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