fs: assign sb->s_bdi to default_backing_dev_info if the bdi is going away
[linux-3.10.git] / 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 #ifdef CONFIG_DEBUG_FS
49 #include <linux/debugfs.h>
50 #include <linux/seq_file.h>
51
52 static struct dentry *bdi_debug_root;
53
54 static void bdi_debug_init(void)
55 {
56         bdi_debug_root = debugfs_create_dir("bdi", NULL);
57 }
58
59 static int bdi_debug_stats_show(struct seq_file *m, void *v)
60 {
61         struct backing_dev_info *bdi = m->private;
62         struct bdi_writeback *wb = &bdi->wb;
63         unsigned long background_thresh;
64         unsigned long dirty_thresh;
65         unsigned long bdi_thresh;
66         unsigned long nr_dirty, nr_io, nr_more_io, nr_wb;
67         struct inode *inode;
68
69         nr_wb = nr_dirty = nr_io = nr_more_io = 0;
70         spin_lock(&inode_lock);
71         list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
72                 nr_dirty++;
73         list_for_each_entry(inode, &wb->b_io, i_wb_list)
74                 nr_io++;
75         list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
76                 nr_more_io++;
77         spin_unlock(&inode_lock);
78
79         global_dirty_limits(&background_thresh, &dirty_thresh);
80         bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
81
82 #define K(x) ((x) << (PAGE_SHIFT - 10))
83         seq_printf(m,
84                    "BdiWriteback:     %8lu kB\n"
85                    "BdiReclaimable:   %8lu kB\n"
86                    "BdiDirtyThresh:   %8lu kB\n"
87                    "DirtyThresh:      %8lu kB\n"
88                    "BackgroundThresh: %8lu kB\n"
89                    "b_dirty:          %8lu\n"
90                    "b_io:             %8lu\n"
91                    "b_more_io:        %8lu\n"
92                    "bdi_list:         %8u\n"
93                    "state:            %8lx\n",
94                    (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
95                    (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
96                    K(bdi_thresh), K(dirty_thresh),
97                    K(background_thresh), nr_dirty, nr_io, nr_more_io,
98                    !list_empty(&bdi->bdi_list), bdi->state);
99 #undef K
100
101         return 0;
102 }
103
104 static int bdi_debug_stats_open(struct inode *inode, struct file *file)
105 {
106         return single_open(file, bdi_debug_stats_show, inode->i_private);
107 }
108
109 static const struct file_operations bdi_debug_stats_fops = {
110         .open           = bdi_debug_stats_open,
111         .read           = seq_read,
112         .llseek         = seq_lseek,
113         .release        = single_release,
114 };
115
116 static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
117 {
118         bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
119         bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
120                                                bdi, &bdi_debug_stats_fops);
121 }
122
123 static void bdi_debug_unregister(struct backing_dev_info *bdi)
124 {
125         debugfs_remove(bdi->debug_stats);
126         debugfs_remove(bdi->debug_dir);
127 }
128 #else
129 static inline void bdi_debug_init(void)
130 {
131 }
132 static inline void bdi_debug_register(struct backing_dev_info *bdi,
133                                       const char *name)
134 {
135 }
136 static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
137 {
138 }
139 #endif
140
141 static ssize_t read_ahead_kb_store(struct device *dev,
142                                   struct device_attribute *attr,
143                                   const char *buf, size_t count)
144 {
145         struct backing_dev_info *bdi = dev_get_drvdata(dev);
146         char *end;
147         unsigned long read_ahead_kb;
148         ssize_t ret = -EINVAL;
149
150         read_ahead_kb = simple_strtoul(buf, &end, 10);
151         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
152                 bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
153                 ret = count;
154         }
155         return ret;
156 }
157
158 #define K(pages) ((pages) << (PAGE_SHIFT - 10))
159
160 #define BDI_SHOW(name, expr)                                            \
161 static ssize_t name##_show(struct device *dev,                          \
162                            struct device_attribute *attr, char *page)   \
163 {                                                                       \
164         struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
165                                                                         \
166         return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
167 }
168
169 BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
170
171 static ssize_t min_ratio_store(struct device *dev,
172                 struct device_attribute *attr, const char *buf, size_t count)
173 {
174         struct backing_dev_info *bdi = dev_get_drvdata(dev);
175         char *end;
176         unsigned int ratio;
177         ssize_t ret = -EINVAL;
178
179         ratio = simple_strtoul(buf, &end, 10);
180         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
181                 ret = bdi_set_min_ratio(bdi, ratio);
182                 if (!ret)
183                         ret = count;
184         }
185         return ret;
186 }
187 BDI_SHOW(min_ratio, bdi->min_ratio)
188
189 static ssize_t max_ratio_store(struct device *dev,
190                 struct device_attribute *attr, const char *buf, size_t count)
191 {
192         struct backing_dev_info *bdi = dev_get_drvdata(dev);
193         char *end;
194         unsigned int ratio;
195         ssize_t ret = -EINVAL;
196
197         ratio = simple_strtoul(buf, &end, 10);
198         if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
199                 ret = bdi_set_max_ratio(bdi, ratio);
200                 if (!ret)
201                         ret = count;
202         }
203         return ret;
204 }
205 BDI_SHOW(max_ratio, bdi->max_ratio)
206
207 #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
208
209 static struct device_attribute bdi_dev_attrs[] = {
210         __ATTR_RW(read_ahead_kb),
211         __ATTR_RW(min_ratio),
212         __ATTR_RW(max_ratio),
213         __ATTR_NULL,
214 };
215
216 static __init int bdi_class_init(void)
217 {
218         bdi_class = class_create(THIS_MODULE, "bdi");
219         if (IS_ERR(bdi_class))
220                 return PTR_ERR(bdi_class);
221
222         bdi_class->dev_attrs = bdi_dev_attrs;
223         bdi_debug_init();
224         return 0;
225 }
226 postcore_initcall(bdi_class_init);
227
228 static int __init default_bdi_init(void)
229 {
230         int err;
231
232         sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
233         BUG_ON(IS_ERR(sync_supers_tsk));
234
235         setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
236         bdi_arm_supers_timer();
237
238         err = bdi_init(&default_backing_dev_info);
239         if (!err)
240                 bdi_register(&default_backing_dev_info, NULL, "default");
241         err = bdi_init(&noop_backing_dev_info);
242
243         return err;
244 }
245 subsys_initcall(default_bdi_init);
246
247 int bdi_has_dirty_io(struct backing_dev_info *bdi)
248 {
249         return wb_has_dirty_io(&bdi->wb);
250 }
251
252 static void bdi_flush_io(struct backing_dev_info *bdi)
253 {
254         struct writeback_control wbc = {
255                 .sync_mode              = WB_SYNC_NONE,
256                 .older_than_this        = NULL,
257                 .range_cyclic           = 1,
258                 .nr_to_write            = 1024,
259         };
260
261         writeback_inodes_wb(&bdi->wb, &wbc);
262 }
263
264 /*
265  * kupdated() used to do this. We cannot do it from the bdi_forker_thread()
266  * or we risk deadlocking on ->s_umount. The longer term solution would be
267  * to implement sync_supers_bdi() or similar and simply do it from the
268  * bdi writeback thread individually.
269  */
270 static int bdi_sync_supers(void *unused)
271 {
272         set_user_nice(current, 0);
273
274         while (!kthread_should_stop()) {
275                 set_current_state(TASK_INTERRUPTIBLE);
276                 schedule();
277
278                 /*
279                  * Do this periodically, like kupdated() did before.
280                  */
281                 sync_supers();
282         }
283
284         return 0;
285 }
286
287 void bdi_arm_supers_timer(void)
288 {
289         unsigned long next;
290
291         if (!dirty_writeback_interval)
292                 return;
293
294         next = msecs_to_jiffies(dirty_writeback_interval * 10) + jiffies;
295         mod_timer(&sync_supers_timer, round_jiffies_up(next));
296 }
297
298 static void sync_supers_timer_fn(unsigned long unused)
299 {
300         wake_up_process(sync_supers_tsk);
301         bdi_arm_supers_timer();
302 }
303
304 static void wakeup_timer_fn(unsigned long data)
305 {
306         struct backing_dev_info *bdi = (struct backing_dev_info *)data;
307
308         spin_lock_bh(&bdi->wb_lock);
309         if (bdi->wb.task) {
310                 trace_writeback_wake_thread(bdi);
311                 wake_up_process(bdi->wb.task);
312         } else {
313                 /*
314                  * When bdi tasks are inactive for long time, they are killed.
315                  * In this case we have to wake-up the forker thread which
316                  * should create and run the bdi thread.
317                  */
318                 trace_writeback_wake_forker_thread(bdi);
319                 wake_up_process(default_backing_dev_info.wb.task);
320         }
321         spin_unlock_bh(&bdi->wb_lock);
322 }
323
324 /*
325  * This function is used when the first inode for this bdi is marked dirty. It
326  * wakes-up the corresponding bdi thread which should then take care of the
327  * periodic background write-out of dirty inodes. Since the write-out would
328  * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
329  * set up a timer which wakes the bdi thread up later.
330  *
331  * Note, we wouldn't bother setting up the timer, but this function is on the
332  * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
333  * by delaying the wake-up.
334  */
335 void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
336 {
337         unsigned long timeout;
338
339         timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
340         mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
341 }
342
343 /*
344  * Calculate the longest interval (jiffies) bdi threads are allowed to be
345  * inactive.
346  */
347 static unsigned long bdi_longest_inactive(void)
348 {
349         unsigned long interval;
350
351         interval = msecs_to_jiffies(dirty_writeback_interval * 10);
352         return max(5UL * 60 * HZ, interval);
353 }
354
355 static int bdi_forker_thread(void *ptr)
356 {
357         struct bdi_writeback *me = ptr;
358
359         current->flags |= PF_SWAPWRITE;
360         set_freezable();
361
362         /*
363          * Our parent may run at a different priority, just set us to normal
364          */
365         set_user_nice(current, 0);
366
367         for (;;) {
368                 struct task_struct *task = NULL;
369                 struct backing_dev_info *bdi;
370                 enum {
371                         NO_ACTION,   /* Nothing to do */
372                         FORK_THREAD, /* Fork bdi thread */
373                         KILL_THREAD, /* Kill inactive bdi thread */
374                 } action = NO_ACTION;
375
376                 /*
377                  * Temporary measure, we want to make sure we don't see
378                  * dirty data on the default backing_dev_info
379                  */
380                 if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) {
381                         del_timer(&me->wakeup_timer);
382                         wb_do_writeback(me, 0);
383                 }
384
385                 spin_lock_bh(&bdi_lock);
386                 set_current_state(TASK_INTERRUPTIBLE);
387
388                 list_for_each_entry(bdi, &bdi_list, bdi_list) {
389                         bool have_dirty_io;
390
391                         if (!bdi_cap_writeback_dirty(bdi) ||
392                              bdi_cap_flush_forker(bdi))
393                                 continue;
394
395                         WARN(!test_bit(BDI_registered, &bdi->state),
396                              "bdi %p/%s is not registered!\n", bdi, bdi->name);
397
398                         have_dirty_io = !list_empty(&bdi->work_list) ||
399                                         wb_has_dirty_io(&bdi->wb);
400
401                         /*
402                          * If the bdi has work to do, but the thread does not
403                          * exist - create it.
404                          */
405                         if (!bdi->wb.task && have_dirty_io) {
406                                 /*
407                                  * Set the pending bit - if someone will try to
408                                  * unregister this bdi - it'll wait on this bit.
409                                  */
410                                 set_bit(BDI_pending, &bdi->state);
411                                 action = FORK_THREAD;
412                                 break;
413                         }
414
415                         spin_lock(&bdi->wb_lock);
416
417                         /*
418                          * If there is no work to do and the bdi thread was
419                          * inactive long enough - kill it. The wb_lock is taken
420                          * to make sure no-one adds more work to this bdi and
421                          * wakes the bdi thread up.
422                          */
423                         if (bdi->wb.task && !have_dirty_io &&
424                             time_after(jiffies, bdi->wb.last_active +
425                                                 bdi_longest_inactive())) {
426                                 task = bdi->wb.task;
427                                 bdi->wb.task = NULL;
428                                 spin_unlock(&bdi->wb_lock);
429                                 set_bit(BDI_pending, &bdi->state);
430                                 action = KILL_THREAD;
431                                 break;
432                         }
433                         spin_unlock(&bdi->wb_lock);
434                 }
435                 spin_unlock_bh(&bdi_lock);
436
437                 /* Keep working if default bdi still has things to do */
438                 if (!list_empty(&me->bdi->work_list))
439                         __set_current_state(TASK_RUNNING);
440
441                 switch (action) {
442                 case FORK_THREAD:
443                         __set_current_state(TASK_RUNNING);
444                         task = kthread_create(bdi_writeback_thread, &bdi->wb,
445                                               "flush-%s", dev_name(bdi->dev));
446                         if (IS_ERR(task)) {
447                                 /*
448                                  * If thread creation fails, force writeout of
449                                  * the bdi from the thread.
450                                  */
451                                 bdi_flush_io(bdi);
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         setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
632 }
633
634 int bdi_init(struct backing_dev_info *bdi)
635 {
636         int i, err;
637
638         bdi->dev = NULL;
639
640         bdi->min_ratio = 0;
641         bdi->max_ratio = 100;
642         bdi->max_prop_frac = PROP_FRAC_BASE;
643         spin_lock_init(&bdi->wb_lock);
644         INIT_LIST_HEAD(&bdi->bdi_list);
645         INIT_LIST_HEAD(&bdi->work_list);
646
647         bdi_wb_init(&bdi->wb, bdi);
648
649         for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
650                 err = percpu_counter_init(&bdi->bdi_stat[i], 0);
651                 if (err)
652                         goto err;
653         }
654
655         bdi->dirty_exceeded = 0;
656         err = prop_local_init_percpu(&bdi->completions);
657
658         if (err) {
659 err:
660                 while (i--)
661                         percpu_counter_destroy(&bdi->bdi_stat[i]);
662         }
663
664         return err;
665 }
666 EXPORT_SYMBOL(bdi_init);
667
668 void bdi_destroy(struct backing_dev_info *bdi)
669 {
670         int i;
671
672         /*
673          * Splice our entries to the default_backing_dev_info, if this
674          * bdi disappears
675          */
676         if (bdi_has_dirty_io(bdi)) {
677                 struct bdi_writeback *dst = &default_backing_dev_info.wb;
678
679                 spin_lock(&inode_lock);
680                 list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
681                 list_splice(&bdi->wb.b_io, &dst->b_io);
682                 list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
683                 spin_unlock(&inode_lock);
684         }
685
686         bdi_unregister(bdi);
687
688         for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
689                 percpu_counter_destroy(&bdi->bdi_stat[i]);
690
691         prop_local_destroy_percpu(&bdi->completions);
692 }
693 EXPORT_SYMBOL(bdi_destroy);
694
695 /*
696  * For use from filesystems to quickly init and register a bdi associated
697  * with dirty writeback
698  */
699 int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
700                            unsigned int cap)
701 {
702         char tmp[32];
703         int err;
704
705         bdi->name = name;
706         bdi->capabilities = cap;
707         err = bdi_init(bdi);
708         if (err)
709                 return err;
710
711         sprintf(tmp, "%.28s%s", name, "-%d");
712         err = bdi_register(bdi, NULL, tmp, atomic_long_inc_return(&bdi_seq));
713         if (err) {
714                 bdi_destroy(bdi);
715                 return err;
716         }
717
718         return 0;
719 }
720 EXPORT_SYMBOL(bdi_setup_and_register);
721
722 static wait_queue_head_t congestion_wqh[2] = {
723                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
724                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
725         };
726 static atomic_t nr_bdi_congested[2];
727
728 void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
729 {
730         enum bdi_state bit;
731         wait_queue_head_t *wqh = &congestion_wqh[sync];
732
733         bit = sync ? BDI_sync_congested : BDI_async_congested;
734         if (test_and_clear_bit(bit, &bdi->state))
735                 atomic_dec(&nr_bdi_congested[sync]);
736         smp_mb__after_clear_bit();
737         if (waitqueue_active(wqh))
738                 wake_up(wqh);
739 }
740 EXPORT_SYMBOL(clear_bdi_congested);
741
742 void set_bdi_congested(struct backing_dev_info *bdi, int sync)
743 {
744         enum bdi_state bit;
745
746         bit = sync ? BDI_sync_congested : BDI_async_congested;
747         if (!test_and_set_bit(bit, &bdi->state))
748                 atomic_inc(&nr_bdi_congested[sync]);
749 }
750 EXPORT_SYMBOL(set_bdi_congested);
751
752 /**
753  * congestion_wait - wait for a backing_dev to become uncongested
754  * @sync: SYNC or ASYNC IO
755  * @timeout: timeout in jiffies
756  *
757  * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
758  * write congestion.  If no backing_devs are congested then just wait for the
759  * next write to be completed.
760  */
761 long congestion_wait(int sync, long timeout)
762 {
763         long ret;
764         unsigned long start = jiffies;
765         DEFINE_WAIT(wait);
766         wait_queue_head_t *wqh = &congestion_wqh[sync];
767
768         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
769         ret = io_schedule_timeout(timeout);
770         finish_wait(wqh, &wait);
771
772         trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
773                                         jiffies_to_usecs(jiffies - start));
774
775         return ret;
776 }
777 EXPORT_SYMBOL(congestion_wait);
778
779 /**
780  * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
781  * @zone: A zone to check if it is heavily congested
782  * @sync: SYNC or ASYNC IO
783  * @timeout: timeout in jiffies
784  *
785  * In the event of a congested backing_dev (any backing_dev) and the given
786  * @zone has experienced recent congestion, this waits for up to @timeout
787  * jiffies for either a BDI to exit congestion of the given @sync queue
788  * or a write to complete.
789  *
790  * In the absense of zone congestion, cond_resched() is called to yield
791  * the processor if necessary but otherwise does not sleep.
792  *
793  * The return value is 0 if the sleep is for the full timeout. Otherwise,
794  * it is the number of jiffies that were still remaining when the function
795  * returned. return_value == timeout implies the function did not sleep.
796  */
797 long wait_iff_congested(struct zone *zone, int sync, long timeout)
798 {
799         long ret;
800         unsigned long start = jiffies;
801         DEFINE_WAIT(wait);
802         wait_queue_head_t *wqh = &congestion_wqh[sync];
803
804         /*
805          * If there is no congestion, or heavy congestion is not being
806          * encountered in the current zone, yield if necessary instead
807          * of sleeping on the congestion queue
808          */
809         if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
810                         !zone_is_reclaim_congested(zone)) {
811                 cond_resched();
812
813                 /* In case we scheduled, work out time remaining */
814                 ret = timeout - (jiffies - start);
815                 if (ret < 0)
816                         ret = 0;
817
818                 goto out;
819         }
820
821         /* Sleep until uncongested or a write happens */
822         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
823         ret = io_schedule_timeout(timeout);
824         finish_wait(wqh, &wait);
825
826 out:
827         trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
828                                         jiffies_to_usecs(jiffies - start));
829
830         return ret;
831 }
832 EXPORT_SYMBOL(wait_iff_congested);