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>
29 #include <linux/device.h>
30 #include <linux/memcontrol.h>
34 * 4MB minimal write chunk size
36 #define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_CACHE_SHIFT - 10))
38 struct wb_completion {
43 * Passed into wb_writeback(), essentially a subset of writeback_control
45 struct wb_writeback_work {
47 struct super_block *sb;
48 unsigned long *older_than_this;
49 enum writeback_sync_modes sync_mode;
50 unsigned int tagged_writepages:1;
51 unsigned int for_kupdate:1;
52 unsigned int range_cyclic:1;
53 unsigned int for_background:1;
54 unsigned int for_sync:1; /* sync(2) WB_SYNC_ALL writeback */
55 unsigned int auto_free:1; /* free on completion */
56 enum wb_reason reason; /* why was writeback initiated? */
58 struct list_head list; /* pending work list */
59 struct wb_completion *done; /* set if the caller waits */
63 * If one wants to wait for one or more wb_writeback_works, each work's
64 * ->done should be set to a wb_completion defined using the following
65 * macro. Once all work items are issued with wb_queue_work(), the caller
66 * can wait for the completion of all using wb_wait_for_completion(). Work
67 * items which are waited upon aren't freed automatically on completion.
69 #define DEFINE_WB_COMPLETION_ONSTACK(cmpl) \
70 struct wb_completion cmpl = { \
71 .cnt = ATOMIC_INIT(1), \
76 * If an inode is constantly having its pages dirtied, but then the
77 * updates stop dirtytime_expire_interval seconds in the past, it's
78 * possible for the worst case time between when an inode has its
79 * timestamps updated and when they finally get written out to be two
80 * dirtytime_expire_intervals. We set the default to 12 hours (in
81 * seconds), which means most of the time inodes will have their
82 * timestamps written to disk after 12 hours, but in the worst case a
83 * few inodes might not their timestamps updated for 24 hours.
85 unsigned int dirtytime_expire_interval = 12 * 60 * 60;
87 static inline struct inode *wb_inode(struct list_head *head)
89 return list_entry(head, struct inode, i_io_list);
93 * Include the creation of the trace points after defining the
94 * wb_writeback_work structure and inline functions so that the definition
95 * remains local to this file.
97 #define CREATE_TRACE_POINTS
98 #include <trace/events/writeback.h>
100 EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
102 static bool wb_io_lists_populated(struct bdi_writeback *wb)
104 if (wb_has_dirty_io(wb)) {
107 set_bit(WB_has_dirty_io, &wb->state);
108 WARN_ON_ONCE(!wb->avg_write_bandwidth);
109 atomic_long_add(wb->avg_write_bandwidth,
110 &wb->bdi->tot_write_bandwidth);
115 static void wb_io_lists_depopulated(struct bdi_writeback *wb)
117 if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
118 list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
119 clear_bit(WB_has_dirty_io, &wb->state);
120 WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
121 &wb->bdi->tot_write_bandwidth) < 0);
126 * inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
127 * @inode: inode to be moved
128 * @wb: target bdi_writeback
129 * @head: one of @wb->b_{dirty|io|more_io}
131 * Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
132 * Returns %true if @inode is the first occupant of the !dirty_time IO
133 * lists; otherwise, %false.
135 static bool inode_io_list_move_locked(struct inode *inode,
136 struct bdi_writeback *wb,
137 struct list_head *head)
139 assert_spin_locked(&wb->list_lock);
141 list_move(&inode->i_io_list, head);
143 /* dirty_time doesn't count as dirty_io until expiration */
144 if (head != &wb->b_dirty_time)
145 return wb_io_lists_populated(wb);
147 wb_io_lists_depopulated(wb);
152 * inode_io_list_del_locked - remove an inode from its bdi_writeback IO list
153 * @inode: inode to be removed
154 * @wb: bdi_writeback @inode is being removed from
156 * Remove @inode which may be on one of @wb->b_{dirty|io|more_io} lists and
157 * clear %WB_has_dirty_io if all are empty afterwards.
159 static void inode_io_list_del_locked(struct inode *inode,
160 struct bdi_writeback *wb)
162 assert_spin_locked(&wb->list_lock);
164 list_del_init(&inode->i_io_list);
165 wb_io_lists_depopulated(wb);
168 static void wb_wakeup(struct bdi_writeback *wb)
170 spin_lock_bh(&wb->work_lock);
171 if (test_bit(WB_registered, &wb->state))
172 mod_delayed_work(bdi_wq, &wb->dwork, 0);
173 spin_unlock_bh(&wb->work_lock);
176 static void wb_queue_work(struct bdi_writeback *wb,
177 struct wb_writeback_work *work)
179 trace_writeback_queue(wb, work);
181 spin_lock_bh(&wb->work_lock);
182 if (!test_bit(WB_registered, &wb->state))
185 atomic_inc(&work->done->cnt);
186 list_add_tail(&work->list, &wb->work_list);
187 mod_delayed_work(bdi_wq, &wb->dwork, 0);
189 spin_unlock_bh(&wb->work_lock);
193 * wb_wait_for_completion - wait for completion of bdi_writeback_works
194 * @bdi: bdi work items were issued to
195 * @done: target wb_completion
197 * Wait for one or more work items issued to @bdi with their ->done field
198 * set to @done, which should have been defined with
199 * DEFINE_WB_COMPLETION_ONSTACK(). This function returns after all such
200 * work items are completed. Work items which are waited upon aren't freed
201 * automatically on completion.
203 static void wb_wait_for_completion(struct backing_dev_info *bdi,
204 struct wb_completion *done)
206 atomic_dec(&done->cnt); /* put down the initial count */
207 wait_event(bdi->wb_waitq, !atomic_read(&done->cnt));
210 #ifdef CONFIG_CGROUP_WRITEBACK
212 /* parameters for foreign inode detection, see wb_detach_inode() */
213 #define WB_FRN_TIME_SHIFT 13 /* 1s = 2^13, upto 8 secs w/ 16bit */
214 #define WB_FRN_TIME_AVG_SHIFT 3 /* avg = avg * 7/8 + new * 1/8 */
215 #define WB_FRN_TIME_CUT_DIV 2 /* ignore rounds < avg / 2 */
216 #define WB_FRN_TIME_PERIOD (2 * (1 << WB_FRN_TIME_SHIFT)) /* 2s */
218 #define WB_FRN_HIST_SLOTS 16 /* inode->i_wb_frn_history is 16bit */
219 #define WB_FRN_HIST_UNIT (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
220 /* each slot's duration is 2s / 16 */
221 #define WB_FRN_HIST_THR_SLOTS (WB_FRN_HIST_SLOTS / 2)
222 /* if foreign slots >= 8, switch */
223 #define WB_FRN_HIST_MAX_SLOTS (WB_FRN_HIST_THR_SLOTS / 2 + 1)
224 /* one round can affect upto 5 slots */
226 void __inode_attach_wb(struct inode *inode, struct page *page)
228 struct backing_dev_info *bdi = inode_to_bdi(inode);
229 struct bdi_writeback *wb = NULL;
231 if (inode_cgwb_enabled(inode)) {
232 struct cgroup_subsys_state *memcg_css;
235 memcg_css = mem_cgroup_css_from_page(page);
236 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
238 /* must pin memcg_css, see wb_get_create() */
239 memcg_css = task_get_css(current, memory_cgrp_id);
240 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
249 * There may be multiple instances of this function racing to
250 * update the same inode. Use cmpxchg() to tell the winner.
252 if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
257 * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
258 * @inode: inode of interest with i_lock held
260 * Returns @inode's wb with its list_lock held. @inode->i_lock must be
261 * held on entry and is released on return. The returned wb is guaranteed
262 * to stay @inode's associated wb until its list_lock is released.
264 static struct bdi_writeback *
265 locked_inode_to_wb_and_lock_list(struct inode *inode)
266 __releases(&inode->i_lock)
267 __acquires(&wb->list_lock)
270 struct bdi_writeback *wb = inode_to_wb(inode);
273 * inode_to_wb() association is protected by both
274 * @inode->i_lock and @wb->list_lock but list_lock nests
275 * outside i_lock. Drop i_lock and verify that the
276 * association hasn't changed after acquiring list_lock.
279 spin_unlock(&inode->i_lock);
280 spin_lock(&wb->list_lock);
281 wb_put(wb); /* not gonna deref it anymore */
283 /* i_wb may have changed inbetween, can't use inode_to_wb() */
284 if (likely(wb == inode->i_wb))
285 return wb; /* @inode already has ref */
287 spin_unlock(&wb->list_lock);
289 spin_lock(&inode->i_lock);
294 * inode_to_wb_and_lock_list - determine an inode's wb and lock it
295 * @inode: inode of interest
297 * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
300 static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
301 __acquires(&wb->list_lock)
303 spin_lock(&inode->i_lock);
304 return locked_inode_to_wb_and_lock_list(inode);
307 struct inode_switch_wbs_context {
309 struct bdi_writeback *new_wb;
311 struct rcu_head rcu_head;
312 struct work_struct work;
315 static void inode_switch_wbs_work_fn(struct work_struct *work)
317 struct inode_switch_wbs_context *isw =
318 container_of(work, struct inode_switch_wbs_context, work);
319 struct inode *inode = isw->inode;
320 struct address_space *mapping = inode->i_mapping;
321 struct bdi_writeback *old_wb = inode->i_wb;
322 struct bdi_writeback *new_wb = isw->new_wb;
323 struct radix_tree_iter iter;
324 bool switched = false;
328 * By the time control reaches here, RCU grace period has passed
329 * since I_WB_SWITCH assertion and all wb stat update transactions
330 * between unlocked_inode_to_wb_begin/end() are guaranteed to be
331 * synchronizing against mapping->tree_lock.
333 * Grabbing old_wb->list_lock, inode->i_lock and mapping->tree_lock
334 * gives us exclusion against all wb related operations on @inode
335 * including IO list manipulations and stat updates.
337 if (old_wb < new_wb) {
338 spin_lock(&old_wb->list_lock);
339 spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
341 spin_lock(&new_wb->list_lock);
342 spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
344 spin_lock(&inode->i_lock);
345 spin_lock_irq(&mapping->tree_lock);
348 * Once I_FREEING is visible under i_lock, the eviction path owns
349 * the inode and we shouldn't modify ->i_io_list.
351 if (unlikely(inode->i_state & I_FREEING))
355 * Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
356 * to possibly dirty pages while PAGECACHE_TAG_WRITEBACK points to
357 * pages actually under underwriteback.
359 radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, 0,
360 PAGECACHE_TAG_DIRTY) {
361 struct page *page = radix_tree_deref_slot_protected(slot,
362 &mapping->tree_lock);
363 if (likely(page) && PageDirty(page)) {
364 __dec_wb_stat(old_wb, WB_RECLAIMABLE);
365 __inc_wb_stat(new_wb, WB_RECLAIMABLE);
369 radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, 0,
370 PAGECACHE_TAG_WRITEBACK) {
371 struct page *page = radix_tree_deref_slot_protected(slot,
372 &mapping->tree_lock);
374 WARN_ON_ONCE(!PageWriteback(page));
375 __dec_wb_stat(old_wb, WB_WRITEBACK);
376 __inc_wb_stat(new_wb, WB_WRITEBACK);
383 * Transfer to @new_wb's IO list if necessary. The specific list
384 * @inode was on is ignored and the inode is put on ->b_dirty which
385 * is always correct including from ->b_dirty_time. The transfer
386 * preserves @inode->dirtied_when ordering.
388 if (!list_empty(&inode->i_io_list)) {
391 inode_io_list_del_locked(inode, old_wb);
392 inode->i_wb = new_wb;
393 list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
394 if (time_after_eq(inode->dirtied_when,
397 inode_io_list_move_locked(inode, new_wb, pos->i_io_list.prev);
399 inode->i_wb = new_wb;
402 /* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
403 inode->i_wb_frn_winner = 0;
404 inode->i_wb_frn_avg_time = 0;
405 inode->i_wb_frn_history = 0;
409 * Paired with load_acquire in unlocked_inode_to_wb_begin() and
410 * ensures that the new wb is visible if they see !I_WB_SWITCH.
412 smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
414 spin_unlock_irq(&mapping->tree_lock);
415 spin_unlock(&inode->i_lock);
416 spin_unlock(&new_wb->list_lock);
417 spin_unlock(&old_wb->list_lock);
429 static void inode_switch_wbs_rcu_fn(struct rcu_head *rcu_head)
431 struct inode_switch_wbs_context *isw = container_of(rcu_head,
432 struct inode_switch_wbs_context, rcu_head);
434 /* needs to grab bh-unsafe locks, bounce to work item */
435 INIT_WORK(&isw->work, inode_switch_wbs_work_fn);
436 schedule_work(&isw->work);
440 * inode_switch_wbs - change the wb association of an inode
441 * @inode: target inode
442 * @new_wb_id: ID of the new wb
444 * Switch @inode's wb association to the wb identified by @new_wb_id. The
445 * switching is performed asynchronously and may fail silently.
447 static void inode_switch_wbs(struct inode *inode, int new_wb_id)
449 struct backing_dev_info *bdi = inode_to_bdi(inode);
450 struct cgroup_subsys_state *memcg_css;
451 struct inode_switch_wbs_context *isw;
453 /* noop if seems to be already in progress */
454 if (inode->i_state & I_WB_SWITCH)
457 isw = kzalloc(sizeof(*isw), GFP_ATOMIC);
461 /* find and pin the new wb */
463 memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
465 isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
470 /* while holding I_WB_SWITCH, no one else can update the association */
471 spin_lock(&inode->i_lock);
472 if (inode->i_state & (I_WB_SWITCH | I_FREEING) ||
473 inode_to_wb(inode) == isw->new_wb) {
474 spin_unlock(&inode->i_lock);
477 inode->i_state |= I_WB_SWITCH;
478 spin_unlock(&inode->i_lock);
484 * In addition to synchronizing among switchers, I_WB_SWITCH tells
485 * the RCU protected stat update paths to grab the mapping's
486 * tree_lock so that stat transfer can synchronize against them.
487 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
489 call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn);
499 * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
500 * @wbc: writeback_control of interest
501 * @inode: target inode
503 * @inode is locked and about to be written back under the control of @wbc.
504 * Record @inode's writeback context into @wbc and unlock the i_lock. On
505 * writeback completion, wbc_detach_inode() should be called. This is used
506 * to track the cgroup writeback context.
508 void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
511 if (!inode_cgwb_enabled(inode)) {
512 spin_unlock(&inode->i_lock);
516 wbc->wb = inode_to_wb(inode);
519 wbc->wb_id = wbc->wb->memcg_css->id;
520 wbc->wb_lcand_id = inode->i_wb_frn_winner;
521 wbc->wb_tcand_id = 0;
523 wbc->wb_lcand_bytes = 0;
524 wbc->wb_tcand_bytes = 0;
527 spin_unlock(&inode->i_lock);
530 * A dying wb indicates that the memcg-blkcg mapping has changed
531 * and a new wb is already serving the memcg. Switch immediately.
533 if (unlikely(wb_dying(wbc->wb)))
534 inode_switch_wbs(inode, wbc->wb_id);
538 * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
539 * @wbc: writeback_control of the just finished writeback
541 * To be called after a writeback attempt of an inode finishes and undoes
542 * wbc_attach_and_unlock_inode(). Can be called under any context.
544 * As concurrent write sharing of an inode is expected to be very rare and
545 * memcg only tracks page ownership on first-use basis severely confining
546 * the usefulness of such sharing, cgroup writeback tracks ownership
547 * per-inode. While the support for concurrent write sharing of an inode
548 * is deemed unnecessary, an inode being written to by different cgroups at
549 * different points in time is a lot more common, and, more importantly,
550 * charging only by first-use can too readily lead to grossly incorrect
551 * behaviors (single foreign page can lead to gigabytes of writeback to be
552 * incorrectly attributed).
554 * To resolve this issue, cgroup writeback detects the majority dirtier of
555 * an inode and transfers the ownership to it. To avoid unnnecessary
556 * oscillation, the detection mechanism keeps track of history and gives
557 * out the switch verdict only if the foreign usage pattern is stable over
558 * a certain amount of time and/or writeback attempts.
560 * On each writeback attempt, @wbc tries to detect the majority writer
561 * using Boyer-Moore majority vote algorithm. In addition to the byte
562 * count from the majority voting, it also counts the bytes written for the
563 * current wb and the last round's winner wb (max of last round's current
564 * wb, the winner from two rounds ago, and the last round's majority
565 * candidate). Keeping track of the historical winner helps the algorithm
566 * to semi-reliably detect the most active writer even when it's not the
569 * Once the winner of the round is determined, whether the winner is
570 * foreign or not and how much IO time the round consumed is recorded in
571 * inode->i_wb_frn_history. If the amount of recorded foreign IO time is
572 * over a certain threshold, the switch verdict is given.
574 void wbc_detach_inode(struct writeback_control *wbc)
576 struct bdi_writeback *wb = wbc->wb;
577 struct inode *inode = wbc->inode;
578 unsigned long avg_time, max_bytes, max_time;
585 history = inode->i_wb_frn_history;
586 avg_time = inode->i_wb_frn_avg_time;
588 /* pick the winner of this round */
589 if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
590 wbc->wb_bytes >= wbc->wb_tcand_bytes) {
592 max_bytes = wbc->wb_bytes;
593 } else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
594 max_id = wbc->wb_lcand_id;
595 max_bytes = wbc->wb_lcand_bytes;
597 max_id = wbc->wb_tcand_id;
598 max_bytes = wbc->wb_tcand_bytes;
602 * Calculate the amount of IO time the winner consumed and fold it
603 * into the running average kept per inode. If the consumed IO
604 * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
605 * deciding whether to switch or not. This is to prevent one-off
606 * small dirtiers from skewing the verdict.
608 max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
609 wb->avg_write_bandwidth);
611 avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
612 (avg_time >> WB_FRN_TIME_AVG_SHIFT);
614 avg_time = max_time; /* immediate catch up on first run */
616 if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
620 * The switch verdict is reached if foreign wb's consume
621 * more than a certain proportion of IO time in a
622 * WB_FRN_TIME_PERIOD. This is loosely tracked by 16 slot
623 * history mask where each bit represents one sixteenth of
624 * the period. Determine the number of slots to shift into
625 * history from @max_time.
627 slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
628 (unsigned long)WB_FRN_HIST_MAX_SLOTS);
630 if (wbc->wb_id != max_id)
631 history |= (1U << slots) - 1;
634 * Switch if the current wb isn't the consistent winner.
635 * If there are multiple closely competing dirtiers, the
636 * inode may switch across them repeatedly over time, which
637 * is okay. The main goal is avoiding keeping an inode on
638 * the wrong wb for an extended period of time.
640 if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
641 inode_switch_wbs(inode, max_id);
645 * Multiple instances of this function may race to update the
646 * following fields but we don't mind occassional inaccuracies.
648 inode->i_wb_frn_winner = max_id;
649 inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
650 inode->i_wb_frn_history = history;
657 * wbc_account_io - account IO issued during writeback
658 * @wbc: writeback_control of the writeback in progress
659 * @page: page being written out
660 * @bytes: number of bytes being written out
662 * @bytes from @page are about to written out during the writeback
663 * controlled by @wbc. Keep the book for foreign inode detection. See
664 * wbc_detach_inode().
666 void wbc_account_io(struct writeback_control *wbc, struct page *page,
672 * pageout() path doesn't attach @wbc to the inode being written
673 * out. This is intentional as we don't want the function to block
674 * behind a slow cgroup. Ultimately, we want pageout() to kick off
675 * regular writeback instead of writing things out itself.
681 id = mem_cgroup_css_from_page(page)->id;
684 if (id == wbc->wb_id) {
685 wbc->wb_bytes += bytes;
689 if (id == wbc->wb_lcand_id)
690 wbc->wb_lcand_bytes += bytes;
692 /* Boyer-Moore majority vote algorithm */
693 if (!wbc->wb_tcand_bytes)
694 wbc->wb_tcand_id = id;
695 if (id == wbc->wb_tcand_id)
696 wbc->wb_tcand_bytes += bytes;
698 wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
700 EXPORT_SYMBOL_GPL(wbc_account_io);
703 * inode_congested - test whether an inode is congested
704 * @inode: inode to test for congestion (may be NULL)
705 * @cong_bits: mask of WB_[a]sync_congested bits to test
707 * Tests whether @inode is congested. @cong_bits is the mask of congestion
708 * bits to test and the return value is the mask of set bits.
710 * If cgroup writeback is enabled for @inode, the congestion state is
711 * determined by whether the cgwb (cgroup bdi_writeback) for the blkcg
712 * associated with @inode is congested; otherwise, the root wb's congestion
715 * @inode is allowed to be NULL as this function is often called on
716 * mapping->host which is NULL for the swapper space.
718 int inode_congested(struct inode *inode, int cong_bits)
721 * Once set, ->i_wb never becomes NULL while the inode is alive.
722 * Start transaction iff ->i_wb is visible.
724 if (inode && inode_to_wb_is_valid(inode)) {
725 struct bdi_writeback *wb;
726 bool locked, congested;
728 wb = unlocked_inode_to_wb_begin(inode, &locked);
729 congested = wb_congested(wb, cong_bits);
730 unlocked_inode_to_wb_end(inode, locked);
734 return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
736 EXPORT_SYMBOL_GPL(inode_congested);
739 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
740 * @wb: target bdi_writeback to split @nr_pages to
741 * @nr_pages: number of pages to write for the whole bdi
743 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
744 * relation to the total write bandwidth of all wb's w/ dirty inodes on
747 static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
749 unsigned long this_bw = wb->avg_write_bandwidth;
750 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
752 if (nr_pages == LONG_MAX)
756 * This may be called on clean wb's and proportional distribution
757 * may not make sense, just use the original @nr_pages in those
758 * cases. In general, we wanna err on the side of writing more.
760 if (!tot_bw || this_bw >= tot_bw)
763 return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
767 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
768 * @bdi: target backing_dev_info
769 * @base_work: wb_writeback_work to issue
770 * @skip_if_busy: skip wb's which already have writeback in progress
772 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
773 * have dirty inodes. If @base_work->nr_page isn't %LONG_MAX, it's
774 * distributed to the busy wbs according to each wb's proportion in the
775 * total active write bandwidth of @bdi.
777 static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
778 struct wb_writeback_work *base_work,
781 int next_memcg_id = 0;
782 struct bdi_writeback *wb;
788 bdi_for_each_wb(wb, bdi, &iter, next_memcg_id) {
789 DEFINE_WB_COMPLETION_ONSTACK(fallback_work_done);
790 struct wb_writeback_work fallback_work;
791 struct wb_writeback_work *work;
794 /* SYNC_ALL writes out I_DIRTY_TIME too */
795 if (!wb_has_dirty_io(wb) &&
796 (base_work->sync_mode == WB_SYNC_NONE ||
797 list_empty(&wb->b_dirty_time)))
799 if (skip_if_busy && writeback_in_progress(wb))
802 nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
804 work = kmalloc(sizeof(*work), GFP_ATOMIC);
807 work->nr_pages = nr_pages;
809 wb_queue_work(wb, work);
813 /* alloc failed, execute synchronously using on-stack fallback */
814 work = &fallback_work;
816 work->nr_pages = nr_pages;
818 work->done = &fallback_work_done;
820 wb_queue_work(wb, work);
822 next_memcg_id = wb->memcg_css->id + 1;
824 wb_wait_for_completion(bdi, &fallback_work_done);
830 #else /* CONFIG_CGROUP_WRITEBACK */
832 static struct bdi_writeback *
833 locked_inode_to_wb_and_lock_list(struct inode *inode)
834 __releases(&inode->i_lock)
835 __acquires(&wb->list_lock)
837 struct bdi_writeback *wb = inode_to_wb(inode);
839 spin_unlock(&inode->i_lock);
840 spin_lock(&wb->list_lock);
844 static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
845 __acquires(&wb->list_lock)
847 struct bdi_writeback *wb = inode_to_wb(inode);
849 spin_lock(&wb->list_lock);
853 static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
858 static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
859 struct wb_writeback_work *base_work,
864 if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
865 base_work->auto_free = 0;
866 wb_queue_work(&bdi->wb, base_work);
870 #endif /* CONFIG_CGROUP_WRITEBACK */
872 void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
873 bool range_cyclic, enum wb_reason reason)
875 struct wb_writeback_work *work;
877 if (!wb_has_dirty_io(wb))
881 * This is WB_SYNC_NONE writeback, so if allocation fails just
882 * wakeup the thread for old dirty data writeback
884 work = kzalloc(sizeof(*work), GFP_ATOMIC);
886 trace_writeback_nowork(wb);
891 work->sync_mode = WB_SYNC_NONE;
892 work->nr_pages = nr_pages;
893 work->range_cyclic = range_cyclic;
894 work->reason = reason;
897 wb_queue_work(wb, work);
901 * wb_start_background_writeback - start background writeback
902 * @wb: bdi_writback to write from
905 * This makes sure WB_SYNC_NONE background writeback happens. When
906 * this function returns, it is only guaranteed that for given wb
907 * some IO is happening if we are over background dirty threshold.
908 * Caller need not hold sb s_umount semaphore.
910 void wb_start_background_writeback(struct bdi_writeback *wb)
913 * We just wake up the flusher thread. It will perform background
914 * writeback as soon as there is no other work to do.
916 trace_writeback_wake_background(wb);
921 * Remove the inode from the writeback list it is on.
923 void inode_io_list_del(struct inode *inode)
925 struct bdi_writeback *wb;
927 wb = inode_to_wb_and_lock_list(inode);
928 inode_io_list_del_locked(inode, wb);
929 spin_unlock(&wb->list_lock);
933 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
934 * furthest end of its superblock's dirty-inode list.
936 * Before stamping the inode's ->dirtied_when, we check to see whether it is
937 * already the most-recently-dirtied inode on the b_dirty list. If that is
938 * the case then the inode must have been redirtied while it was being written
939 * out and we don't reset its dirtied_when.
941 static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
943 if (!list_empty(&wb->b_dirty)) {
946 tail = wb_inode(wb->b_dirty.next);
947 if (time_before(inode->dirtied_when, tail->dirtied_when))
948 inode->dirtied_when = jiffies;
950 inode_io_list_move_locked(inode, wb, &wb->b_dirty);
954 * requeue inode for re-scanning after bdi->b_io list is exhausted.
956 static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
958 inode_io_list_move_locked(inode, wb, &wb->b_more_io);
961 static void inode_sync_complete(struct inode *inode)
963 inode->i_state &= ~I_SYNC;
964 /* If inode is clean an unused, put it into LRU now... */
965 inode_add_lru(inode);
966 /* Waiters must see I_SYNC cleared before being woken up */
968 wake_up_bit(&inode->i_state, __I_SYNC);
971 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
973 bool ret = time_after(inode->dirtied_when, t);
976 * For inodes being constantly redirtied, dirtied_when can get stuck.
977 * It _appears_ to be in the future, but is actually in distant past.
978 * This test is necessary to prevent such wrapped-around relative times
979 * from permanently stopping the whole bdi writeback.
981 ret = ret && time_before_eq(inode->dirtied_when, jiffies);
986 #define EXPIRE_DIRTY_ATIME 0x0001
989 * Move expired (dirtied before work->older_than_this) dirty inodes from
990 * @delaying_queue to @dispatch_queue.
992 static int move_expired_inodes(struct list_head *delaying_queue,
993 struct list_head *dispatch_queue,
995 struct wb_writeback_work *work)
997 unsigned long *older_than_this = NULL;
998 unsigned long expire_time;
1000 struct list_head *pos, *node;
1001 struct super_block *sb = NULL;
1002 struct inode *inode;
1006 if ((flags & EXPIRE_DIRTY_ATIME) == 0)
1007 older_than_this = work->older_than_this;
1008 else if (!work->for_sync) {
1009 expire_time = jiffies - (dirtytime_expire_interval * HZ);
1010 older_than_this = &expire_time;
1012 while (!list_empty(delaying_queue)) {
1013 inode = wb_inode(delaying_queue->prev);
1014 if (older_than_this &&
1015 inode_dirtied_after(inode, *older_than_this))
1017 list_move(&inode->i_io_list, &tmp);
1019 if (flags & EXPIRE_DIRTY_ATIME)
1020 set_bit(__I_DIRTY_TIME_EXPIRED, &inode->i_state);
1021 if (sb_is_blkdev_sb(inode->i_sb))
1023 if (sb && sb != inode->i_sb)
1028 /* just one sb in list, splice to dispatch_queue and we're done */
1030 list_splice(&tmp, dispatch_queue);
1034 /* Move inodes from one superblock together */
1035 while (!list_empty(&tmp)) {
1036 sb = wb_inode(tmp.prev)->i_sb;
1037 list_for_each_prev_safe(pos, node, &tmp) {
1038 inode = wb_inode(pos);
1039 if (inode->i_sb == sb)
1040 list_move(&inode->i_io_list, dispatch_queue);
1048 * Queue all expired dirty inodes for io, eldest first.
1050 * newly dirtied b_dirty b_io b_more_io
1051 * =============> gf edc BA
1053 * newly dirtied b_dirty b_io b_more_io
1054 * =============> g fBAedc
1056 * +--> dequeue for IO
1058 static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
1062 assert_spin_locked(&wb->list_lock);
1063 list_splice_init(&wb->b_more_io, &wb->b_io);
1064 moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, 0, work);
1065 moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
1066 EXPIRE_DIRTY_ATIME, work);
1068 wb_io_lists_populated(wb);
1069 trace_writeback_queue_io(wb, work, moved);
1072 static int write_inode(struct inode *inode, struct writeback_control *wbc)
1076 if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1077 trace_writeback_write_inode_start(inode, wbc);
1078 ret = inode->i_sb->s_op->write_inode(inode, wbc);
1079 trace_writeback_write_inode(inode, wbc);
1086 * Wait for writeback on an inode to complete. Called with i_lock held.
1087 * Caller must make sure inode cannot go away when we drop i_lock.
1089 static void __inode_wait_for_writeback(struct inode *inode)
1090 __releases(inode->i_lock)
1091 __acquires(inode->i_lock)
1093 DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1094 wait_queue_head_t *wqh;
1096 wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1097 while (inode->i_state & I_SYNC) {
1098 spin_unlock(&inode->i_lock);
1099 __wait_on_bit(wqh, &wq, bit_wait,
1100 TASK_UNINTERRUPTIBLE);
1101 spin_lock(&inode->i_lock);
1106 * Wait for writeback on an inode to complete. Caller must have inode pinned.
1108 void inode_wait_for_writeback(struct inode *inode)
1110 spin_lock(&inode->i_lock);
1111 __inode_wait_for_writeback(inode);
1112 spin_unlock(&inode->i_lock);
1116 * Sleep until I_SYNC is cleared. This function must be called with i_lock
1117 * held and drops it. It is aimed for callers not holding any inode reference
1118 * so once i_lock is dropped, inode can go away.
1120 static void inode_sleep_on_writeback(struct inode *inode)
1121 __releases(inode->i_lock)
1124 wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1127 prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1128 sleep = inode->i_state & I_SYNC;
1129 spin_unlock(&inode->i_lock);
1132 finish_wait(wqh, &wait);
1136 * Find proper writeback list for the inode depending on its current state and
1137 * possibly also change of its state while we were doing writeback. Here we
1138 * handle things such as livelock prevention or fairness of writeback among
1139 * inodes. This function can be called only by flusher thread - noone else
1140 * processes all inodes in writeback lists and requeueing inodes behind flusher
1141 * thread's back can have unexpected consequences.
1143 static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1144 struct writeback_control *wbc)
1146 if (inode->i_state & I_FREEING)
1150 * Sync livelock prevention. Each inode is tagged and synced in one
1151 * shot. If still dirty, it will be redirty_tail()'ed below. Update
1152 * the dirty time to prevent enqueue and sync it again.
1154 if ((inode->i_state & I_DIRTY) &&
1155 (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1156 inode->dirtied_when = jiffies;
1158 if (wbc->pages_skipped) {
1160 * writeback is not making progress due to locked
1161 * buffers. Skip this inode for now.
1163 redirty_tail(inode, wb);
1167 if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1169 * We didn't write back all the pages. nfs_writepages()
1170 * sometimes bales out without doing anything.
1172 if (wbc->nr_to_write <= 0) {
1173 /* Slice used up. Queue for next turn. */
1174 requeue_io(inode, wb);
1177 * Writeback blocked by something other than
1178 * congestion. Delay the inode for some time to
1179 * avoid spinning on the CPU (100% iowait)
1180 * retrying writeback of the dirty page/inode
1181 * that cannot be performed immediately.
1183 redirty_tail(inode, wb);
1185 } else if (inode->i_state & I_DIRTY) {
1187 * Filesystems can dirty the inode during writeback operations,
1188 * such as delayed allocation during submission or metadata
1189 * updates after data IO completion.
1191 redirty_tail(inode, wb);
1192 } else if (inode->i_state & I_DIRTY_TIME) {
1193 inode->dirtied_when = jiffies;
1194 inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
1196 /* The inode is clean. Remove from writeback lists. */
1197 inode_io_list_del_locked(inode, wb);
1202 * Write out an inode and its dirty pages. Do not update the writeback list
1203 * linkage. That is left to the caller. The caller is also responsible for
1204 * setting I_SYNC flag and calling inode_sync_complete() to clear it.
1207 __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1209 struct address_space *mapping = inode->i_mapping;
1210 long nr_to_write = wbc->nr_to_write;
1214 WARN_ON(!(inode->i_state & I_SYNC));
1216 trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1218 ret = do_writepages(mapping, wbc);
1221 * Make sure to wait on the data before writing out the metadata.
1222 * This is important for filesystems that modify metadata on data
1223 * I/O completion. We don't do it for sync(2) writeback because it has a
1224 * separate, external IO completion path and ->sync_fs for guaranteeing
1225 * inode metadata is written back correctly.
1227 if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
1228 int err = filemap_fdatawait(mapping);
1234 * Some filesystems may redirty the inode during the writeback
1235 * due to delalloc, clear dirty metadata flags right before
1238 spin_lock(&inode->i_lock);
1240 dirty = inode->i_state & I_DIRTY;
1241 if (inode->i_state & I_DIRTY_TIME) {
1242 if ((dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) ||
1243 unlikely(inode->i_state & I_DIRTY_TIME_EXPIRED) ||
1244 unlikely(time_after(jiffies,
1245 (inode->dirtied_time_when +
1246 dirtytime_expire_interval * HZ)))) {
1247 dirty |= I_DIRTY_TIME | I_DIRTY_TIME_EXPIRED;
1248 trace_writeback_lazytime(inode);
1251 inode->i_state &= ~I_DIRTY_TIME_EXPIRED;
1252 inode->i_state &= ~dirty;
1255 * Paired with smp_mb() in __mark_inode_dirty(). This allows
1256 * __mark_inode_dirty() to test i_state without grabbing i_lock -
1257 * either they see the I_DIRTY bits cleared or we see the dirtied
1260 * I_DIRTY_PAGES is always cleared together above even if @mapping
1261 * still has dirty pages. The flag is reinstated after smp_mb() if
1262 * necessary. This guarantees that either __mark_inode_dirty()
1263 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1267 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1268 inode->i_state |= I_DIRTY_PAGES;
1270 spin_unlock(&inode->i_lock);
1272 if (dirty & I_DIRTY_TIME)
1273 mark_inode_dirty_sync(inode);
1274 /* Don't write the inode if only I_DIRTY_PAGES was set */
1275 if (dirty & ~I_DIRTY_PAGES) {
1276 int err = write_inode(inode, wbc);
1280 trace_writeback_single_inode(inode, wbc, nr_to_write);
1285 * Write out an inode's dirty pages. Either the caller has an active reference
1286 * on the inode or the inode has I_WILL_FREE set.
1288 * This function is designed to be called for writing back one inode which
1289 * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
1290 * and does more profound writeback list handling in writeback_sb_inodes().
1293 writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
1294 struct writeback_control *wbc)
1298 spin_lock(&inode->i_lock);
1299 if (!atomic_read(&inode->i_count))
1300 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1302 WARN_ON(inode->i_state & I_WILL_FREE);
1304 if (inode->i_state & I_SYNC) {
1305 if (wbc->sync_mode != WB_SYNC_ALL)
1308 * It's a data-integrity sync. We must wait. Since callers hold
1309 * inode reference or inode has I_WILL_FREE set, it cannot go
1312 __inode_wait_for_writeback(inode);
1314 WARN_ON(inode->i_state & I_SYNC);
1316 * Skip inode if it is clean and we have no outstanding writeback in
1317 * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
1318 * function since flusher thread may be doing for example sync in
1319 * parallel and if we move the inode, it could get skipped. So here we
1320 * make sure inode is on some writeback list and leave it there unless
1321 * we have completely cleaned the inode.
1323 if (!(inode->i_state & I_DIRTY_ALL) &&
1324 (wbc->sync_mode != WB_SYNC_ALL ||
1325 !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
1327 inode->i_state |= I_SYNC;
1328 wbc_attach_and_unlock_inode(wbc, inode);
1330 ret = __writeback_single_inode(inode, wbc);
1332 wbc_detach_inode(wbc);
1333 spin_lock(&wb->list_lock);
1334 spin_lock(&inode->i_lock);
1336 * If inode is clean, remove it from writeback lists. Otherwise don't
1337 * touch it. See comment above for explanation.
1339 if (!(inode->i_state & I_DIRTY_ALL))
1340 inode_io_list_del_locked(inode, wb);
1341 spin_unlock(&wb->list_lock);
1342 inode_sync_complete(inode);
1344 spin_unlock(&inode->i_lock);
1348 static long writeback_chunk_size(struct bdi_writeback *wb,
1349 struct wb_writeback_work *work)
1354 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1355 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1356 * here avoids calling into writeback_inodes_wb() more than once.
1358 * The intended call sequence for WB_SYNC_ALL writeback is:
1361 * writeback_sb_inodes() <== called only once
1362 * write_cache_pages() <== called once for each inode
1363 * (quickly) tag currently dirty pages
1364 * (maybe slowly) sync all tagged pages
1366 if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1369 pages = min(wb->avg_write_bandwidth / 2,
1370 global_wb_domain.dirty_limit / DIRTY_SCOPE);
1371 pages = min(pages, work->nr_pages);
1372 pages = round_down(pages + MIN_WRITEBACK_PAGES,
1373 MIN_WRITEBACK_PAGES);
1380 * Write a portion of b_io inodes which belong to @sb.
1382 * Return the number of pages and/or inodes written.
1384 * NOTE! This is called with wb->list_lock held, and will
1385 * unlock and relock that for each inode it ends up doing
1388 static long writeback_sb_inodes(struct super_block *sb,
1389 struct bdi_writeback *wb,
1390 struct wb_writeback_work *work)
1392 struct writeback_control wbc = {
1393 .sync_mode = work->sync_mode,
1394 .tagged_writepages = work->tagged_writepages,
1395 .for_kupdate = work->for_kupdate,
1396 .for_background = work->for_background,
1397 .for_sync = work->for_sync,
1398 .range_cyclic = work->range_cyclic,
1400 .range_end = LLONG_MAX,
1402 unsigned long start_time = jiffies;
1404 long wrote = 0; /* count both pages and inodes */
1406 while (!list_empty(&wb->b_io)) {
1407 struct inode *inode = wb_inode(wb->b_io.prev);
1409 if (inode->i_sb != sb) {
1412 * We only want to write back data for this
1413 * superblock, move all inodes not belonging
1414 * to it back onto the dirty list.
1416 redirty_tail(inode, wb);
1421 * The inode belongs to a different superblock.
1422 * Bounce back to the caller to unpin this and
1423 * pin the next superblock.
1429 * Don't bother with new inodes or inodes being freed, first
1430 * kind does not need periodic writeout yet, and for the latter
1431 * kind writeout is handled by the freer.
1433 spin_lock(&inode->i_lock);
1434 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
1435 spin_unlock(&inode->i_lock);
1436 redirty_tail(inode, wb);
1439 if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1441 * If this inode is locked for writeback and we are not
1442 * doing writeback-for-data-integrity, move it to
1443 * b_more_io so that writeback can proceed with the
1444 * other inodes on s_io.
1446 * We'll have another go at writing back this inode
1447 * when we completed a full scan of b_io.
1449 spin_unlock(&inode->i_lock);
1450 requeue_io(inode, wb);
1451 trace_writeback_sb_inodes_requeue(inode);
1454 spin_unlock(&wb->list_lock);
1457 * We already requeued the inode if it had I_SYNC set and we
1458 * are doing WB_SYNC_NONE writeback. So this catches only the
1461 if (inode->i_state & I_SYNC) {
1462 /* Wait for I_SYNC. This function drops i_lock... */
1463 inode_sleep_on_writeback(inode);
1464 /* Inode may be gone, start again */
1465 spin_lock(&wb->list_lock);
1468 inode->i_state |= I_SYNC;
1469 wbc_attach_and_unlock_inode(&wbc, inode);
1471 write_chunk = writeback_chunk_size(wb, work);
1472 wbc.nr_to_write = write_chunk;
1473 wbc.pages_skipped = 0;
1476 * We use I_SYNC to pin the inode in memory. While it is set
1477 * evict_inode() will wait so the inode cannot be freed.
1479 __writeback_single_inode(inode, &wbc);
1481 wbc_detach_inode(&wbc);
1482 work->nr_pages -= write_chunk - wbc.nr_to_write;
1483 wrote += write_chunk - wbc.nr_to_write;
1485 if (need_resched()) {
1487 * We're trying to balance between building up a nice
1488 * long list of IOs to improve our merge rate, and
1489 * getting those IOs out quickly for anyone throttling
1490 * in balance_dirty_pages(). cond_resched() doesn't
1491 * unplug, so get our IOs out the door before we
1494 blk_flush_plug(current);
1499 spin_lock(&wb->list_lock);
1500 spin_lock(&inode->i_lock);
1501 if (!(inode->i_state & I_DIRTY_ALL))
1503 requeue_inode(inode, wb, &wbc);
1504 inode_sync_complete(inode);
1505 spin_unlock(&inode->i_lock);
1508 * bail out to wb_writeback() often enough to check
1509 * background threshold and other termination conditions.
1512 if (time_is_before_jiffies(start_time + HZ / 10UL))
1514 if (work->nr_pages <= 0)
1521 static long __writeback_inodes_wb(struct bdi_writeback *wb,
1522 struct wb_writeback_work *work)
1524 unsigned long start_time = jiffies;
1527 while (!list_empty(&wb->b_io)) {
1528 struct inode *inode = wb_inode(wb->b_io.prev);
1529 struct super_block *sb = inode->i_sb;
1531 if (!trylock_super(sb)) {
1533 * trylock_super() may fail consistently due to
1534 * s_umount being grabbed by someone else. Don't use
1535 * requeue_io() to avoid busy retrying the inode/sb.
1537 redirty_tail(inode, wb);
1540 wrote += writeback_sb_inodes(sb, wb, work);
1541 up_read(&sb->s_umount);
1543 /* refer to the same tests at the end of writeback_sb_inodes */
1545 if (time_is_before_jiffies(start_time + HZ / 10UL))
1547 if (work->nr_pages <= 0)
1551 /* Leave any unwritten inodes on b_io */
1555 static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
1556 enum wb_reason reason)
1558 struct wb_writeback_work work = {
1559 .nr_pages = nr_pages,
1560 .sync_mode = WB_SYNC_NONE,
1564 struct blk_plug plug;
1566 blk_start_plug(&plug);
1567 spin_lock(&wb->list_lock);
1568 if (list_empty(&wb->b_io))
1569 queue_io(wb, &work);
1570 __writeback_inodes_wb(wb, &work);
1571 spin_unlock(&wb->list_lock);
1572 blk_finish_plug(&plug);
1574 return nr_pages - work.nr_pages;
1578 * Explicit flushing or periodic writeback of "old" data.
1580 * Define "old": the first time one of an inode's pages is dirtied, we mark the
1581 * dirtying-time in the inode's address_space. So this periodic writeback code
1582 * just walks the superblock inode list, writing back any inodes which are
1583 * older than a specific point in time.
1585 * Try to run once per dirty_writeback_interval. But if a writeback event
1586 * takes longer than a dirty_writeback_interval interval, then leave a
1589 * older_than_this takes precedence over nr_to_write. So we'll only write back
1590 * all dirty pages if they are all attached to "old" mappings.
1592 static long wb_writeback(struct bdi_writeback *wb,
1593 struct wb_writeback_work *work)
1595 unsigned long wb_start = jiffies;
1596 long nr_pages = work->nr_pages;
1597 unsigned long oldest_jif;
1598 struct inode *inode;
1600 struct blk_plug plug;
1602 oldest_jif = jiffies;
1603 work->older_than_this = &oldest_jif;
1605 blk_start_plug(&plug);
1606 spin_lock(&wb->list_lock);
1609 * Stop writeback when nr_pages has been consumed
1611 if (work->nr_pages <= 0)
1615 * Background writeout and kupdate-style writeback may
1616 * run forever. Stop them if there is other work to do
1617 * so that e.g. sync can proceed. They'll be restarted
1618 * after the other works are all done.
1620 if ((work->for_background || work->for_kupdate) &&
1621 !list_empty(&wb->work_list))
1625 * For background writeout, stop when we are below the
1626 * background dirty threshold
1628 if (work->for_background && !wb_over_bg_thresh(wb))
1632 * Kupdate and background works are special and we want to
1633 * include all inodes that need writing. Livelock avoidance is
1634 * handled by these works yielding to any other work so we are
1637 if (work->for_kupdate) {
1638 oldest_jif = jiffies -
1639 msecs_to_jiffies(dirty_expire_interval * 10);
1640 } else if (work->for_background)
1641 oldest_jif = jiffies;
1643 trace_writeback_start(wb, work);
1644 if (list_empty(&wb->b_io))
1647 progress = writeback_sb_inodes(work->sb, wb, work);
1649 progress = __writeback_inodes_wb(wb, work);
1650 trace_writeback_written(wb, work);
1652 wb_update_bandwidth(wb, wb_start);
1655 * Did we write something? Try for more
1657 * Dirty inodes are moved to b_io for writeback in batches.
1658 * The completion of the current batch does not necessarily
1659 * mean the overall work is done. So we keep looping as long
1660 * as made some progress on cleaning pages or inodes.
1665 * No more inodes for IO, bail
1667 if (list_empty(&wb->b_more_io))
1670 * Nothing written. Wait for some inode to
1671 * become available for writeback. Otherwise
1672 * we'll just busyloop.
1674 if (!list_empty(&wb->b_more_io)) {
1675 trace_writeback_wait(wb, work);
1676 inode = wb_inode(wb->b_more_io.prev);
1677 spin_lock(&inode->i_lock);
1678 spin_unlock(&wb->list_lock);
1679 /* This function drops i_lock... */
1680 inode_sleep_on_writeback(inode);
1681 spin_lock(&wb->list_lock);
1684 spin_unlock(&wb->list_lock);
1685 blk_finish_plug(&plug);
1687 return nr_pages - work->nr_pages;
1691 * Return the next wb_writeback_work struct that hasn't been processed yet.
1693 static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
1695 struct wb_writeback_work *work = NULL;
1697 spin_lock_bh(&wb->work_lock);
1698 if (!list_empty(&wb->work_list)) {
1699 work = list_entry(wb->work_list.next,
1700 struct wb_writeback_work, list);
1701 list_del_init(&work->list);
1703 spin_unlock_bh(&wb->work_lock);
1708 * Add in the number of potentially dirty inodes, because each inode
1709 * write can dirty pagecache in the underlying blockdev.
1711 static unsigned long get_nr_dirty_pages(void)
1713 return global_page_state(NR_FILE_DIRTY) +
1714 global_page_state(NR_UNSTABLE_NFS) +
1715 get_nr_dirty_inodes();
1718 static long wb_check_background_flush(struct bdi_writeback *wb)
1720 if (wb_over_bg_thresh(wb)) {
1722 struct wb_writeback_work work = {
1723 .nr_pages = LONG_MAX,
1724 .sync_mode = WB_SYNC_NONE,
1725 .for_background = 1,
1727 .reason = WB_REASON_BACKGROUND,
1730 return wb_writeback(wb, &work);
1736 static long wb_check_old_data_flush(struct bdi_writeback *wb)
1738 unsigned long expired;
1742 * When set to zero, disable periodic writeback
1744 if (!dirty_writeback_interval)
1747 expired = wb->last_old_flush +
1748 msecs_to_jiffies(dirty_writeback_interval * 10);
1749 if (time_before(jiffies, expired))
1752 wb->last_old_flush = jiffies;
1753 nr_pages = get_nr_dirty_pages();
1756 struct wb_writeback_work work = {
1757 .nr_pages = nr_pages,
1758 .sync_mode = WB_SYNC_NONE,
1761 .reason = WB_REASON_PERIODIC,
1764 return wb_writeback(wb, &work);
1771 * Retrieve work items and do the writeback they describe
1773 static long wb_do_writeback(struct bdi_writeback *wb)
1775 struct wb_writeback_work *work;
1778 set_bit(WB_writeback_running, &wb->state);
1779 while ((work = get_next_work_item(wb)) != NULL) {
1780 struct wb_completion *done = work->done;
1782 trace_writeback_exec(wb, work);
1784 wrote += wb_writeback(wb, work);
1786 if (work->auto_free)
1788 if (done && atomic_dec_and_test(&done->cnt))
1789 wake_up_all(&wb->bdi->wb_waitq);
1793 * Check for periodic writeback, kupdated() style
1795 wrote += wb_check_old_data_flush(wb);
1796 wrote += wb_check_background_flush(wb);
1797 clear_bit(WB_writeback_running, &wb->state);
1803 * Handle writeback of dirty data for the device backed by this bdi. Also
1804 * reschedules periodically and does kupdated style flushing.
1806 void wb_workfn(struct work_struct *work)
1808 struct bdi_writeback *wb = container_of(to_delayed_work(work),
1809 struct bdi_writeback, dwork);
1812 set_worker_desc("flush-%s", dev_name(wb->bdi->dev));
1813 current->flags |= PF_SWAPWRITE;
1815 if (likely(!current_is_workqueue_rescuer() ||
1816 !test_bit(WB_registered, &wb->state))) {
1818 * The normal path. Keep writing back @wb until its
1819 * work_list is empty. Note that this path is also taken
1820 * if @wb is shutting down even when we're running off the
1821 * rescuer as work_list needs to be drained.
1824 pages_written = wb_do_writeback(wb);
1825 trace_writeback_pages_written(pages_written);
1826 } while (!list_empty(&wb->work_list));
1829 * bdi_wq can't get enough workers and we're running off
1830 * the emergency worker. Don't hog it. Hopefully, 1024 is
1831 * enough for efficient IO.
1833 pages_written = writeback_inodes_wb(wb, 1024,
1834 WB_REASON_FORKER_THREAD);
1835 trace_writeback_pages_written(pages_written);
1838 if (!list_empty(&wb->work_list))
1839 mod_delayed_work(bdi_wq, &wb->dwork, 0);
1840 else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
1841 wb_wakeup_delayed(wb);
1843 current->flags &= ~PF_SWAPWRITE;
1847 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
1850 void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
1852 struct backing_dev_info *bdi;
1855 nr_pages = get_nr_dirty_pages();
1858 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1859 struct bdi_writeback *wb;
1860 struct wb_iter iter;
1862 if (!bdi_has_dirty_io(bdi))
1865 bdi_for_each_wb(wb, bdi, &iter, 0)
1866 wb_start_writeback(wb, wb_split_bdi_pages(wb, nr_pages),
1873 * Wake up bdi's periodically to make sure dirtytime inodes gets
1874 * written back periodically. We deliberately do *not* check the
1875 * b_dirtytime list in wb_has_dirty_io(), since this would cause the
1876 * kernel to be constantly waking up once there are any dirtytime
1877 * inodes on the system. So instead we define a separate delayed work
1878 * function which gets called much more rarely. (By default, only
1879 * once every 12 hours.)
1881 * If there is any other write activity going on in the file system,
1882 * this function won't be necessary. But if the only thing that has
1883 * happened on the file system is a dirtytime inode caused by an atime
1884 * update, we need this infrastructure below to make sure that inode
1885 * eventually gets pushed out to disk.
1887 static void wakeup_dirtytime_writeback(struct work_struct *w);
1888 static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
1890 static void wakeup_dirtytime_writeback(struct work_struct *w)
1892 struct backing_dev_info *bdi;
1895 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1896 struct bdi_writeback *wb;
1897 struct wb_iter iter;
1899 bdi_for_each_wb(wb, bdi, &iter, 0)
1900 if (!list_empty(&bdi->wb.b_dirty_time))
1901 wb_wakeup(&bdi->wb);
1904 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
1907 static int __init start_dirtytime_writeback(void)
1909 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
1912 __initcall(start_dirtytime_writeback);
1914 int dirtytime_interval_handler(struct ctl_table *table, int write,
1915 void __user *buffer, size_t *lenp, loff_t *ppos)
1919 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
1920 if (ret == 0 && write)
1921 mod_delayed_work(system_wq, &dirtytime_work, 0);
1925 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
1927 if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
1928 struct dentry *dentry;
1929 const char *name = "?";
1931 dentry = d_find_alias(inode);
1933 spin_lock(&dentry->d_lock);
1934 name = (const char *) dentry->d_name.name;
1937 "%s(%d): dirtied inode %lu (%s) on %s\n",
1938 current->comm, task_pid_nr(current), inode->i_ino,
1939 name, inode->i_sb->s_id);
1941 spin_unlock(&dentry->d_lock);
1948 * __mark_inode_dirty - internal function
1949 * @inode: inode to mark
1950 * @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
1951 * Mark an inode as dirty. Callers should use mark_inode_dirty or
1952 * mark_inode_dirty_sync.
1954 * Put the inode on the super block's dirty list.
1956 * CAREFUL! We mark it dirty unconditionally, but move it onto the
1957 * dirty list only if it is hashed or if it refers to a blockdev.
1958 * If it was not hashed, it will never be added to the dirty list
1959 * even if it is later hashed, as it will have been marked dirty already.
1961 * In short, make sure you hash any inodes _before_ you start marking
1964 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
1965 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
1966 * the kernel-internal blockdev inode represents the dirtying time of the
1967 * blockdev's pages. This is why for I_DIRTY_PAGES we always use
1968 * page->mapping->host, so the page-dirtying time is recorded in the internal
1971 #define I_DIRTY_INODE (I_DIRTY_SYNC | I_DIRTY_DATASYNC)
1972 void __mark_inode_dirty(struct inode *inode, int flags)
1974 struct super_block *sb = inode->i_sb;
1977 trace_writeback_mark_inode_dirty(inode, flags);
1980 * Don't do this for I_DIRTY_PAGES - that doesn't actually
1981 * dirty the inode itself
1983 if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_TIME)) {
1984 trace_writeback_dirty_inode_start(inode, flags);
1986 if (sb->s_op->dirty_inode)
1987 sb->s_op->dirty_inode(inode, flags);
1989 trace_writeback_dirty_inode(inode, flags);
1991 if (flags & I_DIRTY_INODE)
1992 flags &= ~I_DIRTY_TIME;
1993 dirtytime = flags & I_DIRTY_TIME;
1996 * Paired with smp_mb() in __writeback_single_inode() for the
1997 * following lockless i_state test. See there for details.
2001 if (((inode->i_state & flags) == flags) ||
2002 (dirtytime && (inode->i_state & I_DIRTY_INODE)))
2005 if (unlikely(block_dump))
2006 block_dump___mark_inode_dirty(inode);
2008 spin_lock(&inode->i_lock);
2009 if (dirtytime && (inode->i_state & I_DIRTY_INODE))
2010 goto out_unlock_inode;
2011 if ((inode->i_state & flags) != flags) {
2012 const int was_dirty = inode->i_state & I_DIRTY;
2014 inode_attach_wb(inode, NULL);
2016 if (flags & I_DIRTY_INODE)
2017 inode->i_state &= ~I_DIRTY_TIME;
2018 inode->i_state |= flags;
2021 * If the inode is being synced, just update its dirty state.
2022 * The unlocker will place the inode on the appropriate
2023 * superblock list, based upon its state.
2025 if (inode->i_state & I_SYNC)
2026 goto out_unlock_inode;
2029 * Only add valid (hashed) inodes to the superblock's
2030 * dirty list. Add blockdev inodes as well.
2032 if (!S_ISBLK(inode->i_mode)) {
2033 if (inode_unhashed(inode))
2034 goto out_unlock_inode;
2036 if (inode->i_state & I_FREEING)
2037 goto out_unlock_inode;
2040 * If the inode was already on b_dirty/b_io/b_more_io, don't
2041 * reposition it (that would break b_dirty time-ordering).
2044 struct bdi_writeback *wb;
2045 struct list_head *dirty_list;
2046 bool wakeup_bdi = false;
2048 wb = locked_inode_to_wb_and_lock_list(inode);
2050 WARN(bdi_cap_writeback_dirty(wb->bdi) &&
2051 !test_bit(WB_registered, &wb->state),
2052 "bdi-%s not registered\n", wb->bdi->name);
2054 inode->dirtied_when = jiffies;
2056 inode->dirtied_time_when = jiffies;
2058 if (inode->i_state & (I_DIRTY_INODE | I_DIRTY_PAGES))
2059 dirty_list = &wb->b_dirty;
2061 dirty_list = &wb->b_dirty_time;
2063 wakeup_bdi = inode_io_list_move_locked(inode, wb,
2066 spin_unlock(&wb->list_lock);
2067 trace_writeback_dirty_inode_enqueue(inode);
2070 * If this is the first dirty inode for this bdi,
2071 * we have to wake-up the corresponding bdi thread
2072 * to make sure background write-back happens
2075 if (bdi_cap_writeback_dirty(wb->bdi) && wakeup_bdi)
2076 wb_wakeup_delayed(wb);
2081 spin_unlock(&inode->i_lock);
2084 EXPORT_SYMBOL(__mark_inode_dirty);
2087 * The @s_sync_lock is used to serialise concurrent sync operations
2088 * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2089 * Concurrent callers will block on the s_sync_lock rather than doing contending
2090 * walks. The queueing maintains sync(2) required behaviour as all the IO that
2091 * has been issued up to the time this function is enter is guaranteed to be
2092 * completed by the time we have gained the lock and waited for all IO that is
2093 * in progress regardless of the order callers are granted the lock.
2095 static void wait_sb_inodes(struct super_block *sb)
2097 struct inode *inode, *old_inode = NULL;
2100 * We need to be protected against the filesystem going from
2101 * r/o to r/w or vice versa.
2103 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2105 mutex_lock(&sb->s_sync_lock);
2106 spin_lock(&sb->s_inode_list_lock);
2109 * Data integrity sync. Must wait for all pages under writeback,
2110 * because there may have been pages dirtied before our sync
2111 * call, but which had writeout started before we write it out.
2112 * In which case, the inode may not be on the dirty list, but
2113 * we still have to wait for that writeout.
2115 list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
2116 struct address_space *mapping = inode->i_mapping;
2118 spin_lock(&inode->i_lock);
2119 if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
2120 (mapping->nrpages == 0)) {
2121 spin_unlock(&inode->i_lock);
2125 spin_unlock(&inode->i_lock);
2126 spin_unlock(&sb->s_inode_list_lock);
2129 * We hold a reference to 'inode' so it couldn't have been
2130 * removed from s_inodes list while we dropped the
2131 * s_inode_list_lock. We cannot iput the inode now as we can
2132 * be holding the last reference and we cannot iput it under
2133 * s_inode_list_lock. So we keep the reference and iput it
2139 filemap_fdatawait(mapping);
2143 spin_lock(&sb->s_inode_list_lock);
2145 spin_unlock(&sb->s_inode_list_lock);
2147 mutex_unlock(&sb->s_sync_lock);
2150 static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2151 enum wb_reason reason, bool skip_if_busy)
2153 DEFINE_WB_COMPLETION_ONSTACK(done);
2154 struct wb_writeback_work work = {
2156 .sync_mode = WB_SYNC_NONE,
2157 .tagged_writepages = 1,
2162 struct backing_dev_info *bdi = sb->s_bdi;
2164 if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
2166 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2168 bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
2169 wb_wait_for_completion(bdi, &done);
2173 * writeback_inodes_sb_nr - writeback dirty inodes from given super_block
2174 * @sb: the superblock
2175 * @nr: the number of pages to write
2176 * @reason: reason why some writeback work initiated
2178 * Start writeback on some inodes on this super_block. No guarantees are made
2179 * on how many (if any) will be written, and this function does not wait
2180 * for IO completion of submitted IO.
2182 void writeback_inodes_sb_nr(struct super_block *sb,
2184 enum wb_reason reason)
2186 __writeback_inodes_sb_nr(sb, nr, reason, false);
2188 EXPORT_SYMBOL(writeback_inodes_sb_nr);
2191 * writeback_inodes_sb - writeback dirty inodes from given super_block
2192 * @sb: the superblock
2193 * @reason: reason why some writeback work was initiated
2195 * Start writeback on some inodes on this super_block. No guarantees are made
2196 * on how many (if any) will be written, and this function does not wait
2197 * for IO completion of submitted IO.
2199 void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2201 return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2203 EXPORT_SYMBOL(writeback_inodes_sb);
2206 * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
2207 * @sb: the superblock
2208 * @nr: the number of pages to write
2209 * @reason: the reason of writeback
2211 * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
2212 * Returns 1 if writeback was started, 0 if not.
2214 bool try_to_writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2215 enum wb_reason reason)
2217 if (!down_read_trylock(&sb->s_umount))
2220 __writeback_inodes_sb_nr(sb, nr, reason, true);
2221 up_read(&sb->s_umount);
2224 EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
2227 * try_to_writeback_inodes_sb - try to start writeback if none underway
2228 * @sb: the superblock
2229 * @reason: reason why some writeback work was initiated
2231 * Implement by try_to_writeback_inodes_sb_nr()
2232 * Returns 1 if writeback was started, 0 if not.
2234 bool try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2236 return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2238 EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2241 * sync_inodes_sb - sync sb inode pages
2242 * @sb: the superblock
2244 * This function writes and waits on any dirty inode belonging to this
2247 void sync_inodes_sb(struct super_block *sb)
2249 DEFINE_WB_COMPLETION_ONSTACK(done);
2250 struct wb_writeback_work work = {
2252 .sync_mode = WB_SYNC_ALL,
2253 .nr_pages = LONG_MAX,
2256 .reason = WB_REASON_SYNC,
2259 struct backing_dev_info *bdi = sb->s_bdi;
2262 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
2263 * inodes under writeback and I_DIRTY_TIME inodes ignored by
2264 * bdi_has_dirty() need to be written out too.
2266 if (bdi == &noop_backing_dev_info)
2268 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2270 bdi_split_work_to_wbs(bdi, &work, false);
2271 wb_wait_for_completion(bdi, &done);
2275 EXPORT_SYMBOL(sync_inodes_sb);
2278 * write_inode_now - write an inode to disk
2279 * @inode: inode to write to disk
2280 * @sync: whether the write should be synchronous or not
2282 * This function commits an inode to disk immediately if it is dirty. This is
2283 * primarily needed by knfsd.
2285 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
2287 int write_inode_now(struct inode *inode, int sync)
2289 struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
2290 struct writeback_control wbc = {
2291 .nr_to_write = LONG_MAX,
2292 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2294 .range_end = LLONG_MAX,
2297 if (!mapping_cap_writeback_dirty(inode->i_mapping))
2298 wbc.nr_to_write = 0;
2301 return writeback_single_inode(inode, wb, &wbc);
2303 EXPORT_SYMBOL(write_inode_now);
2306 * sync_inode - write an inode and its pages to disk.
2307 * @inode: the inode to sync
2308 * @wbc: controls the writeback mode
2310 * sync_inode() will write an inode and its pages to disk. It will also
2311 * correctly update the inode on its superblock's dirty inode lists and will
2312 * update inode->i_state.
2314 * The caller must have a ref on the inode.
2316 int sync_inode(struct inode *inode, struct writeback_control *wbc)
2318 return writeback_single_inode(inode, &inode_to_bdi(inode)->wb, wbc);
2320 EXPORT_SYMBOL(sync_inode);
2323 * sync_inode_metadata - write an inode to disk
2324 * @inode: the inode to sync
2325 * @wait: wait for I/O to complete.
2327 * Write an inode to disk and adjust its dirty state after completion.
2329 * Note: only writes the actual inode, no associated data or other metadata.
2331 int sync_inode_metadata(struct inode *inode, int wait)
2333 struct writeback_control wbc = {
2334 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2335 .nr_to_write = 0, /* metadata-only */
2338 return sync_inode(inode, &wbc);
2340 EXPORT_SYMBOL(sync_inode_metadata);