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1/*
2 * fs/fs-writeback.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 *
6 * Contains all the functions related to writing back and waiting
7 * upon dirty inodes against superblocks, and writing back dirty
8 * pages against inodes. ie: data writeback. Writeout of the
9 * inode itself is not handled here.
10 *
11 * 10Apr2002 Andrew Morton
12 * Split out of fs/inode.c
13 * Additions for address_space-based writeback
14 */
15
16#include <linux/kernel.h>
17#include <linux/export.h>
18#include <linux/spinlock.h>
19#include <linux/slab.h>
20#include <linux/sched.h>
21#include <linux/fs.h>
22#include <linux/mm.h>
23#include <linux/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>
31#include "internal.h"
32
33/*
34 * 4MB minimal write chunk size
35 */
36#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_SHIFT - 10))
37
38struct wb_completion {
39 atomic_t cnt;
40};
41
42/*
43 * Passed into wb_writeback(), essentially a subset of writeback_control
44 */
45struct wb_writeback_work {
46 long nr_pages;
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? */
57
58 struct list_head list; /* pending work list */
59 struct wb_completion *done; /* set if the caller waits */
60};
61
62/*
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.
68 */
69#define DEFINE_WB_COMPLETION_ONSTACK(cmpl) \
70 struct wb_completion cmpl = { \
71 .cnt = ATOMIC_INIT(1), \
72 }
73
74
75/*
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.
84 */
85unsigned int dirtytime_expire_interval = 12 * 60 * 60;
86
87static inline struct inode *wb_inode(struct list_head *head)
88{
89 return list_entry(head, struct inode, i_io_list);
90}
91
92/*
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.
96 */
97#define CREATE_TRACE_POINTS
98#include <trace/events/writeback.h>
99
100EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
101
102static bool wb_io_lists_populated(struct bdi_writeback *wb)
103{
104 if (wb_has_dirty_io(wb)) {
105 return false;
106 } else {
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);
111 return true;
112 }
113}
114
115static void wb_io_lists_depopulated(struct bdi_writeback *wb)
116{
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);
122 }
123}
124
125/**
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}
130 *
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.
134 */
135static bool inode_io_list_move_locked(struct inode *inode,
136 struct bdi_writeback *wb,
137 struct list_head *head)
138{
139 assert_spin_locked(&wb->list_lock);
140
141 list_move(&inode->i_io_list, head);
142
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);
146
147 wb_io_lists_depopulated(wb);
148 return false;
149}
150
151/**
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
155 *
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.
158 */
159static void inode_io_list_del_locked(struct inode *inode,
160 struct bdi_writeback *wb)
161{
162 assert_spin_locked(&wb->list_lock);
163
164 list_del_init(&inode->i_io_list);
165 wb_io_lists_depopulated(wb);
166}
167
168static void wb_wakeup(struct bdi_writeback *wb)
169{
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);
174}
175
176static void wb_queue_work(struct bdi_writeback *wb,
177 struct wb_writeback_work *work)
178{
179 trace_writeback_queue(wb, work);
180
181 spin_lock_bh(&wb->work_lock);
182 if (!test_bit(WB_registered, &wb->state))
183 goto out_unlock;
184 if (work->done)
185 atomic_inc(&work->done->cnt);
186 list_add_tail(&work->list, &wb->work_list);
187 mod_delayed_work(bdi_wq, &wb->dwork, 0);
188out_unlock:
189 spin_unlock_bh(&wb->work_lock);
190}
191
192/**
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
196 *
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.
202 */
203static void wb_wait_for_completion(struct backing_dev_info *bdi,
204 struct wb_completion *done)
205{
206 atomic_dec(&done->cnt); /* put down the initial count */
207 wait_event(bdi->wb_waitq, !atomic_read(&done->cnt));
208}
209
210#ifdef CONFIG_CGROUP_WRITEBACK
211
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 */
217
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 */
225
226static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
227static struct workqueue_struct *isw_wq;
228
229void __inode_attach_wb(struct inode *inode, struct page *page)
230{
231 struct backing_dev_info *bdi = inode_to_bdi(inode);
232 struct bdi_writeback *wb = NULL;
233
234 if (inode_cgwb_enabled(inode)) {
235 struct cgroup_subsys_state *memcg_css;
236
237 if (page) {
238 memcg_css = mem_cgroup_css_from_page(page);
239 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
240 } else {
241 /* must pin memcg_css, see wb_get_create() */
242 memcg_css = task_get_css(current, memory_cgrp_id);
243 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
244 css_put(memcg_css);
245 }
246 }
247
248 if (!wb)
249 wb = &bdi->wb;
250
251 /*
252 * There may be multiple instances of this function racing to
253 * update the same inode. Use cmpxchg() to tell the winner.
254 */
255 if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
256 wb_put(wb);
257}
258
259/**
260 * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
261 * @inode: inode of interest with i_lock held
262 *
263 * Returns @inode's wb with its list_lock held. @inode->i_lock must be
264 * held on entry and is released on return. The returned wb is guaranteed
265 * to stay @inode's associated wb until its list_lock is released.
266 */
267static struct bdi_writeback *
268locked_inode_to_wb_and_lock_list(struct inode *inode)
269 __releases(&inode->i_lock)
270 __acquires(&wb->list_lock)
271{
272 while (true) {
273 struct bdi_writeback *wb = inode_to_wb(inode);
274
275 /*
276 * inode_to_wb() association is protected by both
277 * @inode->i_lock and @wb->list_lock but list_lock nests
278 * outside i_lock. Drop i_lock and verify that the
279 * association hasn't changed after acquiring list_lock.
280 */
281 wb_get(wb);
282 spin_unlock(&inode->i_lock);
283 spin_lock(&wb->list_lock);
284
285 /* i_wb may have changed inbetween, can't use inode_to_wb() */
286 if (likely(wb == inode->i_wb)) {
287 wb_put(wb); /* @inode already has ref */
288 return wb;
289 }
290
291 spin_unlock(&wb->list_lock);
292 wb_put(wb);
293 cpu_relax();
294 spin_lock(&inode->i_lock);
295 }
296}
297
298/**
299 * inode_to_wb_and_lock_list - determine an inode's wb and lock it
300 * @inode: inode of interest
301 *
302 * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
303 * on entry.
304 */
305static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
306 __acquires(&wb->list_lock)
307{
308 spin_lock(&inode->i_lock);
309 return locked_inode_to_wb_and_lock_list(inode);
310}
311
312struct inode_switch_wbs_context {
313 struct inode *inode;
314 struct bdi_writeback *new_wb;
315
316 struct rcu_head rcu_head;
317 struct work_struct work;
318};
319
320static void inode_switch_wbs_work_fn(struct work_struct *work)
321{
322 struct inode_switch_wbs_context *isw =
323 container_of(work, struct inode_switch_wbs_context, work);
324 struct inode *inode = isw->inode;
325 struct address_space *mapping = inode->i_mapping;
326 struct bdi_writeback *old_wb = inode->i_wb;
327 struct bdi_writeback *new_wb = isw->new_wb;
328 struct radix_tree_iter iter;
329 bool switched = false;
330 void **slot;
331
332 /*
333 * By the time control reaches here, RCU grace period has passed
334 * since I_WB_SWITCH assertion and all wb stat update transactions
335 * between unlocked_inode_to_wb_begin/end() are guaranteed to be
336 * synchronizing against mapping->tree_lock.
337 *
338 * Grabbing old_wb->list_lock, inode->i_lock and mapping->tree_lock
339 * gives us exclusion against all wb related operations on @inode
340 * including IO list manipulations and stat updates.
341 */
342 if (old_wb < new_wb) {
343 spin_lock(&old_wb->list_lock);
344 spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
345 } else {
346 spin_lock(&new_wb->list_lock);
347 spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
348 }
349 spin_lock(&inode->i_lock);
350 spin_lock_irq(&mapping->tree_lock);
351
352 /*
353 * Once I_FREEING is visible under i_lock, the eviction path owns
354 * the inode and we shouldn't modify ->i_io_list.
355 */
356 if (unlikely(inode->i_state & I_FREEING))
357 goto skip_switch;
358
359 /*
360 * Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
361 * to possibly dirty pages while PAGECACHE_TAG_WRITEBACK points to
362 * pages actually under underwriteback.
363 */
364 radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, 0,
365 PAGECACHE_TAG_DIRTY) {
366 struct page *page = radix_tree_deref_slot_protected(slot,
367 &mapping->tree_lock);
368 if (likely(page) && PageDirty(page)) {
369 __dec_wb_stat(old_wb, WB_RECLAIMABLE);
370 __inc_wb_stat(new_wb, WB_RECLAIMABLE);
371 }
372 }
373
374 radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, 0,
375 PAGECACHE_TAG_WRITEBACK) {
376 struct page *page = radix_tree_deref_slot_protected(slot,
377 &mapping->tree_lock);
378 if (likely(page)) {
379 WARN_ON_ONCE(!PageWriteback(page));
380 __dec_wb_stat(old_wb, WB_WRITEBACK);
381 __inc_wb_stat(new_wb, WB_WRITEBACK);
382 }
383 }
384
385 wb_get(new_wb);
386
387 /*
388 * Transfer to @new_wb's IO list if necessary. The specific list
389 * @inode was on is ignored and the inode is put on ->b_dirty which
390 * is always correct including from ->b_dirty_time. The transfer
391 * preserves @inode->dirtied_when ordering.
392 */
393 if (!list_empty(&inode->i_io_list)) {
394 struct inode *pos;
395
396 inode_io_list_del_locked(inode, old_wb);
397 inode->i_wb = new_wb;
398 list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
399 if (time_after_eq(inode->dirtied_when,
400 pos->dirtied_when))
401 break;
402 inode_io_list_move_locked(inode, new_wb, pos->i_io_list.prev);
403 } else {
404 inode->i_wb = new_wb;
405 }
406
407 /* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
408 inode->i_wb_frn_winner = 0;
409 inode->i_wb_frn_avg_time = 0;
410 inode->i_wb_frn_history = 0;
411 switched = true;
412skip_switch:
413 /*
414 * Paired with load_acquire in unlocked_inode_to_wb_begin() and
415 * ensures that the new wb is visible if they see !I_WB_SWITCH.
416 */
417 smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
418
419 spin_unlock_irq(&mapping->tree_lock);
420 spin_unlock(&inode->i_lock);
421 spin_unlock(&new_wb->list_lock);
422 spin_unlock(&old_wb->list_lock);
423
424 if (switched) {
425 wb_wakeup(new_wb);
426 wb_put(old_wb);
427 }
428 wb_put(new_wb);
429
430 iput(inode);
431 kfree(isw);
432
433 atomic_dec(&isw_nr_in_flight);
434}
435
436static void inode_switch_wbs_rcu_fn(struct rcu_head *rcu_head)
437{
438 struct inode_switch_wbs_context *isw = container_of(rcu_head,
439 struct inode_switch_wbs_context, rcu_head);
440
441 /* needs to grab bh-unsafe locks, bounce to work item */
442 INIT_WORK(&isw->work, inode_switch_wbs_work_fn);
443 queue_work(isw_wq, &isw->work);
444}
445
446/**
447 * inode_switch_wbs - change the wb association of an inode
448 * @inode: target inode
449 * @new_wb_id: ID of the new wb
450 *
451 * Switch @inode's wb association to the wb identified by @new_wb_id. The
452 * switching is performed asynchronously and may fail silently.
453 */
454static void inode_switch_wbs(struct inode *inode, int new_wb_id)
455{
456 struct backing_dev_info *bdi = inode_to_bdi(inode);
457 struct cgroup_subsys_state *memcg_css;
458 struct inode_switch_wbs_context *isw;
459
460 /* noop if seems to be already in progress */
461 if (inode->i_state & I_WB_SWITCH)
462 return;
463
464 isw = kzalloc(sizeof(*isw), GFP_ATOMIC);
465 if (!isw)
466 return;
467
468 /* find and pin the new wb */
469 rcu_read_lock();
470 memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
471 if (memcg_css)
472 isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
473 rcu_read_unlock();
474 if (!isw->new_wb)
475 goto out_free;
476
477 /* while holding I_WB_SWITCH, no one else can update the association */
478 spin_lock(&inode->i_lock);
479 if (!(inode->i_sb->s_flags & MS_ACTIVE) ||
480 inode->i_state & (I_WB_SWITCH | I_FREEING) ||
481 inode_to_wb(inode) == isw->new_wb) {
482 spin_unlock(&inode->i_lock);
483 goto out_free;
484 }
485 inode->i_state |= I_WB_SWITCH;
486 __iget(inode);
487 spin_unlock(&inode->i_lock);
488
489 isw->inode = inode;
490
491 atomic_inc(&isw_nr_in_flight);
492
493 /*
494 * In addition to synchronizing among switchers, I_WB_SWITCH tells
495 * the RCU protected stat update paths to grab the mapping's
496 * tree_lock so that stat transfer can synchronize against them.
497 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
498 */
499 call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn);
500 return;
501
502out_free:
503 if (isw->new_wb)
504 wb_put(isw->new_wb);
505 kfree(isw);
506}
507
508/**
509 * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
510 * @wbc: writeback_control of interest
511 * @inode: target inode
512 *
513 * @inode is locked and about to be written back under the control of @wbc.
514 * Record @inode's writeback context into @wbc and unlock the i_lock. On
515 * writeback completion, wbc_detach_inode() should be called. This is used
516 * to track the cgroup writeback context.
517 */
518void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
519 struct inode *inode)
520{
521 if (!inode_cgwb_enabled(inode)) {
522 spin_unlock(&inode->i_lock);
523 return;
524 }
525
526 wbc->wb = inode_to_wb(inode);
527 wbc->inode = inode;
528
529 wbc->wb_id = wbc->wb->memcg_css->id;
530 wbc->wb_lcand_id = inode->i_wb_frn_winner;
531 wbc->wb_tcand_id = 0;
532 wbc->wb_bytes = 0;
533 wbc->wb_lcand_bytes = 0;
534 wbc->wb_tcand_bytes = 0;
535
536 wb_get(wbc->wb);
537 spin_unlock(&inode->i_lock);
538
539 /*
540 * A dying wb indicates that the memcg-blkcg mapping has changed
541 * and a new wb is already serving the memcg. Switch immediately.
542 */
543 if (unlikely(wb_dying(wbc->wb)))
544 inode_switch_wbs(inode, wbc->wb_id);
545}
546
547/**
548 * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
549 * @wbc: writeback_control of the just finished writeback
550 *
551 * To be called after a writeback attempt of an inode finishes and undoes
552 * wbc_attach_and_unlock_inode(). Can be called under any context.
553 *
554 * As concurrent write sharing of an inode is expected to be very rare and
555 * memcg only tracks page ownership on first-use basis severely confining
556 * the usefulness of such sharing, cgroup writeback tracks ownership
557 * per-inode. While the support for concurrent write sharing of an inode
558 * is deemed unnecessary, an inode being written to by different cgroups at
559 * different points in time is a lot more common, and, more importantly,
560 * charging only by first-use can too readily lead to grossly incorrect
561 * behaviors (single foreign page can lead to gigabytes of writeback to be
562 * incorrectly attributed).
563 *
564 * To resolve this issue, cgroup writeback detects the majority dirtier of
565 * an inode and transfers the ownership to it. To avoid unnnecessary
566 * oscillation, the detection mechanism keeps track of history and gives
567 * out the switch verdict only if the foreign usage pattern is stable over
568 * a certain amount of time and/or writeback attempts.
569 *
570 * On each writeback attempt, @wbc tries to detect the majority writer
571 * using Boyer-Moore majority vote algorithm. In addition to the byte
572 * count from the majority voting, it also counts the bytes written for the
573 * current wb and the last round's winner wb (max of last round's current
574 * wb, the winner from two rounds ago, and the last round's majority
575 * candidate). Keeping track of the historical winner helps the algorithm
576 * to semi-reliably detect the most active writer even when it's not the
577 * absolute majority.
578 *
579 * Once the winner of the round is determined, whether the winner is
580 * foreign or not and how much IO time the round consumed is recorded in
581 * inode->i_wb_frn_history. If the amount of recorded foreign IO time is
582 * over a certain threshold, the switch verdict is given.
583 */
584void wbc_detach_inode(struct writeback_control *wbc)
585{
586 struct bdi_writeback *wb = wbc->wb;
587 struct inode *inode = wbc->inode;
588 unsigned long avg_time, max_bytes, max_time;
589 u16 history;
590 int max_id;
591
592 if (!wb)
593 return;
594
595 history = inode->i_wb_frn_history;
596 avg_time = inode->i_wb_frn_avg_time;
597
598 /* pick the winner of this round */
599 if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
600 wbc->wb_bytes >= wbc->wb_tcand_bytes) {
601 max_id = wbc->wb_id;
602 max_bytes = wbc->wb_bytes;
603 } else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
604 max_id = wbc->wb_lcand_id;
605 max_bytes = wbc->wb_lcand_bytes;
606 } else {
607 max_id = wbc->wb_tcand_id;
608 max_bytes = wbc->wb_tcand_bytes;
609 }
610
611 /*
612 * Calculate the amount of IO time the winner consumed and fold it
613 * into the running average kept per inode. If the consumed IO
614 * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
615 * deciding whether to switch or not. This is to prevent one-off
616 * small dirtiers from skewing the verdict.
617 */
618 max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
619 wb->avg_write_bandwidth);
620 if (avg_time)
621 avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
622 (avg_time >> WB_FRN_TIME_AVG_SHIFT);
623 else
624 avg_time = max_time; /* immediate catch up on first run */
625
626 if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
627 int slots;
628
629 /*
630 * The switch verdict is reached if foreign wb's consume
631 * more than a certain proportion of IO time in a
632 * WB_FRN_TIME_PERIOD. This is loosely tracked by 16 slot
633 * history mask where each bit represents one sixteenth of
634 * the period. Determine the number of slots to shift into
635 * history from @max_time.
636 */
637 slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
638 (unsigned long)WB_FRN_HIST_MAX_SLOTS);
639 history <<= slots;
640 if (wbc->wb_id != max_id)
641 history |= (1U << slots) - 1;
642
643 /*
644 * Switch if the current wb isn't the consistent winner.
645 * If there are multiple closely competing dirtiers, the
646 * inode may switch across them repeatedly over time, which
647 * is okay. The main goal is avoiding keeping an inode on
648 * the wrong wb for an extended period of time.
649 */
650 if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
651 inode_switch_wbs(inode, max_id);
652 }
653
654 /*
655 * Multiple instances of this function may race to update the
656 * following fields but we don't mind occassional inaccuracies.
657 */
658 inode->i_wb_frn_winner = max_id;
659 inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
660 inode->i_wb_frn_history = history;
661
662 wb_put(wbc->wb);
663 wbc->wb = NULL;
664}
665
666/**
667 * wbc_account_io - account IO issued during writeback
668 * @wbc: writeback_control of the writeback in progress
669 * @page: page being written out
670 * @bytes: number of bytes being written out
671 *
672 * @bytes from @page are about to written out during the writeback
673 * controlled by @wbc. Keep the book for foreign inode detection. See
674 * wbc_detach_inode().
675 */
676void wbc_account_io(struct writeback_control *wbc, struct page *page,
677 size_t bytes)
678{
679 int id;
680
681 /*
682 * pageout() path doesn't attach @wbc to the inode being written
683 * out. This is intentional as we don't want the function to block
684 * behind a slow cgroup. Ultimately, we want pageout() to kick off
685 * regular writeback instead of writing things out itself.
686 */
687 if (!wbc->wb)
688 return;
689
690 id = mem_cgroup_css_from_page(page)->id;
691
692 if (id == wbc->wb_id) {
693 wbc->wb_bytes += bytes;
694 return;
695 }
696
697 if (id == wbc->wb_lcand_id)
698 wbc->wb_lcand_bytes += bytes;
699
700 /* Boyer-Moore majority vote algorithm */
701 if (!wbc->wb_tcand_bytes)
702 wbc->wb_tcand_id = id;
703 if (id == wbc->wb_tcand_id)
704 wbc->wb_tcand_bytes += bytes;
705 else
706 wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
707}
708EXPORT_SYMBOL_GPL(wbc_account_io);
709
710/**
711 * inode_congested - test whether an inode is congested
712 * @inode: inode to test for congestion (may be NULL)
713 * @cong_bits: mask of WB_[a]sync_congested bits to test
714 *
715 * Tests whether @inode is congested. @cong_bits is the mask of congestion
716 * bits to test and the return value is the mask of set bits.
717 *
718 * If cgroup writeback is enabled for @inode, the congestion state is
719 * determined by whether the cgwb (cgroup bdi_writeback) for the blkcg
720 * associated with @inode is congested; otherwise, the root wb's congestion
721 * state is used.
722 *
723 * @inode is allowed to be NULL as this function is often called on
724 * mapping->host which is NULL for the swapper space.
725 */
726int inode_congested(struct inode *inode, int cong_bits)
727{
728 /*
729 * Once set, ->i_wb never becomes NULL while the inode is alive.
730 * Start transaction iff ->i_wb is visible.
731 */
732 if (inode && inode_to_wb_is_valid(inode)) {
733 struct bdi_writeback *wb;
734 bool locked, congested;
735
736 wb = unlocked_inode_to_wb_begin(inode, &locked);
737 congested = wb_congested(wb, cong_bits);
738 unlocked_inode_to_wb_end(inode, locked);
739 return congested;
740 }
741
742 return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
743}
744EXPORT_SYMBOL_GPL(inode_congested);
745
746/**
747 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
748 * @wb: target bdi_writeback to split @nr_pages to
749 * @nr_pages: number of pages to write for the whole bdi
750 *
751 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
752 * relation to the total write bandwidth of all wb's w/ dirty inodes on
753 * @wb->bdi.
754 */
755static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
756{
757 unsigned long this_bw = wb->avg_write_bandwidth;
758 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
759
760 if (nr_pages == LONG_MAX)
761 return LONG_MAX;
762
763 /*
764 * This may be called on clean wb's and proportional distribution
765 * may not make sense, just use the original @nr_pages in those
766 * cases. In general, we wanna err on the side of writing more.
767 */
768 if (!tot_bw || this_bw >= tot_bw)
769 return nr_pages;
770 else
771 return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
772}
773
774/**
775 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
776 * @bdi: target backing_dev_info
777 * @base_work: wb_writeback_work to issue
778 * @skip_if_busy: skip wb's which already have writeback in progress
779 *
780 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
781 * have dirty inodes. If @base_work->nr_page isn't %LONG_MAX, it's
782 * distributed to the busy wbs according to each wb's proportion in the
783 * total active write bandwidth of @bdi.
784 */
785static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
786 struct wb_writeback_work *base_work,
787 bool skip_if_busy)
788{
789 struct bdi_writeback *last_wb = NULL;
790 struct bdi_writeback *wb = list_entry(&bdi->wb_list,
791 struct bdi_writeback, bdi_node);
792
793 might_sleep();
794restart:
795 rcu_read_lock();
796 list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
797 DEFINE_WB_COMPLETION_ONSTACK(fallback_work_done);
798 struct wb_writeback_work fallback_work;
799 struct wb_writeback_work *work;
800 long nr_pages;
801
802 if (last_wb) {
803 wb_put(last_wb);
804 last_wb = NULL;
805 }
806
807 /* SYNC_ALL writes out I_DIRTY_TIME too */
808 if (!wb_has_dirty_io(wb) &&
809 (base_work->sync_mode == WB_SYNC_NONE ||
810 list_empty(&wb->b_dirty_time)))
811 continue;
812 if (skip_if_busy && writeback_in_progress(wb))
813 continue;
814
815 nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
816
817 work = kmalloc(sizeof(*work), GFP_ATOMIC);
818 if (work) {
819 *work = *base_work;
820 work->nr_pages = nr_pages;
821 work->auto_free = 1;
822 wb_queue_work(wb, work);
823 continue;
824 }
825
826 /* alloc failed, execute synchronously using on-stack fallback */
827 work = &fallback_work;
828 *work = *base_work;
829 work->nr_pages = nr_pages;
830 work->auto_free = 0;
831 work->done = &fallback_work_done;
832
833 wb_queue_work(wb, work);
834
835 /*
836 * Pin @wb so that it stays on @bdi->wb_list. This allows
837 * continuing iteration from @wb after dropping and
838 * regrabbing rcu read lock.
839 */
840 wb_get(wb);
841 last_wb = wb;
842
843 rcu_read_unlock();
844 wb_wait_for_completion(bdi, &fallback_work_done);
845 goto restart;
846 }
847 rcu_read_unlock();
848
849 if (last_wb)
850 wb_put(last_wb);
851}
852
853/**
854 * cgroup_writeback_umount - flush inode wb switches for umount
855 *
856 * This function is called when a super_block is about to be destroyed and
857 * flushes in-flight inode wb switches. An inode wb switch goes through
858 * RCU and then workqueue, so the two need to be flushed in order to ensure
859 * that all previously scheduled switches are finished. As wb switches are
860 * rare occurrences and synchronize_rcu() can take a while, perform
861 * flushing iff wb switches are in flight.
862 */
863void cgroup_writeback_umount(void)
864{
865 if (atomic_read(&isw_nr_in_flight)) {
866 synchronize_rcu();
867 flush_workqueue(isw_wq);
868 }
869}
870
871static int __init cgroup_writeback_init(void)
872{
873 isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
874 if (!isw_wq)
875 return -ENOMEM;
876 return 0;
877}
878fs_initcall(cgroup_writeback_init);
879
880#else /* CONFIG_CGROUP_WRITEBACK */
881
882static struct bdi_writeback *
883locked_inode_to_wb_and_lock_list(struct inode *inode)
884 __releases(&inode->i_lock)
885 __acquires(&wb->list_lock)
886{
887 struct bdi_writeback *wb = inode_to_wb(inode);
888
889 spin_unlock(&inode->i_lock);
890 spin_lock(&wb->list_lock);
891 return wb;
892}
893
894static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
895 __acquires(&wb->list_lock)
896{
897 struct bdi_writeback *wb = inode_to_wb(inode);
898
899 spin_lock(&wb->list_lock);
900 return wb;
901}
902
903static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
904{
905 return nr_pages;
906}
907
908static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
909 struct wb_writeback_work *base_work,
910 bool skip_if_busy)
911{
912 might_sleep();
913
914 if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
915 base_work->auto_free = 0;
916 wb_queue_work(&bdi->wb, base_work);
917 }
918}
919
920#endif /* CONFIG_CGROUP_WRITEBACK */
921
922void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
923 bool range_cyclic, enum wb_reason reason)
924{
925 struct wb_writeback_work *work;
926
927 if (!wb_has_dirty_io(wb))
928 return;
929
930 /*
931 * This is WB_SYNC_NONE writeback, so if allocation fails just
932 * wakeup the thread for old dirty data writeback
933 */
934 work = kzalloc(sizeof(*work),
935 GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN);
936 if (!work) {
937 trace_writeback_nowork(wb);
938 wb_wakeup(wb);
939 return;
940 }
941
942 work->sync_mode = WB_SYNC_NONE;
943 work->nr_pages = nr_pages;
944 work->range_cyclic = range_cyclic;
945 work->reason = reason;
946 work->auto_free = 1;
947
948 wb_queue_work(wb, work);
949}
950
951/**
952 * wb_start_background_writeback - start background writeback
953 * @wb: bdi_writback to write from
954 *
955 * Description:
956 * This makes sure WB_SYNC_NONE background writeback happens. When
957 * this function returns, it is only guaranteed that for given wb
958 * some IO is happening if we are over background dirty threshold.
959 * Caller need not hold sb s_umount semaphore.
960 */
961void wb_start_background_writeback(struct bdi_writeback *wb)
962{
963 /*
964 * We just wake up the flusher thread. It will perform background
965 * writeback as soon as there is no other work to do.
966 */
967 trace_writeback_wake_background(wb);
968 wb_wakeup(wb);
969}
970
971/*
972 * Remove the inode from the writeback list it is on.
973 */
974void inode_io_list_del(struct inode *inode)
975{
976 struct bdi_writeback *wb;
977
978 wb = inode_to_wb_and_lock_list(inode);
979 inode_io_list_del_locked(inode, wb);
980 spin_unlock(&wb->list_lock);
981}
982
983/*
984 * mark an inode as under writeback on the sb
985 */
986void sb_mark_inode_writeback(struct inode *inode)
987{
988 struct super_block *sb = inode->i_sb;
989 unsigned long flags;
990
991 if (list_empty(&inode->i_wb_list)) {
992 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
993 if (list_empty(&inode->i_wb_list)) {
994 list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
995 trace_sb_mark_inode_writeback(inode);
996 }
997 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
998 }
999}
1000
1001/*
1002 * clear an inode as under writeback on the sb
1003 */
1004void sb_clear_inode_writeback(struct inode *inode)
1005{
1006 struct super_block *sb = inode->i_sb;
1007 unsigned long flags;
1008
1009 if (!list_empty(&inode->i_wb_list)) {
1010 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1011 if (!list_empty(&inode->i_wb_list)) {
1012 list_del_init(&inode->i_wb_list);
1013 trace_sb_clear_inode_writeback(inode);
1014 }
1015 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1016 }
1017}
1018
1019/*
1020 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1021 * furthest end of its superblock's dirty-inode list.
1022 *
1023 * Before stamping the inode's ->dirtied_when, we check to see whether it is
1024 * already the most-recently-dirtied inode on the b_dirty list. If that is
1025 * the case then the inode must have been redirtied while it was being written
1026 * out and we don't reset its dirtied_when.
1027 */
1028static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
1029{
1030 if (!list_empty(&wb->b_dirty)) {
1031 struct inode *tail;
1032
1033 tail = wb_inode(wb->b_dirty.next);
1034 if (time_before(inode->dirtied_when, tail->dirtied_when))
1035 inode->dirtied_when = jiffies;
1036 }
1037 inode_io_list_move_locked(inode, wb, &wb->b_dirty);
1038}
1039
1040/*
1041 * requeue inode for re-scanning after bdi->b_io list is exhausted.
1042 */
1043static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
1044{
1045 inode_io_list_move_locked(inode, wb, &wb->b_more_io);
1046}
1047
1048static void inode_sync_complete(struct inode *inode)
1049{
1050 inode->i_state &= ~I_SYNC;
1051 /* If inode is clean an unused, put it into LRU now... */
1052 inode_add_lru(inode);
1053 /* Waiters must see I_SYNC cleared before being woken up */
1054 smp_mb();
1055 wake_up_bit(&inode->i_state, __I_SYNC);
1056}
1057
1058static bool inode_dirtied_after(struct inode *inode, unsigned long t)
1059{
1060 bool ret = time_after(inode->dirtied_when, t);
1061#ifndef CONFIG_64BIT
1062 /*
1063 * For inodes being constantly redirtied, dirtied_when can get stuck.
1064 * It _appears_ to be in the future, but is actually in distant past.
1065 * This test is necessary to prevent such wrapped-around relative times
1066 * from permanently stopping the whole bdi writeback.
1067 */
1068 ret = ret && time_before_eq(inode->dirtied_when, jiffies);
1069#endif
1070 return ret;
1071}
1072
1073#define EXPIRE_DIRTY_ATIME 0x0001
1074
1075/*
1076 * Move expired (dirtied before work->older_than_this) dirty inodes from
1077 * @delaying_queue to @dispatch_queue.
1078 */
1079static int move_expired_inodes(struct list_head *delaying_queue,
1080 struct list_head *dispatch_queue,
1081 int flags,
1082 struct wb_writeback_work *work)
1083{
1084 unsigned long *older_than_this = NULL;
1085 unsigned long expire_time;
1086 LIST_HEAD(tmp);
1087 struct list_head *pos, *node;
1088 struct super_block *sb = NULL;
1089 struct inode *inode;
1090 int do_sb_sort = 0;
1091 int moved = 0;
1092
1093 if ((flags & EXPIRE_DIRTY_ATIME) == 0)
1094 older_than_this = work->older_than_this;
1095 else if (!work->for_sync) {
1096 expire_time = jiffies - (dirtytime_expire_interval * HZ);
1097 older_than_this = &expire_time;
1098 }
1099 while (!list_empty(delaying_queue)) {
1100 inode = wb_inode(delaying_queue->prev);
1101 if (older_than_this &&
1102 inode_dirtied_after(inode, *older_than_this))
1103 break;
1104 list_move(&inode->i_io_list, &tmp);
1105 moved++;
1106 if (flags & EXPIRE_DIRTY_ATIME)
1107 set_bit(__I_DIRTY_TIME_EXPIRED, &inode->i_state);
1108 if (sb_is_blkdev_sb(inode->i_sb))
1109 continue;
1110 if (sb && sb != inode->i_sb)
1111 do_sb_sort = 1;
1112 sb = inode->i_sb;
1113 }
1114
1115 /* just one sb in list, splice to dispatch_queue and we're done */
1116 if (!do_sb_sort) {
1117 list_splice(&tmp, dispatch_queue);
1118 goto out;
1119 }
1120
1121 /* Move inodes from one superblock together */
1122 while (!list_empty(&tmp)) {
1123 sb = wb_inode(tmp.prev)->i_sb;
1124 list_for_each_prev_safe(pos, node, &tmp) {
1125 inode = wb_inode(pos);
1126 if (inode->i_sb == sb)
1127 list_move(&inode->i_io_list, dispatch_queue);
1128 }
1129 }
1130out:
1131 return moved;
1132}
1133
1134/*
1135 * Queue all expired dirty inodes for io, eldest first.
1136 * Before
1137 * newly dirtied b_dirty b_io b_more_io
1138 * =============> gf edc BA
1139 * After
1140 * newly dirtied b_dirty b_io b_more_io
1141 * =============> g fBAedc
1142 * |
1143 * +--> dequeue for IO
1144 */
1145static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
1146{
1147 int moved;
1148
1149 assert_spin_locked(&wb->list_lock);
1150 list_splice_init(&wb->b_more_io, &wb->b_io);
1151 moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, 0, work);
1152 moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
1153 EXPIRE_DIRTY_ATIME, work);
1154 if (moved)
1155 wb_io_lists_populated(wb);
1156 trace_writeback_queue_io(wb, work, moved);
1157}
1158
1159static int write_inode(struct inode *inode, struct writeback_control *wbc)
1160{
1161 int ret;
1162
1163 if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1164 trace_writeback_write_inode_start(inode, wbc);
1165 ret = inode->i_sb->s_op->write_inode(inode, wbc);
1166 trace_writeback_write_inode(inode, wbc);
1167 return ret;
1168 }
1169 return 0;
1170}
1171
1172/*
1173 * Wait for writeback on an inode to complete. Called with i_lock held.
1174 * Caller must make sure inode cannot go away when we drop i_lock.
1175 */
1176static void __inode_wait_for_writeback(struct inode *inode)
1177 __releases(inode->i_lock)
1178 __acquires(inode->i_lock)
1179{
1180 DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1181 wait_queue_head_t *wqh;
1182
1183 wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1184 while (inode->i_state & I_SYNC) {
1185 spin_unlock(&inode->i_lock);
1186 __wait_on_bit(wqh, &wq, bit_wait,
1187 TASK_UNINTERRUPTIBLE);
1188 spin_lock(&inode->i_lock);
1189 }
1190}
1191
1192/*
1193 * Wait for writeback on an inode to complete. Caller must have inode pinned.
1194 */
1195void inode_wait_for_writeback(struct inode *inode)
1196{
1197 spin_lock(&inode->i_lock);
1198 __inode_wait_for_writeback(inode);
1199 spin_unlock(&inode->i_lock);
1200}
1201
1202/*
1203 * Sleep until I_SYNC is cleared. This function must be called with i_lock
1204 * held and drops it. It is aimed for callers not holding any inode reference
1205 * so once i_lock is dropped, inode can go away.
1206 */
1207static void inode_sleep_on_writeback(struct inode *inode)
1208 __releases(inode->i_lock)
1209{
1210 DEFINE_WAIT(wait);
1211 wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1212 int sleep;
1213
1214 prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1215 sleep = inode->i_state & I_SYNC;
1216 spin_unlock(&inode->i_lock);
1217 if (sleep)
1218 schedule();
1219 finish_wait(wqh, &wait);
1220}
1221
1222/*
1223 * Find proper writeback list for the inode depending on its current state and
1224 * possibly also change of its state while we were doing writeback. Here we
1225 * handle things such as livelock prevention or fairness of writeback among
1226 * inodes. This function can be called only by flusher thread - noone else
1227 * processes all inodes in writeback lists and requeueing inodes behind flusher
1228 * thread's back can have unexpected consequences.
1229 */
1230static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1231 struct writeback_control *wbc)
1232{
1233 if (inode->i_state & I_FREEING)
1234 return;
1235
1236 /*
1237 * Sync livelock prevention. Each inode is tagged and synced in one
1238 * shot. If still dirty, it will be redirty_tail()'ed below. Update
1239 * the dirty time to prevent enqueue and sync it again.
1240 */
1241 if ((inode->i_state & I_DIRTY) &&
1242 (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1243 inode->dirtied_when = jiffies;
1244
1245 if (wbc->pages_skipped) {
1246 /*
1247 * writeback is not making progress due to locked
1248 * buffers. Skip this inode for now.
1249 */
1250 redirty_tail(inode, wb);
1251 return;
1252 }
1253
1254 if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1255 /*
1256 * We didn't write back all the pages. nfs_writepages()
1257 * sometimes bales out without doing anything.
1258 */
1259 if (wbc->nr_to_write <= 0) {
1260 /* Slice used up. Queue for next turn. */
1261 requeue_io(inode, wb);
1262 } else {
1263 /*
1264 * Writeback blocked by something other than
1265 * congestion. Delay the inode for some time to
1266 * avoid spinning on the CPU (100% iowait)
1267 * retrying writeback of the dirty page/inode
1268 * that cannot be performed immediately.
1269 */
1270 redirty_tail(inode, wb);
1271 }
1272 } else if (inode->i_state & I_DIRTY) {
1273 /*
1274 * Filesystems can dirty the inode during writeback operations,
1275 * such as delayed allocation during submission or metadata
1276 * updates after data IO completion.
1277 */
1278 redirty_tail(inode, wb);
1279 } else if (inode->i_state & I_DIRTY_TIME) {
1280 inode->dirtied_when = jiffies;
1281 inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
1282 } else {
1283 /* The inode is clean. Remove from writeback lists. */
1284 inode_io_list_del_locked(inode, wb);
1285 }
1286}
1287
1288/*
1289 * Write out an inode and its dirty pages. Do not update the writeback list
1290 * linkage. That is left to the caller. The caller is also responsible for
1291 * setting I_SYNC flag and calling inode_sync_complete() to clear it.
1292 */
1293static int
1294__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1295{
1296 struct address_space *mapping = inode->i_mapping;
1297 long nr_to_write = wbc->nr_to_write;
1298 unsigned dirty;
1299 int ret;
1300
1301 WARN_ON(!(inode->i_state & I_SYNC));
1302
1303 trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1304
1305 ret = do_writepages(mapping, wbc);
1306
1307 /*
1308 * Make sure to wait on the data before writing out the metadata.
1309 * This is important for filesystems that modify metadata on data
1310 * I/O completion. We don't do it for sync(2) writeback because it has a
1311 * separate, external IO completion path and ->sync_fs for guaranteeing
1312 * inode metadata is written back correctly.
1313 */
1314 if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
1315 int err = filemap_fdatawait(mapping);
1316 if (ret == 0)
1317 ret = err;
1318 }
1319
1320 /*
1321 * Some filesystems may redirty the inode during the writeback
1322 * due to delalloc, clear dirty metadata flags right before
1323 * write_inode()
1324 */
1325 spin_lock(&inode->i_lock);
1326
1327 dirty = inode->i_state & I_DIRTY;
1328 if (inode->i_state & I_DIRTY_TIME) {
1329 if ((dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) ||
1330 wbc->sync_mode == WB_SYNC_ALL ||
1331 unlikely(inode->i_state & I_DIRTY_TIME_EXPIRED) ||
1332 unlikely(time_after(jiffies,
1333 (inode->dirtied_time_when +
1334 dirtytime_expire_interval * HZ)))) {
1335 dirty |= I_DIRTY_TIME | I_DIRTY_TIME_EXPIRED;
1336 trace_writeback_lazytime(inode);
1337 }
1338 } else
1339 inode->i_state &= ~I_DIRTY_TIME_EXPIRED;
1340 inode->i_state &= ~dirty;
1341
1342 /*
1343 * Paired with smp_mb() in __mark_inode_dirty(). This allows
1344 * __mark_inode_dirty() to test i_state without grabbing i_lock -
1345 * either they see the I_DIRTY bits cleared or we see the dirtied
1346 * inode.
1347 *
1348 * I_DIRTY_PAGES is always cleared together above even if @mapping
1349 * still has dirty pages. The flag is reinstated after smp_mb() if
1350 * necessary. This guarantees that either __mark_inode_dirty()
1351 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1352 */
1353 smp_mb();
1354
1355 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1356 inode->i_state |= I_DIRTY_PAGES;
1357
1358 spin_unlock(&inode->i_lock);
1359
1360 if (dirty & I_DIRTY_TIME)
1361 mark_inode_dirty_sync(inode);
1362 /* Don't write the inode if only I_DIRTY_PAGES was set */
1363 if (dirty & ~I_DIRTY_PAGES) {
1364 int err = write_inode(inode, wbc);
1365 if (ret == 0)
1366 ret = err;
1367 }
1368 trace_writeback_single_inode(inode, wbc, nr_to_write);
1369 return ret;
1370}
1371
1372/*
1373 * Write out an inode's dirty pages. Either the caller has an active reference
1374 * on the inode or the inode has I_WILL_FREE set.
1375 *
1376 * This function is designed to be called for writing back one inode which
1377 * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
1378 * and does more profound writeback list handling in writeback_sb_inodes().
1379 */
1380static int writeback_single_inode(struct inode *inode,
1381 struct writeback_control *wbc)
1382{
1383 struct bdi_writeback *wb;
1384 int ret = 0;
1385
1386 spin_lock(&inode->i_lock);
1387 if (!atomic_read(&inode->i_count))
1388 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1389 else
1390 WARN_ON(inode->i_state & I_WILL_FREE);
1391
1392 if (inode->i_state & I_SYNC) {
1393 if (wbc->sync_mode != WB_SYNC_ALL)
1394 goto out;
1395 /*
1396 * It's a data-integrity sync. We must wait. Since callers hold
1397 * inode reference or inode has I_WILL_FREE set, it cannot go
1398 * away under us.
1399 */
1400 __inode_wait_for_writeback(inode);
1401 }
1402 WARN_ON(inode->i_state & I_SYNC);
1403 /*
1404 * Skip inode if it is clean and we have no outstanding writeback in
1405 * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
1406 * function since flusher thread may be doing for example sync in
1407 * parallel and if we move the inode, it could get skipped. So here we
1408 * make sure inode is on some writeback list and leave it there unless
1409 * we have completely cleaned the inode.
1410 */
1411 if (!(inode->i_state & I_DIRTY_ALL) &&
1412 (wbc->sync_mode != WB_SYNC_ALL ||
1413 !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
1414 goto out;
1415 inode->i_state |= I_SYNC;
1416 wbc_attach_and_unlock_inode(wbc, inode);
1417
1418 ret = __writeback_single_inode(inode, wbc);
1419
1420 wbc_detach_inode(wbc);
1421
1422 wb = inode_to_wb_and_lock_list(inode);
1423 spin_lock(&inode->i_lock);
1424 /*
1425 * If inode is clean, remove it from writeback lists. Otherwise don't
1426 * touch it. See comment above for explanation.
1427 */
1428 if (!(inode->i_state & I_DIRTY_ALL))
1429 inode_io_list_del_locked(inode, wb);
1430 spin_unlock(&wb->list_lock);
1431 inode_sync_complete(inode);
1432out:
1433 spin_unlock(&inode->i_lock);
1434 return ret;
1435}
1436
1437static long writeback_chunk_size(struct bdi_writeback *wb,
1438 struct wb_writeback_work *work)
1439{
1440 long pages;
1441
1442 /*
1443 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1444 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1445 * here avoids calling into writeback_inodes_wb() more than once.
1446 *
1447 * The intended call sequence for WB_SYNC_ALL writeback is:
1448 *
1449 * wb_writeback()
1450 * writeback_sb_inodes() <== called only once
1451 * write_cache_pages() <== called once for each inode
1452 * (quickly) tag currently dirty pages
1453 * (maybe slowly) sync all tagged pages
1454 */
1455 if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1456 pages = LONG_MAX;
1457 else {
1458 pages = min(wb->avg_write_bandwidth / 2,
1459 global_wb_domain.dirty_limit / DIRTY_SCOPE);
1460 pages = min(pages, work->nr_pages);
1461 pages = round_down(pages + MIN_WRITEBACK_PAGES,
1462 MIN_WRITEBACK_PAGES);
1463 }
1464
1465 return pages;
1466}
1467
1468/*
1469 * Write a portion of b_io inodes which belong to @sb.
1470 *
1471 * Return the number of pages and/or inodes written.
1472 *
1473 * NOTE! This is called with wb->list_lock held, and will
1474 * unlock and relock that for each inode it ends up doing
1475 * IO for.
1476 */
1477static long writeback_sb_inodes(struct super_block *sb,
1478 struct bdi_writeback *wb,
1479 struct wb_writeback_work *work)
1480{
1481 struct writeback_control wbc = {
1482 .sync_mode = work->sync_mode,
1483 .tagged_writepages = work->tagged_writepages,
1484 .for_kupdate = work->for_kupdate,
1485 .for_background = work->for_background,
1486 .for_sync = work->for_sync,
1487 .range_cyclic = work->range_cyclic,
1488 .range_start = 0,
1489 .range_end = LLONG_MAX,
1490 };
1491 unsigned long start_time = jiffies;
1492 long write_chunk;
1493 long wrote = 0; /* count both pages and inodes */
1494
1495 while (!list_empty(&wb->b_io)) {
1496 struct inode *inode = wb_inode(wb->b_io.prev);
1497 struct bdi_writeback *tmp_wb;
1498
1499 if (inode->i_sb != sb) {
1500 if (work->sb) {
1501 /*
1502 * We only want to write back data for this
1503 * superblock, move all inodes not belonging
1504 * to it back onto the dirty list.
1505 */
1506 redirty_tail(inode, wb);
1507 continue;
1508 }
1509
1510 /*
1511 * The inode belongs to a different superblock.
1512 * Bounce back to the caller to unpin this and
1513 * pin the next superblock.
1514 */
1515 break;
1516 }
1517
1518 /*
1519 * Don't bother with new inodes or inodes being freed, first
1520 * kind does not need periodic writeout yet, and for the latter
1521 * kind writeout is handled by the freer.
1522 */
1523 spin_lock(&inode->i_lock);
1524 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
1525 spin_unlock(&inode->i_lock);
1526 redirty_tail(inode, wb);
1527 continue;
1528 }
1529 if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1530 /*
1531 * If this inode is locked for writeback and we are not
1532 * doing writeback-for-data-integrity, move it to
1533 * b_more_io so that writeback can proceed with the
1534 * other inodes on s_io.
1535 *
1536 * We'll have another go at writing back this inode
1537 * when we completed a full scan of b_io.
1538 */
1539 spin_unlock(&inode->i_lock);
1540 requeue_io(inode, wb);
1541 trace_writeback_sb_inodes_requeue(inode);
1542 continue;
1543 }
1544 spin_unlock(&wb->list_lock);
1545
1546 /*
1547 * We already requeued the inode if it had I_SYNC set and we
1548 * are doing WB_SYNC_NONE writeback. So this catches only the
1549 * WB_SYNC_ALL case.
1550 */
1551 if (inode->i_state & I_SYNC) {
1552 /* Wait for I_SYNC. This function drops i_lock... */
1553 inode_sleep_on_writeback(inode);
1554 /* Inode may be gone, start again */
1555 spin_lock(&wb->list_lock);
1556 continue;
1557 }
1558 inode->i_state |= I_SYNC;
1559 wbc_attach_and_unlock_inode(&wbc, inode);
1560
1561 write_chunk = writeback_chunk_size(wb, work);
1562 wbc.nr_to_write = write_chunk;
1563 wbc.pages_skipped = 0;
1564
1565 /*
1566 * We use I_SYNC to pin the inode in memory. While it is set
1567 * evict_inode() will wait so the inode cannot be freed.
1568 */
1569 __writeback_single_inode(inode, &wbc);
1570
1571 wbc_detach_inode(&wbc);
1572 work->nr_pages -= write_chunk - wbc.nr_to_write;
1573 wrote += write_chunk - wbc.nr_to_write;
1574
1575 if (need_resched()) {
1576 /*
1577 * We're trying to balance between building up a nice
1578 * long list of IOs to improve our merge rate, and
1579 * getting those IOs out quickly for anyone throttling
1580 * in balance_dirty_pages(). cond_resched() doesn't
1581 * unplug, so get our IOs out the door before we
1582 * give up the CPU.
1583 */
1584 blk_flush_plug(current);
1585 cond_resched();
1586 }
1587
1588 /*
1589 * Requeue @inode if still dirty. Be careful as @inode may
1590 * have been switched to another wb in the meantime.
1591 */
1592 tmp_wb = inode_to_wb_and_lock_list(inode);
1593 spin_lock(&inode->i_lock);
1594 if (!(inode->i_state & I_DIRTY_ALL))
1595 wrote++;
1596 requeue_inode(inode, tmp_wb, &wbc);
1597 inode_sync_complete(inode);
1598 spin_unlock(&inode->i_lock);
1599
1600 if (unlikely(tmp_wb != wb)) {
1601 spin_unlock(&tmp_wb->list_lock);
1602 spin_lock(&wb->list_lock);
1603 }
1604
1605 /*
1606 * bail out to wb_writeback() often enough to check
1607 * background threshold and other termination conditions.
1608 */
1609 if (wrote) {
1610 if (time_is_before_jiffies(start_time + HZ / 10UL))
1611 break;
1612 if (work->nr_pages <= 0)
1613 break;
1614 }
1615 }
1616 return wrote;
1617}
1618
1619static long __writeback_inodes_wb(struct bdi_writeback *wb,
1620 struct wb_writeback_work *work)
1621{
1622 unsigned long start_time = jiffies;
1623 long wrote = 0;
1624
1625 while (!list_empty(&wb->b_io)) {
1626 struct inode *inode = wb_inode(wb->b_io.prev);
1627 struct super_block *sb = inode->i_sb;
1628
1629 if (!trylock_super(sb)) {
1630 /*
1631 * trylock_super() may fail consistently due to
1632 * s_umount being grabbed by someone else. Don't use
1633 * requeue_io() to avoid busy retrying the inode/sb.
1634 */
1635 redirty_tail(inode, wb);
1636 continue;
1637 }
1638 wrote += writeback_sb_inodes(sb, wb, work);
1639 up_read(&sb->s_umount);
1640
1641 /* refer to the same tests at the end of writeback_sb_inodes */
1642 if (wrote) {
1643 if (time_is_before_jiffies(start_time + HZ / 10UL))
1644 break;
1645 if (work->nr_pages <= 0)
1646 break;
1647 }
1648 }
1649 /* Leave any unwritten inodes on b_io */
1650 return wrote;
1651}
1652
1653static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
1654 enum wb_reason reason)
1655{
1656 struct wb_writeback_work work = {
1657 .nr_pages = nr_pages,
1658 .sync_mode = WB_SYNC_NONE,
1659 .range_cyclic = 1,
1660 .reason = reason,
1661 };
1662 struct blk_plug plug;
1663
1664 blk_start_plug(&plug);
1665 spin_lock(&wb->list_lock);
1666 if (list_empty(&wb->b_io))
1667 queue_io(wb, &work);
1668 __writeback_inodes_wb(wb, &work);
1669 spin_unlock(&wb->list_lock);
1670 blk_finish_plug(&plug);
1671
1672 return nr_pages - work.nr_pages;
1673}
1674
1675/*
1676 * Explicit flushing or periodic writeback of "old" data.
1677 *
1678 * Define "old": the first time one of an inode's pages is dirtied, we mark the
1679 * dirtying-time in the inode's address_space. So this periodic writeback code
1680 * just walks the superblock inode list, writing back any inodes which are
1681 * older than a specific point in time.
1682 *
1683 * Try to run once per dirty_writeback_interval. But if a writeback event
1684 * takes longer than a dirty_writeback_interval interval, then leave a
1685 * one-second gap.
1686 *
1687 * older_than_this takes precedence over nr_to_write. So we'll only write back
1688 * all dirty pages if they are all attached to "old" mappings.
1689 */
1690static long wb_writeback(struct bdi_writeback *wb,
1691 struct wb_writeback_work *work)
1692{
1693 unsigned long wb_start = jiffies;
1694 long nr_pages = work->nr_pages;
1695 unsigned long oldest_jif;
1696 struct inode *inode;
1697 long progress;
1698 struct blk_plug plug;
1699
1700 oldest_jif = jiffies;
1701 work->older_than_this = &oldest_jif;
1702
1703 blk_start_plug(&plug);
1704 spin_lock(&wb->list_lock);
1705 for (;;) {
1706 /*
1707 * Stop writeback when nr_pages has been consumed
1708 */
1709 if (work->nr_pages <= 0)
1710 break;
1711
1712 /*
1713 * Background writeout and kupdate-style writeback may
1714 * run forever. Stop them if there is other work to do
1715 * so that e.g. sync can proceed. They'll be restarted
1716 * after the other works are all done.
1717 */
1718 if ((work->for_background || work->for_kupdate) &&
1719 !list_empty(&wb->work_list))
1720 break;
1721
1722 /*
1723 * For background writeout, stop when we are below the
1724 * background dirty threshold
1725 */
1726 if (work->for_background && !wb_over_bg_thresh(wb))
1727 break;
1728
1729 /*
1730 * Kupdate and background works are special and we want to
1731 * include all inodes that need writing. Livelock avoidance is
1732 * handled by these works yielding to any other work so we are
1733 * safe.
1734 */
1735 if (work->for_kupdate) {
1736 oldest_jif = jiffies -
1737 msecs_to_jiffies(dirty_expire_interval * 10);
1738 } else if (work->for_background)
1739 oldest_jif = jiffies;
1740
1741 trace_writeback_start(wb, work);
1742 if (list_empty(&wb->b_io))
1743 queue_io(wb, work);
1744 if (work->sb)
1745 progress = writeback_sb_inodes(work->sb, wb, work);
1746 else
1747 progress = __writeback_inodes_wb(wb, work);
1748 trace_writeback_written(wb, work);
1749
1750 wb_update_bandwidth(wb, wb_start);
1751
1752 /*
1753 * Did we write something? Try for more
1754 *
1755 * Dirty inodes are moved to b_io for writeback in batches.
1756 * The completion of the current batch does not necessarily
1757 * mean the overall work is done. So we keep looping as long
1758 * as made some progress on cleaning pages or inodes.
1759 */
1760 if (progress)
1761 continue;
1762 /*
1763 * No more inodes for IO, bail
1764 */
1765 if (list_empty(&wb->b_more_io))
1766 break;
1767 /*
1768 * Nothing written. Wait for some inode to
1769 * become available for writeback. Otherwise
1770 * we'll just busyloop.
1771 */
1772 trace_writeback_wait(wb, work);
1773 inode = wb_inode(wb->b_more_io.prev);
1774 spin_lock(&inode->i_lock);
1775 spin_unlock(&wb->list_lock);
1776 /* This function drops i_lock... */
1777 inode_sleep_on_writeback(inode);
1778 spin_lock(&wb->list_lock);
1779 }
1780 spin_unlock(&wb->list_lock);
1781 blk_finish_plug(&plug);
1782
1783 return nr_pages - work->nr_pages;
1784}
1785
1786/*
1787 * Return the next wb_writeback_work struct that hasn't been processed yet.
1788 */
1789static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
1790{
1791 struct wb_writeback_work *work = NULL;
1792
1793 spin_lock_bh(&wb->work_lock);
1794 if (!list_empty(&wb->work_list)) {
1795 work = list_entry(wb->work_list.next,
1796 struct wb_writeback_work, list);
1797 list_del_init(&work->list);
1798 }
1799 spin_unlock_bh(&wb->work_lock);
1800 return work;
1801}
1802
1803/*
1804 * Add in the number of potentially dirty inodes, because each inode
1805 * write can dirty pagecache in the underlying blockdev.
1806 */
1807static unsigned long get_nr_dirty_pages(void)
1808{
1809 return global_node_page_state(NR_FILE_DIRTY) +
1810 global_node_page_state(NR_UNSTABLE_NFS) +
1811 get_nr_dirty_inodes();
1812}
1813
1814static long wb_check_background_flush(struct bdi_writeback *wb)
1815{
1816 if (wb_over_bg_thresh(wb)) {
1817
1818 struct wb_writeback_work work = {
1819 .nr_pages = LONG_MAX,
1820 .sync_mode = WB_SYNC_NONE,
1821 .for_background = 1,
1822 .range_cyclic = 1,
1823 .reason = WB_REASON_BACKGROUND,
1824 };
1825
1826 return wb_writeback(wb, &work);
1827 }
1828
1829 return 0;
1830}
1831
1832static long wb_check_old_data_flush(struct bdi_writeback *wb)
1833{
1834 unsigned long expired;
1835 long nr_pages;
1836
1837 /*
1838 * When set to zero, disable periodic writeback
1839 */
1840 if (!dirty_writeback_interval)
1841 return 0;
1842
1843 expired = wb->last_old_flush +
1844 msecs_to_jiffies(dirty_writeback_interval * 10);
1845 if (time_before(jiffies, expired))
1846 return 0;
1847
1848 wb->last_old_flush = jiffies;
1849 nr_pages = get_nr_dirty_pages();
1850
1851 if (nr_pages) {
1852 struct wb_writeback_work work = {
1853 .nr_pages = nr_pages,
1854 .sync_mode = WB_SYNC_NONE,
1855 .for_kupdate = 1,
1856 .range_cyclic = 1,
1857 .reason = WB_REASON_PERIODIC,
1858 };
1859
1860 return wb_writeback(wb, &work);
1861 }
1862
1863 return 0;
1864}
1865
1866/*
1867 * Retrieve work items and do the writeback they describe
1868 */
1869static long wb_do_writeback(struct bdi_writeback *wb)
1870{
1871 struct wb_writeback_work *work;
1872 long wrote = 0;
1873
1874 set_bit(WB_writeback_running, &wb->state);
1875 while ((work = get_next_work_item(wb)) != NULL) {
1876 struct wb_completion *done = work->done;
1877
1878 trace_writeback_exec(wb, work);
1879
1880 wrote += wb_writeback(wb, work);
1881
1882 if (work->auto_free)
1883 kfree(work);
1884 if (done && atomic_dec_and_test(&done->cnt))
1885 wake_up_all(&wb->bdi->wb_waitq);
1886 }
1887
1888 /*
1889 * Check for periodic writeback, kupdated() style
1890 */
1891 wrote += wb_check_old_data_flush(wb);
1892 wrote += wb_check_background_flush(wb);
1893 clear_bit(WB_writeback_running, &wb->state);
1894
1895 return wrote;
1896}
1897
1898/*
1899 * Handle writeback of dirty data for the device backed by this bdi. Also
1900 * reschedules periodically and does kupdated style flushing.
1901 */
1902void wb_workfn(struct work_struct *work)
1903{
1904 struct bdi_writeback *wb = container_of(to_delayed_work(work),
1905 struct bdi_writeback, dwork);
1906 long pages_written;
1907
1908 set_worker_desc("flush-%s", dev_name(wb->bdi->dev));
1909 current->flags |= PF_SWAPWRITE;
1910
1911 if (likely(!current_is_workqueue_rescuer() ||
1912 !test_bit(WB_registered, &wb->state))) {
1913 /*
1914 * The normal path. Keep writing back @wb until its
1915 * work_list is empty. Note that this path is also taken
1916 * if @wb is shutting down even when we're running off the
1917 * rescuer as work_list needs to be drained.
1918 */
1919 do {
1920 pages_written = wb_do_writeback(wb);
1921 trace_writeback_pages_written(pages_written);
1922 } while (!list_empty(&wb->work_list));
1923 } else {
1924 /*
1925 * bdi_wq can't get enough workers and we're running off
1926 * the emergency worker. Don't hog it. Hopefully, 1024 is
1927 * enough for efficient IO.
1928 */
1929 pages_written = writeback_inodes_wb(wb, 1024,
1930 WB_REASON_FORKER_THREAD);
1931 trace_writeback_pages_written(pages_written);
1932 }
1933
1934 if (!list_empty(&wb->work_list))
1935 mod_delayed_work(bdi_wq, &wb->dwork, 0);
1936 else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
1937 wb_wakeup_delayed(wb);
1938
1939 current->flags &= ~PF_SWAPWRITE;
1940}
1941
1942/*
1943 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
1944 * the whole world.
1945 */
1946void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
1947{
1948 struct backing_dev_info *bdi;
1949
1950 /*
1951 * If we are expecting writeback progress we must submit plugged IO.
1952 */
1953 if (blk_needs_flush_plug(current))
1954 blk_schedule_flush_plug(current);
1955
1956 if (!nr_pages)
1957 nr_pages = get_nr_dirty_pages();
1958
1959 rcu_read_lock();
1960 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1961 struct bdi_writeback *wb;
1962
1963 if (!bdi_has_dirty_io(bdi))
1964 continue;
1965
1966 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
1967 wb_start_writeback(wb, wb_split_bdi_pages(wb, nr_pages),
1968 false, reason);
1969 }
1970 rcu_read_unlock();
1971}
1972
1973/*
1974 * Wake up bdi's periodically to make sure dirtytime inodes gets
1975 * written back periodically. We deliberately do *not* check the
1976 * b_dirtytime list in wb_has_dirty_io(), since this would cause the
1977 * kernel to be constantly waking up once there are any dirtytime
1978 * inodes on the system. So instead we define a separate delayed work
1979 * function which gets called much more rarely. (By default, only
1980 * once every 12 hours.)
1981 *
1982 * If there is any other write activity going on in the file system,
1983 * this function won't be necessary. But if the only thing that has
1984 * happened on the file system is a dirtytime inode caused by an atime
1985 * update, we need this infrastructure below to make sure that inode
1986 * eventually gets pushed out to disk.
1987 */
1988static void wakeup_dirtytime_writeback(struct work_struct *w);
1989static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
1990
1991static void wakeup_dirtytime_writeback(struct work_struct *w)
1992{
1993 struct backing_dev_info *bdi;
1994
1995 rcu_read_lock();
1996 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1997 struct bdi_writeback *wb;
1998
1999 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2000 if (!list_empty(&wb->b_dirty_time))
2001 wb_wakeup(wb);
2002 }
2003 rcu_read_unlock();
2004 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2005}
2006
2007static int __init start_dirtytime_writeback(void)
2008{
2009 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2010 return 0;
2011}
2012__initcall(start_dirtytime_writeback);
2013
2014int dirtytime_interval_handler(struct ctl_table *table, int write,
2015 void __user *buffer, size_t *lenp, loff_t *ppos)
2016{
2017 int ret;
2018
2019 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
2020 if (ret == 0 && write)
2021 mod_delayed_work(system_wq, &dirtytime_work, 0);
2022 return ret;
2023}
2024
2025static noinline void block_dump___mark_inode_dirty(struct inode *inode)
2026{
2027 if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
2028 struct dentry *dentry;
2029 const char *name = "?";
2030
2031 dentry = d_find_alias(inode);
2032 if (dentry) {
2033 spin_lock(&dentry->d_lock);
2034 name = (const char *) dentry->d_name.name;
2035 }
2036 printk(KERN_DEBUG
2037 "%s(%d): dirtied inode %lu (%s) on %s\n",
2038 current->comm, task_pid_nr(current), inode->i_ino,
2039 name, inode->i_sb->s_id);
2040 if (dentry) {
2041 spin_unlock(&dentry->d_lock);
2042 dput(dentry);
2043 }
2044 }
2045}
2046
2047/**
2048 * __mark_inode_dirty - internal function
2049 * @inode: inode to mark
2050 * @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
2051 * Mark an inode as dirty. Callers should use mark_inode_dirty or
2052 * mark_inode_dirty_sync.
2053 *
2054 * Put the inode on the super block's dirty list.
2055 *
2056 * CAREFUL! We mark it dirty unconditionally, but move it onto the
2057 * dirty list only if it is hashed or if it refers to a blockdev.
2058 * If it was not hashed, it will never be added to the dirty list
2059 * even if it is later hashed, as it will have been marked dirty already.
2060 *
2061 * In short, make sure you hash any inodes _before_ you start marking
2062 * them dirty.
2063 *
2064 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2065 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
2066 * the kernel-internal blockdev inode represents the dirtying time of the
2067 * blockdev's pages. This is why for I_DIRTY_PAGES we always use
2068 * page->mapping->host, so the page-dirtying time is recorded in the internal
2069 * blockdev inode.
2070 */
2071void __mark_inode_dirty(struct inode *inode, int flags)
2072{
2073#define I_DIRTY_INODE (I_DIRTY_SYNC | I_DIRTY_DATASYNC)
2074 struct super_block *sb = inode->i_sb;
2075 int dirtytime;
2076
2077 trace_writeback_mark_inode_dirty(inode, flags);
2078
2079 /*
2080 * Don't do this for I_DIRTY_PAGES - that doesn't actually
2081 * dirty the inode itself
2082 */
2083 if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_TIME)) {
2084 trace_writeback_dirty_inode_start(inode, flags);
2085
2086 if (sb->s_op->dirty_inode)
2087 sb->s_op->dirty_inode(inode, flags);
2088
2089 trace_writeback_dirty_inode(inode, flags);
2090 }
2091 if (flags & I_DIRTY_INODE)
2092 flags &= ~I_DIRTY_TIME;
2093 dirtytime = flags & I_DIRTY_TIME;
2094
2095 /*
2096 * Paired with smp_mb() in __writeback_single_inode() for the
2097 * following lockless i_state test. See there for details.
2098 */
2099 smp_mb();
2100
2101 if (((inode->i_state & flags) == flags) ||
2102 (dirtytime && (inode->i_state & I_DIRTY_INODE)))
2103 return;
2104
2105 if (unlikely(block_dump))
2106 block_dump___mark_inode_dirty(inode);
2107
2108 spin_lock(&inode->i_lock);
2109 if (dirtytime && (inode->i_state & I_DIRTY_INODE))
2110 goto out_unlock_inode;
2111 if ((inode->i_state & flags) != flags) {
2112 const int was_dirty = inode->i_state & I_DIRTY;
2113
2114 inode_attach_wb(inode, NULL);
2115
2116 if (flags & I_DIRTY_INODE)
2117 inode->i_state &= ~I_DIRTY_TIME;
2118 inode->i_state |= flags;
2119
2120 /*
2121 * If the inode is being synced, just update its dirty state.
2122 * The unlocker will place the inode on the appropriate
2123 * superblock list, based upon its state.
2124 */
2125 if (inode->i_state & I_SYNC)
2126 goto out_unlock_inode;
2127
2128 /*
2129 * Only add valid (hashed) inodes to the superblock's
2130 * dirty list. Add blockdev inodes as well.
2131 */
2132 if (!S_ISBLK(inode->i_mode)) {
2133 if (inode_unhashed(inode))
2134 goto out_unlock_inode;
2135 }
2136 if (inode->i_state & I_FREEING)
2137 goto out_unlock_inode;
2138
2139 /*
2140 * If the inode was already on b_dirty/b_io/b_more_io, don't
2141 * reposition it (that would break b_dirty time-ordering).
2142 */
2143 if (!was_dirty) {
2144 struct bdi_writeback *wb;
2145 struct list_head *dirty_list;
2146 bool wakeup_bdi = false;
2147
2148 wb = locked_inode_to_wb_and_lock_list(inode);
2149
2150 WARN(bdi_cap_writeback_dirty(wb->bdi) &&
2151 !test_bit(WB_registered, &wb->state),
2152 "bdi-%s not registered\n", wb->bdi->name);
2153
2154 inode->dirtied_when = jiffies;
2155 if (dirtytime)
2156 inode->dirtied_time_when = jiffies;
2157
2158 if (inode->i_state & (I_DIRTY_INODE | I_DIRTY_PAGES))
2159 dirty_list = &wb->b_dirty;
2160 else
2161 dirty_list = &wb->b_dirty_time;
2162
2163 wakeup_bdi = inode_io_list_move_locked(inode, wb,
2164 dirty_list);
2165
2166 spin_unlock(&wb->list_lock);
2167 trace_writeback_dirty_inode_enqueue(inode);
2168
2169 /*
2170 * If this is the first dirty inode for this bdi,
2171 * we have to wake-up the corresponding bdi thread
2172 * to make sure background write-back happens
2173 * later.
2174 */
2175 if (bdi_cap_writeback_dirty(wb->bdi) && wakeup_bdi)
2176 wb_wakeup_delayed(wb);
2177 return;
2178 }
2179 }
2180out_unlock_inode:
2181 spin_unlock(&inode->i_lock);
2182
2183#undef I_DIRTY_INODE
2184}
2185EXPORT_SYMBOL(__mark_inode_dirty);
2186
2187/*
2188 * The @s_sync_lock is used to serialise concurrent sync operations
2189 * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2190 * Concurrent callers will block on the s_sync_lock rather than doing contending
2191 * walks. The queueing maintains sync(2) required behaviour as all the IO that
2192 * has been issued up to the time this function is enter is guaranteed to be
2193 * completed by the time we have gained the lock and waited for all IO that is
2194 * in progress regardless of the order callers are granted the lock.
2195 */
2196static void wait_sb_inodes(struct super_block *sb)
2197{
2198 LIST_HEAD(sync_list);
2199
2200 /*
2201 * We need to be protected against the filesystem going from
2202 * r/o to r/w or vice versa.
2203 */
2204 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2205
2206 mutex_lock(&sb->s_sync_lock);
2207
2208 /*
2209 * Splice the writeback list onto a temporary list to avoid waiting on
2210 * inodes that have started writeback after this point.
2211 *
2212 * Use rcu_read_lock() to keep the inodes around until we have a
2213 * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2214 * the local list because inodes can be dropped from either by writeback
2215 * completion.
2216 */
2217 rcu_read_lock();
2218 spin_lock_irq(&sb->s_inode_wblist_lock);
2219 list_splice_init(&sb->s_inodes_wb, &sync_list);
2220
2221 /*
2222 * Data integrity sync. Must wait for all pages under writeback, because
2223 * there may have been pages dirtied before our sync call, but which had
2224 * writeout started before we write it out. In which case, the inode
2225 * may not be on the dirty list, but we still have to wait for that
2226 * writeout.
2227 */
2228 while (!list_empty(&sync_list)) {
2229 struct inode *inode = list_first_entry(&sync_list, struct inode,
2230 i_wb_list);
2231 struct address_space *mapping = inode->i_mapping;
2232
2233 /*
2234 * Move each inode back to the wb list before we drop the lock
2235 * to preserve consistency between i_wb_list and the mapping
2236 * writeback tag. Writeback completion is responsible to remove
2237 * the inode from either list once the writeback tag is cleared.
2238 */
2239 list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
2240
2241 /*
2242 * The mapping can appear untagged while still on-list since we
2243 * do not have the mapping lock. Skip it here, wb completion
2244 * will remove it.
2245 */
2246 if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2247 continue;
2248
2249 spin_unlock_irq(&sb->s_inode_wblist_lock);
2250
2251 spin_lock(&inode->i_lock);
2252 if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
2253 spin_unlock(&inode->i_lock);
2254
2255 spin_lock_irq(&sb->s_inode_wblist_lock);
2256 continue;
2257 }
2258 __iget(inode);
2259 spin_unlock(&inode->i_lock);
2260 rcu_read_unlock();
2261
2262 /*
2263 * We keep the error status of individual mapping so that
2264 * applications can catch the writeback error using fsync(2).
2265 * See filemap_fdatawait_keep_errors() for details.
2266 */
2267 filemap_fdatawait_keep_errors(mapping);
2268
2269 cond_resched();
2270
2271 iput(inode);
2272
2273 rcu_read_lock();
2274 spin_lock_irq(&sb->s_inode_wblist_lock);
2275 }
2276 spin_unlock_irq(&sb->s_inode_wblist_lock);
2277 rcu_read_unlock();
2278 mutex_unlock(&sb->s_sync_lock);
2279}
2280
2281static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2282 enum wb_reason reason, bool skip_if_busy)
2283{
2284 DEFINE_WB_COMPLETION_ONSTACK(done);
2285 struct wb_writeback_work work = {
2286 .sb = sb,
2287 .sync_mode = WB_SYNC_NONE,
2288 .tagged_writepages = 1,
2289 .done = &done,
2290 .nr_pages = nr,
2291 .reason = reason,
2292 };
2293 struct backing_dev_info *bdi = sb->s_bdi;
2294
2295 if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
2296 return;
2297 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2298
2299 bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
2300 wb_wait_for_completion(bdi, &done);
2301}
2302
2303/**
2304 * writeback_inodes_sb_nr - writeback dirty inodes from given super_block
2305 * @sb: the superblock
2306 * @nr: the number of pages to write
2307 * @reason: reason why some writeback work initiated
2308 *
2309 * Start writeback on some inodes on this super_block. No guarantees are made
2310 * on how many (if any) will be written, and this function does not wait
2311 * for IO completion of submitted IO.
2312 */
2313void writeback_inodes_sb_nr(struct super_block *sb,
2314 unsigned long nr,
2315 enum wb_reason reason)
2316{
2317 __writeback_inodes_sb_nr(sb, nr, reason, false);
2318}
2319EXPORT_SYMBOL(writeback_inodes_sb_nr);
2320
2321/**
2322 * writeback_inodes_sb - writeback dirty inodes from given super_block
2323 * @sb: the superblock
2324 * @reason: reason why some writeback work was initiated
2325 *
2326 * Start writeback on some inodes on this super_block. No guarantees are made
2327 * on how many (if any) will be written, and this function does not wait
2328 * for IO completion of submitted IO.
2329 */
2330void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2331{
2332 return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2333}
2334EXPORT_SYMBOL(writeback_inodes_sb);
2335
2336/**
2337 * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
2338 * @sb: the superblock
2339 * @nr: the number of pages to write
2340 * @reason: the reason of writeback
2341 *
2342 * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
2343 * Returns 1 if writeback was started, 0 if not.
2344 */
2345bool try_to_writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2346 enum wb_reason reason)
2347{
2348 if (!down_read_trylock(&sb->s_umount))
2349 return false;
2350
2351 __writeback_inodes_sb_nr(sb, nr, reason, true);
2352 up_read(&sb->s_umount);
2353 return true;
2354}
2355EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
2356
2357/**
2358 * try_to_writeback_inodes_sb - try to start writeback if none underway
2359 * @sb: the superblock
2360 * @reason: reason why some writeback work was initiated
2361 *
2362 * Implement by try_to_writeback_inodes_sb_nr()
2363 * Returns 1 if writeback was started, 0 if not.
2364 */
2365bool try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2366{
2367 return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2368}
2369EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2370
2371/**
2372 * sync_inodes_sb - sync sb inode pages
2373 * @sb: the superblock
2374 *
2375 * This function writes and waits on any dirty inode belonging to this
2376 * super_block.
2377 */
2378void sync_inodes_sb(struct super_block *sb)
2379{
2380 DEFINE_WB_COMPLETION_ONSTACK(done);
2381 struct wb_writeback_work work = {
2382 .sb = sb,
2383 .sync_mode = WB_SYNC_ALL,
2384 .nr_pages = LONG_MAX,
2385 .range_cyclic = 0,
2386 .done = &done,
2387 .reason = WB_REASON_SYNC,
2388 .for_sync = 1,
2389 };
2390 struct backing_dev_info *bdi = sb->s_bdi;
2391
2392 /*
2393 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
2394 * inodes under writeback and I_DIRTY_TIME inodes ignored by
2395 * bdi_has_dirty() need to be written out too.
2396 */
2397 if (bdi == &noop_backing_dev_info)
2398 return;
2399 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2400
2401 bdi_split_work_to_wbs(bdi, &work, false);
2402 wb_wait_for_completion(bdi, &done);
2403
2404 wait_sb_inodes(sb);
2405}
2406EXPORT_SYMBOL(sync_inodes_sb);
2407
2408/**
2409 * write_inode_now - write an inode to disk
2410 * @inode: inode to write to disk
2411 * @sync: whether the write should be synchronous or not
2412 *
2413 * This function commits an inode to disk immediately if it is dirty. This is
2414 * primarily needed by knfsd.
2415 *
2416 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
2417 */
2418int write_inode_now(struct inode *inode, int sync)
2419{
2420 struct writeback_control wbc = {
2421 .nr_to_write = LONG_MAX,
2422 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2423 .range_start = 0,
2424 .range_end = LLONG_MAX,
2425 };
2426
2427 if (!mapping_cap_writeback_dirty(inode->i_mapping))
2428 wbc.nr_to_write = 0;
2429
2430 might_sleep();
2431 return writeback_single_inode(inode, &wbc);
2432}
2433EXPORT_SYMBOL(write_inode_now);
2434
2435/**
2436 * sync_inode - write an inode and its pages to disk.
2437 * @inode: the inode to sync
2438 * @wbc: controls the writeback mode
2439 *
2440 * sync_inode() will write an inode and its pages to disk. It will also
2441 * correctly update the inode on its superblock's dirty inode lists and will
2442 * update inode->i_state.
2443 *
2444 * The caller must have a ref on the inode.
2445 */
2446int sync_inode(struct inode *inode, struct writeback_control *wbc)
2447{
2448 return writeback_single_inode(inode, wbc);
2449}
2450EXPORT_SYMBOL(sync_inode);
2451
2452/**
2453 * sync_inode_metadata - write an inode to disk
2454 * @inode: the inode to sync
2455 * @wait: wait for I/O to complete.
2456 *
2457 * Write an inode to disk and adjust its dirty state after completion.
2458 *
2459 * Note: only writes the actual inode, no associated data or other metadata.
2460 */
2461int sync_inode_metadata(struct inode *inode, int wait)
2462{
2463 struct writeback_control wbc = {
2464 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2465 .nr_to_write = 0, /* metadata-only */
2466 };
2467
2468 return sync_inode(inode, &wbc);
2469}
2470EXPORT_SYMBOL(sync_inode_metadata);
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * fs/fs-writeback.c
4 *
5 * Copyright (C) 2002, Linus Torvalds.
6 *
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.
11 *
12 * 10Apr2002 Andrew Morton
13 * Split out of fs/inode.c
14 * Additions for address_space-based writeback
15 */
16
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>
22#include <linux/fs.h>
23#include <linux/mm.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>
32#include "internal.h"
33
34/*
35 * 4MB minimal write chunk size
36 */
37#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_SHIFT - 10))
38
39/*
40 * Passed into wb_writeback(), essentially a subset of writeback_control
41 */
42struct wb_writeback_work {
43 long nr_pages;
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? */
53
54 struct list_head list; /* pending work list */
55 struct wb_completion *done; /* set if the caller waits */
56};
57
58/*
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.
67 */
68unsigned int dirtytime_expire_interval = 12 * 60 * 60;
69
70static inline struct inode *wb_inode(struct list_head *head)
71{
72 return list_entry(head, struct inode, i_io_list);
73}
74
75/*
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.
79 */
80#define CREATE_TRACE_POINTS
81#include <trace/events/writeback.h>
82
83EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
84
85static bool wb_io_lists_populated(struct bdi_writeback *wb)
86{
87 if (wb_has_dirty_io(wb)) {
88 return false;
89 } else {
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);
94 return true;
95 }
96}
97
98static void wb_io_lists_depopulated(struct bdi_writeback *wb)
99{
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);
105 }
106}
107
108/**
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}
113 *
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.
117 */
118static bool inode_io_list_move_locked(struct inode *inode,
119 struct bdi_writeback *wb,
120 struct list_head *head)
121{
122 assert_spin_locked(&wb->list_lock);
123 assert_spin_locked(&inode->i_lock);
124 WARN_ON_ONCE(inode->i_state & I_FREEING);
125
126 list_move(&inode->i_io_list, head);
127
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);
131
132 wb_io_lists_depopulated(wb);
133 return false;
134}
135
136static void wb_wakeup(struct bdi_writeback *wb)
137{
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);
142}
143
144/*
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.
150 *
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.
154 *
155 * We have to be careful not to postpone flush work if it is scheduled for
156 * earlier. Thus we use queue_delayed_work().
157 */
158static void wb_wakeup_delayed(struct bdi_writeback *wb)
159{
160 unsigned long timeout;
161
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);
167}
168
169static void finish_writeback_work(struct bdi_writeback *wb,
170 struct wb_writeback_work *work)
171{
172 struct wb_completion *done = work->done;
173
174 if (work->auto_free)
175 kfree(work);
176 if (done) {
177 wait_queue_head_t *waitq = done->waitq;
178
179 /* @done can't be accessed after the following dec */
180 if (atomic_dec_and_test(&done->cnt))
181 wake_up_all(waitq);
182 }
183}
184
185static void wb_queue_work(struct bdi_writeback *wb,
186 struct wb_writeback_work *work)
187{
188 trace_writeback_queue(wb, work);
189
190 if (work->done)
191 atomic_inc(&work->done->cnt);
192
193 spin_lock_irq(&wb->work_lock);
194
195 if (test_bit(WB_registered, &wb->state)) {
196 list_add_tail(&work->list, &wb->work_list);
197 mod_delayed_work(bdi_wq, &wb->dwork, 0);
198 } else
199 finish_writeback_work(wb, work);
200
201 spin_unlock_irq(&wb->work_lock);
202}
203
204/**
205 * wb_wait_for_completion - wait for completion of bdi_writeback_works
206 * @done: target wb_completion
207 *
208 * Wait for one or more work items issued to @bdi with their ->done field
209 * set to @done, which should have been initialized with
210 * DEFINE_WB_COMPLETION(). This function returns after all such work items
211 * are completed. Work items which are waited upon aren't freed
212 * automatically on completion.
213 */
214void wb_wait_for_completion(struct wb_completion *done)
215{
216 atomic_dec(&done->cnt); /* put down the initial count */
217 wait_event(*done->waitq, !atomic_read(&done->cnt));
218}
219
220#ifdef CONFIG_CGROUP_WRITEBACK
221
222/*
223 * Parameters for foreign inode detection, see wbc_detach_inode() to see
224 * how they're used.
225 *
226 * These paramters are inherently heuristical as the detection target
227 * itself is fuzzy. All we want to do is detaching an inode from the
228 * current owner if it's being written to by some other cgroups too much.
229 *
230 * The current cgroup writeback is built on the assumption that multiple
231 * cgroups writing to the same inode concurrently is very rare and a mode
232 * of operation which isn't well supported. As such, the goal is not
233 * taking too long when a different cgroup takes over an inode while
234 * avoiding too aggressive flip-flops from occasional foreign writes.
235 *
236 * We record, very roughly, 2s worth of IO time history and if more than
237 * half of that is foreign, trigger the switch. The recording is quantized
238 * to 16 slots. To avoid tiny writes from swinging the decision too much,
239 * writes smaller than 1/8 of avg size are ignored.
240 */
241#define WB_FRN_TIME_SHIFT 13 /* 1s = 2^13, upto 8 secs w/ 16bit */
242#define WB_FRN_TIME_AVG_SHIFT 3 /* avg = avg * 7/8 + new * 1/8 */
243#define WB_FRN_TIME_CUT_DIV 8 /* ignore rounds < avg / 8 */
244#define WB_FRN_TIME_PERIOD (2 * (1 << WB_FRN_TIME_SHIFT)) /* 2s */
245
246#define WB_FRN_HIST_SLOTS 16 /* inode->i_wb_frn_history is 16bit */
247#define WB_FRN_HIST_UNIT (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
248 /* each slot's duration is 2s / 16 */
249#define WB_FRN_HIST_THR_SLOTS (WB_FRN_HIST_SLOTS / 2)
250 /* if foreign slots >= 8, switch */
251#define WB_FRN_HIST_MAX_SLOTS (WB_FRN_HIST_THR_SLOTS / 2 + 1)
252 /* one round can affect upto 5 slots */
253#define WB_FRN_MAX_IN_FLIGHT 1024 /* don't queue too many concurrently */
254
255/*
256 * Maximum inodes per isw. A specific value has been chosen to make
257 * struct inode_switch_wbs_context fit into 1024 bytes kmalloc.
258 */
259#define WB_MAX_INODES_PER_ISW ((1024UL - sizeof(struct inode_switch_wbs_context)) \
260 / sizeof(struct inode *))
261
262static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
263static struct workqueue_struct *isw_wq;
264
265void __inode_attach_wb(struct inode *inode, struct folio *folio)
266{
267 struct backing_dev_info *bdi = inode_to_bdi(inode);
268 struct bdi_writeback *wb = NULL;
269
270 if (inode_cgwb_enabled(inode)) {
271 struct cgroup_subsys_state *memcg_css;
272
273 if (folio) {
274 memcg_css = mem_cgroup_css_from_folio(folio);
275 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
276 } else {
277 /* must pin memcg_css, see wb_get_create() */
278 memcg_css = task_get_css(current, memory_cgrp_id);
279 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
280 css_put(memcg_css);
281 }
282 }
283
284 if (!wb)
285 wb = &bdi->wb;
286
287 /*
288 * There may be multiple instances of this function racing to
289 * update the same inode. Use cmpxchg() to tell the winner.
290 */
291 if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
292 wb_put(wb);
293}
294EXPORT_SYMBOL_GPL(__inode_attach_wb);
295
296/**
297 * inode_cgwb_move_to_attached - put the inode onto wb->b_attached list
298 * @inode: inode of interest with i_lock held
299 * @wb: target bdi_writeback
300 *
301 * Remove the inode from wb's io lists and if necessarily put onto b_attached
302 * list. Only inodes attached to cgwb's are kept on this list.
303 */
304static void inode_cgwb_move_to_attached(struct inode *inode,
305 struct bdi_writeback *wb)
306{
307 assert_spin_locked(&wb->list_lock);
308 assert_spin_locked(&inode->i_lock);
309 WARN_ON_ONCE(inode->i_state & I_FREEING);
310
311 inode->i_state &= ~I_SYNC_QUEUED;
312 if (wb != &wb->bdi->wb)
313 list_move(&inode->i_io_list, &wb->b_attached);
314 else
315 list_del_init(&inode->i_io_list);
316 wb_io_lists_depopulated(wb);
317}
318
319/**
320 * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
321 * @inode: inode of interest with i_lock held
322 *
323 * Returns @inode's wb with its list_lock held. @inode->i_lock must be
324 * held on entry and is released on return. The returned wb is guaranteed
325 * to stay @inode's associated wb until its list_lock is released.
326 */
327static struct bdi_writeback *
328locked_inode_to_wb_and_lock_list(struct inode *inode)
329 __releases(&inode->i_lock)
330 __acquires(&wb->list_lock)
331{
332 while (true) {
333 struct bdi_writeback *wb = inode_to_wb(inode);
334
335 /*
336 * inode_to_wb() association is protected by both
337 * @inode->i_lock and @wb->list_lock but list_lock nests
338 * outside i_lock. Drop i_lock and verify that the
339 * association hasn't changed after acquiring list_lock.
340 */
341 wb_get(wb);
342 spin_unlock(&inode->i_lock);
343 spin_lock(&wb->list_lock);
344
345 /* i_wb may have changed inbetween, can't use inode_to_wb() */
346 if (likely(wb == inode->i_wb)) {
347 wb_put(wb); /* @inode already has ref */
348 return wb;
349 }
350
351 spin_unlock(&wb->list_lock);
352 wb_put(wb);
353 cpu_relax();
354 spin_lock(&inode->i_lock);
355 }
356}
357
358/**
359 * inode_to_wb_and_lock_list - determine an inode's wb and lock it
360 * @inode: inode of interest
361 *
362 * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
363 * on entry.
364 */
365static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
366 __acquires(&wb->list_lock)
367{
368 spin_lock(&inode->i_lock);
369 return locked_inode_to_wb_and_lock_list(inode);
370}
371
372struct inode_switch_wbs_context {
373 struct rcu_work work;
374
375 /*
376 * Multiple inodes can be switched at once. The switching procedure
377 * consists of two parts, separated by a RCU grace period. To make
378 * sure that the second part is executed for each inode gone through
379 * the first part, all inode pointers are placed into a NULL-terminated
380 * array embedded into struct inode_switch_wbs_context. Otherwise
381 * an inode could be left in a non-consistent state.
382 */
383 struct bdi_writeback *new_wb;
384 struct inode *inodes[];
385};
386
387static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
388{
389 down_write(&bdi->wb_switch_rwsem);
390}
391
392static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
393{
394 up_write(&bdi->wb_switch_rwsem);
395}
396
397static bool inode_do_switch_wbs(struct inode *inode,
398 struct bdi_writeback *old_wb,
399 struct bdi_writeback *new_wb)
400{
401 struct address_space *mapping = inode->i_mapping;
402 XA_STATE(xas, &mapping->i_pages, 0);
403 struct folio *folio;
404 bool switched = false;
405
406 spin_lock(&inode->i_lock);
407 xa_lock_irq(&mapping->i_pages);
408
409 /*
410 * Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
411 * path owns the inode and we shouldn't modify ->i_io_list.
412 */
413 if (unlikely(inode->i_state & (I_FREEING | I_WILL_FREE)))
414 goto skip_switch;
415
416 trace_inode_switch_wbs(inode, old_wb, new_wb);
417
418 /*
419 * Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
420 * to possibly dirty folios while PAGECACHE_TAG_WRITEBACK points to
421 * folios actually under writeback.
422 */
423 xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
424 if (folio_test_dirty(folio)) {
425 long nr = folio_nr_pages(folio);
426 wb_stat_mod(old_wb, WB_RECLAIMABLE, -nr);
427 wb_stat_mod(new_wb, WB_RECLAIMABLE, nr);
428 }
429 }
430
431 xas_set(&xas, 0);
432 xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_WRITEBACK) {
433 long nr = folio_nr_pages(folio);
434 WARN_ON_ONCE(!folio_test_writeback(folio));
435 wb_stat_mod(old_wb, WB_WRITEBACK, -nr);
436 wb_stat_mod(new_wb, WB_WRITEBACK, nr);
437 }
438
439 if (mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK)) {
440 atomic_dec(&old_wb->writeback_inodes);
441 atomic_inc(&new_wb->writeback_inodes);
442 }
443
444 wb_get(new_wb);
445
446 /*
447 * Transfer to @new_wb's IO list if necessary. If the @inode is dirty,
448 * the specific list @inode was on is ignored and the @inode is put on
449 * ->b_dirty which is always correct including from ->b_dirty_time.
450 * The transfer preserves @inode->dirtied_when ordering. If the @inode
451 * was clean, it means it was on the b_attached list, so move it onto
452 * the b_attached list of @new_wb.
453 */
454 if (!list_empty(&inode->i_io_list)) {
455 inode->i_wb = new_wb;
456
457 if (inode->i_state & I_DIRTY_ALL) {
458 struct inode *pos;
459
460 list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
461 if (time_after_eq(inode->dirtied_when,
462 pos->dirtied_when))
463 break;
464 inode_io_list_move_locked(inode, new_wb,
465 pos->i_io_list.prev);
466 } else {
467 inode_cgwb_move_to_attached(inode, new_wb);
468 }
469 } else {
470 inode->i_wb = new_wb;
471 }
472
473 /* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
474 inode->i_wb_frn_winner = 0;
475 inode->i_wb_frn_avg_time = 0;
476 inode->i_wb_frn_history = 0;
477 switched = true;
478skip_switch:
479 /*
480 * Paired with load_acquire in unlocked_inode_to_wb_begin() and
481 * ensures that the new wb is visible if they see !I_WB_SWITCH.
482 */
483 smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
484
485 xa_unlock_irq(&mapping->i_pages);
486 spin_unlock(&inode->i_lock);
487
488 return switched;
489}
490
491static void inode_switch_wbs_work_fn(struct work_struct *work)
492{
493 struct inode_switch_wbs_context *isw =
494 container_of(to_rcu_work(work), struct inode_switch_wbs_context, work);
495 struct backing_dev_info *bdi = inode_to_bdi(isw->inodes[0]);
496 struct bdi_writeback *old_wb = isw->inodes[0]->i_wb;
497 struct bdi_writeback *new_wb = isw->new_wb;
498 unsigned long nr_switched = 0;
499 struct inode **inodep;
500
501 /*
502 * If @inode switches cgwb membership while sync_inodes_sb() is
503 * being issued, sync_inodes_sb() might miss it. Synchronize.
504 */
505 down_read(&bdi->wb_switch_rwsem);
506
507 /*
508 * By the time control reaches here, RCU grace period has passed
509 * since I_WB_SWITCH assertion and all wb stat update transactions
510 * between unlocked_inode_to_wb_begin/end() are guaranteed to be
511 * synchronizing against the i_pages lock.
512 *
513 * Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
514 * gives us exclusion against all wb related operations on @inode
515 * including IO list manipulations and stat updates.
516 */
517 if (old_wb < new_wb) {
518 spin_lock(&old_wb->list_lock);
519 spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
520 } else {
521 spin_lock(&new_wb->list_lock);
522 spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
523 }
524
525 for (inodep = isw->inodes; *inodep; inodep++) {
526 WARN_ON_ONCE((*inodep)->i_wb != old_wb);
527 if (inode_do_switch_wbs(*inodep, old_wb, new_wb))
528 nr_switched++;
529 }
530
531 spin_unlock(&new_wb->list_lock);
532 spin_unlock(&old_wb->list_lock);
533
534 up_read(&bdi->wb_switch_rwsem);
535
536 if (nr_switched) {
537 wb_wakeup(new_wb);
538 wb_put_many(old_wb, nr_switched);
539 }
540
541 for (inodep = isw->inodes; *inodep; inodep++)
542 iput(*inodep);
543 wb_put(new_wb);
544 kfree(isw);
545 atomic_dec(&isw_nr_in_flight);
546}
547
548static bool inode_prepare_wbs_switch(struct inode *inode,
549 struct bdi_writeback *new_wb)
550{
551 /*
552 * Paired with smp_mb() in cgroup_writeback_umount().
553 * isw_nr_in_flight must be increased before checking SB_ACTIVE and
554 * grabbing an inode, otherwise isw_nr_in_flight can be observed as 0
555 * in cgroup_writeback_umount() and the isw_wq will be not flushed.
556 */
557 smp_mb();
558
559 if (IS_DAX(inode))
560 return false;
561
562 /* while holding I_WB_SWITCH, no one else can update the association */
563 spin_lock(&inode->i_lock);
564 if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
565 inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) ||
566 inode_to_wb(inode) == new_wb) {
567 spin_unlock(&inode->i_lock);
568 return false;
569 }
570 inode->i_state |= I_WB_SWITCH;
571 __iget(inode);
572 spin_unlock(&inode->i_lock);
573
574 return true;
575}
576
577/**
578 * inode_switch_wbs - change the wb association of an inode
579 * @inode: target inode
580 * @new_wb_id: ID of the new wb
581 *
582 * Switch @inode's wb association to the wb identified by @new_wb_id. The
583 * switching is performed asynchronously and may fail silently.
584 */
585static void inode_switch_wbs(struct inode *inode, int new_wb_id)
586{
587 struct backing_dev_info *bdi = inode_to_bdi(inode);
588 struct cgroup_subsys_state *memcg_css;
589 struct inode_switch_wbs_context *isw;
590
591 /* noop if seems to be already in progress */
592 if (inode->i_state & I_WB_SWITCH)
593 return;
594
595 /* avoid queueing a new switch if too many are already in flight */
596 if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
597 return;
598
599 isw = kzalloc(struct_size(isw, inodes, 2), GFP_ATOMIC);
600 if (!isw)
601 return;
602
603 atomic_inc(&isw_nr_in_flight);
604
605 /* find and pin the new wb */
606 rcu_read_lock();
607 memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
608 if (memcg_css && !css_tryget(memcg_css))
609 memcg_css = NULL;
610 rcu_read_unlock();
611 if (!memcg_css)
612 goto out_free;
613
614 isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
615 css_put(memcg_css);
616 if (!isw->new_wb)
617 goto out_free;
618
619 if (!inode_prepare_wbs_switch(inode, isw->new_wb))
620 goto out_free;
621
622 isw->inodes[0] = inode;
623
624 /*
625 * In addition to synchronizing among switchers, I_WB_SWITCH tells
626 * the RCU protected stat update paths to grab the i_page
627 * lock so that stat transfer can synchronize against them.
628 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
629 */
630 INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
631 queue_rcu_work(isw_wq, &isw->work);
632 return;
633
634out_free:
635 atomic_dec(&isw_nr_in_flight);
636 if (isw->new_wb)
637 wb_put(isw->new_wb);
638 kfree(isw);
639}
640
641static bool isw_prepare_wbs_switch(struct inode_switch_wbs_context *isw,
642 struct list_head *list, int *nr)
643{
644 struct inode *inode;
645
646 list_for_each_entry(inode, list, i_io_list) {
647 if (!inode_prepare_wbs_switch(inode, isw->new_wb))
648 continue;
649
650 isw->inodes[*nr] = inode;
651 (*nr)++;
652
653 if (*nr >= WB_MAX_INODES_PER_ISW - 1)
654 return true;
655 }
656 return false;
657}
658
659/**
660 * cleanup_offline_cgwb - detach associated inodes
661 * @wb: target wb
662 *
663 * Switch all inodes attached to @wb to a nearest living ancestor's wb in order
664 * to eventually release the dying @wb. Returns %true if not all inodes were
665 * switched and the function has to be restarted.
666 */
667bool cleanup_offline_cgwb(struct bdi_writeback *wb)
668{
669 struct cgroup_subsys_state *memcg_css;
670 struct inode_switch_wbs_context *isw;
671 int nr;
672 bool restart = false;
673
674 isw = kzalloc(struct_size(isw, inodes, WB_MAX_INODES_PER_ISW),
675 GFP_KERNEL);
676 if (!isw)
677 return restart;
678
679 atomic_inc(&isw_nr_in_flight);
680
681 for (memcg_css = wb->memcg_css->parent; memcg_css;
682 memcg_css = memcg_css->parent) {
683 isw->new_wb = wb_get_create(wb->bdi, memcg_css, GFP_KERNEL);
684 if (isw->new_wb)
685 break;
686 }
687 if (unlikely(!isw->new_wb))
688 isw->new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */
689
690 nr = 0;
691 spin_lock(&wb->list_lock);
692 /*
693 * In addition to the inodes that have completed writeback, also switch
694 * cgwbs for those inodes only with dirty timestamps. Otherwise, those
695 * inodes won't be written back for a long time when lazytime is
696 * enabled, and thus pinning the dying cgwbs. It won't break the
697 * bandwidth restrictions, as writeback of inode metadata is not
698 * accounted for.
699 */
700 restart = isw_prepare_wbs_switch(isw, &wb->b_attached, &nr);
701 if (!restart)
702 restart = isw_prepare_wbs_switch(isw, &wb->b_dirty_time, &nr);
703 spin_unlock(&wb->list_lock);
704
705 /* no attached inodes? bail out */
706 if (nr == 0) {
707 atomic_dec(&isw_nr_in_flight);
708 wb_put(isw->new_wb);
709 kfree(isw);
710 return restart;
711 }
712
713 /*
714 * In addition to synchronizing among switchers, I_WB_SWITCH tells
715 * the RCU protected stat update paths to grab the i_page
716 * lock so that stat transfer can synchronize against them.
717 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
718 */
719 INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
720 queue_rcu_work(isw_wq, &isw->work);
721
722 return restart;
723}
724
725/**
726 * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
727 * @wbc: writeback_control of interest
728 * @inode: target inode
729 *
730 * @inode is locked and about to be written back under the control of @wbc.
731 * Record @inode's writeback context into @wbc and unlock the i_lock. On
732 * writeback completion, wbc_detach_inode() should be called. This is used
733 * to track the cgroup writeback context.
734 */
735void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
736 struct inode *inode)
737{
738 if (!inode_cgwb_enabled(inode)) {
739 spin_unlock(&inode->i_lock);
740 return;
741 }
742
743 wbc->wb = inode_to_wb(inode);
744 wbc->inode = inode;
745
746 wbc->wb_id = wbc->wb->memcg_css->id;
747 wbc->wb_lcand_id = inode->i_wb_frn_winner;
748 wbc->wb_tcand_id = 0;
749 wbc->wb_bytes = 0;
750 wbc->wb_lcand_bytes = 0;
751 wbc->wb_tcand_bytes = 0;
752
753 wb_get(wbc->wb);
754 spin_unlock(&inode->i_lock);
755
756 /*
757 * A dying wb indicates that either the blkcg associated with the
758 * memcg changed or the associated memcg is dying. In the first
759 * case, a replacement wb should already be available and we should
760 * refresh the wb immediately. In the second case, trying to
761 * refresh will keep failing.
762 */
763 if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
764 inode_switch_wbs(inode, wbc->wb_id);
765}
766EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
767
768/**
769 * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
770 * @wbc: writeback_control of the just finished writeback
771 *
772 * To be called after a writeback attempt of an inode finishes and undoes
773 * wbc_attach_and_unlock_inode(). Can be called under any context.
774 *
775 * As concurrent write sharing of an inode is expected to be very rare and
776 * memcg only tracks page ownership on first-use basis severely confining
777 * the usefulness of such sharing, cgroup writeback tracks ownership
778 * per-inode. While the support for concurrent write sharing of an inode
779 * is deemed unnecessary, an inode being written to by different cgroups at
780 * different points in time is a lot more common, and, more importantly,
781 * charging only by first-use can too readily lead to grossly incorrect
782 * behaviors (single foreign page can lead to gigabytes of writeback to be
783 * incorrectly attributed).
784 *
785 * To resolve this issue, cgroup writeback detects the majority dirtier of
786 * an inode and transfers the ownership to it. To avoid unnecessary
787 * oscillation, the detection mechanism keeps track of history and gives
788 * out the switch verdict only if the foreign usage pattern is stable over
789 * a certain amount of time and/or writeback attempts.
790 *
791 * On each writeback attempt, @wbc tries to detect the majority writer
792 * using Boyer-Moore majority vote algorithm. In addition to the byte
793 * count from the majority voting, it also counts the bytes written for the
794 * current wb and the last round's winner wb (max of last round's current
795 * wb, the winner from two rounds ago, and the last round's majority
796 * candidate). Keeping track of the historical winner helps the algorithm
797 * to semi-reliably detect the most active writer even when it's not the
798 * absolute majority.
799 *
800 * Once the winner of the round is determined, whether the winner is
801 * foreign or not and how much IO time the round consumed is recorded in
802 * inode->i_wb_frn_history. If the amount of recorded foreign IO time is
803 * over a certain threshold, the switch verdict is given.
804 */
805void wbc_detach_inode(struct writeback_control *wbc)
806{
807 struct bdi_writeback *wb = wbc->wb;
808 struct inode *inode = wbc->inode;
809 unsigned long avg_time, max_bytes, max_time;
810 u16 history;
811 int max_id;
812
813 if (!wb)
814 return;
815
816 history = inode->i_wb_frn_history;
817 avg_time = inode->i_wb_frn_avg_time;
818
819 /* pick the winner of this round */
820 if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
821 wbc->wb_bytes >= wbc->wb_tcand_bytes) {
822 max_id = wbc->wb_id;
823 max_bytes = wbc->wb_bytes;
824 } else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
825 max_id = wbc->wb_lcand_id;
826 max_bytes = wbc->wb_lcand_bytes;
827 } else {
828 max_id = wbc->wb_tcand_id;
829 max_bytes = wbc->wb_tcand_bytes;
830 }
831
832 /*
833 * Calculate the amount of IO time the winner consumed and fold it
834 * into the running average kept per inode. If the consumed IO
835 * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
836 * deciding whether to switch or not. This is to prevent one-off
837 * small dirtiers from skewing the verdict.
838 */
839 max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
840 wb->avg_write_bandwidth);
841 if (avg_time)
842 avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
843 (avg_time >> WB_FRN_TIME_AVG_SHIFT);
844 else
845 avg_time = max_time; /* immediate catch up on first run */
846
847 if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
848 int slots;
849
850 /*
851 * The switch verdict is reached if foreign wb's consume
852 * more than a certain proportion of IO time in a
853 * WB_FRN_TIME_PERIOD. This is loosely tracked by 16 slot
854 * history mask where each bit represents one sixteenth of
855 * the period. Determine the number of slots to shift into
856 * history from @max_time.
857 */
858 slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
859 (unsigned long)WB_FRN_HIST_MAX_SLOTS);
860 history <<= slots;
861 if (wbc->wb_id != max_id)
862 history |= (1U << slots) - 1;
863
864 if (history)
865 trace_inode_foreign_history(inode, wbc, history);
866
867 /*
868 * Switch if the current wb isn't the consistent winner.
869 * If there are multiple closely competing dirtiers, the
870 * inode may switch across them repeatedly over time, which
871 * is okay. The main goal is avoiding keeping an inode on
872 * the wrong wb for an extended period of time.
873 */
874 if (hweight16(history) > WB_FRN_HIST_THR_SLOTS)
875 inode_switch_wbs(inode, max_id);
876 }
877
878 /*
879 * Multiple instances of this function may race to update the
880 * following fields but we don't mind occassional inaccuracies.
881 */
882 inode->i_wb_frn_winner = max_id;
883 inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
884 inode->i_wb_frn_history = history;
885
886 wb_put(wbc->wb);
887 wbc->wb = NULL;
888}
889EXPORT_SYMBOL_GPL(wbc_detach_inode);
890
891/**
892 * wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
893 * @wbc: writeback_control of the writeback in progress
894 * @page: page being written out
895 * @bytes: number of bytes being written out
896 *
897 * @bytes from @page are about to written out during the writeback
898 * controlled by @wbc. Keep the book for foreign inode detection. See
899 * wbc_detach_inode().
900 */
901void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
902 size_t bytes)
903{
904 struct folio *folio;
905 struct cgroup_subsys_state *css;
906 int id;
907
908 /*
909 * pageout() path doesn't attach @wbc to the inode being written
910 * out. This is intentional as we don't want the function to block
911 * behind a slow cgroup. Ultimately, we want pageout() to kick off
912 * regular writeback instead of writing things out itself.
913 */
914 if (!wbc->wb || wbc->no_cgroup_owner)
915 return;
916
917 folio = page_folio(page);
918 css = mem_cgroup_css_from_folio(folio);
919 /* dead cgroups shouldn't contribute to inode ownership arbitration */
920 if (!(css->flags & CSS_ONLINE))
921 return;
922
923 id = css->id;
924
925 if (id == wbc->wb_id) {
926 wbc->wb_bytes += bytes;
927 return;
928 }
929
930 if (id == wbc->wb_lcand_id)
931 wbc->wb_lcand_bytes += bytes;
932
933 /* Boyer-Moore majority vote algorithm */
934 if (!wbc->wb_tcand_bytes)
935 wbc->wb_tcand_id = id;
936 if (id == wbc->wb_tcand_id)
937 wbc->wb_tcand_bytes += bytes;
938 else
939 wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
940}
941EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);
942
943/**
944 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
945 * @wb: target bdi_writeback to split @nr_pages to
946 * @nr_pages: number of pages to write for the whole bdi
947 *
948 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
949 * relation to the total write bandwidth of all wb's w/ dirty inodes on
950 * @wb->bdi.
951 */
952static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
953{
954 unsigned long this_bw = wb->avg_write_bandwidth;
955 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
956
957 if (nr_pages == LONG_MAX)
958 return LONG_MAX;
959
960 /*
961 * This may be called on clean wb's and proportional distribution
962 * may not make sense, just use the original @nr_pages in those
963 * cases. In general, we wanna err on the side of writing more.
964 */
965 if (!tot_bw || this_bw >= tot_bw)
966 return nr_pages;
967 else
968 return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
969}
970
971/**
972 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
973 * @bdi: target backing_dev_info
974 * @base_work: wb_writeback_work to issue
975 * @skip_if_busy: skip wb's which already have writeback in progress
976 *
977 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
978 * have dirty inodes. If @base_work->nr_page isn't %LONG_MAX, it's
979 * distributed to the busy wbs according to each wb's proportion in the
980 * total active write bandwidth of @bdi.
981 */
982static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
983 struct wb_writeback_work *base_work,
984 bool skip_if_busy)
985{
986 struct bdi_writeback *last_wb = NULL;
987 struct bdi_writeback *wb = list_entry(&bdi->wb_list,
988 struct bdi_writeback, bdi_node);
989
990 might_sleep();
991restart:
992 rcu_read_lock();
993 list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
994 DEFINE_WB_COMPLETION(fallback_work_done, bdi);
995 struct wb_writeback_work fallback_work;
996 struct wb_writeback_work *work;
997 long nr_pages;
998
999 if (last_wb) {
1000 wb_put(last_wb);
1001 last_wb = NULL;
1002 }
1003
1004 /* SYNC_ALL writes out I_DIRTY_TIME too */
1005 if (!wb_has_dirty_io(wb) &&
1006 (base_work->sync_mode == WB_SYNC_NONE ||
1007 list_empty(&wb->b_dirty_time)))
1008 continue;
1009 if (skip_if_busy && writeback_in_progress(wb))
1010 continue;
1011
1012 nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
1013
1014 work = kmalloc(sizeof(*work), GFP_ATOMIC);
1015 if (work) {
1016 *work = *base_work;
1017 work->nr_pages = nr_pages;
1018 work->auto_free = 1;
1019 wb_queue_work(wb, work);
1020 continue;
1021 }
1022
1023 /*
1024 * If wb_tryget fails, the wb has been shutdown, skip it.
1025 *
1026 * Pin @wb so that it stays on @bdi->wb_list. This allows
1027 * continuing iteration from @wb after dropping and
1028 * regrabbing rcu read lock.
1029 */
1030 if (!wb_tryget(wb))
1031 continue;
1032
1033 /* alloc failed, execute synchronously using on-stack fallback */
1034 work = &fallback_work;
1035 *work = *base_work;
1036 work->nr_pages = nr_pages;
1037 work->auto_free = 0;
1038 work->done = &fallback_work_done;
1039
1040 wb_queue_work(wb, work);
1041 last_wb = wb;
1042
1043 rcu_read_unlock();
1044 wb_wait_for_completion(&fallback_work_done);
1045 goto restart;
1046 }
1047 rcu_read_unlock();
1048
1049 if (last_wb)
1050 wb_put(last_wb);
1051}
1052
1053/**
1054 * cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
1055 * @bdi_id: target bdi id
1056 * @memcg_id: target memcg css id
1057 * @reason: reason why some writeback work initiated
1058 * @done: target wb_completion
1059 *
1060 * Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
1061 * with the specified parameters.
1062 */
1063int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,
1064 enum wb_reason reason, struct wb_completion *done)
1065{
1066 struct backing_dev_info *bdi;
1067 struct cgroup_subsys_state *memcg_css;
1068 struct bdi_writeback *wb;
1069 struct wb_writeback_work *work;
1070 unsigned long dirty;
1071 int ret;
1072
1073 /* lookup bdi and memcg */
1074 bdi = bdi_get_by_id(bdi_id);
1075 if (!bdi)
1076 return -ENOENT;
1077
1078 rcu_read_lock();
1079 memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
1080 if (memcg_css && !css_tryget(memcg_css))
1081 memcg_css = NULL;
1082 rcu_read_unlock();
1083 if (!memcg_css) {
1084 ret = -ENOENT;
1085 goto out_bdi_put;
1086 }
1087
1088 /*
1089 * And find the associated wb. If the wb isn't there already
1090 * there's nothing to flush, don't create one.
1091 */
1092 wb = wb_get_lookup(bdi, memcg_css);
1093 if (!wb) {
1094 ret = -ENOENT;
1095 goto out_css_put;
1096 }
1097
1098 /*
1099 * The caller is attempting to write out most of
1100 * the currently dirty pages. Let's take the current dirty page
1101 * count and inflate it by 25% which should be large enough to
1102 * flush out most dirty pages while avoiding getting livelocked by
1103 * concurrent dirtiers.
1104 *
1105 * BTW the memcg stats are flushed periodically and this is best-effort
1106 * estimation, so some potential error is ok.
1107 */
1108 dirty = memcg_page_state(mem_cgroup_from_css(memcg_css), NR_FILE_DIRTY);
1109 dirty = dirty * 10 / 8;
1110
1111 /* issue the writeback work */
1112 work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
1113 if (work) {
1114 work->nr_pages = dirty;
1115 work->sync_mode = WB_SYNC_NONE;
1116 work->range_cyclic = 1;
1117 work->reason = reason;
1118 work->done = done;
1119 work->auto_free = 1;
1120 wb_queue_work(wb, work);
1121 ret = 0;
1122 } else {
1123 ret = -ENOMEM;
1124 }
1125
1126 wb_put(wb);
1127out_css_put:
1128 css_put(memcg_css);
1129out_bdi_put:
1130 bdi_put(bdi);
1131 return ret;
1132}
1133
1134/**
1135 * cgroup_writeback_umount - flush inode wb switches for umount
1136 *
1137 * This function is called when a super_block is about to be destroyed and
1138 * flushes in-flight inode wb switches. An inode wb switch goes through
1139 * RCU and then workqueue, so the two need to be flushed in order to ensure
1140 * that all previously scheduled switches are finished. As wb switches are
1141 * rare occurrences and synchronize_rcu() can take a while, perform
1142 * flushing iff wb switches are in flight.
1143 */
1144void cgroup_writeback_umount(void)
1145{
1146 /*
1147 * SB_ACTIVE should be reliably cleared before checking
1148 * isw_nr_in_flight, see generic_shutdown_super().
1149 */
1150 smp_mb();
1151
1152 if (atomic_read(&isw_nr_in_flight)) {
1153 /*
1154 * Use rcu_barrier() to wait for all pending callbacks to
1155 * ensure that all in-flight wb switches are in the workqueue.
1156 */
1157 rcu_barrier();
1158 flush_workqueue(isw_wq);
1159 }
1160}
1161
1162static int __init cgroup_writeback_init(void)
1163{
1164 isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
1165 if (!isw_wq)
1166 return -ENOMEM;
1167 return 0;
1168}
1169fs_initcall(cgroup_writeback_init);
1170
1171#else /* CONFIG_CGROUP_WRITEBACK */
1172
1173static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1174static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1175
1176static void inode_cgwb_move_to_attached(struct inode *inode,
1177 struct bdi_writeback *wb)
1178{
1179 assert_spin_locked(&wb->list_lock);
1180 assert_spin_locked(&inode->i_lock);
1181 WARN_ON_ONCE(inode->i_state & I_FREEING);
1182
1183 inode->i_state &= ~I_SYNC_QUEUED;
1184 list_del_init(&inode->i_io_list);
1185 wb_io_lists_depopulated(wb);
1186}
1187
1188static struct bdi_writeback *
1189locked_inode_to_wb_and_lock_list(struct inode *inode)
1190 __releases(&inode->i_lock)
1191 __acquires(&wb->list_lock)
1192{
1193 struct bdi_writeback *wb = inode_to_wb(inode);
1194
1195 spin_unlock(&inode->i_lock);
1196 spin_lock(&wb->list_lock);
1197 return wb;
1198}
1199
1200static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
1201 __acquires(&wb->list_lock)
1202{
1203 struct bdi_writeback *wb = inode_to_wb(inode);
1204
1205 spin_lock(&wb->list_lock);
1206 return wb;
1207}
1208
1209static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
1210{
1211 return nr_pages;
1212}
1213
1214static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
1215 struct wb_writeback_work *base_work,
1216 bool skip_if_busy)
1217{
1218 might_sleep();
1219
1220 if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
1221 base_work->auto_free = 0;
1222 wb_queue_work(&bdi->wb, base_work);
1223 }
1224}
1225
1226#endif /* CONFIG_CGROUP_WRITEBACK */
1227
1228/*
1229 * Add in the number of potentially dirty inodes, because each inode
1230 * write can dirty pagecache in the underlying blockdev.
1231 */
1232static unsigned long get_nr_dirty_pages(void)
1233{
1234 return global_node_page_state(NR_FILE_DIRTY) +
1235 get_nr_dirty_inodes();
1236}
1237
1238static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
1239{
1240 if (!wb_has_dirty_io(wb))
1241 return;
1242
1243 /*
1244 * All callers of this function want to start writeback of all
1245 * dirty pages. Places like vmscan can call this at a very
1246 * high frequency, causing pointless allocations of tons of
1247 * work items and keeping the flusher threads busy retrieving
1248 * that work. Ensure that we only allow one of them pending and
1249 * inflight at the time.
1250 */
1251 if (test_bit(WB_start_all, &wb->state) ||
1252 test_and_set_bit(WB_start_all, &wb->state))
1253 return;
1254
1255 wb->start_all_reason = reason;
1256 wb_wakeup(wb);
1257}
1258
1259/**
1260 * wb_start_background_writeback - start background writeback
1261 * @wb: bdi_writback to write from
1262 *
1263 * Description:
1264 * This makes sure WB_SYNC_NONE background writeback happens. When
1265 * this function returns, it is only guaranteed that for given wb
1266 * some IO is happening if we are over background dirty threshold.
1267 * Caller need not hold sb s_umount semaphore.
1268 */
1269void wb_start_background_writeback(struct bdi_writeback *wb)
1270{
1271 /*
1272 * We just wake up the flusher thread. It will perform background
1273 * writeback as soon as there is no other work to do.
1274 */
1275 trace_writeback_wake_background(wb);
1276 wb_wakeup(wb);
1277}
1278
1279/*
1280 * Remove the inode from the writeback list it is on.
1281 */
1282void inode_io_list_del(struct inode *inode)
1283{
1284 struct bdi_writeback *wb;
1285
1286 wb = inode_to_wb_and_lock_list(inode);
1287 spin_lock(&inode->i_lock);
1288
1289 inode->i_state &= ~I_SYNC_QUEUED;
1290 list_del_init(&inode->i_io_list);
1291 wb_io_lists_depopulated(wb);
1292
1293 spin_unlock(&inode->i_lock);
1294 spin_unlock(&wb->list_lock);
1295}
1296EXPORT_SYMBOL(inode_io_list_del);
1297
1298/*
1299 * mark an inode as under writeback on the sb
1300 */
1301void sb_mark_inode_writeback(struct inode *inode)
1302{
1303 struct super_block *sb = inode->i_sb;
1304 unsigned long flags;
1305
1306 if (list_empty(&inode->i_wb_list)) {
1307 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1308 if (list_empty(&inode->i_wb_list)) {
1309 list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
1310 trace_sb_mark_inode_writeback(inode);
1311 }
1312 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1313 }
1314}
1315
1316/*
1317 * clear an inode as under writeback on the sb
1318 */
1319void sb_clear_inode_writeback(struct inode *inode)
1320{
1321 struct super_block *sb = inode->i_sb;
1322 unsigned long flags;
1323
1324 if (!list_empty(&inode->i_wb_list)) {
1325 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1326 if (!list_empty(&inode->i_wb_list)) {
1327 list_del_init(&inode->i_wb_list);
1328 trace_sb_clear_inode_writeback(inode);
1329 }
1330 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1331 }
1332}
1333
1334/*
1335 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1336 * furthest end of its superblock's dirty-inode list.
1337 *
1338 * Before stamping the inode's ->dirtied_when, we check to see whether it is
1339 * already the most-recently-dirtied inode on the b_dirty list. If that is
1340 * the case then the inode must have been redirtied while it was being written
1341 * out and we don't reset its dirtied_when.
1342 */
1343static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
1344{
1345 assert_spin_locked(&inode->i_lock);
1346
1347 inode->i_state &= ~I_SYNC_QUEUED;
1348 /*
1349 * When the inode is being freed just don't bother with dirty list
1350 * tracking. Flush worker will ignore this inode anyway and it will
1351 * trigger assertions in inode_io_list_move_locked().
1352 */
1353 if (inode->i_state & I_FREEING) {
1354 list_del_init(&inode->i_io_list);
1355 wb_io_lists_depopulated(wb);
1356 return;
1357 }
1358 if (!list_empty(&wb->b_dirty)) {
1359 struct inode *tail;
1360
1361 tail = wb_inode(wb->b_dirty.next);
1362 if (time_before(inode->dirtied_when, tail->dirtied_when))
1363 inode->dirtied_when = jiffies;
1364 }
1365 inode_io_list_move_locked(inode, wb, &wb->b_dirty);
1366}
1367
1368static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
1369{
1370 spin_lock(&inode->i_lock);
1371 redirty_tail_locked(inode, wb);
1372 spin_unlock(&inode->i_lock);
1373}
1374
1375/*
1376 * requeue inode for re-scanning after bdi->b_io list is exhausted.
1377 */
1378static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
1379{
1380 inode_io_list_move_locked(inode, wb, &wb->b_more_io);
1381}
1382
1383static void inode_sync_complete(struct inode *inode)
1384{
1385 inode->i_state &= ~I_SYNC;
1386 /* If inode is clean an unused, put it into LRU now... */
1387 inode_add_lru(inode);
1388 /* Waiters must see I_SYNC cleared before being woken up */
1389 smp_mb();
1390 wake_up_bit(&inode->i_state, __I_SYNC);
1391}
1392
1393static bool inode_dirtied_after(struct inode *inode, unsigned long t)
1394{
1395 bool ret = time_after(inode->dirtied_when, t);
1396#ifndef CONFIG_64BIT
1397 /*
1398 * For inodes being constantly redirtied, dirtied_when can get stuck.
1399 * It _appears_ to be in the future, but is actually in distant past.
1400 * This test is necessary to prevent such wrapped-around relative times
1401 * from permanently stopping the whole bdi writeback.
1402 */
1403 ret = ret && time_before_eq(inode->dirtied_when, jiffies);
1404#endif
1405 return ret;
1406}
1407
1408/*
1409 * Move expired (dirtied before dirtied_before) dirty inodes from
1410 * @delaying_queue to @dispatch_queue.
1411 */
1412static int move_expired_inodes(struct list_head *delaying_queue,
1413 struct list_head *dispatch_queue,
1414 unsigned long dirtied_before)
1415{
1416 LIST_HEAD(tmp);
1417 struct list_head *pos, *node;
1418 struct super_block *sb = NULL;
1419 struct inode *inode;
1420 int do_sb_sort = 0;
1421 int moved = 0;
1422
1423 while (!list_empty(delaying_queue)) {
1424 inode = wb_inode(delaying_queue->prev);
1425 if (inode_dirtied_after(inode, dirtied_before))
1426 break;
1427 spin_lock(&inode->i_lock);
1428 list_move(&inode->i_io_list, &tmp);
1429 moved++;
1430 inode->i_state |= I_SYNC_QUEUED;
1431 spin_unlock(&inode->i_lock);
1432 if (sb_is_blkdev_sb(inode->i_sb))
1433 continue;
1434 if (sb && sb != inode->i_sb)
1435 do_sb_sort = 1;
1436 sb = inode->i_sb;
1437 }
1438
1439 /* just one sb in list, splice to dispatch_queue and we're done */
1440 if (!do_sb_sort) {
1441 list_splice(&tmp, dispatch_queue);
1442 goto out;
1443 }
1444
1445 /*
1446 * Although inode's i_io_list is moved from 'tmp' to 'dispatch_queue',
1447 * we don't take inode->i_lock here because it is just a pointless overhead.
1448 * Inode is already marked as I_SYNC_QUEUED so writeback list handling is
1449 * fully under our control.
1450 */
1451 while (!list_empty(&tmp)) {
1452 sb = wb_inode(tmp.prev)->i_sb;
1453 list_for_each_prev_safe(pos, node, &tmp) {
1454 inode = wb_inode(pos);
1455 if (inode->i_sb == sb)
1456 list_move(&inode->i_io_list, dispatch_queue);
1457 }
1458 }
1459out:
1460 return moved;
1461}
1462
1463/*
1464 * Queue all expired dirty inodes for io, eldest first.
1465 * Before
1466 * newly dirtied b_dirty b_io b_more_io
1467 * =============> gf edc BA
1468 * After
1469 * newly dirtied b_dirty b_io b_more_io
1470 * =============> g fBAedc
1471 * |
1472 * +--> dequeue for IO
1473 */
1474static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
1475 unsigned long dirtied_before)
1476{
1477 int moved;
1478 unsigned long time_expire_jif = dirtied_before;
1479
1480 assert_spin_locked(&wb->list_lock);
1481 list_splice_init(&wb->b_more_io, &wb->b_io);
1482 moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, dirtied_before);
1483 if (!work->for_sync)
1484 time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
1485 moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
1486 time_expire_jif);
1487 if (moved)
1488 wb_io_lists_populated(wb);
1489 trace_writeback_queue_io(wb, work, dirtied_before, moved);
1490}
1491
1492static int write_inode(struct inode *inode, struct writeback_control *wbc)
1493{
1494 int ret;
1495
1496 if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1497 trace_writeback_write_inode_start(inode, wbc);
1498 ret = inode->i_sb->s_op->write_inode(inode, wbc);
1499 trace_writeback_write_inode(inode, wbc);
1500 return ret;
1501 }
1502 return 0;
1503}
1504
1505/*
1506 * Wait for writeback on an inode to complete. Called with i_lock held.
1507 * Caller must make sure inode cannot go away when we drop i_lock.
1508 */
1509static void __inode_wait_for_writeback(struct inode *inode)
1510 __releases(inode->i_lock)
1511 __acquires(inode->i_lock)
1512{
1513 DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1514 wait_queue_head_t *wqh;
1515
1516 wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1517 while (inode->i_state & I_SYNC) {
1518 spin_unlock(&inode->i_lock);
1519 __wait_on_bit(wqh, &wq, bit_wait,
1520 TASK_UNINTERRUPTIBLE);
1521 spin_lock(&inode->i_lock);
1522 }
1523}
1524
1525/*
1526 * Wait for writeback on an inode to complete. Caller must have inode pinned.
1527 */
1528void inode_wait_for_writeback(struct inode *inode)
1529{
1530 spin_lock(&inode->i_lock);
1531 __inode_wait_for_writeback(inode);
1532 spin_unlock(&inode->i_lock);
1533}
1534
1535/*
1536 * Sleep until I_SYNC is cleared. This function must be called with i_lock
1537 * held and drops it. It is aimed for callers not holding any inode reference
1538 * so once i_lock is dropped, inode can go away.
1539 */
1540static void inode_sleep_on_writeback(struct inode *inode)
1541 __releases(inode->i_lock)
1542{
1543 DEFINE_WAIT(wait);
1544 wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1545 int sleep;
1546
1547 prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1548 sleep = inode->i_state & I_SYNC;
1549 spin_unlock(&inode->i_lock);
1550 if (sleep)
1551 schedule();
1552 finish_wait(wqh, &wait);
1553}
1554
1555/*
1556 * Find proper writeback list for the inode depending on its current state and
1557 * possibly also change of its state while we were doing writeback. Here we
1558 * handle things such as livelock prevention or fairness of writeback among
1559 * inodes. This function can be called only by flusher thread - noone else
1560 * processes all inodes in writeback lists and requeueing inodes behind flusher
1561 * thread's back can have unexpected consequences.
1562 */
1563static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1564 struct writeback_control *wbc)
1565{
1566 if (inode->i_state & I_FREEING)
1567 return;
1568
1569 /*
1570 * Sync livelock prevention. Each inode is tagged and synced in one
1571 * shot. If still dirty, it will be redirty_tail()'ed below. Update
1572 * the dirty time to prevent enqueue and sync it again.
1573 */
1574 if ((inode->i_state & I_DIRTY) &&
1575 (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1576 inode->dirtied_when = jiffies;
1577
1578 if (wbc->pages_skipped) {
1579 /*
1580 * Writeback is not making progress due to locked buffers.
1581 * Skip this inode for now. Although having skipped pages
1582 * is odd for clean inodes, it can happen for some
1583 * filesystems so handle that gracefully.
1584 */
1585 if (inode->i_state & I_DIRTY_ALL)
1586 redirty_tail_locked(inode, wb);
1587 else
1588 inode_cgwb_move_to_attached(inode, wb);
1589 return;
1590 }
1591
1592 if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1593 /*
1594 * We didn't write back all the pages. nfs_writepages()
1595 * sometimes bales out without doing anything.
1596 */
1597 if (wbc->nr_to_write <= 0) {
1598 /* Slice used up. Queue for next turn. */
1599 requeue_io(inode, wb);
1600 } else {
1601 /*
1602 * Writeback blocked by something other than
1603 * congestion. Delay the inode for some time to
1604 * avoid spinning on the CPU (100% iowait)
1605 * retrying writeback of the dirty page/inode
1606 * that cannot be performed immediately.
1607 */
1608 redirty_tail_locked(inode, wb);
1609 }
1610 } else if (inode->i_state & I_DIRTY) {
1611 /*
1612 * Filesystems can dirty the inode during writeback operations,
1613 * such as delayed allocation during submission or metadata
1614 * updates after data IO completion.
1615 */
1616 redirty_tail_locked(inode, wb);
1617 } else if (inode->i_state & I_DIRTY_TIME) {
1618 inode->dirtied_when = jiffies;
1619 inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
1620 inode->i_state &= ~I_SYNC_QUEUED;
1621 } else {
1622 /* The inode is clean. Remove from writeback lists. */
1623 inode_cgwb_move_to_attached(inode, wb);
1624 }
1625}
1626
1627/*
1628 * Write out an inode and its dirty pages (or some of its dirty pages, depending
1629 * on @wbc->nr_to_write), and clear the relevant dirty flags from i_state.
1630 *
1631 * This doesn't remove the inode from the writeback list it is on, except
1632 * potentially to move it from b_dirty_time to b_dirty due to timestamp
1633 * expiration. The caller is otherwise responsible for writeback list handling.
1634 *
1635 * The caller is also responsible for setting the I_SYNC flag beforehand and
1636 * calling inode_sync_complete() to clear it afterwards.
1637 */
1638static int
1639__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1640{
1641 struct address_space *mapping = inode->i_mapping;
1642 long nr_to_write = wbc->nr_to_write;
1643 unsigned dirty;
1644 int ret;
1645
1646 WARN_ON(!(inode->i_state & I_SYNC));
1647
1648 trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1649
1650 ret = do_writepages(mapping, wbc);
1651
1652 /*
1653 * Make sure to wait on the data before writing out the metadata.
1654 * This is important for filesystems that modify metadata on data
1655 * I/O completion. We don't do it for sync(2) writeback because it has a
1656 * separate, external IO completion path and ->sync_fs for guaranteeing
1657 * inode metadata is written back correctly.
1658 */
1659 if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
1660 int err = filemap_fdatawait(mapping);
1661 if (ret == 0)
1662 ret = err;
1663 }
1664
1665 /*
1666 * If the inode has dirty timestamps and we need to write them, call
1667 * mark_inode_dirty_sync() to notify the filesystem about it and to
1668 * change I_DIRTY_TIME into I_DIRTY_SYNC.
1669 */
1670 if ((inode->i_state & I_DIRTY_TIME) &&
1671 (wbc->sync_mode == WB_SYNC_ALL ||
1672 time_after(jiffies, inode->dirtied_time_when +
1673 dirtytime_expire_interval * HZ))) {
1674 trace_writeback_lazytime(inode);
1675 mark_inode_dirty_sync(inode);
1676 }
1677
1678 /*
1679 * Get and clear the dirty flags from i_state. This needs to be done
1680 * after calling writepages because some filesystems may redirty the
1681 * inode during writepages due to delalloc. It also needs to be done
1682 * after handling timestamp expiration, as that may dirty the inode too.
1683 */
1684 spin_lock(&inode->i_lock);
1685 dirty = inode->i_state & I_DIRTY;
1686 inode->i_state &= ~dirty;
1687
1688 /*
1689 * Paired with smp_mb() in __mark_inode_dirty(). This allows
1690 * __mark_inode_dirty() to test i_state without grabbing i_lock -
1691 * either they see the I_DIRTY bits cleared or we see the dirtied
1692 * inode.
1693 *
1694 * I_DIRTY_PAGES is always cleared together above even if @mapping
1695 * still has dirty pages. The flag is reinstated after smp_mb() if
1696 * necessary. This guarantees that either __mark_inode_dirty()
1697 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1698 */
1699 smp_mb();
1700
1701 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1702 inode->i_state |= I_DIRTY_PAGES;
1703 else if (unlikely(inode->i_state & I_PINNING_NETFS_WB)) {
1704 if (!(inode->i_state & I_DIRTY_PAGES)) {
1705 inode->i_state &= ~I_PINNING_NETFS_WB;
1706 wbc->unpinned_netfs_wb = true;
1707 dirty |= I_PINNING_NETFS_WB; /* Cause write_inode */
1708 }
1709 }
1710
1711 spin_unlock(&inode->i_lock);
1712
1713 /* Don't write the inode if only I_DIRTY_PAGES was set */
1714 if (dirty & ~I_DIRTY_PAGES) {
1715 int err = write_inode(inode, wbc);
1716 if (ret == 0)
1717 ret = err;
1718 }
1719 wbc->unpinned_netfs_wb = false;
1720 trace_writeback_single_inode(inode, wbc, nr_to_write);
1721 return ret;
1722}
1723
1724/*
1725 * Write out an inode's dirty data and metadata on-demand, i.e. separately from
1726 * the regular batched writeback done by the flusher threads in
1727 * writeback_sb_inodes(). @wbc controls various aspects of the write, such as
1728 * whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE).
1729 *
1730 * To prevent the inode from going away, either the caller must have a reference
1731 * to the inode, or the inode must have I_WILL_FREE or I_FREEING set.
1732 */
1733static int writeback_single_inode(struct inode *inode,
1734 struct writeback_control *wbc)
1735{
1736 struct bdi_writeback *wb;
1737 int ret = 0;
1738
1739 spin_lock(&inode->i_lock);
1740 if (!atomic_read(&inode->i_count))
1741 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1742 else
1743 WARN_ON(inode->i_state & I_WILL_FREE);
1744
1745 if (inode->i_state & I_SYNC) {
1746 /*
1747 * Writeback is already running on the inode. For WB_SYNC_NONE,
1748 * that's enough and we can just return. For WB_SYNC_ALL, we
1749 * must wait for the existing writeback to complete, then do
1750 * writeback again if there's anything left.
1751 */
1752 if (wbc->sync_mode != WB_SYNC_ALL)
1753 goto out;
1754 __inode_wait_for_writeback(inode);
1755 }
1756 WARN_ON(inode->i_state & I_SYNC);
1757 /*
1758 * If the inode is already fully clean, then there's nothing to do.
1759 *
1760 * For data-integrity syncs we also need to check whether any pages are
1761 * still under writeback, e.g. due to prior WB_SYNC_NONE writeback. If
1762 * there are any such pages, we'll need to wait for them.
1763 */
1764 if (!(inode->i_state & I_DIRTY_ALL) &&
1765 (wbc->sync_mode != WB_SYNC_ALL ||
1766 !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
1767 goto out;
1768 inode->i_state |= I_SYNC;
1769 wbc_attach_and_unlock_inode(wbc, inode);
1770
1771 ret = __writeback_single_inode(inode, wbc);
1772
1773 wbc_detach_inode(wbc);
1774
1775 wb = inode_to_wb_and_lock_list(inode);
1776 spin_lock(&inode->i_lock);
1777 /*
1778 * If the inode is freeing, its i_io_list shoudn't be updated
1779 * as it can be finally deleted at this moment.
1780 */
1781 if (!(inode->i_state & I_FREEING)) {
1782 /*
1783 * If the inode is now fully clean, then it can be safely
1784 * removed from its writeback list (if any). Otherwise the
1785 * flusher threads are responsible for the writeback lists.
1786 */
1787 if (!(inode->i_state & I_DIRTY_ALL))
1788 inode_cgwb_move_to_attached(inode, wb);
1789 else if (!(inode->i_state & I_SYNC_QUEUED)) {
1790 if ((inode->i_state & I_DIRTY))
1791 redirty_tail_locked(inode, wb);
1792 else if (inode->i_state & I_DIRTY_TIME) {
1793 inode->dirtied_when = jiffies;
1794 inode_io_list_move_locked(inode,
1795 wb,
1796 &wb->b_dirty_time);
1797 }
1798 }
1799 }
1800
1801 spin_unlock(&wb->list_lock);
1802 inode_sync_complete(inode);
1803out:
1804 spin_unlock(&inode->i_lock);
1805 return ret;
1806}
1807
1808static long writeback_chunk_size(struct bdi_writeback *wb,
1809 struct wb_writeback_work *work)
1810{
1811 long pages;
1812
1813 /*
1814 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1815 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1816 * here avoids calling into writeback_inodes_wb() more than once.
1817 *
1818 * The intended call sequence for WB_SYNC_ALL writeback is:
1819 *
1820 * wb_writeback()
1821 * writeback_sb_inodes() <== called only once
1822 * write_cache_pages() <== called once for each inode
1823 * (quickly) tag currently dirty pages
1824 * (maybe slowly) sync all tagged pages
1825 */
1826 if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1827 pages = LONG_MAX;
1828 else {
1829 pages = min(wb->avg_write_bandwidth / 2,
1830 global_wb_domain.dirty_limit / DIRTY_SCOPE);
1831 pages = min(pages, work->nr_pages);
1832 pages = round_down(pages + MIN_WRITEBACK_PAGES,
1833 MIN_WRITEBACK_PAGES);
1834 }
1835
1836 return pages;
1837}
1838
1839/*
1840 * Write a portion of b_io inodes which belong to @sb.
1841 *
1842 * Return the number of pages and/or inodes written.
1843 *
1844 * NOTE! This is called with wb->list_lock held, and will
1845 * unlock and relock that for each inode it ends up doing
1846 * IO for.
1847 */
1848static long writeback_sb_inodes(struct super_block *sb,
1849 struct bdi_writeback *wb,
1850 struct wb_writeback_work *work)
1851{
1852 struct writeback_control wbc = {
1853 .sync_mode = work->sync_mode,
1854 .tagged_writepages = work->tagged_writepages,
1855 .for_kupdate = work->for_kupdate,
1856 .for_background = work->for_background,
1857 .for_sync = work->for_sync,
1858 .range_cyclic = work->range_cyclic,
1859 .range_start = 0,
1860 .range_end = LLONG_MAX,
1861 };
1862 unsigned long start_time = jiffies;
1863 long write_chunk;
1864 long total_wrote = 0; /* count both pages and inodes */
1865
1866 while (!list_empty(&wb->b_io)) {
1867 struct inode *inode = wb_inode(wb->b_io.prev);
1868 struct bdi_writeback *tmp_wb;
1869 long wrote;
1870
1871 if (inode->i_sb != sb) {
1872 if (work->sb) {
1873 /*
1874 * We only want to write back data for this
1875 * superblock, move all inodes not belonging
1876 * to it back onto the dirty list.
1877 */
1878 redirty_tail(inode, wb);
1879 continue;
1880 }
1881
1882 /*
1883 * The inode belongs to a different superblock.
1884 * Bounce back to the caller to unpin this and
1885 * pin the next superblock.
1886 */
1887 break;
1888 }
1889
1890 /*
1891 * Don't bother with new inodes or inodes being freed, first
1892 * kind does not need periodic writeout yet, and for the latter
1893 * kind writeout is handled by the freer.
1894 */
1895 spin_lock(&inode->i_lock);
1896 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
1897 redirty_tail_locked(inode, wb);
1898 spin_unlock(&inode->i_lock);
1899 continue;
1900 }
1901 if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1902 /*
1903 * If this inode is locked for writeback and we are not
1904 * doing writeback-for-data-integrity, move it to
1905 * b_more_io so that writeback can proceed with the
1906 * other inodes on s_io.
1907 *
1908 * We'll have another go at writing back this inode
1909 * when we completed a full scan of b_io.
1910 */
1911 requeue_io(inode, wb);
1912 spin_unlock(&inode->i_lock);
1913 trace_writeback_sb_inodes_requeue(inode);
1914 continue;
1915 }
1916 spin_unlock(&wb->list_lock);
1917
1918 /*
1919 * We already requeued the inode if it had I_SYNC set and we
1920 * are doing WB_SYNC_NONE writeback. So this catches only the
1921 * WB_SYNC_ALL case.
1922 */
1923 if (inode->i_state & I_SYNC) {
1924 /* Wait for I_SYNC. This function drops i_lock... */
1925 inode_sleep_on_writeback(inode);
1926 /* Inode may be gone, start again */
1927 spin_lock(&wb->list_lock);
1928 continue;
1929 }
1930 inode->i_state |= I_SYNC;
1931 wbc_attach_and_unlock_inode(&wbc, inode);
1932
1933 write_chunk = writeback_chunk_size(wb, work);
1934 wbc.nr_to_write = write_chunk;
1935 wbc.pages_skipped = 0;
1936
1937 /*
1938 * We use I_SYNC to pin the inode in memory. While it is set
1939 * evict_inode() will wait so the inode cannot be freed.
1940 */
1941 __writeback_single_inode(inode, &wbc);
1942
1943 wbc_detach_inode(&wbc);
1944 work->nr_pages -= write_chunk - wbc.nr_to_write;
1945 wrote = write_chunk - wbc.nr_to_write - wbc.pages_skipped;
1946 wrote = wrote < 0 ? 0 : wrote;
1947 total_wrote += wrote;
1948
1949 if (need_resched()) {
1950 /*
1951 * We're trying to balance between building up a nice
1952 * long list of IOs to improve our merge rate, and
1953 * getting those IOs out quickly for anyone throttling
1954 * in balance_dirty_pages(). cond_resched() doesn't
1955 * unplug, so get our IOs out the door before we
1956 * give up the CPU.
1957 */
1958 blk_flush_plug(current->plug, false);
1959 cond_resched();
1960 }
1961
1962 /*
1963 * Requeue @inode if still dirty. Be careful as @inode may
1964 * have been switched to another wb in the meantime.
1965 */
1966 tmp_wb = inode_to_wb_and_lock_list(inode);
1967 spin_lock(&inode->i_lock);
1968 if (!(inode->i_state & I_DIRTY_ALL))
1969 total_wrote++;
1970 requeue_inode(inode, tmp_wb, &wbc);
1971 inode_sync_complete(inode);
1972 spin_unlock(&inode->i_lock);
1973
1974 if (unlikely(tmp_wb != wb)) {
1975 spin_unlock(&tmp_wb->list_lock);
1976 spin_lock(&wb->list_lock);
1977 }
1978
1979 /*
1980 * bail out to wb_writeback() often enough to check
1981 * background threshold and other termination conditions.
1982 */
1983 if (total_wrote) {
1984 if (time_is_before_jiffies(start_time + HZ / 10UL))
1985 break;
1986 if (work->nr_pages <= 0)
1987 break;
1988 }
1989 }
1990 return total_wrote;
1991}
1992
1993static long __writeback_inodes_wb(struct bdi_writeback *wb,
1994 struct wb_writeback_work *work)
1995{
1996 unsigned long start_time = jiffies;
1997 long wrote = 0;
1998
1999 while (!list_empty(&wb->b_io)) {
2000 struct inode *inode = wb_inode(wb->b_io.prev);
2001 struct super_block *sb = inode->i_sb;
2002
2003 if (!super_trylock_shared(sb)) {
2004 /*
2005 * super_trylock_shared() may fail consistently due to
2006 * s_umount being grabbed by someone else. Don't use
2007 * requeue_io() to avoid busy retrying the inode/sb.
2008 */
2009 redirty_tail(inode, wb);
2010 continue;
2011 }
2012 wrote += writeback_sb_inodes(sb, wb, work);
2013 up_read(&sb->s_umount);
2014
2015 /* refer to the same tests at the end of writeback_sb_inodes */
2016 if (wrote) {
2017 if (time_is_before_jiffies(start_time + HZ / 10UL))
2018 break;
2019 if (work->nr_pages <= 0)
2020 break;
2021 }
2022 }
2023 /* Leave any unwritten inodes on b_io */
2024 return wrote;
2025}
2026
2027static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
2028 enum wb_reason reason)
2029{
2030 struct wb_writeback_work work = {
2031 .nr_pages = nr_pages,
2032 .sync_mode = WB_SYNC_NONE,
2033 .range_cyclic = 1,
2034 .reason = reason,
2035 };
2036 struct blk_plug plug;
2037
2038 blk_start_plug(&plug);
2039 spin_lock(&wb->list_lock);
2040 if (list_empty(&wb->b_io))
2041 queue_io(wb, &work, jiffies);
2042 __writeback_inodes_wb(wb, &work);
2043 spin_unlock(&wb->list_lock);
2044 blk_finish_plug(&plug);
2045
2046 return nr_pages - work.nr_pages;
2047}
2048
2049/*
2050 * Explicit flushing or periodic writeback of "old" data.
2051 *
2052 * Define "old": the first time one of an inode's pages is dirtied, we mark the
2053 * dirtying-time in the inode's address_space. So this periodic writeback code
2054 * just walks the superblock inode list, writing back any inodes which are
2055 * older than a specific point in time.
2056 *
2057 * Try to run once per dirty_writeback_interval. But if a writeback event
2058 * takes longer than a dirty_writeback_interval interval, then leave a
2059 * one-second gap.
2060 *
2061 * dirtied_before takes precedence over nr_to_write. So we'll only write back
2062 * all dirty pages if they are all attached to "old" mappings.
2063 */
2064static long wb_writeback(struct bdi_writeback *wb,
2065 struct wb_writeback_work *work)
2066{
2067 long nr_pages = work->nr_pages;
2068 unsigned long dirtied_before = jiffies;
2069 struct inode *inode;
2070 long progress;
2071 struct blk_plug plug;
2072
2073 blk_start_plug(&plug);
2074 for (;;) {
2075 /*
2076 * Stop writeback when nr_pages has been consumed
2077 */
2078 if (work->nr_pages <= 0)
2079 break;
2080
2081 /*
2082 * Background writeout and kupdate-style writeback may
2083 * run forever. Stop them if there is other work to do
2084 * so that e.g. sync can proceed. They'll be restarted
2085 * after the other works are all done.
2086 */
2087 if ((work->for_background || work->for_kupdate) &&
2088 !list_empty(&wb->work_list))
2089 break;
2090
2091 /*
2092 * For background writeout, stop when we are below the
2093 * background dirty threshold
2094 */
2095 if (work->for_background && !wb_over_bg_thresh(wb))
2096 break;
2097
2098
2099 spin_lock(&wb->list_lock);
2100
2101 /*
2102 * Kupdate and background works are special and we want to
2103 * include all inodes that need writing. Livelock avoidance is
2104 * handled by these works yielding to any other work so we are
2105 * safe.
2106 */
2107 if (work->for_kupdate) {
2108 dirtied_before = jiffies -
2109 msecs_to_jiffies(dirty_expire_interval * 10);
2110 } else if (work->for_background)
2111 dirtied_before = jiffies;
2112
2113 trace_writeback_start(wb, work);
2114 if (list_empty(&wb->b_io))
2115 queue_io(wb, work, dirtied_before);
2116 if (work->sb)
2117 progress = writeback_sb_inodes(work->sb, wb, work);
2118 else
2119 progress = __writeback_inodes_wb(wb, work);
2120 trace_writeback_written(wb, work);
2121
2122 /*
2123 * Did we write something? Try for more
2124 *
2125 * Dirty inodes are moved to b_io for writeback in batches.
2126 * The completion of the current batch does not necessarily
2127 * mean the overall work is done. So we keep looping as long
2128 * as made some progress on cleaning pages or inodes.
2129 */
2130 if (progress) {
2131 spin_unlock(&wb->list_lock);
2132 continue;
2133 }
2134
2135 /*
2136 * No more inodes for IO, bail
2137 */
2138 if (list_empty(&wb->b_more_io)) {
2139 spin_unlock(&wb->list_lock);
2140 break;
2141 }
2142
2143 /*
2144 * Nothing written. Wait for some inode to
2145 * become available for writeback. Otherwise
2146 * we'll just busyloop.
2147 */
2148 trace_writeback_wait(wb, work);
2149 inode = wb_inode(wb->b_more_io.prev);
2150 spin_lock(&inode->i_lock);
2151 spin_unlock(&wb->list_lock);
2152 /* This function drops i_lock... */
2153 inode_sleep_on_writeback(inode);
2154 }
2155 blk_finish_plug(&plug);
2156
2157 return nr_pages - work->nr_pages;
2158}
2159
2160/*
2161 * Return the next wb_writeback_work struct that hasn't been processed yet.
2162 */
2163static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
2164{
2165 struct wb_writeback_work *work = NULL;
2166
2167 spin_lock_irq(&wb->work_lock);
2168 if (!list_empty(&wb->work_list)) {
2169 work = list_entry(wb->work_list.next,
2170 struct wb_writeback_work, list);
2171 list_del_init(&work->list);
2172 }
2173 spin_unlock_irq(&wb->work_lock);
2174 return work;
2175}
2176
2177static long wb_check_background_flush(struct bdi_writeback *wb)
2178{
2179 if (wb_over_bg_thresh(wb)) {
2180
2181 struct wb_writeback_work work = {
2182 .nr_pages = LONG_MAX,
2183 .sync_mode = WB_SYNC_NONE,
2184 .for_background = 1,
2185 .range_cyclic = 1,
2186 .reason = WB_REASON_BACKGROUND,
2187 };
2188
2189 return wb_writeback(wb, &work);
2190 }
2191
2192 return 0;
2193}
2194
2195static long wb_check_old_data_flush(struct bdi_writeback *wb)
2196{
2197 unsigned long expired;
2198 long nr_pages;
2199
2200 /*
2201 * When set to zero, disable periodic writeback
2202 */
2203 if (!dirty_writeback_interval)
2204 return 0;
2205
2206 expired = wb->last_old_flush +
2207 msecs_to_jiffies(dirty_writeback_interval * 10);
2208 if (time_before(jiffies, expired))
2209 return 0;
2210
2211 wb->last_old_flush = jiffies;
2212 nr_pages = get_nr_dirty_pages();
2213
2214 if (nr_pages) {
2215 struct wb_writeback_work work = {
2216 .nr_pages = nr_pages,
2217 .sync_mode = WB_SYNC_NONE,
2218 .for_kupdate = 1,
2219 .range_cyclic = 1,
2220 .reason = WB_REASON_PERIODIC,
2221 };
2222
2223 return wb_writeback(wb, &work);
2224 }
2225
2226 return 0;
2227}
2228
2229static long wb_check_start_all(struct bdi_writeback *wb)
2230{
2231 long nr_pages;
2232
2233 if (!test_bit(WB_start_all, &wb->state))
2234 return 0;
2235
2236 nr_pages = get_nr_dirty_pages();
2237 if (nr_pages) {
2238 struct wb_writeback_work work = {
2239 .nr_pages = wb_split_bdi_pages(wb, nr_pages),
2240 .sync_mode = WB_SYNC_NONE,
2241 .range_cyclic = 1,
2242 .reason = wb->start_all_reason,
2243 };
2244
2245 nr_pages = wb_writeback(wb, &work);
2246 }
2247
2248 clear_bit(WB_start_all, &wb->state);
2249 return nr_pages;
2250}
2251
2252
2253/*
2254 * Retrieve work items and do the writeback they describe
2255 */
2256static long wb_do_writeback(struct bdi_writeback *wb)
2257{
2258 struct wb_writeback_work *work;
2259 long wrote = 0;
2260
2261 set_bit(WB_writeback_running, &wb->state);
2262 while ((work = get_next_work_item(wb)) != NULL) {
2263 trace_writeback_exec(wb, work);
2264 wrote += wb_writeback(wb, work);
2265 finish_writeback_work(wb, work);
2266 }
2267
2268 /*
2269 * Check for a flush-everything request
2270 */
2271 wrote += wb_check_start_all(wb);
2272
2273 /*
2274 * Check for periodic writeback, kupdated() style
2275 */
2276 wrote += wb_check_old_data_flush(wb);
2277 wrote += wb_check_background_flush(wb);
2278 clear_bit(WB_writeback_running, &wb->state);
2279
2280 return wrote;
2281}
2282
2283/*
2284 * Handle writeback of dirty data for the device backed by this bdi. Also
2285 * reschedules periodically and does kupdated style flushing.
2286 */
2287void wb_workfn(struct work_struct *work)
2288{
2289 struct bdi_writeback *wb = container_of(to_delayed_work(work),
2290 struct bdi_writeback, dwork);
2291 long pages_written;
2292
2293 set_worker_desc("flush-%s", bdi_dev_name(wb->bdi));
2294
2295 if (likely(!current_is_workqueue_rescuer() ||
2296 !test_bit(WB_registered, &wb->state))) {
2297 /*
2298 * The normal path. Keep writing back @wb until its
2299 * work_list is empty. Note that this path is also taken
2300 * if @wb is shutting down even when we're running off the
2301 * rescuer as work_list needs to be drained.
2302 */
2303 do {
2304 pages_written = wb_do_writeback(wb);
2305 trace_writeback_pages_written(pages_written);
2306 } while (!list_empty(&wb->work_list));
2307 } else {
2308 /*
2309 * bdi_wq can't get enough workers and we're running off
2310 * the emergency worker. Don't hog it. Hopefully, 1024 is
2311 * enough for efficient IO.
2312 */
2313 pages_written = writeback_inodes_wb(wb, 1024,
2314 WB_REASON_FORKER_THREAD);
2315 trace_writeback_pages_written(pages_written);
2316 }
2317
2318 if (!list_empty(&wb->work_list))
2319 wb_wakeup(wb);
2320 else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
2321 wb_wakeup_delayed(wb);
2322}
2323
2324/*
2325 * Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
2326 * write back the whole world.
2327 */
2328static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2329 enum wb_reason reason)
2330{
2331 struct bdi_writeback *wb;
2332
2333 if (!bdi_has_dirty_io(bdi))
2334 return;
2335
2336 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2337 wb_start_writeback(wb, reason);
2338}
2339
2340void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2341 enum wb_reason reason)
2342{
2343 rcu_read_lock();
2344 __wakeup_flusher_threads_bdi(bdi, reason);
2345 rcu_read_unlock();
2346}
2347
2348/*
2349 * Wakeup the flusher threads to start writeback of all currently dirty pages
2350 */
2351void wakeup_flusher_threads(enum wb_reason reason)
2352{
2353 struct backing_dev_info *bdi;
2354
2355 /*
2356 * If we are expecting writeback progress we must submit plugged IO.
2357 */
2358 blk_flush_plug(current->plug, true);
2359
2360 rcu_read_lock();
2361 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2362 __wakeup_flusher_threads_bdi(bdi, reason);
2363 rcu_read_unlock();
2364}
2365
2366/*
2367 * Wake up bdi's periodically to make sure dirtytime inodes gets
2368 * written back periodically. We deliberately do *not* check the
2369 * b_dirtytime list in wb_has_dirty_io(), since this would cause the
2370 * kernel to be constantly waking up once there are any dirtytime
2371 * inodes on the system. So instead we define a separate delayed work
2372 * function which gets called much more rarely. (By default, only
2373 * once every 12 hours.)
2374 *
2375 * If there is any other write activity going on in the file system,
2376 * this function won't be necessary. But if the only thing that has
2377 * happened on the file system is a dirtytime inode caused by an atime
2378 * update, we need this infrastructure below to make sure that inode
2379 * eventually gets pushed out to disk.
2380 */
2381static void wakeup_dirtytime_writeback(struct work_struct *w);
2382static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
2383
2384static void wakeup_dirtytime_writeback(struct work_struct *w)
2385{
2386 struct backing_dev_info *bdi;
2387
2388 rcu_read_lock();
2389 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
2390 struct bdi_writeback *wb;
2391
2392 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2393 if (!list_empty(&wb->b_dirty_time))
2394 wb_wakeup(wb);
2395 }
2396 rcu_read_unlock();
2397 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2398}
2399
2400static int __init start_dirtytime_writeback(void)
2401{
2402 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2403 return 0;
2404}
2405__initcall(start_dirtytime_writeback);
2406
2407int dirtytime_interval_handler(struct ctl_table *table, int write,
2408 void *buffer, size_t *lenp, loff_t *ppos)
2409{
2410 int ret;
2411
2412 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
2413 if (ret == 0 && write)
2414 mod_delayed_work(system_wq, &dirtytime_work, 0);
2415 return ret;
2416}
2417
2418/**
2419 * __mark_inode_dirty - internal function to mark an inode dirty
2420 *
2421 * @inode: inode to mark
2422 * @flags: what kind of dirty, e.g. I_DIRTY_SYNC. This can be a combination of
2423 * multiple I_DIRTY_* flags, except that I_DIRTY_TIME can't be combined
2424 * with I_DIRTY_PAGES.
2425 *
2426 * Mark an inode as dirty. We notify the filesystem, then update the inode's
2427 * dirty flags. Then, if needed we add the inode to the appropriate dirty list.
2428 *
2429 * Most callers should use mark_inode_dirty() or mark_inode_dirty_sync()
2430 * instead of calling this directly.
2431 *
2432 * CAREFUL! We only add the inode to the dirty list if it is hashed or if it
2433 * refers to a blockdev. Unhashed inodes will never be added to the dirty list
2434 * even if they are later hashed, as they will have been marked dirty already.
2435 *
2436 * In short, ensure you hash any inodes _before_ you start marking them dirty.
2437 *
2438 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2439 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
2440 * the kernel-internal blockdev inode represents the dirtying time of the
2441 * blockdev's pages. This is why for I_DIRTY_PAGES we always use
2442 * page->mapping->host, so the page-dirtying time is recorded in the internal
2443 * blockdev inode.
2444 */
2445void __mark_inode_dirty(struct inode *inode, int flags)
2446{
2447 struct super_block *sb = inode->i_sb;
2448 int dirtytime = 0;
2449 struct bdi_writeback *wb = NULL;
2450
2451 trace_writeback_mark_inode_dirty(inode, flags);
2452
2453 if (flags & I_DIRTY_INODE) {
2454 /*
2455 * Inode timestamp update will piggback on this dirtying.
2456 * We tell ->dirty_inode callback that timestamps need to
2457 * be updated by setting I_DIRTY_TIME in flags.
2458 */
2459 if (inode->i_state & I_DIRTY_TIME) {
2460 spin_lock(&inode->i_lock);
2461 if (inode->i_state & I_DIRTY_TIME) {
2462 inode->i_state &= ~I_DIRTY_TIME;
2463 flags |= I_DIRTY_TIME;
2464 }
2465 spin_unlock(&inode->i_lock);
2466 }
2467
2468 /*
2469 * Notify the filesystem about the inode being dirtied, so that
2470 * (if needed) it can update on-disk fields and journal the
2471 * inode. This is only needed when the inode itself is being
2472 * dirtied now. I.e. it's only needed for I_DIRTY_INODE, not
2473 * for just I_DIRTY_PAGES or I_DIRTY_TIME.
2474 */
2475 trace_writeback_dirty_inode_start(inode, flags);
2476 if (sb->s_op->dirty_inode)
2477 sb->s_op->dirty_inode(inode,
2478 flags & (I_DIRTY_INODE | I_DIRTY_TIME));
2479 trace_writeback_dirty_inode(inode, flags);
2480
2481 /* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
2482 flags &= ~I_DIRTY_TIME;
2483 } else {
2484 /*
2485 * Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
2486 * (We don't support setting both I_DIRTY_PAGES and I_DIRTY_TIME
2487 * in one call to __mark_inode_dirty().)
2488 */
2489 dirtytime = flags & I_DIRTY_TIME;
2490 WARN_ON_ONCE(dirtytime && flags != I_DIRTY_TIME);
2491 }
2492
2493 /*
2494 * Paired with smp_mb() in __writeback_single_inode() for the
2495 * following lockless i_state test. See there for details.
2496 */
2497 smp_mb();
2498
2499 if ((inode->i_state & flags) == flags)
2500 return;
2501
2502 spin_lock(&inode->i_lock);
2503 if ((inode->i_state & flags) != flags) {
2504 const int was_dirty = inode->i_state & I_DIRTY;
2505
2506 inode_attach_wb(inode, NULL);
2507
2508 inode->i_state |= flags;
2509
2510 /*
2511 * Grab inode's wb early because it requires dropping i_lock and we
2512 * need to make sure following checks happen atomically with dirty
2513 * list handling so that we don't move inodes under flush worker's
2514 * hands.
2515 */
2516 if (!was_dirty) {
2517 wb = locked_inode_to_wb_and_lock_list(inode);
2518 spin_lock(&inode->i_lock);
2519 }
2520
2521 /*
2522 * If the inode is queued for writeback by flush worker, just
2523 * update its dirty state. Once the flush worker is done with
2524 * the inode it will place it on the appropriate superblock
2525 * list, based upon its state.
2526 */
2527 if (inode->i_state & I_SYNC_QUEUED)
2528 goto out_unlock;
2529
2530 /*
2531 * Only add valid (hashed) inodes to the superblock's
2532 * dirty list. Add blockdev inodes as well.
2533 */
2534 if (!S_ISBLK(inode->i_mode)) {
2535 if (inode_unhashed(inode))
2536 goto out_unlock;
2537 }
2538 if (inode->i_state & I_FREEING)
2539 goto out_unlock;
2540
2541 /*
2542 * If the inode was already on b_dirty/b_io/b_more_io, don't
2543 * reposition it (that would break b_dirty time-ordering).
2544 */
2545 if (!was_dirty) {
2546 struct list_head *dirty_list;
2547 bool wakeup_bdi = false;
2548
2549 inode->dirtied_when = jiffies;
2550 if (dirtytime)
2551 inode->dirtied_time_when = jiffies;
2552
2553 if (inode->i_state & I_DIRTY)
2554 dirty_list = &wb->b_dirty;
2555 else
2556 dirty_list = &wb->b_dirty_time;
2557
2558 wakeup_bdi = inode_io_list_move_locked(inode, wb,
2559 dirty_list);
2560
2561 spin_unlock(&wb->list_lock);
2562 spin_unlock(&inode->i_lock);
2563 trace_writeback_dirty_inode_enqueue(inode);
2564
2565 /*
2566 * If this is the first dirty inode for this bdi,
2567 * we have to wake-up the corresponding bdi thread
2568 * to make sure background write-back happens
2569 * later.
2570 */
2571 if (wakeup_bdi &&
2572 (wb->bdi->capabilities & BDI_CAP_WRITEBACK))
2573 wb_wakeup_delayed(wb);
2574 return;
2575 }
2576 }
2577out_unlock:
2578 if (wb)
2579 spin_unlock(&wb->list_lock);
2580 spin_unlock(&inode->i_lock);
2581}
2582EXPORT_SYMBOL(__mark_inode_dirty);
2583
2584/*
2585 * The @s_sync_lock is used to serialise concurrent sync operations
2586 * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2587 * Concurrent callers will block on the s_sync_lock rather than doing contending
2588 * walks. The queueing maintains sync(2) required behaviour as all the IO that
2589 * has been issued up to the time this function is enter is guaranteed to be
2590 * completed by the time we have gained the lock and waited for all IO that is
2591 * in progress regardless of the order callers are granted the lock.
2592 */
2593static void wait_sb_inodes(struct super_block *sb)
2594{
2595 LIST_HEAD(sync_list);
2596
2597 /*
2598 * We need to be protected against the filesystem going from
2599 * r/o to r/w or vice versa.
2600 */
2601 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2602
2603 mutex_lock(&sb->s_sync_lock);
2604
2605 /*
2606 * Splice the writeback list onto a temporary list to avoid waiting on
2607 * inodes that have started writeback after this point.
2608 *
2609 * Use rcu_read_lock() to keep the inodes around until we have a
2610 * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2611 * the local list because inodes can be dropped from either by writeback
2612 * completion.
2613 */
2614 rcu_read_lock();
2615 spin_lock_irq(&sb->s_inode_wblist_lock);
2616 list_splice_init(&sb->s_inodes_wb, &sync_list);
2617
2618 /*
2619 * Data integrity sync. Must wait for all pages under writeback, because
2620 * there may have been pages dirtied before our sync call, but which had
2621 * writeout started before we write it out. In which case, the inode
2622 * may not be on the dirty list, but we still have to wait for that
2623 * writeout.
2624 */
2625 while (!list_empty(&sync_list)) {
2626 struct inode *inode = list_first_entry(&sync_list, struct inode,
2627 i_wb_list);
2628 struct address_space *mapping = inode->i_mapping;
2629
2630 /*
2631 * Move each inode back to the wb list before we drop the lock
2632 * to preserve consistency between i_wb_list and the mapping
2633 * writeback tag. Writeback completion is responsible to remove
2634 * the inode from either list once the writeback tag is cleared.
2635 */
2636 list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
2637
2638 /*
2639 * The mapping can appear untagged while still on-list since we
2640 * do not have the mapping lock. Skip it here, wb completion
2641 * will remove it.
2642 */
2643 if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2644 continue;
2645
2646 spin_unlock_irq(&sb->s_inode_wblist_lock);
2647
2648 spin_lock(&inode->i_lock);
2649 if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
2650 spin_unlock(&inode->i_lock);
2651
2652 spin_lock_irq(&sb->s_inode_wblist_lock);
2653 continue;
2654 }
2655 __iget(inode);
2656 spin_unlock(&inode->i_lock);
2657 rcu_read_unlock();
2658
2659 /*
2660 * We keep the error status of individual mapping so that
2661 * applications can catch the writeback error using fsync(2).
2662 * See filemap_fdatawait_keep_errors() for details.
2663 */
2664 filemap_fdatawait_keep_errors(mapping);
2665
2666 cond_resched();
2667
2668 iput(inode);
2669
2670 rcu_read_lock();
2671 spin_lock_irq(&sb->s_inode_wblist_lock);
2672 }
2673 spin_unlock_irq(&sb->s_inode_wblist_lock);
2674 rcu_read_unlock();
2675 mutex_unlock(&sb->s_sync_lock);
2676}
2677
2678static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2679 enum wb_reason reason, bool skip_if_busy)
2680{
2681 struct backing_dev_info *bdi = sb->s_bdi;
2682 DEFINE_WB_COMPLETION(done, bdi);
2683 struct wb_writeback_work work = {
2684 .sb = sb,
2685 .sync_mode = WB_SYNC_NONE,
2686 .tagged_writepages = 1,
2687 .done = &done,
2688 .nr_pages = nr,
2689 .reason = reason,
2690 };
2691
2692 if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
2693 return;
2694 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2695
2696 bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
2697 wb_wait_for_completion(&done);
2698}
2699
2700/**
2701 * writeback_inodes_sb_nr - writeback dirty inodes from given super_block
2702 * @sb: the superblock
2703 * @nr: the number of pages to write
2704 * @reason: reason why some writeback work initiated
2705 *
2706 * Start writeback on some inodes on this super_block. No guarantees are made
2707 * on how many (if any) will be written, and this function does not wait
2708 * for IO completion of submitted IO.
2709 */
2710void writeback_inodes_sb_nr(struct super_block *sb,
2711 unsigned long nr,
2712 enum wb_reason reason)
2713{
2714 __writeback_inodes_sb_nr(sb, nr, reason, false);
2715}
2716EXPORT_SYMBOL(writeback_inodes_sb_nr);
2717
2718/**
2719 * writeback_inodes_sb - writeback dirty inodes from given super_block
2720 * @sb: the superblock
2721 * @reason: reason why some writeback work was initiated
2722 *
2723 * Start writeback on some inodes on this super_block. No guarantees are made
2724 * on how many (if any) will be written, and this function does not wait
2725 * for IO completion of submitted IO.
2726 */
2727void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2728{
2729 return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2730}
2731EXPORT_SYMBOL(writeback_inodes_sb);
2732
2733/**
2734 * try_to_writeback_inodes_sb - try to start writeback if none underway
2735 * @sb: the superblock
2736 * @reason: reason why some writeback work was initiated
2737 *
2738 * Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
2739 */
2740void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2741{
2742 if (!down_read_trylock(&sb->s_umount))
2743 return;
2744
2745 __writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason, true);
2746 up_read(&sb->s_umount);
2747}
2748EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2749
2750/**
2751 * sync_inodes_sb - sync sb inode pages
2752 * @sb: the superblock
2753 *
2754 * This function writes and waits on any dirty inode belonging to this
2755 * super_block.
2756 */
2757void sync_inodes_sb(struct super_block *sb)
2758{
2759 struct backing_dev_info *bdi = sb->s_bdi;
2760 DEFINE_WB_COMPLETION(done, bdi);
2761 struct wb_writeback_work work = {
2762 .sb = sb,
2763 .sync_mode = WB_SYNC_ALL,
2764 .nr_pages = LONG_MAX,
2765 .range_cyclic = 0,
2766 .done = &done,
2767 .reason = WB_REASON_SYNC,
2768 .for_sync = 1,
2769 };
2770
2771 /*
2772 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
2773 * inodes under writeback and I_DIRTY_TIME inodes ignored by
2774 * bdi_has_dirty() need to be written out too.
2775 */
2776 if (bdi == &noop_backing_dev_info)
2777 return;
2778 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2779
2780 /* protect against inode wb switch, see inode_switch_wbs_work_fn() */
2781 bdi_down_write_wb_switch_rwsem(bdi);
2782 bdi_split_work_to_wbs(bdi, &work, false);
2783 wb_wait_for_completion(&done);
2784 bdi_up_write_wb_switch_rwsem(bdi);
2785
2786 wait_sb_inodes(sb);
2787}
2788EXPORT_SYMBOL(sync_inodes_sb);
2789
2790/**
2791 * write_inode_now - write an inode to disk
2792 * @inode: inode to write to disk
2793 * @sync: whether the write should be synchronous or not
2794 *
2795 * This function commits an inode to disk immediately if it is dirty. This is
2796 * primarily needed by knfsd.
2797 *
2798 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
2799 */
2800int write_inode_now(struct inode *inode, int sync)
2801{
2802 struct writeback_control wbc = {
2803 .nr_to_write = LONG_MAX,
2804 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2805 .range_start = 0,
2806 .range_end = LLONG_MAX,
2807 };
2808
2809 if (!mapping_can_writeback(inode->i_mapping))
2810 wbc.nr_to_write = 0;
2811
2812 might_sleep();
2813 return writeback_single_inode(inode, &wbc);
2814}
2815EXPORT_SYMBOL(write_inode_now);
2816
2817/**
2818 * sync_inode_metadata - write an inode to disk
2819 * @inode: the inode to sync
2820 * @wait: wait for I/O to complete.
2821 *
2822 * Write an inode to disk and adjust its dirty state after completion.
2823 *
2824 * Note: only writes the actual inode, no associated data or other metadata.
2825 */
2826int sync_inode_metadata(struct inode *inode, int wait)
2827{
2828 struct writeback_control wbc = {
2829 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2830 .nr_to_write = 0, /* metadata-only */
2831 };
2832
2833 return writeback_single_inode(inode, &wbc);
2834}
2835EXPORT_SYMBOL(sync_inode_metadata);