linux/mm/page-writeback.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * mm/page-writeback.c
   4 *
   5 * Copyright (C) 2002, Linus Torvalds.
   6 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
   7 *
   8 * Contains functions related to writing back dirty pages at the
   9 * address_space level.
  10 *
  11 * 10Apr2002    Andrew Morton
  12 *              Initial version
  13 */
  14
  15#include <linux/kernel.h>
  16#include <linux/export.h>
  17#include <linux/spinlock.h>
  18#include <linux/fs.h>
  19#include <linux/mm.h>
  20#include <linux/swap.h>
  21#include <linux/slab.h>
  22#include <linux/pagemap.h>
  23#include <linux/writeback.h>
  24#include <linux/init.h>
  25#include <linux/backing-dev.h>
  26#include <linux/task_io_accounting_ops.h>
  27#include <linux/blkdev.h>
  28#include <linux/mpage.h>
  29#include <linux/rmap.h>
  30#include <linux/percpu.h>
  31#include <linux/smp.h>
  32#include <linux/sysctl.h>
  33#include <linux/cpu.h>
  34#include <linux/syscalls.h>
  35#include <linux/pagevec.h>
  36#include <linux/timer.h>
  37#include <linux/sched/rt.h>
  38#include <linux/sched/signal.h>
  39#include <linux/mm_inline.h>
  40#include <trace/events/writeback.h>
  41
  42#include "internal.h"
  43
  44/*
  45 * Sleep at most 200ms at a time in balance_dirty_pages().
  46 */
  47#define MAX_PAUSE               max(HZ/5, 1)
  48
  49/*
  50 * Try to keep balance_dirty_pages() call intervals higher than this many pages
  51 * by raising pause time to max_pause when falls below it.
  52 */
  53#define DIRTY_POLL_THRESH       (128 >> (PAGE_SHIFT - 10))
  54
  55/*
  56 * Estimate write bandwidth at 200ms intervals.
  57 */
  58#define BANDWIDTH_INTERVAL      max(HZ/5, 1)
  59
  60#define RATELIMIT_CALC_SHIFT    10
  61
  62/*
  63 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
  64 * will look to see if it needs to force writeback or throttling.
  65 */
  66static long ratelimit_pages = 32;
  67
  68/* The following parameters are exported via /proc/sys/vm */
  69
  70/*
  71 * Start background writeback (via writeback threads) at this percentage
  72 */
  73int dirty_background_ratio = 10;
  74
  75/*
  76 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
  77 * dirty_background_ratio * the amount of dirtyable memory
  78 */
  79unsigned long dirty_background_bytes;
  80
  81/*
  82 * free highmem will not be subtracted from the total free memory
  83 * for calculating free ratios if vm_highmem_is_dirtyable is true
  84 */
  85int vm_highmem_is_dirtyable;
  86
  87/*
  88 * The generator of dirty data starts writeback at this percentage
  89 */
  90int vm_dirty_ratio = 20;
  91
  92/*
  93 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
  94 * vm_dirty_ratio * the amount of dirtyable memory
  95 */
  96unsigned long vm_dirty_bytes;
  97
  98/*
  99 * The interval between `kupdate'-style writebacks
 100 */
 101unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
 102
 103EXPORT_SYMBOL_GPL(dirty_writeback_interval);
 104
 105/*
 106 * The longest time for which data is allowed to remain dirty
 107 */
 108unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
 109
 110/*
 111 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
 112 * a full sync is triggered after this time elapses without any disk activity.
 113 */
 114int laptop_mode;
 115
 116EXPORT_SYMBOL(laptop_mode);
 117
 118/* End of sysctl-exported parameters */
 119
 120struct wb_domain global_wb_domain;
 121
 122/* consolidated parameters for balance_dirty_pages() and its subroutines */
 123struct dirty_throttle_control {
 124#ifdef CONFIG_CGROUP_WRITEBACK
 125        struct wb_domain        *dom;
 126        struct dirty_throttle_control *gdtc;    /* only set in memcg dtc's */
 127#endif
 128        struct bdi_writeback    *wb;
 129        struct fprop_local_percpu *wb_completions;
 130
 131        unsigned long           avail;          /* dirtyable */
 132        unsigned long           dirty;          /* file_dirty + write + nfs */
 133        unsigned long           thresh;         /* dirty threshold */
 134        unsigned long           bg_thresh;      /* dirty background threshold */
 135
 136        unsigned long           wb_dirty;       /* per-wb counterparts */
 137        unsigned long           wb_thresh;
 138        unsigned long           wb_bg_thresh;
 139
 140        unsigned long           pos_ratio;
 141};
 142
 143/*
 144 * Length of period for aging writeout fractions of bdis. This is an
 145 * arbitrarily chosen number. The longer the period, the slower fractions will
 146 * reflect changes in current writeout rate.
 147 */
 148#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
 149
 150#ifdef CONFIG_CGROUP_WRITEBACK
 151
 152#define GDTC_INIT(__wb)         .wb = (__wb),                           \
 153                                .dom = &global_wb_domain,               \
 154                                .wb_completions = &(__wb)->completions
 155
 156#define GDTC_INIT_NO_WB         .dom = &global_wb_domain
 157
 158#define MDTC_INIT(__wb, __gdtc) .wb = (__wb),                           \
 159                                .dom = mem_cgroup_wb_domain(__wb),      \
 160                                .wb_completions = &(__wb)->memcg_completions, \
 161                                .gdtc = __gdtc
 162
 163static bool mdtc_valid(struct dirty_throttle_control *dtc)
 164{
 165        return dtc->dom;
 166}
 167
 168static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
 169{
 170        return dtc->dom;
 171}
 172
 173static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
 174{
 175        return mdtc->gdtc;
 176}
 177
 178static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
 179{
 180        return &wb->memcg_completions;
 181}
 182
 183static void wb_min_max_ratio(struct bdi_writeback *wb,
 184                             unsigned long *minp, unsigned long *maxp)
 185{
 186        unsigned long this_bw = wb->avg_write_bandwidth;
 187        unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
 188        unsigned long long min = wb->bdi->min_ratio;
 189        unsigned long long max = wb->bdi->max_ratio;
 190
 191        /*
 192         * @wb may already be clean by the time control reaches here and
 193         * the total may not include its bw.
 194         */
 195        if (this_bw < tot_bw) {
 196                if (min) {
 197                        min *= this_bw;
 198                        min = div64_ul(min, tot_bw);
 199                }
 200                if (max < 100) {
 201                        max *= this_bw;
 202                        max = div64_ul(max, tot_bw);
 203                }
 204        }
 205
 206        *minp = min;
 207        *maxp = max;
 208}
 209
 210#else   /* CONFIG_CGROUP_WRITEBACK */
 211
 212#define GDTC_INIT(__wb)         .wb = (__wb),                           \
 213                                .wb_completions = &(__wb)->completions
 214#define GDTC_INIT_NO_WB
 215#define MDTC_INIT(__wb, __gdtc)
 216
 217static bool mdtc_valid(struct dirty_throttle_control *dtc)
 218{
 219        return false;
 220}
 221
 222static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
 223{
 224        return &global_wb_domain;
 225}
 226
 227static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
 228{
 229        return NULL;
 230}
 231
 232static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
 233{
 234        return NULL;
 235}
 236
 237static void wb_min_max_ratio(struct bdi_writeback *wb,
 238                             unsigned long *minp, unsigned long *maxp)
 239{
 240        *minp = wb->bdi->min_ratio;
 241        *maxp = wb->bdi->max_ratio;
 242}
 243
 244#endif  /* CONFIG_CGROUP_WRITEBACK */
 245
 246/*
 247 * In a memory zone, there is a certain amount of pages we consider
 248 * available for the page cache, which is essentially the number of
 249 * free and reclaimable pages, minus some zone reserves to protect
 250 * lowmem and the ability to uphold the zone's watermarks without
 251 * requiring writeback.
 252 *
 253 * This number of dirtyable pages is the base value of which the
 254 * user-configurable dirty ratio is the effective number of pages that
 255 * are allowed to be actually dirtied.  Per individual zone, or
 256 * globally by using the sum of dirtyable pages over all zones.
 257 *
 258 * Because the user is allowed to specify the dirty limit globally as
 259 * absolute number of bytes, calculating the per-zone dirty limit can
 260 * require translating the configured limit into a percentage of
 261 * global dirtyable memory first.
 262 */
 263
 264/**
 265 * node_dirtyable_memory - number of dirtyable pages in a node
 266 * @pgdat: the node
 267 *
 268 * Return: the node's number of pages potentially available for dirty
 269 * page cache.  This is the base value for the per-node dirty limits.
 270 */
 271static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
 272{
 273        unsigned long nr_pages = 0;
 274        int z;
 275
 276        for (z = 0; z < MAX_NR_ZONES; z++) {
 277                struct zone *zone = pgdat->node_zones + z;
 278
 279                if (!populated_zone(zone))
 280                        continue;
 281
 282                nr_pages += zone_page_state(zone, NR_FREE_PAGES);
 283        }
 284
 285        /*
 286         * Pages reserved for the kernel should not be considered
 287         * dirtyable, to prevent a situation where reclaim has to
 288         * clean pages in order to balance the zones.
 289         */
 290        nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
 291
 292        nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
 293        nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
 294
 295        return nr_pages;
 296}
 297
 298static unsigned long highmem_dirtyable_memory(unsigned long total)
 299{
 300#ifdef CONFIG_HIGHMEM
 301        int node;
 302        unsigned long x = 0;
 303        int i;
 304
 305        for_each_node_state(node, N_HIGH_MEMORY) {
 306                for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
 307                        struct zone *z;
 308                        unsigned long nr_pages;
 309
 310                        if (!is_highmem_idx(i))
 311                                continue;
 312
 313                        z = &NODE_DATA(node)->node_zones[i];
 314                        if (!populated_zone(z))
 315                                continue;
 316
 317                        nr_pages = zone_page_state(z, NR_FREE_PAGES);
 318                        /* watch for underflows */
 319                        nr_pages -= min(nr_pages, high_wmark_pages(z));
 320                        nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
 321                        nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
 322                        x += nr_pages;
 323                }
 324        }
 325
 326        /*
 327         * Unreclaimable memory (kernel memory or anonymous memory
 328         * without swap) can bring down the dirtyable pages below
 329         * the zone's dirty balance reserve and the above calculation
 330         * will underflow.  However we still want to add in nodes
 331         * which are below threshold (negative values) to get a more
 332         * accurate calculation but make sure that the total never
 333         * underflows.
 334         */
 335        if ((long)x < 0)
 336                x = 0;
 337
 338        /*
 339         * Make sure that the number of highmem pages is never larger
 340         * than the number of the total dirtyable memory. This can only
 341         * occur in very strange VM situations but we want to make sure
 342         * that this does not occur.
 343         */
 344        return min(x, total);
 345#else
 346        return 0;
 347#endif
 348}
 349
 350/**
 351 * global_dirtyable_memory - number of globally dirtyable pages
 352 *
 353 * Return: the global number of pages potentially available for dirty
 354 * page cache.  This is the base value for the global dirty limits.
 355 */
 356static unsigned long global_dirtyable_memory(void)
 357{
 358        unsigned long x;
 359
 360        x = global_zone_page_state(NR_FREE_PAGES);
 361        /*
 362         * Pages reserved for the kernel should not be considered
 363         * dirtyable, to prevent a situation where reclaim has to
 364         * clean pages in order to balance the zones.
 365         */
 366        x -= min(x, totalreserve_pages);
 367
 368        x += global_node_page_state(NR_INACTIVE_FILE);
 369        x += global_node_page_state(NR_ACTIVE_FILE);
 370
 371        if (!vm_highmem_is_dirtyable)
 372                x -= highmem_dirtyable_memory(x);
 373
 374        return x + 1;   /* Ensure that we never return 0 */
 375}
 376
 377/**
 378 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
 379 * @dtc: dirty_throttle_control of interest
 380 *
 381 * Calculate @dtc->thresh and ->bg_thresh considering
 382 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}.  The caller
 383 * must ensure that @dtc->avail is set before calling this function.  The
 384 * dirty limits will be lifted by 1/4 for real-time tasks.
 385 */
 386static void domain_dirty_limits(struct dirty_throttle_control *dtc)
 387{
 388        const unsigned long available_memory = dtc->avail;
 389        struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
 390        unsigned long bytes = vm_dirty_bytes;
 391        unsigned long bg_bytes = dirty_background_bytes;
 392        /* convert ratios to per-PAGE_SIZE for higher precision */
 393        unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
 394        unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
 395        unsigned long thresh;
 396        unsigned long bg_thresh;
 397        struct task_struct *tsk;
 398
 399        /* gdtc is !NULL iff @dtc is for memcg domain */
 400        if (gdtc) {
 401                unsigned long global_avail = gdtc->avail;
 402
 403                /*
 404                 * The byte settings can't be applied directly to memcg
 405                 * domains.  Convert them to ratios by scaling against
 406                 * globally available memory.  As the ratios are in
 407                 * per-PAGE_SIZE, they can be obtained by dividing bytes by
 408                 * number of pages.
 409                 */
 410                if (bytes)
 411                        ratio = min(DIV_ROUND_UP(bytes, global_avail),
 412                                    PAGE_SIZE);
 413                if (bg_bytes)
 414                        bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
 415                                       PAGE_SIZE);
 416                bytes = bg_bytes = 0;
 417        }
 418
 419        if (bytes)
 420                thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
 421        else
 422                thresh = (ratio * available_memory) / PAGE_SIZE;
 423
 424        if (bg_bytes)
 425                bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
 426        else
 427                bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
 428
 429        if (bg_thresh >= thresh)
 430                bg_thresh = thresh / 2;
 431        tsk = current;
 432        if (rt_task(tsk)) {
 433                bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
 434                thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
 435        }
 436        dtc->thresh = thresh;
 437        dtc->bg_thresh = bg_thresh;
 438
 439        /* we should eventually report the domain in the TP */
 440        if (!gdtc)
 441                trace_global_dirty_state(bg_thresh, thresh);
 442}
 443
 444/**
 445 * global_dirty_limits - background-writeback and dirty-throttling thresholds
 446 * @pbackground: out parameter for bg_thresh
 447 * @pdirty: out parameter for thresh
 448 *
 449 * Calculate bg_thresh and thresh for global_wb_domain.  See
 450 * domain_dirty_limits() for details.
 451 */
 452void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
 453{
 454        struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
 455
 456        gdtc.avail = global_dirtyable_memory();
 457        domain_dirty_limits(&gdtc);
 458
 459        *pbackground = gdtc.bg_thresh;
 460        *pdirty = gdtc.thresh;
 461}
 462
 463/**
 464 * node_dirty_limit - maximum number of dirty pages allowed in a node
 465 * @pgdat: the node
 466 *
 467 * Return: the maximum number of dirty pages allowed in a node, based
 468 * on the node's dirtyable memory.
 469 */
 470static unsigned long node_dirty_limit(struct pglist_data *pgdat)
 471{
 472        unsigned long node_memory = node_dirtyable_memory(pgdat);
 473        struct task_struct *tsk = current;
 474        unsigned long dirty;
 475
 476        if (vm_dirty_bytes)
 477                dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
 478                        node_memory / global_dirtyable_memory();
 479        else
 480                dirty = vm_dirty_ratio * node_memory / 100;
 481
 482        if (rt_task(tsk))
 483                dirty += dirty / 4;
 484
 485        return dirty;
 486}
 487
 488/**
 489 * node_dirty_ok - tells whether a node is within its dirty limits
 490 * @pgdat: the node to check
 491 *
 492 * Return: %true when the dirty pages in @pgdat are within the node's
 493 * dirty limit, %false if the limit is exceeded.
 494 */
 495bool node_dirty_ok(struct pglist_data *pgdat)
 496{
 497        unsigned long limit = node_dirty_limit(pgdat);
 498        unsigned long nr_pages = 0;
 499
 500        nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
 501        nr_pages += node_page_state(pgdat, NR_WRITEBACK);
 502
 503        return nr_pages <= limit;
 504}
 505
 506int dirty_background_ratio_handler(struct ctl_table *table, int write,
 507                void *buffer, size_t *lenp, loff_t *ppos)
 508{
 509        int ret;
 510
 511        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 512        if (ret == 0 && write)
 513                dirty_background_bytes = 0;
 514        return ret;
 515}
 516
 517int dirty_background_bytes_handler(struct ctl_table *table, int write,
 518                void *buffer, size_t *lenp, loff_t *ppos)
 519{
 520        int ret;
 521
 522        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 523        if (ret == 0 && write)
 524                dirty_background_ratio = 0;
 525        return ret;
 526}
 527
 528int dirty_ratio_handler(struct ctl_table *table, int write, void *buffer,
 529                size_t *lenp, loff_t *ppos)
 530{
 531        int old_ratio = vm_dirty_ratio;
 532        int ret;
 533
 534        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 535        if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
 536                writeback_set_ratelimit();
 537                vm_dirty_bytes = 0;
 538        }
 539        return ret;
 540}
 541
 542int dirty_bytes_handler(struct ctl_table *table, int write,
 543                void *buffer, size_t *lenp, loff_t *ppos)
 544{
 545        unsigned long old_bytes = vm_dirty_bytes;
 546        int ret;
 547
 548        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 549        if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
 550                writeback_set_ratelimit();
 551                vm_dirty_ratio = 0;
 552        }
 553        return ret;
 554}
 555
 556static unsigned long wp_next_time(unsigned long cur_time)
 557{
 558        cur_time += VM_COMPLETIONS_PERIOD_LEN;
 559        /* 0 has a special meaning... */
 560        if (!cur_time)
 561                return 1;
 562        return cur_time;
 563}
 564
 565static void wb_domain_writeout_inc(struct wb_domain *dom,
 566                                   struct fprop_local_percpu *completions,
 567                                   unsigned int max_prop_frac)
 568{
 569        __fprop_inc_percpu_max(&dom->completions, completions,
 570                               max_prop_frac);
 571        /* First event after period switching was turned off? */
 572        if (unlikely(!dom->period_time)) {
 573                /*
 574                 * We can race with other __bdi_writeout_inc calls here but
 575                 * it does not cause any harm since the resulting time when
 576                 * timer will fire and what is in writeout_period_time will be
 577                 * roughly the same.
 578                 */
 579                dom->period_time = wp_next_time(jiffies);
 580                mod_timer(&dom->period_timer, dom->period_time);
 581        }
 582}
 583
 584/*
 585 * Increment @wb's writeout completion count and the global writeout
 586 * completion count. Called from test_clear_page_writeback().
 587 */
 588static inline void __wb_writeout_inc(struct bdi_writeback *wb)
 589{
 590        struct wb_domain *cgdom;
 591
 592        inc_wb_stat(wb, WB_WRITTEN);
 593        wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
 594                               wb->bdi->max_prop_frac);
 595
 596        cgdom = mem_cgroup_wb_domain(wb);
 597        if (cgdom)
 598                wb_domain_writeout_inc(cgdom, wb_memcg_completions(wb),
 599                                       wb->bdi->max_prop_frac);
 600}
 601
 602void wb_writeout_inc(struct bdi_writeback *wb)
 603{
 604        unsigned long flags;
 605
 606        local_irq_save(flags);
 607        __wb_writeout_inc(wb);
 608        local_irq_restore(flags);
 609}
 610EXPORT_SYMBOL_GPL(wb_writeout_inc);
 611
 612/*
 613 * On idle system, we can be called long after we scheduled because we use
 614 * deferred timers so count with missed periods.
 615 */
 616static void writeout_period(struct timer_list *t)
 617{
 618        struct wb_domain *dom = from_timer(dom, t, period_timer);
 619        int miss_periods = (jiffies - dom->period_time) /
 620                                                 VM_COMPLETIONS_PERIOD_LEN;
 621
 622        if (fprop_new_period(&dom->completions, miss_periods + 1)) {
 623                dom->period_time = wp_next_time(dom->period_time +
 624                                miss_periods * VM_COMPLETIONS_PERIOD_LEN);
 625                mod_timer(&dom->period_timer, dom->period_time);
 626        } else {
 627                /*
 628                 * Aging has zeroed all fractions. Stop wasting CPU on period
 629                 * updates.
 630                 */
 631                dom->period_time = 0;
 632        }
 633}
 634
 635int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
 636{
 637        memset(dom, 0, sizeof(*dom));
 638
 639        spin_lock_init(&dom->lock);
 640
 641        timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
 642
 643        dom->dirty_limit_tstamp = jiffies;
 644
 645        return fprop_global_init(&dom->completions, gfp);
 646}
 647
 648#ifdef CONFIG_CGROUP_WRITEBACK
 649void wb_domain_exit(struct wb_domain *dom)
 650{
 651        del_timer_sync(&dom->period_timer);
 652        fprop_global_destroy(&dom->completions);
 653}
 654#endif
 655
 656/*
 657 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
 658 * registered backing devices, which, for obvious reasons, can not
 659 * exceed 100%.
 660 */
 661static unsigned int bdi_min_ratio;
 662
 663int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 664{
 665        int ret = 0;
 666
 667        spin_lock_bh(&bdi_lock);
 668        if (min_ratio > bdi->max_ratio) {
 669                ret = -EINVAL;
 670        } else {
 671                min_ratio -= bdi->min_ratio;
 672                if (bdi_min_ratio + min_ratio < 100) {
 673                        bdi_min_ratio += min_ratio;
 674                        bdi->min_ratio += min_ratio;
 675                } else {
 676                        ret = -EINVAL;
 677                }
 678        }
 679        spin_unlock_bh(&bdi_lock);
 680
 681        return ret;
 682}
 683
 684int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 685{
 686        int ret = 0;
 687
 688        if (max_ratio > 100)
 689                return -EINVAL;
 690
 691        spin_lock_bh(&bdi_lock);
 692        if (bdi->min_ratio > max_ratio) {
 693                ret = -EINVAL;
 694        } else {
 695                bdi->max_ratio = max_ratio;
 696                bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
 697        }
 698        spin_unlock_bh(&bdi_lock);
 699
 700        return ret;
 701}
 702EXPORT_SYMBOL(bdi_set_max_ratio);
 703
 704static unsigned long dirty_freerun_ceiling(unsigned long thresh,
 705                                           unsigned long bg_thresh)
 706{
 707        return (thresh + bg_thresh) / 2;
 708}
 709
 710static unsigned long hard_dirty_limit(struct wb_domain *dom,
 711                                      unsigned long thresh)
 712{
 713        return max(thresh, dom->dirty_limit);
 714}
 715
 716/*
 717 * Memory which can be further allocated to a memcg domain is capped by
 718 * system-wide clean memory excluding the amount being used in the domain.
 719 */
 720static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
 721                            unsigned long filepages, unsigned long headroom)
 722{
 723        struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
 724        unsigned long clean = filepages - min(filepages, mdtc->dirty);
 725        unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
 726        unsigned long other_clean = global_clean - min(global_clean, clean);
 727
 728        mdtc->avail = filepages + min(headroom, other_clean);
 729}
 730
 731/**
 732 * __wb_calc_thresh - @wb's share of dirty throttling threshold
 733 * @dtc: dirty_throttle_context of interest
 734 *
 735 * Note that balance_dirty_pages() will only seriously take it as a hard limit
 736 * when sleeping max_pause per page is not enough to keep the dirty pages under
 737 * control. For example, when the device is completely stalled due to some error
 738 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
 739 * In the other normal situations, it acts more gently by throttling the tasks
 740 * more (rather than completely block them) when the wb dirty pages go high.
 741 *
 742 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
 743 * - starving fast devices
 744 * - piling up dirty pages (that will take long time to sync) on slow devices
 745 *
 746 * The wb's share of dirty limit will be adapting to its throughput and
 747 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
 748 *
 749 * Return: @wb's dirty limit in pages. The term "dirty" in the context of
 750 * dirty balancing includes all PG_dirty and PG_writeback pages.
 751 */
 752static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
 753{
 754        struct wb_domain *dom = dtc_dom(dtc);
 755        unsigned long thresh = dtc->thresh;
 756        u64 wb_thresh;
 757        unsigned long numerator, denominator;
 758        unsigned long wb_min_ratio, wb_max_ratio;
 759
 760        /*
 761         * Calculate this BDI's share of the thresh ratio.
 762         */
 763        fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
 764                              &numerator, &denominator);
 765
 766        wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
 767        wb_thresh *= numerator;
 768        wb_thresh = div64_ul(wb_thresh, denominator);
 769
 770        wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
 771
 772        wb_thresh += (thresh * wb_min_ratio) / 100;
 773        if (wb_thresh > (thresh * wb_max_ratio) / 100)
 774                wb_thresh = thresh * wb_max_ratio / 100;
 775
 776        return wb_thresh;
 777}
 778
 779unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
 780{
 781        struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
 782                                               .thresh = thresh };
 783        return __wb_calc_thresh(&gdtc);
 784}
 785
 786/*
 787 *                           setpoint - dirty 3
 788 *        f(dirty) := 1.0 + (----------------)
 789 *                           limit - setpoint
 790 *
 791 * it's a 3rd order polynomial that subjects to
 792 *
 793 * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
 794 * (2) f(setpoint) = 1.0 => the balance point
 795 * (3) f(limit)    = 0   => the hard limit
 796 * (4) df/dx      <= 0   => negative feedback control
 797 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
 798 *     => fast response on large errors; small oscillation near setpoint
 799 */
 800static long long pos_ratio_polynom(unsigned long setpoint,
 801                                          unsigned long dirty,
 802                                          unsigned long limit)
 803{
 804        long long pos_ratio;
 805        long x;
 806
 807        x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
 808                      (limit - setpoint) | 1);
 809        pos_ratio = x;
 810        pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
 811        pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
 812        pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
 813
 814        return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
 815}
 816
 817/*
 818 * Dirty position control.
 819 *
 820 * (o) global/bdi setpoints
 821 *
 822 * We want the dirty pages be balanced around the global/wb setpoints.
 823 * When the number of dirty pages is higher/lower than the setpoint, the
 824 * dirty position control ratio (and hence task dirty ratelimit) will be
 825 * decreased/increased to bring the dirty pages back to the setpoint.
 826 *
 827 *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
 828 *
 829 *     if (dirty < setpoint) scale up   pos_ratio
 830 *     if (dirty > setpoint) scale down pos_ratio
 831 *
 832 *     if (wb_dirty < wb_setpoint) scale up   pos_ratio
 833 *     if (wb_dirty > wb_setpoint) scale down pos_ratio
 834 *
 835 *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
 836 *
 837 * (o) global control line
 838 *
 839 *     ^ pos_ratio
 840 *     |
 841 *     |            |<===== global dirty control scope ======>|
 842 * 2.0  * * * * * * *
 843 *     |            .*
 844 *     |            . *
 845 *     |            .   *
 846 *     |            .     *
 847 *     |            .        *
 848 *     |            .            *
 849 * 1.0 ................................*
 850 *     |            .                  .     *
 851 *     |            .                  .          *
 852 *     |            .                  .              *
 853 *     |            .                  .                 *
 854 *     |            .                  .                    *
 855 *   0 +------------.------------------.----------------------*------------->
 856 *           freerun^          setpoint^                 limit^   dirty pages
 857 *
 858 * (o) wb control line
 859 *
 860 *     ^ pos_ratio
 861 *     |
 862 *     |            *
 863 *     |              *
 864 *     |                *
 865 *     |                  *
 866 *     |                    * |<=========== span ============>|
 867 * 1.0 .......................*
 868 *     |                      . *
 869 *     |                      .   *
 870 *     |                      .     *
 871 *     |                      .       *
 872 *     |                      .         *
 873 *     |                      .           *
 874 *     |                      .             *
 875 *     |                      .               *
 876 *     |                      .                 *
 877 *     |                      .                   *
 878 *     |                      .                     *
 879 * 1/4 ...............................................* * * * * * * * * * * *
 880 *     |                      .                         .
 881 *     |                      .                           .
 882 *     |                      .                             .
 883 *   0 +----------------------.-------------------------------.------------->
 884 *                wb_setpoint^                    x_intercept^
 885 *
 886 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
 887 * be smoothly throttled down to normal if it starts high in situations like
 888 * - start writing to a slow SD card and a fast disk at the same time. The SD
 889 *   card's wb_dirty may rush to many times higher than wb_setpoint.
 890 * - the wb dirty thresh drops quickly due to change of JBOD workload
 891 */
 892static void wb_position_ratio(struct dirty_throttle_control *dtc)
 893{
 894        struct bdi_writeback *wb = dtc->wb;
 895        unsigned long write_bw = wb->avg_write_bandwidth;
 896        unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
 897        unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
 898        unsigned long wb_thresh = dtc->wb_thresh;
 899        unsigned long x_intercept;
 900        unsigned long setpoint;         /* dirty pages' target balance point */
 901        unsigned long wb_setpoint;
 902        unsigned long span;
 903        long long pos_ratio;            /* for scaling up/down the rate limit */
 904        long x;
 905
 906        dtc->pos_ratio = 0;
 907
 908        if (unlikely(dtc->dirty >= limit))
 909                return;
 910
 911        /*
 912         * global setpoint
 913         *
 914         * See comment for pos_ratio_polynom().
 915         */
 916        setpoint = (freerun + limit) / 2;
 917        pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
 918
 919        /*
 920         * The strictlimit feature is a tool preventing mistrusted filesystems
 921         * from growing a large number of dirty pages before throttling. For
 922         * such filesystems balance_dirty_pages always checks wb counters
 923         * against wb limits. Even if global "nr_dirty" is under "freerun".
 924         * This is especially important for fuse which sets bdi->max_ratio to
 925         * 1% by default. Without strictlimit feature, fuse writeback may
 926         * consume arbitrary amount of RAM because it is accounted in
 927         * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
 928         *
 929         * Here, in wb_position_ratio(), we calculate pos_ratio based on
 930         * two values: wb_dirty and wb_thresh. Let's consider an example:
 931         * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
 932         * limits are set by default to 10% and 20% (background and throttle).
 933         * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
 934         * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
 935         * about ~6K pages (as the average of background and throttle wb
 936         * limits). The 3rd order polynomial will provide positive feedback if
 937         * wb_dirty is under wb_setpoint and vice versa.
 938         *
 939         * Note, that we cannot use global counters in these calculations
 940         * because we want to throttle process writing to a strictlimit wb
 941         * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
 942         * in the example above).
 943         */
 944        if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
 945                long long wb_pos_ratio;
 946
 947                if (dtc->wb_dirty < 8) {
 948                        dtc->pos_ratio = min_t(long long, pos_ratio * 2,
 949                                           2 << RATELIMIT_CALC_SHIFT);
 950                        return;
 951                }
 952
 953                if (dtc->wb_dirty >= wb_thresh)
 954                        return;
 955
 956                wb_setpoint = dirty_freerun_ceiling(wb_thresh,
 957                                                    dtc->wb_bg_thresh);
 958
 959                if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
 960                        return;
 961
 962                wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
 963                                                 wb_thresh);
 964
 965                /*
 966                 * Typically, for strictlimit case, wb_setpoint << setpoint
 967                 * and pos_ratio >> wb_pos_ratio. In the other words global
 968                 * state ("dirty") is not limiting factor and we have to
 969                 * make decision based on wb counters. But there is an
 970                 * important case when global pos_ratio should get precedence:
 971                 * global limits are exceeded (e.g. due to activities on other
 972                 * wb's) while given strictlimit wb is below limit.
 973                 *
 974                 * "pos_ratio * wb_pos_ratio" would work for the case above,
 975                 * but it would look too non-natural for the case of all
 976                 * activity in the system coming from a single strictlimit wb
 977                 * with bdi->max_ratio == 100%.
 978                 *
 979                 * Note that min() below somewhat changes the dynamics of the
 980                 * control system. Normally, pos_ratio value can be well over 3
 981                 * (when globally we are at freerun and wb is well below wb
 982                 * setpoint). Now the maximum pos_ratio in the same situation
 983                 * is 2. We might want to tweak this if we observe the control
 984                 * system is too slow to adapt.
 985                 */
 986                dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
 987                return;
 988        }
 989
 990        /*
 991         * We have computed basic pos_ratio above based on global situation. If
 992         * the wb is over/under its share of dirty pages, we want to scale
 993         * pos_ratio further down/up. That is done by the following mechanism.
 994         */
 995
 996        /*
 997         * wb setpoint
 998         *
 999         *        f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1000         *
1001         *                        x_intercept - wb_dirty
1002         *                     := --------------------------
1003         *                        x_intercept - wb_setpoint
1004         *
1005         * The main wb control line is a linear function that subjects to
1006         *
1007         * (1) f(wb_setpoint) = 1.0
1008         * (2) k = - 1 / (8 * write_bw)  (in single wb case)
1009         *     or equally: x_intercept = wb_setpoint + 8 * write_bw
1010         *
1011         * For single wb case, the dirty pages are observed to fluctuate
1012         * regularly within range
1013         *        [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1014         * for various filesystems, where (2) can yield in a reasonable 12.5%
1015         * fluctuation range for pos_ratio.
1016         *
1017         * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1018         * own size, so move the slope over accordingly and choose a slope that
1019         * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1020         */
1021        if (unlikely(wb_thresh > dtc->thresh))
1022                wb_thresh = dtc->thresh;
1023        /*
1024         * It's very possible that wb_thresh is close to 0 not because the
1025         * device is slow, but that it has remained inactive for long time.
1026         * Honour such devices a reasonable good (hopefully IO efficient)
1027         * threshold, so that the occasional writes won't be blocked and active
1028         * writes can rampup the threshold quickly.
1029         */
1030        wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1031        /*
1032         * scale global setpoint to wb's:
1033         *      wb_setpoint = setpoint * wb_thresh / thresh
1034         */
1035        x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1036        wb_setpoint = setpoint * (u64)x >> 16;
1037        /*
1038         * Use span=(8*write_bw) in single wb case as indicated by
1039         * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1040         *
1041         *        wb_thresh                    thresh - wb_thresh
1042         * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1043         *         thresh                           thresh
1044         */
1045        span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1046        x_intercept = wb_setpoint + span;
1047
1048        if (dtc->wb_dirty < x_intercept - span / 4) {
1049                pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1050                                      (x_intercept - wb_setpoint) | 1);
1051        } else
1052                pos_ratio /= 4;
1053
1054        /*
1055         * wb reserve area, safeguard against dirty pool underrun and disk idle
1056         * It may push the desired control point of global dirty pages higher
1057         * than setpoint.
1058         */
1059        x_intercept = wb_thresh / 2;
1060        if (dtc->wb_dirty < x_intercept) {
1061                if (dtc->wb_dirty > x_intercept / 8)
1062                        pos_ratio = div_u64(pos_ratio * x_intercept,
1063                                            dtc->wb_dirty);
1064                else
1065                        pos_ratio *= 8;
1066        }
1067
1068        dtc->pos_ratio = pos_ratio;
1069}
1070
1071static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1072                                      unsigned long elapsed,
1073                                      unsigned long written)
1074{
1075        const unsigned long period = roundup_pow_of_two(3 * HZ);
1076        unsigned long avg = wb->avg_write_bandwidth;
1077        unsigned long old = wb->write_bandwidth;
1078        u64 bw;
1079
1080        /*
1081         * bw = written * HZ / elapsed
1082         *
1083         *                   bw * elapsed + write_bandwidth * (period - elapsed)
1084         * write_bandwidth = ---------------------------------------------------
1085         *                                          period
1086         *
1087         * @written may have decreased due to account_page_redirty().
1088         * Avoid underflowing @bw calculation.
1089         */
1090        bw = written - min(written, wb->written_stamp);
1091        bw *= HZ;
1092        if (unlikely(elapsed > period)) {
1093                bw = div64_ul(bw, elapsed);
1094                avg = bw;
1095                goto out;
1096        }
1097        bw += (u64)wb->write_bandwidth * (period - elapsed);
1098        bw >>= ilog2(period);
1099
1100        /*
1101         * one more level of smoothing, for filtering out sudden spikes
1102         */
1103        if (avg > old && old >= (unsigned long)bw)
1104                avg -= (avg - old) >> 3;
1105
1106        if (avg < old && old <= (unsigned long)bw)
1107                avg += (old - avg) >> 3;
1108
1109out:
1110        /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1111        avg = max(avg, 1LU);
1112        if (wb_has_dirty_io(wb)) {
1113                long delta = avg - wb->avg_write_bandwidth;
1114                WARN_ON_ONCE(atomic_long_add_return(delta,
1115                                        &wb->bdi->tot_write_bandwidth) <= 0);
1116        }
1117        wb->write_bandwidth = bw;
1118        wb->avg_write_bandwidth = avg;
1119}
1120
1121static void update_dirty_limit(struct dirty_throttle_control *dtc)
1122{
1123        struct wb_domain *dom = dtc_dom(dtc);
1124        unsigned long thresh = dtc->thresh;
1125        unsigned long limit = dom->dirty_limit;
1126
1127        /*
1128         * Follow up in one step.
1129         */
1130        if (limit < thresh) {
1131                limit = thresh;
1132                goto update;
1133        }
1134
1135        /*
1136         * Follow down slowly. Use the higher one as the target, because thresh
1137         * may drop below dirty. This is exactly the reason to introduce
1138         * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1139         */
1140        thresh = max(thresh, dtc->dirty);
1141        if (limit > thresh) {
1142                limit -= (limit - thresh) >> 5;
1143                goto update;
1144        }
1145        return;
1146update:
1147        dom->dirty_limit = limit;
1148}
1149
1150static void domain_update_bandwidth(struct dirty_throttle_control *dtc,
1151                                    unsigned long now)
1152{
1153        struct wb_domain *dom = dtc_dom(dtc);
1154
1155        /*
1156         * check locklessly first to optimize away locking for the most time
1157         */
1158        if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1159                return;
1160
1161        spin_lock(&dom->lock);
1162        if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1163                update_dirty_limit(dtc);
1164                dom->dirty_limit_tstamp = now;
1165        }
1166        spin_unlock(&dom->lock);
1167}
1168
1169/*
1170 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1171 *
1172 * Normal wb tasks will be curbed at or below it in long term.
1173 * Obviously it should be around (write_bw / N) when there are N dd tasks.
1174 */
1175static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1176                                      unsigned long dirtied,
1177                                      unsigned long elapsed)
1178{
1179        struct bdi_writeback *wb = dtc->wb;
1180        unsigned long dirty = dtc->dirty;
1181        unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1182        unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1183        unsigned long setpoint = (freerun + limit) / 2;
1184        unsigned long write_bw = wb->avg_write_bandwidth;
1185        unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1186        unsigned long dirty_rate;
1187        unsigned long task_ratelimit;
1188        unsigned long balanced_dirty_ratelimit;
1189        unsigned long step;
1190        unsigned long x;
1191        unsigned long shift;
1192
1193        /*
1194         * The dirty rate will match the writeout rate in long term, except
1195         * when dirty pages are truncated by userspace or re-dirtied by FS.
1196         */
1197        dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1198
1199        /*
1200         * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1201         */
1202        task_ratelimit = (u64)dirty_ratelimit *
1203                                        dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1204        task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1205
1206        /*
1207         * A linear estimation of the "balanced" throttle rate. The theory is,
1208         * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1209         * dirty_rate will be measured to be (N * task_ratelimit). So the below
1210         * formula will yield the balanced rate limit (write_bw / N).
1211         *
1212         * Note that the expanded form is not a pure rate feedback:
1213         *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate)              (1)
1214         * but also takes pos_ratio into account:
1215         *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
1216         *
1217         * (1) is not realistic because pos_ratio also takes part in balancing
1218         * the dirty rate.  Consider the state
1219         *      pos_ratio = 0.5                                              (3)
1220         *      rate = 2 * (write_bw / N)                                    (4)
1221         * If (1) is used, it will stuck in that state! Because each dd will
1222         * be throttled at
1223         *      task_ratelimit = pos_ratio * rate = (write_bw / N)           (5)
1224         * yielding
1225         *      dirty_rate = N * task_ratelimit = write_bw                   (6)
1226         * put (6) into (1) we get
1227         *      rate_(i+1) = rate_(i)                                        (7)
1228         *
1229         * So we end up using (2) to always keep
1230         *      rate_(i+1) ~= (write_bw / N)                                 (8)
1231         * regardless of the value of pos_ratio. As long as (8) is satisfied,
1232         * pos_ratio is able to drive itself to 1.0, which is not only where
1233         * the dirty count meet the setpoint, but also where the slope of
1234         * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1235         */
1236        balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1237                                           dirty_rate | 1);
1238        /*
1239         * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1240         */
1241        if (unlikely(balanced_dirty_ratelimit > write_bw))
1242                balanced_dirty_ratelimit = write_bw;
1243
1244        /*
1245         * We could safely do this and return immediately:
1246         *
1247         *      wb->dirty_ratelimit = balanced_dirty_ratelimit;
1248         *
1249         * However to get a more stable dirty_ratelimit, the below elaborated
1250         * code makes use of task_ratelimit to filter out singular points and
1251         * limit the step size.
1252         *
1253         * The below code essentially only uses the relative value of
1254         *
1255         *      task_ratelimit - dirty_ratelimit
1256         *      = (pos_ratio - 1) * dirty_ratelimit
1257         *
1258         * which reflects the direction and size of dirty position error.
1259         */
1260
1261        /*
1262         * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1263         * task_ratelimit is on the same side of dirty_ratelimit, too.
1264         * For example, when
1265         * - dirty_ratelimit > balanced_dirty_ratelimit
1266         * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1267         * lowering dirty_ratelimit will help meet both the position and rate
1268         * control targets. Otherwise, don't update dirty_ratelimit if it will
1269         * only help meet the rate target. After all, what the users ultimately
1270         * feel and care are stable dirty rate and small position error.
1271         *
1272         * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1273         * and filter out the singular points of balanced_dirty_ratelimit. Which
1274         * keeps jumping around randomly and can even leap far away at times
1275         * due to the small 200ms estimation period of dirty_rate (we want to
1276         * keep that period small to reduce time lags).
1277         */
1278        step = 0;
1279
1280        /*
1281         * For strictlimit case, calculations above were based on wb counters
1282         * and limits (starting from pos_ratio = wb_position_ratio() and up to
1283         * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1284         * Hence, to calculate "step" properly, we have to use wb_dirty as
1285         * "dirty" and wb_setpoint as "setpoint".
1286         *
1287         * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1288         * it's possible that wb_thresh is close to zero due to inactivity
1289         * of backing device.
1290         */
1291        if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1292                dirty = dtc->wb_dirty;
1293                if (dtc->wb_dirty < 8)
1294                        setpoint = dtc->wb_dirty + 1;
1295                else
1296                        setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1297        }
1298
1299        if (dirty < setpoint) {
1300                x = min3(wb->balanced_dirty_ratelimit,
1301                         balanced_dirty_ratelimit, task_ratelimit);
1302                if (dirty_ratelimit < x)
1303                        step = x - dirty_ratelimit;
1304        } else {
1305                x = max3(wb->balanced_dirty_ratelimit,
1306                         balanced_dirty_ratelimit, task_ratelimit);
1307                if (dirty_ratelimit > x)
1308                        step = dirty_ratelimit - x;
1309        }
1310
1311        /*
1312         * Don't pursue 100% rate matching. It's impossible since the balanced
1313         * rate itself is constantly fluctuating. So decrease the track speed
1314         * when it gets close to the target. Helps eliminate pointless tremors.
1315         */
1316        shift = dirty_ratelimit / (2 * step + 1);
1317        if (shift < BITS_PER_LONG)
1318                step = DIV_ROUND_UP(step >> shift, 8);
1319        else
1320                step = 0;
1321
1322        if (dirty_ratelimit < balanced_dirty_ratelimit)
1323                dirty_ratelimit += step;
1324        else
1325                dirty_ratelimit -= step;
1326
1327        wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1328        wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1329
1330        trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1331}
1332
1333static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1334                                  struct dirty_throttle_control *mdtc,
1335                                  unsigned long start_time,
1336                                  bool update_ratelimit)
1337{
1338        struct bdi_writeback *wb = gdtc->wb;
1339        unsigned long now = jiffies;
1340        unsigned long elapsed = now - wb->bw_time_stamp;
1341        unsigned long dirtied;
1342        unsigned long written;
1343
1344        lockdep_assert_held(&wb->list_lock);
1345
1346        /*
1347         * rate-limit, only update once every 200ms.
1348         */
1349        if (elapsed < BANDWIDTH_INTERVAL)
1350                return;
1351
1352        dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1353        written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1354
1355        /*
1356         * Skip quiet periods when disk bandwidth is under-utilized.
1357         * (at least 1s idle time between two flusher runs)
1358         */
1359        if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
1360                goto snapshot;
1361
1362        if (update_ratelimit) {
1363                domain_update_bandwidth(gdtc, now);
1364                wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1365
1366                /*
1367                 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1368                 * compiler has no way to figure that out.  Help it.
1369                 */
1370                if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1371                        domain_update_bandwidth(mdtc, now);
1372                        wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1373                }
1374        }
1375        wb_update_write_bandwidth(wb, elapsed, written);
1376
1377snapshot:
1378        wb->dirtied_stamp = dirtied;
1379        wb->written_stamp = written;
1380        wb->bw_time_stamp = now;
1381}
1382
1383void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
1384{
1385        struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1386
1387        __wb_update_bandwidth(&gdtc, NULL, start_time, false);
1388}
1389
1390/*
1391 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1392 * will look to see if it needs to start dirty throttling.
1393 *
1394 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1395 * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1396 * (the number of pages we may dirty without exceeding the dirty limits).
1397 */
1398static unsigned long dirty_poll_interval(unsigned long dirty,
1399                                         unsigned long thresh)
1400{
1401        if (thresh > dirty)
1402                return 1UL << (ilog2(thresh - dirty) >> 1);
1403
1404        return 1;
1405}
1406
1407static unsigned long wb_max_pause(struct bdi_writeback *wb,
1408                                  unsigned long wb_dirty)
1409{
1410        unsigned long bw = wb->avg_write_bandwidth;
1411        unsigned long t;
1412
1413        /*
1414         * Limit pause time for small memory systems. If sleeping for too long
1415         * time, a small pool of dirty/writeback pages may go empty and disk go
1416         * idle.
1417         *
1418         * 8 serves as the safety ratio.
1419         */
1420        t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1421        t++;
1422
1423        return min_t(unsigned long, t, MAX_PAUSE);
1424}
1425
1426static long wb_min_pause(struct bdi_writeback *wb,
1427                         long max_pause,
1428                         unsigned long task_ratelimit,
1429                         unsigned long dirty_ratelimit,
1430                         int *nr_dirtied_pause)
1431{
1432        long hi = ilog2(wb->avg_write_bandwidth);
1433        long lo = ilog2(wb->dirty_ratelimit);
1434        long t;         /* target pause */
1435        long pause;     /* estimated next pause */
1436        int pages;      /* target nr_dirtied_pause */
1437
1438        /* target for 10ms pause on 1-dd case */
1439        t = max(1, HZ / 100);
1440
1441        /*
1442         * Scale up pause time for concurrent dirtiers in order to reduce CPU
1443         * overheads.
1444         *
1445         * (N * 10ms) on 2^N concurrent tasks.
1446         */
1447        if (hi > lo)
1448                t += (hi - lo) * (10 * HZ) / 1024;
1449
1450        /*
1451         * This is a bit convoluted. We try to base the next nr_dirtied_pause
1452         * on the much more stable dirty_ratelimit. However the next pause time
1453         * will be computed based on task_ratelimit and the two rate limits may
1454         * depart considerably at some time. Especially if task_ratelimit goes
1455         * below dirty_ratelimit/2 and the target pause is max_pause, the next
1456         * pause time will be max_pause*2 _trimmed down_ to max_pause.  As a
1457         * result task_ratelimit won't be executed faithfully, which could
1458         * eventually bring down dirty_ratelimit.
1459         *
1460         * We apply two rules to fix it up:
1461         * 1) try to estimate the next pause time and if necessary, use a lower
1462         *    nr_dirtied_pause so as not to exceed max_pause. When this happens,
1463         *    nr_dirtied_pause will be "dancing" with task_ratelimit.
1464         * 2) limit the target pause time to max_pause/2, so that the normal
1465         *    small fluctuations of task_ratelimit won't trigger rule (1) and
1466         *    nr_dirtied_pause will remain as stable as dirty_ratelimit.
1467         */
1468        t = min(t, 1 + max_pause / 2);
1469        pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1470
1471        /*
1472         * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1473         * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1474         * When the 16 consecutive reads are often interrupted by some dirty
1475         * throttling pause during the async writes, cfq will go into idles
1476         * (deadline is fine). So push nr_dirtied_pause as high as possible
1477         * until reaches DIRTY_POLL_THRESH=32 pages.
1478         */
1479        if (pages < DIRTY_POLL_THRESH) {
1480                t = max_pause;
1481                pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1482                if (pages > DIRTY_POLL_THRESH) {
1483                        pages = DIRTY_POLL_THRESH;
1484                        t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1485                }
1486        }
1487
1488        pause = HZ * pages / (task_ratelimit + 1);
1489        if (pause > max_pause) {
1490                t = max_pause;
1491                pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1492        }
1493
1494        *nr_dirtied_pause = pages;
1495        /*
1496         * The minimal pause time will normally be half the target pause time.
1497         */
1498        return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1499}
1500
1501static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1502{
1503        struct bdi_writeback *wb = dtc->wb;
1504        unsigned long wb_reclaimable;
1505
1506        /*
1507         * wb_thresh is not treated as some limiting factor as
1508         * dirty_thresh, due to reasons
1509         * - in JBOD setup, wb_thresh can fluctuate a lot
1510         * - in a system with HDD and USB key, the USB key may somehow
1511         *   go into state (wb_dirty >> wb_thresh) either because
1512         *   wb_dirty starts high, or because wb_thresh drops low.
1513         *   In this case we don't want to hard throttle the USB key
1514         *   dirtiers for 100 seconds until wb_dirty drops under
1515         *   wb_thresh. Instead the auxiliary wb control line in
1516         *   wb_position_ratio() will let the dirtier task progress
1517         *   at some rate <= (write_bw / 2) for bringing down wb_dirty.
1518         */
1519        dtc->wb_thresh = __wb_calc_thresh(dtc);
1520        dtc->wb_bg_thresh = dtc->thresh ?
1521                div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1522
1523        /*
1524         * In order to avoid the stacked BDI deadlock we need
1525         * to ensure we accurately count the 'dirty' pages when
1526         * the threshold is low.
1527         *
1528         * Otherwise it would be possible to get thresh+n pages
1529         * reported dirty, even though there are thresh-m pages
1530         * actually dirty; with m+n sitting in the percpu
1531         * deltas.
1532         */
1533        if (dtc->wb_thresh < 2 * wb_stat_error()) {
1534                wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1535                dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1536        } else {
1537                wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1538                dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1539        }
1540}
1541
1542/*
1543 * balance_dirty_pages() must be called by processes which are generating dirty
1544 * data.  It looks at the number of dirty pages in the machine and will force
1545 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1546 * If we're over `background_thresh' then the writeback threads are woken to
1547 * perform some writeout.
1548 */
1549static void balance_dirty_pages(struct bdi_writeback *wb,
1550                                unsigned long pages_dirtied)
1551{
1552        struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1553        struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1554        struct dirty_throttle_control * const gdtc = &gdtc_stor;
1555        struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1556                                                     &mdtc_stor : NULL;
1557        struct dirty_throttle_control *sdtc;
1558        unsigned long nr_reclaimable;   /* = file_dirty */
1559        long period;
1560        long pause;
1561        long max_pause;
1562        long min_pause;
1563        int nr_dirtied_pause;
1564        bool dirty_exceeded = false;
1565        unsigned long task_ratelimit;
1566        unsigned long dirty_ratelimit;
1567        struct backing_dev_info *bdi = wb->bdi;
1568        bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1569        unsigned long start_time = jiffies;
1570
1571        for (;;) {
1572                unsigned long now = jiffies;
1573                unsigned long dirty, thresh, bg_thresh;
1574                unsigned long m_dirty = 0;      /* stop bogus uninit warnings */
1575                unsigned long m_thresh = 0;
1576                unsigned long m_bg_thresh = 0;
1577
1578                nr_reclaimable = global_node_page_state(NR_FILE_DIRTY);
1579                gdtc->avail = global_dirtyable_memory();
1580                gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
1581
1582                domain_dirty_limits(gdtc);
1583
1584                if (unlikely(strictlimit)) {
1585                        wb_dirty_limits(gdtc);
1586
1587                        dirty = gdtc->wb_dirty;
1588                        thresh = gdtc->wb_thresh;
1589                        bg_thresh = gdtc->wb_bg_thresh;
1590                } else {
1591                        dirty = gdtc->dirty;
1592                        thresh = gdtc->thresh;
1593                        bg_thresh = gdtc->bg_thresh;
1594                }
1595
1596                if (mdtc) {
1597                        unsigned long filepages, headroom, writeback;
1598
1599                        /*
1600                         * If @wb belongs to !root memcg, repeat the same
1601                         * basic calculations for the memcg domain.
1602                         */
1603                        mem_cgroup_wb_stats(wb, &filepages, &headroom,
1604                                            &mdtc->dirty, &writeback);
1605                        mdtc->dirty += writeback;
1606                        mdtc_calc_avail(mdtc, filepages, headroom);
1607
1608                        domain_dirty_limits(mdtc);
1609
1610                        if (unlikely(strictlimit)) {
1611                                wb_dirty_limits(mdtc);
1612                                m_dirty = mdtc->wb_dirty;
1613                                m_thresh = mdtc->wb_thresh;
1614                                m_bg_thresh = mdtc->wb_bg_thresh;
1615                        } else {
1616                                m_dirty = mdtc->dirty;
1617                                m_thresh = mdtc->thresh;
1618                                m_bg_thresh = mdtc->bg_thresh;
1619                        }
1620                }
1621
1622                /*
1623                 * Throttle it only when the background writeback cannot
1624                 * catch-up. This avoids (excessively) small writeouts
1625                 * when the wb limits are ramping up in case of !strictlimit.
1626                 *
1627                 * In strictlimit case make decision based on the wb counters
1628                 * and limits. Small writeouts when the wb limits are ramping
1629                 * up are the price we consciously pay for strictlimit-ing.
1630                 *
1631                 * If memcg domain is in effect, @dirty should be under
1632                 * both global and memcg freerun ceilings.
1633                 */
1634                if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1635                    (!mdtc ||
1636                     m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1637                        unsigned long intv;
1638                        unsigned long m_intv;
1639
1640free_running:
1641                        intv = dirty_poll_interval(dirty, thresh);
1642                        m_intv = ULONG_MAX;
1643
1644                        current->dirty_paused_when = now;
1645                        current->nr_dirtied = 0;
1646                        if (mdtc)
1647                                m_intv = dirty_poll_interval(m_dirty, m_thresh);
1648                        current->nr_dirtied_pause = min(intv, m_intv);
1649                        break;
1650                }
1651
1652                if (unlikely(!writeback_in_progress(wb)))
1653                        wb_start_background_writeback(wb);
1654
1655                mem_cgroup_flush_foreign(wb);
1656
1657                /*
1658                 * Calculate global domain's pos_ratio and select the
1659                 * global dtc by default.
1660                 */
1661                if (!strictlimit) {
1662                        wb_dirty_limits(gdtc);
1663
1664                        if ((current->flags & PF_LOCAL_THROTTLE) &&
1665                            gdtc->wb_dirty <
1666                            dirty_freerun_ceiling(gdtc->wb_thresh,
1667                                                  gdtc->wb_bg_thresh))
1668                                /*
1669                                 * LOCAL_THROTTLE tasks must not be throttled
1670                                 * when below the per-wb freerun ceiling.
1671                                 */
1672                                goto free_running;
1673                }
1674
1675                dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1676                        ((gdtc->dirty > gdtc->thresh) || strictlimit);
1677
1678                wb_position_ratio(gdtc);
1679                sdtc = gdtc;
1680
1681                if (mdtc) {
1682                        /*
1683                         * If memcg domain is in effect, calculate its
1684                         * pos_ratio.  @wb should satisfy constraints from
1685                         * both global and memcg domains.  Choose the one
1686                         * w/ lower pos_ratio.
1687                         */
1688                        if (!strictlimit) {
1689                                wb_dirty_limits(mdtc);
1690
1691                                if ((current->flags & PF_LOCAL_THROTTLE) &&
1692                                    mdtc->wb_dirty <
1693                                    dirty_freerun_ceiling(mdtc->wb_thresh,
1694                                                          mdtc->wb_bg_thresh))
1695                                        /*
1696                                         * LOCAL_THROTTLE tasks must not be
1697                                         * throttled when below the per-wb
1698                                         * freerun ceiling.
1699                                         */
1700                                        goto free_running;
1701                        }
1702                        dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1703                                ((mdtc->dirty > mdtc->thresh) || strictlimit);
1704
1705                        wb_position_ratio(mdtc);
1706                        if (mdtc->pos_ratio < gdtc->pos_ratio)
1707                                sdtc = mdtc;
1708                }
1709
1710                if (dirty_exceeded && !wb->dirty_exceeded)
1711                        wb->dirty_exceeded = 1;
1712
1713                if (time_is_before_jiffies(wb->bw_time_stamp +
1714                                           BANDWIDTH_INTERVAL)) {
1715                        spin_lock(&wb->list_lock);
1716                        __wb_update_bandwidth(gdtc, mdtc, start_time, true);
1717                        spin_unlock(&wb->list_lock);
1718                }
1719
1720                /* throttle according to the chosen dtc */
1721                dirty_ratelimit = wb->dirty_ratelimit;
1722                task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1723                                                        RATELIMIT_CALC_SHIFT;
1724                max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1725                min_pause = wb_min_pause(wb, max_pause,
1726                                         task_ratelimit, dirty_ratelimit,
1727                                         &nr_dirtied_pause);
1728
1729                if (unlikely(task_ratelimit == 0)) {
1730                        period = max_pause;
1731                        pause = max_pause;
1732                        goto pause;
1733                }
1734                period = HZ * pages_dirtied / task_ratelimit;
1735                pause = period;
1736                if (current->dirty_paused_when)
1737                        pause -= now - current->dirty_paused_when;
1738                /*
1739                 * For less than 1s think time (ext3/4 may block the dirtier
1740                 * for up to 800ms from time to time on 1-HDD; so does xfs,
1741                 * however at much less frequency), try to compensate it in
1742                 * future periods by updating the virtual time; otherwise just
1743                 * do a reset, as it may be a light dirtier.
1744                 */
1745                if (pause < min_pause) {
1746                        trace_balance_dirty_pages(wb,
1747                                                  sdtc->thresh,
1748                                                  sdtc->bg_thresh,
1749                                                  sdtc->dirty,
1750                                                  sdtc->wb_thresh,
1751                                                  sdtc->wb_dirty,
1752                                                  dirty_ratelimit,
1753                                                  task_ratelimit,
1754                                                  pages_dirtied,
1755                                                  period,
1756                                                  min(pause, 0L),
1757                                                  start_time);
1758                        if (pause < -HZ) {
1759                                current->dirty_paused_when = now;
1760                                current->nr_dirtied = 0;
1761                        } else if (period) {
1762                                current->dirty_paused_when += period;
1763                                current->nr_dirtied = 0;
1764                        } else if (current->nr_dirtied_pause <= pages_dirtied)
1765                                current->nr_dirtied_pause += pages_dirtied;
1766                        break;
1767                }
1768                if (unlikely(pause > max_pause)) {
1769                        /* for occasional dropped task_ratelimit */
1770                        now += min(pause - max_pause, max_pause);
1771                        pause = max_pause;
1772                }
1773
1774pause:
1775                trace_balance_dirty_pages(wb,
1776                                          sdtc->thresh,
1777                                          sdtc->bg_thresh,
1778                                          sdtc->dirty,
1779                                          sdtc->wb_thresh,
1780                                          sdtc->wb_dirty,
1781                                          dirty_ratelimit,
1782                                          task_ratelimit,
1783                                          pages_dirtied,
1784                                          period,
1785                                          pause,
1786                                          start_time);
1787                __set_current_state(TASK_KILLABLE);
1788                wb->dirty_sleep = now;
1789                io_schedule_timeout(pause);
1790
1791                current->dirty_paused_when = now + pause;
1792                current->nr_dirtied = 0;
1793                current->nr_dirtied_pause = nr_dirtied_pause;
1794
1795                /*
1796                 * This is typically equal to (dirty < thresh) and can also
1797                 * keep "1000+ dd on a slow USB stick" under control.
1798                 */
1799                if (task_ratelimit)
1800                        break;
1801
1802                /*
1803                 * In the case of an unresponsive NFS server and the NFS dirty
1804                 * pages exceeds dirty_thresh, give the other good wb's a pipe
1805                 * to go through, so that tasks on them still remain responsive.
1806                 *
1807                 * In theory 1 page is enough to keep the consumer-producer
1808                 * pipe going: the flusher cleans 1 page => the task dirties 1
1809                 * more page. However wb_dirty has accounting errors.  So use
1810                 * the larger and more IO friendly wb_stat_error.
1811                 */
1812                if (sdtc->wb_dirty <= wb_stat_error())
1813                        break;
1814
1815                if (fatal_signal_pending(current))
1816                        break;
1817        }
1818
1819        if (!dirty_exceeded && wb->dirty_exceeded)
1820                wb->dirty_exceeded = 0;
1821
1822        if (writeback_in_progress(wb))
1823                return;
1824
1825        /*
1826         * In laptop mode, we wait until hitting the higher threshold before
1827         * starting background writeout, and then write out all the way down
1828         * to the lower threshold.  So slow writers cause minimal disk activity.
1829         *
1830         * In normal mode, we start background writeout at the lower
1831         * background_thresh, to keep the amount of dirty memory low.
1832         */
1833        if (laptop_mode)
1834                return;
1835
1836        if (nr_reclaimable > gdtc->bg_thresh)
1837                wb_start_background_writeback(wb);
1838}
1839
1840static DEFINE_PER_CPU(int, bdp_ratelimits);
1841
1842/*
1843 * Normal tasks are throttled by
1844 *      loop {
1845 *              dirty tsk->nr_dirtied_pause pages;
1846 *              take a snap in balance_dirty_pages();
1847 *      }
1848 * However there is a worst case. If every task exit immediately when dirtied
1849 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1850 * called to throttle the page dirties. The solution is to save the not yet
1851 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1852 * randomly into the running tasks. This works well for the above worst case,
1853 * as the new task will pick up and accumulate the old task's leaked dirty
1854 * count and eventually get throttled.
1855 */
1856DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1857
1858/**
1859 * balance_dirty_pages_ratelimited - balance dirty memory state
1860 * @mapping: address_space which was dirtied
1861 *
1862 * Processes which are dirtying memory should call in here once for each page
1863 * which was newly dirtied.  The function will periodically check the system's
1864 * dirty state and will initiate writeback if needed.
1865 *
1866 * Once we're over the dirty memory limit we decrease the ratelimiting
1867 * by a lot, to prevent individual processes from overshooting the limit
1868 * by (ratelimit_pages) each.
1869 */
1870void balance_dirty_pages_ratelimited(struct address_space *mapping)
1871{
1872        struct inode *inode = mapping->host;
1873        struct backing_dev_info *bdi = inode_to_bdi(inode);
1874        struct bdi_writeback *wb = NULL;
1875        int ratelimit;
1876        int *p;
1877
1878        if (!(bdi->capabilities & BDI_CAP_WRITEBACK))
1879                return;
1880
1881        if (inode_cgwb_enabled(inode))
1882                wb = wb_get_create_current(bdi, GFP_KERNEL);
1883        if (!wb)
1884                wb = &bdi->wb;
1885
1886        ratelimit = current->nr_dirtied_pause;
1887        if (wb->dirty_exceeded)
1888                ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1889
1890        preempt_disable();
1891        /*
1892         * This prevents one CPU to accumulate too many dirtied pages without
1893         * calling into balance_dirty_pages(), which can happen when there are
1894         * 1000+ tasks, all of them start dirtying pages at exactly the same
1895         * time, hence all honoured too large initial task->nr_dirtied_pause.
1896         */
1897        p =  this_cpu_ptr(&bdp_ratelimits);
1898        if (unlikely(current->nr_dirtied >= ratelimit))
1899                *p = 0;
1900        else if (unlikely(*p >= ratelimit_pages)) {
1901                *p = 0;
1902                ratelimit = 0;
1903        }
1904        /*
1905         * Pick up the dirtied pages by the exited tasks. This avoids lots of
1906         * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1907         * the dirty throttling and livelock other long-run dirtiers.
1908         */
1909        p = this_cpu_ptr(&dirty_throttle_leaks);
1910        if (*p > 0 && current->nr_dirtied < ratelimit) {
1911                unsigned long nr_pages_dirtied;
1912                nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1913                *p -= nr_pages_dirtied;
1914                current->nr_dirtied += nr_pages_dirtied;
1915        }
1916        preempt_enable();
1917
1918        if (unlikely(current->nr_dirtied >= ratelimit))
1919                balance_dirty_pages(wb, current->nr_dirtied);
1920
1921        wb_put(wb);
1922}
1923EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1924
1925/**
1926 * wb_over_bg_thresh - does @wb need to be written back?
1927 * @wb: bdi_writeback of interest
1928 *
1929 * Determines whether background writeback should keep writing @wb or it's
1930 * clean enough.
1931 *
1932 * Return: %true if writeback should continue.
1933 */
1934bool wb_over_bg_thresh(struct bdi_writeback *wb)
1935{
1936        struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1937        struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1938        struct dirty_throttle_control * const gdtc = &gdtc_stor;
1939        struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1940                                                     &mdtc_stor : NULL;
1941        unsigned long reclaimable;
1942        unsigned long thresh;
1943
1944        /*
1945         * Similar to balance_dirty_pages() but ignores pages being written
1946         * as we're trying to decide whether to put more under writeback.
1947         */
1948        gdtc->avail = global_dirtyable_memory();
1949        gdtc->dirty = global_node_page_state(NR_FILE_DIRTY);
1950        domain_dirty_limits(gdtc);
1951
1952        if (gdtc->dirty > gdtc->bg_thresh)
1953                return true;
1954
1955        thresh = wb_calc_thresh(gdtc->wb, gdtc->bg_thresh);
1956        if (thresh < 2 * wb_stat_error())
1957                reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1958        else
1959                reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1960
1961        if (reclaimable > thresh)
1962                return true;
1963
1964        if (mdtc) {
1965                unsigned long filepages, headroom, writeback;
1966
1967                mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
1968                                    &writeback);
1969                mdtc_calc_avail(mdtc, filepages, headroom);
1970                domain_dirty_limits(mdtc);      /* ditto, ignore writeback */
1971
1972                if (mdtc->dirty > mdtc->bg_thresh)
1973                        return true;
1974
1975                thresh = wb_calc_thresh(mdtc->wb, mdtc->bg_thresh);
1976                if (thresh < 2 * wb_stat_error())
1977                        reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1978                else
1979                        reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1980
1981                if (reclaimable > thresh)
1982                        return true;
1983        }
1984
1985        return false;
1986}
1987
1988/*
1989 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1990 */
1991int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
1992                void *buffer, size_t *length, loff_t *ppos)
1993{
1994        unsigned int old_interval = dirty_writeback_interval;
1995        int ret;
1996
1997        ret = proc_dointvec(table, write, buffer, length, ppos);
1998
1999        /*
2000         * Writing 0 to dirty_writeback_interval will disable periodic writeback
2001         * and a different non-zero value will wakeup the writeback threads.
2002         * wb_wakeup_delayed() would be more appropriate, but it's a pain to
2003         * iterate over all bdis and wbs.
2004         * The reason we do this is to make the change take effect immediately.
2005         */
2006        if (!ret && write && dirty_writeback_interval &&
2007                dirty_writeback_interval != old_interval)
2008                wakeup_flusher_threads(WB_REASON_PERIODIC);
2009
2010        return ret;
2011}
2012
2013#ifdef CONFIG_BLOCK
2014void laptop_mode_timer_fn(struct timer_list *t)
2015{
2016        struct backing_dev_info *backing_dev_info =
2017                from_timer(backing_dev_info, t, laptop_mode_wb_timer);
2018
2019        wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
2020}
2021
2022/*
2023 * We've spun up the disk and we're in laptop mode: schedule writeback
2024 * of all dirty data a few seconds from now.  If the flush is already scheduled
2025 * then push it back - the user is still using the disk.
2026 */
2027void laptop_io_completion(struct backing_dev_info *info)
2028{
2029        mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2030}
2031
2032/*
2033 * We're in laptop mode and we've just synced. The sync's writes will have
2034 * caused another writeback to be scheduled by laptop_io_completion.
2035 * Nothing needs to be written back anymore, so we unschedule the writeback.
2036 */
2037void laptop_sync_completion(void)
2038{
2039        struct backing_dev_info *bdi;
2040
2041        rcu_read_lock();
2042
2043        list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2044                del_timer(&bdi->laptop_mode_wb_timer);
2045
2046        rcu_read_unlock();
2047}
2048#endif
2049
2050/*
2051 * If ratelimit_pages is too high then we can get into dirty-data overload
2052 * if a large number of processes all perform writes at the same time.
2053 *
2054 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2055 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2056 * thresholds.
2057 */
2058
2059void writeback_set_ratelimit(void)
2060{
2061        struct wb_domain *dom = &global_wb_domain;
2062        unsigned long background_thresh;
2063        unsigned long dirty_thresh;
2064
2065        global_dirty_limits(&background_thresh, &dirty_thresh);
2066        dom->dirty_limit = dirty_thresh;
2067        ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2068        if (ratelimit_pages < 16)
2069                ratelimit_pages = 16;
2070}
2071
2072static int page_writeback_cpu_online(unsigned int cpu)
2073{
2074        writeback_set_ratelimit();
2075        return 0;
2076}
2077
2078/*
2079 * Called early on to tune the page writeback dirty limits.
2080 *
2081 * We used to scale dirty pages according to how total memory
2082 * related to pages that could be allocated for buffers.
2083 *
2084 * However, that was when we used "dirty_ratio" to scale with
2085 * all memory, and we don't do that any more. "dirty_ratio"
2086 * is now applied to total non-HIGHPAGE memory, and as such we can't
2087 * get into the old insane situation any more where we had
2088 * large amounts of dirty pages compared to a small amount of
2089 * non-HIGHMEM memory.
2090 *
2091 * But we might still want to scale the dirty_ratio by how
2092 * much memory the box has..
2093 */
2094void __init page_writeback_init(void)
2095{
2096        BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2097
2098        cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2099                          page_writeback_cpu_online, NULL);
2100        cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2101                          page_writeback_cpu_online);
2102}
2103
2104/**
2105 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2106 * @mapping: address space structure to write
2107 * @start: starting page index
2108 * @end: ending page index (inclusive)
2109 *
2110 * This function scans the page range from @start to @end (inclusive) and tags
2111 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2112 * that write_cache_pages (or whoever calls this function) will then use
2113 * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
2114 * used to avoid livelocking of writeback by a process steadily creating new
2115 * dirty pages in the file (thus it is important for this function to be quick
2116 * so that it can tag pages faster than a dirtying process can create them).
2117 */
2118void tag_pages_for_writeback(struct address_space *mapping,
2119                             pgoff_t start, pgoff_t end)
2120{
2121        XA_STATE(xas, &mapping->i_pages, start);
2122        unsigned int tagged = 0;
2123        void *page;
2124
2125        xas_lock_irq(&xas);
2126        xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) {
2127                xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
2128                if (++tagged % XA_CHECK_SCHED)
2129                        continue;
2130
2131                xas_pause(&xas);
2132                xas_unlock_irq(&xas);
2133                cond_resched();
2134                xas_lock_irq(&xas);
2135        }
2136        xas_unlock_irq(&xas);
2137}
2138EXPORT_SYMBOL(tag_pages_for_writeback);
2139
2140/**
2141 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2142 * @mapping: address space structure to write
2143 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2144 * @writepage: function called for each page
2145 * @data: data passed to writepage function
2146 *
2147 * If a page is already under I/O, write_cache_pages() skips it, even
2148 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
2149 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
2150 * and msync() need to guarantee that all the data which was dirty at the time
2151 * the call was made get new I/O started against them.  If wbc->sync_mode is
2152 * WB_SYNC_ALL then we were called for data integrity and we must wait for
2153 * existing IO to complete.
2154 *
2155 * To avoid livelocks (when other process dirties new pages), we first tag
2156 * pages which should be written back with TOWRITE tag and only then start
2157 * writing them. For data-integrity sync we have to be careful so that we do
2158 * not miss some pages (e.g., because some other process has cleared TOWRITE
2159 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2160 * by the process clearing the DIRTY tag (and submitting the page for IO).
2161 *
2162 * To avoid deadlocks between range_cyclic writeback and callers that hold
2163 * pages in PageWriteback to aggregate IO until write_cache_pages() returns,
2164 * we do not loop back to the start of the file. Doing so causes a page
2165 * lock/page writeback access order inversion - we should only ever lock
2166 * multiple pages in ascending page->index order, and looping back to the start
2167 * of the file violates that rule and causes deadlocks.
2168 *
2169 * Return: %0 on success, negative error code otherwise
2170 */
2171int write_cache_pages(struct address_space *mapping,
2172                      struct writeback_control *wbc, writepage_t writepage,
2173                      void *data)
2174{
2175        int ret = 0;
2176        int done = 0;
2177        int error;
2178        struct pagevec pvec;
2179        int nr_pages;
2180        pgoff_t index;
2181        pgoff_t end;            /* Inclusive */
2182        pgoff_t done_index;
2183        int range_whole = 0;
2184        xa_mark_t tag;
2185
2186        pagevec_init(&pvec);
2187        if (wbc->range_cyclic) {
2188                index = mapping->writeback_index; /* prev offset */
2189                end = -1;
2190        } else {
2191                index = wbc->range_start >> PAGE_SHIFT;
2192                end = wbc->range_end >> PAGE_SHIFT;
2193                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2194                        range_whole = 1;
2195        }
2196        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
2197                tag_pages_for_writeback(mapping, index, end);
2198                tag = PAGECACHE_TAG_TOWRITE;
2199        } else {
2200                tag = PAGECACHE_TAG_DIRTY;
2201        }
2202        done_index = index;
2203        while (!done && (index <= end)) {
2204                int i;
2205
2206                nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
2207                                tag);
2208                if (nr_pages == 0)
2209                        break;
2210
2211                for (i = 0; i < nr_pages; i++) {
2212                        struct page *page = pvec.pages[i];
2213
2214                        done_index = page->index;
2215
2216                        lock_page(page);
2217
2218                        /*
2219                         * Page truncated or invalidated. We can freely skip it
2220                         * then, even for data integrity operations: the page
2221                         * has disappeared concurrently, so there could be no
2222                         * real expectation of this data integrity operation
2223                         * even if there is now a new, dirty page at the same
2224                         * pagecache address.
2225                         */
2226                        if (unlikely(page->mapping != mapping)) {
2227continue_unlock:
2228                                unlock_page(page);
2229                                continue;
2230                        }
2231
2232                        if (!PageDirty(page)) {
2233                                /* someone wrote it for us */
2234                                goto continue_unlock;
2235                        }
2236
2237                        if (PageWriteback(page)) {
2238                                if (wbc->sync_mode != WB_SYNC_NONE)
2239                                        wait_on_page_writeback(page);
2240                                else
2241                                        goto continue_unlock;
2242                        }
2243
2244                        BUG_ON(PageWriteback(page));
2245                        if (!clear_page_dirty_for_io(page))
2246                                goto continue_unlock;
2247
2248                        trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2249                        error = (*writepage)(page, wbc, data);
2250                        if (unlikely(error)) {
2251                                /*
2252                                 * Handle errors according to the type of
2253                                 * writeback. There's no need to continue for
2254                                 * background writeback. Just push done_index
2255                                 * past this page so media errors won't choke
2256                                 * writeout for the entire file. For integrity
2257                                 * writeback, we must process the entire dirty
2258                                 * set regardless of errors because the fs may
2259                                 * still have state to clear for each page. In
2260                                 * that case we continue processing and return
2261                                 * the first error.
2262                                 */
2263                                if (error == AOP_WRITEPAGE_ACTIVATE) {
2264                                        unlock_page(page);
2265                                        error = 0;
2266                                } else if (wbc->sync_mode != WB_SYNC_ALL) {
2267                                        ret = error;
2268                                        done_index = page->index + 1;
2269                                        done = 1;
2270                                        break;
2271                                }
2272                                if (!ret)
2273                                        ret = error;
2274                        }
2275
2276                        /*
2277                         * We stop writing back only if we are not doing
2278                         * integrity sync. In case of integrity sync we have to
2279                         * keep going until we have written all the pages
2280                         * we tagged for writeback prior to entering this loop.
2281                         */
2282                        if (--wbc->nr_to_write <= 0 &&
2283                            wbc->sync_mode == WB_SYNC_NONE) {
2284                                done = 1;
2285                                break;
2286                        }
2287                }
2288                pagevec_release(&pvec);
2289                cond_resched();
2290        }
2291
2292        /*
2293         * If we hit the last page and there is more work to be done: wrap
2294         * back the index back to the start of the file for the next
2295         * time we are called.
2296         */
2297        if (wbc->range_cyclic && !done)
2298                done_index = 0;
2299        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2300                mapping->writeback_index = done_index;
2301
2302        return ret;
2303}
2304EXPORT_SYMBOL(write_cache_pages);
2305
2306/*
2307 * Function used by generic_writepages to call the real writepage
2308 * function and set the mapping flags on error
2309 */
2310static int __writepage(struct page *page, struct writeback_control *wbc,
2311                       void *data)
2312{
2313        struct address_space *mapping = data;
2314        int ret = mapping->a_ops->writepage(page, wbc);
2315        mapping_set_error(mapping, ret);
2316        return ret;
2317}
2318
2319/**
2320 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2321 * @mapping: address space structure to write
2322 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2323 *
2324 * This is a library function, which implements the writepages()
2325 * address_space_operation.
2326 *
2327 * Return: %0 on success, negative error code otherwise
2328 */
2329int generic_writepages(struct address_space *mapping,
2330                       struct writeback_control *wbc)
2331{
2332        struct blk_plug plug;
2333        int ret;
2334
2335        /* deal with chardevs and other special file */
2336        if (!mapping->a_ops->writepage)
2337                return 0;
2338
2339        blk_start_plug(&plug);
2340        ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2341        blk_finish_plug(&plug);
2342        return ret;
2343}
2344
2345EXPORT_SYMBOL(generic_writepages);
2346
2347int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2348{
2349        int ret;
2350
2351        if (wbc->nr_to_write <= 0)
2352                return 0;
2353        while (1) {
2354                if (mapping->a_ops->writepages)
2355                        ret = mapping->a_ops->writepages(mapping, wbc);
2356                else
2357                        ret = generic_writepages(mapping, wbc);
2358                if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
2359                        break;
2360                cond_resched();
2361                congestion_wait(BLK_RW_ASYNC, HZ/50);
2362        }
2363        return ret;
2364}
2365
2366/**
2367 * write_one_page - write out a single page and wait on I/O
2368 * @page: the page to write
2369 *
2370 * The page must be locked by the caller and will be unlocked upon return.
2371 *
2372 * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
2373 * function returns.
2374 *
2375 * Return: %0 on success, negative error code otherwise
2376 */
2377int write_one_page(struct page *page)
2378{
2379        struct address_space *mapping = page->mapping;
2380        int ret = 0;
2381        struct writeback_control wbc = {
2382                .sync_mode = WB_SYNC_ALL,
2383                .nr_to_write = 1,
2384        };
2385
2386        BUG_ON(!PageLocked(page));
2387
2388        wait_on_page_writeback(page);
2389
2390        if (clear_page_dirty_for_io(page)) {
2391                get_page(page);
2392                ret = mapping->a_ops->writepage(page, &wbc);
2393                if (ret == 0)
2394                        wait_on_page_writeback(page);
2395                put_page(page);
2396        } else {
2397                unlock_page(page);
2398        }
2399
2400        if (!ret)
2401                ret = filemap_check_errors(mapping);
2402        return ret;
2403}
2404EXPORT_SYMBOL(write_one_page);
2405
2406/*
2407 * For address_spaces which do not use buffers nor write back.
2408 */
2409int __set_page_dirty_no_writeback(struct page *page)
2410{
2411        if (!PageDirty(page))
2412                return !TestSetPageDirty(page);
2413        return 0;
2414}
2415EXPORT_SYMBOL(__set_page_dirty_no_writeback);
2416
2417/*
2418 * Helper function for set_page_dirty family.
2419 *
2420 * Caller must hold lock_page_memcg().
2421 *
2422 * NOTE: This relies on being atomic wrt interrupts.
2423 */
2424static void account_page_dirtied(struct page *page,
2425                struct address_space *mapping)
2426{
2427        struct inode *inode = mapping->host;
2428
2429        trace_writeback_dirty_page(page, mapping);
2430
2431        if (mapping_can_writeback(mapping)) {
2432                struct bdi_writeback *wb;
2433
2434                inode_attach_wb(inode, page);
2435                wb = inode_to_wb(inode);
2436
2437                __inc_lruvec_page_state(page, NR_FILE_DIRTY);
2438                __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2439                __inc_node_page_state(page, NR_DIRTIED);
2440                inc_wb_stat(wb, WB_RECLAIMABLE);
2441                inc_wb_stat(wb, WB_DIRTIED);
2442                task_io_account_write(PAGE_SIZE);
2443                current->nr_dirtied++;
2444                __this_cpu_inc(bdp_ratelimits);
2445
2446                mem_cgroup_track_foreign_dirty(page, wb);
2447        }
2448}
2449
2450/*
2451 * Helper function for deaccounting dirty page without writeback.
2452 *
2453 * Caller must hold lock_page_memcg().
2454 */
2455void account_page_cleaned(struct page *page, struct address_space *mapping,
2456                          struct bdi_writeback *wb)
2457{
2458        if (mapping_can_writeback(mapping)) {
2459                dec_lruvec_page_state(page, NR_FILE_DIRTY);
2460                dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2461                dec_wb_stat(wb, WB_RECLAIMABLE);
2462                task_io_account_cancelled_write(PAGE_SIZE);
2463        }
2464}
2465
2466/*
2467 * Mark the page dirty, and set it dirty in the page cache, and mark the inode
2468 * dirty.
2469 *
2470 * If warn is true, then emit a warning if the page is not uptodate and has
2471 * not been truncated.
2472 *
2473 * The caller must hold lock_page_memcg().
2474 */
2475void __set_page_dirty(struct page *page, struct address_space *mapping,
2476                             int warn)
2477{
2478        unsigned long flags;
2479
2480        xa_lock_irqsave(&mapping->i_pages, flags);
2481        if (page->mapping) {    /* Race with truncate? */
2482                WARN_ON_ONCE(warn && !PageUptodate(page));
2483                account_page_dirtied(page, mapping);
2484                __xa_set_mark(&mapping->i_pages, page_index(page),
2485                                PAGECACHE_TAG_DIRTY);
2486        }
2487        xa_unlock_irqrestore(&mapping->i_pages, flags);
2488}
2489
2490/*
2491 * For address_spaces which do not use buffers.  Just tag the page as dirty in
2492 * the xarray.
2493 *
2494 * This is also used when a single buffer is being dirtied: we want to set the
2495 * page dirty in that case, but not all the buffers.  This is a "bottom-up"
2496 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2497 *
2498 * The caller must ensure this doesn't race with truncation.  Most will simply
2499 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2500 * the pte lock held, which also locks out truncation.
2501 */
2502int __set_page_dirty_nobuffers(struct page *page)
2503{
2504        lock_page_memcg(page);
2505        if (!TestSetPageDirty(page)) {
2506                struct address_space *mapping = page_mapping(page);
2507
2508                if (!mapping) {
2509                        unlock_page_memcg(page);
2510                        return 1;
2511                }
2512                __set_page_dirty(page, mapping, !PagePrivate(page));
2513                unlock_page_memcg(page);
2514
2515                if (mapping->host) {
2516                        /* !PageAnon && !swapper_space */
2517                        __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2518                }
2519                return 1;
2520        }
2521        unlock_page_memcg(page);
2522        return 0;
2523}
2524EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2525
2526/*
2527 * Call this whenever redirtying a page, to de-account the dirty counters
2528 * (NR_DIRTIED, WB_DIRTIED, tsk->nr_dirtied), so that they match the written
2529 * counters (NR_WRITTEN, WB_WRITTEN) in long term. The mismatches will lead to
2530 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2531 * control.
2532 */
2533void account_page_redirty(struct page *page)
2534{
2535        struct address_space *mapping = page->mapping;
2536
2537        if (mapping && mapping_can_writeback(mapping)) {
2538                struct inode *inode = mapping->host;
2539                struct bdi_writeback *wb;
2540                struct wb_lock_cookie cookie = {};
2541
2542                wb = unlocked_inode_to_wb_begin(inode, &cookie);
2543                current->nr_dirtied--;
2544                dec_node_page_state(page, NR_DIRTIED);
2545                dec_wb_stat(wb, WB_DIRTIED);
2546                unlocked_inode_to_wb_end(inode, &cookie);
2547        }
2548}
2549EXPORT_SYMBOL(account_page_redirty);
2550
2551/*
2552 * When a writepage implementation decides that it doesn't want to write this
2553 * page for some reason, it should redirty the locked page via
2554 * redirty_page_for_writepage() and it should then unlock the page and return 0
2555 */
2556int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2557{
2558        int ret;
2559
2560        wbc->pages_skipped++;
2561        ret = __set_page_dirty_nobuffers(page);
2562        account_page_redirty(page);
2563        return ret;
2564}
2565EXPORT_SYMBOL(redirty_page_for_writepage);
2566
2567/*
2568 * Dirty a page.
2569 *
2570 * For pages with a mapping this should be done under the page lock for the
2571 * benefit of asynchronous memory errors who prefer a consistent dirty state.
2572 * This rule can be broken in some special cases, but should be better not to.
2573 */
2574int set_page_dirty(struct page *page)
2575{
2576        struct address_space *mapping = page_mapping(page);
2577
2578        page = compound_head(page);
2579        if (likely(mapping)) {
2580                /*
2581                 * readahead/lru_deactivate_page could remain
2582                 * PG_readahead/PG_reclaim due to race with end_page_writeback
2583                 * About readahead, if the page is written, the flags would be
2584                 * reset. So no problem.
2585                 * About lru_deactivate_page, if the page is redirty, the flag
2586                 * will be reset. So no problem. but if the page is used by readahead
2587                 * it will confuse readahead and make it restart the size rampup
2588                 * process. But it's a trivial problem.
2589                 */
2590                if (PageReclaim(page))
2591                        ClearPageReclaim(page);
2592                return mapping->a_ops->set_page_dirty(page);
2593        }
2594        if (!PageDirty(page)) {
2595                if (!TestSetPageDirty(page))
2596                        return 1;
2597        }
2598        return 0;
2599}
2600EXPORT_SYMBOL(set_page_dirty);
2601
2602/*
2603 * set_page_dirty() is racy if the caller has no reference against
2604 * page->mapping->host, and if the page is unlocked.  This is because another
2605 * CPU could truncate the page off the mapping and then free the mapping.
2606 *
2607 * Usually, the page _is_ locked, or the caller is a user-space process which
2608 * holds a reference on the inode by having an open file.
2609 *
2610 * In other cases, the page should be locked before running set_page_dirty().
2611 */
2612int set_page_dirty_lock(struct page *page)
2613{
2614        int ret;
2615
2616        lock_page(page);
2617        ret = set_page_dirty(page);
2618        unlock_page(page);
2619        return ret;
2620}
2621EXPORT_SYMBOL(set_page_dirty_lock);
2622
2623/*
2624 * This cancels just the dirty bit on the kernel page itself, it does NOT
2625 * actually remove dirty bits on any mmap's that may be around. It also
2626 * leaves the page tagged dirty, so any sync activity will still find it on
2627 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2628 * look at the dirty bits in the VM.
2629 *
2630 * Doing this should *normally* only ever be done when a page is truncated,
2631 * and is not actually mapped anywhere at all. However, fs/buffer.c does
2632 * this when it notices that somebody has cleaned out all the buffers on a
2633 * page without actually doing it through the VM. Can you say "ext3 is
2634 * horribly ugly"? Thought you could.
2635 */
2636void __cancel_dirty_page(struct page *page)
2637{
2638        struct address_space *mapping = page_mapping(page);
2639
2640        if (mapping_can_writeback(mapping)) {
2641                struct inode *inode = mapping->host;
2642                struct bdi_writeback *wb;
2643                struct wb_lock_cookie cookie = {};
2644
2645                lock_page_memcg(page);
2646                wb = unlocked_inode_to_wb_begin(inode, &cookie);
2647
2648                if (TestClearPageDirty(page))
2649                        account_page_cleaned(page, mapping, wb);
2650
2651                unlocked_inode_to_wb_end(inode, &cookie);
2652                unlock_page_memcg(page);
2653        } else {
2654                ClearPageDirty(page);
2655        }
2656}
2657EXPORT_SYMBOL(__cancel_dirty_page);
2658
2659/*
2660 * Clear a page's dirty flag, while caring for dirty memory accounting.
2661 * Returns true if the page was previously dirty.
2662 *
2663 * This is for preparing to put the page under writeout.  We leave the page
2664 * tagged as dirty in the xarray so that a concurrent write-for-sync
2665 * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
2666 * implementation will run either set_page_writeback() or set_page_dirty(),
2667 * at which stage we bring the page's dirty flag and xarray dirty tag
2668 * back into sync.
2669 *
2670 * This incoherency between the page's dirty flag and xarray tag is
2671 * unfortunate, but it only exists while the page is locked.
2672 */
2673int clear_page_dirty_for_io(struct page *page)
2674{
2675        struct address_space *mapping = page_mapping(page);
2676        int ret = 0;
2677
2678        VM_BUG_ON_PAGE(!PageLocked(page), page);
2679
2680        if (mapping && mapping_can_writeback(mapping)) {
2681                struct inode *inode = mapping->host;
2682                struct bdi_writeback *wb;
2683                struct wb_lock_cookie cookie = {};
2684
2685                /*
2686                 * Yes, Virginia, this is indeed insane.
2687                 *
2688                 * We use this sequence to make sure that
2689                 *  (a) we account for dirty stats properly
2690                 *  (b) we tell the low-level filesystem to
2691                 *      mark the whole page dirty if it was
2692                 *      dirty in a pagetable. Only to then
2693                 *  (c) clean the page again and return 1 to
2694                 *      cause the writeback.
2695                 *
2696                 * This way we avoid all nasty races with the
2697                 * dirty bit in multiple places and clearing
2698                 * them concurrently from different threads.
2699                 *
2700                 * Note! Normally the "set_page_dirty(page)"
2701                 * has no effect on the actual dirty bit - since
2702                 * that will already usually be set. But we
2703                 * need the side effects, and it can help us
2704                 * avoid races.
2705                 *
2706                 * We basically use the page "master dirty bit"
2707                 * as a serialization point for all the different
2708                 * threads doing their things.
2709                 */
2710                if (page_mkclean(page))
2711                        set_page_dirty(page);
2712                /*
2713                 * We carefully synchronise fault handlers against
2714                 * installing a dirty pte and marking the page dirty
2715                 * at this point.  We do this by having them hold the
2716                 * page lock while dirtying the page, and pages are
2717                 * always locked coming in here, so we get the desired
2718                 * exclusion.
2719                 */
2720                wb = unlocked_inode_to_wb_begin(inode, &cookie);
2721                if (TestClearPageDirty(page)) {
2722                        dec_lruvec_page_state(page, NR_FILE_DIRTY);
2723                        dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2724                        dec_wb_stat(wb, WB_RECLAIMABLE);
2725                        ret = 1;
2726                }
2727                unlocked_inode_to_wb_end(inode, &cookie);
2728                return ret;
2729        }
2730        return TestClearPageDirty(page);
2731}
2732EXPORT_SYMBOL(clear_page_dirty_for_io);
2733
2734int test_clear_page_writeback(struct page *page)
2735{
2736        struct address_space *mapping = page_mapping(page);
2737        int ret;
2738
2739        lock_page_memcg(page);
2740        if (mapping && mapping_use_writeback_tags(mapping)) {
2741                struct inode *inode = mapping->host;
2742                struct backing_dev_info *bdi = inode_to_bdi(inode);
2743                unsigned long flags;
2744
2745                xa_lock_irqsave(&mapping->i_pages, flags);
2746                ret = TestClearPageWriteback(page);
2747                if (ret) {
2748                        __xa_clear_mark(&mapping->i_pages, page_index(page),
2749                                                PAGECACHE_TAG_WRITEBACK);
2750                        if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
2751                                struct bdi_writeback *wb = inode_to_wb(inode);
2752
2753                                dec_wb_stat(wb, WB_WRITEBACK);
2754                                __wb_writeout_inc(wb);
2755                        }
2756                }
2757
2758                if (mapping->host && !mapping_tagged(mapping,
2759                                                     PAGECACHE_TAG_WRITEBACK))
2760                        sb_clear_inode_writeback(mapping->host);
2761
2762                xa_unlock_irqrestore(&mapping->i_pages, flags);
2763        } else {
2764                ret = TestClearPageWriteback(page);
2765        }
2766        if (ret) {
2767                dec_lruvec_page_state(page, NR_WRITEBACK);
2768                dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2769                inc_node_page_state(page, NR_WRITTEN);
2770        }
2771        unlock_page_memcg(page);
2772        return ret;
2773}
2774
2775int __test_set_page_writeback(struct page *page, bool keep_write)
2776{
2777        struct address_space *mapping = page_mapping(page);
2778        int ret, access_ret;
2779
2780        lock_page_memcg(page);
2781        if (mapping && mapping_use_writeback_tags(mapping)) {
2782                XA_STATE(xas, &mapping->i_pages, page_index(page));
2783                struct inode *inode = mapping->host;
2784                struct backing_dev_info *bdi = inode_to_bdi(inode);
2785                unsigned long flags;
2786
2787                xas_lock_irqsave(&xas, flags);
2788                xas_load(&xas);
2789                ret = TestSetPageWriteback(page);
2790                if (!ret) {
2791                        bool on_wblist;
2792
2793                        on_wblist = mapping_tagged(mapping,
2794                                                   PAGECACHE_TAG_WRITEBACK);
2795
2796                        xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
2797                        if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT)
2798                                inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
2799
2800                        /*
2801                         * We can come through here when swapping anonymous
2802                         * pages, so we don't necessarily have an inode to track
2803                         * for sync.
2804                         */
2805                        if (mapping->host && !on_wblist)
2806                                sb_mark_inode_writeback(mapping->host);
2807                }
2808                if (!PageDirty(page))
2809                        xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
2810                if (!keep_write)
2811                        xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
2812                xas_unlock_irqrestore(&xas, flags);
2813        } else {
2814                ret = TestSetPageWriteback(page);
2815        }
2816        if (!ret) {
2817                inc_lruvec_page_state(page, NR_WRITEBACK);
2818                inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2819        }
2820        unlock_page_memcg(page);
2821        access_ret = arch_make_page_accessible(page);
2822        /*
2823         * If writeback has been triggered on a page that cannot be made
2824         * accessible, it is too late to recover here.
2825         */
2826        VM_BUG_ON_PAGE(access_ret != 0, page);
2827
2828        return ret;
2829
2830}
2831EXPORT_SYMBOL(__test_set_page_writeback);
2832
2833/*
2834 * Wait for a page to complete writeback
2835 */
2836void wait_on_page_writeback(struct page *page)
2837{
2838        while (PageWriteback(page)) {
2839                trace_wait_on_page_writeback(page, page_mapping(page));
2840                wait_on_page_bit(page, PG_writeback);
2841        }
2842}
2843EXPORT_SYMBOL_GPL(wait_on_page_writeback);
2844
2845/*
2846 * Wait for a page to complete writeback.  Returns -EINTR if we get a
2847 * fatal signal while waiting.
2848 */
2849int wait_on_page_writeback_killable(struct page *page)
2850{
2851        while (PageWriteback(page)) {
2852                trace_wait_on_page_writeback(page, page_mapping(page));
2853                if (wait_on_page_bit_killable(page, PG_writeback))
2854                        return -EINTR;
2855        }
2856
2857        return 0;
2858}
2859EXPORT_SYMBOL_GPL(wait_on_page_writeback_killable);
2860
2861/**
2862 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2863 * @page:       The page to wait on.
2864 *
2865 * This function determines if the given page is related to a backing device
2866 * that requires page contents to be held stable during writeback.  If so, then
2867 * it will wait for any pending writeback to complete.
2868 */
2869void wait_for_stable_page(struct page *page)
2870{
2871        page = thp_head(page);
2872        if (page->mapping->host->i_sb->s_iflags & SB_I_STABLE_WRITES)
2873                wait_on_page_writeback(page);
2874}
2875EXPORT_SYMBOL_GPL(wait_for_stable_page);
2876
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