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. bdi_list has RCU reader side
35 * locking.
36 */
37DEFINE_SPINLOCK(bdi_lock);
38LIST_HEAD(bdi_list);
39
40/* bdi_wq serves all asynchronous writeback tasks */
41struct workqueue_struct *bdi_wq;
42
43void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
44{
45    if (wb1 < wb2) {
46        spin_lock(&wb1->list_lock);
47        spin_lock_nested(&wb2->list_lock, 1);
48    } else {
49        spin_lock(&wb2->list_lock);
50        spin_lock_nested(&wb1->list_lock, 1);
51    }
52}
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;
73    struct inode *inode;
74
75    nr_dirty = nr_io = nr_more_io = 0;
76    spin_lock(&wb->list_lock);
77    list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
78        nr_dirty++;
79    list_for_each_entry(inode, &wb->b_io, i_wb_list)
80        nr_io++;
81    list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
82        nr_more_io++;
83    spin_unlock(&wb->list_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: %10lu kB\n"
91           "BdiReclaimable: %10lu kB\n"
92           "BdiDirtyThresh: %10lu kB\n"
93           "DirtyThresh: %10lu kB\n"
94           "BackgroundThresh: %10lu kB\n"
95           "BdiDirtied: %10lu kB\n"
96           "BdiWritten: %10lu kB\n"
97           "BdiWriteBandwidth: %10lu kBps\n"
98           "b_dirty: %10lu\n"
99           "b_io: %10lu\n"
100           "b_more_io: %10lu\n"
101           "bdi_list: %10u\n"
102           "state: %10lx\n",
103           (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
104           (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
105           K(bdi_thresh),
106           K(dirty_thresh),
107           K(background_thresh),
108           (unsigned long) K(bdi_stat(bdi, BDI_DIRTIED)),
109           (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)),
110           (unsigned long) K(bdi->write_bandwidth),
111           nr_dirty,
112           nr_io,
113           nr_more_io,
114           !list_empty(&bdi->bdi_list), bdi->state);
115#undef K
116
117    return 0;
118}
119
120static int bdi_debug_stats_open(struct inode *inode, struct file *file)
121{
122    return single_open(file, bdi_debug_stats_show, inode->i_private);
123}
124
125static const struct file_operations bdi_debug_stats_fops = {
126    .open = bdi_debug_stats_open,
127    .read = seq_read,
128    .llseek = seq_lseek,
129    .release = single_release,
130};
131
132static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
133{
134    bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
135    bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
136                           bdi, &bdi_debug_stats_fops);
137}
138
139static void bdi_debug_unregister(struct backing_dev_info *bdi)
140{
141    debugfs_remove(bdi->debug_stats);
142    debugfs_remove(bdi->debug_dir);
143}
144#else
145static inline void bdi_debug_init(void)
146{
147}
148static inline void bdi_debug_register(struct backing_dev_info *bdi,
149                      const char *name)
150{
151}
152static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
153{
154}
155#endif
156
157static ssize_t read_ahead_kb_store(struct device *dev,
158                  struct device_attribute *attr,
159                  const char *buf, size_t count)
160{
161    struct backing_dev_info *bdi = dev_get_drvdata(dev);
162    unsigned long read_ahead_kb;
163    ssize_t ret;
164
165    ret = kstrtoul(buf, 10, &read_ahead_kb);
166    if (ret < 0)
167        return ret;
168
169    bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
170
171    return count;
172}
173
174#define K(pages) ((pages) << (PAGE_SHIFT - 10))
175
176#define BDI_SHOW(name, expr) \
177static ssize_t name##_show(struct device *dev, \
178               struct device_attribute *attr, char *page) \
179{ \
180    struct backing_dev_info *bdi = dev_get_drvdata(dev); \
181                                    \
182    return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr); \
183} \
184static DEVICE_ATTR_RW(name);
185
186BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
187
188static ssize_t min_ratio_store(struct device *dev,
189        struct device_attribute *attr, const char *buf, size_t count)
190{
191    struct backing_dev_info *bdi = dev_get_drvdata(dev);
192    unsigned int ratio;
193    ssize_t ret;
194
195    ret = kstrtouint(buf, 10, &ratio);
196    if (ret < 0)
197        return ret;
198
199    ret = bdi_set_min_ratio(bdi, ratio);
200    if (!ret)
201        ret = count;
202
203    return ret;
204}
205BDI_SHOW(min_ratio, bdi->min_ratio)
206
207static ssize_t max_ratio_store(struct device *dev,
208        struct device_attribute *attr, const char *buf, size_t count)
209{
210    struct backing_dev_info *bdi = dev_get_drvdata(dev);
211    unsigned int ratio;
212    ssize_t ret;
213
214    ret = kstrtouint(buf, 10, &ratio);
215    if (ret < 0)
216        return ret;
217
218    ret = bdi_set_max_ratio(bdi, ratio);
219    if (!ret)
220        ret = count;
221
222    return ret;
223}
224BDI_SHOW(max_ratio, bdi->max_ratio)
225
226static ssize_t stable_pages_required_show(struct device *dev,
227                      struct device_attribute *attr,
228                      char *page)
229{
230    struct backing_dev_info *bdi = dev_get_drvdata(dev);
231
232    return snprintf(page, PAGE_SIZE-1, "%d\n",
233            bdi_cap_stable_pages_required(bdi) ? 1 : 0);
234}
235static DEVICE_ATTR_RO(stable_pages_required);
236
237static struct attribute *bdi_dev_attrs[] = {
238    &dev_attr_read_ahead_kb.attr,
239    &dev_attr_min_ratio.attr,
240    &dev_attr_max_ratio.attr,
241    &dev_attr_stable_pages_required.attr,
242    NULL,
243};
244ATTRIBUTE_GROUPS(bdi_dev);
245
246static __init int bdi_class_init(void)
247{
248    bdi_class = class_create(THIS_MODULE, "bdi");
249    if (IS_ERR(bdi_class))
250        return PTR_ERR(bdi_class);
251
252    bdi_class->dev_groups = bdi_dev_groups;
253    bdi_debug_init();
254    return 0;
255}
256postcore_initcall(bdi_class_init);
257
258static int __init default_bdi_init(void)
259{
260    int err;
261
262    bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_FREEZABLE |
263                          WQ_UNBOUND | WQ_SYSFS, 0);
264    if (!bdi_wq)
265        return -ENOMEM;
266
267    err = bdi_init(&default_backing_dev_info);
268    if (!err)
269        bdi_register(&default_backing_dev_info, NULL, "default");
270    err = bdi_init(&noop_backing_dev_info);
271
272    return err;
273}
274subsys_initcall(default_bdi_init);
275
276int bdi_has_dirty_io(struct backing_dev_info *bdi)
277{
278    return wb_has_dirty_io(&bdi->wb);
279}
280
281/*
282 * This function is used when the first inode for this bdi is marked dirty. It
283 * wakes-up the corresponding bdi thread which should then take care of the
284 * periodic background write-out of dirty inodes. Since the write-out would
285 * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
286 * set up a timer which wakes the bdi thread up later.
287 *
288 * Note, we wouldn't bother setting up the timer, but this function is on the
289 * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
290 * by delaying the wake-up.
291 */
292void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
293{
294    unsigned long timeout;
295
296    timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
297    mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
298}
299
300/*
301 * Remove bdi from bdi_list, and ensure that it is no longer visible
302 */
303static void bdi_remove_from_list(struct backing_dev_info *bdi)
304{
305    spin_lock_bh(&bdi_lock);
306    list_del_rcu(&bdi->bdi_list);
307    spin_unlock_bh(&bdi_lock);
308
309    synchronize_rcu_expedited();
310
311    /* bdi_list is now unused, clear it to mark @bdi dying */
312    INIT_LIST_HEAD(&bdi->bdi_list);
313}
314
315int bdi_register(struct backing_dev_info *bdi, struct device *parent,
316        const char *fmt, ...)
317{
318    va_list args;
319    struct device *dev;
320
321    if (bdi->dev) /* The driver needs to use separate queues per device */
322        return 0;
323
324    va_start(args, fmt);
325    dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
326    va_end(args);
327    if (IS_ERR(dev))
328        return PTR_ERR(dev);
329
330    bdi->dev = dev;
331
332    bdi_debug_register(bdi, dev_name(dev));
333    set_bit(BDI_registered, &bdi->state);
334
335    spin_lock_bh(&bdi_lock);
336    list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
337    spin_unlock_bh(&bdi_lock);
338
339    trace_writeback_bdi_register(bdi);
340    return 0;
341}
342EXPORT_SYMBOL(bdi_register);
343
344int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
345{
346    return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
347}
348EXPORT_SYMBOL(bdi_register_dev);
349
350/*
351 * Remove bdi from the global list and shutdown any threads we have running
352 */
353static void bdi_wb_shutdown(struct backing_dev_info *bdi)
354{
355    if (!bdi_cap_writeback_dirty(bdi))
356        return;
357
358    /*
359     * Make sure nobody finds us on the bdi_list anymore
360     */
361    bdi_remove_from_list(bdi);
362
363    /*
364     * Drain work list and shutdown the delayed_work. At this point,
365     * @bdi->bdi_list is empty telling bdi_Writeback_workfn() that @bdi
366     * is dying and its work_list needs to be drained no matter what.
367     */
368    mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
369    flush_delayed_work(&bdi->wb.dwork);
370    WARN_ON(!list_empty(&bdi->work_list));
371
372    /*
373     * This shouldn't be necessary unless @bdi for some reason has
374     * unflushed dirty IO after work_list is drained. Do it anyway
375     * just in case.
376     */
377    cancel_delayed_work_sync(&bdi->wb.dwork);
378}
379
380/*
381 * This bdi is going away now, make sure that no super_blocks point to it
382 */
383static void bdi_prune_sb(struct backing_dev_info *bdi)
384{
385    struct super_block *sb;
386
387    spin_lock(&sb_lock);
388    list_for_each_entry(sb, &super_blocks, s_list) {
389        if (sb->s_bdi == bdi)
390            sb->s_bdi = &default_backing_dev_info;
391    }
392    spin_unlock(&sb_lock);
393}
394
395void bdi_unregister(struct backing_dev_info *bdi)
396{
397    struct device *dev = bdi->dev;
398
399    if (dev) {
400        bdi_set_min_ratio(bdi, 0);
401        trace_writeback_bdi_unregister(bdi);
402        bdi_prune_sb(bdi);
403
404        bdi_wb_shutdown(bdi);
405        bdi_debug_unregister(bdi);
406
407        spin_lock_bh(&bdi->wb_lock);
408        bdi->dev = NULL;
409        spin_unlock_bh(&bdi->wb_lock);
410
411        device_unregister(dev);
412    }
413}
414EXPORT_SYMBOL(bdi_unregister);
415
416static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
417{
418    memset(wb, 0, sizeof(*wb));
419
420    wb->bdi = bdi;
421    wb->last_old_flush = jiffies;
422    INIT_LIST_HEAD(&wb->b_dirty);
423    INIT_LIST_HEAD(&wb->b_io);
424    INIT_LIST_HEAD(&wb->b_more_io);
425    spin_lock_init(&wb->list_lock);
426    INIT_DELAYED_WORK(&wb->dwork, bdi_writeback_workfn);
427}
428
429/*
430 * Initial write bandwidth: 100 MB/s
431 */
432#define INIT_BW (100 << (20 - PAGE_SHIFT))
433
434int bdi_init(struct backing_dev_info *bdi)
435{
436    int i, err;
437
438    bdi->dev = NULL;
439
440    bdi->min_ratio = 0;
441    bdi->max_ratio = 100;
442    bdi->max_prop_frac = FPROP_FRAC_BASE;
443    spin_lock_init(&bdi->wb_lock);
444    INIT_LIST_HEAD(&bdi->bdi_list);
445    INIT_LIST_HEAD(&bdi->work_list);
446
447    bdi_wb_init(&bdi->wb, bdi);
448
449    for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
450        err = percpu_counter_init(&bdi->bdi_stat[i], 0);
451        if (err)
452            goto err;
453    }
454
455    bdi->dirty_exceeded = 0;
456
457    bdi->bw_time_stamp = jiffies;
458    bdi->written_stamp = 0;
459
460    bdi->balanced_dirty_ratelimit = INIT_BW;
461    bdi->dirty_ratelimit = INIT_BW;
462    bdi->write_bandwidth = INIT_BW;
463    bdi->avg_write_bandwidth = INIT_BW;
464
465    err = fprop_local_init_percpu(&bdi->completions);
466
467    if (err) {
468err:
469        while (i--)
470            percpu_counter_destroy(&bdi->bdi_stat[i]);
471    }
472
473    return err;
474}
475EXPORT_SYMBOL(bdi_init);
476
477void bdi_destroy(struct backing_dev_info *bdi)
478{
479    int i;
480
481    /*
482     * Splice our entries to the default_backing_dev_info, if this
483     * bdi disappears
484     */
485    if (bdi_has_dirty_io(bdi)) {
486        struct bdi_writeback *dst = &default_backing_dev_info.wb;
487
488        bdi_lock_two(&bdi->wb, dst);
489        list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
490        list_splice(&bdi->wb.b_io, &dst->b_io);
491        list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
492        spin_unlock(&bdi->wb.list_lock);
493        spin_unlock(&dst->list_lock);
494    }
495
496    bdi_unregister(bdi);
497
498    /*
499     * If bdi_unregister() had already been called earlier, the dwork
500     * could still be pending because bdi_prune_sb() can race with the
501     * bdi_wakeup_thread_delayed() calls from __mark_inode_dirty().
502     */
503    cancel_delayed_work_sync(&bdi->wb.dwork);
504
505    for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
506        percpu_counter_destroy(&bdi->bdi_stat[i]);
507
508    fprop_local_destroy_percpu(&bdi->completions);
509}
510EXPORT_SYMBOL(bdi_destroy);
511
512/*
513 * For use from filesystems to quickly init and register a bdi associated
514 * with dirty writeback
515 */
516int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
517               unsigned int cap)
518{
519    int err;
520
521    bdi->name = name;
522    bdi->capabilities = cap;
523    err = bdi_init(bdi);
524    if (err)
525        return err;
526
527    err = bdi_register(bdi, NULL, "%.28s-%ld", name,
528               atomic_long_inc_return(&bdi_seq));
529    if (err) {
530        bdi_destroy(bdi);
531        return err;
532    }
533
534    return 0;
535}
536EXPORT_SYMBOL(bdi_setup_and_register);
537
538static wait_queue_head_t congestion_wqh[2] = {
539        __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
540        __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
541    };
542static atomic_t nr_bdi_congested[2];
543
544void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
545{
546    enum bdi_state bit;
547    wait_queue_head_t *wqh = &congestion_wqh[sync];
548
549    bit = sync ? BDI_sync_congested : BDI_async_congested;
550    if (test_and_clear_bit(bit, &bdi->state))
551        atomic_dec(&nr_bdi_congested[sync]);
552    smp_mb__after_clear_bit();
553    if (waitqueue_active(wqh))
554        wake_up(wqh);
555}
556EXPORT_SYMBOL(clear_bdi_congested);
557
558void set_bdi_congested(struct backing_dev_info *bdi, int sync)
559{
560    enum bdi_state bit;
561
562    bit = sync ? BDI_sync_congested : BDI_async_congested;
563    if (!test_and_set_bit(bit, &bdi->state))
564        atomic_inc(&nr_bdi_congested[sync]);
565}
566EXPORT_SYMBOL(set_bdi_congested);
567
568/**
569 * congestion_wait - wait for a backing_dev to become uncongested
570 * @sync: SYNC or ASYNC IO
571 * @timeout: timeout in jiffies
572 *
573 * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
574 * write congestion. If no backing_devs are congested then just wait for the
575 * next write to be completed.
576 */
577long congestion_wait(int sync, long timeout)
578{
579    long ret;
580    unsigned long start = jiffies;
581    DEFINE_WAIT(wait);
582    wait_queue_head_t *wqh = &congestion_wqh[sync];
583
584    prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
585    ret = io_schedule_timeout(timeout);
586    finish_wait(wqh, &wait);
587
588    trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
589                    jiffies_to_usecs(jiffies - start));
590
591    return ret;
592}
593EXPORT_SYMBOL(congestion_wait);
594
595/**
596 * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
597 * @zone: A zone to check if it is heavily congested
598 * @sync: SYNC or ASYNC IO
599 * @timeout: timeout in jiffies
600 *
601 * In the event of a congested backing_dev (any backing_dev) and the given
602 * @zone has experienced recent congestion, this waits for up to @timeout
603 * jiffies for either a BDI to exit congestion of the given @sync queue
604 * or a write to complete.
605 *
606 * In the absence of zone congestion, cond_resched() is called to yield
607 * the processor if necessary but otherwise does not sleep.
608 *
609 * The return value is 0 if the sleep is for the full timeout. Otherwise,
610 * it is the number of jiffies that were still remaining when the function
611 * returned. return_value == timeout implies the function did not sleep.
612 */
613long wait_iff_congested(struct zone *zone, int sync, long timeout)
614{
615    long ret;
616    unsigned long start = jiffies;
617    DEFINE_WAIT(wait);
618    wait_queue_head_t *wqh = &congestion_wqh[sync];
619
620    /*
621     * If there is no congestion, or heavy congestion is not being
622     * encountered in the current zone, yield if necessary instead
623     * of sleeping on the congestion queue
624     */
625    if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
626            !zone_is_reclaim_congested(zone)) {
627        cond_resched();
628
629        /* In case we scheduled, work out time remaining */
630        ret = timeout - (jiffies - start);
631        if (ret < 0)
632            ret = 0;
633
634        goto out;
635    }
636
637    /* Sleep until uncongested or a write happens */
638    prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
639    ret = io_schedule_timeout(timeout);
640    finish_wait(wqh, &wait);
641
642out:
643    trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
644                    jiffies_to_usecs(jiffies - start));
645
646    return ret;
647}
648EXPORT_SYMBOL(wait_iff_congested);
649
650int pdflush_proc_obsolete(struct ctl_table *table, int write,
651            void __user *buffer, size_t *lenp, loff_t *ppos)
652{
653    char kbuf[] = "0\n";
654
655    if (*ppos || *lenp < sizeof(kbuf)) {
656        *lenp = 0;
657        return 0;
658    }
659
660    if (copy_to_user(buffer, kbuf, sizeof(kbuf)))
661        return -EFAULT;
662    printk_once(KERN_WARNING "%s exported in /proc is scheduled for removal\n",
663            table->procname);
664
665    *lenp = 2;
666    *ppos += *lenp;
667    return 2;
668}
669

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