mm/backing-dev.c

   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
  15 static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
  16
  17 struct 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 };
  23 EXPORT_SYMBOL_GPL(default_backing_dev_info);
  24
  25 struct backing_dev_info noop_backing_dev_info = {
  26         .name           = "noop",
  27         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
  28 };
  29 EXPORT_SYMBOL_GPL(noop_backing_dev_info);
  30
  31 static struct class *bdi_class;
  32
  33 /*
  34  * bdi_lock protects updates to bdi_list. bdi_list has RCU reader side
  35  * locking.
  36  */
  37 DEFINE_SPINLOCK(bdi_lock);
  38 LIST_HEAD(bdi_list);
  39
  40 /* bdi_wq serves all asynchronous writeback tasks */
  41 struct workqueue_struct *bdi_wq;
  42
  43 void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
  44 {
  45         if (wb1 < wb2) {
  46                 spin_lock(&wb1->list_lock);
  47                 spin_lock_nested(&wb2->list_lock, 1);
  48         } else {
  49                 spin_lock(&wb2->list_lock);
  50                 spin_lock_nested(&wb1->list_lock, 1);
  51         }
  52 }
  53
  54 #ifdef CONFIG_DEBUG_FS
  55 #include <linux/debugfs.h>
  56 #include <linux/seq_file.h>
  57
  58 static struct dentry *bdi_debug_root;
  59
  60 static void bdi_debug_init(void)
  61 {
  62         bdi_debug_root = debugfs_create_dir("bdi", NULL);
  63 }
  64
  65 static int bdi_debug_stats_show(struct seq_file *m, void *v)
  66 {
  67         struct backing_dev_info *bdi = m->private;
  68         struct bdi_writeback *wb = &bdi->wb;
  69         unsigned long background_thresh;
  70         unsigned long dirty_thresh;
  71         unsigned long bdi_thresh;
  72         unsigned long nr_dirty, nr_io, nr_more_io;
  73         struct inode *inode;
  74
  75         nr_dirty = nr_io = nr_more_io = 0;
  76         spin_lock(&wb->list_lock);
  77         list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
  78                 nr_dirty++;
  79         list_for_each_entry(inode, &wb->b_io, i_wb_list)
  80                 nr_io++;
  81         list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
  82                 nr_more_io++;
  83         spin_unlock(&wb->list_lock);
  84
  85         global_dirty_limits(&background_thresh, &dirty_thresh);
  86         bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
  87
  88 #define K(x) ((x) << (PAGE_SHIFT - 10))
  89         seq_printf(m,
  90                    "BdiWriteback:       %10lu kB\n"
  91                    "BdiReclaimable:     %10lu kB\n"
  92                    "BdiDirtyThresh:     %10lu kB\n"
  93                    "DirtyThresh:        %10lu kB\n"
  94                    "BackgroundThresh:   %10lu kB\n"
  95                    "BdiDirtied:         %10lu kB\n"
  96                    "BdiWritten:         %10lu kB\n"
  97                    "BdiWriteBandwidth:  %10lu kBps\n"
  98                    "b_dirty:            %10lu\n"
  99                    "b_io:               %10lu\n"
 100                    "b_more_io:          %10lu\n"
 101                    "bdi_list:           %10u\n"
 102                    "state:              %10lx\n",
 103                    (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
 104                    (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
 105                    K(bdi_thresh),
 106                    K(dirty_thresh),
 107                    K(background_thresh),
 108                    (unsigned long) K(bdi_stat(bdi, BDI_DIRTIED)),
 109                    (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)),
 110                    (unsigned long) K(bdi->write_bandwidth),
 111                    nr_dirty,
 112                    nr_io,
 113                    nr_more_io,
 114                    !list_empty(&bdi->bdi_list), bdi->state);
 115 #undef K
 116
 117         return 0;
 118 }
 119
 120 static int bdi_debug_stats_open(struct inode *inode, struct file *file)
 121 {
 122         return single_open(file, bdi_debug_stats_show, inode->i_private);
 123 }
 124
 125 static const struct file_operations bdi_debug_stats_fops = {
 126         .open           = bdi_debug_stats_open,
 127         .read           = seq_read,
 128         .llseek         = seq_lseek,
 129         .release        = single_release,
 130 };
 131
 132 static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
 133 {
 134         bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
 135         bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
 136                                                bdi, &bdi_debug_stats_fops);
 137 }
 138
 139 static void bdi_debug_unregister(struct backing_dev_info *bdi)
 140 {
 141         debugfs_remove(bdi->debug_stats);
 142         debugfs_remove(bdi->debug_dir);
 143 }
 144 #else
 145 static inline void bdi_debug_init(void)
 146 {
 147 }
 148 static inline void bdi_debug_register(struct backing_dev_info *bdi,
 149                                       const char *name)
 150 {
 151 }
 152 static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
 153 {
 154 }
 155 #endif
 156
 157 static ssize_t read_ahead_kb_store(struct device *dev,
 158                                   struct device_attribute *attr,
 159                                   const char *buf, size_t count)
 160 {
 161         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 162         unsigned long read_ahead_kb;
 163         ssize_t ret;
 164
 165         ret = kstrtoul(buf, 10, &read_ahead_kb);
 166         if (ret < 0)
 167                 return ret;
 168
 169         bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
 170
 171         return count;
 172 }
 173
 174 #define K(pages) ((pages) << (PAGE_SHIFT - 10))
 175
 176 #define BDI_SHOW(name, expr)                                            \
 177 static ssize_t name##_show(struct device *dev,                          \
 178                            struct device_attribute *attr, char *page)   \
 179 {                                                                       \
 180         struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
 181                                                                         \
 182         return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
 183 }
 184
 185 BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
 186
 187 static ssize_t min_ratio_store(struct device *dev,
 188                 struct device_attribute *attr, const char *buf, size_t count)
 189 {
 190         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 191         unsigned int ratio;
 192         ssize_t ret;
 193
 194         ret = kstrtouint(buf, 10, &ratio);
 195         if (ret < 0)
 196                 return ret;
 197
 198         ret = bdi_set_min_ratio(bdi, ratio);
 199         if (!ret)
 200                 ret = count;
 201
 202         return ret;
 203 }
 204 BDI_SHOW(min_ratio, bdi->min_ratio)
 205
 206 static ssize_t max_ratio_store(struct device *dev,
 207                 struct device_attribute *attr, const char *buf, size_t count)
 208 {
 209         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 210         unsigned int ratio;
 211         ssize_t ret;
 212
 213         ret = kstrtouint(buf, 10, &ratio);
 214         if (ret < 0)
 215                 return ret;
 216
 217         ret = bdi_set_max_ratio(bdi, ratio);
 218         if (!ret)
 219                 ret = count;
 220
 221         return ret;
 222 }
 223 BDI_SHOW(max_ratio, bdi->max_ratio)
 224
 225 static ssize_t stable_pages_required_show(struct device *dev,
 226                                           struct device_attribute *attr,
 227                                           char *page)
 228 {
 229         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 230
 231         return snprintf(page, PAGE_SIZE-1, "%d\n",
 232                         bdi_cap_stable_pages_required(bdi) ? 1 : 0);
 233 }
 234
 235 static struct device_attribute bdi_dev_attrs[] = {
 236         __ATTR_RW(read_ahead_kb),
 237         __ATTR_RW(min_ratio),
 238         __ATTR_RW(max_ratio),
 239         __ATTR_RO(stable_pages_required),
 240         __ATTR_NULL,
 241 };
 242
 243 static __init int bdi_class_init(void)
 244 {
 245         bdi_class = class_create(THIS_MODULE, "bdi");
 246         if (IS_ERR(bdi_class))
 247                 return PTR_ERR(bdi_class);
 248
 249         bdi_class->dev_attrs = bdi_dev_attrs;
 250         bdi_debug_init();
 251         return 0;
 252 }
 253 postcore_initcall(bdi_class_init);
 254
 255 static int __init default_bdi_init(void)
 256 {
 257         int err;
 258
 259         bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_FREEZABLE |
 260                                               WQ_UNBOUND | WQ_SYSFS, 0);
 261         if (!bdi_wq)
 262                 return -ENOMEM;
 263
 264         err = bdi_init(&default_backing_dev_info);
 265         if (!err)
 266                 bdi_register(&default_backing_dev_info, NULL, "default");
 267         err = bdi_init(&noop_backing_dev_info);
 268
 269         return err;
 270 }
 271 subsys_initcall(default_bdi_init);
 272
 273 int bdi_has_dirty_io(struct backing_dev_info *bdi)
 274 {
 275         return wb_has_dirty_io(&bdi->wb);
 276 }
 277
 278 /*
 279  * This function is used when the first inode for this bdi is marked dirty. It
 280  * wakes-up the corresponding bdi thread which should then take care of the
 281  * periodic background write-out of dirty inodes. Since the write-out would
 282  * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
 283  * set up a timer which wakes the bdi thread up later.
 284  *
 285  * Note, we wouldn't bother setting up the timer, but this function is on the
 286  * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
 287  * by delaying the wake-up.
 288  */
 289 void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
 290 {
 291         unsigned long timeout;
 292
 293         timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
 294         mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
 295 }
 296
 297 /*
 298  * Remove bdi from bdi_list, and ensure that it is no longer visible
 299  */
 300 static void bdi_remove_from_list(struct backing_dev_info *bdi)
 301 {
 302         spin_lock_bh(&bdi_lock);
 303         list_del_rcu(&bdi->bdi_list);
 304         spin_unlock_bh(&bdi_lock);
 305
 306         synchronize_rcu_expedited();
 307
 308         /* bdi_list is now unused, clear it to mark @bdi dying */
 309         INIT_LIST_HEAD(&bdi->bdi_list);
 310 }
 311
 312 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 313                 const char *fmt, ...)
 314 {
 315         va_list args;
 316         struct device *dev;
 317
 318         if (bdi->dev)   /* The driver needs to use separate queues per device */
 319                 return 0;
 320
 321         va_start(args, fmt);
 322         dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
 323         va_end(args);
 324         if (IS_ERR(dev))
 325                 return PTR_ERR(dev);
 326
 327         bdi->dev = dev;
 328
 329         bdi_debug_register(bdi, dev_name(dev));
 330         set_bit(BDI_registered, &bdi->state);
 331
 332         spin_lock_bh(&bdi_lock);
 333         list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
 334         spin_unlock_bh(&bdi_lock);
 335
 336         trace_writeback_bdi_register(bdi);
 337         return 0;
 338 }
 339 EXPORT_SYMBOL(bdi_register);
 340
 341 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 342 {
 343         return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
 344 }
 345 EXPORT_SYMBOL(bdi_register_dev);
 346
 347 /*
 348  * Remove bdi from the global list and shutdown any threads we have running
 349  */
 350 static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 351 {
 352         if (!bdi_cap_writeback_dirty(bdi))
 353                 return;
 354
 355         /*
 356          * Make sure nobody finds us on the bdi_list anymore
 357          */
 358         bdi_remove_from_list(bdi);
 359
 360         /*
 361          * Drain work list and shutdown the delayed_work.  At this point,
 362          * @bdi->bdi_list is empty telling bdi_Writeback_workfn() that @bdi
 363          * is dying and its work_list needs to be drained no matter what.
 364          */
 365         mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
 366         flush_delayed_work(&bdi->wb.dwork);
 367         WARN_ON(!list_empty(&bdi->work_list));
 368
 369         /*
 370          * This shouldn't be necessary unless @bdi for some reason has
 371          * unflushed dirty IO after work_list is drained.  Do it anyway
 372          * just in case.
 373          */
 374         cancel_delayed_work_sync(&bdi->wb.dwork);
 375 }
 376
 377 /*
 378  * This bdi is going away now, make sure that no super_blocks point to it
 379  */
 380 static void bdi_prune_sb(struct backing_dev_info *bdi)
 381 {
 382         struct super_block *sb;
 383
 384         spin_lock(&sb_lock);
 385         list_for_each_entry(sb, &super_blocks, s_list) {
 386                 if (sb->s_bdi == bdi)
 387                         sb->s_bdi = &default_backing_dev_info;
 388         }
 389         spin_unlock(&sb_lock);
 390 }
 391
 392 void bdi_unregister(struct backing_dev_info *bdi)
 393 {
 394         struct device *dev = bdi->dev;
 395
 396         if (dev) {
 397                 bdi_set_min_ratio(bdi, 0);
 398                 trace_writeback_bdi_unregister(bdi);
 399                 bdi_prune_sb(bdi);
 400
 401                 bdi_wb_shutdown(bdi);
 402                 bdi_debug_unregister(bdi);
 403
 404                 spin_lock_bh(&bdi->wb_lock);
 405                 bdi->dev = NULL;
 406                 spin_unlock_bh(&bdi->wb_lock);
 407
 408                 device_unregister(dev);
 409         }
 410 }
 411 EXPORT_SYMBOL(bdi_unregister);
 412
 413 static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
 414 {
 415         memset(wb, 0, sizeof(*wb));
 416
 417         wb->bdi = bdi;
 418         wb->last_old_flush = jiffies;
 419         INIT_LIST_HEAD(&wb->b_dirty);
 420         INIT_LIST_HEAD(&wb->b_io);
 421         INIT_LIST_HEAD(&wb->b_more_io);
 422         spin_lock_init(&wb->list_lock);
 423         INIT_DELAYED_WORK(&wb->dwork, bdi_writeback_workfn);
 424 }
 425
 426 /*
 427  * Initial write bandwidth: 100 MB/s
 428  */
 429 #define INIT_BW         (100 << (20 - PAGE_SHIFT))
 430
 431 int bdi_init(struct backing_dev_info *bdi)
 432 {
 433         int i, err;
 434
 435         bdi->dev = NULL;
 436
 437         bdi->min_ratio = 0;
 438         bdi->max_ratio = 100;
 439         bdi->max_prop_frac = FPROP_FRAC_BASE;
 440         spin_lock_init(&bdi->wb_lock);
 441         INIT_LIST_HEAD(&bdi->bdi_list);
 442         INIT_LIST_HEAD(&bdi->work_list);
 443
 444         bdi_wb_init(&bdi->wb, bdi);
 445
 446         for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
 447                 err = percpu_counter_init(&bdi->bdi_stat[i], 0);
 448                 if (err)
 449                         goto err;
 450         }
 451
 452         bdi->dirty_exceeded = 0;
 453
 454         bdi->bw_time_stamp = jiffies;
 455         bdi->written_stamp = 0;
 456
 457         bdi->balanced_dirty_ratelimit = INIT_BW;
 458         bdi->dirty_ratelimit = INIT_BW;
 459         bdi->write_bandwidth = INIT_BW;
 460         bdi->avg_write_bandwidth = INIT_BW;
 461
 462         err = fprop_local_init_percpu(&bdi->completions);
 463
 464         if (err) {
 465 err:
 466                 while (i--)
 467                         percpu_counter_destroy(&bdi->bdi_stat[i]);
 468         }
 469
 470         return err;
 471 }
 472 EXPORT_SYMBOL(bdi_init);
 473
 474 void bdi_destroy(struct backing_dev_info *bdi)
 475 {
 476         int i;
 477
 478         /*
 479          * Splice our entries to the default_backing_dev_info, if this
 480          * bdi disappears
 481          */
 482         if (bdi_has_dirty_io(bdi)) {
 483                 struct bdi_writeback *dst = &default_backing_dev_info.wb;
 484
 485                 bdi_lock_two(&bdi->wb, dst);
 486                 list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
 487                 list_splice(&bdi->wb.b_io, &dst->b_io);
 488                 list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
 489                 spin_unlock(&bdi->wb.list_lock);
 490                 spin_unlock(&dst->list_lock);
 491         }
 492
 493         bdi_unregister(bdi);
 494
 495         /*
 496          * If bdi_unregister() had already been called earlier, the dwork
 497          * could still be pending because bdi_prune_sb() can race with the
 498          * bdi_wakeup_thread_delayed() calls from __mark_inode_dirty().
 499          */
 500         cancel_delayed_work_sync(&bdi->wb.dwork);
 501
 502         for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
 503                 percpu_counter_destroy(&bdi->bdi_stat[i]);
 504
 505         fprop_local_destroy_percpu(&bdi->completions);
 506 }
 507 EXPORT_SYMBOL(bdi_destroy);
 508
 509 /*
 510  * For use from filesystems to quickly init and register a bdi associated
 511  * with dirty writeback
 512  */
 513 int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
 514                            unsigned int cap)
 515 {
 516         int err;
 517
 518         bdi->name = name;
 519         bdi->capabilities = cap;
 520         err = bdi_init(bdi);
 521         if (err)
 522                 return err;
 523
 524         err = bdi_register(bdi, NULL, "%.28s-%ld", name,
 525                            atomic_long_inc_return(&bdi_seq));
 526         if (err) {
 527                 bdi_destroy(bdi);
 528                 return err;
 529         }
 530
 531         return 0;
 532 }
 533 EXPORT_SYMBOL(bdi_setup_and_register);
 534
 535 static wait_queue_head_t congestion_wqh[2] = {
 536                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 537                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
 538         };
 539 static atomic_t nr_bdi_congested[2];
 540
 541 void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
 542 {
 543         enum bdi_state bit;
 544         wait_queue_head_t *wqh = &congestion_wqh[sync];
 545
 546         bit = sync ? BDI_sync_congested : BDI_async_congested;
 547         if (test_and_clear_bit(bit, &bdi->state))
 548                 atomic_dec(&nr_bdi_congested[sync]);
 549         smp_mb__after_clear_bit();
 550         if (waitqueue_active(wqh))
 551                 wake_up(wqh);
 552 }
 553 EXPORT_SYMBOL(clear_bdi_congested);
 554
 555 void set_bdi_congested(struct backing_dev_info *bdi, int sync)
 556 {
 557         enum bdi_state bit;
 558
 559         bit = sync ? BDI_sync_congested : BDI_async_congested;
 560         if (!test_and_set_bit(bit, &bdi->state))
 561                 atomic_inc(&nr_bdi_congested[sync]);
 562 }
 563 EXPORT_SYMBOL(set_bdi_congested);
 564
 565 /**
 566  * congestion_wait - wait for a backing_dev to become uncongested
 567  * @sync: SYNC or ASYNC IO
 568  * @timeout: timeout in jiffies
 569  *
 570  * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
 571  * write congestion.  If no backing_devs are congested then just wait for the
 572  * next write to be completed.
 573  */
 574 long congestion_wait(int sync, long timeout)
 575 {
 576         long ret;
 577         unsigned long start = jiffies;
 578         DEFINE_WAIT(wait);
 579         wait_queue_head_t *wqh = &congestion_wqh[sync];
 580
 581         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 582         ret = io_schedule_timeout(timeout);
 583         finish_wait(wqh, &wait);
 584
 585         trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
 586                                         jiffies_to_usecs(jiffies - start));
 587
 588         return ret;
 589 }
 590 EXPORT_SYMBOL(congestion_wait);
 591
 592 /**
 593  * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
 594  * @zone: A zone to check if it is heavily congested
 595  * @sync: SYNC or ASYNC IO
 596  * @timeout: timeout in jiffies
 597  *
 598  * In the event of a congested backing_dev (any backing_dev) and the given
 599  * @zone has experienced recent congestion, this waits for up to @timeout
 600  * jiffies for either a BDI to exit congestion of the given @sync queue
 601  * or a write to complete.
 602  *
 603  * In the absence of zone congestion, cond_resched() is called to yield
 604  * the processor if necessary but otherwise does not sleep.
 605  *
 606  * The return value is 0 if the sleep is for the full timeout. Otherwise,
 607  * it is the number of jiffies that were still remaining when the function
 608  * returned. return_value == timeout implies the function did not sleep.
 609  */
 610 long wait_iff_congested(struct zone *zone, int sync, long timeout)
 611 {
 612         long ret;
 613         unsigned long start = jiffies;
 614         DEFINE_WAIT(wait);
 615         wait_queue_head_t *wqh = &congestion_wqh[sync];
 616
 617         /*
 618          * If there is no congestion, or heavy congestion is not being
 619          * encountered in the current zone, yield if necessary instead
 620          * of sleeping on the congestion queue
 621          */
 622         if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
 623                         !zone_is_reclaim_congested(zone)) {
 624                 cond_resched();
 625
 626                 /* In case we scheduled, work out time remaining */
 627                 ret = timeout - (jiffies - start);
 628                 if (ret < 0)
 629                         ret = 0;
 630
 631                 goto out;
 632         }
 633
 634         /* Sleep until uncongested or a write happens */
 635         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 636         ret = io_schedule_timeout(timeout);
 637         finish_wait(wqh, &wait);
 638
 639 out:
 640         trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
 641                                         jiffies_to_usecs(jiffies - start));
 642
 643         return ret;
 644 }
 645 EXPORT_SYMBOL(wait_iff_congested);
 646
 647 int pdflush_proc_obsolete(struct ctl_table *table, int write,
 648                         void __user *buffer, size_t *lenp, loff_t *ppos)
 649 {
 650         char kbuf[] = "0\n";
 651
 652         if (*ppos) {
 653                 *lenp = 0;
 654                 return 0;
 655         }
 656
 657         if (copy_to_user(buffer, kbuf, sizeof(kbuf)))
 658                 return -EFAULT;
 659         printk_once(KERN_WARNING "%s exported in /proc is scheduled for removal\n",
 660                         table->procname);
 661
 662         *lenp = 2;
 663         *ppos += *lenp;
 664         return 2;
 665 }