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
48void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
49{
50    if (wb1 < wb2) {
51        spin_lock(&wb1->list_lock);
52        spin_lock_nested(&wb2->list_lock, 1);
53    } else {
54        spin_lock(&wb2->list_lock);
55        spin_lock_nested(&wb1->list_lock, 1);
56    }
57}
58
59#ifdef CONFIG_DEBUG_FS
60#include <linux/debugfs.h>
61#include <linux/seq_file.h>
62
63static struct dentry *bdi_debug_root;
64
65static void bdi_debug_init(void)
66{
67    bdi_debug_root = debugfs_create_dir("bdi", NULL);
68}
69
70static int bdi_debug_stats_show(struct seq_file *m, void *v)
71{
72    struct backing_dev_info *bdi = m->private;
73    struct bdi_writeback *wb = &bdi->wb;
74    unsigned long background_thresh;
75    unsigned long dirty_thresh;
76    unsigned long bdi_thresh;
77    unsigned long nr_dirty, nr_io, nr_more_io;
78    struct inode *inode;
79
80    nr_dirty = nr_io = nr_more_io = 0;
81    spin_lock(&wb->list_lock);
82    list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
83        nr_dirty++;
84    list_for_each_entry(inode, &wb->b_io, i_wb_list)
85        nr_io++;
86    list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
87        nr_more_io++;
88    spin_unlock(&wb->list_lock);
89
90    global_dirty_limits(&background_thresh, &dirty_thresh);
91    bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
92
93#define K(x) ((x) << (PAGE_SHIFT - 10))
94    seq_printf(m,
95           "BdiWriteback: %10lu kB\n"
96           "BdiReclaimable: %10lu kB\n"
97           "BdiDirtyThresh: %10lu kB\n"
98           "DirtyThresh: %10lu kB\n"
99           "BackgroundThresh: %10lu kB\n"
100           "BdiDirtied: %10lu kB\n"
101           "BdiWritten: %10lu kB\n"
102           "BdiWriteBandwidth: %10lu kBps\n"
103           "b_dirty: %10lu\n"
104           "b_io: %10lu\n"
105           "b_more_io: %10lu\n"
106           "bdi_list: %10u\n"
107           "state: %10lx\n",
108           (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
109           (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
110           K(bdi_thresh),
111           K(dirty_thresh),
112           K(background_thresh),
113           (unsigned long) K(bdi_stat(bdi, BDI_DIRTIED)),
114           (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)),
115           (unsigned long) K(bdi->write_bandwidth),
116           nr_dirty,
117           nr_io,
118           nr_more_io,
119           !list_empty(&bdi->bdi_list), bdi->state);
120#undef K
121
122    return 0;
123}
124
125static int bdi_debug_stats_open(struct inode *inode, struct file *file)
126{
127    return single_open(file, bdi_debug_stats_show, inode->i_private);
128}
129
130static const struct file_operations bdi_debug_stats_fops = {
131    .open = bdi_debug_stats_open,
132    .read = seq_read,
133    .llseek = seq_lseek,
134    .release = single_release,
135};
136
137static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
138{
139    bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
140    bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
141                           bdi, &bdi_debug_stats_fops);
142}
143
144static void bdi_debug_unregister(struct backing_dev_info *bdi)
145{
146    debugfs_remove(bdi->debug_stats);
147    debugfs_remove(bdi->debug_dir);
148}
149#else
150static inline void bdi_debug_init(void)
151{
152}
153static inline void bdi_debug_register(struct backing_dev_info *bdi,
154                      const char *name)
155{
156}
157static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
158{
159}
160#endif
161
162static ssize_t read_ahead_kb_store(struct device *dev,
163                  struct device_attribute *attr,
164                  const char *buf, size_t count)
165{
166    struct backing_dev_info *bdi = dev_get_drvdata(dev);
167    char *end;
168    unsigned long read_ahead_kb;
169    ssize_t ret = -EINVAL;
170
171    read_ahead_kb = simple_strtoul(buf, &end, 10);
172    if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
173        bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
174        ret = count;
175    }
176    return ret;
177}
178
179#define K(pages) ((pages) << (PAGE_SHIFT - 10))
180
181#define BDI_SHOW(name, expr) \
182static ssize_t name##_show(struct device *dev, \
183               struct device_attribute *attr, char *page) \
184{ \
185    struct backing_dev_info *bdi = dev_get_drvdata(dev); \
186                                    \
187    return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr); \
188}
189
190BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
191
192static ssize_t min_ratio_store(struct device *dev,
193        struct device_attribute *attr, const char *buf, size_t count)
194{
195    struct backing_dev_info *bdi = dev_get_drvdata(dev);
196    char *end;
197    unsigned int ratio;
198    ssize_t ret = -EINVAL;
199
200    ratio = simple_strtoul(buf, &end, 10);
201    if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
202        ret = bdi_set_min_ratio(bdi, ratio);
203        if (!ret)
204            ret = count;
205    }
206    return ret;
207}
208BDI_SHOW(min_ratio, bdi->min_ratio)
209
210static ssize_t max_ratio_store(struct device *dev,
211        struct device_attribute *attr, const char *buf, size_t count)
212{
213    struct backing_dev_info *bdi = dev_get_drvdata(dev);
214    char *end;
215    unsigned int ratio;
216    ssize_t ret = -EINVAL;
217
218    ratio = simple_strtoul(buf, &end, 10);
219    if (*buf && (end[0] == '\0' || (end[0] == '\n' && end[1] == '\0'))) {
220        ret = bdi_set_max_ratio(bdi, ratio);
221        if (!ret)
222            ret = count;
223    }
224    return ret;
225}
226BDI_SHOW(max_ratio, bdi->max_ratio)
227
228#define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
229
230static struct device_attribute bdi_dev_attrs[] = {
231    __ATTR_RW(read_ahead_kb),
232    __ATTR_RW(min_ratio),
233    __ATTR_RW(max_ratio),
234    __ATTR_NULL,
235};
236
237static __init int bdi_class_init(void)
238{
239    bdi_class = class_create(THIS_MODULE, "bdi");
240    if (IS_ERR(bdi_class))
241        return PTR_ERR(bdi_class);
242
243    bdi_class->dev_attrs = bdi_dev_attrs;
244    bdi_debug_init();
245    return 0;
246}
247postcore_initcall(bdi_class_init);
248
249static int __init default_bdi_init(void)
250{
251    int err;
252
253    sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
254    BUG_ON(IS_ERR(sync_supers_tsk));
255
256    setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
257    bdi_arm_supers_timer();
258
259    err = bdi_init(&default_backing_dev_info);
260    if (!err)
261        bdi_register(&default_backing_dev_info, NULL, "default");
262    err = bdi_init(&noop_backing_dev_info);
263
264    return err;
265}
266subsys_initcall(default_bdi_init);
267
268int bdi_has_dirty_io(struct backing_dev_info *bdi)
269{
270    return wb_has_dirty_io(&bdi->wb);
271}
272
273/*
274 * kupdated() used to do this. We cannot do it from the bdi_forker_thread()
275 * or we risk deadlocking on ->s_umount. The longer term solution would be
276 * to implement sync_supers_bdi() or similar and simply do it from the
277 * bdi writeback thread individually.
278 */
279static int bdi_sync_supers(void *unused)
280{
281    set_user_nice(current, 0);
282
283    while (!kthread_should_stop()) {
284        set_current_state(TASK_INTERRUPTIBLE);
285        schedule();
286
287        /*
288         * Do this periodically, like kupdated() did before.
289         */
290        sync_supers();
291    }
292
293    return 0;
294}
295
296void bdi_arm_supers_timer(void)
297{
298    unsigned long next;
299
300    if (!dirty_writeback_interval)
301        return;
302
303    next = msecs_to_jiffies(dirty_writeback_interval * 10) + jiffies;
304    mod_timer(&sync_supers_timer, round_jiffies_up(next));
305}
306
307static void sync_supers_timer_fn(unsigned long unused)
308{
309    wake_up_process(sync_supers_tsk);
310    bdi_arm_supers_timer();
311}
312
313static void wakeup_timer_fn(unsigned long data)
314{
315    struct backing_dev_info *bdi = (struct backing_dev_info *)data;
316
317    spin_lock_bh(&bdi->wb_lock);
318    if (bdi->wb.task) {
319        trace_writeback_wake_thread(bdi);
320        wake_up_process(bdi->wb.task);
321    } else if (bdi->dev) {
322        /*
323         * When bdi tasks are inactive for long time, they are killed.
324         * In this case we have to wake-up the forker thread which
325         * should create and run the bdi thread.
326         */
327        trace_writeback_wake_forker_thread(bdi);
328        wake_up_process(default_backing_dev_info.wb.task);
329    }
330    spin_unlock_bh(&bdi->wb_lock);
331}
332
333/*
334 * This function is used when the first inode for this bdi is marked dirty. It
335 * wakes-up the corresponding bdi thread which should then take care of the
336 * periodic background write-out of dirty inodes. Since the write-out would
337 * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
338 * set up a timer which wakes the bdi thread up later.
339 *
340 * Note, we wouldn't bother setting up the timer, but this function is on the
341 * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
342 * by delaying the wake-up.
343 */
344void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
345{
346    unsigned long timeout;
347
348    timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
349    mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
350}
351
352/*
353 * Calculate the longest interval (jiffies) bdi threads are allowed to be
354 * inactive.
355 */
356static unsigned long bdi_longest_inactive(void)
357{
358    unsigned long interval;
359
360    interval = msecs_to_jiffies(dirty_writeback_interval * 10);
361    return max(5UL * 60 * HZ, interval);
362}
363
364/*
365 * Clear pending bit and wakeup anybody waiting for flusher thread creation or
366 * shutdown
367 */
368static void bdi_clear_pending(struct backing_dev_info *bdi)
369{
370    clear_bit(BDI_pending, &bdi->state);
371    smp_mb__after_clear_bit();
372    wake_up_bit(&bdi->state, BDI_pending);
373}
374
375static int bdi_forker_thread(void *ptr)
376{
377    struct bdi_writeback *me = ptr;
378
379    current->flags |= PF_SWAPWRITE;
380    set_freezable();
381
382    /*
383     * Our parent may run at a different priority, just set us to normal
384     */
385    set_user_nice(current, 0);
386
387    for (;;) {
388        struct task_struct *task = NULL;
389        struct backing_dev_info *bdi;
390        enum {
391            NO_ACTION, /* Nothing to do */
392            FORK_THREAD, /* Fork bdi thread */
393            KILL_THREAD, /* Kill inactive bdi thread */
394        } action = NO_ACTION;
395
396        /*
397         * Temporary measure, we want to make sure we don't see
398         * dirty data on the default backing_dev_info
399         */
400        if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) {
401            del_timer(&me->wakeup_timer);
402            wb_do_writeback(me, 0);
403        }
404
405        spin_lock_bh(&bdi_lock);
406        /*
407         * In the following loop we are going to check whether we have
408         * some work to do without any synchronization with tasks
409         * waking us up to do work for them. Set the task state here
410         * so that we don't miss wakeups after verifying conditions.
411         */
412        set_current_state(TASK_INTERRUPTIBLE);
413
414        list_for_each_entry(bdi, &bdi_list, bdi_list) {
415            bool have_dirty_io;
416
417            if (!bdi_cap_writeback_dirty(bdi) ||
418                 bdi_cap_flush_forker(bdi))
419                continue;
420
421            WARN(!test_bit(BDI_registered, &bdi->state),
422                 "bdi %p/%s is not registered!\n", bdi, bdi->name);
423
424            have_dirty_io = !list_empty(&bdi->work_list) ||
425                    wb_has_dirty_io(&bdi->wb);
426
427            /*
428             * If the bdi has work to do, but the thread does not
429             * exist - create it.
430             */
431            if (!bdi->wb.task && have_dirty_io) {
432                /*
433                 * Set the pending bit - if someone will try to
434                 * unregister this bdi - it'll wait on this bit.
435                 */
436                set_bit(BDI_pending, &bdi->state);
437                action = FORK_THREAD;
438                break;
439            }
440
441            spin_lock(&bdi->wb_lock);
442
443            /*
444             * If there is no work to do and the bdi thread was
445             * inactive long enough - kill it. The wb_lock is taken
446             * to make sure no-one adds more work to this bdi and
447             * wakes the bdi thread up.
448             */
449            if (bdi->wb.task && !have_dirty_io &&
450                time_after(jiffies, bdi->wb.last_active +
451                        bdi_longest_inactive())) {
452                task = bdi->wb.task;
453                bdi->wb.task = NULL;
454                spin_unlock(&bdi->wb_lock);
455                set_bit(BDI_pending, &bdi->state);
456                action = KILL_THREAD;
457                break;
458            }
459            spin_unlock(&bdi->wb_lock);
460        }
461        spin_unlock_bh(&bdi_lock);
462
463        /* Keep working if default bdi still has things to do */
464        if (!list_empty(&me->bdi->work_list))
465            __set_current_state(TASK_RUNNING);
466
467        switch (action) {
468        case FORK_THREAD:
469            __set_current_state(TASK_RUNNING);
470            task = kthread_create(bdi_writeback_thread, &bdi->wb,
471                          "flush-%s", dev_name(bdi->dev));
472            if (IS_ERR(task)) {
473                /*
474                 * If thread creation fails, force writeout of
475                 * the bdi from the thread. Hopefully 1024 is
476                 * large enough for efficient IO.
477                 */
478                writeback_inodes_wb(&bdi->wb, 1024,
479                            WB_REASON_FORKER_THREAD);
480            } else {
481                /*
482                 * The spinlock makes sure we do not lose
483                 * wake-ups when racing with 'bdi_queue_work()'.
484                 * And as soon as the bdi thread is visible, we
485                 * can start it.
486                 */
487                spin_lock_bh(&bdi->wb_lock);
488                bdi->wb.task = task;
489                spin_unlock_bh(&bdi->wb_lock);
490                wake_up_process(task);
491            }
492            bdi_clear_pending(bdi);
493            break;
494
495        case KILL_THREAD:
496            __set_current_state(TASK_RUNNING);
497            kthread_stop(task);
498            bdi_clear_pending(bdi);
499            break;
500
501        case NO_ACTION:
502            if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
503                /*
504                 * There are no dirty data. The only thing we
505                 * should now care about is checking for
506                 * inactive bdi threads and killing them. Thus,
507                 * let's sleep for longer time, save energy and
508                 * be friendly for battery-driven devices.
509                 */
510                schedule_timeout(bdi_longest_inactive());
511            else
512                schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
513            try_to_freeze();
514            break;
515        }
516    }
517
518    return 0;
519}
520
521/*
522 * Remove bdi from bdi_list, and ensure that it is no longer visible
523 */
524static void bdi_remove_from_list(struct backing_dev_info *bdi)
525{
526    spin_lock_bh(&bdi_lock);
527    list_del_rcu(&bdi->bdi_list);
528    spin_unlock_bh(&bdi_lock);
529
530    synchronize_rcu_expedited();
531}
532
533int bdi_register(struct backing_dev_info *bdi, struct device *parent,
534        const char *fmt, ...)
535{
536    va_list args;
537    struct device *dev;
538
539    if (bdi->dev) /* The driver needs to use separate queues per device */
540        return 0;
541
542    va_start(args, fmt);
543    dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
544    va_end(args);
545    if (IS_ERR(dev))
546        return PTR_ERR(dev);
547
548    bdi->dev = dev;
549
550    /*
551     * Just start the forker thread for our default backing_dev_info,
552     * and add other bdi's to the list. They will get a thread created
553     * on-demand when they need it.
554     */
555    if (bdi_cap_flush_forker(bdi)) {
556        struct bdi_writeback *wb = &bdi->wb;
557
558        wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s",
559                        dev_name(dev));
560        if (IS_ERR(wb->task))
561            return PTR_ERR(wb->task);
562    }
563
564    bdi_debug_register(bdi, dev_name(dev));
565    set_bit(BDI_registered, &bdi->state);
566
567    spin_lock_bh(&bdi_lock);
568    list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
569    spin_unlock_bh(&bdi_lock);
570
571    trace_writeback_bdi_register(bdi);
572    return 0;
573}
574EXPORT_SYMBOL(bdi_register);
575
576int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
577{
578    return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
579}
580EXPORT_SYMBOL(bdi_register_dev);
581
582/*
583 * Remove bdi from the global list and shutdown any threads we have running
584 */
585static void bdi_wb_shutdown(struct backing_dev_info *bdi)
586{
587    struct task_struct *task;
588
589    if (!bdi_cap_writeback_dirty(bdi))
590        return;
591
592    /*
593     * Make sure nobody finds us on the bdi_list anymore
594     */
595    bdi_remove_from_list(bdi);
596
597    /*
598     * If setup is pending, wait for that to complete first
599     */
600    wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
601            TASK_UNINTERRUPTIBLE);
602
603    /*
604     * Finally, kill the kernel thread. We don't need to be RCU
605     * safe anymore, since the bdi is gone from visibility.
606     */
607    spin_lock_bh(&bdi->wb_lock);
608    task = bdi->wb.task;
609    bdi->wb.task = NULL;
610    spin_unlock_bh(&bdi->wb_lock);
611
612    if (task)
613        kthread_stop(task);
614}
615
616/*
617 * This bdi is going away now, make sure that no super_blocks point to it
618 */
619static void bdi_prune_sb(struct backing_dev_info *bdi)
620{
621    struct super_block *sb;
622
623    spin_lock(&sb_lock);
624    list_for_each_entry(sb, &super_blocks, s_list) {
625        if (sb->s_bdi == bdi)
626            sb->s_bdi = &default_backing_dev_info;
627    }
628    spin_unlock(&sb_lock);
629}
630
631void bdi_unregister(struct backing_dev_info *bdi)
632{
633    struct device *dev = bdi->dev;
634
635    if (dev) {
636        bdi_set_min_ratio(bdi, 0);
637        trace_writeback_bdi_unregister(bdi);
638        bdi_prune_sb(bdi);
639        del_timer_sync(&bdi->wb.wakeup_timer);
640
641        if (!bdi_cap_flush_forker(bdi))
642            bdi_wb_shutdown(bdi);
643        bdi_debug_unregister(bdi);
644
645        spin_lock_bh(&bdi->wb_lock);
646        bdi->dev = NULL;
647        spin_unlock_bh(&bdi->wb_lock);
648
649        device_unregister(dev);
650    }
651}
652EXPORT_SYMBOL(bdi_unregister);
653
654static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
655{
656    memset(wb, 0, sizeof(*wb));
657
658    wb->bdi = bdi;
659    wb->last_old_flush = jiffies;
660    INIT_LIST_HEAD(&wb->b_dirty);
661    INIT_LIST_HEAD(&wb->b_io);
662    INIT_LIST_HEAD(&wb->b_more_io);
663    spin_lock_init(&wb->list_lock);
664    setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
665}
666
667/*
668 * Initial write bandwidth: 100 MB/s
669 */
670#define INIT_BW (100 << (20 - PAGE_SHIFT))
671
672int bdi_init(struct backing_dev_info *bdi)
673{
674    int i, err;
675
676    bdi->dev = NULL;
677
678    bdi->min_ratio = 0;
679    bdi->max_ratio = 100;
680    bdi->max_prop_frac = PROP_FRAC_BASE;
681    spin_lock_init(&bdi->wb_lock);
682    INIT_LIST_HEAD(&bdi->bdi_list);
683    INIT_LIST_HEAD(&bdi->work_list);
684
685    bdi_wb_init(&bdi->wb, bdi);
686
687    for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
688        err = percpu_counter_init(&bdi->bdi_stat[i], 0);
689        if (err)
690            goto err;
691    }
692
693    bdi->dirty_exceeded = 0;
694
695    bdi->bw_time_stamp = jiffies;
696    bdi->written_stamp = 0;
697
698    bdi->balanced_dirty_ratelimit = INIT_BW;
699    bdi->dirty_ratelimit = INIT_BW;
700    bdi->write_bandwidth = INIT_BW;
701    bdi->avg_write_bandwidth = INIT_BW;
702
703    err = prop_local_init_percpu(&bdi->completions);
704
705    if (err) {
706err:
707        while (i--)
708            percpu_counter_destroy(&bdi->bdi_stat[i]);
709    }
710
711    return err;
712}
713EXPORT_SYMBOL(bdi_init);
714
715void bdi_destroy(struct backing_dev_info *bdi)
716{
717    int i;
718
719    /*
720     * Splice our entries to the default_backing_dev_info, if this
721     * bdi disappears
722     */
723    if (bdi_has_dirty_io(bdi)) {
724        struct bdi_writeback *dst = &default_backing_dev_info.wb;
725
726        bdi_lock_two(&bdi->wb, dst);
727        list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
728        list_splice(&bdi->wb.b_io, &dst->b_io);
729        list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
730        spin_unlock(&bdi->wb.list_lock);
731        spin_unlock(&dst->list_lock);
732    }
733
734    bdi_unregister(bdi);
735
736    /*
737     * If bdi_unregister() had already been called earlier, the
738     * wakeup_timer could still be armed because bdi_prune_sb()
739     * can race with the bdi_wakeup_thread_delayed() calls from
740     * __mark_inode_dirty().
741     */
742    del_timer_sync(&bdi->wb.wakeup_timer);
743
744    for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
745        percpu_counter_destroy(&bdi->bdi_stat[i]);
746
747    prop_local_destroy_percpu(&bdi->completions);
748}
749EXPORT_SYMBOL(bdi_destroy);
750
751/*
752 * For use from filesystems to quickly init and register a bdi associated
753 * with dirty writeback
754 */
755int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
756               unsigned int cap)
757{
758    char tmp[32];
759    int err;
760
761    bdi->name = name;
762    bdi->capabilities = cap;
763    err = bdi_init(bdi);
764    if (err)
765        return err;
766
767    sprintf(tmp, "%.28s%s", name, "-%d");
768    err = bdi_register(bdi, NULL, tmp, atomic_long_inc_return(&bdi_seq));
769    if (err) {
770        bdi_destroy(bdi);
771        return err;
772    }
773
774    return 0;
775}
776EXPORT_SYMBOL(bdi_setup_and_register);
777
778static wait_queue_head_t congestion_wqh[2] = {
779        __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
780        __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
781    };
782static atomic_t nr_bdi_congested[2];
783
784void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
785{
786    enum bdi_state bit;
787    wait_queue_head_t *wqh = &congestion_wqh[sync];
788
789    bit = sync ? BDI_sync_congested : BDI_async_congested;
790    if (test_and_clear_bit(bit, &bdi->state))
791        atomic_dec(&nr_bdi_congested[sync]);
792    smp_mb__after_clear_bit();
793    if (waitqueue_active(wqh))
794        wake_up(wqh);
795}
796EXPORT_SYMBOL(clear_bdi_congested);
797
798void set_bdi_congested(struct backing_dev_info *bdi, int sync)
799{
800    enum bdi_state bit;
801
802    bit = sync ? BDI_sync_congested : BDI_async_congested;
803    if (!test_and_set_bit(bit, &bdi->state))
804        atomic_inc(&nr_bdi_congested[sync]);
805}
806EXPORT_SYMBOL(set_bdi_congested);
807
808/**
809 * congestion_wait - wait for a backing_dev to become uncongested
810 * @sync: SYNC or ASYNC IO
811 * @timeout: timeout in jiffies
812 *
813 * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
814 * write congestion. If no backing_devs are congested then just wait for the
815 * next write to be completed.
816 */
817long congestion_wait(int sync, long timeout)
818{
819    long ret;
820    unsigned long start = jiffies;
821    DEFINE_WAIT(wait);
822    wait_queue_head_t *wqh = &congestion_wqh[sync];
823
824    prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
825    ret = io_schedule_timeout(timeout);
826    finish_wait(wqh, &wait);
827
828    trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
829                    jiffies_to_usecs(jiffies - start));
830
831    return ret;
832}
833EXPORT_SYMBOL(congestion_wait);
834
835/**
836 * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
837 * @zone: A zone to check if it is heavily congested
838 * @sync: SYNC or ASYNC IO
839 * @timeout: timeout in jiffies
840 *
841 * In the event of a congested backing_dev (any backing_dev) and the given
842 * @zone has experienced recent congestion, this waits for up to @timeout
843 * jiffies for either a BDI to exit congestion of the given @sync queue
844 * or a write to complete.
845 *
846 * In the absence of zone congestion, cond_resched() is called to yield
847 * the processor if necessary but otherwise does not sleep.
848 *
849 * The return value is 0 if the sleep is for the full timeout. Otherwise,
850 * it is the number of jiffies that were still remaining when the function
851 * returned. return_value == timeout implies the function did not sleep.
852 */
853long wait_iff_congested(struct zone *zone, int sync, long timeout)
854{
855    long ret;
856    unsigned long start = jiffies;
857    DEFINE_WAIT(wait);
858    wait_queue_head_t *wqh = &congestion_wqh[sync];
859
860    /*
861     * If there is no congestion, or heavy congestion is not being
862     * encountered in the current zone, yield if necessary instead
863     * of sleeping on the congestion queue
864     */
865    if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
866            !zone_is_reclaim_congested(zone)) {
867        cond_resched();
868
869        /* In case we scheduled, work out time remaining */
870        ret = timeout - (jiffies - start);
871        if (ret < 0)
872            ret = 0;
873
874        goto out;
875    }
876
877    /* Sleep until uncongested or a write happens */
878    prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
879    ret = io_schedule_timeout(timeout);
880    finish_wait(wqh, &wait);
881
882out:
883    trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
884                    jiffies_to_usecs(jiffies - start));
885
886    return ret;
887}
888EXPORT_SYMBOL(wait_iff_congested);
889

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