linux/mm/page-writeback.c
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   1/*
   2 * mm/page-writeback.c
   3 *
   4 * Copyright (C) 2002, Linus Torvalds.
   5 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
   6 *
   7 * Contains functions related to writing back dirty pages at the
   8 * address_space level.
   9 *
  10 * 10Apr2002    Andrew Morton
  11 *              Initial version
  12 */
  13
  14#include <linux/kernel.h>
  15#include <linux/module.h>
  16#include <linux/spinlock.h>
  17#include <linux/fs.h>
  18#include <linux/mm.h>
  19#include <linux/swap.h>
  20#include <linux/slab.h>
  21#include <linux/pagemap.h>
  22#include <linux/writeback.h>
  23#include <linux/init.h>
  24#include <linux/backing-dev.h>
  25#include <linux/task_io_accounting_ops.h>
  26#include <linux/blkdev.h>
  27#include <linux/mpage.h>
  28#include <linux/rmap.h>
  29#include <linux/percpu.h>
  30#include <linux/notifier.h>
  31#include <linux/smp.h>
  32#include <linux/sysctl.h>
  33#include <linux/cpu.h>
  34#include <linux/syscalls.h>
  35#include <linux/buffer_head.h>
  36#include <linux/pagevec.h>
  37
  38/*
  39 * The maximum number of pages to writeout in a single bdflush/kupdate
  40 * operation.  We do this so we don't hold I_SYNC against an inode for
  41 * enormous amounts of time, which would block a userspace task which has
  42 * been forced to throttle against that inode.  Also, the code reevaluates
  43 * the dirty each time it has written this many pages.
  44 */
  45#define MAX_WRITEBACK_PAGES     1024
  46
  47/*
  48 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
  49 * will look to see if it needs to force writeback or throttling.
  50 */
  51static long ratelimit_pages = 32;
  52
  53/*
  54 * When balance_dirty_pages decides that the caller needs to perform some
  55 * non-background writeback, this is how many pages it will attempt to write.
  56 * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
  57 * large amounts of I/O are submitted.
  58 */
  59static inline long sync_writeback_pages(void)
  60{
  61        return ratelimit_pages + ratelimit_pages / 2;
  62}
  63
  64/* The following parameters are exported via /proc/sys/vm */
  65
  66/*
  67 * Start background writeback (via pdflush) at this percentage
  68 */
  69int dirty_background_ratio = 5;
  70
  71/*
  72 * free highmem will not be subtracted from the total free memory
  73 * for calculating free ratios if vm_highmem_is_dirtyable is true
  74 */
  75int vm_highmem_is_dirtyable;
  76
  77/*
  78 * The generator of dirty data starts writeback at this percentage
  79 */
  80int vm_dirty_ratio = 10;
  81
  82/*
  83 * The interval between `kupdate'-style writebacks, in jiffies
  84 */
  85int dirty_writeback_interval = 5 * HZ;
  86
  87/*
  88 * The longest number of jiffies for which data is allowed to remain dirty
  89 */
  90int dirty_expire_interval = 30 * HZ;
  91
  92/*
  93 * Flag that makes the machine dump writes/reads and block dirtyings.
  94 */
  95int block_dump;
  96
  97/*
  98 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
  99 * a full sync is triggered after this time elapses without any disk activity.
 100 */
 101int laptop_mode;
 102
 103EXPORT_SYMBOL(laptop_mode);
 104
 105/* End of sysctl-exported parameters */
 106
 107
 108static void background_writeout(unsigned long _min_pages);
 109
 110/*
 111 * Scale the writeback cache size proportional to the relative writeout speeds.
 112 *
 113 * We do this by keeping a floating proportion between BDIs, based on page
 114 * writeback completions [end_page_writeback()]. Those devices that write out
 115 * pages fastest will get the larger share, while the slower will get a smaller
 116 * share.
 117 *
 118 * We use page writeout completions because we are interested in getting rid of
 119 * dirty pages. Having them written out is the primary goal.
 120 *
 121 * We introduce a concept of time, a period over which we measure these events,
 122 * because demand can/will vary over time. The length of this period itself is
 123 * measured in page writeback completions.
 124 *
 125 */
 126static struct prop_descriptor vm_completions;
 127static struct prop_descriptor vm_dirties;
 128
 129/*
 130 * couple the period to the dirty_ratio:
 131 *
 132 *   period/2 ~ roundup_pow_of_two(dirty limit)
 133 */
 134static int calc_period_shift(void)
 135{
 136        unsigned long dirty_total;
 137
 138        dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / 100;
 139        return 2 + ilog2(dirty_total - 1);
 140}
 141
 142/*
 143 * update the period when the dirty ratio changes.
 144 */
 145int dirty_ratio_handler(struct ctl_table *table, int write,
 146                struct file *filp, void __user *buffer, size_t *lenp,
 147                loff_t *ppos)
 148{
 149        int old_ratio = vm_dirty_ratio;
 150        int ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
 151        if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
 152                int shift = calc_period_shift();
 153                prop_change_shift(&vm_completions, shift);
 154                prop_change_shift(&vm_dirties, shift);
 155        }
 156        return ret;
 157}
 158
 159/*
 160 * Increment the BDI's writeout completion count and the global writeout
 161 * completion count. Called from test_clear_page_writeback().
 162 */
 163static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
 164{
 165        __prop_inc_percpu_max(&vm_completions, &bdi->completions,
 166                              bdi->max_prop_frac);
 167}
 168
 169void bdi_writeout_inc(struct backing_dev_info *bdi)
 170{
 171        unsigned long flags;
 172
 173        local_irq_save(flags);
 174        __bdi_writeout_inc(bdi);
 175        local_irq_restore(flags);
 176}
 177EXPORT_SYMBOL_GPL(bdi_writeout_inc);
 178
 179static inline void task_dirty_inc(struct task_struct *tsk)
 180{
 181        prop_inc_single(&vm_dirties, &tsk->dirties);
 182}
 183
 184/*
 185 * Obtain an accurate fraction of the BDI's portion.
 186 */
 187static void bdi_writeout_fraction(struct backing_dev_info *bdi,
 188                long *numerator, long *denominator)
 189{
 190        if (bdi_cap_writeback_dirty(bdi)) {
 191                prop_fraction_percpu(&vm_completions, &bdi->completions,
 192                                numerator, denominator);
 193        } else {
 194                *numerator = 0;
 195                *denominator = 1;
 196        }
 197}
 198
 199/*
 200 * Clip the earned share of dirty pages to that which is actually available.
 201 * This avoids exceeding the total dirty_limit when the floating averages
 202 * fluctuate too quickly.
 203 */
 204static void
 205clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long *pbdi_dirty)
 206{
 207        long avail_dirty;
 208
 209        avail_dirty = dirty -
 210                (global_page_state(NR_FILE_DIRTY) +
 211                 global_page_state(NR_WRITEBACK) +
 212                 global_page_state(NR_UNSTABLE_NFS) +
 213                 global_page_state(NR_WRITEBACK_TEMP));
 214
 215        if (avail_dirty < 0)
 216                avail_dirty = 0;
 217
 218        avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) +
 219                bdi_stat(bdi, BDI_WRITEBACK);
 220
 221        *pbdi_dirty = min(*pbdi_dirty, avail_dirty);
 222}
 223
 224static inline void task_dirties_fraction(struct task_struct *tsk,
 225                long *numerator, long *denominator)
 226{
 227        prop_fraction_single(&vm_dirties, &tsk->dirties,
 228                                numerator, denominator);
 229}
 230
 231/*
 232 * scale the dirty limit
 233 *
 234 * task specific dirty limit:
 235 *
 236 *   dirty -= (dirty/8) * p_{t}
 237 */
 238static void task_dirty_limit(struct task_struct *tsk, long *pdirty)
 239{
 240        long numerator, denominator;
 241        long dirty = *pdirty;
 242        u64 inv = dirty >> 3;
 243
 244        task_dirties_fraction(tsk, &numerator, &denominator);
 245        inv *= numerator;
 246        do_div(inv, denominator);
 247
 248        dirty -= inv;
 249        if (dirty < *pdirty/2)
 250                dirty = *pdirty/2;
 251
 252        *pdirty = dirty;
 253}
 254
 255/*
 256 *
 257 */
 258static DEFINE_SPINLOCK(bdi_lock);
 259static unsigned int bdi_min_ratio;
 260
 261int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 262{
 263        int ret = 0;
 264        unsigned long flags;
 265
 266        spin_lock_irqsave(&bdi_lock, flags);
 267        if (min_ratio > bdi->max_ratio) {
 268                ret = -EINVAL;
 269        } else {
 270                min_ratio -= bdi->min_ratio;
 271                if (bdi_min_ratio + min_ratio < 100) {
 272                        bdi_min_ratio += min_ratio;
 273                        bdi->min_ratio += min_ratio;
 274                } else {
 275                        ret = -EINVAL;
 276                }
 277        }
 278        spin_unlock_irqrestore(&bdi_lock, flags);
 279
 280        return ret;
 281}
 282
 283int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 284{
 285        unsigned long flags;
 286        int ret = 0;
 287
 288        if (max_ratio > 100)
 289                return -EINVAL;
 290
 291        spin_lock_irqsave(&bdi_lock, flags);
 292        if (bdi->min_ratio > max_ratio) {
 293                ret = -EINVAL;
 294        } else {
 295                bdi->max_ratio = max_ratio;
 296                bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
 297        }
 298        spin_unlock_irqrestore(&bdi_lock, flags);
 299
 300        return ret;
 301}
 302EXPORT_SYMBOL(bdi_set_max_ratio);
 303
 304/*
 305 * Work out the current dirty-memory clamping and background writeout
 306 * thresholds.
 307 *
 308 * The main aim here is to lower them aggressively if there is a lot of mapped
 309 * memory around.  To avoid stressing page reclaim with lots of unreclaimable
 310 * pages.  It is better to clamp down on writers than to start swapping, and
 311 * performing lots of scanning.
 312 *
 313 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
 314 *
 315 * We don't permit the clamping level to fall below 5% - that is getting rather
 316 * excessive.
 317 *
 318 * We make sure that the background writeout level is below the adjusted
 319 * clamping level.
 320 */
 321
 322static unsigned long highmem_dirtyable_memory(unsigned long total)
 323{
 324#ifdef CONFIG_HIGHMEM
 325        int node;
 326        unsigned long x = 0;
 327
 328        for_each_node_state(node, N_HIGH_MEMORY) {
 329                struct zone *z =
 330                        &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
 331
 332                x += zone_page_state(z, NR_FREE_PAGES) + zone_lru_pages(z);
 333        }
 334        /*
 335         * Make sure that the number of highmem pages is never larger
 336         * than the number of the total dirtyable memory. This can only
 337         * occur in very strange VM situations but we want to make sure
 338         * that this does not occur.
 339         */
 340        return min(x, total);
 341#else
 342        return 0;
 343#endif
 344}
 345
 346/**
 347 * determine_dirtyable_memory - amount of memory that may be used
 348 *
 349 * Returns the numebr of pages that can currently be freed and used
 350 * by the kernel for direct mappings.
 351 */
 352unsigned long determine_dirtyable_memory(void)
 353{
 354        unsigned long x;
 355
 356        x = global_page_state(NR_FREE_PAGES) + global_lru_pages();
 357
 358        if (!vm_highmem_is_dirtyable)
 359                x -= highmem_dirtyable_memory(x);
 360
 361        return x + 1;   /* Ensure that we never return 0 */
 362}
 363
 364void
 365get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty,
 366                 struct backing_dev_info *bdi)
 367{
 368        int background_ratio;           /* Percentages */
 369        int dirty_ratio;
 370        long background;
 371        long dirty;
 372        unsigned long available_memory = determine_dirtyable_memory();
 373        struct task_struct *tsk;
 374
 375        dirty_ratio = vm_dirty_ratio;
 376        if (dirty_ratio < 5)
 377                dirty_ratio = 5;
 378
 379        background_ratio = dirty_background_ratio;
 380        if (background_ratio >= dirty_ratio)
 381                background_ratio = dirty_ratio / 2;
 382
 383        background = (background_ratio * available_memory) / 100;
 384        dirty = (dirty_ratio * available_memory) / 100;
 385        tsk = current;
 386        if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
 387                background += background / 4;
 388                dirty += dirty / 4;
 389        }
 390        *pbackground = background;
 391        *pdirty = dirty;
 392
 393        if (bdi) {
 394                u64 bdi_dirty;
 395                long numerator, denominator;
 396
 397                /*
 398                 * Calculate this BDI's share of the dirty ratio.
 399                 */
 400                bdi_writeout_fraction(bdi, &numerator, &denominator);
 401
 402                bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
 403                bdi_dirty *= numerator;
 404                do_div(bdi_dirty, denominator);
 405                bdi_dirty += (dirty * bdi->min_ratio) / 100;
 406                if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
 407                        bdi_dirty = dirty * bdi->max_ratio / 100;
 408
 409                *pbdi_dirty = bdi_dirty;
 410                clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);
 411                task_dirty_limit(current, pbdi_dirty);
 412        }
 413}
 414
 415/*
 416 * balance_dirty_pages() must be called by processes which are generating dirty
 417 * data.  It looks at the number of dirty pages in the machine and will force
 418 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
 419 * If we're over `background_thresh' then pdflush is woken to perform some
 420 * writeout.
 421 */
 422static void balance_dirty_pages(struct address_space *mapping)
 423{
 424        long nr_reclaimable, bdi_nr_reclaimable;
 425        long nr_writeback, bdi_nr_writeback;
 426        long background_thresh;
 427        long dirty_thresh;
 428        long bdi_thresh;
 429        unsigned long pages_written = 0;
 430        unsigned long write_chunk = sync_writeback_pages();
 431
 432        struct backing_dev_info *bdi = mapping->backing_dev_info;
 433
 434        for (;;) {
 435                struct writeback_control wbc = {
 436                        .bdi            = bdi,
 437                        .sync_mode      = WB_SYNC_NONE,
 438                        .older_than_this = NULL,
 439                        .nr_to_write    = write_chunk,
 440                        .range_cyclic   = 1,
 441                };
 442
 443                get_dirty_limits(&background_thresh, &dirty_thresh,
 444                                &bdi_thresh, bdi);
 445
 446                nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
 447                                        global_page_state(NR_UNSTABLE_NFS);
 448                nr_writeback = global_page_state(NR_WRITEBACK);
 449
 450                bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
 451                bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
 452
 453                if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
 454                        break;
 455
 456                /*
 457                 * Throttle it only when the background writeback cannot
 458                 * catch-up. This avoids (excessively) small writeouts
 459                 * when the bdi limits are ramping up.
 460                 */
 461                if (nr_reclaimable + nr_writeback <
 462                                (background_thresh + dirty_thresh) / 2)
 463                        break;
 464
 465                if (!bdi->dirty_exceeded)
 466                        bdi->dirty_exceeded = 1;
 467
 468                /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
 469                 * Unstable writes are a feature of certain networked
 470                 * filesystems (i.e. NFS) in which data may have been
 471                 * written to the server's write cache, but has not yet
 472                 * been flushed to permanent storage.
 473                 */
 474                if (bdi_nr_reclaimable) {
 475                        writeback_inodes(&wbc);
 476                        pages_written += write_chunk - wbc.nr_to_write;
 477                        get_dirty_limits(&background_thresh, &dirty_thresh,
 478                                       &bdi_thresh, bdi);
 479                }
 480
 481                /*
 482                 * In order to avoid the stacked BDI deadlock we need
 483                 * to ensure we accurately count the 'dirty' pages when
 484                 * the threshold is low.
 485                 *
 486                 * Otherwise it would be possible to get thresh+n pages
 487                 * reported dirty, even though there are thresh-m pages
 488                 * actually dirty; with m+n sitting in the percpu
 489                 * deltas.
 490                 */
 491                if (bdi_thresh < 2*bdi_stat_error(bdi)) {
 492                        bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
 493                        bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
 494                } else if (bdi_nr_reclaimable) {
 495                        bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
 496                        bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
 497                }
 498
 499                if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
 500                        break;
 501                if (pages_written >= write_chunk)
 502                        break;          /* We've done our duty */
 503
 504                congestion_wait(WRITE, HZ/10);
 505        }
 506
 507        if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh &&
 508                        bdi->dirty_exceeded)
 509                bdi->dirty_exceeded = 0;
 510
 511        if (writeback_in_progress(bdi))
 512                return;         /* pdflush is already working this queue */
 513
 514        /*
 515         * In laptop mode, we wait until hitting the higher threshold before
 516         * starting background writeout, and then write out all the way down
 517         * to the lower threshold.  So slow writers cause minimal disk activity.
 518         *
 519         * In normal mode, we start background writeout at the lower
 520         * background_thresh, to keep the amount of dirty memory low.
 521         */
 522        if ((laptop_mode && pages_written) ||
 523                        (!laptop_mode && (global_page_state(NR_FILE_DIRTY)
 524                                          + global_page_state(NR_UNSTABLE_NFS)
 525                                          > background_thresh)))
 526                pdflush_operation(background_writeout, 0);
 527}
 528
 529void set_page_dirty_balance(struct page *page, int page_mkwrite)
 530{
 531        if (set_page_dirty(page) || page_mkwrite) {
 532                struct address_space *mapping = page_mapping(page);
 533
 534                if (mapping)
 535                        balance_dirty_pages_ratelimited(mapping);
 536        }
 537}
 538
 539/**
 540 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
 541 * @mapping: address_space which was dirtied
 542 * @nr_pages_dirtied: number of pages which the caller has just dirtied
 543 *
 544 * Processes which are dirtying memory should call in here once for each page
 545 * which was newly dirtied.  The function will periodically check the system's
 546 * dirty state and will initiate writeback if needed.
 547 *
 548 * On really big machines, get_writeback_state is expensive, so try to avoid
 549 * calling it too often (ratelimiting).  But once we're over the dirty memory
 550 * limit we decrease the ratelimiting by a lot, to prevent individual processes
 551 * from overshooting the limit by (ratelimit_pages) each.
 552 */
 553void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
 554                                        unsigned long nr_pages_dirtied)
 555{
 556        static DEFINE_PER_CPU(unsigned long, ratelimits) = 0;
 557        unsigned long ratelimit;
 558        unsigned long *p;
 559
 560        ratelimit = ratelimit_pages;
 561        if (mapping->backing_dev_info->dirty_exceeded)
 562                ratelimit = 8;
 563
 564        /*
 565         * Check the rate limiting. Also, we do not want to throttle real-time
 566         * tasks in balance_dirty_pages(). Period.
 567         */
 568        preempt_disable();
 569        p =  &__get_cpu_var(ratelimits);
 570        *p += nr_pages_dirtied;
 571        if (unlikely(*p >= ratelimit)) {
 572                *p = 0;
 573                preempt_enable();
 574                balance_dirty_pages(mapping);
 575                return;
 576        }
 577        preempt_enable();
 578}
 579EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
 580
 581void throttle_vm_writeout(gfp_t gfp_mask)
 582{
 583        long background_thresh;
 584        long dirty_thresh;
 585
 586        for ( ; ; ) {
 587                get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
 588
 589                /*
 590                 * Boost the allowable dirty threshold a bit for page
 591                 * allocators so they don't get DoS'ed by heavy writers
 592                 */
 593                dirty_thresh += dirty_thresh / 10;      /* wheeee... */
 594
 595                if (global_page_state(NR_UNSTABLE_NFS) +
 596                        global_page_state(NR_WRITEBACK) <= dirty_thresh)
 597                                break;
 598                congestion_wait(WRITE, HZ/10);
 599
 600                /*
 601                 * The caller might hold locks which can prevent IO completion
 602                 * or progress in the filesystem.  So we cannot just sit here
 603                 * waiting for IO to complete.
 604                 */
 605                if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
 606                        break;
 607        }
 608}
 609
 610/*
 611 * writeback at least _min_pages, and keep writing until the amount of dirty
 612 * memory is less than the background threshold, or until we're all clean.
 613 */
 614static void background_writeout(unsigned long _min_pages)
 615{
 616        long min_pages = _min_pages;
 617        struct writeback_control wbc = {
 618                .bdi            = NULL,
 619                .sync_mode      = WB_SYNC_NONE,
 620                .older_than_this = NULL,
 621                .nr_to_write    = 0,
 622                .nonblocking    = 1,
 623                .range_cyclic   = 1,
 624        };
 625
 626        for ( ; ; ) {
 627                long background_thresh;
 628                long dirty_thresh;
 629
 630                get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
 631                if (global_page_state(NR_FILE_DIRTY) +
 632                        global_page_state(NR_UNSTABLE_NFS) < background_thresh
 633                                && min_pages <= 0)
 634                        break;
 635                wbc.more_io = 0;
 636                wbc.encountered_congestion = 0;
 637                wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 638                wbc.pages_skipped = 0;
 639                writeback_inodes(&wbc);
 640                min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 641                if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
 642                        /* Wrote less than expected */
 643                        if (wbc.encountered_congestion || wbc.more_io)
 644                                congestion_wait(WRITE, HZ/10);
 645                        else
 646                                break;
 647                }
 648        }
 649}
 650
 651/*
 652 * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
 653 * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
 654 * -1 if all pdflush threads were busy.
 655 */
 656int wakeup_pdflush(long nr_pages)
 657{
 658        if (nr_pages == 0)
 659                nr_pages = global_page_state(NR_FILE_DIRTY) +
 660                                global_page_state(NR_UNSTABLE_NFS);
 661        return pdflush_operation(background_writeout, nr_pages);
 662}
 663
 664static void wb_timer_fn(unsigned long unused);
 665static void laptop_timer_fn(unsigned long unused);
 666
 667static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
 668static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
 669
 670/*
 671 * Periodic writeback of "old" data.
 672 *
 673 * Define "old": the first time one of an inode's pages is dirtied, we mark the
 674 * dirtying-time in the inode's address_space.  So this periodic writeback code
 675 * just walks the superblock inode list, writing back any inodes which are
 676 * older than a specific point in time.
 677 *
 678 * Try to run once per dirty_writeback_interval.  But if a writeback event
 679 * takes longer than a dirty_writeback_interval interval, then leave a
 680 * one-second gap.
 681 *
 682 * older_than_this takes precedence over nr_to_write.  So we'll only write back
 683 * all dirty pages if they are all attached to "old" mappings.
 684 */
 685static void wb_kupdate(unsigned long arg)
 686{
 687        unsigned long oldest_jif;
 688        unsigned long start_jif;
 689        unsigned long next_jif;
 690        long nr_to_write;
 691        struct writeback_control wbc = {
 692                .bdi            = NULL,
 693                .sync_mode      = WB_SYNC_NONE,
 694                .older_than_this = &oldest_jif,
 695                .nr_to_write    = 0,
 696                .nonblocking    = 1,
 697                .for_kupdate    = 1,
 698                .range_cyclic   = 1,
 699        };
 700
 701        sync_supers();
 702
 703        oldest_jif = jiffies - dirty_expire_interval;
 704        start_jif = jiffies;
 705        next_jif = start_jif + dirty_writeback_interval;
 706        nr_to_write = global_page_state(NR_FILE_DIRTY) +
 707                        global_page_state(NR_UNSTABLE_NFS) +
 708                        (inodes_stat.nr_inodes - inodes_stat.nr_unused);
 709        while (nr_to_write > 0) {
 710                wbc.more_io = 0;
 711                wbc.encountered_congestion = 0;
 712                wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 713                writeback_inodes(&wbc);
 714                if (wbc.nr_to_write > 0) {
 715                        if (wbc.encountered_congestion || wbc.more_io)
 716                                congestion_wait(WRITE, HZ/10);
 717                        else
 718                                break;  /* All the old data is written */
 719                }
 720                nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 721        }
 722        if (time_before(next_jif, jiffies + HZ))
 723                next_jif = jiffies + HZ;
 724        if (dirty_writeback_interval)
 725                mod_timer(&wb_timer, next_jif);
 726}
 727
 728/*
 729 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
 730 */
 731int dirty_writeback_centisecs_handler(ctl_table *table, int write,
 732        struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
 733{
 734        proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
 735        if (dirty_writeback_interval)
 736                mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
 737        else
 738                del_timer(&wb_timer);
 739        return 0;
 740}
 741
 742static void wb_timer_fn(unsigned long unused)
 743{
 744        if (pdflush_operation(wb_kupdate, 0) < 0)
 745                mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
 746}
 747
 748static void laptop_flush(unsigned long unused)
 749{
 750        sys_sync();
 751}
 752
 753static void laptop_timer_fn(unsigned long unused)
 754{
 755        pdflush_operation(laptop_flush, 0);
 756}
 757
 758/*
 759 * We've spun up the disk and we're in laptop mode: schedule writeback
 760 * of all dirty data a few seconds from now.  If the flush is already scheduled
 761 * then push it back - the user is still using the disk.
 762 */
 763void laptop_io_completion(void)
 764{
 765        mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
 766}
 767
 768/*
 769 * We're in laptop mode and we've just synced. The sync's writes will have
 770 * caused another writeback to be scheduled by laptop_io_completion.
 771 * Nothing needs to be written back anymore, so we unschedule the writeback.
 772 */
 773void laptop_sync_completion(void)
 774{
 775        del_timer(&laptop_mode_wb_timer);
 776}
 777
 778/*
 779 * If ratelimit_pages is too high then we can get into dirty-data overload
 780 * if a large number of processes all perform writes at the same time.
 781 * If it is too low then SMP machines will call the (expensive)
 782 * get_writeback_state too often.
 783 *
 784 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
 785 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
 786 * thresholds before writeback cuts in.
 787 *
 788 * But the limit should not be set too high.  Because it also controls the
 789 * amount of memory which the balance_dirty_pages() caller has to write back.
 790 * If this is too large then the caller will block on the IO queue all the
 791 * time.  So limit it to four megabytes - the balance_dirty_pages() caller
 792 * will write six megabyte chunks, max.
 793 */
 794
 795void writeback_set_ratelimit(void)
 796{
 797        ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
 798        if (ratelimit_pages < 16)
 799                ratelimit_pages = 16;
 800        if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
 801                ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
 802}
 803
 804static int __cpuinit
 805ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
 806{
 807        writeback_set_ratelimit();
 808        return NOTIFY_DONE;
 809}
 810
 811static struct notifier_block __cpuinitdata ratelimit_nb = {
 812        .notifier_call  = ratelimit_handler,
 813        .next           = NULL,
 814};
 815
 816/*
 817 * Called early on to tune the page writeback dirty limits.
 818 *
 819 * We used to scale dirty pages according to how total memory
 820 * related to pages that could be allocated for buffers (by
 821 * comparing nr_free_buffer_pages() to vm_total_pages.
 822 *
 823 * However, that was when we used "dirty_ratio" to scale with
 824 * all memory, and we don't do that any more. "dirty_ratio"
 825 * is now applied to total non-HIGHPAGE memory (by subtracting
 826 * totalhigh_pages from vm_total_pages), and as such we can't
 827 * get into the old insane situation any more where we had
 828 * large amounts of dirty pages compared to a small amount of
 829 * non-HIGHMEM memory.
 830 *
 831 * But we might still want to scale the dirty_ratio by how
 832 * much memory the box has..
 833 */
 834void __init page_writeback_init(void)
 835{
 836        int shift;
 837
 838        mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
 839        writeback_set_ratelimit();
 840        register_cpu_notifier(&ratelimit_nb);
 841
 842        shift = calc_period_shift();
 843        prop_descriptor_init(&vm_completions, shift);
 844        prop_descriptor_init(&vm_dirties, shift);
 845}
 846
 847/**
 848 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
 849 * @mapping: address space structure to write
 850 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 851 * @writepage: function called for each page
 852 * @data: data passed to writepage function
 853 *
 854 * If a page is already under I/O, write_cache_pages() skips it, even
 855 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 856 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 857 * and msync() need to guarantee that all the data which was dirty at the time
 858 * the call was made get new I/O started against them.  If wbc->sync_mode is
 859 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 860 * existing IO to complete.
 861 */
 862int write_cache_pages(struct address_space *mapping,
 863                      struct writeback_control *wbc, writepage_t writepage,
 864                      void *data)
 865{
 866        struct backing_dev_info *bdi = mapping->backing_dev_info;
 867        int ret = 0;
 868        int done = 0;
 869        struct pagevec pvec;
 870        int nr_pages;
 871        pgoff_t index;
 872        pgoff_t end;            /* Inclusive */
 873        int scanned = 0;
 874        int range_whole = 0;
 875        long nr_to_write = wbc->nr_to_write;
 876
 877        if (wbc->nonblocking && bdi_write_congested(bdi)) {
 878                wbc->encountered_congestion = 1;
 879                return 0;
 880        }
 881
 882        pagevec_init(&pvec, 0);
 883        if (wbc->range_cyclic) {
 884                index = mapping->writeback_index; /* Start from prev offset */
 885                end = -1;
 886        } else {
 887                index = wbc->range_start >> PAGE_CACHE_SHIFT;
 888                end = wbc->range_end >> PAGE_CACHE_SHIFT;
 889                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
 890                        range_whole = 1;
 891                scanned = 1;
 892        }
 893retry:
 894        while (!done && (index <= end) &&
 895               (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
 896                                              PAGECACHE_TAG_DIRTY,
 897                                              min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
 898                unsigned i;
 899
 900                scanned = 1;
 901                for (i = 0; i < nr_pages; i++) {
 902                        struct page *page = pvec.pages[i];
 903
 904                        /*
 905                         * At this point we hold neither mapping->tree_lock nor
 906                         * lock on the page itself: the page may be truncated or
 907                         * invalidated (changing page->mapping to NULL), or even
 908                         * swizzled back from swapper_space to tmpfs file
 909                         * mapping
 910                         */
 911                        lock_page(page);
 912
 913                        if (unlikely(page->mapping != mapping)) {
 914                                unlock_page(page);
 915                                continue;
 916                        }
 917
 918                        if (!wbc->range_cyclic && page->index > end) {
 919                                done = 1;
 920                                unlock_page(page);
 921                                continue;
 922                        }
 923
 924                        if (wbc->sync_mode != WB_SYNC_NONE)
 925                                wait_on_page_writeback(page);
 926
 927                        if (PageWriteback(page) ||
 928                            !clear_page_dirty_for_io(page)) {
 929                                unlock_page(page);
 930                                continue;
 931                        }
 932
 933                        ret = (*writepage)(page, wbc, data);
 934
 935                        if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
 936                                unlock_page(page);
 937                                ret = 0;
 938                        }
 939                        if (ret || (--nr_to_write <= 0))
 940                                done = 1;
 941                        if (wbc->nonblocking && bdi_write_congested(bdi)) {
 942                                wbc->encountered_congestion = 1;
 943                                done = 1;
 944                        }
 945                }
 946                pagevec_release(&pvec);
 947                cond_resched();
 948        }
 949        if (!scanned && !done) {
 950                /*
 951                 * We hit the last page and there is more work to be done: wrap
 952                 * back to the start of the file
 953                 */
 954                scanned = 1;
 955                index = 0;
 956                goto retry;
 957        }
 958        if (!wbc->no_nrwrite_index_update) {
 959                if (wbc->range_cyclic || (range_whole && nr_to_write > 0))
 960                        mapping->writeback_index = index;
 961                wbc->nr_to_write = nr_to_write;
 962        }
 963
 964        return ret;
 965}
 966EXPORT_SYMBOL(write_cache_pages);
 967
 968/*
 969 * Function used by generic_writepages to call the real writepage
 970 * function and set the mapping flags on error
 971 */
 972static int __writepage(struct page *page, struct writeback_control *wbc,
 973                       void *data)
 974{
 975        struct address_space *mapping = data;
 976        int ret = mapping->a_ops->writepage(page, wbc);
 977        mapping_set_error(mapping, ret);
 978        return ret;
 979}
 980
 981/**
 982 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
 983 * @mapping: address space structure to write
 984 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 985 *
 986 * This is a library function, which implements the writepages()
 987 * address_space_operation.
 988 */
 989int generic_writepages(struct address_space *mapping,
 990                       struct writeback_control *wbc)
 991{
 992        /* deal with chardevs and other special file */
 993        if (!mapping->a_ops->writepage)
 994                return 0;
 995
 996        return write_cache_pages(mapping, wbc, __writepage, mapping);
 997}
 998
 999EXPORT_SYMBOL(generic_writepages);
1000
1001int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1002{
1003        int ret;
1004
1005        if (wbc->nr_to_write <= 0)
1006                return 0;
1007        wbc->for_writepages = 1;
1008        if (mapping->a_ops->writepages)
1009                ret = mapping->a_ops->writepages(mapping, wbc);
1010        else
1011                ret = generic_writepages(mapping, wbc);
1012        wbc->for_writepages = 0;
1013        return ret;
1014}
1015
1016/**
1017 * write_one_page - write out a single page and optionally wait on I/O
1018 * @page: the page to write
1019 * @wait: if true, wait on writeout
1020 *
1021 * The page must be locked by the caller and will be unlocked upon return.
1022 *
1023 * write_one_page() returns a negative error code if I/O failed.
1024 */
1025int write_one_page(struct page *page, int wait)
1026{
1027        struct address_space *mapping = page->mapping;
1028        int ret = 0;
1029        struct writeback_control wbc = {
1030                .sync_mode = WB_SYNC_ALL,
1031                .nr_to_write = 1,
1032        };
1033
1034        BUG_ON(!PageLocked(page));
1035
1036        if (wait)
1037                wait_on_page_writeback(page);
1038
1039        if (clear_page_dirty_for_io(page)) {
1040                page_cache_get(page);
1041                ret = mapping->a_ops->writepage(page, &wbc);
1042                if (ret == 0 && wait) {
1043                        wait_on_page_writeback(page);
1044                        if (PageError(page))
1045                                ret = -EIO;
1046                }
1047                page_cache_release(page);
1048        } else {
1049                unlock_page(page);
1050        }
1051        return ret;
1052}
1053EXPORT_SYMBOL(write_one_page);
1054
1055/*
1056 * For address_spaces which do not use buffers nor write back.
1057 */
1058int __set_page_dirty_no_writeback(struct page *page)
1059{
1060        if (!PageDirty(page))
1061                SetPageDirty(page);
1062        return 0;
1063}
1064
1065/*
1066 * For address_spaces which do not use buffers.  Just tag the page as dirty in
1067 * its radix tree.
1068 *
1069 * This is also used when a single buffer is being dirtied: we want to set the
1070 * page dirty in that case, but not all the buffers.  This is a "bottom-up"
1071 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1072 *
1073 * Most callers have locked the page, which pins the address_space in memory.
1074 * But zap_pte_range() does not lock the page, however in that case the
1075 * mapping is pinned by the vma's ->vm_file reference.
1076 *
1077 * We take care to handle the case where the page was truncated from the
1078 * mapping by re-checking page_mapping() inside tree_lock.
1079 */
1080int __set_page_dirty_nobuffers(struct page *page)
1081{
1082        if (!TestSetPageDirty(page)) {
1083                struct address_space *mapping = page_mapping(page);
1084                struct address_space *mapping2;
1085
1086                if (!mapping)
1087                        return 1;
1088
1089                spin_lock_irq(&mapping->tree_lock);
1090                mapping2 = page_mapping(page);
1091                if (mapping2) { /* Race with truncate? */
1092                        BUG_ON(mapping2 != mapping);
1093                        WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
1094                        if (mapping_cap_account_dirty(mapping)) {
1095                                __inc_zone_page_state(page, NR_FILE_DIRTY);
1096                                __inc_bdi_stat(mapping->backing_dev_info,
1097                                                BDI_RECLAIMABLE);
1098                                task_io_account_write(PAGE_CACHE_SIZE);
1099                        }
1100                        radix_tree_tag_set(&mapping->page_tree,
1101                                page_index(page), PAGECACHE_TAG_DIRTY);
1102                }
1103                spin_unlock_irq(&mapping->tree_lock);
1104                if (mapping->host) {
1105                        /* !PageAnon && !swapper_space */
1106                        __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1107                }
1108                return 1;
1109        }
1110        return 0;
1111}
1112EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1113
1114/*
1115 * When a writepage implementation decides that it doesn't want to write this
1116 * page for some reason, it should redirty the locked page via
1117 * redirty_page_for_writepage() and it should then unlock the page and return 0
1118 */
1119int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1120{
1121        wbc->pages_skipped++;
1122        return __set_page_dirty_nobuffers(page);
1123}
1124EXPORT_SYMBOL(redirty_page_for_writepage);
1125
1126/*
1127 * If the mapping doesn't provide a set_page_dirty a_op, then
1128 * just fall through and assume that it wants buffer_heads.
1129 */
1130static int __set_page_dirty(struct page *page)
1131{
1132        struct address_space *mapping = page_mapping(page);
1133
1134        if (likely(mapping)) {
1135                int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
1136#ifdef CONFIG_BLOCK
1137                if (!spd)
1138                        spd = __set_page_dirty_buffers;
1139#endif
1140                return (*spd)(page);
1141        }
1142        if (!PageDirty(page)) {
1143                if (!TestSetPageDirty(page))
1144                        return 1;
1145        }
1146        return 0;
1147}
1148
1149int set_page_dirty(struct page *page)
1150{
1151        int ret = __set_page_dirty(page);
1152        if (ret)
1153                task_dirty_inc(current);
1154        return ret;
1155}
1156EXPORT_SYMBOL(set_page_dirty);
1157
1158/*
1159 * set_page_dirty() is racy if the caller has no reference against
1160 * page->mapping->host, and if the page is unlocked.  This is because another
1161 * CPU could truncate the page off the mapping and then free the mapping.
1162 *
1163 * Usually, the page _is_ locked, or the caller is a user-space process which
1164 * holds a reference on the inode by having an open file.
1165 *
1166 * In other cases, the page should be locked before running set_page_dirty().
1167 */
1168int set_page_dirty_lock(struct page *page)
1169{
1170        int ret;
1171
1172        lock_page_nosync(page);
1173        ret = set_page_dirty(page);
1174        unlock_page(page);
1175        return ret;
1176}
1177EXPORT_SYMBOL(set_page_dirty_lock);
1178
1179/*
1180 * Clear a page's dirty flag, while caring for dirty memory accounting.
1181 * Returns true if the page was previously dirty.
1182 *
1183 * This is for preparing to put the page under writeout.  We leave the page
1184 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1185 * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
1186 * implementation will run either set_page_writeback() or set_page_dirty(),
1187 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1188 * back into sync.
1189 *
1190 * This incoherency between the page's dirty flag and radix-tree tag is
1191 * unfortunate, but it only exists while the page is locked.
1192 */
1193int clear_page_dirty_for_io(struct page *page)
1194{
1195        struct address_space *mapping = page_mapping(page);
1196
1197        BUG_ON(!PageLocked(page));
1198
1199        ClearPageReclaim(page);
1200        if (mapping && mapping_cap_account_dirty(mapping)) {
1201                /*
1202                 * Yes, Virginia, this is indeed insane.
1203                 *
1204                 * We use this sequence to make sure that
1205                 *  (a) we account for dirty stats properly
1206                 *  (b) we tell the low-level filesystem to
1207                 *      mark the whole page dirty if it was
1208                 *      dirty in a pagetable. Only to then
1209                 *  (c) clean the page again and return 1 to
1210                 *      cause the writeback.
1211                 *
1212                 * This way we avoid all nasty races with the
1213                 * dirty bit in multiple places and clearing
1214                 * them concurrently from different threads.
1215                 *
1216                 * Note! Normally the "set_page_dirty(page)"
1217                 * has no effect on the actual dirty bit - since
1218                 * that will already usually be set. But we
1219                 * need the side effects, and it can help us
1220                 * avoid races.
1221                 *
1222                 * We basically use the page "master dirty bit"
1223                 * as a serialization point for all the different
1224                 * threads doing their things.
1225                 */
1226                if (page_mkclean(page))
1227                        set_page_dirty(page);
1228                /*
1229                 * We carefully synchronise fault handlers against
1230                 * installing a dirty pte and marking the page dirty
1231                 * at this point. We do this by having them hold the
1232                 * page lock at some point after installing their
1233                 * pte, but before marking the page dirty.
1234                 * Pages are always locked coming in here, so we get
1235                 * the desired exclusion. See mm/memory.c:do_wp_page()
1236                 * for more comments.
1237                 */
1238                if (TestClearPageDirty(page)) {
1239                        dec_zone_page_state(page, NR_FILE_DIRTY);
1240                        dec_bdi_stat(mapping->backing_dev_info,
1241                                        BDI_RECLAIMABLE);
1242                        return 1;
1243                }
1244                return 0;
1245        }
1246        return TestClearPageDirty(page);
1247}
1248EXPORT_SYMBOL(clear_page_dirty_for_io);
1249
1250int test_clear_page_writeback(struct page *page)
1251{
1252        struct address_space *mapping = page_mapping(page);
1253        int ret;
1254
1255        if (mapping) {
1256                struct backing_dev_info *bdi = mapping->backing_dev_info;
1257                unsigned long flags;
1258
1259                spin_lock_irqsave(&mapping->tree_lock, flags);
1260                ret = TestClearPageWriteback(page);
1261                if (ret) {
1262                        radix_tree_tag_clear(&mapping->page_tree,
1263                                                page_index(page),
1264                                                PAGECACHE_TAG_WRITEBACK);
1265                        if (bdi_cap_account_writeback(bdi)) {
1266                                __dec_bdi_stat(bdi, BDI_WRITEBACK);
1267                                __bdi_writeout_inc(bdi);
1268                        }
1269                }
1270                spin_unlock_irqrestore(&mapping->tree_lock, flags);
1271        } else {
1272                ret = TestClearPageWriteback(page);
1273        }
1274        if (ret)
1275                dec_zone_page_state(page, NR_WRITEBACK);
1276        return ret;
1277}
1278
1279int test_set_page_writeback(struct page *page)
1280{
1281        struct address_space *mapping = page_mapping(page);
1282        int ret;
1283
1284        if (mapping) {
1285                struct backing_dev_info *bdi = mapping->backing_dev_info;
1286                unsigned long flags;
1287
1288                spin_lock_irqsave(&mapping->tree_lock, flags);
1289                ret = TestSetPageWriteback(page);
1290                if (!ret) {
1291                        radix_tree_tag_set(&mapping->page_tree,
1292                                                page_index(page),
1293                                                PAGECACHE_TAG_WRITEBACK);
1294                        if (bdi_cap_account_writeback(bdi))
1295                                __inc_bdi_stat(bdi, BDI_WRITEBACK);
1296                }
1297                if (!PageDirty(page))
1298                        radix_tree_tag_clear(&mapping->page_tree,
1299                                                page_index(page),
1300                                                PAGECACHE_TAG_DIRTY);
1301                spin_unlock_irqrestore(&mapping->tree_lock, flags);
1302        } else {
1303                ret = TestSetPageWriteback(page);
1304        }
1305        if (!ret)
1306                inc_zone_page_state(page, NR_WRITEBACK);
1307        return ret;
1308
1309}
1310EXPORT_SYMBOL(test_set_page_writeback);
1311
1312/*
1313 * Return true if any of the pages in the mapping are marked with the
1314 * passed tag.
1315 */
1316int mapping_tagged(struct address_space *mapping, int tag)
1317{
1318        int ret;
1319        rcu_read_lock();
1320        ret = radix_tree_tagged(&mapping->page_tree, tag);
1321        rcu_read_unlock();
1322        return ret;
1323}
1324EXPORT_SYMBOL(mapping_tagged);
1325