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
17struct 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};
23EXPORT_SYMBOL_GPL(default_backing_dev_info);
24
25struct backing_dev_info noop_backing_dev_info = {
26    .name = "noop",
27    .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK,
28};
29EXPORT_SYMBOL_GPL(noop_backing_dev_info);
30
31static 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 */
38DEFINE_SPINLOCK(bdi_lock);
39LIST_HEAD(bdi_list);
40LIST_HEAD(bdi_pending_list);
41
42static struct task_struct *sync_supers_tsk;
43static struct timer_list sync_supers_timer;
44
45static int bdi_sync_supers(void *);
46static 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
52static struct dentry *bdi_debug_root;
53
54static void bdi_debug_init(void)
55{
56    bdi_debug_root = debugfs_create_dir("bdi", NULL);
57}
58
59static 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;
67    struct inode *inode;
68
69    nr_dirty = nr_io = nr_more_io = 0;
70    spin_lock(&inode_wb_list_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_wb_list_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
104static 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
109static 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
116static 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
123static 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
129static inline void bdi_debug_init(void)
130{
131}
132static inline void bdi_debug_register(struct backing_dev_info *bdi,
133                      const char *name)
134{
135}
136static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
137{
138}
139#endif
140
141static 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) \
161static 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
169BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
170
171static 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}
187BDI_SHOW(min_ratio, bdi->min_ratio)
188
189static 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}
205BDI_SHOW(max_ratio, bdi->max_ratio)
206
207#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
208
209static 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
216static __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}
226postcore_initcall(bdi_class_init);
227
228static 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}
245subsys_initcall(default_bdi_init);
246
247int bdi_has_dirty_io(struct backing_dev_info *bdi)
248{
249    return wb_has_dirty_io(&bdi->wb);
250}
251
252static 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 */
270static 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
287void 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
298static void sync_supers_timer_fn(unsigned long unused)
299{
300    wake_up_process(sync_supers_tsk);
301    bdi_arm_supers_timer();
302}
303
304static 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 */
335void 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 */
347static 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
355static 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 */
502static 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
511int 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}
552EXPORT_SYMBOL(bdi_register);
553
554int 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}
558EXPORT_SYMBOL(bdi_register_dev);
559
560/*
561 * Remove bdi from the global list and shutdown any threads we have running
562 */
563static 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 */
594static 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
606void 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}
620EXPORT_SYMBOL(bdi_unregister);
621
622static 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
634int 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) {
659err:
660        while (i--)
661            percpu_counter_destroy(&bdi->bdi_stat[i]);
662    }
663
664    return err;
665}
666EXPORT_SYMBOL(bdi_init);
667
668void 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_wb_list_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_wb_list_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}
693EXPORT_SYMBOL(bdi_destroy);
694
695/*
696 * For use from filesystems to quickly init and register a bdi associated
697 * with dirty writeback
698 */
699int 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}
720EXPORT_SYMBOL(bdi_setup_and_register);
721
722static wait_queue_head_t congestion_wqh[2] = {
723        __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
724        __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
725    };
726static atomic_t nr_bdi_congested[2];
727
728void 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}
740EXPORT_SYMBOL(clear_bdi_congested);
741
742void 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}
750EXPORT_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 */
761long 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}
777EXPORT_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 absence 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 */
797long 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
826out:
827    trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
828                    jiffies_to_usecs(jiffies - start));
829
830    return ret;
831}
832EXPORT_SYMBOL(wait_iff_congested);
833

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