4 * Copyright (C) 2002, Linus Torvalds.
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.
11 * 10Apr2002 Andrew Morton
12 * Split out of fs/inode.c
13 * Additions for address_space-based writeback
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>
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>
31 #define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)
34 * We don't actually have pdflush, but this one is exported though /proc...
36 int nr_pdflush_threads;
39 * Passed into wb_writeback(), essentially a subset of writeback_control
41 struct wb_writeback_args {
43 struct super_block *sb;
44 enum writeback_sync_modes sync_mode;
52 * Work items for the bdi_writeback threads
55 struct list_head list; /* pending work list */
56 struct rcu_head rcu_head; /* for RCU free/clear of work */
58 unsigned long seen; /* threads that have seen this work */
59 atomic_t pending; /* number of threads still to do work */
61 struct wb_writeback_args args; /* writeback arguments */
63 unsigned long state; /* flag bits, see WS_* */
71 #define WS_USED (1 << WS_USED_B)
72 #define WS_ONSTACK (1 << WS_ONSTACK_B)
74 static inline bool bdi_work_on_stack(struct bdi_work *work)
76 return test_bit(WS_ONSTACK_B, &work->state);
79 static inline void bdi_work_init(struct bdi_work *work,
80 struct wb_writeback_args *args)
82 INIT_RCU_HEAD(&work->rcu_head);
84 work->state = WS_USED;
88 * writeback_in_progress - determine whether there is writeback in progress
89 * @bdi: the device's backing_dev_info structure.
91 * Determine whether there is writeback waiting to be handled against a
94 int writeback_in_progress(struct backing_dev_info *bdi)
96 return !list_empty(&bdi->work_list);
99 static void bdi_work_clear(struct bdi_work *work)
101 clear_bit(WS_USED_B, &work->state);
102 smp_mb__after_clear_bit();
104 * work can have disappeared at this point. bit waitq functions
105 * should be able to tolerate this, provided bdi_sched_wait does
106 * not dereference it's pointer argument.
108 wake_up_bit(&work->state, WS_USED_B);
111 static void bdi_work_free(struct rcu_head *head)
113 struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);
115 if (!bdi_work_on_stack(work))
118 bdi_work_clear(work);
121 static void wb_work_complete(struct bdi_work *work)
123 const enum writeback_sync_modes sync_mode = work->args.sync_mode;
124 int onstack = bdi_work_on_stack(work);
127 * For allocated work, we can clear the done/seen bit right here.
128 * For on-stack work, we need to postpone both the clear and free
129 * to after the RCU grace period, since the stack could be invalidated
130 * as soon as bdi_work_clear() has done the wakeup.
133 bdi_work_clear(work);
134 if (sync_mode == WB_SYNC_NONE || onstack)
135 call_rcu(&work->rcu_head, bdi_work_free);
138 static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
141 * The caller has retrieved the work arguments from this work,
142 * drop our reference. If this is the last ref, delete and free it
144 if (atomic_dec_and_test(&work->pending)) {
145 struct backing_dev_info *bdi = wb->bdi;
147 spin_lock(&bdi->wb_lock);
148 list_del_rcu(&work->list);
149 spin_unlock(&bdi->wb_lock);
151 wb_work_complete(work);
155 static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
157 work->seen = bdi->wb_mask;
159 atomic_set(&work->pending, bdi->wb_cnt);
160 BUG_ON(!bdi->wb_cnt);
163 * list_add_tail_rcu() contains the necessary barriers to
164 * make sure the above stores are seen before the item is
165 * noticed on the list
167 spin_lock(&bdi->wb_lock);
168 list_add_tail_rcu(&work->list, &bdi->work_list);
169 spin_unlock(&bdi->wb_lock);
172 * If the default thread isn't there, make sure we add it. When
173 * it gets created and wakes up, we'll run this work.
175 if (unlikely(list_empty_careful(&bdi->wb_list)))
176 wake_up_process(default_backing_dev_info.wb.task);
178 struct bdi_writeback *wb = &bdi->wb;
181 wake_up_process(wb->task);
186 * Used for on-stack allocated work items. The caller needs to wait until
187 * the wb threads have acked the work before it's safe to continue.
189 static void bdi_wait_on_work_clear(struct bdi_work *work)
191 wait_on_bit(&work->state, WS_USED_B, bdi_sched_wait,
192 TASK_UNINTERRUPTIBLE);
195 static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
196 struct wb_writeback_args *args)
198 struct bdi_work *work;
201 * This is WB_SYNC_NONE writeback, so if allocation fails just
202 * wakeup the thread for old dirty data writeback
204 work = kmalloc(sizeof(*work), GFP_ATOMIC);
206 bdi_work_init(work, args);
207 bdi_queue_work(bdi, work);
209 struct bdi_writeback *wb = &bdi->wb;
212 wake_up_process(wb->task);
217 * bdi_sync_writeback - start and wait for writeback
218 * @bdi: the backing device to write from
219 * @sb: write inodes from this super_block
222 * This does WB_SYNC_ALL data integrity writeback and waits for the
223 * IO to complete. Callers must hold the sb s_umount semaphore for
224 * reading, to avoid having the super disappear before we are done.
226 static void bdi_sync_writeback(struct backing_dev_info *bdi,
227 struct super_block *sb)
229 struct wb_writeback_args args = {
231 .sync_mode = WB_SYNC_ALL,
232 .nr_pages = LONG_MAX,
235 * Setting sb_pinned is not necessary for WB_SYNC_ALL, but
236 * lets make it explicitly clear.
240 struct bdi_work work;
242 bdi_work_init(&work, &args);
243 work.state |= WS_ONSTACK;
245 bdi_queue_work(bdi, &work);
246 bdi_wait_on_work_clear(&work);
250 * bdi_start_writeback - start writeback
251 * @bdi: the backing device to write from
252 * @sb: write inodes from this super_block
253 * @nr_pages: the number of pages to write
254 * @sb_locked: caller already holds sb umount sem.
257 * This does WB_SYNC_NONE opportunistic writeback. The IO is only
258 * started when this function returns, we make no guarentees on
259 * completion. Caller specifies whether sb umount sem is held already or not.
262 void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
263 long nr_pages, int sb_locked)
265 struct wb_writeback_args args = {
267 .sync_mode = WB_SYNC_NONE,
268 .nr_pages = nr_pages,
270 .sb_pinned = sb_locked,
274 * We treat @nr_pages=0 as the special case to do background writeback,
275 * ie. to sync pages until the background dirty threshold is reached.
278 args.nr_pages = LONG_MAX;
279 args.for_background = 1;
282 bdi_alloc_queue_work(bdi, &args);
286 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
287 * furthest end of its superblock's dirty-inode list.
289 * Before stamping the inode's ->dirtied_when, we check to see whether it is
290 * already the most-recently-dirtied inode on the b_dirty list. If that is
291 * the case then the inode must have been redirtied while it was being written
292 * out and we don't reset its dirtied_when.
294 static void redirty_tail(struct inode *inode)
296 struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
298 if (!list_empty(&wb->b_dirty)) {
301 tail = list_entry(wb->b_dirty.next, struct inode, i_list);
302 if (time_before(inode->dirtied_when, tail->dirtied_when))
303 inode->dirtied_when = jiffies;
305 list_move(&inode->i_list, &wb->b_dirty);
309 * requeue inode for re-scanning after bdi->b_io list is exhausted.
311 static void requeue_io(struct inode *inode)
313 struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
315 list_move(&inode->i_list, &wb->b_more_io);
318 static void inode_sync_complete(struct inode *inode)
321 * Prevent speculative execution through spin_unlock(&inode_lock);
324 wake_up_bit(&inode->i_state, __I_SYNC);
327 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
329 bool ret = time_after(inode->dirtied_when, t);
332 * For inodes being constantly redirtied, dirtied_when can get stuck.
333 * It _appears_ to be in the future, but is actually in distant past.
334 * This test is necessary to prevent such wrapped-around relative times
335 * from permanently stopping the whole bdi writeback.
337 ret = ret && time_before_eq(inode->dirtied_when, jiffies);
343 * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
345 static void move_expired_inodes(struct list_head *delaying_queue,
346 struct list_head *dispatch_queue,
347 unsigned long *older_than_this)
350 struct list_head *pos, *node;
351 struct super_block *sb = NULL;
355 while (!list_empty(delaying_queue)) {
356 inode = list_entry(delaying_queue->prev, struct inode, i_list);
357 if (older_than_this &&
358 inode_dirtied_after(inode, *older_than_this))
360 if (sb && sb != inode->i_sb)
363 list_move(&inode->i_list, &tmp);
366 /* just one sb in list, splice to dispatch_queue and we're done */
368 list_splice(&tmp, dispatch_queue);
372 /* Move inodes from one superblock together */
373 while (!list_empty(&tmp)) {
374 inode = list_entry(tmp.prev, struct inode, i_list);
376 list_for_each_prev_safe(pos, node, &tmp) {
377 inode = list_entry(pos, struct inode, i_list);
378 if (inode->i_sb == sb)
379 list_move(&inode->i_list, dispatch_queue);
385 * Queue all expired dirty inodes for io, eldest first.
387 static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
389 list_splice_init(&wb->b_more_io, wb->b_io.prev);
390 move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
393 static int write_inode(struct inode *inode, struct writeback_control *wbc)
395 if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
396 return inode->i_sb->s_op->write_inode(inode, wbc);
401 * Wait for writeback on an inode to complete.
403 static void inode_wait_for_writeback(struct inode *inode)
405 DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
406 wait_queue_head_t *wqh;
408 wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
410 spin_unlock(&inode_lock);
411 __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
412 spin_lock(&inode_lock);
413 } while (inode->i_state & I_SYNC);
417 * Write out an inode's dirty pages. Called under inode_lock. Either the
418 * caller has ref on the inode (either via __iget or via syscall against an fd)
419 * or the inode has I_WILL_FREE set (via generic_forget_inode)
421 * If `wait' is set, wait on the writeout.
423 * The whole writeout design is quite complex and fragile. We want to avoid
424 * starvation of particular inodes when others are being redirtied, prevent
427 * Called under inode_lock.
430 writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
432 struct address_space *mapping = inode->i_mapping;
436 if (!atomic_read(&inode->i_count))
437 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
439 WARN_ON(inode->i_state & I_WILL_FREE);
441 if (inode->i_state & I_SYNC) {
443 * If this inode is locked for writeback and we are not doing
444 * writeback-for-data-integrity, move it to b_more_io so that
445 * writeback can proceed with the other inodes on s_io.
447 * We'll have another go at writing back this inode when we
448 * completed a full scan of b_io.
450 if (wbc->sync_mode != WB_SYNC_ALL) {
456 * It's a data-integrity sync. We must wait.
458 inode_wait_for_writeback(inode);
461 BUG_ON(inode->i_state & I_SYNC);
463 /* Set I_SYNC, reset I_DIRTY_PAGES */
464 inode->i_state |= I_SYNC;
465 inode->i_state &= ~I_DIRTY_PAGES;
466 spin_unlock(&inode_lock);
468 ret = do_writepages(mapping, wbc);
471 * Make sure to wait on the data before writing out the metadata.
472 * This is important for filesystems that modify metadata on data
475 if (wbc->sync_mode == WB_SYNC_ALL) {
476 int err = filemap_fdatawait(mapping);
482 * Some filesystems may redirty the inode during the writeback
483 * due to delalloc, clear dirty metadata flags right before
486 spin_lock(&inode_lock);
487 dirty = inode->i_state & I_DIRTY;
488 inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
489 spin_unlock(&inode_lock);
490 /* Don't write the inode if only I_DIRTY_PAGES was set */
491 if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
492 int err = write_inode(inode, wbc);
497 spin_lock(&inode_lock);
498 inode->i_state &= ~I_SYNC;
499 if (!(inode->i_state & (I_FREEING | I_CLEAR))) {
500 if ((inode->i_state & I_DIRTY_PAGES) && wbc->for_kupdate) {
502 * More pages get dirtied by a fast dirtier.
505 } else if (inode->i_state & I_DIRTY) {
507 * At least XFS will redirty the inode during the
508 * writeback (delalloc) and on io completion (isize).
511 } else if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
513 * We didn't write back all the pages. nfs_writepages()
514 * sometimes bales out without doing anything. Redirty
515 * the inode; Move it from b_io onto b_more_io/b_dirty.
518 * akpm: if the caller was the kupdate function we put
519 * this inode at the head of b_dirty so it gets first
520 * consideration. Otherwise, move it to the tail, for
521 * the reasons described there. I'm not really sure
522 * how much sense this makes. Presumably I had a good
523 * reasons for doing it this way, and I'd rather not
524 * muck with it at present.
526 if (wbc->for_kupdate) {
528 * For the kupdate function we move the inode
529 * to b_more_io so it will get more writeout as
530 * soon as the queue becomes uncongested.
532 inode->i_state |= I_DIRTY_PAGES;
534 if (wbc->nr_to_write <= 0) {
536 * slice used up: queue for next turn
541 * somehow blocked: retry later
547 * Otherwise fully redirty the inode so that
548 * other inodes on this superblock will get some
549 * writeout. Otherwise heavy writing to one
550 * file would indefinitely suspend writeout of
551 * all the other files.
553 inode->i_state |= I_DIRTY_PAGES;
556 } else if (atomic_read(&inode->i_count)) {
558 * The inode is clean, inuse
560 list_move(&inode->i_list, &inode_in_use);
563 * The inode is clean, unused
565 list_move(&inode->i_list, &inode_unused);
568 inode_sync_complete(inode);
572 static void unpin_sb_for_writeback(struct super_block *sb)
574 up_read(&sb->s_umount);
585 * For WB_SYNC_NONE writeback, the caller does not have the sb pinned
586 * before calling writeback. So make sure that we do pin it, so it doesn't
587 * go away while we are writing inodes from it.
589 static enum sb_pin_state pin_sb_for_writeback(struct writeback_control *wbc,
590 struct super_block *sb)
593 * Caller must already hold the ref for this
595 if (wbc->sync_mode == WB_SYNC_ALL || wbc->sb_pinned) {
596 WARN_ON(!rwsem_is_locked(&sb->s_umount));
597 return SB_NOT_PINNED;
601 if (down_read_trylock(&sb->s_umount)) {
603 spin_unlock(&sb_lock);
607 * umounted, drop rwsem again and fall through to failure
609 up_read(&sb->s_umount);
612 spin_unlock(&sb_lock);
613 return SB_PIN_FAILED;
617 * Write a portion of b_io inodes which belong to @sb.
618 * If @wbc->sb != NULL, then find and write all such
619 * inodes. Otherwise write only ones which go sequentially
621 * Return 1, if the caller writeback routine should be
622 * interrupted. Otherwise return 0.
624 static int writeback_sb_inodes(struct super_block *sb,
625 struct bdi_writeback *wb,
626 struct writeback_control *wbc)
628 while (!list_empty(&wb->b_io)) {
630 struct inode *inode = list_entry(wb->b_io.prev,
631 struct inode, i_list);
632 if (wbc->sb && sb != inode->i_sb) {
633 /* super block given and doesn't
634 match, skip this inode */
638 if (sb != inode->i_sb)
639 /* finish with this superblock */
641 if (inode->i_state & (I_NEW | I_WILL_FREE)) {
646 * Was this inode dirtied after sync_sb_inodes was called?
647 * This keeps sync from extra jobs and livelock.
649 if (inode_dirtied_after(inode, wbc->wb_start))
652 BUG_ON(inode->i_state & (I_FREEING | I_CLEAR));
654 pages_skipped = wbc->pages_skipped;
655 writeback_single_inode(inode, wbc);
656 if (wbc->pages_skipped != pages_skipped) {
658 * writeback is not making progress due to locked
659 * buffers. Skip this inode for now.
663 spin_unlock(&inode_lock);
666 spin_lock(&inode_lock);
667 if (wbc->nr_to_write <= 0) {
671 if (!list_empty(&wb->b_more_io))
678 static void writeback_inodes_wb(struct bdi_writeback *wb,
679 struct writeback_control *wbc)
683 wbc->wb_start = jiffies; /* livelock avoidance */
684 spin_lock(&inode_lock);
685 if (!wbc->for_kupdate || list_empty(&wb->b_io))
686 queue_io(wb, wbc->older_than_this);
688 while (!list_empty(&wb->b_io)) {
689 struct inode *inode = list_entry(wb->b_io.prev,
690 struct inode, i_list);
691 struct super_block *sb = inode->i_sb;
692 enum sb_pin_state state;
694 if (wbc->sb && sb != wbc->sb) {
695 /* super block given and doesn't
696 match, skip this inode */
700 state = pin_sb_for_writeback(wbc, sb);
702 if (state == SB_PIN_FAILED) {
706 ret = writeback_sb_inodes(sb, wb, wbc);
708 if (state == SB_PINNED)
709 unpin_sb_for_writeback(sb);
713 spin_unlock(&inode_lock);
714 /* Leave any unwritten inodes on b_io */
717 void writeback_inodes_wbc(struct writeback_control *wbc)
719 struct backing_dev_info *bdi = wbc->bdi;
721 writeback_inodes_wb(&bdi->wb, wbc);
725 * The maximum number of pages to writeout in a single bdi flush/kupdate
726 * operation. We do this so we don't hold I_SYNC against an inode for
727 * enormous amounts of time, which would block a userspace task which has
728 * been forced to throttle against that inode. Also, the code reevaluates
729 * the dirty each time it has written this many pages.
731 #define MAX_WRITEBACK_PAGES 1024
733 static inline bool over_bground_thresh(void)
735 unsigned long background_thresh, dirty_thresh;
737 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
739 return (global_page_state(NR_FILE_DIRTY) +
740 global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
744 * Explicit flushing or periodic writeback of "old" data.
746 * Define "old": the first time one of an inode's pages is dirtied, we mark the
747 * dirtying-time in the inode's address_space. So this periodic writeback code
748 * just walks the superblock inode list, writing back any inodes which are
749 * older than a specific point in time.
751 * Try to run once per dirty_writeback_interval. But if a writeback event
752 * takes longer than a dirty_writeback_interval interval, then leave a
755 * older_than_this takes precedence over nr_to_write. So we'll only write back
756 * all dirty pages if they are all attached to "old" mappings.
758 static long wb_writeback(struct bdi_writeback *wb,
759 struct wb_writeback_args *args)
761 struct writeback_control wbc = {
764 .sync_mode = args->sync_mode,
765 .older_than_this = NULL,
766 .for_kupdate = args->for_kupdate,
767 .for_background = args->for_background,
768 .range_cyclic = args->range_cyclic,
769 .sb_pinned = args->sb_pinned,
771 unsigned long oldest_jif;
775 if (wbc.for_kupdate) {
776 wbc.older_than_this = &oldest_jif;
777 oldest_jif = jiffies -
778 msecs_to_jiffies(dirty_expire_interval * 10);
780 if (!wbc.range_cyclic) {
782 wbc.range_end = LLONG_MAX;
787 * Stop writeback when nr_pages has been consumed
789 if (args->nr_pages <= 0)
793 * For background writeout, stop when we are below the
794 * background dirty threshold
796 if (args->for_background && !over_bground_thresh())
800 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
801 wbc.pages_skipped = 0;
802 writeback_inodes_wb(wb, &wbc);
803 args->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
804 wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
807 * If we consumed everything, see if we have more
809 if (wbc.nr_to_write <= 0)
812 * Didn't write everything and we don't have more IO, bail
817 * Did we write something? Try for more
819 if (wbc.nr_to_write < MAX_WRITEBACK_PAGES)
822 * Nothing written. Wait for some inode to
823 * become available for writeback. Otherwise
824 * we'll just busyloop.
826 spin_lock(&inode_lock);
827 if (!list_empty(&wb->b_more_io)) {
828 inode = list_entry(wb->b_more_io.prev,
829 struct inode, i_list);
830 inode_wait_for_writeback(inode);
832 spin_unlock(&inode_lock);
839 * Return the next bdi_work struct that hasn't been processed by this
840 * wb thread yet. ->seen is initially set for each thread that exists
841 * for this device, when a thread first notices a piece of work it
842 * clears its bit. Depending on writeback type, the thread will notify
843 * completion on either receiving the work (WB_SYNC_NONE) or after
844 * it is done (WB_SYNC_ALL).
846 static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
847 struct bdi_writeback *wb)
849 struct bdi_work *work, *ret = NULL;
853 list_for_each_entry_rcu(work, &bdi->work_list, list) {
854 if (!test_bit(wb->nr, &work->seen))
856 clear_bit(wb->nr, &work->seen);
866 static long wb_check_old_data_flush(struct bdi_writeback *wb)
868 unsigned long expired;
872 * When set to zero, disable periodic writeback
874 if (!dirty_writeback_interval)
877 expired = wb->last_old_flush +
878 msecs_to_jiffies(dirty_writeback_interval * 10);
879 if (time_before(jiffies, expired))
882 wb->last_old_flush = jiffies;
883 nr_pages = global_page_state(NR_FILE_DIRTY) +
884 global_page_state(NR_UNSTABLE_NFS) +
885 (inodes_stat.nr_inodes - inodes_stat.nr_unused);
888 struct wb_writeback_args args = {
889 .nr_pages = nr_pages,
890 .sync_mode = WB_SYNC_NONE,
895 return wb_writeback(wb, &args);
902 * Retrieve work items and do the writeback they describe
904 long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
906 struct backing_dev_info *bdi = wb->bdi;
907 struct bdi_work *work;
910 while ((work = get_next_work_item(bdi, wb)) != NULL) {
911 struct wb_writeback_args args = work->args;
914 * Override sync mode, in case we must wait for completion
917 work->args.sync_mode = args.sync_mode = WB_SYNC_ALL;
920 * If this isn't a data integrity operation, just notify
921 * that we have seen this work and we are now starting it.
923 if (args.sync_mode == WB_SYNC_NONE)
924 wb_clear_pending(wb, work);
926 wrote += wb_writeback(wb, &args);
929 * This is a data integrity writeback, so only do the
930 * notification when we have completed the work.
932 if (args.sync_mode == WB_SYNC_ALL)
933 wb_clear_pending(wb, work);
937 * Check for periodic writeback, kupdated() style
939 wrote += wb_check_old_data_flush(wb);
945 * Handle writeback of dirty data for the device backed by this bdi. Also
946 * wakes up periodically and does kupdated style flushing.
948 int bdi_writeback_task(struct bdi_writeback *wb)
950 unsigned long last_active = jiffies;
951 unsigned long wait_jiffies = -1UL;
954 while (!kthread_should_stop()) {
955 pages_written = wb_do_writeback(wb, 0);
958 last_active = jiffies;
959 else if (wait_jiffies != -1UL) {
960 unsigned long max_idle;
963 * Longest period of inactivity that we tolerate. If we
964 * see dirty data again later, the task will get
965 * recreated automatically.
967 max_idle = max(5UL * 60 * HZ, wait_jiffies);
968 if (time_after(jiffies, max_idle + last_active))
972 if (dirty_writeback_interval) {
973 wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
974 schedule_timeout_interruptible(wait_jiffies);
985 * Schedule writeback for all backing devices. This does WB_SYNC_NONE
986 * writeback, for integrity writeback see bdi_sync_writeback().
988 static void bdi_writeback_all(struct super_block *sb, long nr_pages)
990 struct wb_writeback_args args = {
992 .nr_pages = nr_pages,
993 .sync_mode = WB_SYNC_NONE,
995 struct backing_dev_info *bdi;
999 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1000 if (!bdi_has_dirty_io(bdi))
1003 bdi_alloc_queue_work(bdi, &args);
1010 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
1013 void wakeup_flusher_threads(long nr_pages)
1016 nr_pages = global_page_state(NR_FILE_DIRTY) +
1017 global_page_state(NR_UNSTABLE_NFS);
1018 bdi_writeback_all(NULL, nr_pages);
1021 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
1023 if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
1024 struct dentry *dentry;
1025 const char *name = "?";
1027 dentry = d_find_alias(inode);
1029 spin_lock(&dentry->d_lock);
1030 name = (const char *) dentry->d_name.name;
1033 "%s(%d): dirtied inode %lu (%s) on %s\n",
1034 current->comm, task_pid_nr(current), inode->i_ino,
1035 name, inode->i_sb->s_id);
1037 spin_unlock(&dentry->d_lock);
1044 * __mark_inode_dirty - internal function
1045 * @inode: inode to mark
1046 * @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
1047 * Mark an inode as dirty. Callers should use mark_inode_dirty or
1048 * mark_inode_dirty_sync.
1050 * Put the inode on the super block's dirty list.
1052 * CAREFUL! We mark it dirty unconditionally, but move it onto the
1053 * dirty list only if it is hashed or if it refers to a blockdev.
1054 * If it was not hashed, it will never be added to the dirty list
1055 * even if it is later hashed, as it will have been marked dirty already.
1057 * In short, make sure you hash any inodes _before_ you start marking
1060 * This function *must* be atomic for the I_DIRTY_PAGES case -
1061 * set_page_dirty() is called under spinlock in several places.
1063 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
1064 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
1065 * the kernel-internal blockdev inode represents the dirtying time of the
1066 * blockdev's pages. This is why for I_DIRTY_PAGES we always use
1067 * page->mapping->host, so the page-dirtying time is recorded in the internal
1070 void __mark_inode_dirty(struct inode *inode, int flags)
1072 struct super_block *sb = inode->i_sb;
1075 * Don't do this for I_DIRTY_PAGES - that doesn't actually
1076 * dirty the inode itself
1078 if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
1079 if (sb->s_op->dirty_inode)
1080 sb->s_op->dirty_inode(inode);
1084 * make sure that changes are seen by all cpus before we test i_state
1089 /* avoid the locking if we can */
1090 if ((inode->i_state & flags) == flags)
1093 if (unlikely(block_dump))
1094 block_dump___mark_inode_dirty(inode);
1096 spin_lock(&inode_lock);
1097 if ((inode->i_state & flags) != flags) {
1098 const int was_dirty = inode->i_state & I_DIRTY;
1100 inode->i_state |= flags;
1103 * If the inode is being synced, just update its dirty state.
1104 * The unlocker will place the inode on the appropriate
1105 * superblock list, based upon its state.
1107 if (inode->i_state & I_SYNC)
1111 * Only add valid (hashed) inodes to the superblock's
1112 * dirty list. Add blockdev inodes as well.
1114 if (!S_ISBLK(inode->i_mode)) {
1115 if (hlist_unhashed(&inode->i_hash))
1118 if (inode->i_state & (I_FREEING|I_CLEAR))
1122 * If the inode was already on b_dirty/b_io/b_more_io, don't
1123 * reposition it (that would break b_dirty time-ordering).
1126 struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
1127 struct backing_dev_info *bdi = wb->bdi;
1129 if (bdi_cap_writeback_dirty(bdi) &&
1130 !test_bit(BDI_registered, &bdi->state)) {
1132 printk(KERN_ERR "bdi-%s not registered\n",
1136 inode->dirtied_when = jiffies;
1137 list_move(&inode->i_list, &wb->b_dirty);
1141 spin_unlock(&inode_lock);
1143 EXPORT_SYMBOL(__mark_inode_dirty);
1146 * Write out a superblock's list of dirty inodes. A wait will be performed
1147 * upon no inodes, all inodes or the final one, depending upon sync_mode.
1149 * If older_than_this is non-NULL, then only write out inodes which
1150 * had their first dirtying at a time earlier than *older_than_this.
1152 * If `bdi' is non-zero then we're being asked to writeback a specific queue.
1153 * This function assumes that the blockdev superblock's inodes are backed by
1154 * a variety of queues, so all inodes are searched. For other superblocks,
1155 * assume that all inodes are backed by the same queue.
1157 * The inodes to be written are parked on bdi->b_io. They are moved back onto
1158 * bdi->b_dirty as they are selected for writing. This way, none can be missed
1159 * on the writer throttling path, and we get decent balancing between many
1160 * throttled threads: we don't want them all piling up on inode_sync_wait.
1162 static void wait_sb_inodes(struct super_block *sb)
1164 struct inode *inode, *old_inode = NULL;
1167 * We need to be protected against the filesystem going from
1168 * r/o to r/w or vice versa.
1170 WARN_ON(!rwsem_is_locked(&sb->s_umount));
1172 spin_lock(&inode_lock);
1175 * Data integrity sync. Must wait for all pages under writeback,
1176 * because there may have been pages dirtied before our sync
1177 * call, but which had writeout started before we write it out.
1178 * In which case, the inode may not be on the dirty list, but
1179 * we still have to wait for that writeout.
1181 list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1182 struct address_space *mapping;
1184 if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
1186 mapping = inode->i_mapping;
1187 if (mapping->nrpages == 0)
1190 spin_unlock(&inode_lock);
1192 * We hold a reference to 'inode' so it couldn't have
1193 * been removed from s_inodes list while we dropped the
1194 * inode_lock. We cannot iput the inode now as we can
1195 * be holding the last reference and we cannot iput it
1196 * under inode_lock. So we keep the reference and iput
1202 filemap_fdatawait(mapping);
1206 spin_lock(&inode_lock);
1208 spin_unlock(&inode_lock);
1212 static void __writeback_inodes_sb(struct super_block *sb, int sb_locked)
1214 unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
1215 unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
1218 nr_to_write = nr_dirty + nr_unstable +
1219 (inodes_stat.nr_inodes - inodes_stat.nr_unused);
1221 bdi_start_writeback(sb->s_bdi, sb, nr_to_write, sb_locked);
1225 * writeback_inodes_sb - writeback dirty inodes from given super_block
1226 * @sb: the superblock
1228 * Start writeback on some inodes on this super_block. No guarantees are made
1229 * on how many (if any) will be written, and this function does not wait
1230 * for IO completion of submitted IO. The number of pages submitted is
1233 void writeback_inodes_sb(struct super_block *sb)
1235 __writeback_inodes_sb(sb, 0);
1237 EXPORT_SYMBOL(writeback_inodes_sb);
1240 * writeback_inodes_sb_locked - writeback dirty inodes from given super_block
1241 * @sb: the superblock
1243 * Like writeback_inodes_sb(), except the caller already holds the
1246 void writeback_inodes_sb_locked(struct super_block *sb)
1248 __writeback_inodes_sb(sb, 1);
1252 * writeback_inodes_sb_if_idle - start writeback if none underway
1253 * @sb: the superblock
1255 * Invoke writeback_inodes_sb if no writeback is currently underway.
1256 * Returns 1 if writeback was started, 0 if not.
1258 int writeback_inodes_sb_if_idle(struct super_block *sb)
1260 if (!writeback_in_progress(sb->s_bdi)) {
1261 writeback_inodes_sb(sb);
1266 EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
1269 * sync_inodes_sb - sync sb inode pages
1270 * @sb: the superblock
1272 * This function writes and waits on any dirty inode belonging to this
1273 * super_block. The number of pages synced is returned.
1275 void sync_inodes_sb(struct super_block *sb)
1277 bdi_sync_writeback(sb->s_bdi, sb);
1280 EXPORT_SYMBOL(sync_inodes_sb);
1283 * write_inode_now - write an inode to disk
1284 * @inode: inode to write to disk
1285 * @sync: whether the write should be synchronous or not
1287 * This function commits an inode to disk immediately if it is dirty. This is
1288 * primarily needed by knfsd.
1290 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1292 int write_inode_now(struct inode *inode, int sync)
1295 struct writeback_control wbc = {
1296 .nr_to_write = LONG_MAX,
1297 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1299 .range_end = LLONG_MAX,
1302 if (!mapping_cap_writeback_dirty(inode->i_mapping))
1303 wbc.nr_to_write = 0;
1306 spin_lock(&inode_lock);
1307 ret = writeback_single_inode(inode, &wbc);
1308 spin_unlock(&inode_lock);
1310 inode_sync_wait(inode);
1313 EXPORT_SYMBOL(write_inode_now);
1316 * sync_inode - write an inode and its pages to disk.
1317 * @inode: the inode to sync
1318 * @wbc: controls the writeback mode
1320 * sync_inode() will write an inode and its pages to disk. It will also
1321 * correctly update the inode on its superblock's dirty inode lists and will
1322 * update inode->i_state.
1324 * The caller must have a ref on the inode.
1326 int sync_inode(struct inode *inode, struct writeback_control *wbc)
1330 spin_lock(&inode_lock);
1331 ret = writeback_single_inode(inode, wbc);
1332 spin_unlock(&inode_lock);
1335 EXPORT_SYMBOL(sync_inode);