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