Root/fs/fs-writeback.c

1/*
2 * fs/fs-writeback.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 *
6 * Contains all the functions related to writing back and waiting
7 * upon dirty inodes against superblocks, and writing back dirty
8 * pages against inodes. ie: data writeback. Writeout of the
9 * inode itself is not handled here.
10 *
11 * 10Apr2002 Andrew Morton
12 * Split out of fs/inode.c
13 * Additions for address_space-based writeback
14 */
15
16#include <linux/kernel.h>
17#include <linux/module.h>
18#include <linux/spinlock.h>
19#include <linux/slab.h>
20#include <linux/sched.h>
21#include <linux/fs.h>
22#include <linux/mm.h>
23#include <linux/kthread.h>
24#include <linux/freezer.h>
25#include <linux/writeback.h>
26#include <linux/blkdev.h>
27#include <linux/backing-dev.h>
28#include <linux/buffer_head.h>
29#include "internal.h"
30
31#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)
32
33/*
34 * We don't actually have pdflush, but this one is exported though /proc...
35 */
36int nr_pdflush_threads;
37
38/*
39 * Passed into wb_writeback(), essentially a subset of writeback_control
40 */
41struct wb_writeback_args {
42    long nr_pages;
43    struct super_block *sb;
44    enum writeback_sync_modes sync_mode;
45    int for_kupdate:1;
46    int range_cyclic:1;
47    int for_background:1;
48};
49
50/*
51 * Work items for the bdi_writeback threads
52 */
53struct bdi_work {
54    struct list_head list; /* pending work list */
55    struct rcu_head rcu_head; /* for RCU free/clear of work */
56
57    unsigned long seen; /* threads that have seen this work */
58    atomic_t pending; /* number of threads still to do work */
59
60    struct wb_writeback_args args; /* writeback arguments */
61
62    unsigned long state; /* flag bits, see WS_* */
63};
64
65enum {
66    WS_USED_B = 0,
67    WS_ONSTACK_B,
68};
69
70#define WS_USED (1 << WS_USED_B)
71#define WS_ONSTACK (1 << WS_ONSTACK_B)
72
73static inline bool bdi_work_on_stack(struct bdi_work *work)
74{
75    return test_bit(WS_ONSTACK_B, &work->state);
76}
77
78static inline void bdi_work_init(struct bdi_work *work,
79                 struct wb_writeback_args *args)
80{
81    INIT_RCU_HEAD(&work->rcu_head);
82    work->args = *args;
83    work->state = WS_USED;
84}
85
86/**
87 * writeback_in_progress - determine whether there is writeback in progress
88 * @bdi: the device's backing_dev_info structure.
89 *
90 * Determine whether there is writeback waiting to be handled against a
91 * backing device.
92 */
93int writeback_in_progress(struct backing_dev_info *bdi)
94{
95    return !list_empty(&bdi->work_list);
96}
97
98static void bdi_work_clear(struct bdi_work *work)
99{
100    clear_bit(WS_USED_B, &work->state);
101    smp_mb__after_clear_bit();
102    /*
103     * work can have disappeared at this point. bit waitq functions
104     * should be able to tolerate this, provided bdi_sched_wait does
105     * not dereference it's pointer argument.
106    */
107    wake_up_bit(&work->state, WS_USED_B);
108}
109
110static void bdi_work_free(struct rcu_head *head)
111{
112    struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);
113
114    if (!bdi_work_on_stack(work))
115        kfree(work);
116    else
117        bdi_work_clear(work);
118}
119
120static void wb_work_complete(struct bdi_work *work)
121{
122    const enum writeback_sync_modes sync_mode = work->args.sync_mode;
123    int onstack = bdi_work_on_stack(work);
124
125    /*
126     * For allocated work, we can clear the done/seen bit right here.
127     * For on-stack work, we need to postpone both the clear and free
128     * to after the RCU grace period, since the stack could be invalidated
129     * as soon as bdi_work_clear() has done the wakeup.
130     */
131    if (!onstack)
132        bdi_work_clear(work);
133    if (sync_mode == WB_SYNC_NONE || onstack)
134        call_rcu(&work->rcu_head, bdi_work_free);
135}
136
137static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
138{
139    /*
140     * The caller has retrieved the work arguments from this work,
141     * drop our reference. If this is the last ref, delete and free it
142     */
143    if (atomic_dec_and_test(&work->pending)) {
144        struct backing_dev_info *bdi = wb->bdi;
145
146        spin_lock(&bdi->wb_lock);
147        list_del_rcu(&work->list);
148        spin_unlock(&bdi->wb_lock);
149
150        wb_work_complete(work);
151    }
152}
153
154static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
155{
156    work->seen = bdi->wb_mask;
157    BUG_ON(!work->seen);
158    atomic_set(&work->pending, bdi->wb_cnt);
159    BUG_ON(!bdi->wb_cnt);
160
161    /*
162     * list_add_tail_rcu() contains the necessary barriers to
163     * make sure the above stores are seen before the item is
164     * noticed on the list
165     */
166    spin_lock(&bdi->wb_lock);
167    list_add_tail_rcu(&work->list, &bdi->work_list);
168    spin_unlock(&bdi->wb_lock);
169
170    /*
171     * If the default thread isn't there, make sure we add it. When
172     * it gets created and wakes up, we'll run this work.
173     */
174    if (unlikely(list_empty_careful(&bdi->wb_list)))
175        wake_up_process(default_backing_dev_info.wb.task);
176    else {
177        struct bdi_writeback *wb = &bdi->wb;
178
179        if (wb->task)
180            wake_up_process(wb->task);
181    }
182}
183
184/*
185 * Used for on-stack allocated work items. The caller needs to wait until
186 * the wb threads have acked the work before it's safe to continue.
187 */
188static void bdi_wait_on_work_clear(struct bdi_work *work)
189{
190    wait_on_bit(&work->state, WS_USED_B, bdi_sched_wait,
191            TASK_UNINTERRUPTIBLE);
192}
193
194static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
195                 struct wb_writeback_args *args)
196{
197    struct bdi_work *work;
198
199    /*
200     * This is WB_SYNC_NONE writeback, so if allocation fails just
201     * wakeup the thread for old dirty data writeback
202     */
203    work = kmalloc(sizeof(*work), GFP_ATOMIC);
204    if (work) {
205        bdi_work_init(work, args);
206        bdi_queue_work(bdi, work);
207    } else {
208        struct bdi_writeback *wb = &bdi->wb;
209
210        if (wb->task)
211            wake_up_process(wb->task);
212    }
213}
214
215/**
216 * bdi_sync_writeback - start and wait for writeback
217 * @bdi: the backing device to write from
218 * @sb: write inodes from this super_block
219 *
220 * Description:
221 * This does WB_SYNC_ALL data integrity writeback and waits for the
222 * IO to complete. Callers must hold the sb s_umount semaphore for
223 * reading, to avoid having the super disappear before we are done.
224 */
225static void bdi_sync_writeback(struct backing_dev_info *bdi,
226                   struct super_block *sb)
227{
228    struct wb_writeback_args args = {
229        .sb = sb,
230        .sync_mode = WB_SYNC_ALL,
231        .nr_pages = LONG_MAX,
232        .range_cyclic = 0,
233    };
234    struct bdi_work work;
235
236    bdi_work_init(&work, &args);
237    work.state |= WS_ONSTACK;
238
239    bdi_queue_work(bdi, &work);
240    bdi_wait_on_work_clear(&work);
241}
242
243/**
244 * bdi_start_writeback - start writeback
245 * @bdi: the backing device to write from
246 * @sb: write inodes from this super_block
247 * @nr_pages: the number of pages to write
248 *
249 * Description:
250 * This does WB_SYNC_NONE opportunistic writeback. The IO is only
251 * started when this function returns, we make no guarentees on
252 * completion. Caller need not hold sb s_umount semaphore.
253 *
254 */
255void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
256             long nr_pages)
257{
258    struct wb_writeback_args args = {
259        .sb = sb,
260        .sync_mode = WB_SYNC_NONE,
261        .nr_pages = nr_pages,
262        .range_cyclic = 1,
263    };
264
265    /*
266     * We treat @nr_pages=0 as the special case to do background writeback,
267     * ie. to sync pages until the background dirty threshold is reached.
268     */
269    if (!nr_pages) {
270        args.nr_pages = LONG_MAX;
271        args.for_background = 1;
272    }
273
274    bdi_alloc_queue_work(bdi, &args);
275}
276
277/*
278 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
279 * furthest end of its superblock's dirty-inode list.
280 *
281 * Before stamping the inode's ->dirtied_when, we check to see whether it is
282 * already the most-recently-dirtied inode on the b_dirty list. If that is
283 * the case then the inode must have been redirtied while it was being written
284 * out and we don't reset its dirtied_when.
285 */
286static void redirty_tail(struct inode *inode)
287{
288    struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
289
290    if (!list_empty(&wb->b_dirty)) {
291        struct inode *tail;
292
293        tail = list_entry(wb->b_dirty.next, struct inode, i_list);
294        if (time_before(inode->dirtied_when, tail->dirtied_when))
295            inode->dirtied_when = jiffies;
296    }
297    list_move(&inode->i_list, &wb->b_dirty);
298}
299
300/*
301 * requeue inode for re-scanning after bdi->b_io list is exhausted.
302 */
303static void requeue_io(struct inode *inode)
304{
305    struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
306
307    list_move(&inode->i_list, &wb->b_more_io);
308}
309
310static void inode_sync_complete(struct inode *inode)
311{
312    /*
313     * Prevent speculative execution through spin_unlock(&inode_lock);
314     */
315    smp_mb();
316    wake_up_bit(&inode->i_state, __I_SYNC);
317}
318
319static bool inode_dirtied_after(struct inode *inode, unsigned long t)
320{
321    bool ret = time_after(inode->dirtied_when, t);
322#ifndef CONFIG_64BIT
323    /*
324     * For inodes being constantly redirtied, dirtied_when can get stuck.
325     * It _appears_ to be in the future, but is actually in distant past.
326     * This test is necessary to prevent such wrapped-around relative times
327     * from permanently stopping the whole bdi writeback.
328     */
329    ret = ret && time_before_eq(inode->dirtied_when, jiffies);
330#endif
331    return ret;
332}
333
334/*
335 * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
336 */
337static void move_expired_inodes(struct list_head *delaying_queue,
338                   struct list_head *dispatch_queue,
339                unsigned long *older_than_this)
340{
341    LIST_HEAD(tmp);
342    struct list_head *pos, *node;
343    struct super_block *sb = NULL;
344    struct inode *inode;
345    int do_sb_sort = 0;
346
347    while (!list_empty(delaying_queue)) {
348        inode = list_entry(delaying_queue->prev, struct inode, i_list);
349        if (older_than_this &&
350            inode_dirtied_after(inode, *older_than_this))
351            break;
352        if (sb && sb != inode->i_sb)
353            do_sb_sort = 1;
354        sb = inode->i_sb;
355        list_move(&inode->i_list, &tmp);
356    }
357
358    /* just one sb in list, splice to dispatch_queue and we're done */
359    if (!do_sb_sort) {
360        list_splice(&tmp, dispatch_queue);
361        return;
362    }
363
364    /* Move inodes from one superblock together */
365    while (!list_empty(&tmp)) {
366        inode = list_entry(tmp.prev, struct inode, i_list);
367        sb = inode->i_sb;
368        list_for_each_prev_safe(pos, node, &tmp) {
369            inode = list_entry(pos, struct inode, i_list);
370            if (inode->i_sb == sb)
371                list_move(&inode->i_list, dispatch_queue);
372        }
373    }
374}
375
376/*
377 * Queue all expired dirty inodes for io, eldest first.
378 */
379static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
380{
381    list_splice_init(&wb->b_more_io, wb->b_io.prev);
382    move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
383}
384
385static int write_inode(struct inode *inode, struct writeback_control *wbc)
386{
387    if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
388        return inode->i_sb->s_op->write_inode(inode, wbc);
389    return 0;
390}
391
392/*
393 * Wait for writeback on an inode to complete.
394 */
395static void inode_wait_for_writeback(struct inode *inode)
396{
397    DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
398    wait_queue_head_t *wqh;
399
400    wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
401    do {
402        spin_unlock(&inode_lock);
403        __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
404        spin_lock(&inode_lock);
405    } while (inode->i_state & I_SYNC);
406}
407
408/*
409 * Write out an inode's dirty pages. Called under inode_lock. Either the
410 * caller has ref on the inode (either via __iget or via syscall against an fd)
411 * or the inode has I_WILL_FREE set (via generic_forget_inode)
412 *
413 * If `wait' is set, wait on the writeout.
414 *
415 * The whole writeout design is quite complex and fragile. We want to avoid
416 * starvation of particular inodes when others are being redirtied, prevent
417 * livelocks, etc.
418 *
419 * Called under inode_lock.
420 */
421static int
422writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
423{
424    struct address_space *mapping = inode->i_mapping;
425    unsigned dirty;
426    int ret;
427
428    if (!atomic_read(&inode->i_count))
429        WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
430    else
431        WARN_ON(inode->i_state & I_WILL_FREE);
432
433    if (inode->i_state & I_SYNC) {
434        /*
435         * If this inode is locked for writeback and we are not doing
436         * writeback-for-data-integrity, move it to b_more_io so that
437         * writeback can proceed with the other inodes on s_io.
438         *
439         * We'll have another go at writing back this inode when we
440         * completed a full scan of b_io.
441         */
442        if (wbc->sync_mode != WB_SYNC_ALL) {
443            requeue_io(inode);
444            return 0;
445        }
446
447        /*
448         * It's a data-integrity sync. We must wait.
449         */
450        inode_wait_for_writeback(inode);
451    }
452
453    BUG_ON(inode->i_state & I_SYNC);
454
455    /* Set I_SYNC, reset I_DIRTY */
456    dirty = inode->i_state & I_DIRTY;
457    inode->i_state |= I_SYNC;
458    inode->i_state &= ~I_DIRTY;
459
460    spin_unlock(&inode_lock);
461
462    ret = do_writepages(mapping, wbc);
463
464    /*
465     * Make sure to wait on the data before writing out the metadata.
466     * This is important for filesystems that modify metadata on data
467     * I/O completion.
468     */
469    if (wbc->sync_mode == WB_SYNC_ALL) {
470        int err = filemap_fdatawait(mapping);
471        if (ret == 0)
472            ret = err;
473    }
474
475    /* Don't write the inode if only I_DIRTY_PAGES was set */
476    if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
477        int err = write_inode(inode, wbc);
478        if (ret == 0)
479            ret = err;
480    }
481
482    spin_lock(&inode_lock);
483    inode->i_state &= ~I_SYNC;
484    if (!(inode->i_state & (I_FREEING | I_CLEAR))) {
485        if ((inode->i_state & I_DIRTY_PAGES) && wbc->for_kupdate) {
486            /*
487             * More pages get dirtied by a fast dirtier.
488             */
489            goto select_queue;
490        } else if (inode->i_state & I_DIRTY) {
491            /*
492             * At least XFS will redirty the inode during the
493             * writeback (delalloc) and on io completion (isize).
494             */
495            redirty_tail(inode);
496        } else if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
497            /*
498             * We didn't write back all the pages. nfs_writepages()
499             * sometimes bales out without doing anything. Redirty
500             * the inode; Move it from b_io onto b_more_io/b_dirty.
501             */
502            /*
503             * akpm: if the caller was the kupdate function we put
504             * this inode at the head of b_dirty so it gets first
505             * consideration. Otherwise, move it to the tail, for
506             * the reasons described there. I'm not really sure
507             * how much sense this makes. Presumably I had a good
508             * reasons for doing it this way, and I'd rather not
509             * muck with it at present.
510             */
511            if (wbc->for_kupdate) {
512                /*
513                 * For the kupdate function we move the inode
514                 * to b_more_io so it will get more writeout as
515                 * soon as the queue becomes uncongested.
516                 */
517                inode->i_state |= I_DIRTY_PAGES;
518select_queue:
519                if (wbc->nr_to_write <= 0) {
520                    /*
521                     * slice used up: queue for next turn
522                     */
523                    requeue_io(inode);
524                } else {
525                    /*
526                     * somehow blocked: retry later
527                     */
528                    redirty_tail(inode);
529                }
530            } else {
531                /*
532                 * Otherwise fully redirty the inode so that
533                 * other inodes on this superblock will get some
534                 * writeout. Otherwise heavy writing to one
535                 * file would indefinitely suspend writeout of
536                 * all the other files.
537                 */
538                inode->i_state |= I_DIRTY_PAGES;
539                redirty_tail(inode);
540            }
541        } else if (atomic_read(&inode->i_count)) {
542            /*
543             * The inode is clean, inuse
544             */
545            list_move(&inode->i_list, &inode_in_use);
546        } else {
547            /*
548             * The inode is clean, unused
549             */
550            list_move(&inode->i_list, &inode_unused);
551        }
552    }
553    inode_sync_complete(inode);
554    return ret;
555}
556
557static void unpin_sb_for_writeback(struct super_block *sb)
558{
559    up_read(&sb->s_umount);
560    put_super(sb);
561}
562
563enum sb_pin_state {
564    SB_PINNED,
565    SB_NOT_PINNED,
566    SB_PIN_FAILED
567};
568
569/*
570 * For WB_SYNC_NONE writeback, the caller does not have the sb pinned
571 * before calling writeback. So make sure that we do pin it, so it doesn't
572 * go away while we are writing inodes from it.
573 */
574static enum sb_pin_state pin_sb_for_writeback(struct writeback_control *wbc,
575                          struct super_block *sb)
576{
577    /*
578     * Caller must already hold the ref for this
579     */
580    if (wbc->sync_mode == WB_SYNC_ALL) {
581        WARN_ON(!rwsem_is_locked(&sb->s_umount));
582        return SB_NOT_PINNED;
583    }
584    spin_lock(&sb_lock);
585    sb->s_count++;
586    if (down_read_trylock(&sb->s_umount)) {
587        if (sb->s_root) {
588            spin_unlock(&sb_lock);
589            return SB_PINNED;
590        }
591        /*
592         * umounted, drop rwsem again and fall through to failure
593         */
594        up_read(&sb->s_umount);
595    }
596    sb->s_count--;
597    spin_unlock(&sb_lock);
598    return SB_PIN_FAILED;
599}
600
601/*
602 * Write a portion of b_io inodes which belong to @sb.
603 * If @wbc->sb != NULL, then find and write all such
604 * inodes. Otherwise write only ones which go sequentially
605 * in reverse order.
606 * Return 1, if the caller writeback routine should be
607 * interrupted. Otherwise return 0.
608 */
609static int writeback_sb_inodes(struct super_block *sb,
610                   struct bdi_writeback *wb,
611                   struct writeback_control *wbc)
612{
613    while (!list_empty(&wb->b_io)) {
614        long pages_skipped;
615        struct inode *inode = list_entry(wb->b_io.prev,
616                         struct inode, i_list);
617        if (wbc->sb && sb != inode->i_sb) {
618            /* super block given and doesn't
619               match, skip this inode */
620            redirty_tail(inode);
621            continue;
622        }
623        if (sb != inode->i_sb)
624            /* finish with this superblock */
625            return 0;
626        if (inode->i_state & (I_NEW | I_WILL_FREE)) {
627            requeue_io(inode);
628            continue;
629        }
630        /*
631         * Was this inode dirtied after sync_sb_inodes was called?
632         * This keeps sync from extra jobs and livelock.
633         */
634        if (inode_dirtied_after(inode, wbc->wb_start))
635            return 1;
636
637        BUG_ON(inode->i_state & (I_FREEING | I_CLEAR));
638        __iget(inode);
639        pages_skipped = wbc->pages_skipped;
640        writeback_single_inode(inode, wbc);
641        if (wbc->pages_skipped != pages_skipped) {
642            /*
643             * writeback is not making progress due to locked
644             * buffers. Skip this inode for now.
645             */
646            redirty_tail(inode);
647        }
648        spin_unlock(&inode_lock);
649        iput(inode);
650        cond_resched();
651        spin_lock(&inode_lock);
652        if (wbc->nr_to_write <= 0) {
653            wbc->more_io = 1;
654            return 1;
655        }
656        if (!list_empty(&wb->b_more_io))
657            wbc->more_io = 1;
658    }
659    /* b_io is empty */
660    return 1;
661}
662
663static void writeback_inodes_wb(struct bdi_writeback *wb,
664                struct writeback_control *wbc)
665{
666    int ret = 0;
667
668    wbc->wb_start = jiffies; /* livelock avoidance */
669    spin_lock(&inode_lock);
670    if (!wbc->for_kupdate || list_empty(&wb->b_io))
671        queue_io(wb, wbc->older_than_this);
672
673    while (!list_empty(&wb->b_io)) {
674        struct inode *inode = list_entry(wb->b_io.prev,
675                         struct inode, i_list);
676        struct super_block *sb = inode->i_sb;
677        enum sb_pin_state state;
678
679        if (wbc->sb && sb != wbc->sb) {
680            /* super block given and doesn't
681               match, skip this inode */
682            redirty_tail(inode);
683            continue;
684        }
685        state = pin_sb_for_writeback(wbc, sb);
686
687        if (state == SB_PIN_FAILED) {
688            requeue_io(inode);
689            continue;
690        }
691        ret = writeback_sb_inodes(sb, wb, wbc);
692
693        if (state == SB_PINNED)
694            unpin_sb_for_writeback(sb);
695        if (ret)
696            break;
697    }
698    spin_unlock(&inode_lock);
699    /* Leave any unwritten inodes on b_io */
700}
701
702void writeback_inodes_wbc(struct writeback_control *wbc)
703{
704    struct backing_dev_info *bdi = wbc->bdi;
705
706    writeback_inodes_wb(&bdi->wb, wbc);
707}
708
709/*
710 * The maximum number of pages to writeout in a single bdi flush/kupdate
711 * operation. We do this so we don't hold I_SYNC against an inode for
712 * enormous amounts of time, which would block a userspace task which has
713 * been forced to throttle against that inode. Also, the code reevaluates
714 * the dirty each time it has written this many pages.
715 */
716#define MAX_WRITEBACK_PAGES 1024
717
718static inline bool over_bground_thresh(void)
719{
720    unsigned long background_thresh, dirty_thresh;
721
722    get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
723
724    return (global_page_state(NR_FILE_DIRTY) +
725        global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
726}
727
728/*
729 * Explicit flushing or periodic writeback of "old" data.
730 *
731 * Define "old": the first time one of an inode's pages is dirtied, we mark the
732 * dirtying-time in the inode's address_space. So this periodic writeback code
733 * just walks the superblock inode list, writing back any inodes which are
734 * older than a specific point in time.
735 *
736 * Try to run once per dirty_writeback_interval. But if a writeback event
737 * takes longer than a dirty_writeback_interval interval, then leave a
738 * one-second gap.
739 *
740 * older_than_this takes precedence over nr_to_write. So we'll only write back
741 * all dirty pages if they are all attached to "old" mappings.
742 */
743static long wb_writeback(struct bdi_writeback *wb,
744             struct wb_writeback_args *args)
745{
746    struct writeback_control wbc = {
747        .bdi = wb->bdi,
748        .sb = args->sb,
749        .sync_mode = args->sync_mode,
750        .older_than_this = NULL,
751        .for_kupdate = args->for_kupdate,
752        .for_background = args->for_background,
753        .range_cyclic = args->range_cyclic,
754    };
755    unsigned long oldest_jif;
756    long wrote = 0;
757    struct inode *inode;
758
759    if (wbc.for_kupdate) {
760        wbc.older_than_this = &oldest_jif;
761        oldest_jif = jiffies -
762                msecs_to_jiffies(dirty_expire_interval * 10);
763    }
764    if (!wbc.range_cyclic) {
765        wbc.range_start = 0;
766        wbc.range_end = LLONG_MAX;
767    }
768
769    for (;;) {
770        /*
771         * Stop writeback when nr_pages has been consumed
772         */
773        if (args->nr_pages <= 0)
774            break;
775
776        /*
777         * For background writeout, stop when we are below the
778         * background dirty threshold
779         */
780        if (args->for_background && !over_bground_thresh())
781            break;
782
783        wbc.more_io = 0;
784        wbc.nr_to_write = MAX_WRITEBACK_PAGES;
785        wbc.pages_skipped = 0;
786        writeback_inodes_wb(wb, &wbc);
787        args->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
788        wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
789
790        /*
791         * If we consumed everything, see if we have more
792         */
793        if (wbc.nr_to_write <= 0)
794            continue;
795        /*
796         * Didn't write everything and we don't have more IO, bail
797         */
798        if (!wbc.more_io)
799            break;
800        /*
801         * Did we write something? Try for more
802         */
803        if (wbc.nr_to_write < MAX_WRITEBACK_PAGES)
804            continue;
805        /*
806         * Nothing written. Wait for some inode to
807         * become available for writeback. Otherwise
808         * we'll just busyloop.
809         */
810        spin_lock(&inode_lock);
811        if (!list_empty(&wb->b_more_io)) {
812            inode = list_entry(wb->b_more_io.prev,
813                        struct inode, i_list);
814            inode_wait_for_writeback(inode);
815        }
816        spin_unlock(&inode_lock);
817    }
818
819    return wrote;
820}
821
822/*
823 * Return the next bdi_work struct that hasn't been processed by this
824 * wb thread yet. ->seen is initially set for each thread that exists
825 * for this device, when a thread first notices a piece of work it
826 * clears its bit. Depending on writeback type, the thread will notify
827 * completion on either receiving the work (WB_SYNC_NONE) or after
828 * it is done (WB_SYNC_ALL).
829 */
830static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
831                       struct bdi_writeback *wb)
832{
833    struct bdi_work *work, *ret = NULL;
834
835    rcu_read_lock();
836
837    list_for_each_entry_rcu(work, &bdi->work_list, list) {
838        if (!test_bit(wb->nr, &work->seen))
839            continue;
840        clear_bit(wb->nr, &work->seen);
841
842        ret = work;
843        break;
844    }
845
846    rcu_read_unlock();
847    return ret;
848}
849
850static long wb_check_old_data_flush(struct bdi_writeback *wb)
851{
852    unsigned long expired;
853    long nr_pages;
854
855    expired = wb->last_old_flush +
856            msecs_to_jiffies(dirty_writeback_interval * 10);
857    if (time_before(jiffies, expired))
858        return 0;
859
860    wb->last_old_flush = jiffies;
861    nr_pages = global_page_state(NR_FILE_DIRTY) +
862            global_page_state(NR_UNSTABLE_NFS) +
863            (inodes_stat.nr_inodes - inodes_stat.nr_unused);
864
865    if (nr_pages) {
866        struct wb_writeback_args args = {
867            .nr_pages = nr_pages,
868            .sync_mode = WB_SYNC_NONE,
869            .for_kupdate = 1,
870            .range_cyclic = 1,
871        };
872
873        return wb_writeback(wb, &args);
874    }
875
876    return 0;
877}
878
879/*
880 * Retrieve work items and do the writeback they describe
881 */
882long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
883{
884    struct backing_dev_info *bdi = wb->bdi;
885    struct bdi_work *work;
886    long wrote = 0;
887
888    while ((work = get_next_work_item(bdi, wb)) != NULL) {
889        struct wb_writeback_args args = work->args;
890
891        /*
892         * Override sync mode, in case we must wait for completion
893         */
894        if (force_wait)
895            work->args.sync_mode = args.sync_mode = WB_SYNC_ALL;
896
897        /*
898         * If this isn't a data integrity operation, just notify
899         * that we have seen this work and we are now starting it.
900         */
901        if (args.sync_mode == WB_SYNC_NONE)
902            wb_clear_pending(wb, work);
903
904        wrote += wb_writeback(wb, &args);
905
906        /*
907         * This is a data integrity writeback, so only do the
908         * notification when we have completed the work.
909         */
910        if (args.sync_mode == WB_SYNC_ALL)
911            wb_clear_pending(wb, work);
912    }
913
914    /*
915     * Check for periodic writeback, kupdated() style
916     */
917    wrote += wb_check_old_data_flush(wb);
918
919    return wrote;
920}
921
922/*
923 * Handle writeback of dirty data for the device backed by this bdi. Also
924 * wakes up periodically and does kupdated style flushing.
925 */
926int bdi_writeback_task(struct bdi_writeback *wb)
927{
928    unsigned long last_active = jiffies;
929    unsigned long wait_jiffies = -1UL;
930    long pages_written;
931
932    while (!kthread_should_stop()) {
933        pages_written = wb_do_writeback(wb, 0);
934
935        if (pages_written)
936            last_active = jiffies;
937        else if (wait_jiffies != -1UL) {
938            unsigned long max_idle;
939
940            /*
941             * Longest period of inactivity that we tolerate. If we
942             * see dirty data again later, the task will get
943             * recreated automatically.
944             */
945            max_idle = max(5UL * 60 * HZ, wait_jiffies);
946            if (time_after(jiffies, max_idle + last_active))
947                break;
948        }
949
950        wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
951        schedule_timeout_interruptible(wait_jiffies);
952        try_to_freeze();
953    }
954
955    return 0;
956}
957
958/*
959 * Schedule writeback for all backing devices. This does WB_SYNC_NONE
960 * writeback, for integrity writeback see bdi_sync_writeback().
961 */
962static void bdi_writeback_all(struct super_block *sb, long nr_pages)
963{
964    struct wb_writeback_args args = {
965        .sb = sb,
966        .nr_pages = nr_pages,
967        .sync_mode = WB_SYNC_NONE,
968    };
969    struct backing_dev_info *bdi;
970
971    rcu_read_lock();
972
973    list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
974        if (!bdi_has_dirty_io(bdi))
975            continue;
976
977        bdi_alloc_queue_work(bdi, &args);
978    }
979
980    rcu_read_unlock();
981}
982
983/*
984 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
985 * the whole world.
986 */
987void wakeup_flusher_threads(long nr_pages)
988{
989    if (nr_pages == 0)
990        nr_pages = global_page_state(NR_FILE_DIRTY) +
991                global_page_state(NR_UNSTABLE_NFS);
992    bdi_writeback_all(NULL, nr_pages);
993}
994
995static noinline void block_dump___mark_inode_dirty(struct inode *inode)
996{
997    if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
998        struct dentry *dentry;
999        const char *name = "?";
1000
1001        dentry = d_find_alias(inode);
1002        if (dentry) {
1003            spin_lock(&dentry->d_lock);
1004            name = (const char *) dentry->d_name.name;
1005        }
1006        printk(KERN_DEBUG
1007               "%s(%d): dirtied inode %lu (%s) on %s\n",
1008               current->comm, task_pid_nr(current), inode->i_ino,
1009               name, inode->i_sb->s_id);
1010        if (dentry) {
1011            spin_unlock(&dentry->d_lock);
1012            dput(dentry);
1013        }
1014    }
1015}
1016
1017/**
1018 * __mark_inode_dirty - internal function
1019 * @inode: inode to mark
1020 * @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
1021 * Mark an inode as dirty. Callers should use mark_inode_dirty or
1022 * mark_inode_dirty_sync.
1023 *
1024 * Put the inode on the super block's dirty list.
1025 *
1026 * CAREFUL! We mark it dirty unconditionally, but move it onto the
1027 * dirty list only if it is hashed or if it refers to a blockdev.
1028 * If it was not hashed, it will never be added to the dirty list
1029 * even if it is later hashed, as it will have been marked dirty already.
1030 *
1031 * In short, make sure you hash any inodes _before_ you start marking
1032 * them dirty.
1033 *
1034 * This function *must* be atomic for the I_DIRTY_PAGES case -
1035 * set_page_dirty() is called under spinlock in several places.
1036 *
1037 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
1038 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
1039 * the kernel-internal blockdev inode represents the dirtying time of the
1040 * blockdev's pages. This is why for I_DIRTY_PAGES we always use
1041 * page->mapping->host, so the page-dirtying time is recorded in the internal
1042 * blockdev inode.
1043 */
1044void __mark_inode_dirty(struct inode *inode, int flags)
1045{
1046    struct super_block *sb = inode->i_sb;
1047
1048    /*
1049     * Don't do this for I_DIRTY_PAGES - that doesn't actually
1050     * dirty the inode itself
1051     */
1052    if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
1053        if (sb->s_op->dirty_inode)
1054            sb->s_op->dirty_inode(inode);
1055    }
1056
1057    /*
1058     * make sure that changes are seen by all cpus before we test i_state
1059     * -- mikulas
1060     */
1061    smp_mb();
1062
1063    /* avoid the locking if we can */
1064    if ((inode->i_state & flags) == flags)
1065        return;
1066
1067    if (unlikely(block_dump))
1068        block_dump___mark_inode_dirty(inode);
1069
1070    spin_lock(&inode_lock);
1071    if ((inode->i_state & flags) != flags) {
1072        const int was_dirty = inode->i_state & I_DIRTY;
1073
1074        inode->i_state |= flags;
1075
1076        /*
1077         * If the inode is being synced, just update its dirty state.
1078         * The unlocker will place the inode on the appropriate
1079         * superblock list, based upon its state.
1080         */
1081        if (inode->i_state & I_SYNC)
1082            goto out;
1083
1084        /*
1085         * Only add valid (hashed) inodes to the superblock's
1086         * dirty list. Add blockdev inodes as well.
1087         */
1088        if (!S_ISBLK(inode->i_mode)) {
1089            if (hlist_unhashed(&inode->i_hash))
1090                goto out;
1091        }
1092        if (inode->i_state & (I_FREEING|I_CLEAR))
1093            goto out;
1094
1095        /*
1096         * If the inode was already on b_dirty/b_io/b_more_io, don't
1097         * reposition it (that would break b_dirty time-ordering).
1098         */
1099        if (!was_dirty) {
1100            struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
1101            struct backing_dev_info *bdi = wb->bdi;
1102
1103            if (bdi_cap_writeback_dirty(bdi) &&
1104                !test_bit(BDI_registered, &bdi->state)) {
1105                WARN_ON(1);
1106                printk(KERN_ERR "bdi-%s not registered\n",
1107                                bdi->name);
1108            }
1109
1110            inode->dirtied_when = jiffies;
1111            list_move(&inode->i_list, &wb->b_dirty);
1112        }
1113    }
1114out:
1115    spin_unlock(&inode_lock);
1116}
1117EXPORT_SYMBOL(__mark_inode_dirty);
1118
1119/*
1120 * Write out a superblock's list of dirty inodes. A wait will be performed
1121 * upon no inodes, all inodes or the final one, depending upon sync_mode.
1122 *
1123 * If older_than_this is non-NULL, then only write out inodes which
1124 * had their first dirtying at a time earlier than *older_than_this.
1125 *
1126 * If `bdi' is non-zero then we're being asked to writeback a specific queue.
1127 * This function assumes that the blockdev superblock's inodes are backed by
1128 * a variety of queues, so all inodes are searched. For other superblocks,
1129 * assume that all inodes are backed by the same queue.
1130 *
1131 * The inodes to be written are parked on bdi->b_io. They are moved back onto
1132 * bdi->b_dirty as they are selected for writing. This way, none can be missed
1133 * on the writer throttling path, and we get decent balancing between many
1134 * throttled threads: we don't want them all piling up on inode_sync_wait.
1135 */
1136static void wait_sb_inodes(struct super_block *sb)
1137{
1138    struct inode *inode, *old_inode = NULL;
1139
1140    /*
1141     * We need to be protected against the filesystem going from
1142     * r/o to r/w or vice versa.
1143     */
1144    WARN_ON(!rwsem_is_locked(&sb->s_umount));
1145
1146    spin_lock(&inode_lock);
1147
1148    /*
1149     * Data integrity sync. Must wait for all pages under writeback,
1150     * because there may have been pages dirtied before our sync
1151     * call, but which had writeout started before we write it out.
1152     * In which case, the inode may not be on the dirty list, but
1153     * we still have to wait for that writeout.
1154     */
1155    list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1156        struct address_space *mapping;
1157
1158        if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
1159            continue;
1160        mapping = inode->i_mapping;
1161        if (mapping->nrpages == 0)
1162            continue;
1163        __iget(inode);
1164        spin_unlock(&inode_lock);
1165        /*
1166         * We hold a reference to 'inode' so it couldn't have
1167         * been removed from s_inodes list while we dropped the
1168         * inode_lock. We cannot iput the inode now as we can
1169         * be holding the last reference and we cannot iput it
1170         * under inode_lock. So we keep the reference and iput
1171         * it later.
1172         */
1173        iput(old_inode);
1174        old_inode = inode;
1175
1176        filemap_fdatawait(mapping);
1177
1178        cond_resched();
1179
1180        spin_lock(&inode_lock);
1181    }
1182    spin_unlock(&inode_lock);
1183    iput(old_inode);
1184}
1185
1186/**
1187 * writeback_inodes_sb - writeback dirty inodes from given super_block
1188 * @sb: the superblock
1189 *
1190 * Start writeback on some inodes on this super_block. No guarantees are made
1191 * on how many (if any) will be written, and this function does not wait
1192 * for IO completion of submitted IO. The number of pages submitted is
1193 * returned.
1194 */
1195void writeback_inodes_sb(struct super_block *sb)
1196{
1197    unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
1198    unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
1199    long nr_to_write;
1200
1201    nr_to_write = nr_dirty + nr_unstable +
1202            (inodes_stat.nr_inodes - inodes_stat.nr_unused);
1203
1204    bdi_start_writeback(sb->s_bdi, sb, nr_to_write);
1205}
1206EXPORT_SYMBOL(writeback_inodes_sb);
1207
1208/**
1209 * writeback_inodes_sb_if_idle - start writeback if none underway
1210 * @sb: the superblock
1211 *
1212 * Invoke writeback_inodes_sb if no writeback is currently underway.
1213 * Returns 1 if writeback was started, 0 if not.
1214 */
1215int writeback_inodes_sb_if_idle(struct super_block *sb)
1216{
1217    if (!writeback_in_progress(sb->s_bdi)) {
1218        writeback_inodes_sb(sb);
1219        return 1;
1220    } else
1221        return 0;
1222}
1223EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
1224
1225/**
1226 * sync_inodes_sb - sync sb inode pages
1227 * @sb: the superblock
1228 *
1229 * This function writes and waits on any dirty inode belonging to this
1230 * super_block. The number of pages synced is returned.
1231 */
1232void sync_inodes_sb(struct super_block *sb)
1233{
1234    bdi_sync_writeback(sb->s_bdi, sb);
1235    wait_sb_inodes(sb);
1236}
1237EXPORT_SYMBOL(sync_inodes_sb);
1238
1239/**
1240 * write_inode_now - write an inode to disk
1241 * @inode: inode to write to disk
1242 * @sync: whether the write should be synchronous or not
1243 *
1244 * This function commits an inode to disk immediately if it is dirty. This is
1245 * primarily needed by knfsd.
1246 *
1247 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1248 */
1249int write_inode_now(struct inode *inode, int sync)
1250{
1251    int ret;
1252    struct writeback_control wbc = {
1253        .nr_to_write = LONG_MAX,
1254        .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1255        .range_start = 0,
1256        .range_end = LLONG_MAX,
1257    };
1258
1259    if (!mapping_cap_writeback_dirty(inode->i_mapping))
1260        wbc.nr_to_write = 0;
1261
1262    might_sleep();
1263    spin_lock(&inode_lock);
1264    ret = writeback_single_inode(inode, &wbc);
1265    spin_unlock(&inode_lock);
1266    if (sync)
1267        inode_sync_wait(inode);
1268    return ret;
1269}
1270EXPORT_SYMBOL(write_inode_now);
1271
1272/**
1273 * sync_inode - write an inode and its pages to disk.
1274 * @inode: the inode to sync
1275 * @wbc: controls the writeback mode
1276 *
1277 * sync_inode() will write an inode and its pages to disk. It will also
1278 * correctly update the inode on its superblock's dirty inode lists and will
1279 * update inode->i_state.
1280 *
1281 * The caller must have a ref on the inode.
1282 */
1283int sync_inode(struct inode *inode, struct writeback_control *wbc)
1284{
1285    int ret;
1286
1287    spin_lock(&inode_lock);
1288    ret = writeback_single_inode(inode, wbc);
1289    spin_unlock(&inode_lock);
1290    return ret;
1291}
1292EXPORT_SYMBOL(sync_inode);
1293

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