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