Root/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
15static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
16
17void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
18{
19}
20EXPORT_SYMBOL(default_unplug_io_fn);
21
22struct backing_dev_info default_backing_dev_info = {
23    .name = "default",
24    .ra_pages = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
25    .state = 0,
26    .capabilities = BDI_CAP_MAP_COPY,
27    .unplug_io_fn = default_unplug_io_fn,
28};
29EXPORT_SYMBOL_GPL(default_backing_dev_info);
30
31struct backing_dev_info noop_backing_dev_info = {
32    .name = "noop",
33    .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK,
34};
35EXPORT_SYMBOL_GPL(noop_backing_dev_info);
36
37static struct class *bdi_class;
38
39/*
40 * bdi_lock protects updates to bdi_list and bdi_pending_list, as well as
41 * reader side protection for bdi_pending_list. bdi_list has RCU reader side
42 * locking.
43 */
44DEFINE_SPINLOCK(bdi_lock);
45LIST_HEAD(bdi_list);
46LIST_HEAD(bdi_pending_list);
47
48static struct task_struct *sync_supers_tsk;
49static struct timer_list sync_supers_timer;
50
51static int bdi_sync_supers(void *);
52static void sync_supers_timer_fn(unsigned long);
53
54#ifdef CONFIG_DEBUG_FS
55#include <linux/debugfs.h>
56#include <linux/seq_file.h>
57
58static struct dentry *bdi_debug_root;
59
60static void bdi_debug_init(void)
61{
62    bdi_debug_root = debugfs_create_dir("bdi", NULL);
63}
64
65static int bdi_debug_stats_show(struct seq_file *m, void *v)
66{
67    struct backing_dev_info *bdi = m->private;
68    struct bdi_writeback *wb = &bdi->wb;
69    unsigned long background_thresh;
70    unsigned long dirty_thresh;
71    unsigned long bdi_thresh;
72    unsigned long nr_dirty, nr_io, nr_more_io, nr_wb;
73    struct inode *inode;
74
75    nr_wb = nr_dirty = nr_io = nr_more_io = 0;
76    spin_lock(&inode_lock);
77    list_for_each_entry(inode, &wb->b_dirty, i_list)
78        nr_dirty++;
79    list_for_each_entry(inode, &wb->b_io, i_list)
80        nr_io++;
81    list_for_each_entry(inode, &wb->b_more_io, i_list)
82        nr_more_io++;
83    spin_unlock(&inode_lock);
84
85    global_dirty_limits(&background_thresh, &dirty_thresh);
86    bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
87
88#define K(x) ((x) << (PAGE_SHIFT - 10))
89    seq_printf(m,
90           "BdiWriteback: %8lu kB\n"
91           "BdiReclaimable: %8lu kB\n"
92           "BdiDirtyThresh: %8lu kB\n"
93           "DirtyThresh: %8lu kB\n"
94           "BackgroundThresh: %8lu kB\n"
95           "b_dirty: %8lu\n"
96           "b_io: %8lu\n"
97           "b_more_io: %8lu\n"
98           "bdi_list: %8u\n"
99           "state: %8lx\n",
100           (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
101           (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
102           K(bdi_thresh), K(dirty_thresh),
103           K(background_thresh), nr_dirty, nr_io, nr_more_io,
104           !list_empty(&bdi->bdi_list), bdi->state);
105#undef K
106
107    return 0;
108}
109
110static int bdi_debug_stats_open(struct inode *inode, struct file *file)
111{
112    return single_open(file, bdi_debug_stats_show, inode->i_private);
113}
114
115static const struct file_operations bdi_debug_stats_fops = {
116    .open = bdi_debug_stats_open,
117    .read = seq_read,
118    .llseek = seq_lseek,
119    .release = single_release,
120};
121
122static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
123{
124    bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
125    bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
126                           bdi, &bdi_debug_stats_fops);
127}
128
129static void bdi_debug_unregister(struct backing_dev_info *bdi)
130{
131    debugfs_remove(bdi->debug_stats);
132    debugfs_remove(bdi->debug_dir);
133}
134#else
135static inline void bdi_debug_init(void)
136{
137}
138static inline void bdi_debug_register(struct backing_dev_info *bdi,
139                      const char *name)
140{
141}
142static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
143{
144}
145#endif
146
147static ssize_t read_ahead_kb_store(struct device *dev,
148                  struct device_attribute *attr,
149                  const char *buf, size_t count)
150{
151    struct backing_dev_info *bdi = dev_get_drvdata(dev);
152    char *end;
153    unsigned long read_ahead_kb;
154    ssize_t ret = -EINVAL;
155
156    read_ahead_kb = simple_strtoul(buf, &end, 10);
157    if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
158        bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
159        ret = count;
160    }
161    return ret;
162}
163
164#define K(pages) ((pages) << (PAGE_SHIFT - 10))
165
166#define BDI_SHOW(name, expr) \
167static ssize_t name##_show(struct device *dev, \
168               struct device_attribute *attr, char *page) \
169{ \
170    struct backing_dev_info *bdi = dev_get_drvdata(dev); \
171                                    \
172    return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr); \
173}
174
175BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
176
177static ssize_t min_ratio_store(struct device *dev,
178        struct device_attribute *attr, const char *buf, size_t count)
179{
180    struct backing_dev_info *bdi = dev_get_drvdata(dev);
181    char *end;
182    unsigned int ratio;
183    ssize_t ret = -EINVAL;
184
185    ratio = simple_strtoul(buf, &end, 10);
186    if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
187        ret = bdi_set_min_ratio(bdi, ratio);
188        if (!ret)
189            ret = count;
190    }
191    return ret;
192}
193BDI_SHOW(min_ratio, bdi->min_ratio)
194
195static ssize_t max_ratio_store(struct device *dev,
196        struct device_attribute *attr, const char *buf, size_t count)
197{
198    struct backing_dev_info *bdi = dev_get_drvdata(dev);
199    char *end;
200    unsigned int ratio;
201    ssize_t ret = -EINVAL;
202
203    ratio = simple_strtoul(buf, &end, 10);
204    if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
205        ret = bdi_set_max_ratio(bdi, ratio);
206        if (!ret)
207            ret = count;
208    }
209    return ret;
210}
211BDI_SHOW(max_ratio, bdi->max_ratio)
212
213#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
214
215static struct device_attribute bdi_dev_attrs[] = {
216    __ATTR_RW(read_ahead_kb),
217    __ATTR_RW(min_ratio),
218    __ATTR_RW(max_ratio),
219    __ATTR_NULL,
220};
221
222static __init int bdi_class_init(void)
223{
224    bdi_class = class_create(THIS_MODULE, "bdi");
225    if (IS_ERR(bdi_class))
226        return PTR_ERR(bdi_class);
227
228    bdi_class->dev_attrs = bdi_dev_attrs;
229    bdi_debug_init();
230    return 0;
231}
232postcore_initcall(bdi_class_init);
233
234static int __init default_bdi_init(void)
235{
236    int err;
237
238    sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
239    BUG_ON(IS_ERR(sync_supers_tsk));
240
241    setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
242    bdi_arm_supers_timer();
243
244    err = bdi_init(&default_backing_dev_info);
245    if (!err)
246        bdi_register(&default_backing_dev_info, NULL, "default");
247    err = bdi_init(&noop_backing_dev_info);
248
249    return err;
250}
251subsys_initcall(default_bdi_init);
252
253int bdi_has_dirty_io(struct backing_dev_info *bdi)
254{
255    return wb_has_dirty_io(&bdi->wb);
256}
257
258static void bdi_flush_io(struct backing_dev_info *bdi)
259{
260    struct writeback_control wbc = {
261        .sync_mode = WB_SYNC_NONE,
262        .older_than_this = NULL,
263        .range_cyclic = 1,
264        .nr_to_write = 1024,
265    };
266
267    writeback_inodes_wb(&bdi->wb, &wbc);
268}
269
270/*
271 * kupdated() used to do this. We cannot do it from the bdi_forker_thread()
272 * or we risk deadlocking on ->s_umount. The longer term solution would be
273 * to implement sync_supers_bdi() or similar and simply do it from the
274 * bdi writeback thread individually.
275 */
276static int bdi_sync_supers(void *unused)
277{
278    set_user_nice(current, 0);
279
280    while (!kthread_should_stop()) {
281        set_current_state(TASK_INTERRUPTIBLE);
282        schedule();
283
284        /*
285         * Do this periodically, like kupdated() did before.
286         */
287        sync_supers();
288    }
289
290    return 0;
291}
292
293void bdi_arm_supers_timer(void)
294{
295    unsigned long next;
296
297    if (!dirty_writeback_interval)
298        return;
299
300    next = msecs_to_jiffies(dirty_writeback_interval * 10) + jiffies;
301    mod_timer(&sync_supers_timer, round_jiffies_up(next));
302}
303
304static void sync_supers_timer_fn(unsigned long unused)
305{
306    wake_up_process(sync_supers_tsk);
307    bdi_arm_supers_timer();
308}
309
310static void wakeup_timer_fn(unsigned long data)
311{
312    struct backing_dev_info *bdi = (struct backing_dev_info *)data;
313
314    spin_lock_bh(&bdi->wb_lock);
315    if (bdi->wb.task) {
316        trace_writeback_wake_thread(bdi);
317        wake_up_process(bdi->wb.task);
318    } else {
319        /*
320         * When bdi tasks are inactive for long time, they are killed.
321         * In this case we have to wake-up the forker thread which
322         * should create and run the bdi thread.
323         */
324        trace_writeback_wake_forker_thread(bdi);
325        wake_up_process(default_backing_dev_info.wb.task);
326    }
327    spin_unlock_bh(&bdi->wb_lock);
328}
329
330/*
331 * This function is used when the first inode for this bdi is marked dirty. It
332 * wakes-up the corresponding bdi thread which should then take care of the
333 * periodic background write-out of dirty inodes. Since the write-out would
334 * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
335 * set up a timer which wakes the bdi thread up later.
336 *
337 * Note, we wouldn't bother setting up the timer, but this function is on the
338 * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
339 * by delaying the wake-up.
340 */
341void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
342{
343    unsigned long timeout;
344
345    timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
346    mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
347}
348
349/*
350 * Calculate the longest interval (jiffies) bdi threads are allowed to be
351 * inactive.
352 */
353static unsigned long bdi_longest_inactive(void)
354{
355    unsigned long interval;
356
357    interval = msecs_to_jiffies(dirty_writeback_interval * 10);
358    return max(5UL * 60 * HZ, interval);
359}
360
361static int bdi_forker_thread(void *ptr)
362{
363    struct bdi_writeback *me = ptr;
364
365    current->flags |= PF_FLUSHER | PF_SWAPWRITE;
366    set_freezable();
367
368    /*
369     * Our parent may run at a different priority, just set us to normal
370     */
371    set_user_nice(current, 0);
372
373    for (;;) {
374        struct task_struct *task = NULL;
375        struct backing_dev_info *bdi;
376        enum {
377            NO_ACTION, /* Nothing to do */
378            FORK_THREAD, /* Fork bdi thread */
379            KILL_THREAD, /* Kill inactive bdi thread */
380        } action = NO_ACTION;
381
382        /*
383         * Temporary measure, we want to make sure we don't see
384         * dirty data on the default backing_dev_info
385         */
386        if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) {
387            del_timer(&me->wakeup_timer);
388            wb_do_writeback(me, 0);
389        }
390
391        spin_lock_bh(&bdi_lock);
392        set_current_state(TASK_INTERRUPTIBLE);
393
394        list_for_each_entry(bdi, &bdi_list, bdi_list) {
395            bool have_dirty_io;
396
397            if (!bdi_cap_writeback_dirty(bdi) ||
398                 bdi_cap_flush_forker(bdi))
399                continue;
400
401            WARN(!test_bit(BDI_registered, &bdi->state),
402                 "bdi %p/%s is not registered!\n", bdi, bdi->name);
403
404            have_dirty_io = !list_empty(&bdi->work_list) ||
405                    wb_has_dirty_io(&bdi->wb);
406
407            /*
408             * If the bdi has work to do, but the thread does not
409             * exist - create it.
410             */
411            if (!bdi->wb.task && have_dirty_io) {
412                /*
413                 * Set the pending bit - if someone will try to
414                 * unregister this bdi - it'll wait on this bit.
415                 */
416                set_bit(BDI_pending, &bdi->state);
417                action = FORK_THREAD;
418                break;
419            }
420
421            spin_lock(&bdi->wb_lock);
422
423            /*
424             * If there is no work to do and the bdi thread was
425             * inactive long enough - kill it. The wb_lock is taken
426             * to make sure no-one adds more work to this bdi and
427             * wakes the bdi thread up.
428             */
429            if (bdi->wb.task && !have_dirty_io &&
430                time_after(jiffies, bdi->wb.last_active +
431                        bdi_longest_inactive())) {
432                task = bdi->wb.task;
433                bdi->wb.task = NULL;
434                spin_unlock(&bdi->wb_lock);
435                set_bit(BDI_pending, &bdi->state);
436                action = KILL_THREAD;
437                break;
438            }
439            spin_unlock(&bdi->wb_lock);
440        }
441        spin_unlock_bh(&bdi_lock);
442
443        /* Keep working if default bdi still has things to do */
444        if (!list_empty(&me->bdi->work_list))
445            __set_current_state(TASK_RUNNING);
446
447        switch (action) {
448        case FORK_THREAD:
449            __set_current_state(TASK_RUNNING);
450            task = kthread_create(bdi_writeback_thread, &bdi->wb,
451                          "flush-%s", dev_name(bdi->dev));
452            if (IS_ERR(task)) {
453                /*
454                 * If thread creation fails, force writeout of
455                 * the bdi from the thread.
456                 */
457                bdi_flush_io(bdi);
458            } else {
459                /*
460                 * The spinlock makes sure we do not lose
461                 * wake-ups when racing with 'bdi_queue_work()'.
462                 * And as soon as the bdi thread is visible, we
463                 * can start it.
464                 */
465                spin_lock_bh(&bdi->wb_lock);
466                bdi->wb.task = task;
467                spin_unlock_bh(&bdi->wb_lock);
468                wake_up_process(task);
469            }
470            break;
471
472        case KILL_THREAD:
473            __set_current_state(TASK_RUNNING);
474            kthread_stop(task);
475            break;
476
477        case NO_ACTION:
478            if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
479                /*
480                 * There are no dirty data. The only thing we
481                 * should now care about is checking for
482                 * inactive bdi threads and killing them. Thus,
483                 * let's sleep for longer time, save energy and
484                 * be friendly for battery-driven devices.
485                 */
486                schedule_timeout(bdi_longest_inactive());
487            else
488                schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
489            try_to_freeze();
490            /* Back to the main loop */
491            continue;
492        }
493
494        /*
495         * Clear pending bit and wakeup anybody waiting to tear us down.
496         */
497        clear_bit(BDI_pending, &bdi->state);
498        smp_mb__after_clear_bit();
499        wake_up_bit(&bdi->state, BDI_pending);
500    }
501
502    return 0;
503}
504
505/*
506 * Remove bdi from bdi_list, and ensure that it is no longer visible
507 */
508static void bdi_remove_from_list(struct backing_dev_info *bdi)
509{
510    spin_lock_bh(&bdi_lock);
511    list_del_rcu(&bdi->bdi_list);
512    spin_unlock_bh(&bdi_lock);
513
514    synchronize_rcu();
515}
516
517int bdi_register(struct backing_dev_info *bdi, struct device *parent,
518        const char *fmt, ...)
519{
520    va_list args;
521    struct device *dev;
522
523    if (bdi->dev) /* The driver needs to use separate queues per device */
524        return 0;
525
526    va_start(args, fmt);
527    dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
528    va_end(args);
529    if (IS_ERR(dev))
530        return PTR_ERR(dev);
531
532    bdi->dev = dev;
533
534    /*
535     * Just start the forker thread for our default backing_dev_info,
536     * and add other bdi's to the list. They will get a thread created
537     * on-demand when they need it.
538     */
539    if (bdi_cap_flush_forker(bdi)) {
540        struct bdi_writeback *wb = &bdi->wb;
541
542        wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s",
543                        dev_name(dev));
544        if (IS_ERR(wb->task))
545            return PTR_ERR(wb->task);
546    }
547
548    bdi_debug_register(bdi, dev_name(dev));
549    set_bit(BDI_registered, &bdi->state);
550
551    spin_lock_bh(&bdi_lock);
552    list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
553    spin_unlock_bh(&bdi_lock);
554
555    trace_writeback_bdi_register(bdi);
556    return 0;
557}
558EXPORT_SYMBOL(bdi_register);
559
560int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
561{
562    return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
563}
564EXPORT_SYMBOL(bdi_register_dev);
565
566/*
567 * Remove bdi from the global list and shutdown any threads we have running
568 */
569static void bdi_wb_shutdown(struct backing_dev_info *bdi)
570{
571    if (!bdi_cap_writeback_dirty(bdi))
572        return;
573
574    /*
575     * Make sure nobody finds us on the bdi_list anymore
576     */
577    bdi_remove_from_list(bdi);
578
579    /*
580     * If setup is pending, wait for that to complete first
581     */
582    wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
583            TASK_UNINTERRUPTIBLE);
584
585    /*
586     * Finally, kill the kernel thread. We don't need to be RCU
587     * safe anymore, since the bdi is gone from visibility. Force
588     * unfreeze of the thread before calling kthread_stop(), otherwise
589     * it would never exet if it is currently stuck in the refrigerator.
590     */
591    if (bdi->wb.task) {
592        thaw_process(bdi->wb.task);
593        kthread_stop(bdi->wb.task);
594    }
595}
596
597/*
598 * This bdi is going away now, make sure that no super_blocks point to it
599 */
600static void bdi_prune_sb(struct backing_dev_info *bdi)
601{
602    struct super_block *sb;
603
604    spin_lock(&sb_lock);
605    list_for_each_entry(sb, &super_blocks, s_list) {
606        if (sb->s_bdi == bdi)
607            sb->s_bdi = NULL;
608    }
609    spin_unlock(&sb_lock);
610}
611
612void bdi_unregister(struct backing_dev_info *bdi)
613{
614    if (bdi->dev) {
615        trace_writeback_bdi_unregister(bdi);
616        bdi_prune_sb(bdi);
617        del_timer_sync(&bdi->wb.wakeup_timer);
618
619        if (!bdi_cap_flush_forker(bdi))
620            bdi_wb_shutdown(bdi);
621        bdi_debug_unregister(bdi);
622        device_unregister(bdi->dev);
623        bdi->dev = NULL;
624    }
625}
626EXPORT_SYMBOL(bdi_unregister);
627
628static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
629{
630    memset(wb, 0, sizeof(*wb));
631
632    wb->bdi = bdi;
633    wb->last_old_flush = jiffies;
634    INIT_LIST_HEAD(&wb->b_dirty);
635    INIT_LIST_HEAD(&wb->b_io);
636    INIT_LIST_HEAD(&wb->b_more_io);
637    setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
638}
639
640int bdi_init(struct backing_dev_info *bdi)
641{
642    int i, err;
643
644    bdi->dev = NULL;
645
646    bdi->min_ratio = 0;
647    bdi->max_ratio = 100;
648    bdi->max_prop_frac = PROP_FRAC_BASE;
649    spin_lock_init(&bdi->wb_lock);
650    INIT_LIST_HEAD(&bdi->bdi_list);
651    INIT_LIST_HEAD(&bdi->work_list);
652
653    bdi_wb_init(&bdi->wb, bdi);
654
655    for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
656        err = percpu_counter_init(&bdi->bdi_stat[i], 0);
657        if (err)
658            goto err;
659    }
660
661    bdi->dirty_exceeded = 0;
662    err = prop_local_init_percpu(&bdi->completions);
663
664    if (err) {
665err:
666        while (i--)
667            percpu_counter_destroy(&bdi->bdi_stat[i]);
668    }
669
670    return err;
671}
672EXPORT_SYMBOL(bdi_init);
673
674void bdi_destroy(struct backing_dev_info *bdi)
675{
676    int i;
677
678    /*
679     * Splice our entries to the default_backing_dev_info, if this
680     * bdi disappears
681     */
682    if (bdi_has_dirty_io(bdi)) {
683        struct bdi_writeback *dst = &default_backing_dev_info.wb;
684
685        spin_lock(&inode_lock);
686        list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
687        list_splice(&bdi->wb.b_io, &dst->b_io);
688        list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
689        spin_unlock(&inode_lock);
690    }
691
692    bdi_unregister(bdi);
693
694    for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
695        percpu_counter_destroy(&bdi->bdi_stat[i]);
696
697    prop_local_destroy_percpu(&bdi->completions);
698}
699EXPORT_SYMBOL(bdi_destroy);
700
701/*
702 * For use from filesystems to quickly init and register a bdi associated
703 * with dirty writeback
704 */
705int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
706               unsigned int cap)
707{
708    char tmp[32];
709    int err;
710
711    bdi->name = name;
712    bdi->capabilities = cap;
713    err = bdi_init(bdi);
714    if (err)
715        return err;
716
717    sprintf(tmp, "%.28s%s", name, "-%d");
718    err = bdi_register(bdi, NULL, tmp, atomic_long_inc_return(&bdi_seq));
719    if (err) {
720        bdi_destroy(bdi);
721        return err;
722    }
723
724    return 0;
725}
726EXPORT_SYMBOL(bdi_setup_and_register);
727
728static wait_queue_head_t congestion_wqh[2] = {
729        __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
730        __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
731    };
732
733void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
734{
735    enum bdi_state bit;
736    wait_queue_head_t *wqh = &congestion_wqh[sync];
737
738    bit = sync ? BDI_sync_congested : BDI_async_congested;
739    clear_bit(bit, &bdi->state);
740    smp_mb__after_clear_bit();
741    if (waitqueue_active(wqh))
742        wake_up(wqh);
743}
744EXPORT_SYMBOL(clear_bdi_congested);
745
746void set_bdi_congested(struct backing_dev_info *bdi, int sync)
747{
748    enum bdi_state bit;
749
750    bit = sync ? BDI_sync_congested : BDI_async_congested;
751    set_bit(bit, &bdi->state);
752}
753EXPORT_SYMBOL(set_bdi_congested);
754
755/**
756 * congestion_wait - wait for a backing_dev to become uncongested
757 * @sync: SYNC or ASYNC IO
758 * @timeout: timeout in jiffies
759 *
760 * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
761 * write congestion. If no backing_devs are congested then just wait for the
762 * next write to be completed.
763 */
764long congestion_wait(int sync, long timeout)
765{
766    long ret;
767    DEFINE_WAIT(wait);
768    wait_queue_head_t *wqh = &congestion_wqh[sync];
769
770    prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
771    ret = io_schedule_timeout(timeout);
772    finish_wait(wqh, &wait);
773    return ret;
774}
775EXPORT_SYMBOL(congestion_wait);
776
777

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