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
14static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
15
16void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
17{
18}
19EXPORT_SYMBOL(default_unplug_io_fn);
20
21struct backing_dev_info default_backing_dev_info = {
22    .name = "default",
23    .ra_pages = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
24    .state = 0,
25    .capabilities = BDI_CAP_MAP_COPY,
26    .unplug_io_fn = default_unplug_io_fn,
27};
28EXPORT_SYMBOL_GPL(default_backing_dev_info);
29
30struct backing_dev_info noop_backing_dev_info = {
31    .name = "noop",
32};
33EXPORT_SYMBOL_GPL(noop_backing_dev_info);
34
35static struct class *bdi_class;
36
37/*
38 * bdi_lock protects updates to bdi_list and bdi_pending_list, as well as
39 * reader side protection for bdi_pending_list. bdi_list has RCU reader side
40 * locking.
41 */
42DEFINE_SPINLOCK(bdi_lock);
43LIST_HEAD(bdi_list);
44LIST_HEAD(bdi_pending_list);
45
46static struct task_struct *sync_supers_tsk;
47static struct timer_list sync_supers_timer;
48
49static int bdi_sync_supers(void *);
50static void sync_supers_timer_fn(unsigned long);
51
52static void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
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;
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    /*
76     * inode lock is enough here, the bdi->wb_list is protected by
77     * RCU on the reader side
78     */
79    nr_wb = nr_dirty = nr_io = nr_more_io = 0;
80    spin_lock(&inode_lock);
81    list_for_each_entry(wb, &bdi->wb_list, list) {
82        nr_wb++;
83        list_for_each_entry(inode, &wb->b_dirty, i_list)
84            nr_dirty++;
85        list_for_each_entry(inode, &wb->b_io, i_list)
86            nr_io++;
87        list_for_each_entry(inode, &wb->b_more_io, i_list)
88            nr_more_io++;
89    }
90    spin_unlock(&inode_lock);
91
92    get_dirty_limits(&background_thresh, &dirty_thresh, &bdi_thresh, bdi);
93
94#define K(x) ((x) << (PAGE_SHIFT - 10))
95    seq_printf(m,
96           "BdiWriteback: %8lu kB\n"
97           "BdiReclaimable: %8lu kB\n"
98           "BdiDirtyThresh: %8lu kB\n"
99           "DirtyThresh: %8lu kB\n"
100           "BackgroundThresh: %8lu kB\n"
101           "WritebackThreads: %8lu\n"
102           "b_dirty: %8lu\n"
103           "b_io: %8lu\n"
104           "b_more_io: %8lu\n"
105           "bdi_list: %8u\n"
106           "state: %8lx\n"
107           "wb_list: %8u\n",
108           (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
109           (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
110           K(bdi_thresh), K(dirty_thresh),
111           K(background_thresh), nr_wb, nr_dirty, nr_io, nr_more_io,
112           !list_empty(&bdi->bdi_list), bdi->state,
113           !list_empty(&bdi->wb_list));
114#undef K
115
116    return 0;
117}
118
119static int bdi_debug_stats_open(struct inode *inode, struct file *file)
120{
121    return single_open(file, bdi_debug_stats_show, inode->i_private);
122}
123
124static const struct file_operations bdi_debug_stats_fops = {
125    .open = bdi_debug_stats_open,
126    .read = seq_read,
127    .llseek = seq_lseek,
128    .release = single_release,
129};
130
131static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
132{
133    bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
134    bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
135                           bdi, &bdi_debug_stats_fops);
136}
137
138static void bdi_debug_unregister(struct backing_dev_info *bdi)
139{
140    debugfs_remove(bdi->debug_stats);
141    debugfs_remove(bdi->debug_dir);
142}
143#else
144static inline void bdi_debug_init(void)
145{
146}
147static inline void bdi_debug_register(struct backing_dev_info *bdi,
148                      const char *name)
149{
150}
151static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
152{
153}
154#endif
155
156static ssize_t read_ahead_kb_store(struct device *dev,
157                  struct device_attribute *attr,
158                  const char *buf, size_t count)
159{
160    struct backing_dev_info *bdi = dev_get_drvdata(dev);
161    char *end;
162    unsigned long read_ahead_kb;
163    ssize_t ret = -EINVAL;
164
165    read_ahead_kb = simple_strtoul(buf, &end, 10);
166    if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
167        bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
168        ret = count;
169    }
170    return ret;
171}
172
173#define K(pages) ((pages) << (PAGE_SHIFT - 10))
174
175#define BDI_SHOW(name, expr) \
176static ssize_t name##_show(struct device *dev, \
177               struct device_attribute *attr, char *page) \
178{ \
179    struct backing_dev_info *bdi = dev_get_drvdata(dev); \
180                                    \
181    return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr); \
182}
183
184BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
185
186static ssize_t min_ratio_store(struct device *dev,
187        struct device_attribute *attr, const char *buf, size_t count)
188{
189    struct backing_dev_info *bdi = dev_get_drvdata(dev);
190    char *end;
191    unsigned int ratio;
192    ssize_t ret = -EINVAL;
193
194    ratio = simple_strtoul(buf, &end, 10);
195    if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
196        ret = bdi_set_min_ratio(bdi, ratio);
197        if (!ret)
198            ret = count;
199    }
200    return ret;
201}
202BDI_SHOW(min_ratio, bdi->min_ratio)
203
204static ssize_t max_ratio_store(struct device *dev,
205        struct device_attribute *attr, const char *buf, size_t count)
206{
207    struct backing_dev_info *bdi = dev_get_drvdata(dev);
208    char *end;
209    unsigned int ratio;
210    ssize_t ret = -EINVAL;
211
212    ratio = simple_strtoul(buf, &end, 10);
213    if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
214        ret = bdi_set_max_ratio(bdi, ratio);
215        if (!ret)
216            ret = count;
217    }
218    return ret;
219}
220BDI_SHOW(max_ratio, bdi->max_ratio)
221
222#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
223
224static struct device_attribute bdi_dev_attrs[] = {
225    __ATTR_RW(read_ahead_kb),
226    __ATTR_RW(min_ratio),
227    __ATTR_RW(max_ratio),
228    __ATTR_NULL,
229};
230
231static __init int bdi_class_init(void)
232{
233    bdi_class = class_create(THIS_MODULE, "bdi");
234    if (IS_ERR(bdi_class))
235        return PTR_ERR(bdi_class);
236
237    bdi_class->dev_attrs = bdi_dev_attrs;
238    bdi_debug_init();
239    return 0;
240}
241postcore_initcall(bdi_class_init);
242
243static int __init default_bdi_init(void)
244{
245    int err;
246
247    sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
248    BUG_ON(IS_ERR(sync_supers_tsk));
249
250    init_timer(&sync_supers_timer);
251    setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
252    bdi_arm_supers_timer();
253
254    err = bdi_init(&default_backing_dev_info);
255    if (!err)
256        bdi_register(&default_backing_dev_info, NULL, "default");
257
258    return err;
259}
260subsys_initcall(default_bdi_init);
261
262static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
263{
264    memset(wb, 0, sizeof(*wb));
265
266    wb->bdi = bdi;
267    wb->last_old_flush = jiffies;
268    INIT_LIST_HEAD(&wb->b_dirty);
269    INIT_LIST_HEAD(&wb->b_io);
270    INIT_LIST_HEAD(&wb->b_more_io);
271}
272
273static void bdi_task_init(struct backing_dev_info *bdi,
274              struct bdi_writeback *wb)
275{
276    struct task_struct *tsk = current;
277
278    spin_lock(&bdi->wb_lock);
279    list_add_tail_rcu(&wb->list, &bdi->wb_list);
280    spin_unlock(&bdi->wb_lock);
281
282    tsk->flags |= PF_FLUSHER | PF_SWAPWRITE;
283    set_freezable();
284
285    /*
286     * Our parent may run at a different priority, just set us to normal
287     */
288    set_user_nice(tsk, 0);
289}
290
291static int bdi_start_fn(void *ptr)
292{
293    struct bdi_writeback *wb = ptr;
294    struct backing_dev_info *bdi = wb->bdi;
295    int ret;
296
297    /*
298     * Add us to the active bdi_list
299     */
300    spin_lock_bh(&bdi_lock);
301    list_add_rcu(&bdi->bdi_list, &bdi_list);
302    spin_unlock_bh(&bdi_lock);
303
304    bdi_task_init(bdi, wb);
305
306    /*
307     * Clear pending bit and wakeup anybody waiting to tear us down
308     */
309    clear_bit(BDI_pending, &bdi->state);
310    smp_mb__after_clear_bit();
311    wake_up_bit(&bdi->state, BDI_pending);
312
313    ret = bdi_writeback_task(wb);
314
315    /*
316     * Remove us from the list
317     */
318    spin_lock(&bdi->wb_lock);
319    list_del_rcu(&wb->list);
320    spin_unlock(&bdi->wb_lock);
321
322    /*
323     * Flush any work that raced with us exiting. No new work
324     * will be added, since this bdi isn't discoverable anymore.
325     */
326    if (!list_empty(&bdi->work_list))
327        wb_do_writeback(wb, 1);
328
329    wb->task = NULL;
330    return ret;
331}
332
333int bdi_has_dirty_io(struct backing_dev_info *bdi)
334{
335    return wb_has_dirty_io(&bdi->wb);
336}
337
338static void bdi_flush_io(struct backing_dev_info *bdi)
339{
340    struct writeback_control wbc = {
341        .sync_mode = WB_SYNC_NONE,
342        .older_than_this = NULL,
343        .range_cyclic = 1,
344        .nr_to_write = 1024,
345    };
346
347    writeback_inodes_wb(&bdi->wb, &wbc);
348}
349
350/*
351 * kupdated() used to do this. We cannot do it from the bdi_forker_task()
352 * or we risk deadlocking on ->s_umount. The longer term solution would be
353 * to implement sync_supers_bdi() or similar and simply do it from the
354 * bdi writeback tasks individually.
355 */
356static int bdi_sync_supers(void *unused)
357{
358    set_user_nice(current, 0);
359
360    while (!kthread_should_stop()) {
361        set_current_state(TASK_INTERRUPTIBLE);
362        schedule();
363
364        /*
365         * Do this periodically, like kupdated() did before.
366         */
367        sync_supers();
368    }
369
370    return 0;
371}
372
373void bdi_arm_supers_timer(void)
374{
375    unsigned long next;
376
377    if (!dirty_writeback_interval)
378        return;
379
380    next = msecs_to_jiffies(dirty_writeback_interval * 10) + jiffies;
381    mod_timer(&sync_supers_timer, round_jiffies_up(next));
382}
383
384static void sync_supers_timer_fn(unsigned long unused)
385{
386    wake_up_process(sync_supers_tsk);
387    bdi_arm_supers_timer();
388}
389
390static int bdi_forker_task(void *ptr)
391{
392    struct bdi_writeback *me = ptr;
393
394    bdi_task_init(me->bdi, me);
395
396    for (;;) {
397        struct backing_dev_info *bdi, *tmp;
398        struct bdi_writeback *wb;
399
400        /*
401         * Temporary measure, we want to make sure we don't see
402         * dirty data on the default backing_dev_info
403         */
404        if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list))
405            wb_do_writeback(me, 0);
406
407        spin_lock_bh(&bdi_lock);
408
409        /*
410         * Check if any existing bdi's have dirty data without
411         * a thread registered. If so, set that up.
412         */
413        list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
414            if (bdi->wb.task)
415                continue;
416            if (list_empty(&bdi->work_list) &&
417                !bdi_has_dirty_io(bdi))
418                continue;
419
420            bdi_add_default_flusher_task(bdi);
421        }
422
423        set_current_state(TASK_INTERRUPTIBLE);
424
425        if (list_empty(&bdi_pending_list)) {
426            unsigned long wait;
427
428            spin_unlock_bh(&bdi_lock);
429            wait = msecs_to_jiffies(dirty_writeback_interval * 10);
430            if (wait)
431                schedule_timeout(wait);
432            else
433                schedule();
434            try_to_freeze();
435            continue;
436        }
437
438        __set_current_state(TASK_RUNNING);
439
440        /*
441         * This is our real job - check for pending entries in
442         * bdi_pending_list, and create the tasks that got added
443         */
444        bdi = list_entry(bdi_pending_list.next, struct backing_dev_info,
445                 bdi_list);
446        list_del_init(&bdi->bdi_list);
447        spin_unlock_bh(&bdi_lock);
448
449        wb = &bdi->wb;
450        wb->task = kthread_run(bdi_start_fn, wb, "flush-%s",
451                    dev_name(bdi->dev));
452        /*
453         * If task creation fails, then readd the bdi to
454         * the pending list and force writeout of the bdi
455         * from this forker thread. That will free some memory
456         * and we can try again.
457         */
458        if (IS_ERR(wb->task)) {
459            wb->task = NULL;
460
461            /*
462             * Add this 'bdi' to the back, so we get
463             * a chance to flush other bdi's to free
464             * memory.
465             */
466            spin_lock_bh(&bdi_lock);
467            list_add_tail(&bdi->bdi_list, &bdi_pending_list);
468            spin_unlock_bh(&bdi_lock);
469
470            bdi_flush_io(bdi);
471        }
472    }
473
474    return 0;
475}
476
477static void bdi_add_to_pending(struct rcu_head *head)
478{
479    struct backing_dev_info *bdi;
480
481    bdi = container_of(head, struct backing_dev_info, rcu_head);
482    INIT_LIST_HEAD(&bdi->bdi_list);
483
484    spin_lock(&bdi_lock);
485    list_add_tail(&bdi->bdi_list, &bdi_pending_list);
486    spin_unlock(&bdi_lock);
487
488    /*
489     * We are now on the pending list, wake up bdi_forker_task()
490     * to finish the job and add us back to the active bdi_list
491     */
492    wake_up_process(default_backing_dev_info.wb.task);
493}
494
495/*
496 * Add the default flusher task that gets created for any bdi
497 * that has dirty data pending writeout
498 */
499void static bdi_add_default_flusher_task(struct backing_dev_info *bdi)
500{
501    if (!bdi_cap_writeback_dirty(bdi))
502        return;
503
504    if (WARN_ON(!test_bit(BDI_registered, &bdi->state))) {
505        printk(KERN_ERR "bdi %p/%s is not registered!\n",
506                            bdi, bdi->name);
507        return;
508    }
509
510    /*
511     * Check with the helper whether to proceed adding a task. Will only
512     * abort if we two or more simultanous calls to
513     * bdi_add_default_flusher_task() occured, further additions will block
514     * waiting for previous additions to finish.
515     */
516    if (!test_and_set_bit(BDI_pending, &bdi->state)) {
517        list_del_rcu(&bdi->bdi_list);
518
519        /*
520         * We must wait for the current RCU period to end before
521         * moving to the pending list. So schedule that operation
522         * from an RCU callback.
523         */
524        call_rcu(&bdi->rcu_head, bdi_add_to_pending);
525    }
526}
527
528/*
529 * Remove bdi from bdi_list, and ensure that it is no longer visible
530 */
531static void bdi_remove_from_list(struct backing_dev_info *bdi)
532{
533    spin_lock_bh(&bdi_lock);
534    list_del_rcu(&bdi->bdi_list);
535    spin_unlock_bh(&bdi_lock);
536
537    synchronize_rcu();
538}
539
540int bdi_register(struct backing_dev_info *bdi, struct device *parent,
541        const char *fmt, ...)
542{
543    va_list args;
544    int ret = 0;
545    struct device *dev;
546
547    if (bdi->dev) /* The driver needs to use separate queues per device */
548        goto exit;
549
550    va_start(args, fmt);
551    dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
552    va_end(args);
553    if (IS_ERR(dev)) {
554        ret = PTR_ERR(dev);
555        goto exit;
556    }
557
558    spin_lock_bh(&bdi_lock);
559    list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
560    spin_unlock_bh(&bdi_lock);
561
562    bdi->dev = dev;
563
564    /*
565     * Just start the forker thread for our default backing_dev_info,
566     * and add other bdi's to the list. They will get a thread created
567     * on-demand when they need it.
568     */
569    if (bdi_cap_flush_forker(bdi)) {
570        struct bdi_writeback *wb = &bdi->wb;
571
572        wb->task = kthread_run(bdi_forker_task, wb, "bdi-%s",
573                        dev_name(dev));
574        if (IS_ERR(wb->task)) {
575            wb->task = NULL;
576            ret = -ENOMEM;
577
578            bdi_remove_from_list(bdi);
579            goto exit;
580        }
581    }
582
583    bdi_debug_register(bdi, dev_name(dev));
584    set_bit(BDI_registered, &bdi->state);
585exit:
586    return ret;
587}
588EXPORT_SYMBOL(bdi_register);
589
590int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
591{
592    return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
593}
594EXPORT_SYMBOL(bdi_register_dev);
595
596/*
597 * Remove bdi from the global list and shutdown any threads we have running
598 */
599static void bdi_wb_shutdown(struct backing_dev_info *bdi)
600{
601    struct bdi_writeback *wb;
602
603    if (!bdi_cap_writeback_dirty(bdi))
604        return;
605
606    /*
607     * If setup is pending, wait for that to complete first
608     */
609    wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
610            TASK_UNINTERRUPTIBLE);
611
612    /*
613     * Make sure nobody finds us on the bdi_list anymore
614     */
615    bdi_remove_from_list(bdi);
616
617    /*
618     * Finally, kill the kernel threads. We don't need to be RCU
619     * safe anymore, since the bdi is gone from visibility. Force
620     * unfreeze of the thread before calling kthread_stop(), otherwise
621     * it would never exet if it is currently stuck in the refrigerator.
622     */
623    list_for_each_entry(wb, &bdi->wb_list, list) {
624        thaw_process(wb->task);
625        kthread_stop(wb->task);
626    }
627}
628
629/*
630 * This bdi is going away now, make sure that no super_blocks point to it
631 */
632static void bdi_prune_sb(struct backing_dev_info *bdi)
633{
634    struct super_block *sb;
635
636    spin_lock(&sb_lock);
637    list_for_each_entry(sb, &super_blocks, s_list) {
638        if (sb->s_bdi == bdi)
639            sb->s_bdi = NULL;
640    }
641    spin_unlock(&sb_lock);
642}
643
644void bdi_unregister(struct backing_dev_info *bdi)
645{
646    if (bdi->dev) {
647        bdi_prune_sb(bdi);
648
649        if (!bdi_cap_flush_forker(bdi))
650            bdi_wb_shutdown(bdi);
651        bdi_debug_unregister(bdi);
652        device_unregister(bdi->dev);
653        bdi->dev = NULL;
654    }
655}
656EXPORT_SYMBOL(bdi_unregister);
657
658int bdi_init(struct backing_dev_info *bdi)
659{
660    int i, err;
661
662    bdi->dev = NULL;
663
664    bdi->min_ratio = 0;
665    bdi->max_ratio = 100;
666    bdi->max_prop_frac = PROP_FRAC_BASE;
667    spin_lock_init(&bdi->wb_lock);
668    INIT_RCU_HEAD(&bdi->rcu_head);
669    INIT_LIST_HEAD(&bdi->bdi_list);
670    INIT_LIST_HEAD(&bdi->wb_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    err = prop_local_init_percpu(&bdi->completions);
683
684    if (err) {
685err:
686        while (i--)
687            percpu_counter_destroy(&bdi->bdi_stat[i]);
688    }
689
690    return err;
691}
692EXPORT_SYMBOL(bdi_init);
693
694void bdi_destroy(struct backing_dev_info *bdi)
695{
696    int i;
697
698    /*
699     * Splice our entries to the default_backing_dev_info, if this
700     * bdi disappears
701     */
702    if (bdi_has_dirty_io(bdi)) {
703        struct bdi_writeback *dst = &default_backing_dev_info.wb;
704
705        spin_lock(&inode_lock);
706        list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
707        list_splice(&bdi->wb.b_io, &dst->b_io);
708        list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
709        spin_unlock(&inode_lock);
710    }
711
712    bdi_unregister(bdi);
713
714    for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
715        percpu_counter_destroy(&bdi->bdi_stat[i]);
716
717    prop_local_destroy_percpu(&bdi->completions);
718}
719EXPORT_SYMBOL(bdi_destroy);
720
721/*
722 * For use from filesystems to quickly init and register a bdi associated
723 * with dirty writeback
724 */
725int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
726               unsigned int cap)
727{
728    char tmp[32];
729    int err;
730
731    bdi->name = name;
732    bdi->capabilities = cap;
733    err = bdi_init(bdi);
734    if (err)
735        return err;
736
737    sprintf(tmp, "%.28s%s", name, "-%d");
738    err = bdi_register(bdi, NULL, tmp, atomic_long_inc_return(&bdi_seq));
739    if (err) {
740        bdi_destroy(bdi);
741        return err;
742    }
743
744    return 0;
745}
746EXPORT_SYMBOL(bdi_setup_and_register);
747
748static wait_queue_head_t congestion_wqh[2] = {
749        __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
750        __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
751    };
752
753void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
754{
755    enum bdi_state bit;
756    wait_queue_head_t *wqh = &congestion_wqh[sync];
757
758    bit = sync ? BDI_sync_congested : BDI_async_congested;
759    clear_bit(bit, &bdi->state);
760    smp_mb__after_clear_bit();
761    if (waitqueue_active(wqh))
762        wake_up(wqh);
763}
764EXPORT_SYMBOL(clear_bdi_congested);
765
766void set_bdi_congested(struct backing_dev_info *bdi, int sync)
767{
768    enum bdi_state bit;
769
770    bit = sync ? BDI_sync_congested : BDI_async_congested;
771    set_bit(bit, &bdi->state);
772}
773EXPORT_SYMBOL(set_bdi_congested);
774
775/**
776 * congestion_wait - wait for a backing_dev to become uncongested
777 * @sync: SYNC or ASYNC IO
778 * @timeout: timeout in jiffies
779 *
780 * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
781 * write congestion. If no backing_devs are congested then just wait for the
782 * next write to be completed.
783 */
784long congestion_wait(int sync, long timeout)
785{
786    long ret;
787    DEFINE_WAIT(wait);
788    wait_queue_head_t *wqh = &congestion_wqh[sync];
789
790    prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
791    ret = io_schedule_timeout(timeout);
792    finish_wait(wqh, &wait);
793    return ret;
794}
795EXPORT_SYMBOL(congestion_wait);
796
797

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