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/export.h>
18 #include <linux/spinlock.h>
19 #include <linux/slab.h>
20 #include <linux/sched.h>
23 #include <linux/pagemap.h>
24 #include <linux/kthread.h>
25 #include <linux/writeback.h>
26 #include <linux/blkdev.h>
27 #include <linux/backing-dev.h>
28 #include <linux/tracepoint.h>
32 * 4MB minimal write chunk size
34 #define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_CACHE_SHIFT - 10))
37 * Passed into wb_writeback(), essentially a subset of writeback_control
39 struct wb_writeback_work {
41 struct super_block *sb;
42 unsigned long *older_than_this;
43 enum writeback_sync_modes sync_mode;
44 unsigned int tagged_writepages:1;
45 unsigned int for_kupdate:1;
46 unsigned int range_cyclic:1;
47 unsigned int for_background:1;
48 enum wb_reason reason; /* why was writeback initiated? */
50 struct list_head list; /* pending work list */
51 struct completion *done; /* set if the caller waits */
55 * writeback_in_progress - determine whether there is writeback in progress
56 * @bdi: the device's backing_dev_info structure.
58 * Determine whether there is writeback waiting to be handled against a
61 int writeback_in_progress(struct backing_dev_info *bdi)
63 return test_bit(BDI_writeback_running, &bdi->state);
65 EXPORT_SYMBOL(writeback_in_progress);
67 static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
69 struct super_block *sb = inode->i_sb;
71 if (strcmp(sb->s_type->name, "bdev") == 0)
72 return inode->i_mapping->backing_dev_info;
77 static inline struct inode *wb_inode(struct list_head *head)
79 return list_entry(head, struct inode, i_wb_list);
83 * Include the creation of the trace points after defining the
84 * wb_writeback_work structure and inline functions so that the definition
85 * remains local to this file.
87 #define CREATE_TRACE_POINTS
88 #include <trace/events/writeback.h>
90 static void bdi_queue_work(struct backing_dev_info *bdi,
91 struct wb_writeback_work *work)
93 trace_writeback_queue(bdi, work);
95 spin_lock_bh(&bdi->wb_lock);
96 list_add_tail(&work->list, &bdi->work_list);
97 spin_unlock_bh(&bdi->wb_lock);
99 mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
103 __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
104 bool range_cyclic, enum wb_reason reason)
106 struct wb_writeback_work *work;
109 * This is WB_SYNC_NONE writeback, so if allocation fails just
110 * wakeup the thread for old dirty data writeback
112 work = kzalloc(sizeof(*work), GFP_ATOMIC);
114 trace_writeback_nowork(bdi);
115 mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
119 work->sync_mode = WB_SYNC_NONE;
120 work->nr_pages = nr_pages;
121 work->range_cyclic = range_cyclic;
122 work->reason = reason;
124 bdi_queue_work(bdi, work);
128 * bdi_start_writeback - start writeback
129 * @bdi: the backing device to write from
130 * @nr_pages: the number of pages to write
131 * @reason: reason why some writeback work was initiated
134 * This does WB_SYNC_NONE opportunistic writeback. The IO is only
135 * started when this function returns, we make no guarantees on
136 * completion. Caller need not hold sb s_umount semaphore.
139 void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
140 enum wb_reason reason)
142 __bdi_start_writeback(bdi, nr_pages, true, reason);
146 * bdi_start_background_writeback - start background writeback
147 * @bdi: the backing device to write from
150 * This makes sure WB_SYNC_NONE background writeback happens. When
151 * this function returns, it is only guaranteed that for given BDI
152 * some IO is happening if we are over background dirty threshold.
153 * Caller need not hold sb s_umount semaphore.
155 void bdi_start_background_writeback(struct backing_dev_info *bdi)
158 * We just wake up the flusher thread. It will perform background
159 * writeback as soon as there is no other work to do.
161 trace_writeback_wake_background(bdi);
162 mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
166 * Remove the inode from the writeback list it is on.
168 void inode_wb_list_del(struct inode *inode)
170 struct backing_dev_info *bdi = inode_to_bdi(inode);
172 spin_lock(&bdi->wb.list_lock);
173 list_del_init(&inode->i_wb_list);
174 spin_unlock(&bdi->wb.list_lock);
178 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
179 * furthest end of its superblock's dirty-inode list.
181 * Before stamping the inode's ->dirtied_when, we check to see whether it is
182 * already the most-recently-dirtied inode on the b_dirty list. If that is
183 * the case then the inode must have been redirtied while it was being written
184 * out and we don't reset its dirtied_when.
186 static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
188 assert_spin_locked(&wb->list_lock);
189 if (!list_empty(&wb->b_dirty)) {
192 tail = wb_inode(wb->b_dirty.next);
193 if (time_before(inode->dirtied_when, tail->dirtied_when))
194 inode->dirtied_when = jiffies;
196 list_move(&inode->i_wb_list, &wb->b_dirty);
200 * requeue inode for re-scanning after bdi->b_io list is exhausted.
202 static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
204 assert_spin_locked(&wb->list_lock);
205 list_move(&inode->i_wb_list, &wb->b_more_io);
208 static void inode_sync_complete(struct inode *inode)
210 inode->i_state &= ~I_SYNC;
211 /* If inode is clean an unused, put it into LRU now... */
212 inode_add_lru(inode);
213 /* Waiters must see I_SYNC cleared before being woken up */
215 wake_up_bit(&inode->i_state, __I_SYNC);
218 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
220 bool ret = time_after(inode->dirtied_when, t);
223 * For inodes being constantly redirtied, dirtied_when can get stuck.
224 * It _appears_ to be in the future, but is actually in distant past.
225 * This test is necessary to prevent such wrapped-around relative times
226 * from permanently stopping the whole bdi writeback.
228 ret = ret && time_before_eq(inode->dirtied_when, jiffies);
234 * Move expired (dirtied before work->older_than_this) dirty inodes from
235 * @delaying_queue to @dispatch_queue.
237 static int move_expired_inodes(struct list_head *delaying_queue,
238 struct list_head *dispatch_queue,
239 struct wb_writeback_work *work)
242 struct list_head *pos, *node;
243 struct super_block *sb = NULL;
248 while (!list_empty(delaying_queue)) {
249 inode = wb_inode(delaying_queue->prev);
250 if (work->older_than_this &&
251 inode_dirtied_after(inode, *work->older_than_this))
253 if (sb && sb != inode->i_sb)
256 list_move(&inode->i_wb_list, &tmp);
260 /* just one sb in list, splice to dispatch_queue and we're done */
262 list_splice(&tmp, dispatch_queue);
266 /* Move inodes from one superblock together */
267 while (!list_empty(&tmp)) {
268 sb = wb_inode(tmp.prev)->i_sb;
269 list_for_each_prev_safe(pos, node, &tmp) {
270 inode = wb_inode(pos);
271 if (inode->i_sb == sb)
272 list_move(&inode->i_wb_list, dispatch_queue);
280 * Queue all expired dirty inodes for io, eldest first.
282 * newly dirtied b_dirty b_io b_more_io
283 * =============> gf edc BA
285 * newly dirtied b_dirty b_io b_more_io
286 * =============> g fBAedc
288 * +--> dequeue for IO
290 static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
293 assert_spin_locked(&wb->list_lock);
294 list_splice_init(&wb->b_more_io, &wb->b_io);
295 moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
296 trace_writeback_queue_io(wb, work, moved);
299 static int write_inode(struct inode *inode, struct writeback_control *wbc)
303 if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
304 trace_writeback_write_inode_start(inode, wbc);
305 ret = inode->i_sb->s_op->write_inode(inode, wbc);
306 trace_writeback_write_inode(inode, wbc);
313 * Wait for writeback on an inode to complete. Called with i_lock held.
314 * Caller must make sure inode cannot go away when we drop i_lock.
316 static void __inode_wait_for_writeback(struct inode *inode)
317 __releases(inode->i_lock)
318 __acquires(inode->i_lock)
320 DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
321 wait_queue_head_t *wqh;
323 wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
324 while (inode->i_state & I_SYNC) {
325 spin_unlock(&inode->i_lock);
326 __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
327 spin_lock(&inode->i_lock);
332 * Wait for writeback on an inode to complete. Caller must have inode pinned.
334 void inode_wait_for_writeback(struct inode *inode)
336 spin_lock(&inode->i_lock);
337 __inode_wait_for_writeback(inode);
338 spin_unlock(&inode->i_lock);
342 * Sleep until I_SYNC is cleared. This function must be called with i_lock
343 * held and drops it. It is aimed for callers not holding any inode reference
344 * so once i_lock is dropped, inode can go away.
346 static void inode_sleep_on_writeback(struct inode *inode)
347 __releases(inode->i_lock)
350 wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
353 prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
354 sleep = inode->i_state & I_SYNC;
355 spin_unlock(&inode->i_lock);
358 finish_wait(wqh, &wait);
362 * Find proper writeback list for the inode depending on its current state and
363 * possibly also change of its state while we were doing writeback. Here we
364 * handle things such as livelock prevention or fairness of writeback among
365 * inodes. This function can be called only by flusher thread - noone else
366 * processes all inodes in writeback lists and requeueing inodes behind flusher
367 * thread's back can have unexpected consequences.
369 static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
370 struct writeback_control *wbc)
372 if (inode->i_state & I_FREEING)
376 * Sync livelock prevention. Each inode is tagged and synced in one
377 * shot. If still dirty, it will be redirty_tail()'ed below. Update
378 * the dirty time to prevent enqueue and sync it again.
380 if ((inode->i_state & I_DIRTY) &&
381 (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
382 inode->dirtied_when = jiffies;
384 if (wbc->pages_skipped) {
386 * writeback is not making progress due to locked
387 * buffers. Skip this inode for now.
389 redirty_tail(inode, wb);
393 if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
395 * We didn't write back all the pages. nfs_writepages()
396 * sometimes bales out without doing anything.
398 if (wbc->nr_to_write <= 0) {
399 /* Slice used up. Queue for next turn. */
400 requeue_io(inode, wb);
403 * Writeback blocked by something other than
404 * congestion. Delay the inode for some time to
405 * avoid spinning on the CPU (100% iowait)
406 * retrying writeback of the dirty page/inode
407 * that cannot be performed immediately.
409 redirty_tail(inode, wb);
411 } else if (inode->i_state & I_DIRTY) {
413 * Filesystems can dirty the inode during writeback operations,
414 * such as delayed allocation during submission or metadata
415 * updates after data IO completion.
417 redirty_tail(inode, wb);
419 /* The inode is clean. Remove from writeback lists. */
420 list_del_init(&inode->i_wb_list);
425 * Write out an inode and its dirty pages. Do not update the writeback list
426 * linkage. That is left to the caller. The caller is also responsible for
427 * setting I_SYNC flag and calling inode_sync_complete() to clear it.
430 __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
432 struct address_space *mapping = inode->i_mapping;
433 long nr_to_write = wbc->nr_to_write;
437 WARN_ON(!(inode->i_state & I_SYNC));
439 trace_writeback_single_inode_start(inode, wbc, nr_to_write);
441 ret = do_writepages(mapping, wbc);
444 * Make sure to wait on the data before writing out the metadata.
445 * This is important for filesystems that modify metadata on data
448 if (wbc->sync_mode == WB_SYNC_ALL) {
449 int err = filemap_fdatawait(mapping);
455 * Some filesystems may redirty the inode during the writeback
456 * due to delalloc, clear dirty metadata flags right before
459 spin_lock(&inode->i_lock);
460 /* Clear I_DIRTY_PAGES if we've written out all dirty pages */
461 if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
462 inode->i_state &= ~I_DIRTY_PAGES;
463 dirty = inode->i_state & I_DIRTY;
464 inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
465 spin_unlock(&inode->i_lock);
466 /* Don't write the inode if only I_DIRTY_PAGES was set */
467 if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
468 int err = write_inode(inode, wbc);
472 trace_writeback_single_inode(inode, wbc, nr_to_write);
477 * Write out an inode's dirty pages. Either the caller has an active reference
478 * on the inode or the inode has I_WILL_FREE set.
480 * This function is designed to be called for writing back one inode which
481 * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
482 * and does more profound writeback list handling in writeback_sb_inodes().
485 writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
486 struct writeback_control *wbc)
490 spin_lock(&inode->i_lock);
491 if (!atomic_read(&inode->i_count))
492 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
494 WARN_ON(inode->i_state & I_WILL_FREE);
496 if (inode->i_state & I_SYNC) {
497 if (wbc->sync_mode != WB_SYNC_ALL)
500 * It's a data-integrity sync. We must wait. Since callers hold
501 * inode reference or inode has I_WILL_FREE set, it cannot go
504 __inode_wait_for_writeback(inode);
506 WARN_ON(inode->i_state & I_SYNC);
508 * Skip inode if it is clean. We don't want to mess with writeback
509 * lists in this function since flusher thread may be doing for example
510 * sync in parallel and if we move the inode, it could get skipped. So
511 * here we make sure inode is on some writeback list and leave it there
512 * unless we have completely cleaned the inode.
514 if (!(inode->i_state & I_DIRTY))
516 inode->i_state |= I_SYNC;
517 spin_unlock(&inode->i_lock);
519 ret = __writeback_single_inode(inode, wbc);
521 spin_lock(&wb->list_lock);
522 spin_lock(&inode->i_lock);
524 * If inode is clean, remove it from writeback lists. Otherwise don't
525 * touch it. See comment above for explanation.
527 if (!(inode->i_state & I_DIRTY))
528 list_del_init(&inode->i_wb_list);
529 spin_unlock(&wb->list_lock);
530 inode_sync_complete(inode);
532 spin_unlock(&inode->i_lock);
536 static long writeback_chunk_size(struct backing_dev_info *bdi,
537 struct wb_writeback_work *work)
542 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
543 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
544 * here avoids calling into writeback_inodes_wb() more than once.
546 * The intended call sequence for WB_SYNC_ALL writeback is:
549 * writeback_sb_inodes() <== called only once
550 * write_cache_pages() <== called once for each inode
551 * (quickly) tag currently dirty pages
552 * (maybe slowly) sync all tagged pages
554 if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
557 pages = min(bdi->avg_write_bandwidth / 2,
558 global_dirty_limit / DIRTY_SCOPE);
559 pages = min(pages, work->nr_pages);
560 pages = round_down(pages + MIN_WRITEBACK_PAGES,
561 MIN_WRITEBACK_PAGES);
568 * Write a portion of b_io inodes which belong to @sb.
570 * Return the number of pages and/or inodes written.
572 static long writeback_sb_inodes(struct super_block *sb,
573 struct bdi_writeback *wb,
574 struct wb_writeback_work *work)
576 struct writeback_control wbc = {
577 .sync_mode = work->sync_mode,
578 .tagged_writepages = work->tagged_writepages,
579 .for_kupdate = work->for_kupdate,
580 .for_background = work->for_background,
581 .range_cyclic = work->range_cyclic,
583 .range_end = LLONG_MAX,
585 unsigned long start_time = jiffies;
587 long wrote = 0; /* count both pages and inodes */
589 while (!list_empty(&wb->b_io)) {
590 struct inode *inode = wb_inode(wb->b_io.prev);
592 if (inode->i_sb != sb) {
595 * We only want to write back data for this
596 * superblock, move all inodes not belonging
597 * to it back onto the dirty list.
599 redirty_tail(inode, wb);
604 * The inode belongs to a different superblock.
605 * Bounce back to the caller to unpin this and
606 * pin the next superblock.
612 * Don't bother with new inodes or inodes being freed, first
613 * kind does not need periodic writeout yet, and for the latter
614 * kind writeout is handled by the freer.
616 spin_lock(&inode->i_lock);
617 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
618 spin_unlock(&inode->i_lock);
619 redirty_tail(inode, wb);
622 if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
624 * If this inode is locked for writeback and we are not
625 * doing writeback-for-data-integrity, move it to
626 * b_more_io so that writeback can proceed with the
627 * other inodes on s_io.
629 * We'll have another go at writing back this inode
630 * when we completed a full scan of b_io.
632 spin_unlock(&inode->i_lock);
633 requeue_io(inode, wb);
634 trace_writeback_sb_inodes_requeue(inode);
637 spin_unlock(&wb->list_lock);
640 * We already requeued the inode if it had I_SYNC set and we
641 * are doing WB_SYNC_NONE writeback. So this catches only the
644 if (inode->i_state & I_SYNC) {
645 /* Wait for I_SYNC. This function drops i_lock... */
646 inode_sleep_on_writeback(inode);
647 /* Inode may be gone, start again */
648 spin_lock(&wb->list_lock);
651 inode->i_state |= I_SYNC;
652 spin_unlock(&inode->i_lock);
654 write_chunk = writeback_chunk_size(wb->bdi, work);
655 wbc.nr_to_write = write_chunk;
656 wbc.pages_skipped = 0;
659 * We use I_SYNC to pin the inode in memory. While it is set
660 * evict_inode() will wait so the inode cannot be freed.
662 __writeback_single_inode(inode, &wbc);
664 work->nr_pages -= write_chunk - wbc.nr_to_write;
665 wrote += write_chunk - wbc.nr_to_write;
666 spin_lock(&wb->list_lock);
667 spin_lock(&inode->i_lock);
668 if (!(inode->i_state & I_DIRTY))
670 requeue_inode(inode, wb, &wbc);
671 inode_sync_complete(inode);
672 spin_unlock(&inode->i_lock);
673 cond_resched_lock(&wb->list_lock);
675 * bail out to wb_writeback() often enough to check
676 * background threshold and other termination conditions.
679 if (time_is_before_jiffies(start_time + HZ / 10UL))
681 if (work->nr_pages <= 0)
688 static long __writeback_inodes_wb(struct bdi_writeback *wb,
689 struct wb_writeback_work *work)
691 unsigned long start_time = jiffies;
694 while (!list_empty(&wb->b_io)) {
695 struct inode *inode = wb_inode(wb->b_io.prev);
696 struct super_block *sb = inode->i_sb;
698 if (!grab_super_passive(sb)) {
700 * grab_super_passive() may fail consistently due to
701 * s_umount being grabbed by someone else. Don't use
702 * requeue_io() to avoid busy retrying the inode/sb.
704 redirty_tail(inode, wb);
707 wrote += writeback_sb_inodes(sb, wb, work);
710 /* refer to the same tests at the end of writeback_sb_inodes */
712 if (time_is_before_jiffies(start_time + HZ / 10UL))
714 if (work->nr_pages <= 0)
718 /* Leave any unwritten inodes on b_io */
722 long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
723 enum wb_reason reason)
725 struct wb_writeback_work work = {
726 .nr_pages = nr_pages,
727 .sync_mode = WB_SYNC_NONE,
732 spin_lock(&wb->list_lock);
733 if (list_empty(&wb->b_io))
735 __writeback_inodes_wb(wb, &work);
736 spin_unlock(&wb->list_lock);
738 return nr_pages - work.nr_pages;
741 static bool over_bground_thresh(struct backing_dev_info *bdi)
743 unsigned long background_thresh, dirty_thresh;
745 global_dirty_limits(&background_thresh, &dirty_thresh);
747 if (global_page_state(NR_FILE_DIRTY) +
748 global_page_state(NR_UNSTABLE_NFS) > background_thresh)
751 if (bdi_stat(bdi, BDI_RECLAIMABLE) >
752 bdi_dirty_limit(bdi, background_thresh))
759 * Called under wb->list_lock. If there are multiple wb per bdi,
760 * only the flusher working on the first wb should do it.
762 static void wb_update_bandwidth(struct bdi_writeback *wb,
763 unsigned long start_time)
765 __bdi_update_bandwidth(wb->bdi, 0, 0, 0, 0, 0, start_time);
769 * Explicit flushing or periodic writeback of "old" data.
771 * Define "old": the first time one of an inode's pages is dirtied, we mark the
772 * dirtying-time in the inode's address_space. So this periodic writeback code
773 * just walks the superblock inode list, writing back any inodes which are
774 * older than a specific point in time.
776 * Try to run once per dirty_writeback_interval. But if a writeback event
777 * takes longer than a dirty_writeback_interval interval, then leave a
780 * older_than_this takes precedence over nr_to_write. So we'll only write back
781 * all dirty pages if they are all attached to "old" mappings.
783 static long wb_writeback(struct bdi_writeback *wb,
784 struct wb_writeback_work *work)
786 unsigned long wb_start = jiffies;
787 long nr_pages = work->nr_pages;
788 unsigned long oldest_jif;
792 oldest_jif = jiffies;
793 work->older_than_this = &oldest_jif;
795 spin_lock(&wb->list_lock);
798 * Stop writeback when nr_pages has been consumed
800 if (work->nr_pages <= 0)
804 * Background writeout and kupdate-style writeback may
805 * run forever. Stop them if there is other work to do
806 * so that e.g. sync can proceed. They'll be restarted
807 * after the other works are all done.
809 if ((work->for_background || work->for_kupdate) &&
810 !list_empty(&wb->bdi->work_list))
814 * For background writeout, stop when we are below the
815 * background dirty threshold
817 if (work->for_background && !over_bground_thresh(wb->bdi))
821 * Kupdate and background works are special and we want to
822 * include all inodes that need writing. Livelock avoidance is
823 * handled by these works yielding to any other work so we are
826 if (work->for_kupdate) {
827 oldest_jif = jiffies -
828 msecs_to_jiffies(dirty_expire_interval * 10);
829 } else if (work->for_background)
830 oldest_jif = jiffies;
832 trace_writeback_start(wb->bdi, work);
833 if (list_empty(&wb->b_io))
836 progress = writeback_sb_inodes(work->sb, wb, work);
838 progress = __writeback_inodes_wb(wb, work);
839 trace_writeback_written(wb->bdi, work);
841 wb_update_bandwidth(wb, wb_start);
844 * Did we write something? Try for more
846 * Dirty inodes are moved to b_io for writeback in batches.
847 * The completion of the current batch does not necessarily
848 * mean the overall work is done. So we keep looping as long
849 * as made some progress on cleaning pages or inodes.
854 * No more inodes for IO, bail
856 if (list_empty(&wb->b_more_io))
859 * Nothing written. Wait for some inode to
860 * become available for writeback. Otherwise
861 * we'll just busyloop.
863 if (!list_empty(&wb->b_more_io)) {
864 trace_writeback_wait(wb->bdi, work);
865 inode = wb_inode(wb->b_more_io.prev);
866 spin_lock(&inode->i_lock);
867 spin_unlock(&wb->list_lock);
868 /* This function drops i_lock... */
869 inode_sleep_on_writeback(inode);
870 spin_lock(&wb->list_lock);
873 spin_unlock(&wb->list_lock);
875 return nr_pages - work->nr_pages;
879 * Return the next wb_writeback_work struct that hasn't been processed yet.
881 static struct wb_writeback_work *
882 get_next_work_item(struct backing_dev_info *bdi)
884 struct wb_writeback_work *work = NULL;
886 spin_lock_bh(&bdi->wb_lock);
887 if (!list_empty(&bdi->work_list)) {
888 work = list_entry(bdi->work_list.next,
889 struct wb_writeback_work, list);
890 list_del_init(&work->list);
892 spin_unlock_bh(&bdi->wb_lock);
897 * Add in the number of potentially dirty inodes, because each inode
898 * write can dirty pagecache in the underlying blockdev.
900 static unsigned long get_nr_dirty_pages(void)
902 return global_page_state(NR_FILE_DIRTY) +
903 global_page_state(NR_UNSTABLE_NFS) +
904 get_nr_dirty_inodes();
907 static long wb_check_background_flush(struct bdi_writeback *wb)
909 if (over_bground_thresh(wb->bdi)) {
911 struct wb_writeback_work work = {
912 .nr_pages = LONG_MAX,
913 .sync_mode = WB_SYNC_NONE,
916 .reason = WB_REASON_BACKGROUND,
919 return wb_writeback(wb, &work);
925 static long wb_check_old_data_flush(struct bdi_writeback *wb)
927 unsigned long expired;
931 * When set to zero, disable periodic writeback
933 if (!dirty_writeback_interval)
936 expired = wb->last_old_flush +
937 msecs_to_jiffies(dirty_writeback_interval * 10);
938 if (time_before(jiffies, expired))
941 wb->last_old_flush = jiffies;
942 nr_pages = get_nr_dirty_pages();
945 struct wb_writeback_work work = {
946 .nr_pages = nr_pages,
947 .sync_mode = WB_SYNC_NONE,
950 .reason = WB_REASON_PERIODIC,
953 return wb_writeback(wb, &work);
960 * Retrieve work items and do the writeback they describe
962 long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
964 struct backing_dev_info *bdi = wb->bdi;
965 struct wb_writeback_work *work;
968 set_bit(BDI_writeback_running, &wb->bdi->state);
969 while ((work = get_next_work_item(bdi)) != NULL) {
971 * Override sync mode, in case we must wait for completion
972 * because this thread is exiting now.
975 work->sync_mode = WB_SYNC_ALL;
977 trace_writeback_exec(bdi, work);
979 wrote += wb_writeback(wb, work);
982 * Notify the caller of completion if this is a synchronous
983 * work item, otherwise just free it.
986 complete(work->done);
992 * Check for periodic writeback, kupdated() style
994 wrote += wb_check_old_data_flush(wb);
995 wrote += wb_check_background_flush(wb);
996 clear_bit(BDI_writeback_running, &wb->bdi->state);
1002 * Handle writeback of dirty data for the device backed by this bdi. Also
1003 * reschedules periodically and does kupdated style flushing.
1005 void bdi_writeback_workfn(struct work_struct *work)
1007 struct bdi_writeback *wb = container_of(to_delayed_work(work),
1008 struct bdi_writeback, dwork);
1009 struct backing_dev_info *bdi = wb->bdi;
1012 current->flags |= PF_SWAPWRITE;
1014 if (likely(!current_is_workqueue_rescuer() ||
1015 list_empty(&bdi->bdi_list))) {
1017 * The normal path. Keep writing back @bdi until its
1018 * work_list is empty. Note that this path is also taken
1019 * if @bdi is shutting down even when we're running off the
1020 * rescuer as work_list needs to be drained.
1023 pages_written = wb_do_writeback(wb, 0);
1024 trace_writeback_pages_written(pages_written);
1025 } while (!list_empty(&bdi->work_list));
1028 * bdi_wq can't get enough workers and we're running off
1029 * the emergency worker. Don't hog it. Hopefully, 1024 is
1030 * enough for efficient IO.
1032 pages_written = writeback_inodes_wb(&bdi->wb, 1024,
1033 WB_REASON_FORKER_THREAD);
1034 trace_writeback_pages_written(pages_written);
1037 if (!list_empty(&bdi->work_list) ||
1038 (wb_has_dirty_io(wb) && dirty_writeback_interval))
1039 queue_delayed_work(bdi_wq, &wb->dwork,
1040 msecs_to_jiffies(dirty_writeback_interval * 10));
1042 current->flags &= ~PF_SWAPWRITE;
1046 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
1049 void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
1051 struct backing_dev_info *bdi;
1054 nr_pages = global_page_state(NR_FILE_DIRTY) +
1055 global_page_state(NR_UNSTABLE_NFS);
1059 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1060 if (!bdi_has_dirty_io(bdi))
1062 __bdi_start_writeback(bdi, nr_pages, false, reason);
1067 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
1069 if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
1070 struct dentry *dentry;
1071 const char *name = "?";
1073 dentry = d_find_alias(inode);
1075 spin_lock(&dentry->d_lock);
1076 name = (const char *) dentry->d_name.name;
1079 "%s(%d): dirtied inode %lu (%s) on %s\n",
1080 current->comm, task_pid_nr(current), inode->i_ino,
1081 name, inode->i_sb->s_id);
1083 spin_unlock(&dentry->d_lock);
1090 * __mark_inode_dirty - internal function
1091 * @inode: inode to mark
1092 * @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
1093 * Mark an inode as dirty. Callers should use mark_inode_dirty or
1094 * mark_inode_dirty_sync.
1096 * Put the inode on the super block's dirty list.
1098 * CAREFUL! We mark it dirty unconditionally, but move it onto the
1099 * dirty list only if it is hashed or if it refers to a blockdev.
1100 * If it was not hashed, it will never be added to the dirty list
1101 * even if it is later hashed, as it will have been marked dirty already.
1103 * In short, make sure you hash any inodes _before_ you start marking
1106 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
1107 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
1108 * the kernel-internal blockdev inode represents the dirtying time of the
1109 * blockdev's pages. This is why for I_DIRTY_PAGES we always use
1110 * page->mapping->host, so the page-dirtying time is recorded in the internal
1113 void __mark_inode_dirty(struct inode *inode, int flags)
1115 struct super_block *sb = inode->i_sb;
1116 struct backing_dev_info *bdi = NULL;
1119 * Don't do this for I_DIRTY_PAGES - that doesn't actually
1120 * dirty the inode itself
1122 if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
1123 trace_writeback_dirty_inode_start(inode, flags);
1125 if (sb->s_op->dirty_inode)
1126 sb->s_op->dirty_inode(inode, flags);
1128 trace_writeback_dirty_inode(inode, flags);
1132 * make sure that changes are seen by all cpus before we test i_state
1137 /* avoid the locking if we can */
1138 if ((inode->i_state & flags) == flags)
1141 if (unlikely(block_dump))
1142 block_dump___mark_inode_dirty(inode);
1144 spin_lock(&inode->i_lock);
1145 if ((inode->i_state & flags) != flags) {
1146 const int was_dirty = inode->i_state & I_DIRTY;
1148 inode->i_state |= flags;
1151 * If the inode is being synced, just update its dirty state.
1152 * The unlocker will place the inode on the appropriate
1153 * superblock list, based upon its state.
1155 if (inode->i_state & I_SYNC)
1156 goto out_unlock_inode;
1159 * Only add valid (hashed) inodes to the superblock's
1160 * dirty list. Add blockdev inodes as well.
1162 if (!S_ISBLK(inode->i_mode)) {
1163 if (inode_unhashed(inode))
1164 goto out_unlock_inode;
1166 if (inode->i_state & I_FREEING)
1167 goto out_unlock_inode;
1170 * If the inode was already on b_dirty/b_io/b_more_io, don't
1171 * reposition it (that would break b_dirty time-ordering).
1174 bool wakeup_bdi = false;
1175 bdi = inode_to_bdi(inode);
1177 if (bdi_cap_writeback_dirty(bdi)) {
1178 WARN(!test_bit(BDI_registered, &bdi->state),
1179 "bdi-%s not registered\n", bdi->name);
1182 * If this is the first dirty inode for this
1183 * bdi, we have to wake-up the corresponding
1184 * bdi thread to make sure background
1185 * write-back happens later.
1187 if (!wb_has_dirty_io(&bdi->wb))
1191 spin_unlock(&inode->i_lock);
1192 spin_lock(&bdi->wb.list_lock);
1193 inode->dirtied_when = jiffies;
1194 list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
1195 spin_unlock(&bdi->wb.list_lock);
1198 bdi_wakeup_thread_delayed(bdi);
1203 spin_unlock(&inode->i_lock);
1206 EXPORT_SYMBOL(__mark_inode_dirty);
1208 static void wait_sb_inodes(struct super_block *sb)
1210 struct inode *inode, *old_inode = NULL;
1213 * We need to be protected against the filesystem going from
1214 * r/o to r/w or vice versa.
1216 WARN_ON(!rwsem_is_locked(&sb->s_umount));
1218 spin_lock(&inode_sb_list_lock);
1221 * Data integrity sync. Must wait for all pages under writeback,
1222 * because there may have been pages dirtied before our sync
1223 * call, but which had writeout started before we write it out.
1224 * In which case, the inode may not be on the dirty list, but
1225 * we still have to wait for that writeout.
1227 list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1228 struct address_space *mapping = inode->i_mapping;
1230 spin_lock(&inode->i_lock);
1231 if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
1232 (mapping->nrpages == 0)) {
1233 spin_unlock(&inode->i_lock);
1237 spin_unlock(&inode->i_lock);
1238 spin_unlock(&inode_sb_list_lock);
1241 * We hold a reference to 'inode' so it couldn't have been
1242 * removed from s_inodes list while we dropped the
1243 * inode_sb_list_lock. We cannot iput the inode now as we can
1244 * be holding the last reference and we cannot iput it under
1245 * inode_sb_list_lock. So we keep the reference and iput it
1251 filemap_fdatawait(mapping);
1255 spin_lock(&inode_sb_list_lock);
1257 spin_unlock(&inode_sb_list_lock);
1262 * writeback_inodes_sb_nr - writeback dirty inodes from given super_block
1263 * @sb: the superblock
1264 * @nr: the number of pages to write
1265 * @reason: reason why some writeback work initiated
1267 * Start writeback on some inodes on this super_block. No guarantees are made
1268 * on how many (if any) will be written, and this function does not wait
1269 * for IO completion of submitted IO.
1271 void writeback_inodes_sb_nr(struct super_block *sb,
1273 enum wb_reason reason)
1275 DECLARE_COMPLETION_ONSTACK(done);
1276 struct wb_writeback_work work = {
1278 .sync_mode = WB_SYNC_NONE,
1279 .tagged_writepages = 1,
1285 if (sb->s_bdi == &noop_backing_dev_info)
1287 WARN_ON(!rwsem_is_locked(&sb->s_umount));
1288 bdi_queue_work(sb->s_bdi, &work);
1289 wait_for_completion(&done);
1291 EXPORT_SYMBOL(writeback_inodes_sb_nr);
1294 * writeback_inodes_sb - writeback dirty inodes from given super_block
1295 * @sb: the superblock
1296 * @reason: reason why some writeback work was initiated
1298 * Start writeback on some inodes on this super_block. No guarantees are made
1299 * on how many (if any) will be written, and this function does not wait
1300 * for IO completion of submitted IO.
1302 void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
1304 return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
1306 EXPORT_SYMBOL(writeback_inodes_sb);
1309 * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
1310 * @sb: the superblock
1311 * @nr: the number of pages to write
1312 * @reason: the reason of writeback
1314 * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
1315 * Returns 1 if writeback was started, 0 if not.
1317 int try_to_writeback_inodes_sb_nr(struct super_block *sb,
1319 enum wb_reason reason)
1321 if (writeback_in_progress(sb->s_bdi))
1324 if (!down_read_trylock(&sb->s_umount))
1327 writeback_inodes_sb_nr(sb, nr, reason);
1328 up_read(&sb->s_umount);
1331 EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
1334 * try_to_writeback_inodes_sb - try to start writeback if none underway
1335 * @sb: the superblock
1336 * @reason: reason why some writeback work was initiated
1338 * Implement by try_to_writeback_inodes_sb_nr()
1339 * Returns 1 if writeback was started, 0 if not.
1341 int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
1343 return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
1345 EXPORT_SYMBOL(try_to_writeback_inodes_sb);
1348 * sync_inodes_sb - sync sb inode pages
1349 * @sb: the superblock
1351 * This function writes and waits on any dirty inode belonging to this
1354 void sync_inodes_sb(struct super_block *sb)
1356 DECLARE_COMPLETION_ONSTACK(done);
1357 struct wb_writeback_work work = {
1359 .sync_mode = WB_SYNC_ALL,
1360 .nr_pages = LONG_MAX,
1363 .reason = WB_REASON_SYNC,
1366 /* Nothing to do? */
1367 if (sb->s_bdi == &noop_backing_dev_info)
1369 WARN_ON(!rwsem_is_locked(&sb->s_umount));
1371 bdi_queue_work(sb->s_bdi, &work);
1372 wait_for_completion(&done);
1376 EXPORT_SYMBOL(sync_inodes_sb);
1379 * write_inode_now - write an inode to disk
1380 * @inode: inode to write to disk
1381 * @sync: whether the write should be synchronous or not
1383 * This function commits an inode to disk immediately if it is dirty. This is
1384 * primarily needed by knfsd.
1386 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1388 int write_inode_now(struct inode *inode, int sync)
1390 struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
1391 struct writeback_control wbc = {
1392 .nr_to_write = LONG_MAX,
1393 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1395 .range_end = LLONG_MAX,
1398 if (!mapping_cap_writeback_dirty(inode->i_mapping))
1399 wbc.nr_to_write = 0;
1402 return writeback_single_inode(inode, wb, &wbc);
1404 EXPORT_SYMBOL(write_inode_now);
1407 * sync_inode - write an inode and its pages to disk.
1408 * @inode: the inode to sync
1409 * @wbc: controls the writeback mode
1411 * sync_inode() will write an inode and its pages to disk. It will also
1412 * correctly update the inode on its superblock's dirty inode lists and will
1413 * update inode->i_state.
1415 * The caller must have a ref on the inode.
1417 int sync_inode(struct inode *inode, struct writeback_control *wbc)
1419 return writeback_single_inode(inode, &inode_to_bdi(inode)->wb, wbc);
1421 EXPORT_SYMBOL(sync_inode);
1424 * sync_inode_metadata - write an inode to disk
1425 * @inode: the inode to sync
1426 * @wait: wait for I/O to complete.
1428 * Write an inode to disk and adjust its dirty state after completion.
1430 * Note: only writes the actual inode, no associated data or other metadata.
1432 int sync_inode_metadata(struct inode *inode, int wait)
1434 struct writeback_control wbc = {
1435 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
1436 .nr_to_write = 0, /* metadata-only */
1439 return sync_inode(inode, &wbc);
1441 EXPORT_SYMBOL(sync_inode_metadata);