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 void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
  18 {
  19 }
  20 EXPORT_SYMBOL(default_unplug_io_fn);
  21
  22 struct backing_dev_info default_backing_dev_info = {
  23         .name           = "default",
  24         .ra_pages       = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
  25         .state          = 0,
  26         .capabilities   = BDI_CAP_MAP_COPY,
  27         .unplug_io_fn   = default_unplug_io_fn,
  28 };
  29 EXPORT_SYMBOL_GPL(default_backing_dev_info);
  30
  31 struct backing_dev_info noop_backing_dev_info = {
  32         .name           = "noop",
  33         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
  34 };
  35 EXPORT_SYMBOL_GPL(noop_backing_dev_info);
  36
  37 static struct class *bdi_class;
  38
  39 /*
  40  * bdi_lock protects updates to bdi_list and bdi_pending_list, as well as
  41  * reader side protection for bdi_pending_list. bdi_list has RCU reader side
  42  * locking.
  43  */
  44 DEFINE_SPINLOCK(bdi_lock);
  45 LIST_HEAD(bdi_list);
  46 LIST_HEAD(bdi_pending_list);
  47
  48 static struct task_struct *sync_supers_tsk;
  49 static struct timer_list sync_supers_timer;
  50
  51 static int bdi_sync_supers(void *);
  52 static void sync_supers_timer_fn(unsigned long);
  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, nr_wb;
  73         struct inode *inode;
  74
  75         nr_wb = nr_dirty = nr_io = nr_more_io = 0;
  76         spin_lock(&inode_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(&inode_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:     %8lu kB\n"
  91                    "BdiReclaimable:   %8lu kB\n"
  92                    "BdiDirtyThresh:   %8lu kB\n"
  93                    "DirtyThresh:      %8lu kB\n"
  94                    "BackgroundThresh: %8lu kB\n"
  95                    "b_dirty:          %8lu\n"
  96                    "b_io:             %8lu\n"
  97                    "b_more_io:        %8lu\n"
  98                    "bdi_list:         %8u\n"
  99                    "state:            %8lx\n",
 100                    (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
 101                    (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
 102                    K(bdi_thresh), K(dirty_thresh),
 103                    K(background_thresh), nr_dirty, nr_io, nr_more_io,
 104                    !list_empty(&bdi->bdi_list), bdi->state);
 105 #undef K
 106
 107         return 0;
 108 }
 109
 110 static int bdi_debug_stats_open(struct inode *inode, struct file *file)
 111 {
 112         return single_open(file, bdi_debug_stats_show, inode->i_private);
 113 }
 114
 115 static const struct file_operations bdi_debug_stats_fops = {
 116         .open           = bdi_debug_stats_open,
 117         .read           = seq_read,
 118         .llseek         = seq_lseek,
 119         .release        = single_release,
 120 };
 121
 122 static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
 123 {
 124         bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
 125         bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
 126                                                bdi, &bdi_debug_stats_fops);
 127 }
 128
 129 static void bdi_debug_unregister(struct backing_dev_info *bdi)
 130 {
 131         debugfs_remove(bdi->debug_stats);
 132         debugfs_remove(bdi->debug_dir);
 133 }
 134 #else
 135 static inline void bdi_debug_init(void)
 136 {
 137 }
 138 static inline void bdi_debug_register(struct backing_dev_info *bdi,
 139                                       const char *name)
 140 {
 141 }
 142 static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
 143 {
 144 }
 145 #endif
 146
 147 static ssize_t read_ahead_kb_store(struct device *dev,
 148                                   struct device_attribute *attr,
 149                                   const char *buf, size_t count)
 150 {
 151         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 152         char *end;
 153         unsigned long read_ahead_kb;
 154         ssize_t ret = -EINVAL;
 155
 156         read_ahead_kb = simple_strtoul(buf, &end, 10);
 157         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
 158                 bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
 159                 ret = count;
 160         }
 161         return ret;
 162 }
 163
 164 #define K(pages) ((pages) << (PAGE_SHIFT - 10))
 165
 166 #define BDI_SHOW(name, expr)                                            \
 167 static ssize_t name##_show(struct device *dev,                          \
 168                            struct device_attribute *attr, char *page)   \
 169 {                                                                       \
 170         struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
 171                                                                         \
 172         return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
 173 }
 174
 175 BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
 176
 177 static ssize_t min_ratio_store(struct device *dev,
 178                 struct device_attribute *attr, const char *buf, size_t count)
 179 {
 180         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 181         char *end;
 182         unsigned int ratio;
 183         ssize_t ret = -EINVAL;
 184
 185         ratio = simple_strtoul(buf, &end, 10);
 186         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
 187                 ret = bdi_set_min_ratio(bdi, ratio);
 188                 if (!ret)
 189                         ret = count;
 190         }
 191         return ret;
 192 }
 193 BDI_SHOW(min_ratio, bdi->min_ratio)
 194
 195 static ssize_t max_ratio_store(struct device *dev,
 196                 struct device_attribute *attr, const char *buf, size_t count)
 197 {
 198         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 199         char *end;
 200         unsigned int ratio;
 201         ssize_t ret = -EINVAL;
 202
 203         ratio = simple_strtoul(buf, &end, 10);
 204         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
 205                 ret = bdi_set_max_ratio(bdi, ratio);
 206                 if (!ret)
 207                         ret = count;
 208         }
 209         return ret;
 210 }
 211 BDI_SHOW(max_ratio, bdi->max_ratio)
 212
 213 #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
 214
 215 static struct device_attribute bdi_dev_attrs[] = {
 216         __ATTR_RW(read_ahead_kb),
 217         __ATTR_RW(min_ratio),
 218         __ATTR_RW(max_ratio),
 219         __ATTR_NULL,
 220 };
 221
 222 static __init int bdi_class_init(void)
 223 {
 224         bdi_class = class_create(THIS_MODULE, "bdi");
 225         if (IS_ERR(bdi_class))
 226                 return PTR_ERR(bdi_class);
 227
 228         bdi_class->dev_attrs = bdi_dev_attrs;
 229         bdi_debug_init();
 230         return 0;
 231 }
 232 postcore_initcall(bdi_class_init);
 233
 234 static int __init default_bdi_init(void)
 235 {
 236         int err;
 237
 238         sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
 239         BUG_ON(IS_ERR(sync_supers_tsk));
 240
 241         setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
 242         bdi_arm_supers_timer();
 243
 244         err = bdi_init(&default_backing_dev_info);
 245         if (!err)
 246                 bdi_register(&default_backing_dev_info, NULL, "default");
 247         err = bdi_init(&noop_backing_dev_info);
 248
 249         return err;
 250 }
 251 subsys_initcall(default_bdi_init);
 252
 253 int bdi_has_dirty_io(struct backing_dev_info *bdi)
 254 {
 255         return wb_has_dirty_io(&bdi->wb);
 256 }
 257
 258 static void bdi_flush_io(struct backing_dev_info *bdi)
 259 {
 260         struct writeback_control wbc = {
 261                 .sync_mode              = WB_SYNC_NONE,
 262                 .older_than_this        = NULL,
 263                 .range_cyclic           = 1,
 264                 .nr_to_write            = 1024,
 265         };
 266
 267         writeback_inodes_wb(&bdi->wb, &wbc);
 268 }
 269
 270 /*
 271  * kupdated() used to do this. We cannot do it from the bdi_forker_thread()
 272  * or we risk deadlocking on ->s_umount. The longer term solution would be
 273  * to implement sync_supers_bdi() or similar and simply do it from the
 274  * bdi writeback thread individually.
 275  */
 276 static int bdi_sync_supers(void *unused)
 277 {
 278         set_user_nice(current, 0);
 279
 280         while (!kthread_should_stop()) {
 281                 set_current_state(TASK_INTERRUPTIBLE);
 282                 schedule();
 283
 284                 /*
 285                  * Do this periodically, like kupdated() did before.
 286                  */
 287                 sync_supers();
 288         }
 289
 290         return 0;
 291 }
 292
 293 void bdi_arm_supers_timer(void)
 294 {
 295         unsigned long next;
 296
 297         if (!dirty_writeback_interval)
 298                 return;
 299
 300         next = msecs_to_jiffies(dirty_writeback_interval * 10) + jiffies;
 301         mod_timer(&sync_supers_timer, round_jiffies_up(next));
 302 }
 303
 304 static void sync_supers_timer_fn(unsigned long unused)
 305 {
 306         wake_up_process(sync_supers_tsk);
 307         bdi_arm_supers_timer();
 308 }
 309
 310 static void wakeup_timer_fn(unsigned long data)
 311 {
 312         struct backing_dev_info *bdi = (struct backing_dev_info *)data;
 313
 314         spin_lock_bh(&bdi->wb_lock);
 315         if (bdi->wb.task) {
 316                 trace_writeback_wake_thread(bdi);
 317                 wake_up_process(bdi->wb.task);
 318         } else {
 319                 /*
 320                  * When bdi tasks are inactive for long time, they are killed.
 321                  * In this case we have to wake-up the forker thread which
 322                  * should create and run the bdi thread.
 323                  */
 324                 trace_writeback_wake_forker_thread(bdi);
 325                 wake_up_process(default_backing_dev_info.wb.task);
 326         }
 327         spin_unlock_bh(&bdi->wb_lock);
 328 }
 329
 330 /*
 331  * This function is used when the first inode for this bdi is marked dirty. It
 332  * wakes-up the corresponding bdi thread which should then take care of the
 333  * periodic background write-out of dirty inodes. Since the write-out would
 334  * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
 335  * set up a timer which wakes the bdi thread up later.
 336  *
 337  * Note, we wouldn't bother setting up the timer, but this function is on the
 338  * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
 339  * by delaying the wake-up.
 340  */
 341 void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
 342 {
 343         unsigned long timeout;
 344
 345         timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
 346         mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
 347 }
 348
 349 /*
 350  * Calculate the longest interval (jiffies) bdi threads are allowed to be
 351  * inactive.
 352  */
 353 static unsigned long bdi_longest_inactive(void)
 354 {
 355         unsigned long interval;
 356
 357         interval = msecs_to_jiffies(dirty_writeback_interval * 10);
 358         return max(5UL * 60 * HZ, interval);
 359 }
 360
 361 static int bdi_forker_thread(void *ptr)
 362 {
 363         struct bdi_writeback *me = ptr;
 364
 365         current->flags |= PF_SWAPWRITE;
 366         set_freezable();
 367
 368         /*
 369          * Our parent may run at a different priority, just set us to normal
 370          */
 371         set_user_nice(current, 0);
 372
 373         for (;;) {
 374                 struct task_struct *task = NULL;
 375                 struct backing_dev_info *bdi;
 376                 enum {
 377                         NO_ACTION,   /* Nothing to do */
 378                         FORK_THREAD, /* Fork bdi thread */
 379                         KILL_THREAD, /* Kill inactive bdi thread */
 380                 } action = NO_ACTION;
 381
 382                 /*
 383                  * Temporary measure, we want to make sure we don't see
 384                  * dirty data on the default backing_dev_info
 385                  */
 386                 if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) {
 387                         del_timer(&me->wakeup_timer);
 388                         wb_do_writeback(me, 0);
 389                 }
 390
 391                 spin_lock_bh(&bdi_lock);
 392                 set_current_state(TASK_INTERRUPTIBLE);
 393
 394                 list_for_each_entry(bdi, &bdi_list, bdi_list) {
 395                         bool have_dirty_io;
 396
 397                         if (!bdi_cap_writeback_dirty(bdi) ||
 398                              bdi_cap_flush_forker(bdi))
 399                                 continue;
 400
 401                         WARN(!test_bit(BDI_registered, &bdi->state),
 402                              "bdi %p/%s is not registered!\n", bdi, bdi->name);
 403
 404                         have_dirty_io = !list_empty(&bdi->work_list) ||
 405                                         wb_has_dirty_io(&bdi->wb);
 406
 407                         /*
 408                          * If the bdi has work to do, but the thread does not
 409                          * exist - create it.
 410                          */
 411                         if (!bdi->wb.task && have_dirty_io) {
 412                                 /*
 413                                  * Set the pending bit - if someone will try to
 414                                  * unregister this bdi - it'll wait on this bit.
 415                                  */
 416                                 set_bit(BDI_pending, &bdi->state);
 417                                 action = FORK_THREAD;
 418                                 break;
 419                         }
 420
 421                         spin_lock(&bdi->wb_lock);
 422
 423                         /*
 424                          * If there is no work to do and the bdi thread was
 425                          * inactive long enough - kill it. The wb_lock is taken
 426                          * to make sure no-one adds more work to this bdi and
 427                          * wakes the bdi thread up.
 428                          */
 429                         if (bdi->wb.task && !have_dirty_io &&
 430                             time_after(jiffies, bdi->wb.last_active +
 431                                                 bdi_longest_inactive())) {
 432                                 task = bdi->wb.task;
 433                                 bdi->wb.task = NULL;
 434                                 spin_unlock(&bdi->wb_lock);
 435                                 set_bit(BDI_pending, &bdi->state);
 436                                 action = KILL_THREAD;
 437                                 break;
 438                         }
 439                         spin_unlock(&bdi->wb_lock);
 440                 }
 441                 spin_unlock_bh(&bdi_lock);
 442
 443                 /* Keep working if default bdi still has things to do */
 444                 if (!list_empty(&me->bdi->work_list))
 445                         __set_current_state(TASK_RUNNING);
 446
 447                 switch (action) {
 448                 case FORK_THREAD:
 449                         __set_current_state(TASK_RUNNING);
 450                         task = kthread_create(bdi_writeback_thread, &bdi->wb,
 451                                               "flush-%s", dev_name(bdi->dev));
 452                         if (IS_ERR(task)) {
 453                                 /*
 454                                  * If thread creation fails, force writeout of
 455                                  * the bdi from the thread.
 456                                  */
 457                                 bdi_flush_io(bdi);
 458                         } else {
 459                                 /*
 460                                  * The spinlock makes sure we do not lose
 461                                  * wake-ups when racing with 'bdi_queue_work()'.
 462                                  * And as soon as the bdi thread is visible, we
 463                                  * can start it.
 464                                  */
 465                                 spin_lock_bh(&bdi->wb_lock);
 466                                 bdi->wb.task = task;
 467                                 spin_unlock_bh(&bdi->wb_lock);
 468                                 wake_up_process(task);
 469                         }
 470                         break;
 471
 472                 case KILL_THREAD:
 473                         __set_current_state(TASK_RUNNING);
 474                         kthread_stop(task);
 475                         break;
 476
 477                 case NO_ACTION:
 478                         if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
 479                                 /*
 480                                  * There are no dirty data. The only thing we
 481                                  * should now care about is checking for
 482                                  * inactive bdi threads and killing them. Thus,
 483                                  * let's sleep for longer time, save energy and
 484                                  * be friendly for battery-driven devices.
 485                                  */
 486                                 schedule_timeout(bdi_longest_inactive());
 487                         else
 488                                 schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
 489                         try_to_freeze();
 490                         /* Back to the main loop */
 491                         continue;
 492                 }
 493
 494                 /*
 495                  * Clear pending bit and wakeup anybody waiting to tear us down.
 496                  */
 497                 clear_bit(BDI_pending, &bdi->state);
 498                 smp_mb__after_clear_bit();
 499                 wake_up_bit(&bdi->state, BDI_pending);
 500         }
 501
 502         return 0;
 503 }
 504
 505 /*
 506  * Remove bdi from bdi_list, and ensure that it is no longer visible
 507  */
 508 static void bdi_remove_from_list(struct backing_dev_info *bdi)
 509 {
 510         spin_lock_bh(&bdi_lock);
 511         list_del_rcu(&bdi->bdi_list);
 512         spin_unlock_bh(&bdi_lock);
 513
 514         synchronize_rcu();
 515 }
 516
 517 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 518                 const char *fmt, ...)
 519 {
 520         va_list args;
 521         struct device *dev;
 522
 523         if (bdi->dev)   /* The driver needs to use separate queues per device */
 524                 return 0;
 525
 526         va_start(args, fmt);
 527         dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
 528         va_end(args);
 529         if (IS_ERR(dev))
 530                 return PTR_ERR(dev);
 531
 532         bdi->dev = dev;
 533
 534         /*
 535          * Just start the forker thread for our default backing_dev_info,
 536          * and add other bdi's to the list. They will get a thread created
 537          * on-demand when they need it.
 538          */
 539         if (bdi_cap_flush_forker(bdi)) {
 540                 struct bdi_writeback *wb = &bdi->wb;
 541
 542                 wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s",
 543                                                 dev_name(dev));
 544                 if (IS_ERR(wb->task))
 545                         return PTR_ERR(wb->task);
 546         }
 547
 548         bdi_debug_register(bdi, dev_name(dev));
 549         set_bit(BDI_registered, &bdi->state);
 550
 551         spin_lock_bh(&bdi_lock);
 552         list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
 553         spin_unlock_bh(&bdi_lock);
 554
 555         trace_writeback_bdi_register(bdi);
 556         return 0;
 557 }
 558 EXPORT_SYMBOL(bdi_register);
 559
 560 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 561 {
 562         return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
 563 }
 564 EXPORT_SYMBOL(bdi_register_dev);
 565
 566 /*
 567  * Remove bdi from the global list and shutdown any threads we have running
 568  */
 569 static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 570 {
 571         if (!bdi_cap_writeback_dirty(bdi))
 572                 return;
 573
 574         /*
 575          * Make sure nobody finds us on the bdi_list anymore
 576          */
 577         bdi_remove_from_list(bdi);
 578
 579         /*
 580          * If setup is pending, wait for that to complete first
 581          */
 582         wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
 583                         TASK_UNINTERRUPTIBLE);
 584
 585         /*
 586          * Finally, kill the kernel thread. We don't need to be RCU
 587          * safe anymore, since the bdi is gone from visibility. Force
 588          * unfreeze of the thread before calling kthread_stop(), otherwise
 589          * it would never exet if it is currently stuck in the refrigerator.
 590          */
 591         if (bdi->wb.task) {
 592                 thaw_process(bdi->wb.task);
 593                 kthread_stop(bdi->wb.task);
 594         }
 595 }
 596
 597 /*
 598  * This bdi is going away now, make sure that no super_blocks point to it
 599  */
 600 static void bdi_prune_sb(struct backing_dev_info *bdi)
 601 {
 602         struct super_block *sb;
 603
 604         spin_lock(&sb_lock);
 605         list_for_each_entry(sb, &super_blocks, s_list) {
 606                 if (sb->s_bdi == bdi)
 607                         sb->s_bdi = NULL;
 608         }
 609         spin_unlock(&sb_lock);
 610 }
 611
 612 void bdi_unregister(struct backing_dev_info *bdi)
 613 {
 614         if (bdi->dev) {
 615                 trace_writeback_bdi_unregister(bdi);
 616                 bdi_prune_sb(bdi);
 617                 del_timer_sync(&bdi->wb.wakeup_timer);
 618
 619                 if (!bdi_cap_flush_forker(bdi))
 620                         bdi_wb_shutdown(bdi);
 621                 bdi_debug_unregister(bdi);
 622                 device_unregister(bdi->dev);
 623                 bdi->dev = NULL;
 624         }
 625 }
 626 EXPORT_SYMBOL(bdi_unregister);
 627
 628 static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
 629 {
 630         memset(wb, 0, sizeof(*wb));
 631
 632         wb->bdi = bdi;
 633         wb->last_old_flush = jiffies;
 634         INIT_LIST_HEAD(&wb->b_dirty);
 635         INIT_LIST_HEAD(&wb->b_io);
 636         INIT_LIST_HEAD(&wb->b_more_io);
 637         setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
 638 }
 639
 640 int bdi_init(struct backing_dev_info *bdi)
 641 {
 642         int i, err;
 643
 644         bdi->dev = NULL;
 645
 646         bdi->min_ratio = 0;
 647         bdi->max_ratio = 100;
 648         bdi->max_prop_frac = PROP_FRAC_BASE;
 649         spin_lock_init(&bdi->wb_lock);
 650         INIT_LIST_HEAD(&bdi->bdi_list);
 651         INIT_LIST_HEAD(&bdi->work_list);
 652
 653         bdi_wb_init(&bdi->wb, bdi);
 654
 655         for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
 656                 err = percpu_counter_init(&bdi->bdi_stat[i], 0);
 657                 if (err)
 658                         goto err;
 659         }
 660
 661         bdi->dirty_exceeded = 0;
 662         err = prop_local_init_percpu(&bdi->completions);
 663
 664         if (err) {
 665 err:
 666                 while (i--)
 667                         percpu_counter_destroy(&bdi->bdi_stat[i]);
 668         }
 669
 670         return err;
 671 }
 672 EXPORT_SYMBOL(bdi_init);
 673
 674 void bdi_destroy(struct backing_dev_info *bdi)
 675 {
 676         int i;
 677
 678         /*
 679          * Splice our entries to the default_backing_dev_info, if this
 680          * bdi disappears
 681          */
 682         if (bdi_has_dirty_io(bdi)) {
 683                 struct bdi_writeback *dst = &default_backing_dev_info.wb;
 684
 685                 spin_lock(&inode_lock);
 686                 list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
 687                 list_splice(&bdi->wb.b_io, &dst->b_io);
 688                 list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
 689                 spin_unlock(&inode_lock);
 690         }
 691
 692         bdi_unregister(bdi);
 693
 694         for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
 695                 percpu_counter_destroy(&bdi->bdi_stat[i]);
 696
 697         prop_local_destroy_percpu(&bdi->completions);
 698 }
 699 EXPORT_SYMBOL(bdi_destroy);
 700
 701 /*
 702  * For use from filesystems to quickly init and register a bdi associated
 703  * with dirty writeback
 704  */
 705 int 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 }
 726 EXPORT_SYMBOL(bdi_setup_and_register);
 727
 728 static wait_queue_head_t congestion_wqh[2] = {
 729                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 730                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
 731         };
 732 static atomic_t nr_bdi_congested[2];
 733
 734 void 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 }
 746 EXPORT_SYMBOL(clear_bdi_congested);
 747
 748 void 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 }
 756 EXPORT_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  */
 767 long 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 }
 783 EXPORT_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 absense 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  */
 803 long 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
 832 out:
 833         trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
 834                                         jiffies_to_usecs(jiffies - start));
 835
 836         return ret;
 837 }
 838 EXPORT_SYMBOL(wait_iff_congested);