  (c) clean the page again and return 1 to
2182                 *      cause the writeback.
2183                 *
2184                 * This way we avoid all nasty races with the
2185                 * dirty bit in multiple places and clearing
2186                 * them concurrently from different threads.
2187                 *
2188                 * Note! Normally the "set_page_dirty(page)"
2189                 * has no effect on the actual dirty bit - since
2190                 * that will already usually be set. But we
2191                 * need the side effects, and it can help us
2192                 * avoid races.
2193                 *
2194                 * We basically use the page "master dirty bit"
2195                 * as a serialization point for all the different
2196                 * threads doing their things.
2197                 */
2198                if (page_mkclean(page))
2199                        set_page_dirty(page);
2200                /*
2201                 * We carefully synchronise fault handlers against
2202                 * installing a dirty pte and marking the page dirty
2203                 * at this point. We do this by having them hold the
2204                 * page lock at some point after installing their
2205                 * pte, but before marking the page dirty.
2206                 * Pages are always locked coming in here, so we get
2207                 * the desired exclusion. See mm/memory.c:do_wp_page()
2208                 * for more comments.
2209                 */
2210                if (TestClearPageDirty(page)) {
2211                        dec_zone_page_state(page, NR_FILE_DIRTY);
2212                        dec_bdi_stat(mapping->backing_dev_info,
2213                                        BDI_RECLAIMABLE);
2214                        return 1;
2215                }
2216                return 0;
2217        }
2218        return TestClearPageDirty(page);
2219}
2220EXPORT_SYMBOL(clear_page_dirty_for_io);
2221
2222int test_clear_page_writeback(struct page *page)
2223{
2224        struct address_space *mapping = page_mapping(page);
2225        int ret;
2226
2227        if (mapping) {
2228                struct backing_dev_info *bdi = mapping->backing_dev_info;
2229                unsigned long flags;
2230
2231                spin_lock_irqsave(&mapping->tree_lock, flags);
2232                ret = TestClearPageWriteback(page);
2233                if (ret) {
2234                        radix_tree_tag_clear(&mapping->page_tree,
2235                                                page_index(page),
2236                                                PAGECACHE_TAG_WRITEBACK);
2237                        if (bdi_cap_account_writeback(bdi)) {
2238                                __dec_bdi_stat(bdi, BDI_WRITEBACK);
2239                                __bdi_writeout_inc(bdi);
2240                        }
2241                }
2242                spin_unlock_irqrestore(&mapping->tree_lock, flags);
2243        } else {
2244                ret = TestClearPageWriteback(page);
2245        }
2246        if (ret) {
2247                dec_zone_page_state(page, NR_WRITEBACK);
2248                inc_zone_page_state(page, NR_WRITTEN);
2249        }
2250        return ret;
2251}
2252
2253int test_set_page_writeback(struct page *page)
2254{
2255        struct address_space *mapping = page_mapping(page);
2256        int ret;
2257
2258        if (mapping) {
2259                struct backing_dev_info *bdi = mapping->backing_dev_info;
2260                unsigned long flags;
2261
2262                spin_lock_irqsave(&mapping->tree_lock, flags);
2263                ret = TestSetPageWriteback(page);
2264                if (!ret) {
2265                        radix_tree_tag_set(&mapping->page_tree,
2266                                                page_index(page),
2267                                                PAGECACHE_TAG_WRITEBACK);
2268                        if (bdi_cap_account_writeback(bdi))
2269                                __inc_bdi_stat(bdi, BDI_WRITEBACK);
2270                }
2271                if (!PageDirty(page))
2272                        radix_tree_tag_clear(&mapping->page_tree,
2273                                                page_index(page),
2274                                                PAGECACHE_TAG_DIRTY);
2275                radix_tree_tag_clear(&mapping->page_tree,
2276                                     page_index(page),
2277                                     PAGECACHE_TAG_TOWRITE);
2278                spin_unlock_irqrestore(&mapping->tree_lock, flags);
2279        } else {
2280                ret = TestSetPageWriteback(page);
2281        }
2282        if (!ret)
2283                account_page_writeback(page);
2284        return ret;
2285
2286}
2287EXPORT_SYMBOL(test_set_page_writeback);
2288
2289/*
2290 * Return true if any of the pages in the mapping are marked with the
2291 * passed tag.
2292 */
2293int mapping_tagged(struct address_space *mapping, int tag)
2294{
2295        return radix_tree_tagged(&mapping->page_tree, tag);
2296}
2297EXPORT_SYMBOL(mapping_tagged);
2298
2299/**
2300 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2301 * @page:       The page to wait on.
2302 *
2303 * This function determines if the given page is related to a backing device
2304 * that requires page contents to be held stable during writeback.  If so, then
2305 * it will wait for any pending writeback to complete.
2306 */
2307void wait_for_stable_page(struct page *page)
2308{
2309        struct address_space *mapping = page_mapping(page);
2310        struct backing_dev_info *bdi = mapping->backing_dev_info;
2311
2312        if (!bdi_cap_stable_pages_required(bdi))
2313                return;
2314
2315        wait_on_page_writeback(page);
2316}
2317EXPORT_SYMBOL_GPL(wait_for_stable_page);
2318
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