linux/mm/backing-dev.c
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   1
   2#include <linux/wait.h>
   3#include <linux/backing-dev.h>
   4#include <linux/kthread.h>
   5#include <linux/freezer.h>
   6#include <linux/fs.h>
   7#include <linux/pagemap.h>
   8#include <linux/mm.h>
   9#include <linux/sched.h>
  10#include <linux/module.h>
  11#include <linux/writeback.h>
  12#include <linux/device.h>
  13#include <trace/events/writeback.h>
  14
  15static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
  16
  17struct backing_dev_info default_backing_dev_info = {
  18        .name           = "default",
  19        .ra_pages       = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
  20        .state          = 0,
  21        .capabilities   = BDI_CAP_MAP_COPY,
  22};
  23EXPORT_SYMBOL_GPL(default_backing_dev_info);
  24
  25struct backing_dev_info noop_backing_dev_info = {
  26        .name           = "noop",
  27        .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
  28};
  29EXPORT_SYMBOL_GPL(noop_backing_dev_info);
  30
  31static struct class *bdi_class;
  32
  33/*
  34 * bdi_lock protects updates to bdi_list and bdi_pending_list, as well as
  35 * reader side protection for bdi_pending_list. bdi_list has RCU reader side
  36 * locking.
  37 */
  38DEFINE_SPINLOCK(bdi_lock);
  39LIST_HEAD(bdi_list);
  40LIST_HEAD(bdi_pending_list);
  41
  42void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
  43{
  44        if (wb1 < wb2) {
  45                spin_lock(&wb1->list_lock);
  46                spin_lock_nested(&wb2->list_lock, 1);
  47        } else {
  48                spin_lock(&wb2->list_lock);
  49                spin_lock_nested(&wb1->list_lock, 1);
  50        }
  51}
  52
  53#ifdef CONFIG_DEBUG_FS
  54#include <linux/debugfs.h>
  55#include <linux/seq_file.h>
  56
  57static struct dentry *bdi_debug_root;
  58
  59static void bdi_debug_init(void)
  60{
  61        bdi_debug_root = debugfs_create_dir("bdi", NULL);
  62}
  63
  64static int bdi_debug_stats_show(struct seq_file *m, void *v)
  65{
  66        struct backing_dev_info *bdi = m->private;
  67        struct bdi_writeback *wb = &bdi->wb;
  68        unsigned long background_thresh;
  69        unsigned long dirty_thresh;
  70        unsigned long bdi_thresh;
  71        unsigned long nr_dirty, nr_io, nr_more_io;
  72        struct inode *inode;
  73
  74        nr_dirty = nr_io = nr_more_io = 0;
  75        spin_lock(&wb->list_lock);
  76        list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
  77                nr_dirty++;
  78        list_for_each_entry(inode, &wb->b_io, i_wb_list)
  79                nr_io++;
  80        list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
  81                nr_more_io++;
  82        spin_unlock(&wb->list_lock);
  83
  84        global_dirty_limits(&background_thresh, &dirty_thresh);
  85        bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
  86
  87#define K(x) ((x) << (PAGE_SHIFT - 10))
  88        seq_printf(m,
  89                   "BdiWriteback:       %10lu kB\n"
  90                   "BdiReclaimable:     %10lu kB\n"
  91                   "BdiDirtyThresh:     %10lu kB\n"
  92                   "DirtyThresh:        %10lu kB\n"
  93                   "BackgroundThresh:   %10lu kB\n"
  94                   "BdiDirtied:         %10lu kB\n"
  95                   "BdiWritten:         %10lu kB\n"
  96                   "BdiWriteBandwidth:  %10lu kBps\n"
  97                   "b_dirty:            %10lu\n"
  98                   "b_io:               %10lu\n"
  99                   "b_more_io:          %10lu\n"
 100                   "bdi_list:           %10u\n"
 101                   "state:              %10lx\n",
 102                   (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
 103                   (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
 104                   K(bdi_thresh),
 105                   K(dirty_thresh),
 106                   K(background_thresh),
 107                   (unsigned long) K(bdi_stat(bdi, BDI_DIRTIED)),
 108                   (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)),
 109                   (unsigned long) K(bdi->write_bandwidth),
 110                   nr_dirty,
 111                   nr_io,
 112                   nr_more_io,
 113                   !list_empty(&bdi->bdi_list), bdi->state);
 114#undef K
 115
 116        return 0;
 117}
 118
 119static int bdi_debug_stats_open(struct inode *inode, struct file *file)
 120{
 121        return single_open(file, bdi_debug_stats_show, inode->i_private);
 122}
 123
 124static const struct file_operations bdi_debug_stats_fops = {
 125        .open           = bdi_debug_stats_open,
 126        .read           = seq_read,
 127        .llseek         = seq_lseek,
 128        .release        = single_release,
 129};
 130
 131static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
 132{
 133        bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
 134        bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
 135                                               bdi, &bdi_debug_stats_fops);
 136}
 137
 138static void bdi_debug_unregister(struct backing_dev_info *bdi)
 139{
 140        debugfs_remove(bdi->debug_stats);
 141        debugfs_remove(bdi->debug_dir);
 142}
 143#else
 144static inline void bdi_debug_init(void)
 145{
 146}
 147static inline void bdi_debug_register(struct backing_dev_info *bdi,
 148                                      const char *name)
 149{
 150}
 151static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
 152{
 153}
 154#endif
 155
 156static ssize_t read_ahead_kb_store(struct device *dev,
 157                                  struct device_attribute *attr,
 158                                  const char *buf, size_t count)
 159{
 160        struct backing_dev_info *bdi = dev_get_drvdata(dev);
 161        unsigned long read_ahead_kb;
 162        ssize_t ret;
 163
 164        ret = kstrtoul(buf, 10, &read_ahead_kb);
 165        if (ret < 0)
 166                return ret;
 167
 168        bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
 169
 170        return count;
 171}
 172
 173#define K(pages) ((pages) << (PAGE_SHIFT - 10))
 174
 175#define BDI_SHOW(name, expr)                                            \
 176static ssize_t name##_show(struct device *dev,                          \
 177                           struct device_attribute *attr, char *page)   \
 178{                                                                       \
 179        struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
 180                                                                        \
 181        return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
 182}
 183
 184BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
 185
 186static ssize_t min_ratio_store(struct device *dev,
 187                struct device_attribute *attr, const char *buf, size_t count)
 188{
 189        struct backing_dev_info *bdi = dev_get_drvdata(dev);
 190        unsigned int ratio;
 191        ssize_t ret;
 192
 193        ret = kstrtouint(buf, 10, &ratio);
 194        if (ret < 0)
 195                return ret;
 196
 197        ret = bdi_set_min_ratio(bdi, ratio);
 198        if (!ret)
 199                ret = count;
 200
 201        return ret;
 202}
 203BDI_SHOW(min_ratio, bdi->min_ratio)
 204
 205static ssize_t max_ratio_store(struct device *dev,
 206                struct device_attribute *attr, const char *buf, size_t count)
 207{
 208        struct backing_dev_info *bdi = dev_get_drvdata(dev);
 209        unsigned int ratio;
 210        ssize_t ret;
 211
 212        ret = kstrtouint(buf, 10, &ratio);
 213        if (ret < 0)
 214                return ret;
 215
 216        ret = bdi_set_max_ratio(bdi, ratio);
 217        if (!ret)
 218                ret = count;
 219
 220        return ret;
 221}
 222BDI_SHOW(max_ratio, bdi->max_ratio)
 223
 224#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
 225
 226static struct device_attribute bdi_dev_attrs[] = {
 227        __ATTR_RW(read_ahead_kb),
 228        __ATTR_RW(min_ratio),
 229        __ATTR_RW(max_ratio),
 230        __ATTR_NULL,
 231};
 232
 233static __init int bdi_class_init(void)
 234{
 235        bdi_class = class_create(THIS_MODULE, "bdi");
 236        if (IS_ERR(bdi_class))
 237                return PTR_ERR(bdi_class);
 238
 239        bdi_class->dev_attrs = bdi_dev_attrs;
 240        bdi_debug_init();
 241        return 0;
 242}
 243postcore_initcall(bdi_class_init);
 244
 245static int __init default_bdi_init(void)
 246{
 247        int err;
 248
 249        err = bdi_init(&default_backing_dev_info);
 250        if (!err)
 251                bdi_register(&default_backing_dev_info, NULL, "default");
 252        err = bdi_init(&noop_backing_dev_info);
 253
 254        return err;
 255}
 256subsys_initcall(default_bdi_init);
 257
 258int bdi_has_dirty_io(struct backing_dev_info *bdi)
 259{
 260        return wb_has_dirty_io(&bdi->wb);
 261}
 262
 263static void wakeup_timer_fn(unsigned long data)
 264{
 265        struct backing_dev_info *bdi = (struct backing_dev_info *)data;
 266
 267        spin_lock_bh(&bdi->wb_lock);
 268        if (bdi->wb.task) {
 269                trace_writeback_wake_thread(bdi);
 270                wake_up_process(bdi->wb.task);
 271        } else if (bdi->dev) {
 272                /*
 273                 * When bdi tasks are inactive for long time, they are killed.
 274                 * In this case we have to wake-up the forker thread which
 275                 * should create and run the bdi thread.
 276                 */
 277                trace_writeback_wake_forker_thread(bdi);
 278                wake_up_process(default_backing_dev_info.wb.task);
 279        }
 280        spin_unlock_bh(&bdi->wb_lock);
 281}
 282
 283/*
 284 * This function is used when the first inode for this bdi is marked dirty. It
 285 * wakes-up the corresponding bdi thread which should then take care of the
 286 * periodic background write-out of dirty inodes. Since the write-out would
 287 * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
 288 * set up a timer which wakes the bdi thread up later.
 289 *
 290 * Note, we wouldn't bother setting up the timer, but this function is on the
 291 * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
 292 * by delaying the wake-up.
 293 */
 294void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
 295{
 296        unsigned long timeout;
 297
 298        timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
 299        mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
 300}
 301
 302/*
 303 * Calculate the longest interval (jiffies) bdi threads are allowed to be
 304 * inactive.
 305 */
 306static unsigned long bdi_longest_inactive(void)
 307{
 308        unsigned long interval;
 309
 310        interval = msecs_to_jiffies(dirty_writeback_interval * 10);
 311        return max(5UL * 60 * HZ, interval);
 312}
 313
 314/*
 315 * Clear pending bit and wakeup anybody waiting for flusher thread creation or
 316 * shutdown
 317 */
 318static void bdi_clear_pending(struct backing_dev_info *bdi)
 319{
 320        clear_bit(BDI_pending, &bdi->state);
 321        smp_mb__after_clear_bit();
 322        wake_up_bit(&bdi->state, BDI_pending);
 323}
 324
 325static int bdi_forker_thread(void *ptr)
 326{
 327        struct bdi_writeback *me = ptr;
 328
 329        current->flags |= PF_SWAPWRITE;
 330        set_freezable();
 331
 332        /*
 333         * Our parent may run at a different priority, just set us to normal
 334         */
 335        set_user_nice(current, 0);
 336
 337        for (;;) {
 338                struct task_struct *task = NULL;
 339                struct backing_dev_info *bdi;
 340                enum {
 341                        NO_ACTION,   /* Nothing to do */
 342                        FORK_THREAD, /* Fork bdi thread */
 343                        KILL_THREAD, /* Kill inactive bdi thread */
 344                } action = NO_ACTION;
 345
 346                /*
 347                 * Temporary measure, we want to make sure we don't see
 348                 * dirty data on the default backing_dev_info
 349                 */
 350                if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) {
 351                        del_timer(&me->wakeup_timer);
 352                        wb_do_writeback(me, 0);
 353                }
 354
 355                spin_lock_bh(&bdi_lock);
 356                /*
 357                 * In the following loop we are going to check whether we have
 358                 * some work to do without any synchronization with tasks
 359                 * waking us up to do work for them. Set the task state here
 360                 * so that we don't miss wakeups after verifying conditions.
 361                 */
 362                set_current_state(TASK_INTERRUPTIBLE);
 363
 364                list_for_each_entry(bdi, &bdi_list, bdi_list) {
 365                        bool have_dirty_io;
 366
 367                        if (!bdi_cap_writeback_dirty(bdi) ||
 368                             bdi_cap_flush_forker(bdi))
 369                                continue;
 370
 371                        WARN(!test_bit(BDI_registered, &bdi->state),
 372                             "bdi %p/%s is not registered!\n", bdi, bdi->name);
 373
 374                        have_dirty_io = !list_empty(&bdi->work_list) ||
 375                                        wb_has_dirty_io(&bdi->wb);
 376
 377                        /*
 378                         * If the bdi has work to do, but the thread does not
 379                         * exist - create it.
 380                         */
 381                        if (!bdi->wb.task && have_dirty_io) {
 382                                /*
 383                                 * Set the pending bit - if someone will try to
 384                                 * unregister this bdi - it'll wait on this bit.
 385                                 */
 386                                set_bit(BDI_pending, &bdi->state);
 387                                action = FORK_THREAD;
 388                                break;
 389                        }
 390
 391                        spin_lock(&bdi->wb_lock);
 392
 393                        /*
 394                         * If there is no work to do and the bdi thread was
 395                         * inactive long enough - kill it. The wb_lock is taken
 396                         * to make sure no-one adds more work to this bdi and
 397                         * wakes the bdi thread up.
 398                         */
 399                        if (bdi->wb.task && !have_dirty_io &&
 400                            time_after(jiffies, bdi->wb.last_active +
 401                                                bdi_longest_inactive())) {
 402                                task = bdi->wb.task;
 403                                bdi->wb.task = NULL;
 404                                spin_unlock(&bdi->wb_lock);
 405                                set_bit(BDI_pending, &bdi->state);
 406                                action = KILL_THREAD;
 407                                break;
 408                        }
 409                        spin_unlock(&bdi->wb_lock);
 410                }
 411                spin_unlock_bh(&bdi_lock);
 412
 413                /* Keep working if default bdi still has things to do */
 414                if (!list_empty(&me->bdi->work_list))
 415                        __set_current_state(TASK_RUNNING);
 416
 417                switch (action) {
 418                case FORK_THREAD:
 419                        __set_current_state(TASK_RUNNING);
 420                        task = kthread_create(bdi_writeback_thread, &bdi->wb,
 421                                              "flush-%s", dev_name(bdi->dev));
 422                        if (IS_ERR(task)) {
 423                                /*
 424                                 * If thread creation fails, force writeout of
 425                                 * the bdi from the thread. Hopefully 1024 is
 426                                 * large enough for efficient IO.
 427                                 */
 428                                writeback_inodes_wb(&bdi->wb, 1024,
 429                                                    WB_REASON_FORKER_THREAD);
 430                        } else {
 431                                /*
 432                                 * The spinlock makes sure we do not lose
 433                                 * wake-ups when racing with 'bdi_queue_work()'.
 434                                 * And as soon as the bdi thread is visible, we
 435                                 * can start it.
 436                                 */
 437                                spin_lock_bh(&bdi->wb_lock);
 438                                bdi->wb.task = task;
 439                                spin_unlock_bh(&bdi->wb_lock);
 440                                wake_up_process(task);
 441                        }
 442                        bdi_clear_pending(bdi);
 443                        break;
 444
 445                case KILL_THREAD:
 446                        __set_current_state(TASK_RUNNING);
 447                        kthread_stop(task);
 448                        bdi_clear_pending(bdi);
 449                        break;
 450
 451                case NO_ACTION:
 452                        if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
 453                                /*
 454                                 * There are no dirty data. The only thing we
 455                                 * should now care about is checking for
 456                                 * inactive bdi threads and killing them. Thus,
 457                                 * let's sleep for longer time, save energy and
 458                                 * be friendly for battery-driven devices.
 459                                 */
 460                                schedule_timeout(bdi_longest_inactive());
 461                        else
 462                                schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
 463                        try_to_freeze();
 464                        break;
 465                }
 466        }
 467
 468        return 0;
 469}
 470
 471/*
 472 * Remove bdi from bdi_list, and ensure that it is no longer visible
 473 */
 474static void bdi_remove_from_list(struct backing_dev_info *bdi)
 475{
 476        spin_lock_bh(&bdi_lock);
 477        list_del_rcu(&bdi->bdi_list);
 478        spin_unlock_bh(&bdi_lock);
 479
 480        synchronize_rcu_expedited();
 481}
 482
 483int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 484                const char *fmt, ...)
 485{
 486        va_list args;
 487        struct device *dev;
 488
 489        if (bdi->dev)   /* The driver needs to use separate queues per device */
 490                return 0;
 491
 492        va_start(args, fmt);
 493        dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
 494        va_end(args);
 495        if (IS_ERR(dev))
 496                return PTR_ERR(dev);
 497
 498        bdi->dev = dev;
 499
 500        /*
 501         * Just start the forker thread for our default backing_dev_info,
 502         * and add other bdi's to the list. They will get a thread created
 503         * on-demand when they need it.
 504         */
 505        if (bdi_cap_flush_forker(bdi)) {
 506                struct bdi_writeback *wb = &bdi->wb;
 507
 508                wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s",
 509                                                dev_name(dev));
 510                if (IS_ERR(wb->task))
 511                        return PTR_ERR(wb->task);
 512        }
 513
 514        bdi_debug_register(bdi, dev_name(dev));
 515        set_bit(BDI_registered, &bdi->state);
 516
 517        spin_lock_bh(&bdi_lock);
 518        list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
 519        spin_unlock_bh(&bdi_lock);
 520
 521        trace_writeback_bdi_register(bdi);
 522        return 0;
 523}
 524EXPORT_SYMBOL(bdi_register);
 525
 526int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 527{
 528        return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
 529}
 530EXPORT_SYMBOL(bdi_register_dev);
 531
 532/*
 533 * Remove bdi from the global list and shutdown any threads we have running
 534 */
 535static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 536{
 537        struct task_struct *task;
 538
 539        if (!bdi_cap_writeback_dirty(bdi))
 540                return;
 541
 542        /*
 543         * Make sure nobody finds us on the bdi_list anymore
 544         */
 545        bdi_remove_from_list(bdi);
 546
 547        /*
 548         * If setup is pending, wait for that to complete first
 549         */
 550        wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
 551                        TASK_UNINTERRUPTIBLE);
 552
 553        /*
 554         * Finally, kill the kernel thread. We don't need to be RCU
 555         * safe anymore, since the bdi is gone from visibility.
 556         */
 557        spin_lock_bh(&bdi->wb_lock);
 558        task = bdi->wb.task;
 559        bdi->wb.task = NULL;
 560        spin_unlock_bh(&bdi->wb_lock);
 561
 562        if (task)
 563                kthread_stop(task);
 564}
 565
 566/*
 567 * This bdi is going away now, make sure that no super_blocks point to it
 568 */
 569static void bdi_prune_sb(struct backing_dev_info *bdi)
 570{
 571        struct super_block *sb;
 572
 573        spin_lock(&sb_lock);
 574        list_for_each_entry(sb, &super_blocks, s_list) {
 575                if (sb->s_bdi == bdi)
 576                        sb->s_bdi = &default_backing_dev_info;
 577        }
 578        spin_unlock(&sb_lock);
 579}
 580
 581void bdi_unregister(struct backing_dev_info *bdi)
 582{
 583        struct device *dev = bdi->dev;
 584
 585        if (dev) {
 586                bdi_set_min_ratio(bdi, 0);
 587                trace_writeback_bdi_unregister(bdi);
 588                bdi_prune_sb(bdi);
 589                del_timer_sync(&bdi->wb.wakeup_timer);
 590
 591                if (!bdi_cap_flush_forker(bdi))
 592                        bdi_wb_shutdown(bdi);
 593                bdi_debug_unregister(bdi);
 594
 595                spin_lock_bh(&bdi->wb_lock);
 596                bdi->dev = NULL;
 597                spin_unlock_bh(&bdi->wb_lock);
 598
 599                device_unregister(dev);
 600        }
 601}
 602EXPORT_SYMBOL(bdi_unregister);
 603
 604static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
 605{
 606        memset(wb, 0, sizeof(*wb));
 607
 608        wb->bdi = bdi;
 609        wb->last_old_flush = jiffies;
 610        INIT_LIST_HEAD(&wb->b_dirty);
 611        INIT_LIST_HEAD(&wb->b_io);
 612        INIT_LIST_HEAD(&wb->b_more_io);
 613        spin_lock_init(&wb->list_lock);
 614        setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
 615}
 616
 617/*
 618 * Initial write bandwidth: 100 MB/s
 619 */
 620#define INIT_BW         (100 << (20 - PAGE_SHIFT))
 621
 622int bdi_init(struct backing_dev_info *bdi)
 623{
 624        int i, err;
 625
 626        bdi->dev = NULL;
 627
 628        bdi->min_ratio = 0;
 629        bdi->max_ratio = 100;
 630        bdi->max_prop_frac = FPROP_FRAC_BASE;
 631        spin_lock_init(&bdi->wb_lock);
 632        INIT_LIST_HEAD(&bdi->bdi_list);
 633        INIT_LIST_HEAD(&bdi->work_list);
 634
 635        bdi_wb_init(&bdi->wb, bdi);
 636
 637        for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
 638                err = percpu_counter_init(&bdi->bdi_stat[i], 0);
 639                if (err)
 640                        goto err;
 641        }
 642
 643        bdi->dirty_exceeded = 0;
 644
 645        bdi->bw_time_stamp = jiffies;
 646        bdi->written_stamp = 0;
 647
 648        bdi->balanced_dirty_ratelimit = INIT_BW;
 649        bdi->dirty_ratelimit = INIT_BW;
 650        bdi->write_bandwidth = INIT_BW;
 651        bdi->avg_write_bandwidth = INIT_BW;
 652
 653        err = fprop_local_init_percpu(&bdi->completions);
 654
 655        if (err) {
 656err:
 657                while (i--)
 658                        percpu_counter_destroy(&bdi->bdi_stat[i]);
 659        }
 660
 661        return err;
 662}
 663EXPORT_SYMBOL(bdi_init);
 664
 665void bdi_destroy(struct backing_dev_info *bdi)
 666{
 667        int i;
 668
 669        /*
 670         * Splice our entries to the default_backing_dev_info, if this
 671         * bdi disappears
 672         */
 673        if (bdi_has_dirty_io(bdi)) {
 674                struct bdi_writeback *dst = &default_backing_dev_info.wb;
 675
 676                bdi_lock_two(&bdi->wb, dst);
 677                list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
 678                list_splice(&bdi->wb.b_io, &dst->b_io);
 679                list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
 680                spin_unlock(&bdi->wb.list_lock);
 681                spin_unlock(&dst->list_lock);
 682        }
 683
 684        bdi_unregister(bdi);
 685
 686        /*
 687         * If bdi_unregister() had already been called earlier, the
 688         * wakeup_timer could still be armed because bdi_prune_sb()
 689         * can race with the bdi_wakeup_thread_delayed() calls from
 690         * __mark_inode_dirty().
 691         */
 692        del_timer_sync(&bdi->wb.wakeup_timer);
 693
 694        for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
 695                percpu_counter_destroy(&bdi->bdi_stat[i]);
 696
 697        fprop_local_destroy_percpu(&bdi->completions);
 698}
 699EXPORT_SYMBOL(bdi_destroy);
 700
 701/*
 702 * For use from filesystems to quickly init and register a bdi associated
 703 * with dirty writeback
 704 */
 705int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
 706                           unsigned int cap)
 707{
 708        char tmp[32];
 709        int err;
 710
 711        bdi->name = name;
 712        bdi->capabilities = cap;
 713        err = bdi_init(bdi);
 714        if (err)
 715                return err;
 716
 717        sprintf(tmp, "%.28s%s", name, "-%d");
 718        err = bdi_register(bdi, NULL, tmp, atomic_long_inc_return(&bdi_seq));
 719        if (err) {
 720                bdi_destroy(bdi);
 721                return err;
 722        }
 723
 724        return 0;
 725}
 726EXPORT_SYMBOL(bdi_setup_and_register);
 727
 728static wait_queue_head_t congestion_wqh[2] = {
 729                __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 730                __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
 731        };
 732static atomic_t nr_bdi_congested[2];
 733
 734void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
 735{
 736        enum bdi_state bit;
 737        wait_queue_head_t *wqh = &congestion_wqh[sync];
 738
 739        bit = sync ? BDI_sync_congested : BDI_async_congested;
 740        if (test_and_clear_bit(bit, &bdi->state))
 741                atomic_dec(&nr_bdi_congested[sync]);
 742        smp_mb__after_clear_bit();
 743        if (waitqueue_active(wqh))
 744                wake_up(wqh);
 745}
 746EXPORT_SYMBOL(clear_bdi_congested);
 747
 748void set_bdi_congested(struct backing_dev_info *bdi, int sync)
 749{
 750        enum bdi_state bit;
 751
 752        bit = sync ? BDI_sync_congested : BDI_async_congested;
 753        if (!test_and_set_bit(bit, &bdi->state))
 754                atomic_inc(&nr_bdi_congested[sync]);
 755}
 756EXPORT_SYMBOL(set_bdi_congested);
 757
 758/**
 759 * congestion_wait - wait for a backing_dev to become uncongested
 760 * @sync: SYNC or ASYNC IO
 761 * @timeout: timeout in jiffies
 762 *
 763 * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
 764 * write congestion.  If no backing_devs are congested then just wait for the
 765 * next write to be completed.
 766 */
 767long congestion_wait(int sync, long timeout)
 768{
 769        long ret;
 770        unsigned long start = jiffies;
 771        DEFINE_WAIT(wait);
 772        wait_queue_head_t *wqh = &congestion_wqh[sync];
 773
 774        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 775        ret = io_schedule_timeout(timeout);
 776        finish_wait(wqh, &wait);
 777
 778        trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
 779                                        jiffies_to_usecs(jiffies - start));
 780
 781        return ret;
 782}
 783EXPORT_SYMBOL(congestion_wait);
 784
 785/**
 786 * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
 787 * @zone: A zone to check if it is heavily congested
 788 * @sync: SYNC or ASYNC IO
 789 * @timeout: timeout in jiffies
 790 *
 791 * In the event of a congested backing_dev (any backing_dev) and the given
 792 * @zone has experienced recent congestion, this waits for up to @timeout
 793 * jiffies for either a BDI to exit congestion of the given @sync queue
 794 * or a write to complete.
 795 *
 796 * In the absence of zone congestion, cond_resched() is called to yield
 797 * the processor if necessary but otherwise does not sleep.
 798 *
 799 * The return value is 0 if the sleep is for the full timeout. Otherwise,
 800 * it is the number of jiffies that were still remaining when the function
 801 * returned. return_value == timeout implies the function did not sleep.
 802 */
 803long wait_iff_congested(struct zone *zone, int sync, long timeout)
 804{
 805        long ret;
 806        unsigned long start = jiffies;
 807        DEFINE_WAIT(wait);
 808        wait_queue_head_t *wqh = &congestion_wqh[sync];
 809
 810        /*
 811         * If there is no congestion, or heavy congestion is not being
 812         * encountered in the current zone, yield if necessary instead
 813         * of sleeping on the congestion queue
 814         */
 815        if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
 816                        !zone_is_reclaim_congested(zone)) {
 817                cond_resched();
 818
 819                /* In case we scheduled, work out time remaining */
 820                ret = timeout - (jiffies - start);
 821                if (ret < 0)
 822                        ret = 0;
 823
 824                goto out;
 825        }
 826
 827        /* Sleep until uncongested or a write happens */
 828        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 829        ret = io_schedule_timeout(timeout);
 830        finish_wait(wqh, &wait);
 831
 832out:
 833        trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
 834                                        jiffies_to_usecs(jiffies - start));
 835
 836        return ret;
 837}
 838EXPORT_SYMBOL(wait_iff_congested);
 839
 840int pdflush_proc_obsolete(struct ctl_table *table, int write,
 841                        void __user *buffer, size_t *lenp, loff_t *ppos)
 842{
 843        char kbuf[] = "0\n";
 844
 845        if (*ppos) {
 846                *lenp = 0;
 847                return 0;
 848        }
 849
 850        if (copy_to_user(buffer, kbuf, sizeof(kbuf)))
 851                return -EFAULT;
 852        printk_once(KERN_WARNING "%s exported in /proc is scheduled for removal\n",
 853                        table->procname);
 854
 855        *lenp = 2;
 856        *ppos += *lenp;
 857        return 2;
 858}
 859
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