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:       %10lu kB\n"
  96                    "BdiReclaimable:     %10lu kB\n"
  97                    "BdiDirtyThresh:     %10lu kB\n"
  98                    "DirtyThresh:        %10lu kB\n"
  99                    "BackgroundThresh:   %10lu kB\n"
 100                    "BdiDirtied:         %10lu kB\n"
 101                    "BdiWritten:         %10lu kB\n"
 102                    "BdiWriteBandwidth:  %10lu kBps\n"
 103                    "b_dirty:            %10lu\n"
 104                    "b_io:               %10lu\n"
 105                    "b_more_io:          %10lu\n"
 106                    "bdi_list:           %10u\n"
 107                    "state:              %10lx\n",
 108                    (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
 109                    (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
 110                    K(bdi_thresh),
 111                    K(dirty_thresh),
 112                    K(background_thresh),
 113                    (unsigned long) K(bdi_stat(bdi, BDI_DIRTIED)),
 114                    (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)),
 115                    (unsigned long) K(bdi->write_bandwidth),
 116                    nr_dirty,
 117                    nr_io,
 118                    nr_more_io,
 119                    !list_empty(&bdi->bdi_list), bdi->state);
 120 #undef K
 121
 122         return 0;
 123 }
 124
 125 static int bdi_debug_stats_open(struct inode *inode, struct file *file)
 126 {
 127         return single_open(file, bdi_debug_stats_show, inode->i_private);
 128 }
 129
 130 static const struct file_operations bdi_debug_stats_fops = {
 131         .open           = bdi_debug_stats_open,
 132         .read           = seq_read,
 133         .llseek         = seq_lseek,
 134         .release        = single_release,
 135 };
 136
 137 static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
 138 {
 139         bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
 140         bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
 141                                                bdi, &bdi_debug_stats_fops);
 142 }
 143
 144 static void bdi_debug_unregister(struct backing_dev_info *bdi)
 145 {
 146         debugfs_remove(bdi->debug_stats);
 147         debugfs_remove(bdi->debug_dir);
 148 }
 149 #else
 150 static inline void bdi_debug_init(void)
 151 {
 152 }
 153 static inline void bdi_debug_register(struct backing_dev_info *bdi,
 154                                       const char *name)
 155 {
 156 }
 157 static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
 158 {
 159 }
 160 #endif
 161
 162 static ssize_t read_ahead_kb_store(struct device *dev,
 163                                   struct device_attribute *attr,
 164                                   const char *buf, size_t count)
 165 {
 166         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 167         char *end;
 168         unsigned long read_ahead_kb;
 169         ssize_t ret = -EINVAL;
 170
 171         read_ahead_kb = simple_strtoul(buf, &end, 10);
 172         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
 173                 bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
 174                 ret = count;
 175         }
 176         return ret;
 177 }
 178
 179 #define K(pages) ((pages) << (PAGE_SHIFT - 10))
 180
 181 #define BDI_SHOW(name, expr)                                            \
 182 static ssize_t name##_show(struct device *dev,                          \
 183                            struct device_attribute *attr, char *page)   \
 184 {                                                                       \
 185         struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
 186                                                                         \
 187         return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
 188 }
 189
 190 BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
 191
 192 static ssize_t min_ratio_store(struct device *dev,
 193                 struct device_attribute *attr, const char *buf, size_t count)
 194 {
 195         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 196         char *end;
 197         unsigned int ratio;
 198         ssize_t ret = -EINVAL;
 199
 200         ratio = simple_strtoul(buf, &end, 10);
 201         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
 202                 ret = bdi_set_min_ratio(bdi, ratio);
 203                 if (!ret)
 204                         ret = count;
 205         }
 206         return ret;
 207 }
 208 BDI_SHOW(min_ratio, bdi->min_ratio)
 209
 210 static ssize_t max_ratio_store(struct device *dev,
 211                 struct device_attribute *attr, const char *buf, size_t count)
 212 {
 213         struct backing_dev_info *bdi = dev_get_drvdata(dev);
 214         char *end;
 215         unsigned int ratio;
 216         ssize_t ret = -EINVAL;
 217
 218         ratio = simple_strtoul(buf, &end, 10);
 219         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
 220                 ret = bdi_set_max_ratio(bdi, ratio);
 221                 if (!ret)
 222                         ret = count;
 223         }
 224         return ret;
 225 }
 226 BDI_SHOW(max_ratio, bdi->max_ratio)
 227
 228 #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
 229
 230 static struct device_attribute bdi_dev_attrs[] = {
 231         __ATTR_RW(read_ahead_kb),
 232         __ATTR_RW(min_ratio),
 233         __ATTR_RW(max_ratio),
 234         __ATTR_NULL,
 235 };
 236
 237 static __init int bdi_class_init(void)
 238 {
 239         bdi_class = class_create(THIS_MODULE, "bdi");
 240         if (IS_ERR(bdi_class))
 241                 return PTR_ERR(bdi_class);
 242
 243         bdi_class->dev_attrs = bdi_dev_attrs;
 244         bdi_debug_init();
 245         return 0;
 246 }
 247 postcore_initcall(bdi_class_init);
 248
 249 static int __init default_bdi_init(void)
 250 {
 251         int err;
 252
 253         sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
 254         BUG_ON(IS_ERR(sync_supers_tsk));
 255
 256         setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
 257         bdi_arm_supers_timer();
 258
 259         err = bdi_init(&default_backing_dev_info);
 260         if (!err)
 261                 bdi_register(&default_backing_dev_info, NULL, "default");
 262         err = bdi_init(&noop_backing_dev_info);
 263
 264         return err;
 265 }
 266 subsys_initcall(default_bdi_init);
 267
 268 int bdi_has_dirty_io(struct backing_dev_info *bdi)
 269 {
 270         return wb_has_dirty_io(&bdi->wb);
 271 }
 272
 273 /*
 274  * kupdated() used to do this. We cannot do it from the bdi_forker_thread()
 275  * or we risk deadlocking on ->s_umount. The longer term solution would be
 276  * to implement sync_supers_bdi() or similar and simply do it from the
 277  * bdi writeback thread individually.
 278  */
 279 static int bdi_sync_supers(void *unused)
 280 {
 281         set_user_nice(current, 0);
 282
 283         while (!kthread_should_stop()) {
 284                 set_current_state(TASK_INTERRUPTIBLE);
 285                 schedule();
 286
 287                 /*
 288                  * Do this periodically, like kupdated() did before.
 289                  */
 290                 sync_supers();
 291         }
 292
 293         return 0;
 294 }
 295
 296 void bdi_arm_supers_timer(void)
 297 {
 298         unsigned long next;
 299
 300         if (!dirty_writeback_interval)
 301                 return;
 302
 303         next = msecs_to_jiffies(dirty_writeback_interval * 10) + jiffies;
 304         mod_timer(&sync_supers_timer, round_jiffies_up(next));
 305 }
 306
 307 static void sync_supers_timer_fn(unsigned long unused)
 308 {
 309         wake_up_process(sync_supers_tsk);
 310         bdi_arm_supers_timer();
 311 }
 312
 313 static void wakeup_timer_fn(unsigned long data)
 314 {
 315         struct backing_dev_info *bdi = (struct backing_dev_info *)data;
 316
 317         spin_lock_bh(&bdi->wb_lock);
 318         if (bdi->wb.task) {
 319                 trace_writeback_wake_thread(bdi);
 320                 wake_up_process(bdi->wb.task);
 321         } else if (bdi->dev) {
 322                 /*
 323                  * When bdi tasks are inactive for long time, they are killed.
 324                  * In this case we have to wake-up the forker thread which
 325                  * should create and run the bdi thread.
 326                  */
 327                 trace_writeback_wake_forker_thread(bdi);
 328                 wake_up_process(default_backing_dev_info.wb.task);
 329         }
 330         spin_unlock_bh(&bdi->wb_lock);
 331 }
 332
 333 /*
 334  * This function is used when the first inode for this bdi is marked dirty. It
 335  * wakes-up the corresponding bdi thread which should then take care of the
 336  * periodic background write-out of dirty inodes. Since the write-out would
 337  * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
 338  * set up a timer which wakes the bdi thread up later.
 339  *
 340  * Note, we wouldn't bother setting up the timer, but this function is on the
 341  * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
 342  * by delaying the wake-up.
 343  */
 344 void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
 345 {
 346         unsigned long timeout;
 347
 348         timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
 349         mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
 350 }
 351
 352 /*
 353  * Calculate the longest interval (jiffies) bdi threads are allowed to be
 354  * inactive.
 355  */
 356 static unsigned long bdi_longest_inactive(void)
 357 {
 358         unsigned long interval;
 359
 360         interval = msecs_to_jiffies(dirty_writeback_interval * 10);
 361         return max(5UL * 60 * HZ, interval);
 362 }
 363
 364 /*
 365  * Clear pending bit and wakeup anybody waiting for flusher thread creation or
 366  * shutdown
 367  */
 368 static void bdi_clear_pending(struct backing_dev_info *bdi)
 369 {
 370         clear_bit(BDI_pending, &bdi->state);
 371         smp_mb__after_clear_bit();
 372         wake_up_bit(&bdi->state, BDI_pending);
 373 }
 374
 375 static int bdi_forker_thread(void *ptr)
 376 {
 377         struct bdi_writeback *me = ptr;
 378
 379         current->flags |= PF_SWAPWRITE;
 380         set_freezable();
 381
 382         /*
 383          * Our parent may run at a different priority, just set us to normal
 384          */
 385         set_user_nice(current, 0);
 386
 387         for (;;) {
 388                 struct task_struct *task = NULL;
 389                 struct backing_dev_info *bdi;
 390                 enum {
 391                         NO_ACTION,   /* Nothing to do */
 392                         FORK_THREAD, /* Fork bdi thread */
 393                         KILL_THREAD, /* Kill inactive bdi thread */
 394                 } action = NO_ACTION;
 395
 396                 /*
 397                  * Temporary measure, we want to make sure we don't see
 398                  * dirty data on the default backing_dev_info
 399                  */
 400                 if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) {
 401                         del_timer(&me->wakeup_timer);
 402                         wb_do_writeback(me, 0);
 403                 }
 404
 405                 spin_lock_bh(&bdi_lock);
 406                 /*
 407                  * In the following loop we are going to check whether we have
 408                  * some work to do without any synchronization with tasks
 409                  * waking us up to do work for them. Set the task state here
 410                  * so that we don't miss wakeups after verifying conditions.
 411                  */
 412                 set_current_state(TASK_INTERRUPTIBLE);
 413
 414                 list_for_each_entry(bdi, &bdi_list, bdi_list) {
 415                         bool have_dirty_io;
 416
 417                         if (!bdi_cap_writeback_dirty(bdi) ||
 418                              bdi_cap_flush_forker(bdi))
 419                                 continue;
 420
 421                         WARN(!test_bit(BDI_registered, &bdi->state),
 422                              "bdi %p/%s is not registered!\n", bdi, bdi->name);
 423
 424                         have_dirty_io = !list_empty(&bdi->work_list) ||
 425                                         wb_has_dirty_io(&bdi->wb);
 426
 427                         /*
 428                          * If the bdi has work to do, but the thread does not
 429                          * exist - create it.
 430                          */
 431                         if (!bdi->wb.task && have_dirty_io) {
 432                                 /*
 433                                  * Set the pending bit - if someone will try to
 434                                  * unregister this bdi - it'll wait on this bit.
 435                                  */
 436                                 set_bit(BDI_pending, &bdi->state);
 437                                 action = FORK_THREAD;
 438                                 break;
 439                         }
 440
 441                         spin_lock(&bdi->wb_lock);
 442
 443                         /*
 444                          * If there is no work to do and the bdi thread was
 445                          * inactive long enough - kill it. The wb_lock is taken
 446                          * to make sure no-one adds more work to this bdi and
 447                          * wakes the bdi thread up.
 448                          */
 449                         if (bdi->wb.task && !have_dirty_io &&
 450                             time_after(jiffies, bdi->wb.last_active +
 451                                                 bdi_longest_inactive())) {
 452                                 task = bdi->wb.task;
 453                                 bdi->wb.task = NULL;
 454                                 spin_unlock(&bdi->wb_lock);
 455                                 set_bit(BDI_pending, &bdi->state);
 456                                 action = KILL_THREAD;
 457                                 break;
 458                         }
 459                         spin_unlock(&bdi->wb_lock);
 460                 }
 461                 spin_unlock_bh(&bdi_lock);
 462
 463                 /* Keep working if default bdi still has things to do */
 464                 if (!list_empty(&me->bdi->work_list))
 465                         __set_current_state(TASK_RUNNING);
 466
 467                 switch (action) {
 468                 case FORK_THREAD:
 469                         __set_current_state(TASK_RUNNING);
 470                         task = kthread_create(bdi_writeback_thread, &bdi->wb,
 471                                               "flush-%s", dev_name(bdi->dev));
 472                         if (IS_ERR(task)) {
 473                                 /*
 474                                  * If thread creation fails, force writeout of
 475                                  * the bdi from the thread. Hopefully 1024 is
 476                                  * large enough for efficient IO.
 477                                  */
 478                                 writeback_inodes_wb(&bdi->wb, 1024,
 479                                                     WB_REASON_FORKER_THREAD);
 480                         } else {
 481                                 /*
 482                                  * The spinlock makes sure we do not lose
 483                                  * wake-ups when racing with 'bdi_queue_work()'.
 484                                  * And as soon as the bdi thread is visible, we
 485                                  * can start it.
 486                                  */
 487                                 spin_lock_bh(&bdi->wb_lock);
 488                                 bdi->wb.task = task;
 489                                 spin_unlock_bh(&bdi->wb_lock);
 490                                 wake_up_process(task);
 491                         }
 492                         bdi_clear_pending(bdi);
 493                         break;
 494
 495                 case KILL_THREAD:
 496                         __set_current_state(TASK_RUNNING);
 497                         kthread_stop(task);
 498                         bdi_clear_pending(bdi);
 499                         break;
 500
 501                 case NO_ACTION:
 502                         if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
 503                                 /*
 504                                  * There are no dirty data. The only thing we
 505                                  * should now care about is checking for
 506                                  * inactive bdi threads and killing them. Thus,
 507                                  * let's sleep for longer time, save energy and
 508                                  * be friendly for battery-driven devices.
 509                                  */
 510                                 schedule_timeout(bdi_longest_inactive());
 511                         else
 512                                 schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
 513                         try_to_freeze();
 514                         break;
 515                 }
 516         }
 517
 518         return 0;
 519 }
 520
 521 /*
 522  * Remove bdi from bdi_list, and ensure that it is no longer visible
 523  */
 524 static void bdi_remove_from_list(struct backing_dev_info *bdi)
 525 {
 526         spin_lock_bh(&bdi_lock);
 527         list_del_rcu(&bdi->bdi_list);
 528         spin_unlock_bh(&bdi_lock);
 529
 530         synchronize_rcu_expedited();
 531 }
 532
 533 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 534                 const char *fmt, ...)
 535 {
 536         va_list args;
 537         struct device *dev;
 538
 539         if (bdi->dev)   /* The driver needs to use separate queues per device */
 540                 return 0;
 541
 542         va_start(args, fmt);
 543         dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
 544         va_end(args);
 545         if (IS_ERR(dev))
 546                 return PTR_ERR(dev);
 547
 548         bdi->dev = dev;
 549
 550         /*
 551          * Just start the forker thread for our default backing_dev_info,
 552          * and add other bdi's to the list. They will get a thread created
 553          * on-demand when they need it.
 554          */
 555         if (bdi_cap_flush_forker(bdi)) {
 556                 struct bdi_writeback *wb = &bdi->wb;
 557
 558                 wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s",
 559                                                 dev_name(dev));
 560                 if (IS_ERR(wb->task))
 561                         return PTR_ERR(wb->task);
 562         }
 563
 564         bdi_debug_register(bdi, dev_name(dev));
 565         set_bit(BDI_registered, &bdi->state);
 566
 567         spin_lock_bh(&bdi_lock);
 568         list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
 569         spin_unlock_bh(&bdi_lock);
 570
 571         trace_writeback_bdi_register(bdi);
 572         return 0;
 573 }
 574 EXPORT_SYMBOL(bdi_register);
 575
 576 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 577 {
 578         return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
 579 }
 580 EXPORT_SYMBOL(bdi_register_dev);
 581
 582 /*
 583  * Remove bdi from the global list and shutdown any threads we have running
 584  */
 585 static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 586 {
 587         struct task_struct *task;
 588
 589         if (!bdi_cap_writeback_dirty(bdi))
 590                 return;
 591
 592         /*
 593          * Make sure nobody finds us on the bdi_list anymore
 594          */
 595         bdi_remove_from_list(bdi);
 596
 597         /*
 598          * If setup is pending, wait for that to complete first
 599          */
 600         wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
 601                         TASK_UNINTERRUPTIBLE);
 602
 603         /*
 604          * Finally, kill the kernel thread. We don't need to be RCU
 605          * safe anymore, since the bdi is gone from visibility. Force
 606          * unfreeze of the thread before calling kthread_stop(), otherwise
 607          * it would never exet if it is currently stuck in the refrigerator.
 608          */
 609         spin_lock_bh(&bdi->wb_lock);
 610         task = bdi->wb.task;
 611         bdi->wb.task = NULL;
 612         spin_unlock_bh(&bdi->wb_lock);
 613
 614         if (task) {
 615                 thaw_process(task);
 616                 kthread_stop(task);
 617         }
 618 }
 619
 620 /*
 621  * This bdi is going away now, make sure that no super_blocks point to it
 622  */
 623 static void bdi_prune_sb(struct backing_dev_info *bdi)
 624 {
 625         struct super_block *sb;
 626
 627         spin_lock(&sb_lock);
 628         list_for_each_entry(sb, &super_blocks, s_list) {
 629                 if (sb->s_bdi == bdi)
 630                         sb->s_bdi = &default_backing_dev_info;
 631         }
 632         spin_unlock(&sb_lock);
 633 }
 634
 635 void bdi_unregister(struct backing_dev_info *bdi)
 636 {
 637         struct device *dev = bdi->dev;
 638
 639         if (dev) {
 640                 bdi_set_min_ratio(bdi, 0);
 641                 trace_writeback_bdi_unregister(bdi);
 642                 bdi_prune_sb(bdi);
 643                 del_timer_sync(&bdi->wb.wakeup_timer);
 644
 645                 if (!bdi_cap_flush_forker(bdi))
 646                         bdi_wb_shutdown(bdi);
 647                 bdi_debug_unregister(bdi);
 648
 649                 spin_lock_bh(&bdi->wb_lock);
 650                 bdi->dev = NULL;
 651                 spin_unlock_bh(&bdi->wb_lock);
 652
 653                 device_unregister(dev);
 654         }
 655 }
 656 EXPORT_SYMBOL(bdi_unregister);
 657
 658 static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
 659 {
 660         memset(wb, 0, sizeof(*wb));
 661
 662         wb->bdi = bdi;
 663         wb->last_old_flush = jiffies;
 664         INIT_LIST_HEAD(&wb->b_dirty);
 665         INIT_LIST_HEAD(&wb->b_io);
 666         INIT_LIST_HEAD(&wb->b_more_io);
 667         spin_lock_init(&wb->list_lock);
 668         setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
 669 }
 670
 671 /*
 672  * Initial write bandwidth: 100 MB/s
 673  */
 674 #define INIT_BW         (100 << (20 - PAGE_SHIFT))
 675
 676 int bdi_init(struct backing_dev_info *bdi)
 677 {
 678         int i, err;
 679
 680         bdi->dev = NULL;
 681
 682         bdi->min_ratio = 0;
 683         bdi->max_ratio = 100;
 684         bdi->max_prop_frac = PROP_FRAC_BASE;
 685         spin_lock_init(&bdi->wb_lock);
 686         INIT_LIST_HEAD(&bdi->bdi_list);
 687         INIT_LIST_HEAD(&bdi->work_list);
 688
 689         bdi_wb_init(&bdi->wb, bdi);
 690
 691         for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
 692                 err = percpu_counter_init(&bdi->bdi_stat[i], 0);
 693                 if (err)
 694                         goto err;
 695         }
 696
 697         bdi->dirty_exceeded = 0;
 698
 699         bdi->bw_time_stamp = jiffies;
 700         bdi->written_stamp = 0;
 701
 702         bdi->balanced_dirty_ratelimit = INIT_BW;
 703         bdi->dirty_ratelimit = INIT_BW;
 704         bdi->write_bandwidth = INIT_BW;
 705         bdi->avg_write_bandwidth = INIT_BW;
 706
 707         err = prop_local_init_percpu(&bdi->completions);
 708
 709         if (err) {
 710 err:
 711                 while (i--)
 712                         percpu_counter_destroy(&bdi->bdi_stat[i]);
 713         }
 714
 715         return err;
 716 }
 717 EXPORT_SYMBOL(bdi_init);
 718
 719 void bdi_destroy(struct backing_dev_info *bdi)
 720 {
 721         int i;
 722
 723         /*
 724          * Splice our entries to the default_backing_dev_info, if this
 725          * bdi disappears
 726          */
 727         if (bdi_has_dirty_io(bdi)) {
 728                 struct bdi_writeback *dst = &default_backing_dev_info.wb;
 729
 730                 bdi_lock_two(&bdi->wb, dst);
 731                 list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
 732                 list_splice(&bdi->wb.b_io, &dst->b_io);
 733                 list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
 734                 spin_unlock(&bdi->wb.list_lock);
 735                 spin_unlock(&dst->list_lock);
 736         }
 737
 738         bdi_unregister(bdi);
 739
 740         /*
 741          * If bdi_unregister() had already been called earlier, the
 742          * wakeup_timer could still be armed because bdi_prune_sb()
 743          * can race with the bdi_wakeup_thread_delayed() calls from
 744          * __mark_inode_dirty().
 745          */
 746         del_timer_sync(&bdi->wb.wakeup_timer);
 747
 748         for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
 749                 percpu_counter_destroy(&bdi->bdi_stat[i]);
 750
 751         prop_local_destroy_percpu(&bdi->completions);
 752 }
 753 EXPORT_SYMBOL(bdi_destroy);
 754
 755 /*
 756  * For use from filesystems to quickly init and register a bdi associated
 757  * with dirty writeback
 758  */
 759 int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
 760                            unsigned int cap)
 761 {
 762         char tmp[32];
 763         int err;
 764
 765         bdi->name = name;
 766         bdi->capabilities = cap;
 767         err = bdi_init(bdi);
 768         if (err)
 769                 return err;
 770
 771         sprintf(tmp, "%.28s%s", name, "-%d");
 772         err = bdi_register(bdi, NULL, tmp, atomic_long_inc_return(&bdi_seq));
 773         if (err) {
 774                 bdi_destroy(bdi);
 775                 return err;
 776         }
 777
 778         return 0;
 779 }
 780 EXPORT_SYMBOL(bdi_setup_and_register);
 781
 782 static wait_queue_head_t congestion_wqh[2] = {
 783                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 784                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
 785         };
 786 static atomic_t nr_bdi_congested[2];
 787
 788 void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
 789 {
 790         enum bdi_state bit;
 791         wait_queue_head_t *wqh = &congestion_wqh[sync];
 792
 793         bit = sync ? BDI_sync_congested : BDI_async_congested;
 794         if (test_and_clear_bit(bit, &bdi->state))
 795                 atomic_dec(&nr_bdi_congested[sync]);
 796         smp_mb__after_clear_bit();
 797         if (waitqueue_active(wqh))
 798                 wake_up(wqh);
 799 }
 800 EXPORT_SYMBOL(clear_bdi_congested);
 801
 802 void set_bdi_congested(struct backing_dev_info *bdi, int sync)
 803 {
 804         enum bdi_state bit;
 805
 806         bit = sync ? BDI_sync_congested : BDI_async_congested;
 807         if (!test_and_set_bit(bit, &bdi->state))
 808                 atomic_inc(&nr_bdi_congested[sync]);
 809 }
 810 EXPORT_SYMBOL(set_bdi_congested);
 811
 812 /**
 813  * congestion_wait - wait for a backing_dev to become uncongested
 814  * @sync: SYNC or ASYNC IO
 815  * @timeout: timeout in jiffies
 816  *
 817  * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
 818  * write congestion.  If no backing_devs are congested then just wait for the
 819  * next write to be completed.
 820  */
 821 long congestion_wait(int sync, long timeout)
 822 {
 823         long ret;
 824         unsigned long start = jiffies;
 825         DEFINE_WAIT(wait);
 826         wait_queue_head_t *wqh = &congestion_wqh[sync];
 827
 828         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 829         ret = io_schedule_timeout(timeout);
 830         finish_wait(wqh, &wait);
 831
 832         trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
 833                                         jiffies_to_usecs(jiffies - start));
 834
 835         return ret;
 836 }
 837 EXPORT_SYMBOL(congestion_wait);
 838
 839 /**
 840  * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
 841  * @zone: A zone to check if it is heavily congested
 842  * @sync: SYNC or ASYNC IO
 843  * @timeout: timeout in jiffies
 844  *
 845  * In the event of a congested backing_dev (any backing_dev) and the given
 846  * @zone has experienced recent congestion, this waits for up to @timeout
 847  * jiffies for either a BDI to exit congestion of the given @sync queue
 848  * or a write to complete.
 849  *
 850  * In the absence of zone congestion, a short sleep or a cond_resched is
 851  * performed to yield the processor and to allow other subsystems to make
 852  * a forward progress.
 853  *
 854  * The return value is 0 if the sleep is for the full timeout. Otherwise,
 855  * it is the number of jiffies that were still remaining when the function
 856  * returned. return_value == timeout implies the function did not sleep.
 857  */
 858 long wait_iff_congested(struct zone *zone, int sync, long timeout)
 859 {
 860         long ret;
 861         unsigned long start = jiffies;
 862         DEFINE_WAIT(wait);
 863         wait_queue_head_t *wqh = &congestion_wqh[sync];
 864
 865         /*
 866          * If there is no congestion, or heavy congestion is not being
 867          * encountered in the current zone, yield if necessary instead
 868          * of sleeping on the congestion queue
 869          */
 870         if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
 871                         !zone_is_reclaim_congested(zone)) {
 872
 873                 /*
 874                  * Memory allocation/reclaim might be called from a WQ
 875                  * context and the current implementation of the WQ
 876                  * concurrency control doesn't recognize that a particular
 877                  * WQ is congested if the worker thread is looping without
 878                  * ever sleeping. Therefore we have to do a short sleep
 879                  * here rather than calling cond_resched().
 880                  */
 881                 if (current->flags & PF_WQ_WORKER)
 882                         schedule_timeout_uninterruptible(1);
 883                 else
 884                         cond_resched();
 885
 886                 /* In case we scheduled, work out time remaining */
 887                 ret = timeout - (jiffies - start);
 888                 if (ret < 0)
 889                         ret = 0;
 890
 891                 goto out;
 892         }
 893
 894         /* Sleep until uncongested or a write happens */
 895         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 896         ret = io_schedule_timeout(timeout);
 897         finish_wait(wqh, &wait);
 898
 899 out:
 900         trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
 901                                         jiffies_to_usecs(jiffies - start));
 902
 903         return ret;
 904 }
 905 EXPORT_SYMBOL(wait_iff_congested);