1 // SPDX-License-Identifier: GPL-2.0-only
5 * Copyright (C) 2002, Linus Torvalds.
7 * Contains all the functions related to writing back and waiting
8 * upon dirty inodes against superblocks, and writing back dirty
9 * pages against inodes. ie: data writeback. Writeout of the
10 * inode itself is not handled here.
12 * 10Apr2002 Andrew Morton
13 * Split out of fs/inode.c
14 * Additions for address_space-based writeback
17 #include <linux/kernel.h>
18 #include <linux/export.h>
19 #include <linux/spinlock.h>
20 #include <linux/slab.h>
21 #include <linux/sched.h>
24 #include <linux/pagemap.h>
25 #include <linux/kthread.h>
26 #include <linux/writeback.h>
27 #include <linux/blkdev.h>
28 #include <linux/backing-dev.h>
29 #include <linux/tracepoint.h>
30 #include <linux/device.h>
31 #include <linux/memcontrol.h>
35 * 4MB minimal write chunk size
37 #define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_SHIFT - 10))
40 * Passed into wb_writeback(), essentially a subset of writeback_control
42 struct wb_writeback_work
{
44 struct super_block
*sb
;
45 enum writeback_sync_modes sync_mode
;
46 unsigned int tagged_writepages
:1;
47 unsigned int for_kupdate
:1;
48 unsigned int range_cyclic
:1;
49 unsigned int for_background
:1;
50 unsigned int for_sync
:1; /* sync(2) WB_SYNC_ALL writeback */
51 unsigned int auto_free
:1; /* free on completion */
52 enum wb_reason reason
; /* why was writeback initiated? */
54 struct list_head list
; /* pending work list */
55 struct wb_completion
*done
; /* set if the caller waits */
59 * If an inode is constantly having its pages dirtied, but then the
60 * updates stop dirtytime_expire_interval seconds in the past, it's
61 * possible for the worst case time between when an inode has its
62 * timestamps updated and when they finally get written out to be two
63 * dirtytime_expire_intervals. We set the default to 12 hours (in
64 * seconds), which means most of the time inodes will have their
65 * timestamps written to disk after 12 hours, but in the worst case a
66 * few inodes might not their timestamps updated for 24 hours.
68 unsigned int dirtytime_expire_interval
= 12 * 60 * 60;
70 static inline struct inode
*wb_inode(struct list_head
*head
)
72 return list_entry(head
, struct inode
, i_io_list
);
76 * Include the creation of the trace points after defining the
77 * wb_writeback_work structure and inline functions so that the definition
78 * remains local to this file.
80 #define CREATE_TRACE_POINTS
81 #include <trace/events/writeback.h>
83 EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage
);
85 static bool wb_io_lists_populated(struct bdi_writeback
*wb
)
87 if (wb_has_dirty_io(wb
)) {
90 set_bit(WB_has_dirty_io
, &wb
->state
);
91 WARN_ON_ONCE(!wb
->avg_write_bandwidth
);
92 atomic_long_add(wb
->avg_write_bandwidth
,
93 &wb
->bdi
->tot_write_bandwidth
);
98 static void wb_io_lists_depopulated(struct bdi_writeback
*wb
)
100 if (wb_has_dirty_io(wb
) && list_empty(&wb
->b_dirty
) &&
101 list_empty(&wb
->b_io
) && list_empty(&wb
->b_more_io
)) {
102 clear_bit(WB_has_dirty_io
, &wb
->state
);
103 WARN_ON_ONCE(atomic_long_sub_return(wb
->avg_write_bandwidth
,
104 &wb
->bdi
->tot_write_bandwidth
) < 0);
109 * inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
110 * @inode: inode to be moved
111 * @wb: target bdi_writeback
112 * @head: one of @wb->b_{dirty|io|more_io|dirty_time}
114 * Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
115 * Returns %true if @inode is the first occupant of the !dirty_time IO
116 * lists; otherwise, %false.
118 static bool inode_io_list_move_locked(struct inode
*inode
,
119 struct bdi_writeback
*wb
,
120 struct list_head
*head
)
122 assert_spin_locked(&wb
->list_lock
);
123 assert_spin_locked(&inode
->i_lock
);
124 WARN_ON_ONCE(inode
->i_state
& I_FREEING
);
126 list_move(&inode
->i_io_list
, head
);
128 /* dirty_time doesn't count as dirty_io until expiration */
129 if (head
!= &wb
->b_dirty_time
)
130 return wb_io_lists_populated(wb
);
132 wb_io_lists_depopulated(wb
);
136 static void wb_wakeup(struct bdi_writeback
*wb
)
138 spin_lock_irq(&wb
->work_lock
);
139 if (test_bit(WB_registered
, &wb
->state
))
140 mod_delayed_work(bdi_wq
, &wb
->dwork
, 0);
141 spin_unlock_irq(&wb
->work_lock
);
145 * This function is used when the first inode for this wb is marked dirty. It
146 * wakes-up the corresponding bdi thread which should then take care of the
147 * periodic background write-out of dirty inodes. Since the write-out would
148 * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
149 * set up a timer which wakes the bdi thread up later.
151 * Note, we wouldn't bother setting up the timer, but this function is on the
152 * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
153 * by delaying the wake-up.
155 * We have to be careful not to postpone flush work if it is scheduled for
156 * earlier. Thus we use queue_delayed_work().
158 static void wb_wakeup_delayed(struct bdi_writeback
*wb
)
160 unsigned long timeout
;
162 timeout
= msecs_to_jiffies(dirty_writeback_interval
* 10);
163 spin_lock_irq(&wb
->work_lock
);
164 if (test_bit(WB_registered
, &wb
->state
))
165 queue_delayed_work(bdi_wq
, &wb
->dwork
, timeout
);
166 spin_unlock_irq(&wb
->work_lock
);
169 static void finish_writeback_work(struct wb_writeback_work
*work
)
171 struct wb_completion
*done
= work
->done
;
176 wait_queue_head_t
*waitq
= done
->waitq
;
178 /* @done can't be accessed after the following dec */
179 if (atomic_dec_and_test(&done
->cnt
))
184 static void wb_queue_work(struct bdi_writeback
*wb
,
185 struct wb_writeback_work
*work
)
187 trace_writeback_queue(wb
, work
);
190 atomic_inc(&work
->done
->cnt
);
192 spin_lock_irq(&wb
->work_lock
);
194 if (test_bit(WB_registered
, &wb
->state
)) {
195 list_add_tail(&work
->list
, &wb
->work_list
);
196 mod_delayed_work(bdi_wq
, &wb
->dwork
, 0);
198 finish_writeback_work(work
);
200 spin_unlock_irq(&wb
->work_lock
);
204 * wb_wait_for_completion - wait for completion of bdi_writeback_works
205 * @done: target wb_completion
207 * Wait for one or more work items issued to @bdi with their ->done field
208 * set to @done, which should have been initialized with
209 * DEFINE_WB_COMPLETION(). This function returns after all such work items
210 * are completed. Work items which are waited upon aren't freed
211 * automatically on completion.
213 void wb_wait_for_completion(struct wb_completion
*done
)
215 atomic_dec(&done
->cnt
); /* put down the initial count */
216 wait_event(*done
->waitq
, !atomic_read(&done
->cnt
));
219 #ifdef CONFIG_CGROUP_WRITEBACK
222 * Parameters for foreign inode detection, see wbc_detach_inode() to see
225 * These paramters are inherently heuristical as the detection target
226 * itself is fuzzy. All we want to do is detaching an inode from the
227 * current owner if it's being written to by some other cgroups too much.
229 * The current cgroup writeback is built on the assumption that multiple
230 * cgroups writing to the same inode concurrently is very rare and a mode
231 * of operation which isn't well supported. As such, the goal is not
232 * taking too long when a different cgroup takes over an inode while
233 * avoiding too aggressive flip-flops from occasional foreign writes.
235 * We record, very roughly, 2s worth of IO time history and if more than
236 * half of that is foreign, trigger the switch. The recording is quantized
237 * to 16 slots. To avoid tiny writes from swinging the decision too much,
238 * writes smaller than 1/8 of avg size are ignored.
240 #define WB_FRN_TIME_SHIFT 13 /* 1s = 2^13, upto 8 secs w/ 16bit */
241 #define WB_FRN_TIME_AVG_SHIFT 3 /* avg = avg * 7/8 + new * 1/8 */
242 #define WB_FRN_TIME_CUT_DIV 8 /* ignore rounds < avg / 8 */
243 #define WB_FRN_TIME_PERIOD (2 * (1 << WB_FRN_TIME_SHIFT)) /* 2s */
245 #define WB_FRN_HIST_SLOTS 16 /* inode->i_wb_frn_history is 16bit */
246 #define WB_FRN_HIST_UNIT (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
247 /* each slot's duration is 2s / 16 */
248 #define WB_FRN_HIST_THR_SLOTS (WB_FRN_HIST_SLOTS / 2)
249 /* if foreign slots >= 8, switch */
250 #define WB_FRN_HIST_MAX_SLOTS (WB_FRN_HIST_THR_SLOTS / 2 + 1)
251 /* one round can affect upto 5 slots */
252 #define WB_FRN_MAX_IN_FLIGHT 1024 /* don't queue too many concurrently */
255 * Maximum inodes per isw. A specific value has been chosen to make
256 * struct inode_switch_wbs_context fit into 1024 bytes kmalloc.
258 #define WB_MAX_INODES_PER_ISW ((1024UL - sizeof(struct inode_switch_wbs_context)) \
259 / sizeof(struct inode *))
261 static atomic_t isw_nr_in_flight
= ATOMIC_INIT(0);
262 static struct workqueue_struct
*isw_wq
;
264 void __inode_attach_wb(struct inode
*inode
, struct folio
*folio
)
266 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
267 struct bdi_writeback
*wb
= NULL
;
269 if (inode_cgwb_enabled(inode
)) {
270 struct cgroup_subsys_state
*memcg_css
;
273 memcg_css
= mem_cgroup_css_from_folio(folio
);
274 wb
= wb_get_create(bdi
, memcg_css
, GFP_ATOMIC
);
276 /* must pin memcg_css, see wb_get_create() */
277 memcg_css
= task_get_css(current
, memory_cgrp_id
);
278 wb
= wb_get_create(bdi
, memcg_css
, GFP_ATOMIC
);
287 * There may be multiple instances of this function racing to
288 * update the same inode. Use cmpxchg() to tell the winner.
290 if (unlikely(cmpxchg(&inode
->i_wb
, NULL
, wb
)))
295 * inode_cgwb_move_to_attached - put the inode onto wb->b_attached list
296 * @inode: inode of interest with i_lock held
297 * @wb: target bdi_writeback
299 * Remove the inode from wb's io lists and if necessarily put onto b_attached
300 * list. Only inodes attached to cgwb's are kept on this list.
302 static void inode_cgwb_move_to_attached(struct inode
*inode
,
303 struct bdi_writeback
*wb
)
305 assert_spin_locked(&wb
->list_lock
);
306 assert_spin_locked(&inode
->i_lock
);
307 WARN_ON_ONCE(inode
->i_state
& I_FREEING
);
309 inode
->i_state
&= ~I_SYNC_QUEUED
;
310 if (wb
!= &wb
->bdi
->wb
)
311 list_move(&inode
->i_io_list
, &wb
->b_attached
);
313 list_del_init(&inode
->i_io_list
);
314 wb_io_lists_depopulated(wb
);
318 * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
319 * @inode: inode of interest with i_lock held
321 * Returns @inode's wb with its list_lock held. @inode->i_lock must be
322 * held on entry and is released on return. The returned wb is guaranteed
323 * to stay @inode's associated wb until its list_lock is released.
325 static struct bdi_writeback
*
326 locked_inode_to_wb_and_lock_list(struct inode
*inode
)
327 __releases(&inode
->i_lock
)
328 __acquires(&wb
->list_lock
)
331 struct bdi_writeback
*wb
= inode_to_wb(inode
);
334 * inode_to_wb() association is protected by both
335 * @inode->i_lock and @wb->list_lock but list_lock nests
336 * outside i_lock. Drop i_lock and verify that the
337 * association hasn't changed after acquiring list_lock.
340 spin_unlock(&inode
->i_lock
);
341 spin_lock(&wb
->list_lock
);
343 /* i_wb may have changed inbetween, can't use inode_to_wb() */
344 if (likely(wb
== inode
->i_wb
)) {
345 wb_put(wb
); /* @inode already has ref */
349 spin_unlock(&wb
->list_lock
);
352 spin_lock(&inode
->i_lock
);
357 * inode_to_wb_and_lock_list - determine an inode's wb and lock it
358 * @inode: inode of interest
360 * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
363 static struct bdi_writeback
*inode_to_wb_and_lock_list(struct inode
*inode
)
364 __acquires(&wb
->list_lock
)
366 spin_lock(&inode
->i_lock
);
367 return locked_inode_to_wb_and_lock_list(inode
);
370 struct inode_switch_wbs_context
{
371 struct rcu_work work
;
374 * Multiple inodes can be switched at once. The switching procedure
375 * consists of two parts, separated by a RCU grace period. To make
376 * sure that the second part is executed for each inode gone through
377 * the first part, all inode pointers are placed into a NULL-terminated
378 * array embedded into struct inode_switch_wbs_context. Otherwise
379 * an inode could be left in a non-consistent state.
381 struct bdi_writeback
*new_wb
;
382 struct inode
*inodes
[];
385 static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info
*bdi
)
387 down_write(&bdi
->wb_switch_rwsem
);
390 static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info
*bdi
)
392 up_write(&bdi
->wb_switch_rwsem
);
395 static bool inode_do_switch_wbs(struct inode
*inode
,
396 struct bdi_writeback
*old_wb
,
397 struct bdi_writeback
*new_wb
)
399 struct address_space
*mapping
= inode
->i_mapping
;
400 XA_STATE(xas
, &mapping
->i_pages
, 0);
402 bool switched
= false;
404 spin_lock(&inode
->i_lock
);
405 xa_lock_irq(&mapping
->i_pages
);
408 * Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
409 * path owns the inode and we shouldn't modify ->i_io_list.
411 if (unlikely(inode
->i_state
& (I_FREEING
| I_WILL_FREE
)))
414 trace_inode_switch_wbs(inode
, old_wb
, new_wb
);
417 * Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
418 * to possibly dirty folios while PAGECACHE_TAG_WRITEBACK points to
419 * folios actually under writeback.
421 xas_for_each_marked(&xas
, folio
, ULONG_MAX
, PAGECACHE_TAG_DIRTY
) {
422 if (folio_test_dirty(folio
)) {
423 long nr
= folio_nr_pages(folio
);
424 wb_stat_mod(old_wb
, WB_RECLAIMABLE
, -nr
);
425 wb_stat_mod(new_wb
, WB_RECLAIMABLE
, nr
);
430 xas_for_each_marked(&xas
, folio
, ULONG_MAX
, PAGECACHE_TAG_WRITEBACK
) {
431 long nr
= folio_nr_pages(folio
);
432 WARN_ON_ONCE(!folio_test_writeback(folio
));
433 wb_stat_mod(old_wb
, WB_WRITEBACK
, -nr
);
434 wb_stat_mod(new_wb
, WB_WRITEBACK
, nr
);
437 if (mapping_tagged(mapping
, PAGECACHE_TAG_WRITEBACK
)) {
438 atomic_dec(&old_wb
->writeback_inodes
);
439 atomic_inc(&new_wb
->writeback_inodes
);
445 * Transfer to @new_wb's IO list if necessary. If the @inode is dirty,
446 * the specific list @inode was on is ignored and the @inode is put on
447 * ->b_dirty which is always correct including from ->b_dirty_time.
448 * The transfer preserves @inode->dirtied_when ordering. If the @inode
449 * was clean, it means it was on the b_attached list, so move it onto
450 * the b_attached list of @new_wb.
452 if (!list_empty(&inode
->i_io_list
)) {
453 inode
->i_wb
= new_wb
;
455 if (inode
->i_state
& I_DIRTY_ALL
) {
458 list_for_each_entry(pos
, &new_wb
->b_dirty
, i_io_list
)
459 if (time_after_eq(inode
->dirtied_when
,
462 inode_io_list_move_locked(inode
, new_wb
,
463 pos
->i_io_list
.prev
);
465 inode_cgwb_move_to_attached(inode
, new_wb
);
468 inode
->i_wb
= new_wb
;
471 /* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
472 inode
->i_wb_frn_winner
= 0;
473 inode
->i_wb_frn_avg_time
= 0;
474 inode
->i_wb_frn_history
= 0;
478 * Paired with load_acquire in unlocked_inode_to_wb_begin() and
479 * ensures that the new wb is visible if they see !I_WB_SWITCH.
481 smp_store_release(&inode
->i_state
, inode
->i_state
& ~I_WB_SWITCH
);
483 xa_unlock_irq(&mapping
->i_pages
);
484 spin_unlock(&inode
->i_lock
);
489 static void inode_switch_wbs_work_fn(struct work_struct
*work
)
491 struct inode_switch_wbs_context
*isw
=
492 container_of(to_rcu_work(work
), struct inode_switch_wbs_context
, work
);
493 struct backing_dev_info
*bdi
= inode_to_bdi(isw
->inodes
[0]);
494 struct bdi_writeback
*old_wb
= isw
->inodes
[0]->i_wb
;
495 struct bdi_writeback
*new_wb
= isw
->new_wb
;
496 unsigned long nr_switched
= 0;
497 struct inode
**inodep
;
500 * If @inode switches cgwb membership while sync_inodes_sb() is
501 * being issued, sync_inodes_sb() might miss it. Synchronize.
503 down_read(&bdi
->wb_switch_rwsem
);
506 * By the time control reaches here, RCU grace period has passed
507 * since I_WB_SWITCH assertion and all wb stat update transactions
508 * between unlocked_inode_to_wb_begin/end() are guaranteed to be
509 * synchronizing against the i_pages lock.
511 * Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
512 * gives us exclusion against all wb related operations on @inode
513 * including IO list manipulations and stat updates.
515 if (old_wb
< new_wb
) {
516 spin_lock(&old_wb
->list_lock
);
517 spin_lock_nested(&new_wb
->list_lock
, SINGLE_DEPTH_NESTING
);
519 spin_lock(&new_wb
->list_lock
);
520 spin_lock_nested(&old_wb
->list_lock
, SINGLE_DEPTH_NESTING
);
523 for (inodep
= isw
->inodes
; *inodep
; inodep
++) {
524 WARN_ON_ONCE((*inodep
)->i_wb
!= old_wb
);
525 if (inode_do_switch_wbs(*inodep
, old_wb
, new_wb
))
529 spin_unlock(&new_wb
->list_lock
);
530 spin_unlock(&old_wb
->list_lock
);
532 up_read(&bdi
->wb_switch_rwsem
);
536 wb_put_many(old_wb
, nr_switched
);
539 for (inodep
= isw
->inodes
; *inodep
; inodep
++)
543 atomic_dec(&isw_nr_in_flight
);
546 static bool inode_prepare_wbs_switch(struct inode
*inode
,
547 struct bdi_writeback
*new_wb
)
550 * Paired with smp_mb() in cgroup_writeback_umount().
551 * isw_nr_in_flight must be increased before checking SB_ACTIVE and
552 * grabbing an inode, otherwise isw_nr_in_flight can be observed as 0
553 * in cgroup_writeback_umount() and the isw_wq will be not flushed.
560 /* while holding I_WB_SWITCH, no one else can update the association */
561 spin_lock(&inode
->i_lock
);
562 if (!(inode
->i_sb
->s_flags
& SB_ACTIVE
) ||
563 inode
->i_state
& (I_WB_SWITCH
| I_FREEING
| I_WILL_FREE
) ||
564 inode_to_wb(inode
) == new_wb
) {
565 spin_unlock(&inode
->i_lock
);
568 inode
->i_state
|= I_WB_SWITCH
;
570 spin_unlock(&inode
->i_lock
);
576 * inode_switch_wbs - change the wb association of an inode
577 * @inode: target inode
578 * @new_wb_id: ID of the new wb
580 * Switch @inode's wb association to the wb identified by @new_wb_id. The
581 * switching is performed asynchronously and may fail silently.
583 static void inode_switch_wbs(struct inode
*inode
, int new_wb_id
)
585 struct backing_dev_info
*bdi
= inode_to_bdi(inode
);
586 struct cgroup_subsys_state
*memcg_css
;
587 struct inode_switch_wbs_context
*isw
;
589 /* noop if seems to be already in progress */
590 if (inode
->i_state
& I_WB_SWITCH
)
593 /* avoid queueing a new switch if too many are already in flight */
594 if (atomic_read(&isw_nr_in_flight
) > WB_FRN_MAX_IN_FLIGHT
)
597 isw
= kzalloc(struct_size(isw
, inodes
, 2), GFP_ATOMIC
);
601 atomic_inc(&isw_nr_in_flight
);
603 /* find and pin the new wb */
605 memcg_css
= css_from_id(new_wb_id
, &memory_cgrp_subsys
);
606 if (memcg_css
&& !css_tryget(memcg_css
))
612 isw
->new_wb
= wb_get_create(bdi
, memcg_css
, GFP_ATOMIC
);
617 if (!inode_prepare_wbs_switch(inode
, isw
->new_wb
))
620 isw
->inodes
[0] = inode
;
623 * In addition to synchronizing among switchers, I_WB_SWITCH tells
624 * the RCU protected stat update paths to grab the i_page
625 * lock so that stat transfer can synchronize against them.
626 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
628 INIT_RCU_WORK(&isw
->work
, inode_switch_wbs_work_fn
);
629 queue_rcu_work(isw_wq
, &isw
->work
);
633 atomic_dec(&isw_nr_in_flight
);
639 static bool isw_prepare_wbs_switch(struct inode_switch_wbs_context
*isw
,
640 struct list_head
*list
, int *nr
)
644 list_for_each_entry(inode
, list
, i_io_list
) {
645 if (!inode_prepare_wbs_switch(inode
, isw
->new_wb
))
648 isw
->inodes
[*nr
] = inode
;
651 if (*nr
>= WB_MAX_INODES_PER_ISW
- 1)
658 * cleanup_offline_cgwb - detach associated inodes
661 * Switch all inodes attached to @wb to a nearest living ancestor's wb in order
662 * to eventually release the dying @wb. Returns %true if not all inodes were
663 * switched and the function has to be restarted.
665 bool cleanup_offline_cgwb(struct bdi_writeback
*wb
)
667 struct cgroup_subsys_state
*memcg_css
;
668 struct inode_switch_wbs_context
*isw
;
670 bool restart
= false;
672 isw
= kzalloc(struct_size(isw
, inodes
, WB_MAX_INODES_PER_ISW
),
677 atomic_inc(&isw_nr_in_flight
);
679 for (memcg_css
= wb
->memcg_css
->parent
; memcg_css
;
680 memcg_css
= memcg_css
->parent
) {
681 isw
->new_wb
= wb_get_create(wb
->bdi
, memcg_css
, GFP_KERNEL
);
685 if (unlikely(!isw
->new_wb
))
686 isw
->new_wb
= &wb
->bdi
->wb
; /* wb_get() is noop for bdi's wb */
689 spin_lock(&wb
->list_lock
);
691 * In addition to the inodes that have completed writeback, also switch
692 * cgwbs for those inodes only with dirty timestamps. Otherwise, those
693 * inodes won't be written back for a long time when lazytime is
694 * enabled, and thus pinning the dying cgwbs. It won't break the
695 * bandwidth restrictions, as writeback of inode metadata is not
698 restart
= isw_prepare_wbs_switch(isw
, &wb
->b_attached
, &nr
);
700 restart
= isw_prepare_wbs_switch(isw
, &wb
->b_dirty_time
, &nr
);
701 spin_unlock(&wb
->list_lock
);
703 /* no attached inodes? bail out */
705 atomic_dec(&isw_nr_in_flight
);
712 * In addition to synchronizing among switchers, I_WB_SWITCH tells
713 * the RCU protected stat update paths to grab the i_page
714 * lock so that stat transfer can synchronize against them.
715 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
717 INIT_RCU_WORK(&isw
->work
, inode_switch_wbs_work_fn
);
718 queue_rcu_work(isw_wq
, &isw
->work
);
724 * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
725 * @wbc: writeback_control of interest
726 * @inode: target inode
728 * @inode is locked and about to be written back under the control of @wbc.
729 * Record @inode's writeback context into @wbc and unlock the i_lock. On
730 * writeback completion, wbc_detach_inode() should be called. This is used
731 * to track the cgroup writeback context.
733 static void wbc_attach_and_unlock_inode(struct writeback_control
*wbc
,
735 __releases(&inode
->i_lock
)
737 if (!inode_cgwb_enabled(inode
)) {
738 spin_unlock(&inode
->i_lock
);
742 wbc
->wb
= inode_to_wb(inode
);
745 wbc
->wb_id
= wbc
->wb
->memcg_css
->id
;
746 wbc
->wb_lcand_id
= inode
->i_wb_frn_winner
;
747 wbc
->wb_tcand_id
= 0;
749 wbc
->wb_lcand_bytes
= 0;
750 wbc
->wb_tcand_bytes
= 0;
753 spin_unlock(&inode
->i_lock
);
756 * A dying wb indicates that either the blkcg associated with the
757 * memcg changed or the associated memcg is dying. In the first
758 * case, a replacement wb should already be available and we should
759 * refresh the wb immediately. In the second case, trying to
760 * refresh will keep failing.
762 if (unlikely(wb_dying(wbc
->wb
) && !css_is_dying(wbc
->wb
->memcg_css
)))
763 inode_switch_wbs(inode
, wbc
->wb_id
);
767 * wbc_attach_fdatawrite_inode - associate wbc and inode for fdatawrite
768 * @wbc: writeback_control of interest
769 * @inode: target inode
771 * This function is to be used by __filemap_fdatawrite_range(), which is an
772 * alternative entry point into writeback code, and first ensures @inode is
773 * associated with a bdi_writeback and attaches it to @wbc.
775 void wbc_attach_fdatawrite_inode(struct writeback_control
*wbc
,
778 spin_lock(&inode
->i_lock
);
779 inode_attach_wb(inode
, NULL
);
780 wbc_attach_and_unlock_inode(wbc
, inode
);
782 EXPORT_SYMBOL_GPL(wbc_attach_fdatawrite_inode
);
785 * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
786 * @wbc: writeback_control of the just finished writeback
788 * To be called after a writeback attempt of an inode finishes and undoes
789 * wbc_attach_and_unlock_inode(). Can be called under any context.
791 * As concurrent write sharing of an inode is expected to be very rare and
792 * memcg only tracks page ownership on first-use basis severely confining
793 * the usefulness of such sharing, cgroup writeback tracks ownership
794 * per-inode. While the support for concurrent write sharing of an inode
795 * is deemed unnecessary, an inode being written to by different cgroups at
796 * different points in time is a lot more common, and, more importantly,
797 * charging only by first-use can too readily lead to grossly incorrect
798 * behaviors (single foreign page can lead to gigabytes of writeback to be
799 * incorrectly attributed).
801 * To resolve this issue, cgroup writeback detects the majority dirtier of
802 * an inode and transfers the ownership to it. To avoid unnecessary
803 * oscillation, the detection mechanism keeps track of history and gives
804 * out the switch verdict only if the foreign usage pattern is stable over
805 * a certain amount of time and/or writeback attempts.
807 * On each writeback attempt, @wbc tries to detect the majority writer
808 * using Boyer-Moore majority vote algorithm. In addition to the byte
809 * count from the majority voting, it also counts the bytes written for the
810 * current wb and the last round's winner wb (max of last round's current
811 * wb, the winner from two rounds ago, and the last round's majority
812 * candidate). Keeping track of the historical winner helps the algorithm
813 * to semi-reliably detect the most active writer even when it's not the
816 * Once the winner of the round is determined, whether the winner is
817 * foreign or not and how much IO time the round consumed is recorded in
818 * inode->i_wb_frn_history. If the amount of recorded foreign IO time is
819 * over a certain threshold, the switch verdict is given.
821 void wbc_detach_inode(struct writeback_control
*wbc
)
823 struct bdi_writeback
*wb
= wbc
->wb
;
824 struct inode
*inode
= wbc
->inode
;
825 unsigned long avg_time
, max_bytes
, max_time
;
832 history
= inode
->i_wb_frn_history
;
833 avg_time
= inode
->i_wb_frn_avg_time
;
835 /* pick the winner of this round */
836 if (wbc
->wb_bytes
>= wbc
->wb_lcand_bytes
&&
837 wbc
->wb_bytes
>= wbc
->wb_tcand_bytes
) {
839 max_bytes
= wbc
->wb_bytes
;
840 } else if (wbc
->wb_lcand_bytes
>= wbc
->wb_tcand_bytes
) {
841 max_id
= wbc
->wb_lcand_id
;
842 max_bytes
= wbc
->wb_lcand_bytes
;
844 max_id
= wbc
->wb_tcand_id
;
845 max_bytes
= wbc
->wb_tcand_bytes
;
849 * Calculate the amount of IO time the winner consumed and fold it
850 * into the running average kept per inode. If the consumed IO
851 * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
852 * deciding whether to switch or not. This is to prevent one-off
853 * small dirtiers from skewing the verdict.
855 max_time
= DIV_ROUND_UP((max_bytes
>> PAGE_SHIFT
) << WB_FRN_TIME_SHIFT
,
856 wb
->avg_write_bandwidth
);
858 avg_time
+= (max_time
>> WB_FRN_TIME_AVG_SHIFT
) -
859 (avg_time
>> WB_FRN_TIME_AVG_SHIFT
);
861 avg_time
= max_time
; /* immediate catch up on first run */
863 if (max_time
>= avg_time
/ WB_FRN_TIME_CUT_DIV
) {
867 * The switch verdict is reached if foreign wb's consume
868 * more than a certain proportion of IO time in a
869 * WB_FRN_TIME_PERIOD. This is loosely tracked by 16 slot
870 * history mask where each bit represents one sixteenth of
871 * the period. Determine the number of slots to shift into
872 * history from @max_time.
874 slots
= min(DIV_ROUND_UP(max_time
, WB_FRN_HIST_UNIT
),
875 (unsigned long)WB_FRN_HIST_MAX_SLOTS
);
877 if (wbc
->wb_id
!= max_id
)
878 history
|= (1U << slots
) - 1;
881 trace_inode_foreign_history(inode
, wbc
, history
);
884 * Switch if the current wb isn't the consistent winner.
885 * If there are multiple closely competing dirtiers, the
886 * inode may switch across them repeatedly over time, which
887 * is okay. The main goal is avoiding keeping an inode on
888 * the wrong wb for an extended period of time.
890 if (hweight16(history
) > WB_FRN_HIST_THR_SLOTS
)
891 inode_switch_wbs(inode
, max_id
);
895 * Multiple instances of this function may race to update the
896 * following fields but we don't mind occassional inaccuracies.
898 inode
->i_wb_frn_winner
= max_id
;
899 inode
->i_wb_frn_avg_time
= min(avg_time
, (unsigned long)U16_MAX
);
900 inode
->i_wb_frn_history
= history
;
905 EXPORT_SYMBOL_GPL(wbc_detach_inode
);
908 * wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
909 * @wbc: writeback_control of the writeback in progress
910 * @folio: folio being written out
911 * @bytes: number of bytes being written out
913 * @bytes from @folio are about to written out during the writeback
914 * controlled by @wbc. Keep the book for foreign inode detection. See
915 * wbc_detach_inode().
917 void wbc_account_cgroup_owner(struct writeback_control
*wbc
, struct folio
*folio
,
920 struct cgroup_subsys_state
*css
;
924 * pageout() path doesn't attach @wbc to the inode being written
925 * out. This is intentional as we don't want the function to block
926 * behind a slow cgroup. Ultimately, we want pageout() to kick off
927 * regular writeback instead of writing things out itself.
929 if (!wbc
->wb
|| wbc
->no_cgroup_owner
)
932 css
= mem_cgroup_css_from_folio(folio
);
933 /* dead cgroups shouldn't contribute to inode ownership arbitration */
934 if (!(css
->flags
& CSS_ONLINE
))
939 if (id
== wbc
->wb_id
) {
940 wbc
->wb_bytes
+= bytes
;
944 if (id
== wbc
->wb_lcand_id
)
945 wbc
->wb_lcand_bytes
+= bytes
;
947 /* Boyer-Moore majority vote algorithm */
948 if (!wbc
->wb_tcand_bytes
)
949 wbc
->wb_tcand_id
= id
;
950 if (id
== wbc
->wb_tcand_id
)
951 wbc
->wb_tcand_bytes
+= bytes
;
953 wbc
->wb_tcand_bytes
-= min(bytes
, wbc
->wb_tcand_bytes
);
955 EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner
);
958 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
959 * @wb: target bdi_writeback to split @nr_pages to
960 * @nr_pages: number of pages to write for the whole bdi
962 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
963 * relation to the total write bandwidth of all wb's w/ dirty inodes on
966 static long wb_split_bdi_pages(struct bdi_writeback
*wb
, long nr_pages
)
968 unsigned long this_bw
= wb
->avg_write_bandwidth
;
969 unsigned long tot_bw
= atomic_long_read(&wb
->bdi
->tot_write_bandwidth
);
971 if (nr_pages
== LONG_MAX
)
975 * This may be called on clean wb's and proportional distribution
976 * may not make sense, just use the original @nr_pages in those
977 * cases. In general, we wanna err on the side of writing more.
979 if (!tot_bw
|| this_bw
>= tot_bw
)
982 return DIV_ROUND_UP_ULL((u64
)nr_pages
* this_bw
, tot_bw
);
986 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
987 * @bdi: target backing_dev_info
988 * @base_work: wb_writeback_work to issue
989 * @skip_if_busy: skip wb's which already have writeback in progress
991 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
992 * have dirty inodes. If @base_work->nr_page isn't %LONG_MAX, it's
993 * distributed to the busy wbs according to each wb's proportion in the
994 * total active write bandwidth of @bdi.
996 static void bdi_split_work_to_wbs(struct backing_dev_info
*bdi
,
997 struct wb_writeback_work
*base_work
,
1000 struct bdi_writeback
*last_wb
= NULL
;
1001 struct bdi_writeback
*wb
= list_entry(&bdi
->wb_list
,
1002 struct bdi_writeback
, bdi_node
);
1007 list_for_each_entry_continue_rcu(wb
, &bdi
->wb_list
, bdi_node
) {
1008 DEFINE_WB_COMPLETION(fallback_work_done
, bdi
);
1009 struct wb_writeback_work fallback_work
;
1010 struct wb_writeback_work
*work
;
1018 /* SYNC_ALL writes out I_DIRTY_TIME too */
1019 if (!wb_has_dirty_io(wb
) &&
1020 (base_work
->sync_mode
== WB_SYNC_NONE
||
1021 list_empty(&wb
->b_dirty_time
)))
1023 if (skip_if_busy
&& writeback_in_progress(wb
))
1026 nr_pages
= wb_split_bdi_pages(wb
, base_work
->nr_pages
);
1028 work
= kmalloc(sizeof(*work
), GFP_ATOMIC
);
1031 work
->nr_pages
= nr_pages
;
1032 work
->auto_free
= 1;
1033 wb_queue_work(wb
, work
);
1038 * If wb_tryget fails, the wb has been shutdown, skip it.
1040 * Pin @wb so that it stays on @bdi->wb_list. This allows
1041 * continuing iteration from @wb after dropping and
1042 * regrabbing rcu read lock.
1047 /* alloc failed, execute synchronously using on-stack fallback */
1048 work
= &fallback_work
;
1050 work
->nr_pages
= nr_pages
;
1051 work
->auto_free
= 0;
1052 work
->done
= &fallback_work_done
;
1054 wb_queue_work(wb
, work
);
1058 wb_wait_for_completion(&fallback_work_done
);
1068 * cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
1069 * @bdi_id: target bdi id
1070 * @memcg_id: target memcg css id
1071 * @reason: reason why some writeback work initiated
1072 * @done: target wb_completion
1074 * Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
1075 * with the specified parameters.
1077 int cgroup_writeback_by_id(u64 bdi_id
, int memcg_id
,
1078 enum wb_reason reason
, struct wb_completion
*done
)
1080 struct backing_dev_info
*bdi
;
1081 struct cgroup_subsys_state
*memcg_css
;
1082 struct bdi_writeback
*wb
;
1083 struct wb_writeback_work
*work
;
1084 unsigned long dirty
;
1087 /* lookup bdi and memcg */
1088 bdi
= bdi_get_by_id(bdi_id
);
1093 memcg_css
= css_from_id(memcg_id
, &memory_cgrp_subsys
);
1094 if (memcg_css
&& !css_tryget(memcg_css
))
1103 * And find the associated wb. If the wb isn't there already
1104 * there's nothing to flush, don't create one.
1106 wb
= wb_get_lookup(bdi
, memcg_css
);
1113 * The caller is attempting to write out most of
1114 * the currently dirty pages. Let's take the current dirty page
1115 * count and inflate it by 25% which should be large enough to
1116 * flush out most dirty pages while avoiding getting livelocked by
1117 * concurrent dirtiers.
1119 * BTW the memcg stats are flushed periodically and this is best-effort
1120 * estimation, so some potential error is ok.
1122 dirty
= memcg_page_state(mem_cgroup_from_css(memcg_css
), NR_FILE_DIRTY
);
1123 dirty
= dirty
* 10 / 8;
1125 /* issue the writeback work */
1126 work
= kzalloc(sizeof(*work
), GFP_NOWAIT
| __GFP_NOWARN
);
1128 work
->nr_pages
= dirty
;
1129 work
->sync_mode
= WB_SYNC_NONE
;
1130 work
->range_cyclic
= 1;
1131 work
->reason
= reason
;
1133 work
->auto_free
= 1;
1134 wb_queue_work(wb
, work
);
1149 * cgroup_writeback_umount - flush inode wb switches for umount
1150 * @sb: target super_block
1152 * This function is called when a super_block is about to be destroyed and
1153 * flushes in-flight inode wb switches. An inode wb switch goes through
1154 * RCU and then workqueue, so the two need to be flushed in order to ensure
1155 * that all previously scheduled switches are finished. As wb switches are
1156 * rare occurrences and synchronize_rcu() can take a while, perform
1157 * flushing iff wb switches are in flight.
1159 void cgroup_writeback_umount(struct super_block
*sb
)
1162 if (!(sb
->s_bdi
->capabilities
& BDI_CAP_WRITEBACK
))
1166 * SB_ACTIVE should be reliably cleared before checking
1167 * isw_nr_in_flight, see generic_shutdown_super().
1171 if (atomic_read(&isw_nr_in_flight
)) {
1173 * Use rcu_barrier() to wait for all pending callbacks to
1174 * ensure that all in-flight wb switches are in the workqueue.
1177 flush_workqueue(isw_wq
);
1181 static int __init
cgroup_writeback_init(void)
1183 isw_wq
= alloc_workqueue("inode_switch_wbs", 0, 0);
1188 fs_initcall(cgroup_writeback_init
);
1190 #else /* CONFIG_CGROUP_WRITEBACK */
1192 static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info
*bdi
) { }
1193 static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info
*bdi
) { }
1195 static void inode_cgwb_move_to_attached(struct inode
*inode
,
1196 struct bdi_writeback
*wb
)
1198 assert_spin_locked(&wb
->list_lock
);
1199 assert_spin_locked(&inode
->i_lock
);
1200 WARN_ON_ONCE(inode
->i_state
& I_FREEING
);
1202 inode
->i_state
&= ~I_SYNC_QUEUED
;
1203 list_del_init(&inode
->i_io_list
);
1204 wb_io_lists_depopulated(wb
);
1207 static struct bdi_writeback
*
1208 locked_inode_to_wb_and_lock_list(struct inode
*inode
)
1209 __releases(&inode
->i_lock
)
1210 __acquires(&wb
->list_lock
)
1212 struct bdi_writeback
*wb
= inode_to_wb(inode
);
1214 spin_unlock(&inode
->i_lock
);
1215 spin_lock(&wb
->list_lock
);
1219 static struct bdi_writeback
*inode_to_wb_and_lock_list(struct inode
*inode
)
1220 __acquires(&wb
->list_lock
)
1222 struct bdi_writeback
*wb
= inode_to_wb(inode
);
1224 spin_lock(&wb
->list_lock
);
1228 static long wb_split_bdi_pages(struct bdi_writeback
*wb
, long nr_pages
)
1233 static void bdi_split_work_to_wbs(struct backing_dev_info
*bdi
,
1234 struct wb_writeback_work
*base_work
,
1239 if (!skip_if_busy
|| !writeback_in_progress(&bdi
->wb
)) {
1240 base_work
->auto_free
= 0;
1241 wb_queue_work(&bdi
->wb
, base_work
);
1245 static inline void wbc_attach_and_unlock_inode(struct writeback_control
*wbc
,
1246 struct inode
*inode
)
1247 __releases(&inode
->i_lock
)
1249 spin_unlock(&inode
->i_lock
);
1252 #endif /* CONFIG_CGROUP_WRITEBACK */
1255 * Add in the number of potentially dirty inodes, because each inode
1256 * write can dirty pagecache in the underlying blockdev.
1258 static unsigned long get_nr_dirty_pages(void)
1260 return global_node_page_state(NR_FILE_DIRTY
) +
1261 get_nr_dirty_inodes();
1264 static void wb_start_writeback(struct bdi_writeback
*wb
, enum wb_reason reason
)
1266 if (!wb_has_dirty_io(wb
))
1270 * All callers of this function want to start writeback of all
1271 * dirty pages. Places like vmscan can call this at a very
1272 * high frequency, causing pointless allocations of tons of
1273 * work items and keeping the flusher threads busy retrieving
1274 * that work. Ensure that we only allow one of them pending and
1275 * inflight at the time.
1277 if (test_bit(WB_start_all
, &wb
->state
) ||
1278 test_and_set_bit(WB_start_all
, &wb
->state
))
1281 wb
->start_all_reason
= reason
;
1286 * wb_start_background_writeback - start background writeback
1287 * @wb: bdi_writback to write from
1290 * This makes sure WB_SYNC_NONE background writeback happens. When
1291 * this function returns, it is only guaranteed that for given wb
1292 * some IO is happening if we are over background dirty threshold.
1293 * Caller need not hold sb s_umount semaphore.
1295 void wb_start_background_writeback(struct bdi_writeback
*wb
)
1298 * We just wake up the flusher thread. It will perform background
1299 * writeback as soon as there is no other work to do.
1301 trace_writeback_wake_background(wb
);
1306 * Remove the inode from the writeback list it is on.
1308 void inode_io_list_del(struct inode
*inode
)
1310 struct bdi_writeback
*wb
;
1312 wb
= inode_to_wb_and_lock_list(inode
);
1313 spin_lock(&inode
->i_lock
);
1315 inode
->i_state
&= ~I_SYNC_QUEUED
;
1316 list_del_init(&inode
->i_io_list
);
1317 wb_io_lists_depopulated(wb
);
1319 spin_unlock(&inode
->i_lock
);
1320 spin_unlock(&wb
->list_lock
);
1322 EXPORT_SYMBOL(inode_io_list_del
);
1325 * mark an inode as under writeback on the sb
1327 void sb_mark_inode_writeback(struct inode
*inode
)
1329 struct super_block
*sb
= inode
->i_sb
;
1330 unsigned long flags
;
1332 if (list_empty(&inode
->i_wb_list
)) {
1333 spin_lock_irqsave(&sb
->s_inode_wblist_lock
, flags
);
1334 if (list_empty(&inode
->i_wb_list
)) {
1335 list_add_tail(&inode
->i_wb_list
, &sb
->s_inodes_wb
);
1336 trace_sb_mark_inode_writeback(inode
);
1338 spin_unlock_irqrestore(&sb
->s_inode_wblist_lock
, flags
);
1343 * clear an inode as under writeback on the sb
1345 void sb_clear_inode_writeback(struct inode
*inode
)
1347 struct super_block
*sb
= inode
->i_sb
;
1348 unsigned long flags
;
1350 if (!list_empty(&inode
->i_wb_list
)) {
1351 spin_lock_irqsave(&sb
->s_inode_wblist_lock
, flags
);
1352 if (!list_empty(&inode
->i_wb_list
)) {
1353 list_del_init(&inode
->i_wb_list
);
1354 trace_sb_clear_inode_writeback(inode
);
1356 spin_unlock_irqrestore(&sb
->s_inode_wblist_lock
, flags
);
1361 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1362 * furthest end of its superblock's dirty-inode list.
1364 * Before stamping the inode's ->dirtied_when, we check to see whether it is
1365 * already the most-recently-dirtied inode on the b_dirty list. If that is
1366 * the case then the inode must have been redirtied while it was being written
1367 * out and we don't reset its dirtied_when.
1369 static void redirty_tail_locked(struct inode
*inode
, struct bdi_writeback
*wb
)
1371 assert_spin_locked(&inode
->i_lock
);
1373 inode
->i_state
&= ~I_SYNC_QUEUED
;
1375 * When the inode is being freed just don't bother with dirty list
1376 * tracking. Flush worker will ignore this inode anyway and it will
1377 * trigger assertions in inode_io_list_move_locked().
1379 if (inode
->i_state
& I_FREEING
) {
1380 list_del_init(&inode
->i_io_list
);
1381 wb_io_lists_depopulated(wb
);
1384 if (!list_empty(&wb
->b_dirty
)) {
1387 tail
= wb_inode(wb
->b_dirty
.next
);
1388 if (time_before(inode
->dirtied_when
, tail
->dirtied_when
))
1389 inode
->dirtied_when
= jiffies
;
1391 inode_io_list_move_locked(inode
, wb
, &wb
->b_dirty
);
1394 static void redirty_tail(struct inode
*inode
, struct bdi_writeback
*wb
)
1396 spin_lock(&inode
->i_lock
);
1397 redirty_tail_locked(inode
, wb
);
1398 spin_unlock(&inode
->i_lock
);
1402 * requeue inode for re-scanning after bdi->b_io list is exhausted.
1404 static void requeue_io(struct inode
*inode
, struct bdi_writeback
*wb
)
1406 inode_io_list_move_locked(inode
, wb
, &wb
->b_more_io
);
1409 static void inode_sync_complete(struct inode
*inode
)
1411 assert_spin_locked(&inode
->i_lock
);
1413 inode
->i_state
&= ~I_SYNC
;
1414 /* If inode is clean an unused, put it into LRU now... */
1415 inode_add_lru(inode
);
1416 /* Called with inode->i_lock which ensures memory ordering. */
1417 inode_wake_up_bit(inode
, __I_SYNC
);
1420 static bool inode_dirtied_after(struct inode
*inode
, unsigned long t
)
1422 bool ret
= time_after(inode
->dirtied_when
, t
);
1423 #ifndef CONFIG_64BIT
1425 * For inodes being constantly redirtied, dirtied_when can get stuck.
1426 * It _appears_ to be in the future, but is actually in distant past.
1427 * This test is necessary to prevent such wrapped-around relative times
1428 * from permanently stopping the whole bdi writeback.
1430 ret
= ret
&& time_before_eq(inode
->dirtied_when
, jiffies
);
1436 * Move expired (dirtied before dirtied_before) dirty inodes from
1437 * @delaying_queue to @dispatch_queue.
1439 static int move_expired_inodes(struct list_head
*delaying_queue
,
1440 struct list_head
*dispatch_queue
,
1441 unsigned long dirtied_before
)
1444 struct list_head
*pos
, *node
;
1445 struct super_block
*sb
= NULL
;
1446 struct inode
*inode
;
1450 while (!list_empty(delaying_queue
)) {
1451 inode
= wb_inode(delaying_queue
->prev
);
1452 if (inode_dirtied_after(inode
, dirtied_before
))
1454 spin_lock(&inode
->i_lock
);
1455 list_move(&inode
->i_io_list
, &tmp
);
1457 inode
->i_state
|= I_SYNC_QUEUED
;
1458 spin_unlock(&inode
->i_lock
);
1459 if (sb_is_blkdev_sb(inode
->i_sb
))
1461 if (sb
&& sb
!= inode
->i_sb
)
1466 /* just one sb in list, splice to dispatch_queue and we're done */
1468 list_splice(&tmp
, dispatch_queue
);
1473 * Although inode's i_io_list is moved from 'tmp' to 'dispatch_queue',
1474 * we don't take inode->i_lock here because it is just a pointless overhead.
1475 * Inode is already marked as I_SYNC_QUEUED so writeback list handling is
1476 * fully under our control.
1478 while (!list_empty(&tmp
)) {
1479 sb
= wb_inode(tmp
.prev
)->i_sb
;
1480 list_for_each_prev_safe(pos
, node
, &tmp
) {
1481 inode
= wb_inode(pos
);
1482 if (inode
->i_sb
== sb
)
1483 list_move(&inode
->i_io_list
, dispatch_queue
);
1491 * Queue all expired dirty inodes for io, eldest first.
1493 * newly dirtied b_dirty b_io b_more_io
1494 * =============> gf edc BA
1496 * newly dirtied b_dirty b_io b_more_io
1497 * =============> g fBAedc
1499 * +--> dequeue for IO
1501 static void queue_io(struct bdi_writeback
*wb
, struct wb_writeback_work
*work
,
1502 unsigned long dirtied_before
)
1505 unsigned long time_expire_jif
= dirtied_before
;
1507 assert_spin_locked(&wb
->list_lock
);
1508 list_splice_init(&wb
->b_more_io
, &wb
->b_io
);
1509 moved
= move_expired_inodes(&wb
->b_dirty
, &wb
->b_io
, dirtied_before
);
1510 if (!work
->for_sync
)
1511 time_expire_jif
= jiffies
- dirtytime_expire_interval
* HZ
;
1512 moved
+= move_expired_inodes(&wb
->b_dirty_time
, &wb
->b_io
,
1515 wb_io_lists_populated(wb
);
1516 trace_writeback_queue_io(wb
, work
, dirtied_before
, moved
);
1519 static int write_inode(struct inode
*inode
, struct writeback_control
*wbc
)
1523 if (inode
->i_sb
->s_op
->write_inode
&& !is_bad_inode(inode
)) {
1524 trace_writeback_write_inode_start(inode
, wbc
);
1525 ret
= inode
->i_sb
->s_op
->write_inode(inode
, wbc
);
1526 trace_writeback_write_inode(inode
, wbc
);
1533 * Wait for writeback on an inode to complete. Called with i_lock held.
1534 * Caller must make sure inode cannot go away when we drop i_lock.
1536 void inode_wait_for_writeback(struct inode
*inode
)
1538 struct wait_bit_queue_entry wqe
;
1539 struct wait_queue_head
*wq_head
;
1541 assert_spin_locked(&inode
->i_lock
);
1543 if (!(inode
->i_state
& I_SYNC
))
1546 wq_head
= inode_bit_waitqueue(&wqe
, inode
, __I_SYNC
);
1548 prepare_to_wait_event(wq_head
, &wqe
.wq_entry
, TASK_UNINTERRUPTIBLE
);
1549 /* Checking I_SYNC with inode->i_lock guarantees memory ordering. */
1550 if (!(inode
->i_state
& I_SYNC
))
1552 spin_unlock(&inode
->i_lock
);
1554 spin_lock(&inode
->i_lock
);
1556 finish_wait(wq_head
, &wqe
.wq_entry
);
1560 * Sleep until I_SYNC is cleared. This function must be called with i_lock
1561 * held and drops it. It is aimed for callers not holding any inode reference
1562 * so once i_lock is dropped, inode can go away.
1564 static void inode_sleep_on_writeback(struct inode
*inode
)
1565 __releases(inode
->i_lock
)
1567 struct wait_bit_queue_entry wqe
;
1568 struct wait_queue_head
*wq_head
;
1571 assert_spin_locked(&inode
->i_lock
);
1573 wq_head
= inode_bit_waitqueue(&wqe
, inode
, __I_SYNC
);
1574 prepare_to_wait_event(wq_head
, &wqe
.wq_entry
, TASK_UNINTERRUPTIBLE
);
1575 /* Checking I_SYNC with inode->i_lock guarantees memory ordering. */
1576 sleep
= !!(inode
->i_state
& I_SYNC
);
1577 spin_unlock(&inode
->i_lock
);
1580 finish_wait(wq_head
, &wqe
.wq_entry
);
1584 * Find proper writeback list for the inode depending on its current state and
1585 * possibly also change of its state while we were doing writeback. Here we
1586 * handle things such as livelock prevention or fairness of writeback among
1587 * inodes. This function can be called only by flusher thread - noone else
1588 * processes all inodes in writeback lists and requeueing inodes behind flusher
1589 * thread's back can have unexpected consequences.
1591 static void requeue_inode(struct inode
*inode
, struct bdi_writeback
*wb
,
1592 struct writeback_control
*wbc
,
1593 unsigned long dirtied_before
)
1595 if (inode
->i_state
& I_FREEING
)
1599 * Sync livelock prevention. Each inode is tagged and synced in one
1600 * shot. If still dirty, it will be redirty_tail()'ed below. Update
1601 * the dirty time to prevent enqueue and sync it again.
1603 if ((inode
->i_state
& I_DIRTY
) &&
1604 (wbc
->sync_mode
== WB_SYNC_ALL
|| wbc
->tagged_writepages
))
1605 inode
->dirtied_when
= jiffies
;
1607 if (wbc
->pages_skipped
) {
1609 * Writeback is not making progress due to locked buffers.
1610 * Skip this inode for now. Although having skipped pages
1611 * is odd for clean inodes, it can happen for some
1612 * filesystems so handle that gracefully.
1614 if (inode
->i_state
& I_DIRTY_ALL
)
1615 redirty_tail_locked(inode
, wb
);
1617 inode_cgwb_move_to_attached(inode
, wb
);
1621 if (mapping_tagged(inode
->i_mapping
, PAGECACHE_TAG_DIRTY
)) {
1623 * We didn't write back all the pages. nfs_writepages()
1624 * sometimes bales out without doing anything.
1626 if (wbc
->nr_to_write
<= 0 &&
1627 !inode_dirtied_after(inode
, dirtied_before
)) {
1628 /* Slice used up. Queue for next turn. */
1629 requeue_io(inode
, wb
);
1632 * Writeback blocked by something other than
1633 * congestion. Delay the inode for some time to
1634 * avoid spinning on the CPU (100% iowait)
1635 * retrying writeback of the dirty page/inode
1636 * that cannot be performed immediately.
1638 redirty_tail_locked(inode
, wb
);
1640 } else if (inode
->i_state
& I_DIRTY
) {
1642 * Filesystems can dirty the inode during writeback operations,
1643 * such as delayed allocation during submission or metadata
1644 * updates after data IO completion.
1646 redirty_tail_locked(inode
, wb
);
1647 } else if (inode
->i_state
& I_DIRTY_TIME
) {
1648 inode
->dirtied_when
= jiffies
;
1649 inode_io_list_move_locked(inode
, wb
, &wb
->b_dirty_time
);
1650 inode
->i_state
&= ~I_SYNC_QUEUED
;
1652 /* The inode is clean. Remove from writeback lists. */
1653 inode_cgwb_move_to_attached(inode
, wb
);
1658 * Write out an inode and its dirty pages (or some of its dirty pages, depending
1659 * on @wbc->nr_to_write), and clear the relevant dirty flags from i_state.
1661 * This doesn't remove the inode from the writeback list it is on, except
1662 * potentially to move it from b_dirty_time to b_dirty due to timestamp
1663 * expiration. The caller is otherwise responsible for writeback list handling.
1665 * The caller is also responsible for setting the I_SYNC flag beforehand and
1666 * calling inode_sync_complete() to clear it afterwards.
1669 __writeback_single_inode(struct inode
*inode
, struct writeback_control
*wbc
)
1671 struct address_space
*mapping
= inode
->i_mapping
;
1672 long nr_to_write
= wbc
->nr_to_write
;
1676 WARN_ON(!(inode
->i_state
& I_SYNC
));
1678 trace_writeback_single_inode_start(inode
, wbc
, nr_to_write
);
1680 ret
= do_writepages(mapping
, wbc
);
1683 * Make sure to wait on the data before writing out the metadata.
1684 * This is important for filesystems that modify metadata on data
1685 * I/O completion. We don't do it for sync(2) writeback because it has a
1686 * separate, external IO completion path and ->sync_fs for guaranteeing
1687 * inode metadata is written back correctly.
1689 if (wbc
->sync_mode
== WB_SYNC_ALL
&& !wbc
->for_sync
) {
1690 int err
= filemap_fdatawait(mapping
);
1696 * If the inode has dirty timestamps and we need to write them, call
1697 * mark_inode_dirty_sync() to notify the filesystem about it and to
1698 * change I_DIRTY_TIME into I_DIRTY_SYNC.
1700 if ((inode
->i_state
& I_DIRTY_TIME
) &&
1701 (wbc
->sync_mode
== WB_SYNC_ALL
||
1702 time_after(jiffies
, inode
->dirtied_time_when
+
1703 dirtytime_expire_interval
* HZ
))) {
1704 trace_writeback_lazytime(inode
);
1705 mark_inode_dirty_sync(inode
);
1709 * Get and clear the dirty flags from i_state. This needs to be done
1710 * after calling writepages because some filesystems may redirty the
1711 * inode during writepages due to delalloc. It also needs to be done
1712 * after handling timestamp expiration, as that may dirty the inode too.
1714 spin_lock(&inode
->i_lock
);
1715 dirty
= inode
->i_state
& I_DIRTY
;
1716 inode
->i_state
&= ~dirty
;
1719 * Paired with smp_mb() in __mark_inode_dirty(). This allows
1720 * __mark_inode_dirty() to test i_state without grabbing i_lock -
1721 * either they see the I_DIRTY bits cleared or we see the dirtied
1724 * I_DIRTY_PAGES is always cleared together above even if @mapping
1725 * still has dirty pages. The flag is reinstated after smp_mb() if
1726 * necessary. This guarantees that either __mark_inode_dirty()
1727 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1731 if (mapping_tagged(mapping
, PAGECACHE_TAG_DIRTY
))
1732 inode
->i_state
|= I_DIRTY_PAGES
;
1733 else if (unlikely(inode
->i_state
& I_PINNING_NETFS_WB
)) {
1734 if (!(inode
->i_state
& I_DIRTY_PAGES
)) {
1735 inode
->i_state
&= ~I_PINNING_NETFS_WB
;
1736 wbc
->unpinned_netfs_wb
= true;
1737 dirty
|= I_PINNING_NETFS_WB
; /* Cause write_inode */
1741 spin_unlock(&inode
->i_lock
);
1743 /* Don't write the inode if only I_DIRTY_PAGES was set */
1744 if (dirty
& ~I_DIRTY_PAGES
) {
1745 int err
= write_inode(inode
, wbc
);
1749 wbc
->unpinned_netfs_wb
= false;
1750 trace_writeback_single_inode(inode
, wbc
, nr_to_write
);
1755 * Write out an inode's dirty data and metadata on-demand, i.e. separately from
1756 * the regular batched writeback done by the flusher threads in
1757 * writeback_sb_inodes(). @wbc controls various aspects of the write, such as
1758 * whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE).
1760 * To prevent the inode from going away, either the caller must have a reference
1761 * to the inode, or the inode must have I_WILL_FREE or I_FREEING set.
1763 static int writeback_single_inode(struct inode
*inode
,
1764 struct writeback_control
*wbc
)
1766 struct bdi_writeback
*wb
;
1769 spin_lock(&inode
->i_lock
);
1770 if (!atomic_read(&inode
->i_count
))
1771 WARN_ON(!(inode
->i_state
& (I_WILL_FREE
|I_FREEING
)));
1773 WARN_ON(inode
->i_state
& I_WILL_FREE
);
1775 if (inode
->i_state
& I_SYNC
) {
1777 * Writeback is already running on the inode. For WB_SYNC_NONE,
1778 * that's enough and we can just return. For WB_SYNC_ALL, we
1779 * must wait for the existing writeback to complete, then do
1780 * writeback again if there's anything left.
1782 if (wbc
->sync_mode
!= WB_SYNC_ALL
)
1784 inode_wait_for_writeback(inode
);
1786 WARN_ON(inode
->i_state
& I_SYNC
);
1788 * If the inode is already fully clean, then there's nothing to do.
1790 * For data-integrity syncs we also need to check whether any pages are
1791 * still under writeback, e.g. due to prior WB_SYNC_NONE writeback. If
1792 * there are any such pages, we'll need to wait for them.
1794 if (!(inode
->i_state
& I_DIRTY_ALL
) &&
1795 (wbc
->sync_mode
!= WB_SYNC_ALL
||
1796 !mapping_tagged(inode
->i_mapping
, PAGECACHE_TAG_WRITEBACK
)))
1798 inode
->i_state
|= I_SYNC
;
1799 wbc_attach_and_unlock_inode(wbc
, inode
);
1801 ret
= __writeback_single_inode(inode
, wbc
);
1803 wbc_detach_inode(wbc
);
1805 wb
= inode_to_wb_and_lock_list(inode
);
1806 spin_lock(&inode
->i_lock
);
1808 * If the inode is freeing, its i_io_list shoudn't be updated
1809 * as it can be finally deleted at this moment.
1811 if (!(inode
->i_state
& I_FREEING
)) {
1813 * If the inode is now fully clean, then it can be safely
1814 * removed from its writeback list (if any). Otherwise the
1815 * flusher threads are responsible for the writeback lists.
1817 if (!(inode
->i_state
& I_DIRTY_ALL
))
1818 inode_cgwb_move_to_attached(inode
, wb
);
1819 else if (!(inode
->i_state
& I_SYNC_QUEUED
)) {
1820 if ((inode
->i_state
& I_DIRTY
))
1821 redirty_tail_locked(inode
, wb
);
1822 else if (inode
->i_state
& I_DIRTY_TIME
) {
1823 inode
->dirtied_when
= jiffies
;
1824 inode_io_list_move_locked(inode
,
1831 spin_unlock(&wb
->list_lock
);
1832 inode_sync_complete(inode
);
1834 spin_unlock(&inode
->i_lock
);
1838 static long writeback_chunk_size(struct bdi_writeback
*wb
,
1839 struct wb_writeback_work
*work
)
1844 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1845 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1846 * here avoids calling into writeback_inodes_wb() more than once.
1848 * The intended call sequence for WB_SYNC_ALL writeback is:
1851 * writeback_sb_inodes() <== called only once
1852 * write_cache_pages() <== called once for each inode
1853 * (quickly) tag currently dirty pages
1854 * (maybe slowly) sync all tagged pages
1856 if (work
->sync_mode
== WB_SYNC_ALL
|| work
->tagged_writepages
)
1859 pages
= min(wb
->avg_write_bandwidth
/ 2,
1860 global_wb_domain
.dirty_limit
/ DIRTY_SCOPE
);
1861 pages
= min(pages
, work
->nr_pages
);
1862 pages
= round_down(pages
+ MIN_WRITEBACK_PAGES
,
1863 MIN_WRITEBACK_PAGES
);
1870 * Write a portion of b_io inodes which belong to @sb.
1872 * Return the number of pages and/or inodes written.
1874 * NOTE! This is called with wb->list_lock held, and will
1875 * unlock and relock that for each inode it ends up doing
1878 static long writeback_sb_inodes(struct super_block
*sb
,
1879 struct bdi_writeback
*wb
,
1880 struct wb_writeback_work
*work
)
1882 struct writeback_control wbc
= {
1883 .sync_mode
= work
->sync_mode
,
1884 .tagged_writepages
= work
->tagged_writepages
,
1885 .for_kupdate
= work
->for_kupdate
,
1886 .for_background
= work
->for_background
,
1887 .for_sync
= work
->for_sync
,
1888 .range_cyclic
= work
->range_cyclic
,
1890 .range_end
= LLONG_MAX
,
1892 unsigned long start_time
= jiffies
;
1894 long total_wrote
= 0; /* count both pages and inodes */
1895 unsigned long dirtied_before
= jiffies
;
1897 if (work
->for_kupdate
)
1898 dirtied_before
= jiffies
-
1899 msecs_to_jiffies(dirty_expire_interval
* 10);
1901 while (!list_empty(&wb
->b_io
)) {
1902 struct inode
*inode
= wb_inode(wb
->b_io
.prev
);
1903 struct bdi_writeback
*tmp_wb
;
1906 if (inode
->i_sb
!= sb
) {
1909 * We only want to write back data for this
1910 * superblock, move all inodes not belonging
1911 * to it back onto the dirty list.
1913 redirty_tail(inode
, wb
);
1918 * The inode belongs to a different superblock.
1919 * Bounce back to the caller to unpin this and
1920 * pin the next superblock.
1926 * Don't bother with new inodes or inodes being freed, first
1927 * kind does not need periodic writeout yet, and for the latter
1928 * kind writeout is handled by the freer.
1930 spin_lock(&inode
->i_lock
);
1931 if (inode
->i_state
& (I_NEW
| I_FREEING
| I_WILL_FREE
)) {
1932 redirty_tail_locked(inode
, wb
);
1933 spin_unlock(&inode
->i_lock
);
1936 if ((inode
->i_state
& I_SYNC
) && wbc
.sync_mode
!= WB_SYNC_ALL
) {
1938 * If this inode is locked for writeback and we are not
1939 * doing writeback-for-data-integrity, move it to
1940 * b_more_io so that writeback can proceed with the
1941 * other inodes on s_io.
1943 * We'll have another go at writing back this inode
1944 * when we completed a full scan of b_io.
1946 requeue_io(inode
, wb
);
1947 spin_unlock(&inode
->i_lock
);
1948 trace_writeback_sb_inodes_requeue(inode
);
1951 spin_unlock(&wb
->list_lock
);
1954 * We already requeued the inode if it had I_SYNC set and we
1955 * are doing WB_SYNC_NONE writeback. So this catches only the
1958 if (inode
->i_state
& I_SYNC
) {
1959 /* Wait for I_SYNC. This function drops i_lock... */
1960 inode_sleep_on_writeback(inode
);
1961 /* Inode may be gone, start again */
1962 spin_lock(&wb
->list_lock
);
1965 inode
->i_state
|= I_SYNC
;
1966 wbc_attach_and_unlock_inode(&wbc
, inode
);
1968 write_chunk
= writeback_chunk_size(wb
, work
);
1969 wbc
.nr_to_write
= write_chunk
;
1970 wbc
.pages_skipped
= 0;
1973 * We use I_SYNC to pin the inode in memory. While it is set
1974 * evict_inode() will wait so the inode cannot be freed.
1976 __writeback_single_inode(inode
, &wbc
);
1978 wbc_detach_inode(&wbc
);
1979 work
->nr_pages
-= write_chunk
- wbc
.nr_to_write
;
1980 wrote
= write_chunk
- wbc
.nr_to_write
- wbc
.pages_skipped
;
1981 wrote
= wrote
< 0 ? 0 : wrote
;
1982 total_wrote
+= wrote
;
1984 if (need_resched()) {
1986 * We're trying to balance between building up a nice
1987 * long list of IOs to improve our merge rate, and
1988 * getting those IOs out quickly for anyone throttling
1989 * in balance_dirty_pages(). cond_resched() doesn't
1990 * unplug, so get our IOs out the door before we
1993 blk_flush_plug(current
->plug
, false);
1998 * Requeue @inode if still dirty. Be careful as @inode may
1999 * have been switched to another wb in the meantime.
2001 tmp_wb
= inode_to_wb_and_lock_list(inode
);
2002 spin_lock(&inode
->i_lock
);
2003 if (!(inode
->i_state
& I_DIRTY_ALL
))
2005 requeue_inode(inode
, tmp_wb
, &wbc
, dirtied_before
);
2006 inode_sync_complete(inode
);
2007 spin_unlock(&inode
->i_lock
);
2009 if (unlikely(tmp_wb
!= wb
)) {
2010 spin_unlock(&tmp_wb
->list_lock
);
2011 spin_lock(&wb
->list_lock
);
2015 * bail out to wb_writeback() often enough to check
2016 * background threshold and other termination conditions.
2019 if (time_is_before_jiffies(start_time
+ HZ
/ 10UL))
2021 if (work
->nr_pages
<= 0)
2028 static long __writeback_inodes_wb(struct bdi_writeback
*wb
,
2029 struct wb_writeback_work
*work
)
2031 unsigned long start_time
= jiffies
;
2034 while (!list_empty(&wb
->b_io
)) {
2035 struct inode
*inode
= wb_inode(wb
->b_io
.prev
);
2036 struct super_block
*sb
= inode
->i_sb
;
2038 if (!super_trylock_shared(sb
)) {
2040 * super_trylock_shared() may fail consistently due to
2041 * s_umount being grabbed by someone else. Don't use
2042 * requeue_io() to avoid busy retrying the inode/sb.
2044 redirty_tail(inode
, wb
);
2047 wrote
+= writeback_sb_inodes(sb
, wb
, work
);
2048 up_read(&sb
->s_umount
);
2050 /* refer to the same tests at the end of writeback_sb_inodes */
2052 if (time_is_before_jiffies(start_time
+ HZ
/ 10UL))
2054 if (work
->nr_pages
<= 0)
2058 /* Leave any unwritten inodes on b_io */
2062 static long writeback_inodes_wb(struct bdi_writeback
*wb
, long nr_pages
,
2063 enum wb_reason reason
)
2065 struct wb_writeback_work work
= {
2066 .nr_pages
= nr_pages
,
2067 .sync_mode
= WB_SYNC_NONE
,
2071 struct blk_plug plug
;
2073 blk_start_plug(&plug
);
2074 spin_lock(&wb
->list_lock
);
2075 if (list_empty(&wb
->b_io
))
2076 queue_io(wb
, &work
, jiffies
);
2077 __writeback_inodes_wb(wb
, &work
);
2078 spin_unlock(&wb
->list_lock
);
2079 blk_finish_plug(&plug
);
2081 return nr_pages
- work
.nr_pages
;
2085 * Explicit flushing or periodic writeback of "old" data.
2087 * Define "old": the first time one of an inode's pages is dirtied, we mark the
2088 * dirtying-time in the inode's address_space. So this periodic writeback code
2089 * just walks the superblock inode list, writing back any inodes which are
2090 * older than a specific point in time.
2092 * Try to run once per dirty_writeback_interval. But if a writeback event
2093 * takes longer than a dirty_writeback_interval interval, then leave a
2096 * dirtied_before takes precedence over nr_to_write. So we'll only write back
2097 * all dirty pages if they are all attached to "old" mappings.
2099 static long wb_writeback(struct bdi_writeback
*wb
,
2100 struct wb_writeback_work
*work
)
2102 long nr_pages
= work
->nr_pages
;
2103 unsigned long dirtied_before
= jiffies
;
2104 struct inode
*inode
;
2106 struct blk_plug plug
;
2107 bool queued
= false;
2109 blk_start_plug(&plug
);
2112 * Stop writeback when nr_pages has been consumed
2114 if (work
->nr_pages
<= 0)
2118 * Background writeout and kupdate-style writeback may
2119 * run forever. Stop them if there is other work to do
2120 * so that e.g. sync can proceed. They'll be restarted
2121 * after the other works are all done.
2123 if ((work
->for_background
|| work
->for_kupdate
) &&
2124 !list_empty(&wb
->work_list
))
2128 * For background writeout, stop when we are below the
2129 * background dirty threshold
2131 if (work
->for_background
&& !wb_over_bg_thresh(wb
))
2135 spin_lock(&wb
->list_lock
);
2137 trace_writeback_start(wb
, work
);
2138 if (list_empty(&wb
->b_io
)) {
2140 * Kupdate and background works are special and we want
2141 * to include all inodes that need writing. Livelock
2142 * avoidance is handled by these works yielding to any
2143 * other work so we are safe.
2145 if (work
->for_kupdate
) {
2146 dirtied_before
= jiffies
-
2147 msecs_to_jiffies(dirty_expire_interval
*
2149 } else if (work
->for_background
)
2150 dirtied_before
= jiffies
;
2152 queue_io(wb
, work
, dirtied_before
);
2156 progress
= writeback_sb_inodes(work
->sb
, wb
, work
);
2158 progress
= __writeback_inodes_wb(wb
, work
);
2159 trace_writeback_written(wb
, work
);
2162 * Did we write something? Try for more
2164 * Dirty inodes are moved to b_io for writeback in batches.
2165 * The completion of the current batch does not necessarily
2166 * mean the overall work is done. So we keep looping as long
2167 * as made some progress on cleaning pages or inodes.
2169 if (progress
|| !queued
) {
2170 spin_unlock(&wb
->list_lock
);
2175 * No more inodes for IO, bail
2177 if (list_empty(&wb
->b_more_io
)) {
2178 spin_unlock(&wb
->list_lock
);
2183 * Nothing written. Wait for some inode to
2184 * become available for writeback. Otherwise
2185 * we'll just busyloop.
2187 trace_writeback_wait(wb
, work
);
2188 inode
= wb_inode(wb
->b_more_io
.prev
);
2189 spin_lock(&inode
->i_lock
);
2190 spin_unlock(&wb
->list_lock
);
2191 /* This function drops i_lock... */
2192 inode_sleep_on_writeback(inode
);
2194 blk_finish_plug(&plug
);
2196 return nr_pages
- work
->nr_pages
;
2200 * Return the next wb_writeback_work struct that hasn't been processed yet.
2202 static struct wb_writeback_work
*get_next_work_item(struct bdi_writeback
*wb
)
2204 struct wb_writeback_work
*work
= NULL
;
2206 spin_lock_irq(&wb
->work_lock
);
2207 if (!list_empty(&wb
->work_list
)) {
2208 work
= list_entry(wb
->work_list
.next
,
2209 struct wb_writeback_work
, list
);
2210 list_del_init(&work
->list
);
2212 spin_unlock_irq(&wb
->work_lock
);
2216 static long wb_check_background_flush(struct bdi_writeback
*wb
)
2218 if (wb_over_bg_thresh(wb
)) {
2220 struct wb_writeback_work work
= {
2221 .nr_pages
= LONG_MAX
,
2222 .sync_mode
= WB_SYNC_NONE
,
2223 .for_background
= 1,
2225 .reason
= WB_REASON_BACKGROUND
,
2228 return wb_writeback(wb
, &work
);
2234 static long wb_check_old_data_flush(struct bdi_writeback
*wb
)
2236 unsigned long expired
;
2240 * When set to zero, disable periodic writeback
2242 if (!dirty_writeback_interval
)
2245 expired
= wb
->last_old_flush
+
2246 msecs_to_jiffies(dirty_writeback_interval
* 10);
2247 if (time_before(jiffies
, expired
))
2250 wb
->last_old_flush
= jiffies
;
2251 nr_pages
= get_nr_dirty_pages();
2254 struct wb_writeback_work work
= {
2255 .nr_pages
= nr_pages
,
2256 .sync_mode
= WB_SYNC_NONE
,
2259 .reason
= WB_REASON_PERIODIC
,
2262 return wb_writeback(wb
, &work
);
2268 static long wb_check_start_all(struct bdi_writeback
*wb
)
2272 if (!test_bit(WB_start_all
, &wb
->state
))
2275 nr_pages
= get_nr_dirty_pages();
2277 struct wb_writeback_work work
= {
2278 .nr_pages
= wb_split_bdi_pages(wb
, nr_pages
),
2279 .sync_mode
= WB_SYNC_NONE
,
2281 .reason
= wb
->start_all_reason
,
2284 nr_pages
= wb_writeback(wb
, &work
);
2287 clear_bit(WB_start_all
, &wb
->state
);
2293 * Retrieve work items and do the writeback they describe
2295 static long wb_do_writeback(struct bdi_writeback
*wb
)
2297 struct wb_writeback_work
*work
;
2300 set_bit(WB_writeback_running
, &wb
->state
);
2301 while ((work
= get_next_work_item(wb
)) != NULL
) {
2302 trace_writeback_exec(wb
, work
);
2303 wrote
+= wb_writeback(wb
, work
);
2304 finish_writeback_work(work
);
2308 * Check for a flush-everything request
2310 wrote
+= wb_check_start_all(wb
);
2313 * Check for periodic writeback, kupdated() style
2315 wrote
+= wb_check_old_data_flush(wb
);
2316 wrote
+= wb_check_background_flush(wb
);
2317 clear_bit(WB_writeback_running
, &wb
->state
);
2323 * Handle writeback of dirty data for the device backed by this bdi. Also
2324 * reschedules periodically and does kupdated style flushing.
2326 void wb_workfn(struct work_struct
*work
)
2328 struct bdi_writeback
*wb
= container_of(to_delayed_work(work
),
2329 struct bdi_writeback
, dwork
);
2332 set_worker_desc("flush-%s", bdi_dev_name(wb
->bdi
));
2334 if (likely(!current_is_workqueue_rescuer() ||
2335 !test_bit(WB_registered
, &wb
->state
))) {
2337 * The normal path. Keep writing back @wb until its
2338 * work_list is empty. Note that this path is also taken
2339 * if @wb is shutting down even when we're running off the
2340 * rescuer as work_list needs to be drained.
2343 pages_written
= wb_do_writeback(wb
);
2344 trace_writeback_pages_written(pages_written
);
2345 } while (!list_empty(&wb
->work_list
));
2348 * bdi_wq can't get enough workers and we're running off
2349 * the emergency worker. Don't hog it. Hopefully, 1024 is
2350 * enough for efficient IO.
2352 pages_written
= writeback_inodes_wb(wb
, 1024,
2353 WB_REASON_FORKER_THREAD
);
2354 trace_writeback_pages_written(pages_written
);
2357 if (!list_empty(&wb
->work_list
))
2359 else if (wb_has_dirty_io(wb
) && dirty_writeback_interval
)
2360 wb_wakeup_delayed(wb
);
2364 * Start writeback of all dirty pages on this bdi.
2366 static void __wakeup_flusher_threads_bdi(struct backing_dev_info
*bdi
,
2367 enum wb_reason reason
)
2369 struct bdi_writeback
*wb
;
2371 if (!bdi_has_dirty_io(bdi
))
2374 list_for_each_entry_rcu(wb
, &bdi
->wb_list
, bdi_node
)
2375 wb_start_writeback(wb
, reason
);
2378 void wakeup_flusher_threads_bdi(struct backing_dev_info
*bdi
,
2379 enum wb_reason reason
)
2382 __wakeup_flusher_threads_bdi(bdi
, reason
);
2387 * Wakeup the flusher threads to start writeback of all currently dirty pages
2389 void wakeup_flusher_threads(enum wb_reason reason
)
2391 struct backing_dev_info
*bdi
;
2394 * If we are expecting writeback progress we must submit plugged IO.
2396 blk_flush_plug(current
->plug
, true);
2399 list_for_each_entry_rcu(bdi
, &bdi_list
, bdi_list
)
2400 __wakeup_flusher_threads_bdi(bdi
, reason
);
2405 * Wake up bdi's periodically to make sure dirtytime inodes gets
2406 * written back periodically. We deliberately do *not* check the
2407 * b_dirtytime list in wb_has_dirty_io(), since this would cause the
2408 * kernel to be constantly waking up once there are any dirtytime
2409 * inodes on the system. So instead we define a separate delayed work
2410 * function which gets called much more rarely. (By default, only
2411 * once every 12 hours.)
2413 * If there is any other write activity going on in the file system,
2414 * this function won't be necessary. But if the only thing that has
2415 * happened on the file system is a dirtytime inode caused by an atime
2416 * update, we need this infrastructure below to make sure that inode
2417 * eventually gets pushed out to disk.
2419 static void wakeup_dirtytime_writeback(struct work_struct
*w
);
2420 static DECLARE_DELAYED_WORK(dirtytime_work
, wakeup_dirtytime_writeback
);
2422 static void wakeup_dirtytime_writeback(struct work_struct
*w
)
2424 struct backing_dev_info
*bdi
;
2427 list_for_each_entry_rcu(bdi
, &bdi_list
, bdi_list
) {
2428 struct bdi_writeback
*wb
;
2430 list_for_each_entry_rcu(wb
, &bdi
->wb_list
, bdi_node
)
2431 if (!list_empty(&wb
->b_dirty_time
))
2435 schedule_delayed_work(&dirtytime_work
, dirtytime_expire_interval
* HZ
);
2438 static int __init
start_dirtytime_writeback(void)
2440 schedule_delayed_work(&dirtytime_work
, dirtytime_expire_interval
* HZ
);
2443 __initcall(start_dirtytime_writeback
);
2445 int dirtytime_interval_handler(const struct ctl_table
*table
, int write
,
2446 void *buffer
, size_t *lenp
, loff_t
*ppos
)
2450 ret
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
2451 if (ret
== 0 && write
)
2452 mod_delayed_work(system_wq
, &dirtytime_work
, 0);
2457 * __mark_inode_dirty - internal function to mark an inode dirty
2459 * @inode: inode to mark
2460 * @flags: what kind of dirty, e.g. I_DIRTY_SYNC. This can be a combination of
2461 * multiple I_DIRTY_* flags, except that I_DIRTY_TIME can't be combined
2462 * with I_DIRTY_PAGES.
2464 * Mark an inode as dirty. We notify the filesystem, then update the inode's
2465 * dirty flags. Then, if needed we add the inode to the appropriate dirty list.
2467 * Most callers should use mark_inode_dirty() or mark_inode_dirty_sync()
2468 * instead of calling this directly.
2470 * CAREFUL! We only add the inode to the dirty list if it is hashed or if it
2471 * refers to a blockdev. Unhashed inodes will never be added to the dirty list
2472 * even if they are later hashed, as they will have been marked dirty already.
2474 * In short, ensure you hash any inodes _before_ you start marking them dirty.
2476 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2477 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
2478 * the kernel-internal blockdev inode represents the dirtying time of the
2479 * blockdev's pages. This is why for I_DIRTY_PAGES we always use
2480 * page->mapping->host, so the page-dirtying time is recorded in the internal
2483 void __mark_inode_dirty(struct inode
*inode
, int flags
)
2485 struct super_block
*sb
= inode
->i_sb
;
2487 struct bdi_writeback
*wb
= NULL
;
2489 trace_writeback_mark_inode_dirty(inode
, flags
);
2491 if (flags
& I_DIRTY_INODE
) {
2493 * Inode timestamp update will piggback on this dirtying.
2494 * We tell ->dirty_inode callback that timestamps need to
2495 * be updated by setting I_DIRTY_TIME in flags.
2497 if (inode
->i_state
& I_DIRTY_TIME
) {
2498 spin_lock(&inode
->i_lock
);
2499 if (inode
->i_state
& I_DIRTY_TIME
) {
2500 inode
->i_state
&= ~I_DIRTY_TIME
;
2501 flags
|= I_DIRTY_TIME
;
2503 spin_unlock(&inode
->i_lock
);
2507 * Notify the filesystem about the inode being dirtied, so that
2508 * (if needed) it can update on-disk fields and journal the
2509 * inode. This is only needed when the inode itself is being
2510 * dirtied now. I.e. it's only needed for I_DIRTY_INODE, not
2511 * for just I_DIRTY_PAGES or I_DIRTY_TIME.
2513 trace_writeback_dirty_inode_start(inode
, flags
);
2514 if (sb
->s_op
->dirty_inode
)
2515 sb
->s_op
->dirty_inode(inode
,
2516 flags
& (I_DIRTY_INODE
| I_DIRTY_TIME
));
2517 trace_writeback_dirty_inode(inode
, flags
);
2519 /* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
2520 flags
&= ~I_DIRTY_TIME
;
2523 * Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
2524 * (We don't support setting both I_DIRTY_PAGES and I_DIRTY_TIME
2525 * in one call to __mark_inode_dirty().)
2527 dirtytime
= flags
& I_DIRTY_TIME
;
2528 WARN_ON_ONCE(dirtytime
&& flags
!= I_DIRTY_TIME
);
2532 * Paired with smp_mb() in __writeback_single_inode() for the
2533 * following lockless i_state test. See there for details.
2537 if ((inode
->i_state
& flags
) == flags
)
2540 spin_lock(&inode
->i_lock
);
2541 if ((inode
->i_state
& flags
) != flags
) {
2542 const int was_dirty
= inode
->i_state
& I_DIRTY
;
2544 inode_attach_wb(inode
, NULL
);
2546 inode
->i_state
|= flags
;
2549 * Grab inode's wb early because it requires dropping i_lock and we
2550 * need to make sure following checks happen atomically with dirty
2551 * list handling so that we don't move inodes under flush worker's
2555 wb
= locked_inode_to_wb_and_lock_list(inode
);
2556 spin_lock(&inode
->i_lock
);
2560 * If the inode is queued for writeback by flush worker, just
2561 * update its dirty state. Once the flush worker is done with
2562 * the inode it will place it on the appropriate superblock
2563 * list, based upon its state.
2565 if (inode
->i_state
& I_SYNC_QUEUED
)
2569 * Only add valid (hashed) inodes to the superblock's
2570 * dirty list. Add blockdev inodes as well.
2572 if (!S_ISBLK(inode
->i_mode
)) {
2573 if (inode_unhashed(inode
))
2576 if (inode
->i_state
& I_FREEING
)
2580 * If the inode was already on b_dirty/b_io/b_more_io, don't
2581 * reposition it (that would break b_dirty time-ordering).
2584 struct list_head
*dirty_list
;
2585 bool wakeup_bdi
= false;
2587 inode
->dirtied_when
= jiffies
;
2589 inode
->dirtied_time_when
= jiffies
;
2591 if (inode
->i_state
& I_DIRTY
)
2592 dirty_list
= &wb
->b_dirty
;
2594 dirty_list
= &wb
->b_dirty_time
;
2596 wakeup_bdi
= inode_io_list_move_locked(inode
, wb
,
2599 spin_unlock(&wb
->list_lock
);
2600 spin_unlock(&inode
->i_lock
);
2601 trace_writeback_dirty_inode_enqueue(inode
);
2604 * If this is the first dirty inode for this bdi,
2605 * we have to wake-up the corresponding bdi thread
2606 * to make sure background write-back happens
2610 (wb
->bdi
->capabilities
& BDI_CAP_WRITEBACK
))
2611 wb_wakeup_delayed(wb
);
2617 spin_unlock(&wb
->list_lock
);
2618 spin_unlock(&inode
->i_lock
);
2620 EXPORT_SYMBOL(__mark_inode_dirty
);
2623 * The @s_sync_lock is used to serialise concurrent sync operations
2624 * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2625 * Concurrent callers will block on the s_sync_lock rather than doing contending
2626 * walks. The queueing maintains sync(2) required behaviour as all the IO that
2627 * has been issued up to the time this function is enter is guaranteed to be
2628 * completed by the time we have gained the lock and waited for all IO that is
2629 * in progress regardless of the order callers are granted the lock.
2631 static void wait_sb_inodes(struct super_block
*sb
)
2633 LIST_HEAD(sync_list
);
2636 * We need to be protected against the filesystem going from
2637 * r/o to r/w or vice versa.
2639 WARN_ON(!rwsem_is_locked(&sb
->s_umount
));
2641 mutex_lock(&sb
->s_sync_lock
);
2644 * Splice the writeback list onto a temporary list to avoid waiting on
2645 * inodes that have started writeback after this point.
2647 * Use rcu_read_lock() to keep the inodes around until we have a
2648 * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2649 * the local list because inodes can be dropped from either by writeback
2653 spin_lock_irq(&sb
->s_inode_wblist_lock
);
2654 list_splice_init(&sb
->s_inodes_wb
, &sync_list
);
2657 * Data integrity sync. Must wait for all pages under writeback, because
2658 * there may have been pages dirtied before our sync call, but which had
2659 * writeout started before we write it out. In which case, the inode
2660 * may not be on the dirty list, but we still have to wait for that
2663 while (!list_empty(&sync_list
)) {
2664 struct inode
*inode
= list_first_entry(&sync_list
, struct inode
,
2666 struct address_space
*mapping
= inode
->i_mapping
;
2669 * Move each inode back to the wb list before we drop the lock
2670 * to preserve consistency between i_wb_list and the mapping
2671 * writeback tag. Writeback completion is responsible to remove
2672 * the inode from either list once the writeback tag is cleared.
2674 list_move_tail(&inode
->i_wb_list
, &sb
->s_inodes_wb
);
2677 * The mapping can appear untagged while still on-list since we
2678 * do not have the mapping lock. Skip it here, wb completion
2681 if (!mapping_tagged(mapping
, PAGECACHE_TAG_WRITEBACK
))
2684 spin_unlock_irq(&sb
->s_inode_wblist_lock
);
2686 spin_lock(&inode
->i_lock
);
2687 if (inode
->i_state
& (I_FREEING
|I_WILL_FREE
|I_NEW
)) {
2688 spin_unlock(&inode
->i_lock
);
2690 spin_lock_irq(&sb
->s_inode_wblist_lock
);
2694 spin_unlock(&inode
->i_lock
);
2698 * We keep the error status of individual mapping so that
2699 * applications can catch the writeback error using fsync(2).
2700 * See filemap_fdatawait_keep_errors() for details.
2702 filemap_fdatawait_keep_errors(mapping
);
2709 spin_lock_irq(&sb
->s_inode_wblist_lock
);
2711 spin_unlock_irq(&sb
->s_inode_wblist_lock
);
2713 mutex_unlock(&sb
->s_sync_lock
);
2716 static void __writeback_inodes_sb_nr(struct super_block
*sb
, unsigned long nr
,
2717 enum wb_reason reason
, bool skip_if_busy
)
2719 struct backing_dev_info
*bdi
= sb
->s_bdi
;
2720 DEFINE_WB_COMPLETION(done
, bdi
);
2721 struct wb_writeback_work work
= {
2723 .sync_mode
= WB_SYNC_NONE
,
2724 .tagged_writepages
= 1,
2730 if (!bdi_has_dirty_io(bdi
) || bdi
== &noop_backing_dev_info
)
2732 WARN_ON(!rwsem_is_locked(&sb
->s_umount
));
2734 bdi_split_work_to_wbs(sb
->s_bdi
, &work
, skip_if_busy
);
2735 wb_wait_for_completion(&done
);
2739 * writeback_inodes_sb_nr - writeback dirty inodes from given super_block
2740 * @sb: the superblock
2741 * @nr: the number of pages to write
2742 * @reason: reason why some writeback work initiated
2744 * Start writeback on some inodes on this super_block. No guarantees are made
2745 * on how many (if any) will be written, and this function does not wait
2746 * for IO completion of submitted IO.
2748 void writeback_inodes_sb_nr(struct super_block
*sb
,
2750 enum wb_reason reason
)
2752 __writeback_inodes_sb_nr(sb
, nr
, reason
, false);
2754 EXPORT_SYMBOL(writeback_inodes_sb_nr
);
2757 * writeback_inodes_sb - writeback dirty inodes from given super_block
2758 * @sb: the superblock
2759 * @reason: reason why some writeback work was initiated
2761 * Start writeback on some inodes on this super_block. No guarantees are made
2762 * on how many (if any) will be written, and this function does not wait
2763 * for IO completion of submitted IO.
2765 void writeback_inodes_sb(struct super_block
*sb
, enum wb_reason reason
)
2767 writeback_inodes_sb_nr(sb
, get_nr_dirty_pages(), reason
);
2769 EXPORT_SYMBOL(writeback_inodes_sb
);
2772 * try_to_writeback_inodes_sb - try to start writeback if none underway
2773 * @sb: the superblock
2774 * @reason: reason why some writeback work was initiated
2776 * Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
2778 void try_to_writeback_inodes_sb(struct super_block
*sb
, enum wb_reason reason
)
2780 if (!down_read_trylock(&sb
->s_umount
))
2783 __writeback_inodes_sb_nr(sb
, get_nr_dirty_pages(), reason
, true);
2784 up_read(&sb
->s_umount
);
2786 EXPORT_SYMBOL(try_to_writeback_inodes_sb
);
2789 * sync_inodes_sb - sync sb inode pages
2790 * @sb: the superblock
2792 * This function writes and waits on any dirty inode belonging to this
2795 void sync_inodes_sb(struct super_block
*sb
)
2797 struct backing_dev_info
*bdi
= sb
->s_bdi
;
2798 DEFINE_WB_COMPLETION(done
, bdi
);
2799 struct wb_writeback_work work
= {
2801 .sync_mode
= WB_SYNC_ALL
,
2802 .nr_pages
= LONG_MAX
,
2805 .reason
= WB_REASON_SYNC
,
2810 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
2811 * inodes under writeback and I_DIRTY_TIME inodes ignored by
2812 * bdi_has_dirty() need to be written out too.
2814 if (bdi
== &noop_backing_dev_info
)
2816 WARN_ON(!rwsem_is_locked(&sb
->s_umount
));
2818 /* protect against inode wb switch, see inode_switch_wbs_work_fn() */
2819 bdi_down_write_wb_switch_rwsem(bdi
);
2820 bdi_split_work_to_wbs(bdi
, &work
, false);
2821 wb_wait_for_completion(&done
);
2822 bdi_up_write_wb_switch_rwsem(bdi
);
2826 EXPORT_SYMBOL(sync_inodes_sb
);
2829 * write_inode_now - write an inode to disk
2830 * @inode: inode to write to disk
2831 * @sync: whether the write should be synchronous or not
2833 * This function commits an inode to disk immediately if it is dirty. This is
2834 * primarily needed by knfsd.
2836 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
2838 int write_inode_now(struct inode
*inode
, int sync
)
2840 struct writeback_control wbc
= {
2841 .nr_to_write
= LONG_MAX
,
2842 .sync_mode
= sync
? WB_SYNC_ALL
: WB_SYNC_NONE
,
2844 .range_end
= LLONG_MAX
,
2847 if (!mapping_can_writeback(inode
->i_mapping
))
2848 wbc
.nr_to_write
= 0;
2851 return writeback_single_inode(inode
, &wbc
);
2853 EXPORT_SYMBOL(write_inode_now
);
2856 * sync_inode_metadata - write an inode to disk
2857 * @inode: the inode to sync
2858 * @wait: wait for I/O to complete.
2860 * Write an inode to disk and adjust its dirty state after completion.
2862 * Note: only writes the actual inode, no associated data or other metadata.
2864 int sync_inode_metadata(struct inode
*inode
, int wait
)
2866 struct writeback_control wbc
= {
2867 .sync_mode
= wait
? WB_SYNC_ALL
: WB_SYNC_NONE
,
2868 .nr_to_write
= 0, /* metadata-only */
2871 return writeback_single_inode(inode
, &wbc
);
2873 EXPORT_SYMBOL(sync_inode_metadata
);