linux/mm/page-writeback.c
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   1/*
   2 * mm/page-writeback.c
   3 *
   4 * Copyright (C) 2002, Linus Torvalds.
   5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
   6 *
   7 * Contains functions related to writing back dirty pages at the
   8 * address_space level.
   9 *
  10 * 10Apr2002    Andrew Morton
  11 *              Initial version
  12 */
  13
  14#include <linux/kernel.h>
  15#include <linux/export.h>
  16#include <linux/spinlock.h>
  17#include <linux/fs.h>
  18#include <linux/mm.h>
  19#include <linux/swap.h>
  20#include <linux/slab.h>
  21#include <linux/pagemap.h>
  22#include <linux/writeback.h>
  23#include <linux/init.h>
  24#include <linux/backing-dev.h>
  25#include <linux/task_io_accounting_ops.h>
  26#include <linux/blkdev.h>
  27#include <linux/mpage.h>
  28#include <linux/rmap.h>
  29#include <linux/percpu.h>
  30#include <linux/notifier.h>
  31#include <linux/smp.h>
  32#include <linux/sysctl.h>
  33#include <linux/cpu.h>
  34#include <linux/syscalls.h>
  35#include <linux/buffer_head.h> /* __set_page_dirty_buffers */
  36#include <linux/pagevec.h>
  37#include <trace/events/writeback.h>
  38
  39/*
  40 * Sleep at most 200ms at a time in balance_dirty_pages().
  41 */
  42#define MAX_PAUSE               max(HZ/5, 1)
  43
  44/*
  45 * Try to keep balance_dirty_pages() call intervals higher than this many pages
  46 * by raising pause time to max_pause when falls below it.
  47 */
  48#define DIRTY_POLL_THRESH       (128 >> (PAGE_SHIFT - 10))
  49
  50/*
  51 * Estimate write bandwidth at 200ms intervals.
  52 */
  53#define BANDWIDTH_INTERVAL      max(HZ/5, 1)
  54
  55#define RATELIMIT_CALC_SHIFT    10
  56
  57/*
  58 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
  59 * will look to see if it needs to force writeback or throttling.
  60 */
  61static long ratelimit_pages = 32;
  62
  63/* The following parameters are exported via /proc/sys/vm */
  64
  65/*
  66 * Start background writeback (via writeback threads) at this percentage
  67 */
  68int dirty_background_ratio = 10;
  69
  70/*
  71 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
  72 * dirty_background_ratio * the amount of dirtyable memory
  73 */
  74unsigned long dirty_background_bytes;
  75
  76/*
  77 * free highmem will not be subtracted from the total free memory
  78 * for calculating free ratios if vm_highmem_is_dirtyable is true
  79 */
  80int vm_highmem_is_dirtyable;
  81
  82/*
  83 * The generator of dirty data starts writeback at this percentage
  84 */
  85int vm_dirty_ratio = 20;
  86
  87/*
  88 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
  89 * vm_dirty_ratio * the amount of dirtyable memory
  90 */
  91unsigned long vm_dirty_bytes;
  92
  93/*
  94 * The interval between `kupdate'-style writebacks
  95 */
  96unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
  97
  98EXPORT_SYMBOL_GPL(dirty_writeback_interval);
  99
 100/*
 101 * The longest time for which data is allowed to remain dirty
 102 */
 103unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
 104
 105/*
 106 * Flag that makes the machine dump writes/reads and block dirtyings.
 107 */
 108int block_dump;
 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
 120unsigned long global_dirty_limit;
 121
 122/*
 123 * Scale the writeback cache size proportional to the relative writeout speeds.
 124 *
 125 * We do this by keeping a floating proportion between BDIs, based on page
 126 * writeback completions [end_page_writeback()]. Those devices that write out
 127 * pages fastest will get the larger share, while the slower will get a smaller
 128 * share.
 129 *
 130 * We use page writeout completions because we are interested in getting rid of
 131 * dirty pages. Having them written out is the primary goal.
 132 *
 133 * We introduce a concept of time, a period over which we measure these events,
 134 * because demand can/will vary over time. The length of this period itself is
 135 * measured in page writeback completions.
 136 *
 137 */
 138static struct prop_descriptor vm_completions;
 139
 140/*
 141 * Work out the current dirty-memory clamping and background writeout
 142 * thresholds.
 143 *
 144 * The main aim here is to lower them aggressively if there is a lot of mapped
 145 * memory around.  To avoid stressing page reclaim with lots of unreclaimable
 146 * pages.  It is better to clamp down on writers than to start swapping, and
 147 * performing lots of scanning.
 148 *
 149 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
 150 *
 151 * We don't permit the clamping level to fall below 5% - that is getting rather
 152 * excessive.
 153 *
 154 * We make sure that the background writeout level is below the adjusted
 155 * clamping level.
 156 */
 157
 158/*
 159 * In a memory zone, there is a certain amount of pages we consider
 160 * available for the page cache, which is essentially the number of
 161 * free and reclaimable pages, minus some zone reserves to protect
 162 * lowmem and the ability to uphold the zone's watermarks without
 163 * requiring writeback.
 164 *
 165 * This number of dirtyable pages is the base value of which the
 166 * user-configurable dirty ratio is the effictive number of pages that
 167 * are allowed to be actually dirtied.  Per individual zone, or
 168 * globally by using the sum of dirtyable pages over all zones.
 169 *
 170 * Because the user is allowed to specify the dirty limit globally as
 171 * absolute number of bytes, calculating the per-zone dirty limit can
 172 * require translating the configured limit into a percentage of
 173 * global dirtyable memory first.
 174 */
 175
 176static unsigned long highmem_dirtyable_memory(unsigned long total)
 177{
 178#ifdef CONFIG_HIGHMEM
 179        int node;
 180        unsigned long x = 0;
 181
 182        for_each_node_state(node, N_HIGH_MEMORY) {
 183                struct zone *z =
 184                        &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
 185
 186                x += zone_page_state(z, NR_FREE_PAGES) +
 187                     zone_reclaimable_pages(z) - z->dirty_balance_reserve;
 188        }
 189        /*
 190         * Make sure that the number of highmem pages is never larger
 191         * than the number of the total dirtyable memory. This can only
 192         * occur in very strange VM situations but we want to make sure
 193         * that this does not occur.
 194         */
 195        return min(x, total);
 196#else
 197        return 0;
 198#endif
 199}
 200
 201/**
 202 * global_dirtyable_memory - number of globally dirtyable pages
 203 *
 204 * Returns the global number of pages potentially available for dirty
 205 * page cache.  This is the base value for the global dirty limits.
 206 */
 207static unsigned long global_dirtyable_memory(void)
 208{
 209        unsigned long x;
 210
 211        x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() -
 212            dirty_balance_reserve;
 213
 214        if (!vm_highmem_is_dirtyable)
 215                x -= highmem_dirtyable_memory(x);
 216
 217        return x + 1;   /* Ensure that we never return 0 */
 218}
 219
 220/*
 221 * global_dirty_limits - background-writeback and dirty-throttling thresholds
 222 *
 223 * Calculate the dirty thresholds based on sysctl parameters
 224 * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
 225 * - vm.dirty_ratio             or  vm.dirty_bytes
 226 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
 227 * real-time tasks.
 228 */
 229void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
 230{
 231        unsigned long background;
 232        unsigned long dirty;
 233        unsigned long uninitialized_var(available_memory);
 234        struct task_struct *tsk;
 235
 236        if (!vm_dirty_bytes || !dirty_background_bytes)
 237                available_memory = global_dirtyable_memory();
 238
 239        if (vm_dirty_bytes)
 240                dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
 241        else
 242                dirty = (vm_dirty_ratio * available_memory) / 100;
 243
 244        if (dirty_background_bytes)
 245                background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
 246        else
 247                background = (dirty_background_ratio * available_memory) / 100;
 248
 249        if (background >= dirty)
 250                background = dirty / 2;
 251        tsk = current;
 252        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
 253                background += background / 4;
 254                dirty += dirty / 4;
 255        }
 256        *pbackground = background;
 257        *pdirty = dirty;
 258        trace_global_dirty_state(background, dirty);
 259}
 260
 261/**
 262 * zone_dirtyable_memory - number of dirtyable pages in a zone
 263 * @zone: the zone
 264 *
 265 * Returns the zone's number of pages potentially available for dirty
 266 * page cache.  This is the base value for the per-zone dirty limits.
 267 */
 268static unsigned long zone_dirtyable_memory(struct zone *zone)
 269{
 270        /*
 271         * The effective global number of dirtyable pages may exclude
 272         * highmem as a big-picture measure to keep the ratio between
 273         * dirty memory and lowmem reasonable.
 274         *
 275         * But this function is purely about the individual zone and a
 276         * highmem zone can hold its share of dirty pages, so we don't
 277         * care about vm_highmem_is_dirtyable here.
 278         */
 279        return zone_page_state(zone, NR_FREE_PAGES) +
 280               zone_reclaimable_pages(zone) -
 281               zone->dirty_balance_reserve;
 282}
 283
 284/**
 285 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
 286 * @zone: the zone
 287 *
 288 * Returns the maximum number of dirty pages allowed in a zone, based
 289 * on the zone's dirtyable memory.
 290 */
 291static unsigned long zone_dirty_limit(struct zone *zone)
 292{
 293        unsigned long zone_memory = zone_dirtyable_memory(zone);
 294        struct task_struct *tsk = current;
 295        unsigned long dirty;
 296
 297        if (vm_dirty_bytes)
 298                dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
 299                        zone_memory / global_dirtyable_memory();
 300        else
 301                dirty = vm_dirty_ratio * zone_memory / 100;
 302
 303        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
 304                dirty += dirty / 4;
 305
 306        return dirty;
 307}
 308
 309/**
 310 * zone_dirty_ok - tells whether a zone is within its dirty limits
 311 * @zone: the zone to check
 312 *
 313 * Returns %true when the dirty pages in @zone are within the zone's
 314 * dirty limit, %false if the limit is exceeded.
 315 */
 316bool zone_dirty_ok(struct zone *zone)
 317{
 318        unsigned long limit = zone_dirty_limit(zone);
 319
 320        return zone_page_state(zone, NR_FILE_DIRTY) +
 321               zone_page_state(zone, NR_UNSTABLE_NFS) +
 322               zone_page_state(zone, NR_WRITEBACK) <= limit;
 323}
 324
 325/*
 326 * couple the period to the dirty_ratio:
 327 *
 328 *   period/2 ~ roundup_pow_of_two(dirty limit)
 329 */
 330static int calc_period_shift(void)
 331{
 332        unsigned long dirty_total;
 333
 334        if (vm_dirty_bytes)
 335                dirty_total = vm_dirty_bytes / PAGE_SIZE;
 336        else
 337                dirty_total = (vm_dirty_ratio * global_dirtyable_memory()) /
 338                                100;
 339        return 2 + ilog2(dirty_total - 1);
 340}
 341
 342/*
 343 * update the period when the dirty threshold changes.
 344 */
 345static void update_completion_period(void)
 346{
 347        int shift = calc_period_shift();
 348        prop_change_shift(&vm_completions, shift);
 349
 350        writeback_set_ratelimit();
 351}
 352
 353int dirty_background_ratio_handler(struct ctl_table *table, int write,
 354                void __user *buffer, size_t *lenp,
 355                loff_t *ppos)
 356{
 357        int ret;
 358
 359        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 360        if (ret == 0 && write)
 361                dirty_background_bytes = 0;
 362        return ret;
 363}
 364
 365int dirty_background_bytes_handler(struct ctl_table *table, int write,
 366                void __user *buffer, size_t *lenp,
 367                loff_t *ppos)
 368{
 369        int ret;
 370
 371        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 372        if (ret == 0 && write)
 373                dirty_background_ratio = 0;
 374        return ret;
 375}
 376
 377int dirty_ratio_handler(struct ctl_table *table, int write,
 378                void __user *buffer, size_t *lenp,
 379                loff_t *ppos)
 380{
 381        int old_ratio = vm_dirty_ratio;
 382        int ret;
 383
 384        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 385        if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
 386                update_completion_period();
 387                vm_dirty_bytes = 0;
 388        }
 389        return ret;
 390}
 391
 392int dirty_bytes_handler(struct ctl_table *table, int write,
 393                void __user *buffer, size_t *lenp,
 394                loff_t *ppos)
 395{
 396        unsigned long old_bytes = vm_dirty_bytes;
 397        int ret;
 398
 399        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 400        if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
 401                update_completion_period();
 402                vm_dirty_ratio = 0;
 403        }
 404        return ret;
 405}
 406
 407/*
 408 * Increment the BDI's writeout completion count and the global writeout
 409 * completion count. Called from test_clear_page_writeback().
 410 */
 411static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
 412{
 413        __inc_bdi_stat(bdi, BDI_WRITTEN);
 414        __prop_inc_percpu_max(&vm_completions, &bdi->completions,
 415                              bdi->max_prop_frac);
 416}
 417
 418void bdi_writeout_inc(struct backing_dev_info *bdi)
 419{
 420        unsigned long flags;
 421
 422        local_irq_save(flags);
 423        __bdi_writeout_inc(bdi);
 424        local_irq_restore(flags);
 425}
 426EXPORT_SYMBOL_GPL(bdi_writeout_inc);
 427
 428/*
 429 * Obtain an accurate fraction of the BDI's portion.
 430 */
 431static void bdi_writeout_fraction(struct backing_dev_info *bdi,
 432                long *numerator, long *denominator)
 433{
 434        prop_fraction_percpu(&vm_completions, &bdi->completions,
 435                                numerator, denominator);
 436}
 437
 438/*
 439 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
 440 * registered backing devices, which, for obvious reasons, can not
 441 * exceed 100%.
 442 */
 443static unsigned int bdi_min_ratio;
 444
 445int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 446{
 447        int ret = 0;
 448
 449        spin_lock_bh(&bdi_lock);
 450        if (min_ratio > bdi->max_ratio) {
 451                ret = -EINVAL;
 452        } else {
 453                min_ratio -= bdi->min_ratio;
 454                if (bdi_min_ratio + min_ratio < 100) {
 455                        bdi_min_ratio += min_ratio;
 456                        bdi->min_ratio += min_ratio;
 457                } else {
 458                        ret = -EINVAL;
 459                }
 460        }
 461        spin_unlock_bh(&bdi_lock);
 462
 463        return ret;
 464}
 465
 466int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 467{
 468        int ret = 0;
 469
 470        if (max_ratio > 100)
 471                return -EINVAL;
 472
 473        spin_lock_bh(&bdi_lock);
 474        if (bdi->min_ratio > max_ratio) {
 475                ret = -EINVAL;
 476        } else {
 477                bdi->max_ratio = max_ratio;
 478                bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
 479        }
 480        spin_unlock_bh(&bdi_lock);
 481
 482        return ret;
 483}
 484EXPORT_SYMBOL(bdi_set_max_ratio);
 485
 486static unsigned long dirty_freerun_ceiling(unsigned long thresh,
 487                                           unsigned long bg_thresh)
 488{
 489        return (thresh + bg_thresh) / 2;
 490}
 491
 492static unsigned long hard_dirty_limit(unsigned long thresh)
 493{
 494        return max(thresh, global_dirty_limit);
 495}
 496
 497/**
 498 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
 499 * @bdi: the backing_dev_info to query
 500 * @dirty: global dirty limit in pages
 501 *
 502 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
 503 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
 504 *
 505 * Note that balance_dirty_pages() will only seriously take it as a hard limit
 506 * when sleeping max_pause per page is not enough to keep the dirty pages under
 507 * control. For example, when the device is completely stalled due to some error
 508 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
 509 * In the other normal situations, it acts more gently by throttling the tasks
 510 * more (rather than completely block them) when the bdi dirty pages go high.
 511 *
 512 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
 513 * - starving fast devices
 514 * - piling up dirty pages (that will take long time to sync) on slow devices
 515 *
 516 * The bdi's share of dirty limit will be adapting to its throughput and
 517 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
 518 */
 519unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
 520{
 521        u64 bdi_dirty;
 522        long numerator, denominator;
 523
 524        /*
 525         * Calculate this BDI's share of the dirty ratio.
 526         */
 527        bdi_writeout_fraction(bdi, &numerator, &denominator);
 528
 529        bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
 530        bdi_dirty *= numerator;
 531        do_div(bdi_dirty, denominator);
 532
 533        bdi_dirty += (dirty * bdi->min_ratio) / 100;
 534        if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
 535                bdi_dirty = dirty * bdi->max_ratio / 100;
 536
 537        return bdi_dirty;
 538}
 539
 540/*
 541 * Dirty position control.
 542 *
 543 * (o) global/bdi setpoints
 544 *
 545 * We want the dirty pages be balanced around the global/bdi setpoints.
 546 * When the number of dirty pages is higher/lower than the setpoint, the
 547 * dirty position control ratio (and hence task dirty ratelimit) will be
 548 * decreased/increased to bring the dirty pages back to the setpoint.
 549 *
 550 *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
 551 *
 552 *     if (dirty < setpoint) scale up   pos_ratio
 553 *     if (dirty > setpoint) scale down pos_ratio
 554 *
 555 *     if (bdi_dirty < bdi_setpoint) scale up   pos_ratio
 556 *     if (bdi_dirty > bdi_setpoint) scale down pos_ratio
 557 *
 558 *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
 559 *
 560 * (o) global control line
 561 *
 562 *     ^ pos_ratio
 563 *     |
 564 *     |            |<===== global dirty control scope ======>|
 565 * 2.0 .............*
 566 *     |            .*
 567 *     |            . *
 568 *     |            .   *
 569 *     |            .     *
 570 *     |            .        *
 571 *     |            .            *
 572 * 1.0 ................................*
 573 *     |            .                  .     *
 574 *     |            .                  .          *
 575 *     |            .                  .              *
 576 *     |            .                  .                 *
 577 *     |            .                  .                    *
 578 *   0 +------------.------------------.----------------------*------------->
 579 *           freerun^          setpoint^                 limit^   dirty pages
 580 *
 581 * (o) bdi control line
 582 *
 583 *     ^ pos_ratio
 584 *     |
 585 *     |            *
 586 *     |              *
 587 *     |                *
 588 *     |                  *
 589 *     |                    * |<=========== span ============>|
 590 * 1.0 .......................*
 591 *     |                      . *
 592 *     |                      .   *
 593 *     |                      .     *
 594 *     |                      .       *
 595 *     |                      .         *
 596 *     |                      .           *
 597 *     |                      .             *
 598 *     |                      .               *
 599 *     |                      .                 *
 600 *     |                      .                   *
 601 *     |                      .                     *
 602 * 1/4 ...............................................* * * * * * * * * * * *
 603 *     |                      .                         .
 604 *     |                      .                           .
 605 *     |                      .                             .
 606 *   0 +----------------------.-------------------------------.------------->
 607 *                bdi_setpoint^                    x_intercept^
 608 *
 609 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
 610 * be smoothly throttled down to normal if it starts high in situations like
 611 * - start writing to a slow SD card and a fast disk at the same time. The SD
 612 *   card's bdi_dirty may rush to many times higher than bdi_setpoint.
 613 * - the bdi dirty thresh drops quickly due to change of JBOD workload
 614 */
 615static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
 616                                        unsigned long thresh,
 617                                        unsigned long bg_thresh,
 618                                        unsigned long dirty,
 619                                        unsigned long bdi_thresh,
 620                                        unsigned long bdi_dirty)
 621{
 622        unsigned long write_bw = bdi->avg_write_bandwidth;
 623        unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
 624        unsigned long limit = hard_dirty_limit(thresh);
 625        unsigned long x_intercept;
 626        unsigned long setpoint;         /* dirty pages' target balance point */
 627        unsigned long bdi_setpoint;
 628        unsigned long span;
 629        long long pos_ratio;            /* for scaling up/down the rate limit */
 630        long x;
 631
 632        if (unlikely(dirty >= limit))
 633                return 0;
 634
 635        /*
 636         * global setpoint
 637         *
 638         *                           setpoint - dirty 3
 639         *        f(dirty) := 1.0 + (----------------)
 640         *                           limit - setpoint
 641         *
 642         * it's a 3rd order polynomial that subjects to
 643         *
 644         * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
 645         * (2) f(setpoint) = 1.0 => the balance point
 646         * (3) f(limit)    = 0   => the hard limit
 647         * (4) df/dx      <= 0   => negative feedback control
 648         * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
 649         *     => fast response on large errors; small oscillation near setpoint
 650         */
 651        setpoint = (freerun + limit) / 2;
 652        x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
 653                    limit - setpoint + 1);
 654        pos_ratio = x;
 655        pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
 656        pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
 657        pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
 658
 659        /*
 660         * We have computed basic pos_ratio above based on global situation. If
 661         * the bdi is over/under its share of dirty pages, we want to scale
 662         * pos_ratio further down/up. That is done by the following mechanism.
 663         */
 664
 665        /*
 666         * bdi setpoint
 667         *
 668         *        f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
 669         *
 670         *                        x_intercept - bdi_dirty
 671         *                     := --------------------------
 672         *                        x_intercept - bdi_setpoint
 673         *
 674         * The main bdi control line is a linear function that subjects to
 675         *
 676         * (1) f(bdi_setpoint) = 1.0
 677         * (2) k = - 1 / (8 * write_bw)  (in single bdi case)
 678         *     or equally: x_intercept = bdi_setpoint + 8 * write_bw
 679         *
 680         * For single bdi case, the dirty pages are observed to fluctuate
 681         * regularly within range
 682         *        [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
 683         * for various filesystems, where (2) can yield in a reasonable 12.5%
 684         * fluctuation range for pos_ratio.
 685         *
 686         * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
 687         * own size, so move the slope over accordingly and choose a slope that
 688         * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
 689         */
 690        if (unlikely(bdi_thresh > thresh))
 691                bdi_thresh = thresh;
 692        /*
 693         * It's very possible that bdi_thresh is close to 0 not because the
 694         * device is slow, but that it has remained inactive for long time.
 695         * Honour such devices a reasonable good (hopefully IO efficient)
 696         * threshold, so that the occasional writes won't be blocked and active
 697         * writes can rampup the threshold quickly.
 698         */
 699        bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
 700        /*
 701         * scale global setpoint to bdi's:
 702         *      bdi_setpoint = setpoint * bdi_thresh / thresh
 703         */
 704        x = div_u64((u64)bdi_thresh << 16, thresh + 1);
 705        bdi_setpoint = setpoint * (u64)x >> 16;
 706        /*
 707         * Use span=(8*write_bw) in single bdi case as indicated by
 708         * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
 709         *
 710         *        bdi_thresh                    thresh - bdi_thresh
 711         * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
 712         *          thresh                            thresh
 713         */
 714        span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
 715        x_intercept = bdi_setpoint + span;
 716
 717        if (bdi_dirty < x_intercept - span / 4) {
 718                pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
 719                                    x_intercept - bdi_setpoint + 1);
 720        } else
 721                pos_ratio /= 4;
 722
 723        /*
 724         * bdi reserve area, safeguard against dirty pool underrun and disk idle
 725         * It may push the desired control point of global dirty pages higher
 726         * than setpoint.
 727         */
 728        x_intercept = bdi_thresh / 2;
 729        if (bdi_dirty < x_intercept) {
 730                if (bdi_dirty > x_intercept / 8)
 731                        pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
 732                else
 733                        pos_ratio *= 8;
 734        }
 735
 736        return pos_ratio;
 737}
 738
 739static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
 740                                       unsigned long elapsed,
 741                                       unsigned long written)
 742{
 743        const unsigned long period = roundup_pow_of_two(3 * HZ);
 744        unsigned long avg = bdi->avg_write_bandwidth;
 745        unsigned long old = bdi->write_bandwidth;
 746        u64 bw;
 747
 748        /*
 749         * bw = written * HZ / elapsed
 750         *
 751         *                   bw * elapsed + write_bandwidth * (period - elapsed)
 752         * write_bandwidth = ---------------------------------------------------
 753         *                                          period
 754         */
 755        bw = written - bdi->written_stamp;
 756        bw *= HZ;
 757        if (unlikely(elapsed > period)) {
 758                do_div(bw, elapsed);
 759                avg = bw;
 760                goto out;
 761        }
 762        bw += (u64)bdi->write_bandwidth * (period - elapsed);
 763        bw >>= ilog2(period);
 764
 765        /*
 766         * one more level of smoothing, for filtering out sudden spikes
 767         */
 768        if (avg > old && old >= (unsigned long)bw)
 769                avg -= (avg - old) >> 3;
 770
 771        if (avg < old && old <= (unsigned long)bw)
 772                avg += (old - avg) >> 3;
 773
 774out:
 775        bdi->write_bandwidth = bw;
 776        bdi->avg_write_bandwidth = avg;
 777}
 778
 779/*
 780 * The global dirtyable memory and dirty threshold could be suddenly knocked
 781 * down by a large amount (eg. on the startup of KVM in a swapless system).
 782 * This may throw the system into deep dirty exceeded state and throttle
 783 * heavy/light dirtiers alike. To retain good responsiveness, maintain
 784 * global_dirty_limit for tracking slowly down to the knocked down dirty
 785 * threshold.
 786 */
 787static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
 788{
 789        unsigned long limit = global_dirty_limit;
 790
 791        /*
 792         * Follow up in one step.
 793         */
 794        if (limit < thresh) {
 795                limit = thresh;
 796                goto update;
 797        }
 798
 799        /*
 800         * Follow down slowly. Use the higher one as the target, because thresh
 801         * may drop below dirty. This is exactly the reason to introduce
 802         * global_dirty_limit which is guaranteed to lie above the dirty pages.
 803         */
 804        thresh = max(thresh, dirty);
 805        if (limit > thresh) {
 806                limit -= (limit - thresh) >> 5;
 807                goto update;
 808        }
 809        return;
 810update:
 811        global_dirty_limit = limit;
 812}
 813
 814static void global_update_bandwidth(unsigned long thresh,
 815                                    unsigned long dirty,
 816                                    unsigned long now)
 817{
 818        static DEFINE_SPINLOCK(dirty_lock);
 819        static unsigned long update_time;
 820
 821        /*
 822         * check locklessly first to optimize away locking for the most time
 823         */
 824        if (time_before(now, update_time + BANDWIDTH_INTERVAL))
 825                return;
 826
 827        spin_lock(&dirty_lock);
 828        if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
 829                update_dirty_limit(thresh, dirty);
 830                update_time = now;
 831        }
 832        spin_unlock(&dirty_lock);
 833}
 834
 835/*
 836 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
 837 *
 838 * Normal bdi tasks will be curbed at or below it in long term.
 839 * Obviously it should be around (write_bw / N) when there are N dd tasks.
 840 */
 841static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
 842                                       unsigned long thresh,
 843                                       unsigned long bg_thresh,
 844                                       unsigned long dirty,
 845                                       unsigned long bdi_thresh,
 846                                       unsigned long bdi_dirty,
 847                                       unsigned long dirtied,
 848                                       unsigned long elapsed)
 849{
 850        unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
 851        unsigned long limit = hard_dirty_limit(thresh);
 852        unsigned long setpoint = (freerun + limit) / 2;
 853        unsigned long write_bw = bdi->avg_write_bandwidth;
 854        unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
 855        unsigned long dirty_rate;
 856        unsigned long task_ratelimit;
 857        unsigned long balanced_dirty_ratelimit;
 858        unsigned long pos_ratio;
 859        unsigned long step;
 860        unsigned long x;
 861
 862        /*
 863         * The dirty rate will match the writeout rate in long term, except
 864         * when dirty pages are truncated by userspace or re-dirtied by FS.
 865         */
 866        dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
 867
 868        pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
 869                                       bdi_thresh, bdi_dirty);
 870        /*
 871         * task_ratelimit reflects each dd's dirty rate for the past 200ms.
 872         */
 873        task_ratelimit = (u64)dirty_ratelimit *
 874                                        pos_ratio >> RATELIMIT_CALC_SHIFT;
 875        task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
 876
 877        /*
 878         * A linear estimation of the "balanced" throttle rate. The theory is,
 879         * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
 880         * dirty_rate will be measured to be (N * task_ratelimit). So the below
 881         * formula will yield the balanced rate limit (write_bw / N).
 882         *
 883         * Note that the expanded form is not a pure rate feedback:
 884         *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate)              (1)
 885         * but also takes pos_ratio into account:
 886         *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
 887         *
 888         * (1) is not realistic because pos_ratio also takes part in balancing
 889         * the dirty rate.  Consider the state
 890         *      pos_ratio = 0.5                                              (3)
 891         *      rate = 2 * (write_bw / N)                                    (4)
 892         * If (1) is used, it will stuck in that state! Because each dd will
 893         * be throttled at
 894         *      task_ratelimit = pos_ratio * rate = (write_bw / N)           (5)
 895         * yielding
 896         *      dirty_rate = N * task_ratelimit = write_bw                   (6)
 897         * put (6) into (1) we get
 898         *      rate_(i+1) = rate_(i)                                        (7)
 899         *
 900         * So we end up using (2) to always keep
 901         *      rate_(i+1) ~= (write_bw / N)                                 (8)
 902         * regardless of the value of pos_ratio. As long as (8) is satisfied,
 903         * pos_ratio is able to drive itself to 1.0, which is not only where
 904         * the dirty count meet the setpoint, but also where the slope of
 905         * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
 906         */
 907        balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
 908                                           dirty_rate | 1);
 909        /*
 910         * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
 911         */
 912        if (unlikely(balanced_dirty_ratelimit > write_bw))
 913                balanced_dirty_ratelimit = write_bw;
 914
 915        /*
 916         * We could safely do this and return immediately:
 917         *
 918         *      bdi->dirty_ratelimit = balanced_dirty_ratelimit;
 919         *
 920         * However to get a more stable dirty_ratelimit, the below elaborated
 921         * code makes use of task_ratelimit to filter out sigular points and
 922         * limit the step size.
 923         *
 924         * The below code essentially only uses the relative value of
 925         *
 926         *      task_ratelimit - dirty_ratelimit
 927         *      = (pos_ratio - 1) * dirty_ratelimit
 928         *
 929         * which reflects the direction and size of dirty position error.
 930         */
 931
 932        /*
 933         * dirty_ratelimit will follow balanced_dirty_ratelimit iff
 934         * task_ratelimit is on the same side of dirty_ratelimit, too.
 935         * For example, when
 936         * - dirty_ratelimit > balanced_dirty_ratelimit
 937         * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
 938         * lowering dirty_ratelimit will help meet both the position and rate
 939         * control targets. Otherwise, don't update dirty_ratelimit if it will
 940         * only help meet the rate target. After all, what the users ultimately
 941         * feel and care are stable dirty rate and small position error.
 942         *
 943         * |task_ratelimit - dirty_ratelimit| is used to limit the step size
 944         * and filter out the sigular points of balanced_dirty_ratelimit. Which
 945         * keeps jumping around randomly and can even leap far away at times
 946         * due to the small 200ms estimation period of dirty_rate (we want to
 947         * keep that period small to reduce time lags).
 948         */
 949        step = 0;
 950        if (dirty < setpoint) {
 951                x = min(bdi->balanced_dirty_ratelimit,
 952                         min(balanced_dirty_ratelimit, task_ratelimit));
 953                if (dirty_ratelimit < x)
 954                        step = x - dirty_ratelimit;
 955        } else {
 956                x = max(bdi->balanced_dirty_ratelimit,
 957                         max(balanced_dirty_ratelimit, task_ratelimit));
 958                if (dirty_ratelimit > x)
 959                        step = dirty_ratelimit - x;
 960        }
 961
 962        /*
 963         * Don't pursue 100% rate matching. It's impossible since the balanced
 964         * rate itself is constantly fluctuating. So decrease the track speed
 965         * when it gets close to the target. Helps eliminate pointless tremors.
 966         */
 967        step >>= dirty_ratelimit / (2 * step + 1);
 968        /*
 969         * Limit the tracking speed to avoid overshooting.
 970         */
 971        step = (step + 7) / 8;
 972
 973        if (dirty_ratelimit < balanced_dirty_ratelimit)
 974                dirty_ratelimit += step;
 975        else
 976                dirty_ratelimit -= step;
 977
 978        bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
 979        bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
 980
 981        trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
 982}
 983
 984void __bdi_update_bandwidth(struct backing_dev_info *bdi,
 985                            unsigned long thresh,
 986                            unsigned long bg_thresh,
 987                            unsigned long dirty,
 988                            unsigned long bdi_thresh,
 989                            unsigned long bdi_dirty,
 990                            unsigned long start_time)
 991{
 992        unsigned long now = jiffies;
 993        unsigned long elapsed = now - bdi->bw_time_stamp;
 994        unsigned long dirtied;
 995        unsigned long written;
 996
 997        /*
 998         * rate-limit, only update once every 200ms.
 999         */
1000        if (elapsed < BANDWIDTH_INTERVAL)
1001                return;
1002
1003        dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
1004        written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1005
1006        /*
1007         * Skip quiet periods when disk bandwidth is under-utilized.
1008         * (at least 1s idle time between two flusher runs)
1009         */
1010        if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1011                goto snapshot;
1012
1013        if (thresh) {
1014                global_update_bandwidth(thresh, dirty, now);
1015                bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1016                                           bdi_thresh, bdi_dirty,
1017                                           dirtied, elapsed);
1018        }
1019        bdi_update_write_bandwidth(bdi, elapsed, written);
1020
1021snapshot:
1022        bdi->dirtied_stamp = dirtied;
1023        bdi->written_stamp = written;
1024        bdi->bw_time_stamp = now;
1025}
1026
1027static void bdi_update_bandwidth(struct backing_dev_info *bdi,
1028                                 unsigned long thresh,
1029                                 unsigned long bg_thresh,
1030                                 unsigned long dirty,
1031                                 unsigned long bdi_thresh,
1032                                 unsigned long bdi_dirty,
1033                                 unsigned long start_time)
1034{
1035        if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1036                return;
1037        spin_lock(&bdi->wb.list_lock);
1038        __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1039                               bdi_thresh, bdi_dirty, start_time);
1040        spin_unlock(&bdi->wb.list_lock);
1041}
1042
1043/*
1044 * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
1045 * will look to see if it needs to start dirty throttling.
1046 *
1047 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1048 * global_page_state() too often. So scale it near-sqrt to the safety margin
1049 * (the number of pages we may dirty without exceeding the dirty limits).
1050 */
1051static unsigned long dirty_poll_interval(unsigned long dirty,
1052                                         unsigned long thresh)
1053{
1054        if (thresh > dirty)
1055                return 1UL << (ilog2(thresh - dirty) >> 1);
1056
1057        return 1;
1058}
1059
1060static long bdi_max_pause(struct backing_dev_info *bdi,
1061                          unsigned long bdi_dirty)
1062{
1063        long bw = bdi->avg_write_bandwidth;
1064        long t;
1065
1066        /*
1067         * Limit pause time for small memory systems. If sleeping for too long
1068         * time, a small pool of dirty/writeback pages may go empty and disk go
1069         * idle.
1070         *
1071         * 8 serves as the safety ratio.
1072         */
1073        t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1074        t++;
1075
1076        return min_t(long, t, MAX_PAUSE);
1077}
1078
1079static long bdi_min_pause(struct backing_dev_info *bdi,
1080                          long max_pause,
1081                          unsigned long task_ratelimit,
1082                          unsigned long dirty_ratelimit,
1083                          int *nr_dirtied_pause)
1084{
1085        long hi = ilog2(bdi->avg_write_bandwidth);
1086        long lo = ilog2(bdi->dirty_ratelimit);
1087        long t;         /* target pause */
1088        long pause;     /* estimated next pause */
1089        int pages;      /* target nr_dirtied_pause */
1090
1091        /* target for 10ms pause on 1-dd case */
1092        t = max(1, HZ / 100);
1093
1094        /*
1095         * Scale up pause time for concurrent dirtiers in order to reduce CPU
1096         * overheads.
1097         *
1098         * (N * 10ms) on 2^N concurrent tasks.
1099         */
1100        if (hi > lo)
1101                t += (hi - lo) * (10 * HZ) / 1024;
1102
1103        /*
1104         * This is a bit convoluted. We try to base the next nr_dirtied_pause
1105         * on the much more stable dirty_ratelimit. However the next pause time
1106         * will be computed based on task_ratelimit and the two rate limits may
1107         * depart considerably at some time. Especially if task_ratelimit goes
1108         * below dirty_ratelimit/2 and the target pause is max_pause, the next
1109         * pause time will be max_pause*2 _trimmed down_ to max_pause.  As a
1110         * result task_ratelimit won't be executed faithfully, which could
1111         * eventually bring down dirty_ratelimit.
1112         *
1113         * We apply two rules to fix it up:
1114         * 1) try to estimate the next pause time and if necessary, use a lower
1115         *    nr_dirtied_pause so as not to exceed max_pause. When this happens,
1116         *    nr_dirtied_pause will be "dancing" with task_ratelimit.
1117         * 2) limit the target pause time to max_pause/2, so that the normal
1118         *    small fluctuations of task_ratelimit won't trigger rule (1) and
1119         *    nr_dirtied_pause will remain as stable as dirty_ratelimit.
1120         */
1121        t = min(t, 1 + max_pause / 2);
1122        pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1123
1124        /*
1125         * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1126         * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1127         * When the 16 consecutive reads are often interrupted by some dirty
1128         * throttling pause during the async writes, cfq will go into idles
1129         * (deadline is fine). So push nr_dirtied_pause as high as possible
1130         * until reaches DIRTY_POLL_THRESH=32 pages.
1131         */
1132        if (pages < DIRTY_POLL_THRESH) {
1133                t = max_pause;
1134                pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1135                if (pages > DIRTY_POLL_THRESH) {
1136                        pages = DIRTY_POLL_THRESH;
1137                        t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1138                }
1139        }
1140
1141        pause = HZ * pages / (task_ratelimit + 1);
1142        if (pause > max_pause) {
1143                t = max_pause;
1144                pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1145        }
1146
1147        *nr_dirtied_pause = pages;
1148        /*
1149         * The minimal pause time will normally be half the target pause time.
1150         */
1151        return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1152}
1153
1154/*
1155 * balance_dirty_pages() must be called by processes which are generating dirty
1156 * data.  It looks at the number of dirty pages in the machine and will force
1157 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1158 * If we're over `background_thresh' then the writeback threads are woken to
1159 * perform some writeout.
1160 */
1161static void balance_dirty_pages(struct address_space *mapping,
1162                                unsigned long pages_dirtied)
1163{
1164        unsigned long nr_reclaimable;   /* = file_dirty + unstable_nfs */
1165        unsigned long bdi_reclaimable;
1166        unsigned long nr_dirty;  /* = file_dirty + writeback + unstable_nfs */
1167        unsigned long bdi_dirty;
1168        unsigned long freerun;
1169        unsigned long background_thresh;
1170        unsigned long dirty_thresh;
1171        unsigned long bdi_thresh;
1172        long period;
1173        long pause;
1174        long max_pause;
1175        long min_pause;
1176        int nr_dirtied_pause;
1177        bool dirty_exceeded = false;
1178        unsigned long task_ratelimit;
1179        unsigned long dirty_ratelimit;
1180        unsigned long pos_ratio;
1181        struct backing_dev_info *bdi = mapping->backing_dev_info;
1182        unsigned long start_time = jiffies;
1183
1184        for (;;) {
1185                unsigned long now = jiffies;
1186
1187                /*
1188                 * Unstable writes are a feature of certain networked
1189                 * filesystems (i.e. NFS) in which data may have been
1190                 * written to the server's write cache, but has not yet
1191                 * been flushed to permanent storage.
1192                 */
1193                nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1194                                        global_page_state(NR_UNSTABLE_NFS);
1195                nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1196
1197                global_dirty_limits(&background_thresh, &dirty_thresh);
1198
1199                /*
1200                 * Throttle it only when the background writeback cannot
1201                 * catch-up. This avoids (excessively) small writeouts
1202                 * when the bdi limits are ramping up.
1203                 */
1204                freerun = dirty_freerun_ceiling(dirty_thresh,
1205                                                background_thresh);
1206                if (nr_dirty <= freerun) {
1207                        current->dirty_paused_when = now;
1208                        current->nr_dirtied = 0;
1209                        current->nr_dirtied_pause =
1210                                dirty_poll_interval(nr_dirty, dirty_thresh);
1211                        break;
1212                }
1213
1214                if (unlikely(!writeback_in_progress(bdi)))
1215                        bdi_start_background_writeback(bdi);
1216
1217                /*
1218                 * bdi_thresh is not treated as some limiting factor as
1219                 * dirty_thresh, due to reasons
1220                 * - in JBOD setup, bdi_thresh can fluctuate a lot
1221                 * - in a system with HDD and USB key, the USB key may somehow
1222                 *   go into state (bdi_dirty >> bdi_thresh) either because
1223                 *   bdi_dirty starts high, or because bdi_thresh drops low.
1224                 *   In this case we don't want to hard throttle the USB key
1225                 *   dirtiers for 100 seconds until bdi_dirty drops under
1226                 *   bdi_thresh. Instead the auxiliary bdi control line in
1227                 *   bdi_position_ratio() will let the dirtier task progress
1228                 *   at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1229                 */
1230                bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1231
1232                /*
1233                 * In order to avoid the stacked BDI deadlock we need
1234                 * to ensure we accurately count the 'dirty' pages when
1235                 * the threshold is low.
1236                 *
1237                 * Otherwise it would be possible to get thresh+n pages
1238                 * reported dirty, even though there are thresh-m pages
1239                 * actually dirty; with m+n sitting in the percpu
1240                 * deltas.
1241                 */
1242                if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1243                        bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1244                        bdi_dirty = bdi_reclaimable +
1245                                    bdi_stat_sum(bdi, BDI_WRITEBACK);
1246                } else {
1247                        bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1248                        bdi_dirty = bdi_reclaimable +
1249                                    bdi_stat(bdi, BDI_WRITEBACK);
1250                }
1251
1252                dirty_exceeded = (bdi_dirty > bdi_thresh) &&
1253                                  (nr_dirty > dirty_thresh);
1254                if (dirty_exceeded && !bdi->dirty_exceeded)
1255                        bdi->dirty_exceeded = 1;
1256
1257                bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1258                                     nr_dirty, bdi_thresh, bdi_dirty,
1259                                     start_time);
1260
1261                dirty_ratelimit = bdi->dirty_ratelimit;
1262                pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1263                                               background_thresh, nr_dirty,
1264                                               bdi_thresh, bdi_dirty);
1265                task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1266                                                        RATELIMIT_CALC_SHIFT;
1267                max_pause = bdi_max_pause(bdi, bdi_dirty);
1268                min_pause = bdi_min_pause(bdi, max_pause,
1269                                          task_ratelimit, dirty_ratelimit,
1270                                          &nr_dirtied_pause);
1271
1272                if (unlikely(task_ratelimit == 0)) {
1273                        period = max_pause;
1274                        pause = max_pause;
1275                        goto pause;
1276                }
1277                period = HZ * pages_dirtied / task_ratelimit;
1278                pause = period;
1279                if (current->dirty_paused_when)
1280                        pause -= now - current->dirty_paused_when;
1281                /*
1282                 * For less than 1s think time (ext3/4 may block the dirtier
1283                 * for up to 800ms from time to time on 1-HDD; so does xfs,
1284                 * however at much less frequency), try to compensate it in
1285                 * future periods by updating the virtual time; otherwise just
1286                 * do a reset, as it may be a light dirtier.
1287                 */
1288                if (pause < min_pause) {
1289                        trace_balance_dirty_pages(bdi,
1290                                                  dirty_thresh,
1291                                                  background_thresh,
1292                                                  nr_dirty,
1293                                                  bdi_thresh,
1294                                                  bdi_dirty,
1295                                                  dirty_ratelimit,
1296                                                  task_ratelimit,
1297                                                  pages_dirtied,
1298                                                  period,
1299                                                  min(pause, 0L),
1300                                                  start_time);
1301                        if (pause < -HZ) {
1302                                current->dirty_paused_when = now;
1303                                current->nr_dirtied = 0;
1304                        } else if (period) {
1305                                current->dirty_paused_when += period;
1306                                current->nr_dirtied = 0;
1307                        } else if (current->nr_dirtied_pause <= pages_dirtied)
1308                                current->nr_dirtied_pause += pages_dirtied;
1309                        break;
1310                }
1311                if (unlikely(pause > max_pause)) {
1312                        /* for occasional dropped task_ratelimit */
1313                        now += min(pause - max_pause, max_pause);
1314                        pause = max_pause;
1315                }
1316
1317pause:
1318                trace_balance_dirty_pages(bdi,
1319                                          dirty_thresh,
1320                                          background_thresh,
1321                                          nr_dirty,
1322                                          bdi_thresh,
1323                                          bdi_dirty,
1324                                          dirty_ratelimit,
1325                                          task_ratelimit,
1326                                          pages_dirtied,
1327                                          period,
1328                                          pause,
1329                                          start_time);
1330                __set_current_state(TASK_KILLABLE);
1331                io_schedule_timeout(pause);
1332
1333                current->dirty_paused_when = now + pause;
1334                current->nr_dirtied = 0;
1335                current->nr_dirtied_pause = nr_dirtied_pause;
1336
1337                /*
1338                 * This is typically equal to (nr_dirty < dirty_thresh) and can
1339                 * also keep "1000+ dd on a slow USB stick" under control.
1340                 */
1341                if (task_ratelimit)
1342                        break;
1343
1344                /*
1345                 * In the case of an unresponding NFS server and the NFS dirty
1346                 * pages exceeds dirty_thresh, give the other good bdi's a pipe
1347                 * to go through, so that tasks on them still remain responsive.
1348                 *
1349                 * In theory 1 page is enough to keep the comsumer-producer
1350                 * pipe going: the flusher cleans 1 page => the task dirties 1
1351                 * more page. However bdi_dirty has accounting errors.  So use
1352                 * the larger and more IO friendly bdi_stat_error.
1353                 */
1354                if (bdi_dirty <= bdi_stat_error(bdi))
1355                        break;
1356
1357                if (fatal_signal_pending(current))
1358                        break;
1359        }
1360
1361        if (!dirty_exceeded && bdi->dirty_exceeded)
1362                bdi->dirty_exceeded = 0;
1363
1364        if (writeback_in_progress(bdi))
1365                return;
1366
1367        /*
1368         * In laptop mode, we wait until hitting the higher threshold before
1369         * starting background writeout, and then write out all the way down
1370         * to the lower threshold.  So slow writers cause minimal disk activity.
1371         *
1372         * In normal mode, we start background writeout at the lower
1373         * background_thresh, to keep the amount of dirty memory low.
1374         */
1375        if (laptop_mode)
1376                return;
1377
1378        if (nr_reclaimable > background_thresh)
1379                bdi_start_background_writeback(bdi);
1380}
1381
1382void set_page_dirty_balance(struct page *page, int page_mkwrite)
1383{
1384        if (set_page_dirty(page) || page_mkwrite) {
1385                struct address_space *mapping = page_mapping(page);
1386
1387                if (mapping)
1388                        balance_dirty_pages_ratelimited(mapping);
1389        }
1390}
1391
1392static DEFINE_PER_CPU(int, bdp_ratelimits);
1393
1394/*
1395 * Normal tasks are throttled by
1396 *      loop {
1397 *              dirty tsk->nr_dirtied_pause pages;
1398 *              take a snap in balance_dirty_pages();
1399 *      }
1400 * However there is a worst case. If every task exit immediately when dirtied
1401 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1402 * called to throttle the page dirties. The solution is to save the not yet
1403 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1404 * randomly into the running tasks. This works well for the above worst case,
1405 * as the new task will pick up and accumulate the old task's leaked dirty
1406 * count and eventually get throttled.
1407 */
1408DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1409
1410/**
1411 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
1412 * @mapping: address_space which was dirtied
1413 * @nr_pages_dirtied: number of pages which the caller has just dirtied
1414 *
1415 * Processes which are dirtying memory should call in here once for each page
1416 * which was newly dirtied.  The function will periodically check the system's
1417 * dirty state and will initiate writeback if needed.
1418 *
1419 * On really big machines, get_writeback_state is expensive, so try to avoid
1420 * calling it too often (ratelimiting).  But once we're over the dirty memory
1421 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1422 * from overshooting the limit by (ratelimit_pages) each.
1423 */
1424void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
1425                                        unsigned long nr_pages_dirtied)
1426{
1427        struct backing_dev_info *bdi = mapping->backing_dev_info;
1428        int ratelimit;
1429        int *p;
1430
1431        if (!bdi_cap_account_dirty(bdi))
1432                return;
1433
1434        ratelimit = current->nr_dirtied_pause;
1435        if (bdi->dirty_exceeded)
1436                ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1437
1438        preempt_disable();
1439        /*
1440         * This prevents one CPU to accumulate too many dirtied pages without
1441         * calling into balance_dirty_pages(), which can happen when there are
1442         * 1000+ tasks, all of them start dirtying pages at exactly the same
1443         * time, hence all honoured too large initial task->nr_dirtied_pause.
1444         */
1445        p =  &__get_cpu_var(bdp_ratelimits);
1446        if (unlikely(current->nr_dirtied >= ratelimit))
1447                *p = 0;
1448        else if (unlikely(*p >= ratelimit_pages)) {
1449                *p = 0;
1450                ratelimit = 0;
1451        }
1452        /*
1453         * Pick up the dirtied pages by the exited tasks. This avoids lots of
1454         * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1455         * the dirty throttling and livelock other long-run dirtiers.
1456         */
1457        p = &__get_cpu_var(dirty_throttle_leaks);
1458        if (*p > 0 && current->nr_dirtied < ratelimit) {
1459                nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1460                *p -= nr_pages_dirtied;
1461                current->nr_dirtied += nr_pages_dirtied;
1462        }
1463        preempt_enable();
1464
1465        if (unlikely(current->nr_dirtied >= ratelimit))
1466                balance_dirty_pages(mapping, current->nr_dirtied);
1467}
1468EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
1469
1470void throttle_vm_writeout(gfp_t gfp_mask)
1471{
1472        unsigned long background_thresh;
1473        unsigned long dirty_thresh;
1474
1475        for ( ; ; ) {
1476                global_dirty_limits(&background_thresh, &dirty_thresh);
1477                dirty_thresh = hard_dirty_limit(dirty_thresh);
1478
1479                /*
1480                 * Boost the allowable dirty threshold a bit for page
1481                 * allocators so they don't get DoS'ed by heavy writers
1482                 */
1483                dirty_thresh += dirty_thresh / 10;      /* wheeee... */
1484
1485                if (global_page_state(NR_UNSTABLE_NFS) +
1486                        global_page_state(NR_WRITEBACK) <= dirty_thresh)
1487                                break;
1488                congestion_wait(BLK_RW_ASYNC, HZ/10);
1489
1490                /*
1491                 * The caller might hold locks which can prevent IO completion
1492                 * or progress in the filesystem.  So we cannot just sit here
1493                 * waiting for IO to complete.
1494                 */
1495                if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1496                        break;
1497        }
1498}
1499
1500/*
1501 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1502 */
1503int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1504        void __user *buffer, size_t *length, loff_t *ppos)
1505{
1506        proc_dointvec(table, write, buffer, length, ppos);
1507        bdi_arm_supers_timer();
1508        return 0;
1509}
1510
1511#ifdef CONFIG_BLOCK
1512void laptop_mode_timer_fn(unsigned long data)
1513{
1514        struct request_queue *q = (struct request_queue *)data;
1515        int nr_pages = global_page_state(NR_FILE_DIRTY) +
1516                global_page_state(NR_UNSTABLE_NFS);
1517
1518        /*
1519         * We want to write everything out, not just down to the dirty
1520         * threshold
1521         */
1522        if (bdi_has_dirty_io(&q->backing_dev_info))
1523                bdi_start_writeback(&q->backing_dev_info, nr_pages,
1524                                        WB_REASON_LAPTOP_TIMER);
1525}
1526
1527/*
1528 * We've spun up the disk and we're in laptop mode: schedule writeback
1529 * of all dirty data a few seconds from now.  If the flush is already scheduled
1530 * then push it back - the user is still using the disk.
1531 */
1532void laptop_io_completion(struct backing_dev_info *info)
1533{
1534        mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1535}
1536
1537/*
1538 * We're in laptop mode and we've just synced. The sync's writes will have
1539 * caused another writeback to be scheduled by laptop_io_completion.
1540 * Nothing needs to be written back anymore, so we unschedule the writeback.
1541 */
1542void laptop_sync_completion(void)
1543{
1544        struct backing_dev_info *bdi;
1545
1546        rcu_read_lock();
1547
1548        list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1549                del_timer(&bdi->laptop_mode_wb_timer);
1550
1551        rcu_read_unlock();
1552}
1553#endif
1554
1555/*
1556 * If ratelimit_pages is too high then we can get into dirty-data overload
1557 * if a large number of processes all perform writes at the same time.
1558 * If it is too low then SMP machines will call the (expensive)
1559 * get_writeback_state too often.
1560 *
1561 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1562 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1563 * thresholds.
1564 */
1565
1566void writeback_set_ratelimit(void)
1567{
1568        unsigned long background_thresh;
1569        unsigned long dirty_thresh;
1570        global_dirty_limits(&background_thresh, &dirty_thresh);
1571        global_dirty_limit = dirty_thresh;
1572        ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1573        if (ratelimit_pages < 16)
1574                ratelimit_pages = 16;
1575}
1576
1577static int __cpuinit
1578ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
1579{
1580        writeback_set_ratelimit();
1581        return NOTIFY_DONE;
1582}
1583
1584static struct notifier_block __cpuinitdata ratelimit_nb = {
1585        .notifier_call  = ratelimit_handler,
1586        .next           = NULL,
1587};
1588
1589/*
1590 * Called early on to tune the page writeback dirty limits.
1591 *
1592 * We used to scale dirty pages according to how total memory
1593 * related to pages that could be allocated for buffers (by
1594 * comparing nr_free_buffer_pages() to vm_total_pages.
1595 *
1596 * However, that was when we used "dirty_ratio" to scale with
1597 * all memory, and we don't do that any more. "dirty_ratio"
1598 * is now applied to total non-HIGHPAGE memory (by subtracting
1599 * totalhigh_pages from vm_total_pages), and as such we can't
1600 * get into the old insane situation any more where we had
1601 * large amounts of dirty pages compared to a small amount of
1602 * non-HIGHMEM memory.
1603 *
1604 * But we might still want to scale the dirty_ratio by how
1605 * much memory the box has..
1606 */
1607void __init page_writeback_init(void)
1608{
1609        int shift;
1610
1611        writeback_set_ratelimit();
1612        register_cpu_notifier(&ratelimit_nb);
1613
1614        shift = calc_period_shift();
1615        prop_descriptor_init(&vm_completions, shift);
1616}
1617
1618/**
1619 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1620 * @mapping: address space structure to write
1621 * @start: starting page index
1622 * @end: ending page index (inclusive)
1623 *
1624 * This function scans the page range from @start to @end (inclusive) and tags
1625 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1626 * that write_cache_pages (or whoever calls this function) will then use
1627 * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
1628 * used to avoid livelocking of writeback by a process steadily creating new
1629 * dirty pages in the file (thus it is important for this function to be quick
1630 * so that it can tag pages faster than a dirtying process can create them).
1631 */
1632/*
1633 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1634 */
1635void tag_pages_for_writeback(struct address_space *mapping,
1636                             pgoff_t start, pgoff_t end)
1637{
1638#define WRITEBACK_TAG_BATCH 4096
1639        unsigned long tagged;
1640
1641        do {
1642                spin_lock_irq(&mapping->tree_lock);
1643                tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1644                                &start, end, WRITEBACK_TAG_BATCH,
1645                                PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1646                spin_unlock_irq(&mapping->tree_lock);
1647                WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1648                cond_resched();
1649                /* We check 'start' to handle wrapping when end == ~0UL */
1650        } while (tagged >= WRITEBACK_TAG_BATCH && start);
1651}
1652EXPORT_SYMBOL(tag_pages_for_writeback);
1653
1654/**
1655 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1656 * @mapping: address space structure to write
1657 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1658 * @writepage: function called for each page
1659 * @data: data passed to writepage function
1660 *
1661 * If a page is already under I/O, write_cache_pages() skips it, even
1662 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
1663 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
1664 * and msync() need to guarantee that all the data which was dirty at the time
1665 * the call was made get new I/O started against them.  If wbc->sync_mode is
1666 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1667 * existing IO to complete.
1668 *
1669 * To avoid livelocks (when other process dirties new pages), we first tag
1670 * pages which should be written back with TOWRITE tag and only then start
1671 * writing them. For data-integrity sync we have to be careful so that we do
1672 * not miss some pages (e.g., because some other process has cleared TOWRITE
1673 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1674 * by the process clearing the DIRTY tag (and submitting the page for IO).
1675 */
1676int write_cache_pages(struct address_space *mapping,
1677                      struct writeback_control *wbc, writepage_t writepage,
1678                      void *data)
1679{
1680        int ret = 0;
1681        int done = 0;
1682        struct pagevec pvec;
1683        int nr_pages;
1684        pgoff_t uninitialized_var(writeback_index);
1685        pgoff_t index;
1686        pgoff_t end;            /* Inclusive */
1687        pgoff_t done_index;
1688        int cycled;
1689        int range_whole = 0;
1690        int tag;
1691
1692        pagevec_init(&pvec, 0);
1693        if (wbc->range_cyclic) {
1694                writeback_index = mapping->writeback_index; /* prev offset */
1695                index = writeback_index;
1696                if (index == 0)
1697                        cycled = 1;
1698                else
1699                        cycled = 0;
1700                end = -1;
1701        } else {
1702                index = wbc->range_start >> PAGE_CACHE_SHIFT;
1703                end = wbc->range_end >> PAGE_CACHE_SHIFT;
1704                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1705                        range_whole = 1;
1706                cycled = 1; /* ignore range_cyclic tests */
1707        }
1708        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1709                tag = PAGECACHE_TAG_TOWRITE;
1710        else
1711                tag = PAGECACHE_TAG_DIRTY;
1712retry:
1713        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1714                tag_pages_for_writeback(mapping, index, end);
1715        done_index = index;
1716        while (!done && (index <= end)) {
1717                int i;
1718
1719                nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1720                              min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1721                if (nr_pages == 0)
1722                        break;
1723
1724                for (i = 0; i < nr_pages; i++) {
1725                        struct page *page = pvec.pages[i];
1726
1727                        /*
1728                         * At this point, the page may be truncated or
1729                         * invalidated (changing page->mapping to NULL), or
1730                         * even swizzled back from swapper_space to tmpfs file
1731                         * mapping. However, page->index will not change
1732                         * because we have a reference on the page.
1733                         */
1734                        if (page->index > end) {
1735                                /*
1736                                 * can't be range_cyclic (1st pass) because
1737                                 * end == -1 in that case.
1738                                 */
1739                                done = 1;
1740                                break;
1741                        }
1742
1743                        done_index = page->index;
1744
1745                        lock_page(page);
1746
1747                        /*
1748                         * Page truncated or invalidated. We can freely skip it
1749                         * then, even for data integrity operations: the page
1750                         * has disappeared concurrently, so there could be no
1751                         * real expectation of this data interity operation
1752                         * even if there is now a new, dirty page at the same
1753                         * pagecache address.
1754                         */
1755                        if (unlikely(page->mapping != mapping)) {
1756continue_unlock:
1757                                unlock_page(page);
1758                                continue;
1759                        }
1760
1761                        if (!PageDirty(page)) {
1762                                /* someone wrote it for us */
1763                                goto continue_unlock;
1764                        }
1765
1766                        if (PageWriteback(page)) {
1767                                if (wbc->sync_mode != WB_SYNC_NONE)
1768                                        wait_on_page_writeback(page);
1769                                else
1770                                        goto continue_unlock;
1771                        }
1772
1773                        BUG_ON(PageWriteback(page));
1774                        if (!clear_page_dirty_for_io(page))
1775                                goto continue_unlock;
1776
1777                        trace_wbc_writepage(wbc, mapping->backing_dev_info);
1778                        ret = (*writepage)(page, wbc, data);
1779                        if (unlikely(ret)) {
1780                                if (ret == AOP_WRITEPAGE_ACTIVATE) {
1781                                        unlock_page(page);
1782                                        ret = 0;
1783                                } else {
1784                                        /*
1785                                         * done_index is set past this page,
1786                                         * so media errors will not choke
1787                                         * background writeout for the entire
1788                                         * file. This has consequences for
1789                                         * range_cyclic semantics (ie. it may
1790                                         * not be suitable for data integrity
1791                                         * writeout).
1792                                         */
1793                                        done_index = page->index + 1;
1794                                        done = 1;
1795                                        break;
1796                                }
1797                        }
1798
1799                        /*
1800                         * We stop writing back only if we are not doing
1801                         * integrity sync. In case of integrity sync we have to
1802                         * keep going until we have written all the pages
1803                         * we tagged for writeback prior to entering this loop.
1804                         */
1805                        if (--wbc->nr_to_write <= 0 &&
1806                            wbc->sync_mode == WB_SYNC_NONE) {
1807                                done = 1;
1808                                break;
1809                        }
1810                }
1811                pagevec_release(&pvec);
1812                cond_resched();
1813        }
1814        if (!cycled && !done) {
1815                /*
1816                 * range_cyclic:
1817                 * We hit the last page and there is more work to be done: wrap
1818                 * back to the start of the file
1819                 */
1820                cycled = 1;
1821                index = 0;
1822                end = writeback_index - 1;
1823                goto retry;
1824        }
1825        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1826                mapping->writeback_index = done_index;
1827
1828        return ret;
1829}
1830EXPORT_SYMBOL(write_cache_pages);
1831
1832/*
1833 * Function used by generic_writepages to call the real writepage
1834 * function and set the mapping flags on error
1835 */
1836static int __writepage(struct page *page, struct writeback_control *wbc,
1837                       void *data)
1838{
1839        struct address_space *mapping = data;
1840        int ret = mapping->a_ops->writepage(page, wbc);
1841        mapping_set_error(mapping, ret);
1842        return ret;
1843}
1844
1845/**
1846 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1847 * @mapping: address space structure to write
1848 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1849 *
1850 * This is a library function, which implements the writepages()
1851 * address_space_operation.
1852 */
1853int generic_writepages(struct address_space *mapping,
1854                       struct writeback_control *wbc)
1855{
1856        struct blk_plug plug;
1857        int ret;
1858
1859        /* deal with chardevs and other special file */
1860        if (!mapping->a_ops->writepage)
1861                return 0;
1862
1863        blk_start_plug(&plug);
1864        ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1865        blk_finish_plug(&plug);
1866        return ret;
1867}
1868
1869EXPORT_SYMBOL(generic_writepages);
1870
1871int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1872{
1873        int ret;
1874
1875        if (wbc->nr_to_write <= 0)
1876                return 0;
1877        if (mapping->a_ops->writepages)
1878                ret = mapping->a_ops->writepages(mapping, wbc);
1879        else
1880                ret = generic_writepages(mapping, wbc);
1881        return ret;
1882}
1883
1884/**
1885 * write_one_page - write out a single page and optionally wait on I/O
1886 * @page: the page to write
1887 * @wait: if true, wait on writeout
1888 *
1889 * The page must be locked by the caller and will be unlocked upon return.
1890 *
1891 * write_one_page() returns a negative error code if I/O failed.
1892 */
1893int write_one_page(struct page *page, int wait)
1894{
1895        struct address_space *mapping = page->mapping;
1896        int ret = 0;
1897        struct writeback_control wbc = {
1898                .sync_mode = WB_SYNC_ALL,
1899                .nr_to_write = 1,
1900        };
1901
1902        BUG_ON(!PageLocked(page));
1903
1904        if (wait)
1905                wait_on_page_writeback(page);
1906
1907        if (clear_page_dirty_for_io(page)) {
1908                page_cache_get(page);
1909                ret = mapping->a_ops->writepage(page, &wbc);
1910                if (ret == 0 && wait) {
1911                        wait_on_page_writeback(page);
1912                        if (PageError(page))
1913                                ret = -EIO;
1914                }
1915                page_cache_release(page);
1916        } else {
1917                unlock_page(page);
1918        }
1919        return ret;
1920}
1921EXPORT_SYMBOL(write_one_page);
1922
1923/*
1924 * For address_spaces which do not use buffers nor write back.
1925 */
1926int __set_page_dirty_no_writeback(struct page *page)
1927{
1928        if (!PageDirty(page))
1929                return !TestSetPageDirty(page);
1930        return 0;
1931}
1932
1933/*
1934 * Helper function for set_page_dirty family.
1935 * NOTE: This relies on being atomic wrt interrupts.
1936 */
1937void account_page_dirtied(struct page *page, struct address_space *mapping)
1938{
1939        if (mapping_cap_account_dirty(mapping)) {
1940                __inc_zone_page_state(page, NR_FILE_DIRTY);
1941                __inc_zone_page_state(page, NR_DIRTIED);
1942                __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
1943                __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
1944                task_io_account_write(PAGE_CACHE_SIZE);
1945                current->nr_dirtied++;
1946                this_cpu_inc(bdp_ratelimits);
1947        }
1948}
1949EXPORT_SYMBOL(account_page_dirtied);
1950
1951/*
1952 * Helper function for set_page_writeback family.
1953 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1954 * wrt interrupts.
1955 */
1956void account_page_writeback(struct page *page)
1957{
1958        inc_zone_page_state(page, NR_WRITEBACK);
1959}
1960EXPORT_SYMBOL(account_page_writeback);
1961
1962/*
1963 * For address_spaces which do not use buffers.  Just tag the page as dirty in
1964 * its radix tree.
1965 *
1966 * This is also used when a single buffer is being dirtied: we want to set the
1967 * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1968 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1969 *
1970 * Most callers have locked the page, which pins the address_space in memory.
1971 * But zap_pte_range() does not lock the page, however in that case the
1972 * mapping is pinned by the vma's ->vm_file reference.
1973 *
1974 * We take care to handle the case where the page was truncated from the
1975 * mapping by re-checking page_mapping() inside tree_lock.
1976 */
1977int __set_page_dirty_nobuffers(struct page *page)
1978{
1979        if (!TestSetPageDirty(page)) {
1980                struct address_space *mapping = page_mapping(page);
1981                struct address_space *mapping2;
1982
1983                if (!mapping)
1984                        return 1;
1985
1986                spin_lock_irq(&mapping->tree_lock);
1987                mapping2 = page_mapping(page);
1988                if (mapping2) { /* Race with truncate? */
1989                        BUG_ON(mapping2 != mapping);
1990                        WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1991                        account_page_dirtied(page, mapping);
1992                        radix_tree_tag_set(&mapping->page_tree,
1993                                page_index(page), PAGECACHE_TAG_DIRTY);
1994                }
1995                spin_unlock_irq(&mapping->tree_lock);
1996                if (mapping->host) {
1997                        /* !PageAnon && !swapper_space */
1998                        __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1999                }
2000                return 1;
2001        }
2002        return 0;
2003}
2004EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2005
2006/*
2007 * Call this whenever redirtying a page, to de-account the dirty counters
2008 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2009 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2010 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2011 * control.
2012 */
2013void account_page_redirty(struct page *page)
2014{
2015        struct address_space *mapping = page->mapping;
2016        if (mapping && mapping_cap_account_dirty(mapping)) {
2017                current->nr_dirtied--;
2018                dec_zone_page_state(page, NR_DIRTIED);
2019                dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2020        }
2021}
2022EXPORT_SYMBOL(account_page_redirty);
2023
2024/*
2025 * When a writepage implementation decides that it doesn't want to write this
2026 * page for some reason, it should redirty the locked page via
2027 * redirty_page_for_writepage() and it should then unlock the page and return 0
2028 */
2029int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2030{
2031        wbc->pages_skipped++;
2032        account_page_redirty(page);
2033        return __set_page_dirty_nobuffers(page);
2034}
2035EXPORT_SYMBOL(redirty_page_for_writepage);
2036
2037/*
2038 * Dirty a page.
2039 *
2040 * For pages with a mapping this should be done under the page lock
2041 * for the benefit of asynchronous memory errors who prefer a consistent
2042 * dirty state. This rule can be broken in some special cases,
2043 * but should be better not to.
2044 *
2045 * If the mapping doesn't provide a set_page_dirty a_op, then
2046 * just fall through and assume that it wants buffer_heads.
2047 */
2048int set_page_dirty(struct page *page)
2049{
2050        struct address_space *mapping = page_mapping(page);
2051
2052        if (likely(mapping)) {
2053                int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2054                /*
2055                 * readahead/lru_deactivate_page could remain
2056                 * PG_readahead/PG_reclaim due to race with end_page_writeback
2057                 * About readahead, if the page is written, the flags would be
2058                 * reset. So no problem.
2059                 * About lru_deactivate_page, if the page is redirty, the flag
2060                 * will be reset. So no problem. but if the page is used by readahead
2061                 * it will confuse readahead and make it restart the size rampup
2062                 * process. But it's a trivial problem.
2063                 */
2064                ClearPageReclaim(page);
2065#ifdef CONFIG_BLOCK
2066                if (!spd)
2067                        spd = __set_page_dirty_buffers;
2068#endif
2069                return (*spd)(page);
2070        }
2071        if (!PageDirty(page)) {
2072                if (!TestSetPageDirty(page))
2073                        return 1;
2074        }
2075        return 0;
2076}
2077EXPORT_SYMBOL(set_page_dirty);
2078
2079/*
2080 * set_page_dirty() is racy if the caller has no reference against
2081 * page->mapping->host, and if the page is unlocked.  This is because another
2082 * CPU could truncate the page off the mapping and then free the mapping.
2083 *
2084 * Usually, the page _is_ locked, or the caller is a user-space process which
2085 * holds a reference on the inode by having an open file.
2086 *
2087 * In other cases, the page should be locked before running set_page_dirty().
2088 */
2089int set_page_dirty_lock(struct page *page)
2090{
2091        int ret;
2092
2093        lock_page(page);
2094        ret = set_page_dirty(page);
2095        unlock_page(page);
2096        return ret;
2097}
2098EXPORT_SYMBOL(set_page_dirty_lock);
2099
2100/*
2101 * Clear a page's dirty flag, while caring for dirty memory accounting.
2102 * Returns true if the page was previously dirty.
2103 *
2104 * This is for preparing to put the page under writeout.  We leave the page
2105 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2106 * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
2107 * implementation will run either set_page_writeback() or set_page_dirty(),
2108 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2109 * back into sync.
2110 *
2111 * This incoherency between the page's dirty flag and radix-tree tag is
2112 * unfortunate, but it only exists while the page is locked.
2113 */
2114int clear_page_dirty_for_io(struct page *page)
2115{
2116        struct address_space *mapping = page_mapping(page);
2117
2118        BUG_ON(!PageLocked(page));
2119
2120        if (mapping && mapping_cap_account_dirty(mapping)) {
2121                /*
2122                 * Yes, Virginia, this is indeed insane.
2123                 *
2124                 * We use this sequence to make sure that
2125                 *  (a) we account for dirty stats properly
2126                 *  (b) we tell the low-level filesystem to
2127                 *      mark the whole page dirty if it was
2128                 *      dirty in a pagetable. Only to then
2129                 *  (c) clean the page again and return 1 to
2130                 *      cause the writeback.
2131                 *
2132                 * This way we avoid all nasty races with the
2133                 * dirty bit in multiple places and clearing
2134                 * them concurrently from different threads.
2135                 *
2136                 * Note! Normally the "set_page_dirty(page)"
2137                 * has no effect on the actual dirty bit - since
2138                 * that will already usually be set. But we
2139                 * need the side effects, and it can help us
2140                 * avoid races.
2141                 *
2142                 * We basically use the page "master dirty bit"
2143                 * as a serialization point for all the different
2144                 * threads doing their things.
2145                 */
2146                if (page_mkclean(page))
2147                        set_page_dirty(page);
2148                /*
2149                 * We carefully synchronise fault handlers against
2150                 * installing a dirty pte and marking the page dirty
2151                 * at this point. We do this by having them hold the
2152                 * page lock at some point after installing their
2153                 * pte, but before marking the page dirty.
2154                 * Pages are always locked coming in here, so we get
2155                 * the desired exclusion. See mm/memory.c:do_wp_page()
2156                 * for more comments.
2157                 */
2158                if (TestClearPageDirty(page)) {
2159                        dec_zone_page_state(page, NR_FILE_DIRTY);
2160                        dec_bdi_stat(mapping->backing_dev_info,
2161                                        BDI_RECLAIMABLE);
2162                        return 1;
2163                }
2164                return 0;
2165        }
2166        return TestClearPageDirty(page);
2167}
2168EXPORT_SYMBOL(clear_page_dirty_for_io);
2169
2170int test_clear_page_writeback(struct page *page)
2171{
2172        struct address_space *mapping = page_mapping(page);
2173        int ret;
2174
2175        if (mapping) {
2176                struct backing_dev_info *bdi = mapping->backing_dev_info;
2177                unsigned long flags;
2178
2179                spin_lock_irqsave(&mapping->tree_lock, flags);
2180                ret = TestClearPageWriteback(page);
2181                if (ret) {
2182                        radix_tree_tag_clear(&mapping->page_tree,
2183                                                page_index(page),
2184                                                PAGECACHE_TAG_WRITEBACK);
2185                        if (bdi_cap_account_writeback(bdi)) {
2186                                __dec_bdi_stat(bdi, BDI_WRITEBACK);
2187                                __bdi_writeout_inc(bdi);
2188                        }
2189                }
2190                spin_unlock_irqrestore(&mapping->tree_lock, flags);
2191        } else {
2192                ret = TestClearPageWriteback(page);
2193        }
2194        if (ret) {
2195                dec_zone_page_state(page, NR_WRITEBACK);
2196                inc_zone_page_state(page, NR_WRITTEN);
2197        }
2198        return ret;
2199}
2200
2201int test_set_page_writeback(struct page *page)
2202{
2203        struct address_space *mapping = page_mapping(page);
2204        int ret;
2205
2206        if (mapping) {
2207                struct backing_dev_info *bdi = mapping->backing_dev_info;
2208                unsigned long flags;
2209
2210                spin_lock_irqsave(&mapping->tree_lock, flags);
2211                ret = TestSetPageWriteback(page);
2212                if (!ret) {
2213                        radix_tree_tag_set(&mapping->page_tree,
2214                                                page_index(page),
2215                                                PAGECACHE_TAG_WRITEBACK);
2216                        if (bdi_cap_account_writeback(bdi))
2217                                __inc_bdi_stat(bdi, BDI_WRITEBACK);
2218                }
2219                if (!PageDirty(page))
2220                        radix_tree_tag_clear(&mapping->page_tree,
2221                                                page_index(page),
2222                                                PAGECACHE_TAG_DIRTY);
2223                radix_tree_tag_clear(&mapping->page_tree,
2224                                     page_index(page),
2225                                     PAGECACHE_TAG_TOWRITE);
2226                spin_unlock_irqrestore(&mapping->tree_lock, flags);
2227        } else {
2228                ret = TestSetPageWriteback(page);
2229        }
2230        if (!ret)
2231                account_page_writeback(page);
2232        return ret;
2233
2234}
2235EXPORT_SYMBOL(test_set_page_writeback);
2236
2237/*
2238 * Return true if any of the pages in the mapping are marked with the
2239 * passed tag.
2240 */
2241int mapping_tagged(struct address_space *mapping, int tag)
2242{
2243        return radix_tree_tagged(&mapping->page_tree, tag);
2244}
2245EXPORT_SYMBOL(mapping_tagged);
2246
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