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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
124 list_move(&inode->i_io_list, head);
125
126 /* dirty_time doesn't count as dirty_io until expiration */
127 if (head != &wb->b_dirty_time)
128 return wb_io_lists_populated(wb);
129
130 wb_io_lists_depopulated(wb);
131 return false;
132}
133
134/**
135 * inode_io_list_del_locked - remove an inode from its bdi_writeback IO list
136 * @inode: inode to be removed
137 * @wb: bdi_writeback @inode is being removed from
138 *
139 * Remove @inode which may be on one of @wb->b_{dirty|io|more_io} lists and
140 * clear %WB_has_dirty_io if all are empty afterwards.
141 */
142static void inode_io_list_del_locked(struct inode *inode,
143 struct bdi_writeback *wb)
144{
145 assert_spin_locked(&wb->list_lock);
146 assert_spin_locked(&inode->i_lock);
147
148 inode->i_state &= ~I_SYNC_QUEUED;
149 list_del_init(&inode->i_io_list);
150 wb_io_lists_depopulated(wb);
151}
152
153static void wb_wakeup(struct bdi_writeback *wb)
154{
155 spin_lock_bh(&wb->work_lock);
156 if (test_bit(WB_registered, &wb->state))
157 mod_delayed_work(bdi_wq, &wb->dwork, 0);
158 spin_unlock_bh(&wb->work_lock);
159}
160
161static void finish_writeback_work(struct bdi_writeback *wb,
162 struct wb_writeback_work *work)
163{
164 struct wb_completion *done = work->done;
165
166 if (work->auto_free)
167 kfree(work);
168 if (done) {
169 wait_queue_head_t *waitq = done->waitq;
170
171 /* @done can't be accessed after the following dec */
172 if (atomic_dec_and_test(&done->cnt))
173 wake_up_all(waitq);
174 }
175}
176
177static void wb_queue_work(struct bdi_writeback *wb,
178 struct wb_writeback_work *work)
179{
180 trace_writeback_queue(wb, work);
181
182 if (work->done)
183 atomic_inc(&work->done->cnt);
184
185 spin_lock_bh(&wb->work_lock);
186
187 if (test_bit(WB_registered, &wb->state)) {
188 list_add_tail(&work->list, &wb->work_list);
189 mod_delayed_work(bdi_wq, &wb->dwork, 0);
190 } else
191 finish_writeback_work(wb, work);
192
193 spin_unlock_bh(&wb->work_lock);
194}
195
196/**
197 * wb_wait_for_completion - wait for completion of bdi_writeback_works
198 * @done: target wb_completion
199 *
200 * Wait for one or more work items issued to @bdi with their ->done field
201 * set to @done, which should have been initialized with
202 * DEFINE_WB_COMPLETION(). This function returns after all such work items
203 * are completed. Work items which are waited upon aren't freed
204 * automatically on completion.
205 */
206void wb_wait_for_completion(struct wb_completion *done)
207{
208 atomic_dec(&done->cnt); /* put down the initial count */
209 wait_event(*done->waitq, !atomic_read(&done->cnt));
210}
211
212#ifdef CONFIG_CGROUP_WRITEBACK
213
214/*
215 * Parameters for foreign inode detection, see wbc_detach_inode() to see
216 * how they're used.
217 *
218 * These paramters are inherently heuristical as the detection target
219 * itself is fuzzy. All we want to do is detaching an inode from the
220 * current owner if it's being written to by some other cgroups too much.
221 *
222 * The current cgroup writeback is built on the assumption that multiple
223 * cgroups writing to the same inode concurrently is very rare and a mode
224 * of operation which isn't well supported. As such, the goal is not
225 * taking too long when a different cgroup takes over an inode while
226 * avoiding too aggressive flip-flops from occasional foreign writes.
227 *
228 * We record, very roughly, 2s worth of IO time history and if more than
229 * half of that is foreign, trigger the switch. The recording is quantized
230 * to 16 slots. To avoid tiny writes from swinging the decision too much,
231 * writes smaller than 1/8 of avg size are ignored.
232 */
233#define WB_FRN_TIME_SHIFT 13 /* 1s = 2^13, upto 8 secs w/ 16bit */
234#define WB_FRN_TIME_AVG_SHIFT 3 /* avg = avg * 7/8 + new * 1/8 */
235#define WB_FRN_TIME_CUT_DIV 8 /* ignore rounds < avg / 8 */
236#define WB_FRN_TIME_PERIOD (2 * (1 << WB_FRN_TIME_SHIFT)) /* 2s */
237
238#define WB_FRN_HIST_SLOTS 16 /* inode->i_wb_frn_history is 16bit */
239#define WB_FRN_HIST_UNIT (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
240 /* each slot's duration is 2s / 16 */
241#define WB_FRN_HIST_THR_SLOTS (WB_FRN_HIST_SLOTS / 2)
242 /* if foreign slots >= 8, switch */
243#define WB_FRN_HIST_MAX_SLOTS (WB_FRN_HIST_THR_SLOTS / 2 + 1)
244 /* one round can affect upto 5 slots */
245#define WB_FRN_MAX_IN_FLIGHT 1024 /* don't queue too many concurrently */
246
247static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
248static struct workqueue_struct *isw_wq;
249
250void __inode_attach_wb(struct inode *inode, struct page *page)
251{
252 struct backing_dev_info *bdi = inode_to_bdi(inode);
253 struct bdi_writeback *wb = NULL;
254
255 if (inode_cgwb_enabled(inode)) {
256 struct cgroup_subsys_state *memcg_css;
257
258 if (page) {
259 memcg_css = mem_cgroup_css_from_page(page);
260 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
261 } else {
262 /* must pin memcg_css, see wb_get_create() */
263 memcg_css = task_get_css(current, memory_cgrp_id);
264 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
265 css_put(memcg_css);
266 }
267 }
268
269 if (!wb)
270 wb = &bdi->wb;
271
272 /*
273 * There may be multiple instances of this function racing to
274 * update the same inode. Use cmpxchg() to tell the winner.
275 */
276 if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
277 wb_put(wb);
278}
279EXPORT_SYMBOL_GPL(__inode_attach_wb);
280
281/**
282 * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
283 * @inode: inode of interest with i_lock held
284 *
285 * Returns @inode's wb with its list_lock held. @inode->i_lock must be
286 * held on entry and is released on return. The returned wb is guaranteed
287 * to stay @inode's associated wb until its list_lock is released.
288 */
289static struct bdi_writeback *
290locked_inode_to_wb_and_lock_list(struct inode *inode)
291 __releases(&inode->i_lock)
292 __acquires(&wb->list_lock)
293{
294 while (true) {
295 struct bdi_writeback *wb = inode_to_wb(inode);
296
297 /*
298 * inode_to_wb() association is protected by both
299 * @inode->i_lock and @wb->list_lock but list_lock nests
300 * outside i_lock. Drop i_lock and verify that the
301 * association hasn't changed after acquiring list_lock.
302 */
303 wb_get(wb);
304 spin_unlock(&inode->i_lock);
305 spin_lock(&wb->list_lock);
306
307 /* i_wb may have changed inbetween, can't use inode_to_wb() */
308 if (likely(wb == inode->i_wb)) {
309 wb_put(wb); /* @inode already has ref */
310 return wb;
311 }
312
313 spin_unlock(&wb->list_lock);
314 wb_put(wb);
315 cpu_relax();
316 spin_lock(&inode->i_lock);
317 }
318}
319
320/**
321 * inode_to_wb_and_lock_list - determine an inode's wb and lock it
322 * @inode: inode of interest
323 *
324 * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
325 * on entry.
326 */
327static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
328 __acquires(&wb->list_lock)
329{
330 spin_lock(&inode->i_lock);
331 return locked_inode_to_wb_and_lock_list(inode);
332}
333
334struct inode_switch_wbs_context {
335 struct inode *inode;
336 struct bdi_writeback *new_wb;
337
338 struct rcu_head rcu_head;
339 struct work_struct work;
340};
341
342static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
343{
344 down_write(&bdi->wb_switch_rwsem);
345}
346
347static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
348{
349 up_write(&bdi->wb_switch_rwsem);
350}
351
352static void inode_switch_wbs_work_fn(struct work_struct *work)
353{
354 struct inode_switch_wbs_context *isw =
355 container_of(work, struct inode_switch_wbs_context, work);
356 struct inode *inode = isw->inode;
357 struct backing_dev_info *bdi = inode_to_bdi(inode);
358 struct address_space *mapping = inode->i_mapping;
359 struct bdi_writeback *old_wb = inode->i_wb;
360 struct bdi_writeback *new_wb = isw->new_wb;
361 XA_STATE(xas, &mapping->i_pages, 0);
362 struct page *page;
363 bool switched = false;
364
365 /*
366 * If @inode switches cgwb membership while sync_inodes_sb() is
367 * being issued, sync_inodes_sb() might miss it. Synchronize.
368 */
369 down_read(&bdi->wb_switch_rwsem);
370
371 /*
372 * By the time control reaches here, RCU grace period has passed
373 * since I_WB_SWITCH assertion and all wb stat update transactions
374 * between unlocked_inode_to_wb_begin/end() are guaranteed to be
375 * synchronizing against the i_pages lock.
376 *
377 * Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
378 * gives us exclusion against all wb related operations on @inode
379 * including IO list manipulations and stat updates.
380 */
381 if (old_wb < new_wb) {
382 spin_lock(&old_wb->list_lock);
383 spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
384 } else {
385 spin_lock(&new_wb->list_lock);
386 spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
387 }
388 spin_lock(&inode->i_lock);
389 xa_lock_irq(&mapping->i_pages);
390
391 /*
392 * Once I_FREEING is visible under i_lock, the eviction path owns
393 * the inode and we shouldn't modify ->i_io_list.
394 */
395 if (unlikely(inode->i_state & I_FREEING))
396 goto skip_switch;
397
398 trace_inode_switch_wbs(inode, old_wb, new_wb);
399
400 /*
401 * Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
402 * to possibly dirty pages while PAGECACHE_TAG_WRITEBACK points to
403 * pages actually under writeback.
404 */
405 xas_for_each_marked(&xas, page, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
406 if (PageDirty(page)) {
407 dec_wb_stat(old_wb, WB_RECLAIMABLE);
408 inc_wb_stat(new_wb, WB_RECLAIMABLE);
409 }
410 }
411
412 xas_set(&xas, 0);
413 xas_for_each_marked(&xas, page, ULONG_MAX, PAGECACHE_TAG_WRITEBACK) {
414 WARN_ON_ONCE(!PageWriteback(page));
415 dec_wb_stat(old_wb, WB_WRITEBACK);
416 inc_wb_stat(new_wb, WB_WRITEBACK);
417 }
418
419 wb_get(new_wb);
420
421 /*
422 * Transfer to @new_wb's IO list if necessary. The specific list
423 * @inode was on is ignored and the inode is put on ->b_dirty which
424 * is always correct including from ->b_dirty_time. The transfer
425 * preserves @inode->dirtied_when ordering.
426 */
427 if (!list_empty(&inode->i_io_list)) {
428 struct inode *pos;
429
430 inode_io_list_del_locked(inode, old_wb);
431 inode->i_wb = new_wb;
432 list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
433 if (time_after_eq(inode->dirtied_when,
434 pos->dirtied_when))
435 break;
436 inode_io_list_move_locked(inode, new_wb, pos->i_io_list.prev);
437 } else {
438 inode->i_wb = new_wb;
439 }
440
441 /* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
442 inode->i_wb_frn_winner = 0;
443 inode->i_wb_frn_avg_time = 0;
444 inode->i_wb_frn_history = 0;
445 switched = true;
446skip_switch:
447 /*
448 * Paired with load_acquire in unlocked_inode_to_wb_begin() and
449 * ensures that the new wb is visible if they see !I_WB_SWITCH.
450 */
451 smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
452
453 xa_unlock_irq(&mapping->i_pages);
454 spin_unlock(&inode->i_lock);
455 spin_unlock(&new_wb->list_lock);
456 spin_unlock(&old_wb->list_lock);
457
458 up_read(&bdi->wb_switch_rwsem);
459
460 if (switched) {
461 wb_wakeup(new_wb);
462 wb_put(old_wb);
463 }
464 wb_put(new_wb);
465
466 iput(inode);
467 kfree(isw);
468
469 atomic_dec(&isw_nr_in_flight);
470}
471
472static void inode_switch_wbs_rcu_fn(struct rcu_head *rcu_head)
473{
474 struct inode_switch_wbs_context *isw = container_of(rcu_head,
475 struct inode_switch_wbs_context, rcu_head);
476
477 /* needs to grab bh-unsafe locks, bounce to work item */
478 INIT_WORK(&isw->work, inode_switch_wbs_work_fn);
479 queue_work(isw_wq, &isw->work);
480}
481
482/**
483 * inode_switch_wbs - change the wb association of an inode
484 * @inode: target inode
485 * @new_wb_id: ID of the new wb
486 *
487 * Switch @inode's wb association to the wb identified by @new_wb_id. The
488 * switching is performed asynchronously and may fail silently.
489 */
490static void inode_switch_wbs(struct inode *inode, int new_wb_id)
491{
492 struct backing_dev_info *bdi = inode_to_bdi(inode);
493 struct cgroup_subsys_state *memcg_css;
494 struct inode_switch_wbs_context *isw;
495
496 /* noop if seems to be already in progress */
497 if (inode->i_state & I_WB_SWITCH)
498 return;
499
500 /* avoid queueing a new switch if too many are already in flight */
501 if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
502 return;
503
504 isw = kzalloc(sizeof(*isw), GFP_ATOMIC);
505 if (!isw)
506 return;
507
508 /* find and pin the new wb */
509 rcu_read_lock();
510 memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
511 if (memcg_css)
512 isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
513 rcu_read_unlock();
514 if (!isw->new_wb)
515 goto out_free;
516
517 /* while holding I_WB_SWITCH, no one else can update the association */
518 spin_lock(&inode->i_lock);
519 if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
520 inode->i_state & (I_WB_SWITCH | I_FREEING) ||
521 inode_to_wb(inode) == isw->new_wb) {
522 spin_unlock(&inode->i_lock);
523 goto out_free;
524 }
525 inode->i_state |= I_WB_SWITCH;
526 __iget(inode);
527 spin_unlock(&inode->i_lock);
528
529 isw->inode = inode;
530
531 /*
532 * In addition to synchronizing among switchers, I_WB_SWITCH tells
533 * the RCU protected stat update paths to grab the i_page
534 * lock so that stat transfer can synchronize against them.
535 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
536 */
537 call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn);
538
539 atomic_inc(&isw_nr_in_flight);
540 return;
541
542out_free:
543 if (isw->new_wb)
544 wb_put(isw->new_wb);
545 kfree(isw);
546}
547
548/**
549 * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
550 * @wbc: writeback_control of interest
551 * @inode: target inode
552 *
553 * @inode is locked and about to be written back under the control of @wbc.
554 * Record @inode's writeback context into @wbc and unlock the i_lock. On
555 * writeback completion, wbc_detach_inode() should be called. This is used
556 * to track the cgroup writeback context.
557 */
558void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
559 struct inode *inode)
560{
561 if (!inode_cgwb_enabled(inode)) {
562 spin_unlock(&inode->i_lock);
563 return;
564 }
565
566 wbc->wb = inode_to_wb(inode);
567 wbc->inode = inode;
568
569 wbc->wb_id = wbc->wb->memcg_css->id;
570 wbc->wb_lcand_id = inode->i_wb_frn_winner;
571 wbc->wb_tcand_id = 0;
572 wbc->wb_bytes = 0;
573 wbc->wb_lcand_bytes = 0;
574 wbc->wb_tcand_bytes = 0;
575
576 wb_get(wbc->wb);
577 spin_unlock(&inode->i_lock);
578
579 /*
580 * A dying wb indicates that either the blkcg associated with the
581 * memcg changed or the associated memcg is dying. In the first
582 * case, a replacement wb should already be available and we should
583 * refresh the wb immediately. In the second case, trying to
584 * refresh will keep failing.
585 */
586 if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
587 inode_switch_wbs(inode, wbc->wb_id);
588}
589EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
590
591/**
592 * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
593 * @wbc: writeback_control of the just finished writeback
594 *
595 * To be called after a writeback attempt of an inode finishes and undoes
596 * wbc_attach_and_unlock_inode(). Can be called under any context.
597 *
598 * As concurrent write sharing of an inode is expected to be very rare and
599 * memcg only tracks page ownership on first-use basis severely confining
600 * the usefulness of such sharing, cgroup writeback tracks ownership
601 * per-inode. While the support for concurrent write sharing of an inode
602 * is deemed unnecessary, an inode being written to by different cgroups at
603 * different points in time is a lot more common, and, more importantly,
604 * charging only by first-use can too readily lead to grossly incorrect
605 * behaviors (single foreign page can lead to gigabytes of writeback to be
606 * incorrectly attributed).
607 *
608 * To resolve this issue, cgroup writeback detects the majority dirtier of
609 * an inode and transfers the ownership to it. To avoid unnnecessary
610 * oscillation, the detection mechanism keeps track of history and gives
611 * out the switch verdict only if the foreign usage pattern is stable over
612 * a certain amount of time and/or writeback attempts.
613 *
614 * On each writeback attempt, @wbc tries to detect the majority writer
615 * using Boyer-Moore majority vote algorithm. In addition to the byte
616 * count from the majority voting, it also counts the bytes written for the
617 * current wb and the last round's winner wb (max of last round's current
618 * wb, the winner from two rounds ago, and the last round's majority
619 * candidate). Keeping track of the historical winner helps the algorithm
620 * to semi-reliably detect the most active writer even when it's not the
621 * absolute majority.
622 *
623 * Once the winner of the round is determined, whether the winner is
624 * foreign or not and how much IO time the round consumed is recorded in
625 * inode->i_wb_frn_history. If the amount of recorded foreign IO time is
626 * over a certain threshold, the switch verdict is given.
627 */
628void wbc_detach_inode(struct writeback_control *wbc)
629{
630 struct bdi_writeback *wb = wbc->wb;
631 struct inode *inode = wbc->inode;
632 unsigned long avg_time, max_bytes, max_time;
633 u16 history;
634 int max_id;
635
636 if (!wb)
637 return;
638
639 history = inode->i_wb_frn_history;
640 avg_time = inode->i_wb_frn_avg_time;
641
642 /* pick the winner of this round */
643 if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
644 wbc->wb_bytes >= wbc->wb_tcand_bytes) {
645 max_id = wbc->wb_id;
646 max_bytes = wbc->wb_bytes;
647 } else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
648 max_id = wbc->wb_lcand_id;
649 max_bytes = wbc->wb_lcand_bytes;
650 } else {
651 max_id = wbc->wb_tcand_id;
652 max_bytes = wbc->wb_tcand_bytes;
653 }
654
655 /*
656 * Calculate the amount of IO time the winner consumed and fold it
657 * into the running average kept per inode. If the consumed IO
658 * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
659 * deciding whether to switch or not. This is to prevent one-off
660 * small dirtiers from skewing the verdict.
661 */
662 max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
663 wb->avg_write_bandwidth);
664 if (avg_time)
665 avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
666 (avg_time >> WB_FRN_TIME_AVG_SHIFT);
667 else
668 avg_time = max_time; /* immediate catch up on first run */
669
670 if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
671 int slots;
672
673 /*
674 * The switch verdict is reached if foreign wb's consume
675 * more than a certain proportion of IO time in a
676 * WB_FRN_TIME_PERIOD. This is loosely tracked by 16 slot
677 * history mask where each bit represents one sixteenth of
678 * the period. Determine the number of slots to shift into
679 * history from @max_time.
680 */
681 slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
682 (unsigned long)WB_FRN_HIST_MAX_SLOTS);
683 history <<= slots;
684 if (wbc->wb_id != max_id)
685 history |= (1U << slots) - 1;
686
687 if (history)
688 trace_inode_foreign_history(inode, wbc, history);
689
690 /*
691 * Switch if the current wb isn't the consistent winner.
692 * If there are multiple closely competing dirtiers, the
693 * inode may switch across them repeatedly over time, which
694 * is okay. The main goal is avoiding keeping an inode on
695 * the wrong wb for an extended period of time.
696 */
697 if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
698 inode_switch_wbs(inode, max_id);
699 }
700
701 /*
702 * Multiple instances of this function may race to update the
703 * following fields but we don't mind occassional inaccuracies.
704 */
705 inode->i_wb_frn_winner = max_id;
706 inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
707 inode->i_wb_frn_history = history;
708
709 wb_put(wbc->wb);
710 wbc->wb = NULL;
711}
712EXPORT_SYMBOL_GPL(wbc_detach_inode);
713
714/**
715 * wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
716 * @wbc: writeback_control of the writeback in progress
717 * @page: page being written out
718 * @bytes: number of bytes being written out
719 *
720 * @bytes from @page are about to written out during the writeback
721 * controlled by @wbc. Keep the book for foreign inode detection. See
722 * wbc_detach_inode().
723 */
724void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
725 size_t bytes)
726{
727 struct cgroup_subsys_state *css;
728 int id;
729
730 /*
731 * pageout() path doesn't attach @wbc to the inode being written
732 * out. This is intentional as we don't want the function to block
733 * behind a slow cgroup. Ultimately, we want pageout() to kick off
734 * regular writeback instead of writing things out itself.
735 */
736 if (!wbc->wb || wbc->no_cgroup_owner)
737 return;
738
739 css = mem_cgroup_css_from_page(page);
740 /* dead cgroups shouldn't contribute to inode ownership arbitration */
741 if (!(css->flags & CSS_ONLINE))
742 return;
743
744 id = css->id;
745
746 if (id == wbc->wb_id) {
747 wbc->wb_bytes += bytes;
748 return;
749 }
750
751 if (id == wbc->wb_lcand_id)
752 wbc->wb_lcand_bytes += bytes;
753
754 /* Boyer-Moore majority vote algorithm */
755 if (!wbc->wb_tcand_bytes)
756 wbc->wb_tcand_id = id;
757 if (id == wbc->wb_tcand_id)
758 wbc->wb_tcand_bytes += bytes;
759 else
760 wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
761}
762EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);
763
764/**
765 * inode_congested - test whether an inode is congested
766 * @inode: inode to test for congestion (may be NULL)
767 * @cong_bits: mask of WB_[a]sync_congested bits to test
768 *
769 * Tests whether @inode is congested. @cong_bits is the mask of congestion
770 * bits to test and the return value is the mask of set bits.
771 *
772 * If cgroup writeback is enabled for @inode, the congestion state is
773 * determined by whether the cgwb (cgroup bdi_writeback) for the blkcg
774 * associated with @inode is congested; otherwise, the root wb's congestion
775 * state is used.
776 *
777 * @inode is allowed to be NULL as this function is often called on
778 * mapping->host which is NULL for the swapper space.
779 */
780int inode_congested(struct inode *inode, int cong_bits)
781{
782 /*
783 * Once set, ->i_wb never becomes NULL while the inode is alive.
784 * Start transaction iff ->i_wb is visible.
785 */
786 if (inode && inode_to_wb_is_valid(inode)) {
787 struct bdi_writeback *wb;
788 struct wb_lock_cookie lock_cookie = {};
789 bool congested;
790
791 wb = unlocked_inode_to_wb_begin(inode, &lock_cookie);
792 congested = wb_congested(wb, cong_bits);
793 unlocked_inode_to_wb_end(inode, &lock_cookie);
794 return congested;
795 }
796
797 return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
798}
799EXPORT_SYMBOL_GPL(inode_congested);
800
801/**
802 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
803 * @wb: target bdi_writeback to split @nr_pages to
804 * @nr_pages: number of pages to write for the whole bdi
805 *
806 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
807 * relation to the total write bandwidth of all wb's w/ dirty inodes on
808 * @wb->bdi.
809 */
810static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
811{
812 unsigned long this_bw = wb->avg_write_bandwidth;
813 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
814
815 if (nr_pages == LONG_MAX)
816 return LONG_MAX;
817
818 /*
819 * This may be called on clean wb's and proportional distribution
820 * may not make sense, just use the original @nr_pages in those
821 * cases. In general, we wanna err on the side of writing more.
822 */
823 if (!tot_bw || this_bw >= tot_bw)
824 return nr_pages;
825 else
826 return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
827}
828
829/**
830 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
831 * @bdi: target backing_dev_info
832 * @base_work: wb_writeback_work to issue
833 * @skip_if_busy: skip wb's which already have writeback in progress
834 *
835 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
836 * have dirty inodes. If @base_work->nr_page isn't %LONG_MAX, it's
837 * distributed to the busy wbs according to each wb's proportion in the
838 * total active write bandwidth of @bdi.
839 */
840static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
841 struct wb_writeback_work *base_work,
842 bool skip_if_busy)
843{
844 struct bdi_writeback *last_wb = NULL;
845 struct bdi_writeback *wb = list_entry(&bdi->wb_list,
846 struct bdi_writeback, bdi_node);
847
848 might_sleep();
849restart:
850 rcu_read_lock();
851 list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
852 DEFINE_WB_COMPLETION(fallback_work_done, bdi);
853 struct wb_writeback_work fallback_work;
854 struct wb_writeback_work *work;
855 long nr_pages;
856
857 if (last_wb) {
858 wb_put(last_wb);
859 last_wb = NULL;
860 }
861
862 /* SYNC_ALL writes out I_DIRTY_TIME too */
863 if (!wb_has_dirty_io(wb) &&
864 (base_work->sync_mode == WB_SYNC_NONE ||
865 list_empty(&wb->b_dirty_time)))
866 continue;
867 if (skip_if_busy && writeback_in_progress(wb))
868 continue;
869
870 nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
871
872 work = kmalloc(sizeof(*work), GFP_ATOMIC);
873 if (work) {
874 *work = *base_work;
875 work->nr_pages = nr_pages;
876 work->auto_free = 1;
877 wb_queue_work(wb, work);
878 continue;
879 }
880
881 /* alloc failed, execute synchronously using on-stack fallback */
882 work = &fallback_work;
883 *work = *base_work;
884 work->nr_pages = nr_pages;
885 work->auto_free = 0;
886 work->done = &fallback_work_done;
887
888 wb_queue_work(wb, work);
889
890 /*
891 * Pin @wb so that it stays on @bdi->wb_list. This allows
892 * continuing iteration from @wb after dropping and
893 * regrabbing rcu read lock.
894 */
895 wb_get(wb);
896 last_wb = wb;
897
898 rcu_read_unlock();
899 wb_wait_for_completion(&fallback_work_done);
900 goto restart;
901 }
902 rcu_read_unlock();
903
904 if (last_wb)
905 wb_put(last_wb);
906}
907
908/**
909 * cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
910 * @bdi_id: target bdi id
911 * @memcg_id: target memcg css id
912 * @nr: number of pages to write, 0 for best-effort dirty flushing
913 * @reason: reason why some writeback work initiated
914 * @done: target wb_completion
915 *
916 * Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
917 * with the specified parameters.
918 */
919int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr,
920 enum wb_reason reason, struct wb_completion *done)
921{
922 struct backing_dev_info *bdi;
923 struct cgroup_subsys_state *memcg_css;
924 struct bdi_writeback *wb;
925 struct wb_writeback_work *work;
926 int ret;
927
928 /* lookup bdi and memcg */
929 bdi = bdi_get_by_id(bdi_id);
930 if (!bdi)
931 return -ENOENT;
932
933 rcu_read_lock();
934 memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
935 if (memcg_css && !css_tryget(memcg_css))
936 memcg_css = NULL;
937 rcu_read_unlock();
938 if (!memcg_css) {
939 ret = -ENOENT;
940 goto out_bdi_put;
941 }
942
943 /*
944 * And find the associated wb. If the wb isn't there already
945 * there's nothing to flush, don't create one.
946 */
947 wb = wb_get_lookup(bdi, memcg_css);
948 if (!wb) {
949 ret = -ENOENT;
950 goto out_css_put;
951 }
952
953 /*
954 * If @nr is zero, the caller is attempting to write out most of
955 * the currently dirty pages. Let's take the current dirty page
956 * count and inflate it by 25% which should be large enough to
957 * flush out most dirty pages while avoiding getting livelocked by
958 * concurrent dirtiers.
959 */
960 if (!nr) {
961 unsigned long filepages, headroom, dirty, writeback;
962
963 mem_cgroup_wb_stats(wb, &filepages, &headroom, &dirty,
964 &writeback);
965 nr = dirty * 10 / 8;
966 }
967
968 /* issue the writeback work */
969 work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
970 if (work) {
971 work->nr_pages = nr;
972 work->sync_mode = WB_SYNC_NONE;
973 work->range_cyclic = 1;
974 work->reason = reason;
975 work->done = done;
976 work->auto_free = 1;
977 wb_queue_work(wb, work);
978 ret = 0;
979 } else {
980 ret = -ENOMEM;
981 }
982
983 wb_put(wb);
984out_css_put:
985 css_put(memcg_css);
986out_bdi_put:
987 bdi_put(bdi);
988 return ret;
989}
990
991/**
992 * cgroup_writeback_umount - flush inode wb switches for umount
993 *
994 * This function is called when a super_block is about to be destroyed and
995 * flushes in-flight inode wb switches. An inode wb switch goes through
996 * RCU and then workqueue, so the two need to be flushed in order to ensure
997 * that all previously scheduled switches are finished. As wb switches are
998 * rare occurrences and synchronize_rcu() can take a while, perform
999 * flushing iff wb switches are in flight.
1000 */
1001void cgroup_writeback_umount(void)
1002{
1003 if (atomic_read(&isw_nr_in_flight)) {
1004 /*
1005 * Use rcu_barrier() to wait for all pending callbacks to
1006 * ensure that all in-flight wb switches are in the workqueue.
1007 */
1008 rcu_barrier();
1009 flush_workqueue(isw_wq);
1010 }
1011}
1012
1013static int __init cgroup_writeback_init(void)
1014{
1015 isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
1016 if (!isw_wq)
1017 return -ENOMEM;
1018 return 0;
1019}
1020fs_initcall(cgroup_writeback_init);
1021
1022#else /* CONFIG_CGROUP_WRITEBACK */
1023
1024static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1025static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1026
1027static struct bdi_writeback *
1028locked_inode_to_wb_and_lock_list(struct inode *inode)
1029 __releases(&inode->i_lock)
1030 __acquires(&wb->list_lock)
1031{
1032 struct bdi_writeback *wb = inode_to_wb(inode);
1033
1034 spin_unlock(&inode->i_lock);
1035 spin_lock(&wb->list_lock);
1036 return wb;
1037}
1038
1039static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
1040 __acquires(&wb->list_lock)
1041{
1042 struct bdi_writeback *wb = inode_to_wb(inode);
1043
1044 spin_lock(&wb->list_lock);
1045 return wb;
1046}
1047
1048static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
1049{
1050 return nr_pages;
1051}
1052
1053static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
1054 struct wb_writeback_work *base_work,
1055 bool skip_if_busy)
1056{
1057 might_sleep();
1058
1059 if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
1060 base_work->auto_free = 0;
1061 wb_queue_work(&bdi->wb, base_work);
1062 }
1063}
1064
1065#endif /* CONFIG_CGROUP_WRITEBACK */
1066
1067/*
1068 * Add in the number of potentially dirty inodes, because each inode
1069 * write can dirty pagecache in the underlying blockdev.
1070 */
1071static unsigned long get_nr_dirty_pages(void)
1072{
1073 return global_node_page_state(NR_FILE_DIRTY) +
1074 get_nr_dirty_inodes();
1075}
1076
1077static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
1078{
1079 if (!wb_has_dirty_io(wb))
1080 return;
1081
1082 /*
1083 * All callers of this function want to start writeback of all
1084 * dirty pages. Places like vmscan can call this at a very
1085 * high frequency, causing pointless allocations of tons of
1086 * work items and keeping the flusher threads busy retrieving
1087 * that work. Ensure that we only allow one of them pending and
1088 * inflight at the time.
1089 */
1090 if (test_bit(WB_start_all, &wb->state) ||
1091 test_and_set_bit(WB_start_all, &wb->state))
1092 return;
1093
1094 wb->start_all_reason = reason;
1095 wb_wakeup(wb);
1096}
1097
1098/**
1099 * wb_start_background_writeback - start background writeback
1100 * @wb: bdi_writback to write from
1101 *
1102 * Description:
1103 * This makes sure WB_SYNC_NONE background writeback happens. When
1104 * this function returns, it is only guaranteed that for given wb
1105 * some IO is happening if we are over background dirty threshold.
1106 * Caller need not hold sb s_umount semaphore.
1107 */
1108void wb_start_background_writeback(struct bdi_writeback *wb)
1109{
1110 /*
1111 * We just wake up the flusher thread. It will perform background
1112 * writeback as soon as there is no other work to do.
1113 */
1114 trace_writeback_wake_background(wb);
1115 wb_wakeup(wb);
1116}
1117
1118/*
1119 * Remove the inode from the writeback list it is on.
1120 */
1121void inode_io_list_del(struct inode *inode)
1122{
1123 struct bdi_writeback *wb;
1124
1125 wb = inode_to_wb_and_lock_list(inode);
1126 spin_lock(&inode->i_lock);
1127 inode_io_list_del_locked(inode, wb);
1128 spin_unlock(&inode->i_lock);
1129 spin_unlock(&wb->list_lock);
1130}
1131EXPORT_SYMBOL(inode_io_list_del);
1132
1133/*
1134 * mark an inode as under writeback on the sb
1135 */
1136void sb_mark_inode_writeback(struct inode *inode)
1137{
1138 struct super_block *sb = inode->i_sb;
1139 unsigned long flags;
1140
1141 if (list_empty(&inode->i_wb_list)) {
1142 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1143 if (list_empty(&inode->i_wb_list)) {
1144 list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
1145 trace_sb_mark_inode_writeback(inode);
1146 }
1147 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1148 }
1149}
1150
1151/*
1152 * clear an inode as under writeback on the sb
1153 */
1154void sb_clear_inode_writeback(struct inode *inode)
1155{
1156 struct super_block *sb = inode->i_sb;
1157 unsigned long flags;
1158
1159 if (!list_empty(&inode->i_wb_list)) {
1160 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1161 if (!list_empty(&inode->i_wb_list)) {
1162 list_del_init(&inode->i_wb_list);
1163 trace_sb_clear_inode_writeback(inode);
1164 }
1165 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1166 }
1167}
1168
1169/*
1170 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1171 * furthest end of its superblock's dirty-inode list.
1172 *
1173 * Before stamping the inode's ->dirtied_when, we check to see whether it is
1174 * already the most-recently-dirtied inode on the b_dirty list. If that is
1175 * the case then the inode must have been redirtied while it was being written
1176 * out and we don't reset its dirtied_when.
1177 */
1178static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
1179{
1180 assert_spin_locked(&inode->i_lock);
1181
1182 if (!list_empty(&wb->b_dirty)) {
1183 struct inode *tail;
1184
1185 tail = wb_inode(wb->b_dirty.next);
1186 if (time_before(inode->dirtied_when, tail->dirtied_when))
1187 inode->dirtied_when = jiffies;
1188 }
1189 inode_io_list_move_locked(inode, wb, &wb->b_dirty);
1190 inode->i_state &= ~I_SYNC_QUEUED;
1191}
1192
1193static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
1194{
1195 spin_lock(&inode->i_lock);
1196 redirty_tail_locked(inode, wb);
1197 spin_unlock(&inode->i_lock);
1198}
1199
1200/*
1201 * requeue inode for re-scanning after bdi->b_io list is exhausted.
1202 */
1203static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
1204{
1205 inode_io_list_move_locked(inode, wb, &wb->b_more_io);
1206}
1207
1208static void inode_sync_complete(struct inode *inode)
1209{
1210 inode->i_state &= ~I_SYNC;
1211 /* If inode is clean an unused, put it into LRU now... */
1212 inode_add_lru(inode);
1213 /* Waiters must see I_SYNC cleared before being woken up */
1214 smp_mb();
1215 wake_up_bit(&inode->i_state, __I_SYNC);
1216}
1217
1218static bool inode_dirtied_after(struct inode *inode, unsigned long t)
1219{
1220 bool ret = time_after(inode->dirtied_when, t);
1221#ifndef CONFIG_64BIT
1222 /*
1223 * For inodes being constantly redirtied, dirtied_when can get stuck.
1224 * It _appears_ to be in the future, but is actually in distant past.
1225 * This test is necessary to prevent such wrapped-around relative times
1226 * from permanently stopping the whole bdi writeback.
1227 */
1228 ret = ret && time_before_eq(inode->dirtied_when, jiffies);
1229#endif
1230 return ret;
1231}
1232
1233#define EXPIRE_DIRTY_ATIME 0x0001
1234
1235/*
1236 * Move expired (dirtied before dirtied_before) dirty inodes from
1237 * @delaying_queue to @dispatch_queue.
1238 */
1239static int move_expired_inodes(struct list_head *delaying_queue,
1240 struct list_head *dispatch_queue,
1241 unsigned long dirtied_before)
1242{
1243 LIST_HEAD(tmp);
1244 struct list_head *pos, *node;
1245 struct super_block *sb = NULL;
1246 struct inode *inode;
1247 int do_sb_sort = 0;
1248 int moved = 0;
1249
1250 while (!list_empty(delaying_queue)) {
1251 inode = wb_inode(delaying_queue->prev);
1252 if (inode_dirtied_after(inode, dirtied_before))
1253 break;
1254 list_move(&inode->i_io_list, &tmp);
1255 moved++;
1256 spin_lock(&inode->i_lock);
1257 inode->i_state |= I_SYNC_QUEUED;
1258 spin_unlock(&inode->i_lock);
1259 if (sb_is_blkdev_sb(inode->i_sb))
1260 continue;
1261 if (sb && sb != inode->i_sb)
1262 do_sb_sort = 1;
1263 sb = inode->i_sb;
1264 }
1265
1266 /* just one sb in list, splice to dispatch_queue and we're done */
1267 if (!do_sb_sort) {
1268 list_splice(&tmp, dispatch_queue);
1269 goto out;
1270 }
1271
1272 /* Move inodes from one superblock together */
1273 while (!list_empty(&tmp)) {
1274 sb = wb_inode(tmp.prev)->i_sb;
1275 list_for_each_prev_safe(pos, node, &tmp) {
1276 inode = wb_inode(pos);
1277 if (inode->i_sb == sb)
1278 list_move(&inode->i_io_list, dispatch_queue);
1279 }
1280 }
1281out:
1282 return moved;
1283}
1284
1285/*
1286 * Queue all expired dirty inodes for io, eldest first.
1287 * Before
1288 * newly dirtied b_dirty b_io b_more_io
1289 * =============> gf edc BA
1290 * After
1291 * newly dirtied b_dirty b_io b_more_io
1292 * =============> g fBAedc
1293 * |
1294 * +--> dequeue for IO
1295 */
1296static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
1297 unsigned long dirtied_before)
1298{
1299 int moved;
1300 unsigned long time_expire_jif = dirtied_before;
1301
1302 assert_spin_locked(&wb->list_lock);
1303 list_splice_init(&wb->b_more_io, &wb->b_io);
1304 moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, dirtied_before);
1305 if (!work->for_sync)
1306 time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
1307 moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
1308 time_expire_jif);
1309 if (moved)
1310 wb_io_lists_populated(wb);
1311 trace_writeback_queue_io(wb, work, dirtied_before, moved);
1312}
1313
1314static int write_inode(struct inode *inode, struct writeback_control *wbc)
1315{
1316 int ret;
1317
1318 if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1319 trace_writeback_write_inode_start(inode, wbc);
1320 ret = inode->i_sb->s_op->write_inode(inode, wbc);
1321 trace_writeback_write_inode(inode, wbc);
1322 return ret;
1323 }
1324 return 0;
1325}
1326
1327/*
1328 * Wait for writeback on an inode to complete. Called with i_lock held.
1329 * Caller must make sure inode cannot go away when we drop i_lock.
1330 */
1331static void __inode_wait_for_writeback(struct inode *inode)
1332 __releases(inode->i_lock)
1333 __acquires(inode->i_lock)
1334{
1335 DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1336 wait_queue_head_t *wqh;
1337
1338 wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1339 while (inode->i_state & I_SYNC) {
1340 spin_unlock(&inode->i_lock);
1341 __wait_on_bit(wqh, &wq, bit_wait,
1342 TASK_UNINTERRUPTIBLE);
1343 spin_lock(&inode->i_lock);
1344 }
1345}
1346
1347/*
1348 * Wait for writeback on an inode to complete. Caller must have inode pinned.
1349 */
1350void inode_wait_for_writeback(struct inode *inode)
1351{
1352 spin_lock(&inode->i_lock);
1353 __inode_wait_for_writeback(inode);
1354 spin_unlock(&inode->i_lock);
1355}
1356
1357/*
1358 * Sleep until I_SYNC is cleared. This function must be called with i_lock
1359 * held and drops it. It is aimed for callers not holding any inode reference
1360 * so once i_lock is dropped, inode can go away.
1361 */
1362static void inode_sleep_on_writeback(struct inode *inode)
1363 __releases(inode->i_lock)
1364{
1365 DEFINE_WAIT(wait);
1366 wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1367 int sleep;
1368
1369 prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1370 sleep = inode->i_state & I_SYNC;
1371 spin_unlock(&inode->i_lock);
1372 if (sleep)
1373 schedule();
1374 finish_wait(wqh, &wait);
1375}
1376
1377/*
1378 * Find proper writeback list for the inode depending on its current state and
1379 * possibly also change of its state while we were doing writeback. Here we
1380 * handle things such as livelock prevention or fairness of writeback among
1381 * inodes. This function can be called only by flusher thread - noone else
1382 * processes all inodes in writeback lists and requeueing inodes behind flusher
1383 * thread's back can have unexpected consequences.
1384 */
1385static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1386 struct writeback_control *wbc)
1387{
1388 if (inode->i_state & I_FREEING)
1389 return;
1390
1391 /*
1392 * Sync livelock prevention. Each inode is tagged and synced in one
1393 * shot. If still dirty, it will be redirty_tail()'ed below. Update
1394 * the dirty time to prevent enqueue and sync it again.
1395 */
1396 if ((inode->i_state & I_DIRTY) &&
1397 (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1398 inode->dirtied_when = jiffies;
1399
1400 if (wbc->pages_skipped) {
1401 /*
1402 * writeback is not making progress due to locked
1403 * buffers. Skip this inode for now.
1404 */
1405 redirty_tail_locked(inode, wb);
1406 return;
1407 }
1408
1409 if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1410 /*
1411 * We didn't write back all the pages. nfs_writepages()
1412 * sometimes bales out without doing anything.
1413 */
1414 if (wbc->nr_to_write <= 0) {
1415 /* Slice used up. Queue for next turn. */
1416 requeue_io(inode, wb);
1417 } else {
1418 /*
1419 * Writeback blocked by something other than
1420 * congestion. Delay the inode for some time to
1421 * avoid spinning on the CPU (100% iowait)
1422 * retrying writeback of the dirty page/inode
1423 * that cannot be performed immediately.
1424 */
1425 redirty_tail_locked(inode, wb);
1426 }
1427 } else if (inode->i_state & I_DIRTY) {
1428 /*
1429 * Filesystems can dirty the inode during writeback operations,
1430 * such as delayed allocation during submission or metadata
1431 * updates after data IO completion.
1432 */
1433 redirty_tail_locked(inode, wb);
1434 } else if (inode->i_state & I_DIRTY_TIME) {
1435 inode->dirtied_when = jiffies;
1436 inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
1437 inode->i_state &= ~I_SYNC_QUEUED;
1438 } else {
1439 /* The inode is clean. Remove from writeback lists. */
1440 inode_io_list_del_locked(inode, wb);
1441 }
1442}
1443
1444/*
1445 * Write out an inode and its dirty pages. Do not update the writeback list
1446 * linkage. That is left to the caller. The caller is also responsible for
1447 * setting I_SYNC flag and calling inode_sync_complete() to clear it.
1448 */
1449static int
1450__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1451{
1452 struct address_space *mapping = inode->i_mapping;
1453 long nr_to_write = wbc->nr_to_write;
1454 unsigned dirty;
1455 int ret;
1456
1457 WARN_ON(!(inode->i_state & I_SYNC));
1458
1459 trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1460
1461 ret = do_writepages(mapping, wbc);
1462
1463 /*
1464 * Make sure to wait on the data before writing out the metadata.
1465 * This is important for filesystems that modify metadata on data
1466 * I/O completion. We don't do it for sync(2) writeback because it has a
1467 * separate, external IO completion path and ->sync_fs for guaranteeing
1468 * inode metadata is written back correctly.
1469 */
1470 if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
1471 int err = filemap_fdatawait(mapping);
1472 if (ret == 0)
1473 ret = err;
1474 }
1475
1476 /*
1477 * Some filesystems may redirty the inode during the writeback
1478 * due to delalloc, clear dirty metadata flags right before
1479 * write_inode()
1480 */
1481 spin_lock(&inode->i_lock);
1482
1483 dirty = inode->i_state & I_DIRTY;
1484 if ((inode->i_state & I_DIRTY_TIME) &&
1485 ((dirty & I_DIRTY_INODE) ||
1486 wbc->sync_mode == WB_SYNC_ALL || wbc->for_sync ||
1487 time_after(jiffies, inode->dirtied_time_when +
1488 dirtytime_expire_interval * HZ))) {
1489 dirty |= I_DIRTY_TIME;
1490 trace_writeback_lazytime(inode);
1491 }
1492 inode->i_state &= ~dirty;
1493
1494 /*
1495 * Paired with smp_mb() in __mark_inode_dirty(). This allows
1496 * __mark_inode_dirty() to test i_state without grabbing i_lock -
1497 * either they see the I_DIRTY bits cleared or we see the dirtied
1498 * inode.
1499 *
1500 * I_DIRTY_PAGES is always cleared together above even if @mapping
1501 * still has dirty pages. The flag is reinstated after smp_mb() if
1502 * necessary. This guarantees that either __mark_inode_dirty()
1503 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1504 */
1505 smp_mb();
1506
1507 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1508 inode->i_state |= I_DIRTY_PAGES;
1509
1510 spin_unlock(&inode->i_lock);
1511
1512 if (dirty & I_DIRTY_TIME)
1513 mark_inode_dirty_sync(inode);
1514 /* Don't write the inode if only I_DIRTY_PAGES was set */
1515 if (dirty & ~I_DIRTY_PAGES) {
1516 int err = write_inode(inode, wbc);
1517 if (ret == 0)
1518 ret = err;
1519 }
1520 trace_writeback_single_inode(inode, wbc, nr_to_write);
1521 return ret;
1522}
1523
1524/*
1525 * Write out an inode's dirty pages. Either the caller has an active reference
1526 * on the inode or the inode has I_WILL_FREE set.
1527 *
1528 * This function is designed to be called for writing back one inode which
1529 * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
1530 * and does more profound writeback list handling in writeback_sb_inodes().
1531 */
1532static int writeback_single_inode(struct inode *inode,
1533 struct writeback_control *wbc)
1534{
1535 struct bdi_writeback *wb;
1536 int ret = 0;
1537
1538 spin_lock(&inode->i_lock);
1539 if (!atomic_read(&inode->i_count))
1540 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1541 else
1542 WARN_ON(inode->i_state & I_WILL_FREE);
1543
1544 if (inode->i_state & I_SYNC) {
1545 if (wbc->sync_mode != WB_SYNC_ALL)
1546 goto out;
1547 /*
1548 * It's a data-integrity sync. We must wait. Since callers hold
1549 * inode reference or inode has I_WILL_FREE set, it cannot go
1550 * away under us.
1551 */
1552 __inode_wait_for_writeback(inode);
1553 }
1554 WARN_ON(inode->i_state & I_SYNC);
1555 /*
1556 * Skip inode if it is clean and we have no outstanding writeback in
1557 * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
1558 * function since flusher thread may be doing for example sync in
1559 * parallel and if we move the inode, it could get skipped. So here we
1560 * make sure inode is on some writeback list and leave it there unless
1561 * we have completely cleaned the inode.
1562 */
1563 if (!(inode->i_state & I_DIRTY_ALL) &&
1564 (wbc->sync_mode != WB_SYNC_ALL ||
1565 !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
1566 goto out;
1567 inode->i_state |= I_SYNC;
1568 wbc_attach_and_unlock_inode(wbc, inode);
1569
1570 ret = __writeback_single_inode(inode, wbc);
1571
1572 wbc_detach_inode(wbc);
1573
1574 wb = inode_to_wb_and_lock_list(inode);
1575 spin_lock(&inode->i_lock);
1576 /*
1577 * If inode is clean, remove it from writeback lists. Otherwise don't
1578 * touch it. See comment above for explanation.
1579 */
1580 if (!(inode->i_state & I_DIRTY_ALL))
1581 inode_io_list_del_locked(inode, wb);
1582 spin_unlock(&wb->list_lock);
1583 inode_sync_complete(inode);
1584out:
1585 spin_unlock(&inode->i_lock);
1586 return ret;
1587}
1588
1589static long writeback_chunk_size(struct bdi_writeback *wb,
1590 struct wb_writeback_work *work)
1591{
1592 long pages;
1593
1594 /*
1595 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1596 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1597 * here avoids calling into writeback_inodes_wb() more than once.
1598 *
1599 * The intended call sequence for WB_SYNC_ALL writeback is:
1600 *
1601 * wb_writeback()
1602 * writeback_sb_inodes() <== called only once
1603 * write_cache_pages() <== called once for each inode
1604 * (quickly) tag currently dirty pages
1605 * (maybe slowly) sync all tagged pages
1606 */
1607 if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1608 pages = LONG_MAX;
1609 else {
1610 pages = min(wb->avg_write_bandwidth / 2,
1611 global_wb_domain.dirty_limit / DIRTY_SCOPE);
1612 pages = min(pages, work->nr_pages);
1613 pages = round_down(pages + MIN_WRITEBACK_PAGES,
1614 MIN_WRITEBACK_PAGES);
1615 }
1616
1617 return pages;
1618}
1619
1620/*
1621 * Write a portion of b_io inodes which belong to @sb.
1622 *
1623 * Return the number of pages and/or inodes written.
1624 *
1625 * NOTE! This is called with wb->list_lock held, and will
1626 * unlock and relock that for each inode it ends up doing
1627 * IO for.
1628 */
1629static long writeback_sb_inodes(struct super_block *sb,
1630 struct bdi_writeback *wb,
1631 struct wb_writeback_work *work)
1632{
1633 struct writeback_control wbc = {
1634 .sync_mode = work->sync_mode,
1635 .tagged_writepages = work->tagged_writepages,
1636 .for_kupdate = work->for_kupdate,
1637 .for_background = work->for_background,
1638 .for_sync = work->for_sync,
1639 .range_cyclic = work->range_cyclic,
1640 .range_start = 0,
1641 .range_end = LLONG_MAX,
1642 };
1643 unsigned long start_time = jiffies;
1644 long write_chunk;
1645 long wrote = 0; /* count both pages and inodes */
1646
1647 while (!list_empty(&wb->b_io)) {
1648 struct inode *inode = wb_inode(wb->b_io.prev);
1649 struct bdi_writeback *tmp_wb;
1650
1651 if (inode->i_sb != sb) {
1652 if (work->sb) {
1653 /*
1654 * We only want to write back data for this
1655 * superblock, move all inodes not belonging
1656 * to it back onto the dirty list.
1657 */
1658 redirty_tail(inode, wb);
1659 continue;
1660 }
1661
1662 /*
1663 * The inode belongs to a different superblock.
1664 * Bounce back to the caller to unpin this and
1665 * pin the next superblock.
1666 */
1667 break;
1668 }
1669
1670 /*
1671 * Don't bother with new inodes or inodes being freed, first
1672 * kind does not need periodic writeout yet, and for the latter
1673 * kind writeout is handled by the freer.
1674 */
1675 spin_lock(&inode->i_lock);
1676 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
1677 redirty_tail_locked(inode, wb);
1678 spin_unlock(&inode->i_lock);
1679 continue;
1680 }
1681 if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1682 /*
1683 * If this inode is locked for writeback and we are not
1684 * doing writeback-for-data-integrity, move it to
1685 * b_more_io so that writeback can proceed with the
1686 * other inodes on s_io.
1687 *
1688 * We'll have another go at writing back this inode
1689 * when we completed a full scan of b_io.
1690 */
1691 spin_unlock(&inode->i_lock);
1692 requeue_io(inode, wb);
1693 trace_writeback_sb_inodes_requeue(inode);
1694 continue;
1695 }
1696 spin_unlock(&wb->list_lock);
1697
1698 /*
1699 * We already requeued the inode if it had I_SYNC set and we
1700 * are doing WB_SYNC_NONE writeback. So this catches only the
1701 * WB_SYNC_ALL case.
1702 */
1703 if (inode->i_state & I_SYNC) {
1704 /* Wait for I_SYNC. This function drops i_lock... */
1705 inode_sleep_on_writeback(inode);
1706 /* Inode may be gone, start again */
1707 spin_lock(&wb->list_lock);
1708 continue;
1709 }
1710 inode->i_state |= I_SYNC;
1711 wbc_attach_and_unlock_inode(&wbc, inode);
1712
1713 write_chunk = writeback_chunk_size(wb, work);
1714 wbc.nr_to_write = write_chunk;
1715 wbc.pages_skipped = 0;
1716
1717 /*
1718 * We use I_SYNC to pin the inode in memory. While it is set
1719 * evict_inode() will wait so the inode cannot be freed.
1720 */
1721 __writeback_single_inode(inode, &wbc);
1722
1723 wbc_detach_inode(&wbc);
1724 work->nr_pages -= write_chunk - wbc.nr_to_write;
1725 wrote += write_chunk - wbc.nr_to_write;
1726
1727 if (need_resched()) {
1728 /*
1729 * We're trying to balance between building up a nice
1730 * long list of IOs to improve our merge rate, and
1731 * getting those IOs out quickly for anyone throttling
1732 * in balance_dirty_pages(). cond_resched() doesn't
1733 * unplug, so get our IOs out the door before we
1734 * give up the CPU.
1735 */
1736 blk_flush_plug(current);
1737 cond_resched();
1738 }
1739
1740 /*
1741 * Requeue @inode if still dirty. Be careful as @inode may
1742 * have been switched to another wb in the meantime.
1743 */
1744 tmp_wb = inode_to_wb_and_lock_list(inode);
1745 spin_lock(&inode->i_lock);
1746 if (!(inode->i_state & I_DIRTY_ALL))
1747 wrote++;
1748 requeue_inode(inode, tmp_wb, &wbc);
1749 inode_sync_complete(inode);
1750 spin_unlock(&inode->i_lock);
1751
1752 if (unlikely(tmp_wb != wb)) {
1753 spin_unlock(&tmp_wb->list_lock);
1754 spin_lock(&wb->list_lock);
1755 }
1756
1757 /*
1758 * bail out to wb_writeback() often enough to check
1759 * background threshold and other termination conditions.
1760 */
1761 if (wrote) {
1762 if (time_is_before_jiffies(start_time + HZ / 10UL))
1763 break;
1764 if (work->nr_pages <= 0)
1765 break;
1766 }
1767 }
1768 return wrote;
1769}
1770
1771static long __writeback_inodes_wb(struct bdi_writeback *wb,
1772 struct wb_writeback_work *work)
1773{
1774 unsigned long start_time = jiffies;
1775 long wrote = 0;
1776
1777 while (!list_empty(&wb->b_io)) {
1778 struct inode *inode = wb_inode(wb->b_io.prev);
1779 struct super_block *sb = inode->i_sb;
1780
1781 if (!trylock_super(sb)) {
1782 /*
1783 * trylock_super() may fail consistently due to
1784 * s_umount being grabbed by someone else. Don't use
1785 * requeue_io() to avoid busy retrying the inode/sb.
1786 */
1787 redirty_tail(inode, wb);
1788 continue;
1789 }
1790 wrote += writeback_sb_inodes(sb, wb, work);
1791 up_read(&sb->s_umount);
1792
1793 /* refer to the same tests at the end of writeback_sb_inodes */
1794 if (wrote) {
1795 if (time_is_before_jiffies(start_time + HZ / 10UL))
1796 break;
1797 if (work->nr_pages <= 0)
1798 break;
1799 }
1800 }
1801 /* Leave any unwritten inodes on b_io */
1802 return wrote;
1803}
1804
1805static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
1806 enum wb_reason reason)
1807{
1808 struct wb_writeback_work work = {
1809 .nr_pages = nr_pages,
1810 .sync_mode = WB_SYNC_NONE,
1811 .range_cyclic = 1,
1812 .reason = reason,
1813 };
1814 struct blk_plug plug;
1815
1816 blk_start_plug(&plug);
1817 spin_lock(&wb->list_lock);
1818 if (list_empty(&wb->b_io))
1819 queue_io(wb, &work, jiffies);
1820 __writeback_inodes_wb(wb, &work);
1821 spin_unlock(&wb->list_lock);
1822 blk_finish_plug(&plug);
1823
1824 return nr_pages - work.nr_pages;
1825}
1826
1827/*
1828 * Explicit flushing or periodic writeback of "old" data.
1829 *
1830 * Define "old": the first time one of an inode's pages is dirtied, we mark the
1831 * dirtying-time in the inode's address_space. So this periodic writeback code
1832 * just walks the superblock inode list, writing back any inodes which are
1833 * older than a specific point in time.
1834 *
1835 * Try to run once per dirty_writeback_interval. But if a writeback event
1836 * takes longer than a dirty_writeback_interval interval, then leave a
1837 * one-second gap.
1838 *
1839 * dirtied_before takes precedence over nr_to_write. So we'll only write back
1840 * all dirty pages if they are all attached to "old" mappings.
1841 */
1842static long wb_writeback(struct bdi_writeback *wb,
1843 struct wb_writeback_work *work)
1844{
1845 unsigned long wb_start = jiffies;
1846 long nr_pages = work->nr_pages;
1847 unsigned long dirtied_before = jiffies;
1848 struct inode *inode;
1849 long progress;
1850 struct blk_plug plug;
1851
1852 blk_start_plug(&plug);
1853 spin_lock(&wb->list_lock);
1854 for (;;) {
1855 /*
1856 * Stop writeback when nr_pages has been consumed
1857 */
1858 if (work->nr_pages <= 0)
1859 break;
1860
1861 /*
1862 * Background writeout and kupdate-style writeback may
1863 * run forever. Stop them if there is other work to do
1864 * so that e.g. sync can proceed. They'll be restarted
1865 * after the other works are all done.
1866 */
1867 if ((work->for_background || work->for_kupdate) &&
1868 !list_empty(&wb->work_list))
1869 break;
1870
1871 /*
1872 * For background writeout, stop when we are below the
1873 * background dirty threshold
1874 */
1875 if (work->for_background && !wb_over_bg_thresh(wb))
1876 break;
1877
1878 /*
1879 * Kupdate and background works are special and we want to
1880 * include all inodes that need writing. Livelock avoidance is
1881 * handled by these works yielding to any other work so we are
1882 * safe.
1883 */
1884 if (work->for_kupdate) {
1885 dirtied_before = jiffies -
1886 msecs_to_jiffies(dirty_expire_interval * 10);
1887 } else if (work->for_background)
1888 dirtied_before = jiffies;
1889
1890 trace_writeback_start(wb, work);
1891 if (list_empty(&wb->b_io))
1892 queue_io(wb, work, dirtied_before);
1893 if (work->sb)
1894 progress = writeback_sb_inodes(work->sb, wb, work);
1895 else
1896 progress = __writeback_inodes_wb(wb, work);
1897 trace_writeback_written(wb, work);
1898
1899 wb_update_bandwidth(wb, wb_start);
1900
1901 /*
1902 * Did we write something? Try for more
1903 *
1904 * Dirty inodes are moved to b_io for writeback in batches.
1905 * The completion of the current batch does not necessarily
1906 * mean the overall work is done. So we keep looping as long
1907 * as made some progress on cleaning pages or inodes.
1908 */
1909 if (progress)
1910 continue;
1911 /*
1912 * No more inodes for IO, bail
1913 */
1914 if (list_empty(&wb->b_more_io))
1915 break;
1916 /*
1917 * Nothing written. Wait for some inode to
1918 * become available for writeback. Otherwise
1919 * we'll just busyloop.
1920 */
1921 trace_writeback_wait(wb, work);
1922 inode = wb_inode(wb->b_more_io.prev);
1923 spin_lock(&inode->i_lock);
1924 spin_unlock(&wb->list_lock);
1925 /* This function drops i_lock... */
1926 inode_sleep_on_writeback(inode);
1927 spin_lock(&wb->list_lock);
1928 }
1929 spin_unlock(&wb->list_lock);
1930 blk_finish_plug(&plug);
1931
1932 return nr_pages - work->nr_pages;
1933}
1934
1935/*
1936 * Return the next wb_writeback_work struct that hasn't been processed yet.
1937 */
1938static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
1939{
1940 struct wb_writeback_work *work = NULL;
1941
1942 spin_lock_bh(&wb->work_lock);
1943 if (!list_empty(&wb->work_list)) {
1944 work = list_entry(wb->work_list.next,
1945 struct wb_writeback_work, list);
1946 list_del_init(&work->list);
1947 }
1948 spin_unlock_bh(&wb->work_lock);
1949 return work;
1950}
1951
1952static long wb_check_background_flush(struct bdi_writeback *wb)
1953{
1954 if (wb_over_bg_thresh(wb)) {
1955
1956 struct wb_writeback_work work = {
1957 .nr_pages = LONG_MAX,
1958 .sync_mode = WB_SYNC_NONE,
1959 .for_background = 1,
1960 .range_cyclic = 1,
1961 .reason = WB_REASON_BACKGROUND,
1962 };
1963
1964 return wb_writeback(wb, &work);
1965 }
1966
1967 return 0;
1968}
1969
1970static long wb_check_old_data_flush(struct bdi_writeback *wb)
1971{
1972 unsigned long expired;
1973 long nr_pages;
1974
1975 /*
1976 * When set to zero, disable periodic writeback
1977 */
1978 if (!dirty_writeback_interval)
1979 return 0;
1980
1981 expired = wb->last_old_flush +
1982 msecs_to_jiffies(dirty_writeback_interval * 10);
1983 if (time_before(jiffies, expired))
1984 return 0;
1985
1986 wb->last_old_flush = jiffies;
1987 nr_pages = get_nr_dirty_pages();
1988
1989 if (nr_pages) {
1990 struct wb_writeback_work work = {
1991 .nr_pages = nr_pages,
1992 .sync_mode = WB_SYNC_NONE,
1993 .for_kupdate = 1,
1994 .range_cyclic = 1,
1995 .reason = WB_REASON_PERIODIC,
1996 };
1997
1998 return wb_writeback(wb, &work);
1999 }
2000
2001 return 0;
2002}
2003
2004static long wb_check_start_all(struct bdi_writeback *wb)
2005{
2006 long nr_pages;
2007
2008 if (!test_bit(WB_start_all, &wb->state))
2009 return 0;
2010
2011 nr_pages = get_nr_dirty_pages();
2012 if (nr_pages) {
2013 struct wb_writeback_work work = {
2014 .nr_pages = wb_split_bdi_pages(wb, nr_pages),
2015 .sync_mode = WB_SYNC_NONE,
2016 .range_cyclic = 1,
2017 .reason = wb->start_all_reason,
2018 };
2019
2020 nr_pages = wb_writeback(wb, &work);
2021 }
2022
2023 clear_bit(WB_start_all, &wb->state);
2024 return nr_pages;
2025}
2026
2027
2028/*
2029 * Retrieve work items and do the writeback they describe
2030 */
2031static long wb_do_writeback(struct bdi_writeback *wb)
2032{
2033 struct wb_writeback_work *work;
2034 long wrote = 0;
2035
2036 set_bit(WB_writeback_running, &wb->state);
2037 while ((work = get_next_work_item(wb)) != NULL) {
2038 trace_writeback_exec(wb, work);
2039 wrote += wb_writeback(wb, work);
2040 finish_writeback_work(wb, work);
2041 }
2042
2043 /*
2044 * Check for a flush-everything request
2045 */
2046 wrote += wb_check_start_all(wb);
2047
2048 /*
2049 * Check for periodic writeback, kupdated() style
2050 */
2051 wrote += wb_check_old_data_flush(wb);
2052 wrote += wb_check_background_flush(wb);
2053 clear_bit(WB_writeback_running, &wb->state);
2054
2055 return wrote;
2056}
2057
2058/*
2059 * Handle writeback of dirty data for the device backed by this bdi. Also
2060 * reschedules periodically and does kupdated style flushing.
2061 */
2062void wb_workfn(struct work_struct *work)
2063{
2064 struct bdi_writeback *wb = container_of(to_delayed_work(work),
2065 struct bdi_writeback, dwork);
2066 long pages_written;
2067
2068 set_worker_desc("flush-%s", bdi_dev_name(wb->bdi));
2069 current->flags |= PF_SWAPWRITE;
2070
2071 if (likely(!current_is_workqueue_rescuer() ||
2072 !test_bit(WB_registered, &wb->state))) {
2073 /*
2074 * The normal path. Keep writing back @wb until its
2075 * work_list is empty. Note that this path is also taken
2076 * if @wb is shutting down even when we're running off the
2077 * rescuer as work_list needs to be drained.
2078 */
2079 do {
2080 pages_written = wb_do_writeback(wb);
2081 trace_writeback_pages_written(pages_written);
2082 } while (!list_empty(&wb->work_list));
2083 } else {
2084 /*
2085 * bdi_wq can't get enough workers and we're running off
2086 * the emergency worker. Don't hog it. Hopefully, 1024 is
2087 * enough for efficient IO.
2088 */
2089 pages_written = writeback_inodes_wb(wb, 1024,
2090 WB_REASON_FORKER_THREAD);
2091 trace_writeback_pages_written(pages_written);
2092 }
2093
2094 if (!list_empty(&wb->work_list))
2095 wb_wakeup(wb);
2096 else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
2097 wb_wakeup_delayed(wb);
2098
2099 current->flags &= ~PF_SWAPWRITE;
2100}
2101
2102/*
2103 * Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
2104 * write back the whole world.
2105 */
2106static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2107 enum wb_reason reason)
2108{
2109 struct bdi_writeback *wb;
2110
2111 if (!bdi_has_dirty_io(bdi))
2112 return;
2113
2114 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2115 wb_start_writeback(wb, reason);
2116}
2117
2118void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2119 enum wb_reason reason)
2120{
2121 rcu_read_lock();
2122 __wakeup_flusher_threads_bdi(bdi, reason);
2123 rcu_read_unlock();
2124}
2125
2126/*
2127 * Wakeup the flusher threads to start writeback of all currently dirty pages
2128 */
2129void wakeup_flusher_threads(enum wb_reason reason)
2130{
2131 struct backing_dev_info *bdi;
2132
2133 /*
2134 * If we are expecting writeback progress we must submit plugged IO.
2135 */
2136 if (blk_needs_flush_plug(current))
2137 blk_schedule_flush_plug(current);
2138
2139 rcu_read_lock();
2140 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2141 __wakeup_flusher_threads_bdi(bdi, reason);
2142 rcu_read_unlock();
2143}
2144
2145/*
2146 * Wake up bdi's periodically to make sure dirtytime inodes gets
2147 * written back periodically. We deliberately do *not* check the
2148 * b_dirtytime list in wb_has_dirty_io(), since this would cause the
2149 * kernel to be constantly waking up once there are any dirtytime
2150 * inodes on the system. So instead we define a separate delayed work
2151 * function which gets called much more rarely. (By default, only
2152 * once every 12 hours.)
2153 *
2154 * If there is any other write activity going on in the file system,
2155 * this function won't be necessary. But if the only thing that has
2156 * happened on the file system is a dirtytime inode caused by an atime
2157 * update, we need this infrastructure below to make sure that inode
2158 * eventually gets pushed out to disk.
2159 */
2160static void wakeup_dirtytime_writeback(struct work_struct *w);
2161static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
2162
2163static void wakeup_dirtytime_writeback(struct work_struct *w)
2164{
2165 struct backing_dev_info *bdi;
2166
2167 rcu_read_lock();
2168 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
2169 struct bdi_writeback *wb;
2170
2171 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2172 if (!list_empty(&wb->b_dirty_time))
2173 wb_wakeup(wb);
2174 }
2175 rcu_read_unlock();
2176 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2177}
2178
2179static int __init start_dirtytime_writeback(void)
2180{
2181 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2182 return 0;
2183}
2184__initcall(start_dirtytime_writeback);
2185
2186int dirtytime_interval_handler(struct ctl_table *table, int write,
2187 void *buffer, size_t *lenp, loff_t *ppos)
2188{
2189 int ret;
2190
2191 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
2192 if (ret == 0 && write)
2193 mod_delayed_work(system_wq, &dirtytime_work, 0);
2194 return ret;
2195}
2196
2197static noinline void block_dump___mark_inode_dirty(struct inode *inode)
2198{
2199 if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
2200 struct dentry *dentry;
2201 const char *name = "?";
2202
2203 dentry = d_find_alias(inode);
2204 if (dentry) {
2205 spin_lock(&dentry->d_lock);
2206 name = (const char *) dentry->d_name.name;
2207 }
2208 printk(KERN_DEBUG
2209 "%s(%d): dirtied inode %lu (%s) on %s\n",
2210 current->comm, task_pid_nr(current), inode->i_ino,
2211 name, inode->i_sb->s_id);
2212 if (dentry) {
2213 spin_unlock(&dentry->d_lock);
2214 dput(dentry);
2215 }
2216 }
2217}
2218
2219/**
2220 * __mark_inode_dirty - internal function
2221 *
2222 * @inode: inode to mark
2223 * @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
2224 *
2225 * Mark an inode as dirty. Callers should use mark_inode_dirty or
2226 * mark_inode_dirty_sync.
2227 *
2228 * Put the inode on the super block's dirty list.
2229 *
2230 * CAREFUL! We mark it dirty unconditionally, but move it onto the
2231 * dirty list only if it is hashed or if it refers to a blockdev.
2232 * If it was not hashed, it will never be added to the dirty list
2233 * even if it is later hashed, as it will have been marked dirty already.
2234 *
2235 * In short, make sure you hash any inodes _before_ you start marking
2236 * them dirty.
2237 *
2238 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2239 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
2240 * the kernel-internal blockdev inode represents the dirtying time of the
2241 * blockdev's pages. This is why for I_DIRTY_PAGES we always use
2242 * page->mapping->host, so the page-dirtying time is recorded in the internal
2243 * blockdev inode.
2244 */
2245void __mark_inode_dirty(struct inode *inode, int flags)
2246{
2247 struct super_block *sb = inode->i_sb;
2248 int dirtytime;
2249
2250 trace_writeback_mark_inode_dirty(inode, flags);
2251
2252 /*
2253 * Don't do this for I_DIRTY_PAGES - that doesn't actually
2254 * dirty the inode itself
2255 */
2256 if (flags & (I_DIRTY_INODE | I_DIRTY_TIME)) {
2257 trace_writeback_dirty_inode_start(inode, flags);
2258
2259 if (sb->s_op->dirty_inode)
2260 sb->s_op->dirty_inode(inode, flags);
2261
2262 trace_writeback_dirty_inode(inode, flags);
2263 }
2264 if (flags & I_DIRTY_INODE)
2265 flags &= ~I_DIRTY_TIME;
2266 dirtytime = flags & I_DIRTY_TIME;
2267
2268 /*
2269 * Paired with smp_mb() in __writeback_single_inode() for the
2270 * following lockless i_state test. See there for details.
2271 */
2272 smp_mb();
2273
2274 if (((inode->i_state & flags) == flags) ||
2275 (dirtytime && (inode->i_state & I_DIRTY_INODE)))
2276 return;
2277
2278 if (unlikely(block_dump))
2279 block_dump___mark_inode_dirty(inode);
2280
2281 spin_lock(&inode->i_lock);
2282 if (dirtytime && (inode->i_state & I_DIRTY_INODE))
2283 goto out_unlock_inode;
2284 if ((inode->i_state & flags) != flags) {
2285 const int was_dirty = inode->i_state & I_DIRTY;
2286
2287 inode_attach_wb(inode, NULL);
2288
2289 if (flags & I_DIRTY_INODE)
2290 inode->i_state &= ~I_DIRTY_TIME;
2291 inode->i_state |= flags;
2292
2293 /*
2294 * If the inode is queued for writeback by flush worker, just
2295 * update its dirty state. Once the flush worker is done with
2296 * the inode it will place it on the appropriate superblock
2297 * list, based upon its state.
2298 */
2299 if (inode->i_state & I_SYNC_QUEUED)
2300 goto out_unlock_inode;
2301
2302 /*
2303 * Only add valid (hashed) inodes to the superblock's
2304 * dirty list. Add blockdev inodes as well.
2305 */
2306 if (!S_ISBLK(inode->i_mode)) {
2307 if (inode_unhashed(inode))
2308 goto out_unlock_inode;
2309 }
2310 if (inode->i_state & I_FREEING)
2311 goto out_unlock_inode;
2312
2313 /*
2314 * If the inode was already on b_dirty/b_io/b_more_io, don't
2315 * reposition it (that would break b_dirty time-ordering).
2316 */
2317 if (!was_dirty) {
2318 struct bdi_writeback *wb;
2319 struct list_head *dirty_list;
2320 bool wakeup_bdi = false;
2321
2322 wb = locked_inode_to_wb_and_lock_list(inode);
2323
2324 WARN(bdi_cap_writeback_dirty(wb->bdi) &&
2325 !test_bit(WB_registered, &wb->state),
2326 "bdi-%s not registered\n", bdi_dev_name(wb->bdi));
2327
2328 inode->dirtied_when = jiffies;
2329 if (dirtytime)
2330 inode->dirtied_time_when = jiffies;
2331
2332 if (inode->i_state & I_DIRTY)
2333 dirty_list = &wb->b_dirty;
2334 else
2335 dirty_list = &wb->b_dirty_time;
2336
2337 wakeup_bdi = inode_io_list_move_locked(inode, wb,
2338 dirty_list);
2339
2340 spin_unlock(&wb->list_lock);
2341 trace_writeback_dirty_inode_enqueue(inode);
2342
2343 /*
2344 * If this is the first dirty inode for this bdi,
2345 * we have to wake-up the corresponding bdi thread
2346 * to make sure background write-back happens
2347 * later.
2348 */
2349 if (bdi_cap_writeback_dirty(wb->bdi) && wakeup_bdi)
2350 wb_wakeup_delayed(wb);
2351 return;
2352 }
2353 }
2354out_unlock_inode:
2355 spin_unlock(&inode->i_lock);
2356}
2357EXPORT_SYMBOL(__mark_inode_dirty);
2358
2359/*
2360 * The @s_sync_lock is used to serialise concurrent sync operations
2361 * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2362 * Concurrent callers will block on the s_sync_lock rather than doing contending
2363 * walks. The queueing maintains sync(2) required behaviour as all the IO that
2364 * has been issued up to the time this function is enter is guaranteed to be
2365 * completed by the time we have gained the lock and waited for all IO that is
2366 * in progress regardless of the order callers are granted the lock.
2367 */
2368static void wait_sb_inodes(struct super_block *sb)
2369{
2370 LIST_HEAD(sync_list);
2371
2372 /*
2373 * We need to be protected against the filesystem going from
2374 * r/o to r/w or vice versa.
2375 */
2376 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2377
2378 mutex_lock(&sb->s_sync_lock);
2379
2380 /*
2381 * Splice the writeback list onto a temporary list to avoid waiting on
2382 * inodes that have started writeback after this point.
2383 *
2384 * Use rcu_read_lock() to keep the inodes around until we have a
2385 * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2386 * the local list because inodes can be dropped from either by writeback
2387 * completion.
2388 */
2389 rcu_read_lock();
2390 spin_lock_irq(&sb->s_inode_wblist_lock);
2391 list_splice_init(&sb->s_inodes_wb, &sync_list);
2392
2393 /*
2394 * Data integrity sync. Must wait for all pages under writeback, because
2395 * there may have been pages dirtied before our sync call, but which had
2396 * writeout started before we write it out. In which case, the inode
2397 * may not be on the dirty list, but we still have to wait for that
2398 * writeout.
2399 */
2400 while (!list_empty(&sync_list)) {
2401 struct inode *inode = list_first_entry(&sync_list, struct inode,
2402 i_wb_list);
2403 struct address_space *mapping = inode->i_mapping;
2404
2405 /*
2406 * Move each inode back to the wb list before we drop the lock
2407 * to preserve consistency between i_wb_list and the mapping
2408 * writeback tag. Writeback completion is responsible to remove
2409 * the inode from either list once the writeback tag is cleared.
2410 */
2411 list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
2412
2413 /*
2414 * The mapping can appear untagged while still on-list since we
2415 * do not have the mapping lock. Skip it here, wb completion
2416 * will remove it.
2417 */
2418 if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2419 continue;
2420
2421 spin_unlock_irq(&sb->s_inode_wblist_lock);
2422
2423 spin_lock(&inode->i_lock);
2424 if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
2425 spin_unlock(&inode->i_lock);
2426
2427 spin_lock_irq(&sb->s_inode_wblist_lock);
2428 continue;
2429 }
2430 __iget(inode);
2431 spin_unlock(&inode->i_lock);
2432 rcu_read_unlock();
2433
2434 /*
2435 * We keep the error status of individual mapping so that
2436 * applications can catch the writeback error using fsync(2).
2437 * See filemap_fdatawait_keep_errors() for details.
2438 */
2439 filemap_fdatawait_keep_errors(mapping);
2440
2441 cond_resched();
2442
2443 iput(inode);
2444
2445 rcu_read_lock();
2446 spin_lock_irq(&sb->s_inode_wblist_lock);
2447 }
2448 spin_unlock_irq(&sb->s_inode_wblist_lock);
2449 rcu_read_unlock();
2450 mutex_unlock(&sb->s_sync_lock);
2451}
2452
2453static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2454 enum wb_reason reason, bool skip_if_busy)
2455{
2456 struct backing_dev_info *bdi = sb->s_bdi;
2457 DEFINE_WB_COMPLETION(done, bdi);
2458 struct wb_writeback_work work = {
2459 .sb = sb,
2460 .sync_mode = WB_SYNC_NONE,
2461 .tagged_writepages = 1,
2462 .done = &done,
2463 .nr_pages = nr,
2464 .reason = reason,
2465 };
2466
2467 if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
2468 return;
2469 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2470
2471 bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
2472 wb_wait_for_completion(&done);
2473}
2474
2475/**
2476 * writeback_inodes_sb_nr - writeback dirty inodes from given super_block
2477 * @sb: the superblock
2478 * @nr: the number of pages to write
2479 * @reason: reason why some writeback work initiated
2480 *
2481 * Start writeback on some inodes on this super_block. No guarantees are made
2482 * on how many (if any) will be written, and this function does not wait
2483 * for IO completion of submitted IO.
2484 */
2485void writeback_inodes_sb_nr(struct super_block *sb,
2486 unsigned long nr,
2487 enum wb_reason reason)
2488{
2489 __writeback_inodes_sb_nr(sb, nr, reason, false);
2490}
2491EXPORT_SYMBOL(writeback_inodes_sb_nr);
2492
2493/**
2494 * writeback_inodes_sb - writeback dirty inodes from given super_block
2495 * @sb: the superblock
2496 * @reason: reason why some writeback work was initiated
2497 *
2498 * Start writeback on some inodes on this super_block. No guarantees are made
2499 * on how many (if any) will be written, and this function does not wait
2500 * for IO completion of submitted IO.
2501 */
2502void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2503{
2504 return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2505}
2506EXPORT_SYMBOL(writeback_inodes_sb);
2507
2508/**
2509 * try_to_writeback_inodes_sb - try to start writeback if none underway
2510 * @sb: the superblock
2511 * @reason: reason why some writeback work was initiated
2512 *
2513 * Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
2514 */
2515void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2516{
2517 if (!down_read_trylock(&sb->s_umount))
2518 return;
2519
2520 __writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason, true);
2521 up_read(&sb->s_umount);
2522}
2523EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2524
2525/**
2526 * sync_inodes_sb - sync sb inode pages
2527 * @sb: the superblock
2528 *
2529 * This function writes and waits on any dirty inode belonging to this
2530 * super_block.
2531 */
2532void sync_inodes_sb(struct super_block *sb)
2533{
2534 struct backing_dev_info *bdi = sb->s_bdi;
2535 DEFINE_WB_COMPLETION(done, bdi);
2536 struct wb_writeback_work work = {
2537 .sb = sb,
2538 .sync_mode = WB_SYNC_ALL,
2539 .nr_pages = LONG_MAX,
2540 .range_cyclic = 0,
2541 .done = &done,
2542 .reason = WB_REASON_SYNC,
2543 .for_sync = 1,
2544 };
2545
2546 /*
2547 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
2548 * inodes under writeback and I_DIRTY_TIME inodes ignored by
2549 * bdi_has_dirty() need to be written out too.
2550 */
2551 if (bdi == &noop_backing_dev_info)
2552 return;
2553 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2554
2555 /* protect against inode wb switch, see inode_switch_wbs_work_fn() */
2556 bdi_down_write_wb_switch_rwsem(bdi);
2557 bdi_split_work_to_wbs(bdi, &work, false);
2558 wb_wait_for_completion(&done);
2559 bdi_up_write_wb_switch_rwsem(bdi);
2560
2561 wait_sb_inodes(sb);
2562}
2563EXPORT_SYMBOL(sync_inodes_sb);
2564
2565/**
2566 * write_inode_now - write an inode to disk
2567 * @inode: inode to write to disk
2568 * @sync: whether the write should be synchronous or not
2569 *
2570 * This function commits an inode to disk immediately if it is dirty. This is
2571 * primarily needed by knfsd.
2572 *
2573 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
2574 */
2575int write_inode_now(struct inode *inode, int sync)
2576{
2577 struct writeback_control wbc = {
2578 .nr_to_write = LONG_MAX,
2579 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2580 .range_start = 0,
2581 .range_end = LLONG_MAX,
2582 };
2583
2584 if (!mapping_cap_writeback_dirty(inode->i_mapping))
2585 wbc.nr_to_write = 0;
2586
2587 might_sleep();
2588 return writeback_single_inode(inode, &wbc);
2589}
2590EXPORT_SYMBOL(write_inode_now);
2591
2592/**
2593 * sync_inode - write an inode and its pages to disk.
2594 * @inode: the inode to sync
2595 * @wbc: controls the writeback mode
2596 *
2597 * sync_inode() will write an inode and its pages to disk. It will also
2598 * correctly update the inode on its superblock's dirty inode lists and will
2599 * update inode->i_state.
2600 *
2601 * The caller must have a ref on the inode.
2602 */
2603int sync_inode(struct inode *inode, struct writeback_control *wbc)
2604{
2605 return writeback_single_inode(inode, wbc);
2606}
2607EXPORT_SYMBOL(sync_inode);
2608
2609/**
2610 * sync_inode_metadata - write an inode to disk
2611 * @inode: the inode to sync
2612 * @wait: wait for I/O to complete.
2613 *
2614 * Write an inode to disk and adjust its dirty state after completion.
2615 *
2616 * Note: only writes the actual inode, no associated data or other metadata.
2617 */
2618int sync_inode_metadata(struct inode *inode, int wait)
2619{
2620 struct writeback_control wbc = {
2621 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2622 .nr_to_write = 0, /* metadata-only */
2623 };
2624
2625 return sync_inode(inode, &wbc);
2626}
2627EXPORT_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
124 list_move(&inode->i_io_list, head);
125
126 /* dirty_time doesn't count as dirty_io until expiration */
127 if (head != &wb->b_dirty_time)
128 return wb_io_lists_populated(wb);
129
130 wb_io_lists_depopulated(wb);
131 return false;
132}
133
134static void wb_wakeup(struct bdi_writeback *wb)
135{
136 spin_lock_bh(&wb->work_lock);
137 if (test_bit(WB_registered, &wb->state))
138 mod_delayed_work(bdi_wq, &wb->dwork, 0);
139 spin_unlock_bh(&wb->work_lock);
140}
141
142static void finish_writeback_work(struct bdi_writeback *wb,
143 struct wb_writeback_work *work)
144{
145 struct wb_completion *done = work->done;
146
147 if (work->auto_free)
148 kfree(work);
149 if (done) {
150 wait_queue_head_t *waitq = done->waitq;
151
152 /* @done can't be accessed after the following dec */
153 if (atomic_dec_and_test(&done->cnt))
154 wake_up_all(waitq);
155 }
156}
157
158static void wb_queue_work(struct bdi_writeback *wb,
159 struct wb_writeback_work *work)
160{
161 trace_writeback_queue(wb, work);
162
163 if (work->done)
164 atomic_inc(&work->done->cnt);
165
166 spin_lock_bh(&wb->work_lock);
167
168 if (test_bit(WB_registered, &wb->state)) {
169 list_add_tail(&work->list, &wb->work_list);
170 mod_delayed_work(bdi_wq, &wb->dwork, 0);
171 } else
172 finish_writeback_work(wb, work);
173
174 spin_unlock_bh(&wb->work_lock);
175}
176
177/**
178 * wb_wait_for_completion - wait for completion of bdi_writeback_works
179 * @done: target wb_completion
180 *
181 * Wait for one or more work items issued to @bdi with their ->done field
182 * set to @done, which should have been initialized with
183 * DEFINE_WB_COMPLETION(). This function returns after all such work items
184 * are completed. Work items which are waited upon aren't freed
185 * automatically on completion.
186 */
187void wb_wait_for_completion(struct wb_completion *done)
188{
189 atomic_dec(&done->cnt); /* put down the initial count */
190 wait_event(*done->waitq, !atomic_read(&done->cnt));
191}
192
193#ifdef CONFIG_CGROUP_WRITEBACK
194
195/*
196 * Parameters for foreign inode detection, see wbc_detach_inode() to see
197 * how they're used.
198 *
199 * These paramters are inherently heuristical as the detection target
200 * itself is fuzzy. All we want to do is detaching an inode from the
201 * current owner if it's being written to by some other cgroups too much.
202 *
203 * The current cgroup writeback is built on the assumption that multiple
204 * cgroups writing to the same inode concurrently is very rare and a mode
205 * of operation which isn't well supported. As such, the goal is not
206 * taking too long when a different cgroup takes over an inode while
207 * avoiding too aggressive flip-flops from occasional foreign writes.
208 *
209 * We record, very roughly, 2s worth of IO time history and if more than
210 * half of that is foreign, trigger the switch. The recording is quantized
211 * to 16 slots. To avoid tiny writes from swinging the decision too much,
212 * writes smaller than 1/8 of avg size are ignored.
213 */
214#define WB_FRN_TIME_SHIFT 13 /* 1s = 2^13, upto 8 secs w/ 16bit */
215#define WB_FRN_TIME_AVG_SHIFT 3 /* avg = avg * 7/8 + new * 1/8 */
216#define WB_FRN_TIME_CUT_DIV 8 /* ignore rounds < avg / 8 */
217#define WB_FRN_TIME_PERIOD (2 * (1 << WB_FRN_TIME_SHIFT)) /* 2s */
218
219#define WB_FRN_HIST_SLOTS 16 /* inode->i_wb_frn_history is 16bit */
220#define WB_FRN_HIST_UNIT (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
221 /* each slot's duration is 2s / 16 */
222#define WB_FRN_HIST_THR_SLOTS (WB_FRN_HIST_SLOTS / 2)
223 /* if foreign slots >= 8, switch */
224#define WB_FRN_HIST_MAX_SLOTS (WB_FRN_HIST_THR_SLOTS / 2 + 1)
225 /* one round can affect upto 5 slots */
226#define WB_FRN_MAX_IN_FLIGHT 1024 /* don't queue too many concurrently */
227
228/*
229 * Maximum inodes per isw. A specific value has been chosen to make
230 * struct inode_switch_wbs_context fit into 1024 bytes kmalloc.
231 */
232#define WB_MAX_INODES_PER_ISW ((1024UL - sizeof(struct inode_switch_wbs_context)) \
233 / sizeof(struct inode *))
234
235static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
236static struct workqueue_struct *isw_wq;
237
238void __inode_attach_wb(struct inode *inode, struct page *page)
239{
240 struct backing_dev_info *bdi = inode_to_bdi(inode);
241 struct bdi_writeback *wb = NULL;
242
243 if (inode_cgwb_enabled(inode)) {
244 struct cgroup_subsys_state *memcg_css;
245
246 if (page) {
247 memcg_css = mem_cgroup_css_from_page(page);
248 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
249 } else {
250 /* must pin memcg_css, see wb_get_create() */
251 memcg_css = task_get_css(current, memory_cgrp_id);
252 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
253 css_put(memcg_css);
254 }
255 }
256
257 if (!wb)
258 wb = &bdi->wb;
259
260 /*
261 * There may be multiple instances of this function racing to
262 * update the same inode. Use cmpxchg() to tell the winner.
263 */
264 if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
265 wb_put(wb);
266}
267EXPORT_SYMBOL_GPL(__inode_attach_wb);
268
269/**
270 * inode_cgwb_move_to_attached - put the inode onto wb->b_attached list
271 * @inode: inode of interest with i_lock held
272 * @wb: target bdi_writeback
273 *
274 * Remove the inode from wb's io lists and if necessarily put onto b_attached
275 * list. Only inodes attached to cgwb's are kept on this list.
276 */
277static void inode_cgwb_move_to_attached(struct inode *inode,
278 struct bdi_writeback *wb)
279{
280 assert_spin_locked(&wb->list_lock);
281 assert_spin_locked(&inode->i_lock);
282
283 inode->i_state &= ~I_SYNC_QUEUED;
284 if (wb != &wb->bdi->wb)
285 list_move(&inode->i_io_list, &wb->b_attached);
286 else
287 list_del_init(&inode->i_io_list);
288 wb_io_lists_depopulated(wb);
289}
290
291/**
292 * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
293 * @inode: inode of interest with i_lock held
294 *
295 * Returns @inode's wb with its list_lock held. @inode->i_lock must be
296 * held on entry and is released on return. The returned wb is guaranteed
297 * to stay @inode's associated wb until its list_lock is released.
298 */
299static struct bdi_writeback *
300locked_inode_to_wb_and_lock_list(struct inode *inode)
301 __releases(&inode->i_lock)
302 __acquires(&wb->list_lock)
303{
304 while (true) {
305 struct bdi_writeback *wb = inode_to_wb(inode);
306
307 /*
308 * inode_to_wb() association is protected by both
309 * @inode->i_lock and @wb->list_lock but list_lock nests
310 * outside i_lock. Drop i_lock and verify that the
311 * association hasn't changed after acquiring list_lock.
312 */
313 wb_get(wb);
314 spin_unlock(&inode->i_lock);
315 spin_lock(&wb->list_lock);
316
317 /* i_wb may have changed inbetween, can't use inode_to_wb() */
318 if (likely(wb == inode->i_wb)) {
319 wb_put(wb); /* @inode already has ref */
320 return wb;
321 }
322
323 spin_unlock(&wb->list_lock);
324 wb_put(wb);
325 cpu_relax();
326 spin_lock(&inode->i_lock);
327 }
328}
329
330/**
331 * inode_to_wb_and_lock_list - determine an inode's wb and lock it
332 * @inode: inode of interest
333 *
334 * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
335 * on entry.
336 */
337static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
338 __acquires(&wb->list_lock)
339{
340 spin_lock(&inode->i_lock);
341 return locked_inode_to_wb_and_lock_list(inode);
342}
343
344struct inode_switch_wbs_context {
345 struct rcu_work work;
346
347 /*
348 * Multiple inodes can be switched at once. The switching procedure
349 * consists of two parts, separated by a RCU grace period. To make
350 * sure that the second part is executed for each inode gone through
351 * the first part, all inode pointers are placed into a NULL-terminated
352 * array embedded into struct inode_switch_wbs_context. Otherwise
353 * an inode could be left in a non-consistent state.
354 */
355 struct bdi_writeback *new_wb;
356 struct inode *inodes[];
357};
358
359static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
360{
361 down_write(&bdi->wb_switch_rwsem);
362}
363
364static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
365{
366 up_write(&bdi->wb_switch_rwsem);
367}
368
369static bool inode_do_switch_wbs(struct inode *inode,
370 struct bdi_writeback *old_wb,
371 struct bdi_writeback *new_wb)
372{
373 struct address_space *mapping = inode->i_mapping;
374 XA_STATE(xas, &mapping->i_pages, 0);
375 struct page *page;
376 bool switched = false;
377
378 spin_lock(&inode->i_lock);
379 xa_lock_irq(&mapping->i_pages);
380
381 /*
382 * Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
383 * path owns the inode and we shouldn't modify ->i_io_list.
384 */
385 if (unlikely(inode->i_state & (I_FREEING | I_WILL_FREE)))
386 goto skip_switch;
387
388 trace_inode_switch_wbs(inode, old_wb, new_wb);
389
390 /*
391 * Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
392 * to possibly dirty pages while PAGECACHE_TAG_WRITEBACK points to
393 * pages actually under writeback.
394 */
395 xas_for_each_marked(&xas, page, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
396 if (PageDirty(page)) {
397 dec_wb_stat(old_wb, WB_RECLAIMABLE);
398 inc_wb_stat(new_wb, WB_RECLAIMABLE);
399 }
400 }
401
402 xas_set(&xas, 0);
403 xas_for_each_marked(&xas, page, ULONG_MAX, PAGECACHE_TAG_WRITEBACK) {
404 WARN_ON_ONCE(!PageWriteback(page));
405 dec_wb_stat(old_wb, WB_WRITEBACK);
406 inc_wb_stat(new_wb, WB_WRITEBACK);
407 }
408
409 wb_get(new_wb);
410
411 /*
412 * Transfer to @new_wb's IO list if necessary. If the @inode is dirty,
413 * the specific list @inode was on is ignored and the @inode is put on
414 * ->b_dirty which is always correct including from ->b_dirty_time.
415 * The transfer preserves @inode->dirtied_when ordering. If the @inode
416 * was clean, it means it was on the b_attached list, so move it onto
417 * the b_attached list of @new_wb.
418 */
419 if (!list_empty(&inode->i_io_list)) {
420 inode->i_wb = new_wb;
421
422 if (inode->i_state & I_DIRTY_ALL) {
423 struct inode *pos;
424
425 list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
426 if (time_after_eq(inode->dirtied_when,
427 pos->dirtied_when))
428 break;
429 inode_io_list_move_locked(inode, new_wb,
430 pos->i_io_list.prev);
431 } else {
432 inode_cgwb_move_to_attached(inode, new_wb);
433 }
434 } else {
435 inode->i_wb = new_wb;
436 }
437
438 /* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
439 inode->i_wb_frn_winner = 0;
440 inode->i_wb_frn_avg_time = 0;
441 inode->i_wb_frn_history = 0;
442 switched = true;
443skip_switch:
444 /*
445 * Paired with load_acquire in unlocked_inode_to_wb_begin() and
446 * ensures that the new wb is visible if they see !I_WB_SWITCH.
447 */
448 smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
449
450 xa_unlock_irq(&mapping->i_pages);
451 spin_unlock(&inode->i_lock);
452
453 return switched;
454}
455
456static void inode_switch_wbs_work_fn(struct work_struct *work)
457{
458 struct inode_switch_wbs_context *isw =
459 container_of(to_rcu_work(work), struct inode_switch_wbs_context, work);
460 struct backing_dev_info *bdi = inode_to_bdi(isw->inodes[0]);
461 struct bdi_writeback *old_wb = isw->inodes[0]->i_wb;
462 struct bdi_writeback *new_wb = isw->new_wb;
463 unsigned long nr_switched = 0;
464 struct inode **inodep;
465
466 /*
467 * If @inode switches cgwb membership while sync_inodes_sb() is
468 * being issued, sync_inodes_sb() might miss it. Synchronize.
469 */
470 down_read(&bdi->wb_switch_rwsem);
471
472 /*
473 * By the time control reaches here, RCU grace period has passed
474 * since I_WB_SWITCH assertion and all wb stat update transactions
475 * between unlocked_inode_to_wb_begin/end() are guaranteed to be
476 * synchronizing against the i_pages lock.
477 *
478 * Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
479 * gives us exclusion against all wb related operations on @inode
480 * including IO list manipulations and stat updates.
481 */
482 if (old_wb < new_wb) {
483 spin_lock(&old_wb->list_lock);
484 spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
485 } else {
486 spin_lock(&new_wb->list_lock);
487 spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
488 }
489
490 for (inodep = isw->inodes; *inodep; inodep++) {
491 WARN_ON_ONCE((*inodep)->i_wb != old_wb);
492 if (inode_do_switch_wbs(*inodep, old_wb, new_wb))
493 nr_switched++;
494 }
495
496 spin_unlock(&new_wb->list_lock);
497 spin_unlock(&old_wb->list_lock);
498
499 up_read(&bdi->wb_switch_rwsem);
500
501 if (nr_switched) {
502 wb_wakeup(new_wb);
503 wb_put_many(old_wb, nr_switched);
504 }
505
506 for (inodep = isw->inodes; *inodep; inodep++)
507 iput(*inodep);
508 wb_put(new_wb);
509 kfree(isw);
510 atomic_dec(&isw_nr_in_flight);
511}
512
513static bool inode_prepare_wbs_switch(struct inode *inode,
514 struct bdi_writeback *new_wb)
515{
516 /*
517 * Paired with smp_mb() in cgroup_writeback_umount().
518 * isw_nr_in_flight must be increased before checking SB_ACTIVE and
519 * grabbing an inode, otherwise isw_nr_in_flight can be observed as 0
520 * in cgroup_writeback_umount() and the isw_wq will be not flushed.
521 */
522 smp_mb();
523
524 if (IS_DAX(inode))
525 return false;
526
527 /* while holding I_WB_SWITCH, no one else can update the association */
528 spin_lock(&inode->i_lock);
529 if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
530 inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) ||
531 inode_to_wb(inode) == new_wb) {
532 spin_unlock(&inode->i_lock);
533 return false;
534 }
535 inode->i_state |= I_WB_SWITCH;
536 __iget(inode);
537 spin_unlock(&inode->i_lock);
538
539 return true;
540}
541
542/**
543 * inode_switch_wbs - change the wb association of an inode
544 * @inode: target inode
545 * @new_wb_id: ID of the new wb
546 *
547 * Switch @inode's wb association to the wb identified by @new_wb_id. The
548 * switching is performed asynchronously and may fail silently.
549 */
550static void inode_switch_wbs(struct inode *inode, int new_wb_id)
551{
552 struct backing_dev_info *bdi = inode_to_bdi(inode);
553 struct cgroup_subsys_state *memcg_css;
554 struct inode_switch_wbs_context *isw;
555
556 /* noop if seems to be already in progress */
557 if (inode->i_state & I_WB_SWITCH)
558 return;
559
560 /* avoid queueing a new switch if too many are already in flight */
561 if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
562 return;
563
564 isw = kzalloc(sizeof(*isw) + 2 * sizeof(struct inode *), GFP_ATOMIC);
565 if (!isw)
566 return;
567
568 atomic_inc(&isw_nr_in_flight);
569
570 /* find and pin the new wb */
571 rcu_read_lock();
572 memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
573 if (memcg_css && !css_tryget(memcg_css))
574 memcg_css = NULL;
575 rcu_read_unlock();
576 if (!memcg_css)
577 goto out_free;
578
579 isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
580 css_put(memcg_css);
581 if (!isw->new_wb)
582 goto out_free;
583
584 if (!inode_prepare_wbs_switch(inode, isw->new_wb))
585 goto out_free;
586
587 isw->inodes[0] = inode;
588
589 /*
590 * In addition to synchronizing among switchers, I_WB_SWITCH tells
591 * the RCU protected stat update paths to grab the i_page
592 * lock so that stat transfer can synchronize against them.
593 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
594 */
595 INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
596 queue_rcu_work(isw_wq, &isw->work);
597 return;
598
599out_free:
600 atomic_dec(&isw_nr_in_flight);
601 if (isw->new_wb)
602 wb_put(isw->new_wb);
603 kfree(isw);
604}
605
606/**
607 * cleanup_offline_cgwb - detach associated inodes
608 * @wb: target wb
609 *
610 * Switch all inodes attached to @wb to a nearest living ancestor's wb in order
611 * to eventually release the dying @wb. Returns %true if not all inodes were
612 * switched and the function has to be restarted.
613 */
614bool cleanup_offline_cgwb(struct bdi_writeback *wb)
615{
616 struct cgroup_subsys_state *memcg_css;
617 struct inode_switch_wbs_context *isw;
618 struct inode *inode;
619 int nr;
620 bool restart = false;
621
622 isw = kzalloc(sizeof(*isw) + WB_MAX_INODES_PER_ISW *
623 sizeof(struct inode *), GFP_KERNEL);
624 if (!isw)
625 return restart;
626
627 atomic_inc(&isw_nr_in_flight);
628
629 for (memcg_css = wb->memcg_css->parent; memcg_css;
630 memcg_css = memcg_css->parent) {
631 isw->new_wb = wb_get_create(wb->bdi, memcg_css, GFP_KERNEL);
632 if (isw->new_wb)
633 break;
634 }
635 if (unlikely(!isw->new_wb))
636 isw->new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */
637
638 nr = 0;
639 spin_lock(&wb->list_lock);
640 list_for_each_entry(inode, &wb->b_attached, i_io_list) {
641 if (!inode_prepare_wbs_switch(inode, isw->new_wb))
642 continue;
643
644 isw->inodes[nr++] = inode;
645
646 if (nr >= WB_MAX_INODES_PER_ISW - 1) {
647 restart = true;
648 break;
649 }
650 }
651 spin_unlock(&wb->list_lock);
652
653 /* no attached inodes? bail out */
654 if (nr == 0) {
655 atomic_dec(&isw_nr_in_flight);
656 wb_put(isw->new_wb);
657 kfree(isw);
658 return restart;
659 }
660
661 /*
662 * In addition to synchronizing among switchers, I_WB_SWITCH tells
663 * the RCU protected stat update paths to grab the i_page
664 * lock so that stat transfer can synchronize against them.
665 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
666 */
667 INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
668 queue_rcu_work(isw_wq, &isw->work);
669
670 return restart;
671}
672
673/**
674 * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
675 * @wbc: writeback_control of interest
676 * @inode: target inode
677 *
678 * @inode is locked and about to be written back under the control of @wbc.
679 * Record @inode's writeback context into @wbc and unlock the i_lock. On
680 * writeback completion, wbc_detach_inode() should be called. This is used
681 * to track the cgroup writeback context.
682 */
683void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
684 struct inode *inode)
685{
686 if (!inode_cgwb_enabled(inode)) {
687 spin_unlock(&inode->i_lock);
688 return;
689 }
690
691 wbc->wb = inode_to_wb(inode);
692 wbc->inode = inode;
693
694 wbc->wb_id = wbc->wb->memcg_css->id;
695 wbc->wb_lcand_id = inode->i_wb_frn_winner;
696 wbc->wb_tcand_id = 0;
697 wbc->wb_bytes = 0;
698 wbc->wb_lcand_bytes = 0;
699 wbc->wb_tcand_bytes = 0;
700
701 wb_get(wbc->wb);
702 spin_unlock(&inode->i_lock);
703
704 /*
705 * A dying wb indicates that either the blkcg associated with the
706 * memcg changed or the associated memcg is dying. In the first
707 * case, a replacement wb should already be available and we should
708 * refresh the wb immediately. In the second case, trying to
709 * refresh will keep failing.
710 */
711 if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
712 inode_switch_wbs(inode, wbc->wb_id);
713}
714EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
715
716/**
717 * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
718 * @wbc: writeback_control of the just finished writeback
719 *
720 * To be called after a writeback attempt of an inode finishes and undoes
721 * wbc_attach_and_unlock_inode(). Can be called under any context.
722 *
723 * As concurrent write sharing of an inode is expected to be very rare and
724 * memcg only tracks page ownership on first-use basis severely confining
725 * the usefulness of such sharing, cgroup writeback tracks ownership
726 * per-inode. While the support for concurrent write sharing of an inode
727 * is deemed unnecessary, an inode being written to by different cgroups at
728 * different points in time is a lot more common, and, more importantly,
729 * charging only by first-use can too readily lead to grossly incorrect
730 * behaviors (single foreign page can lead to gigabytes of writeback to be
731 * incorrectly attributed).
732 *
733 * To resolve this issue, cgroup writeback detects the majority dirtier of
734 * an inode and transfers the ownership to it. To avoid unnnecessary
735 * oscillation, the detection mechanism keeps track of history and gives
736 * out the switch verdict only if the foreign usage pattern is stable over
737 * a certain amount of time and/or writeback attempts.
738 *
739 * On each writeback attempt, @wbc tries to detect the majority writer
740 * using Boyer-Moore majority vote algorithm. In addition to the byte
741 * count from the majority voting, it also counts the bytes written for the
742 * current wb and the last round's winner wb (max of last round's current
743 * wb, the winner from two rounds ago, and the last round's majority
744 * candidate). Keeping track of the historical winner helps the algorithm
745 * to semi-reliably detect the most active writer even when it's not the
746 * absolute majority.
747 *
748 * Once the winner of the round is determined, whether the winner is
749 * foreign or not and how much IO time the round consumed is recorded in
750 * inode->i_wb_frn_history. If the amount of recorded foreign IO time is
751 * over a certain threshold, the switch verdict is given.
752 */
753void wbc_detach_inode(struct writeback_control *wbc)
754{
755 struct bdi_writeback *wb = wbc->wb;
756 struct inode *inode = wbc->inode;
757 unsigned long avg_time, max_bytes, max_time;
758 u16 history;
759 int max_id;
760
761 if (!wb)
762 return;
763
764 history = inode->i_wb_frn_history;
765 avg_time = inode->i_wb_frn_avg_time;
766
767 /* pick the winner of this round */
768 if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
769 wbc->wb_bytes >= wbc->wb_tcand_bytes) {
770 max_id = wbc->wb_id;
771 max_bytes = wbc->wb_bytes;
772 } else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
773 max_id = wbc->wb_lcand_id;
774 max_bytes = wbc->wb_lcand_bytes;
775 } else {
776 max_id = wbc->wb_tcand_id;
777 max_bytes = wbc->wb_tcand_bytes;
778 }
779
780 /*
781 * Calculate the amount of IO time the winner consumed and fold it
782 * into the running average kept per inode. If the consumed IO
783 * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
784 * deciding whether to switch or not. This is to prevent one-off
785 * small dirtiers from skewing the verdict.
786 */
787 max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
788 wb->avg_write_bandwidth);
789 if (avg_time)
790 avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
791 (avg_time >> WB_FRN_TIME_AVG_SHIFT);
792 else
793 avg_time = max_time; /* immediate catch up on first run */
794
795 if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
796 int slots;
797
798 /*
799 * The switch verdict is reached if foreign wb's consume
800 * more than a certain proportion of IO time in a
801 * WB_FRN_TIME_PERIOD. This is loosely tracked by 16 slot
802 * history mask where each bit represents one sixteenth of
803 * the period. Determine the number of slots to shift into
804 * history from @max_time.
805 */
806 slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
807 (unsigned long)WB_FRN_HIST_MAX_SLOTS);
808 history <<= slots;
809 if (wbc->wb_id != max_id)
810 history |= (1U << slots) - 1;
811
812 if (history)
813 trace_inode_foreign_history(inode, wbc, history);
814
815 /*
816 * Switch if the current wb isn't the consistent winner.
817 * If there are multiple closely competing dirtiers, the
818 * inode may switch across them repeatedly over time, which
819 * is okay. The main goal is avoiding keeping an inode on
820 * the wrong wb for an extended period of time.
821 */
822 if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
823 inode_switch_wbs(inode, max_id);
824 }
825
826 /*
827 * Multiple instances of this function may race to update the
828 * following fields but we don't mind occassional inaccuracies.
829 */
830 inode->i_wb_frn_winner = max_id;
831 inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
832 inode->i_wb_frn_history = history;
833
834 wb_put(wbc->wb);
835 wbc->wb = NULL;
836}
837EXPORT_SYMBOL_GPL(wbc_detach_inode);
838
839/**
840 * wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
841 * @wbc: writeback_control of the writeback in progress
842 * @page: page being written out
843 * @bytes: number of bytes being written out
844 *
845 * @bytes from @page are about to written out during the writeback
846 * controlled by @wbc. Keep the book for foreign inode detection. See
847 * wbc_detach_inode().
848 */
849void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
850 size_t bytes)
851{
852 struct cgroup_subsys_state *css;
853 int id;
854
855 /*
856 * pageout() path doesn't attach @wbc to the inode being written
857 * out. This is intentional as we don't want the function to block
858 * behind a slow cgroup. Ultimately, we want pageout() to kick off
859 * regular writeback instead of writing things out itself.
860 */
861 if (!wbc->wb || wbc->no_cgroup_owner)
862 return;
863
864 css = mem_cgroup_css_from_page(page);
865 /* dead cgroups shouldn't contribute to inode ownership arbitration */
866 if (!(css->flags & CSS_ONLINE))
867 return;
868
869 id = css->id;
870
871 if (id == wbc->wb_id) {
872 wbc->wb_bytes += bytes;
873 return;
874 }
875
876 if (id == wbc->wb_lcand_id)
877 wbc->wb_lcand_bytes += bytes;
878
879 /* Boyer-Moore majority vote algorithm */
880 if (!wbc->wb_tcand_bytes)
881 wbc->wb_tcand_id = id;
882 if (id == wbc->wb_tcand_id)
883 wbc->wb_tcand_bytes += bytes;
884 else
885 wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
886}
887EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);
888
889/**
890 * inode_congested - test whether an inode is congested
891 * @inode: inode to test for congestion (may be NULL)
892 * @cong_bits: mask of WB_[a]sync_congested bits to test
893 *
894 * Tests whether @inode is congested. @cong_bits is the mask of congestion
895 * bits to test and the return value is the mask of set bits.
896 *
897 * If cgroup writeback is enabled for @inode, the congestion state is
898 * determined by whether the cgwb (cgroup bdi_writeback) for the blkcg
899 * associated with @inode is congested; otherwise, the root wb's congestion
900 * state is used.
901 *
902 * @inode is allowed to be NULL as this function is often called on
903 * mapping->host which is NULL for the swapper space.
904 */
905int inode_congested(struct inode *inode, int cong_bits)
906{
907 /*
908 * Once set, ->i_wb never becomes NULL while the inode is alive.
909 * Start transaction iff ->i_wb is visible.
910 */
911 if (inode && inode_to_wb_is_valid(inode)) {
912 struct bdi_writeback *wb;
913 struct wb_lock_cookie lock_cookie = {};
914 bool congested;
915
916 wb = unlocked_inode_to_wb_begin(inode, &lock_cookie);
917 congested = wb_congested(wb, cong_bits);
918 unlocked_inode_to_wb_end(inode, &lock_cookie);
919 return congested;
920 }
921
922 return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
923}
924EXPORT_SYMBOL_GPL(inode_congested);
925
926/**
927 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
928 * @wb: target bdi_writeback to split @nr_pages to
929 * @nr_pages: number of pages to write for the whole bdi
930 *
931 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
932 * relation to the total write bandwidth of all wb's w/ dirty inodes on
933 * @wb->bdi.
934 */
935static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
936{
937 unsigned long this_bw = wb->avg_write_bandwidth;
938 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
939
940 if (nr_pages == LONG_MAX)
941 return LONG_MAX;
942
943 /*
944 * This may be called on clean wb's and proportional distribution
945 * may not make sense, just use the original @nr_pages in those
946 * cases. In general, we wanna err on the side of writing more.
947 */
948 if (!tot_bw || this_bw >= tot_bw)
949 return nr_pages;
950 else
951 return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
952}
953
954/**
955 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
956 * @bdi: target backing_dev_info
957 * @base_work: wb_writeback_work to issue
958 * @skip_if_busy: skip wb's which already have writeback in progress
959 *
960 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
961 * have dirty inodes. If @base_work->nr_page isn't %LONG_MAX, it's
962 * distributed to the busy wbs according to each wb's proportion in the
963 * total active write bandwidth of @bdi.
964 */
965static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
966 struct wb_writeback_work *base_work,
967 bool skip_if_busy)
968{
969 struct bdi_writeback *last_wb = NULL;
970 struct bdi_writeback *wb = list_entry(&bdi->wb_list,
971 struct bdi_writeback, bdi_node);
972
973 might_sleep();
974restart:
975 rcu_read_lock();
976 list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
977 DEFINE_WB_COMPLETION(fallback_work_done, bdi);
978 struct wb_writeback_work fallback_work;
979 struct wb_writeback_work *work;
980 long nr_pages;
981
982 if (last_wb) {
983 wb_put(last_wb);
984 last_wb = NULL;
985 }
986
987 /* SYNC_ALL writes out I_DIRTY_TIME too */
988 if (!wb_has_dirty_io(wb) &&
989 (base_work->sync_mode == WB_SYNC_NONE ||
990 list_empty(&wb->b_dirty_time)))
991 continue;
992 if (skip_if_busy && writeback_in_progress(wb))
993 continue;
994
995 nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
996
997 work = kmalloc(sizeof(*work), GFP_ATOMIC);
998 if (work) {
999 *work = *base_work;
1000 work->nr_pages = nr_pages;
1001 work->auto_free = 1;
1002 wb_queue_work(wb, work);
1003 continue;
1004 }
1005
1006 /* alloc failed, execute synchronously using on-stack fallback */
1007 work = &fallback_work;
1008 *work = *base_work;
1009 work->nr_pages = nr_pages;
1010 work->auto_free = 0;
1011 work->done = &fallback_work_done;
1012
1013 wb_queue_work(wb, work);
1014
1015 /*
1016 * Pin @wb so that it stays on @bdi->wb_list. This allows
1017 * continuing iteration from @wb after dropping and
1018 * regrabbing rcu read lock.
1019 */
1020 wb_get(wb);
1021 last_wb = wb;
1022
1023 rcu_read_unlock();
1024 wb_wait_for_completion(&fallback_work_done);
1025 goto restart;
1026 }
1027 rcu_read_unlock();
1028
1029 if (last_wb)
1030 wb_put(last_wb);
1031}
1032
1033/**
1034 * cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
1035 * @bdi_id: target bdi id
1036 * @memcg_id: target memcg css id
1037 * @nr: number of pages to write, 0 for best-effort dirty flushing
1038 * @reason: reason why some writeback work initiated
1039 * @done: target wb_completion
1040 *
1041 * Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
1042 * with the specified parameters.
1043 */
1044int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr,
1045 enum wb_reason reason, struct wb_completion *done)
1046{
1047 struct backing_dev_info *bdi;
1048 struct cgroup_subsys_state *memcg_css;
1049 struct bdi_writeback *wb;
1050 struct wb_writeback_work *work;
1051 int ret;
1052
1053 /* lookup bdi and memcg */
1054 bdi = bdi_get_by_id(bdi_id);
1055 if (!bdi)
1056 return -ENOENT;
1057
1058 rcu_read_lock();
1059 memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
1060 if (memcg_css && !css_tryget(memcg_css))
1061 memcg_css = NULL;
1062 rcu_read_unlock();
1063 if (!memcg_css) {
1064 ret = -ENOENT;
1065 goto out_bdi_put;
1066 }
1067
1068 /*
1069 * And find the associated wb. If the wb isn't there already
1070 * there's nothing to flush, don't create one.
1071 */
1072 wb = wb_get_lookup(bdi, memcg_css);
1073 if (!wb) {
1074 ret = -ENOENT;
1075 goto out_css_put;
1076 }
1077
1078 /*
1079 * If @nr is zero, the caller is attempting to write out most of
1080 * the currently dirty pages. Let's take the current dirty page
1081 * count and inflate it by 25% which should be large enough to
1082 * flush out most dirty pages while avoiding getting livelocked by
1083 * concurrent dirtiers.
1084 */
1085 if (!nr) {
1086 unsigned long filepages, headroom, dirty, writeback;
1087
1088 mem_cgroup_wb_stats(wb, &filepages, &headroom, &dirty,
1089 &writeback);
1090 nr = dirty * 10 / 8;
1091 }
1092
1093 /* issue the writeback work */
1094 work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
1095 if (work) {
1096 work->nr_pages = nr;
1097 work->sync_mode = WB_SYNC_NONE;
1098 work->range_cyclic = 1;
1099 work->reason = reason;
1100 work->done = done;
1101 work->auto_free = 1;
1102 wb_queue_work(wb, work);
1103 ret = 0;
1104 } else {
1105 ret = -ENOMEM;
1106 }
1107
1108 wb_put(wb);
1109out_css_put:
1110 css_put(memcg_css);
1111out_bdi_put:
1112 bdi_put(bdi);
1113 return ret;
1114}
1115
1116/**
1117 * cgroup_writeback_umount - flush inode wb switches for umount
1118 *
1119 * This function is called when a super_block is about to be destroyed and
1120 * flushes in-flight inode wb switches. An inode wb switch goes through
1121 * RCU and then workqueue, so the two need to be flushed in order to ensure
1122 * that all previously scheduled switches are finished. As wb switches are
1123 * rare occurrences and synchronize_rcu() can take a while, perform
1124 * flushing iff wb switches are in flight.
1125 */
1126void cgroup_writeback_umount(void)
1127{
1128 /*
1129 * SB_ACTIVE should be reliably cleared before checking
1130 * isw_nr_in_flight, see generic_shutdown_super().
1131 */
1132 smp_mb();
1133
1134 if (atomic_read(&isw_nr_in_flight)) {
1135 /*
1136 * Use rcu_barrier() to wait for all pending callbacks to
1137 * ensure that all in-flight wb switches are in the workqueue.
1138 */
1139 rcu_barrier();
1140 flush_workqueue(isw_wq);
1141 }
1142}
1143
1144static int __init cgroup_writeback_init(void)
1145{
1146 isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
1147 if (!isw_wq)
1148 return -ENOMEM;
1149 return 0;
1150}
1151fs_initcall(cgroup_writeback_init);
1152
1153#else /* CONFIG_CGROUP_WRITEBACK */
1154
1155static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1156static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1157
1158static void inode_cgwb_move_to_attached(struct inode *inode,
1159 struct bdi_writeback *wb)
1160{
1161 assert_spin_locked(&wb->list_lock);
1162 assert_spin_locked(&inode->i_lock);
1163
1164 inode->i_state &= ~I_SYNC_QUEUED;
1165 list_del_init(&inode->i_io_list);
1166 wb_io_lists_depopulated(wb);
1167}
1168
1169static struct bdi_writeback *
1170locked_inode_to_wb_and_lock_list(struct inode *inode)
1171 __releases(&inode->i_lock)
1172 __acquires(&wb->list_lock)
1173{
1174 struct bdi_writeback *wb = inode_to_wb(inode);
1175
1176 spin_unlock(&inode->i_lock);
1177 spin_lock(&wb->list_lock);
1178 return wb;
1179}
1180
1181static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
1182 __acquires(&wb->list_lock)
1183{
1184 struct bdi_writeback *wb = inode_to_wb(inode);
1185
1186 spin_lock(&wb->list_lock);
1187 return wb;
1188}
1189
1190static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
1191{
1192 return nr_pages;
1193}
1194
1195static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
1196 struct wb_writeback_work *base_work,
1197 bool skip_if_busy)
1198{
1199 might_sleep();
1200
1201 if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
1202 base_work->auto_free = 0;
1203 wb_queue_work(&bdi->wb, base_work);
1204 }
1205}
1206
1207#endif /* CONFIG_CGROUP_WRITEBACK */
1208
1209/*
1210 * Add in the number of potentially dirty inodes, because each inode
1211 * write can dirty pagecache in the underlying blockdev.
1212 */
1213static unsigned long get_nr_dirty_pages(void)
1214{
1215 return global_node_page_state(NR_FILE_DIRTY) +
1216 get_nr_dirty_inodes();
1217}
1218
1219static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
1220{
1221 if (!wb_has_dirty_io(wb))
1222 return;
1223
1224 /*
1225 * All callers of this function want to start writeback of all
1226 * dirty pages. Places like vmscan can call this at a very
1227 * high frequency, causing pointless allocations of tons of
1228 * work items and keeping the flusher threads busy retrieving
1229 * that work. Ensure that we only allow one of them pending and
1230 * inflight at the time.
1231 */
1232 if (test_bit(WB_start_all, &wb->state) ||
1233 test_and_set_bit(WB_start_all, &wb->state))
1234 return;
1235
1236 wb->start_all_reason = reason;
1237 wb_wakeup(wb);
1238}
1239
1240/**
1241 * wb_start_background_writeback - start background writeback
1242 * @wb: bdi_writback to write from
1243 *
1244 * Description:
1245 * This makes sure WB_SYNC_NONE background writeback happens. When
1246 * this function returns, it is only guaranteed that for given wb
1247 * some IO is happening if we are over background dirty threshold.
1248 * Caller need not hold sb s_umount semaphore.
1249 */
1250void wb_start_background_writeback(struct bdi_writeback *wb)
1251{
1252 /*
1253 * We just wake up the flusher thread. It will perform background
1254 * writeback as soon as there is no other work to do.
1255 */
1256 trace_writeback_wake_background(wb);
1257 wb_wakeup(wb);
1258}
1259
1260/*
1261 * Remove the inode from the writeback list it is on.
1262 */
1263void inode_io_list_del(struct inode *inode)
1264{
1265 struct bdi_writeback *wb;
1266
1267 wb = inode_to_wb_and_lock_list(inode);
1268 spin_lock(&inode->i_lock);
1269
1270 inode->i_state &= ~I_SYNC_QUEUED;
1271 list_del_init(&inode->i_io_list);
1272 wb_io_lists_depopulated(wb);
1273
1274 spin_unlock(&inode->i_lock);
1275 spin_unlock(&wb->list_lock);
1276}
1277EXPORT_SYMBOL(inode_io_list_del);
1278
1279/*
1280 * mark an inode as under writeback on the sb
1281 */
1282void sb_mark_inode_writeback(struct inode *inode)
1283{
1284 struct super_block *sb = inode->i_sb;
1285 unsigned long flags;
1286
1287 if (list_empty(&inode->i_wb_list)) {
1288 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1289 if (list_empty(&inode->i_wb_list)) {
1290 list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
1291 trace_sb_mark_inode_writeback(inode);
1292 }
1293 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1294 }
1295}
1296
1297/*
1298 * clear an inode as under writeback on the sb
1299 */
1300void sb_clear_inode_writeback(struct inode *inode)
1301{
1302 struct super_block *sb = inode->i_sb;
1303 unsigned long flags;
1304
1305 if (!list_empty(&inode->i_wb_list)) {
1306 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1307 if (!list_empty(&inode->i_wb_list)) {
1308 list_del_init(&inode->i_wb_list);
1309 trace_sb_clear_inode_writeback(inode);
1310 }
1311 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1312 }
1313}
1314
1315/*
1316 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1317 * furthest end of its superblock's dirty-inode list.
1318 *
1319 * Before stamping the inode's ->dirtied_when, we check to see whether it is
1320 * already the most-recently-dirtied inode on the b_dirty list. If that is
1321 * the case then the inode must have been redirtied while it was being written
1322 * out and we don't reset its dirtied_when.
1323 */
1324static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
1325{
1326 assert_spin_locked(&inode->i_lock);
1327
1328 if (!list_empty(&wb->b_dirty)) {
1329 struct inode *tail;
1330
1331 tail = wb_inode(wb->b_dirty.next);
1332 if (time_before(inode->dirtied_when, tail->dirtied_when))
1333 inode->dirtied_when = jiffies;
1334 }
1335 inode_io_list_move_locked(inode, wb, &wb->b_dirty);
1336 inode->i_state &= ~I_SYNC_QUEUED;
1337}
1338
1339static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
1340{
1341 spin_lock(&inode->i_lock);
1342 redirty_tail_locked(inode, wb);
1343 spin_unlock(&inode->i_lock);
1344}
1345
1346/*
1347 * requeue inode for re-scanning after bdi->b_io list is exhausted.
1348 */
1349static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
1350{
1351 inode_io_list_move_locked(inode, wb, &wb->b_more_io);
1352}
1353
1354static void inode_sync_complete(struct inode *inode)
1355{
1356 inode->i_state &= ~I_SYNC;
1357 /* If inode is clean an unused, put it into LRU now... */
1358 inode_add_lru(inode);
1359 /* Waiters must see I_SYNC cleared before being woken up */
1360 smp_mb();
1361 wake_up_bit(&inode->i_state, __I_SYNC);
1362}
1363
1364static bool inode_dirtied_after(struct inode *inode, unsigned long t)
1365{
1366 bool ret = time_after(inode->dirtied_when, t);
1367#ifndef CONFIG_64BIT
1368 /*
1369 * For inodes being constantly redirtied, dirtied_when can get stuck.
1370 * It _appears_ to be in the future, but is actually in distant past.
1371 * This test is necessary to prevent such wrapped-around relative times
1372 * from permanently stopping the whole bdi writeback.
1373 */
1374 ret = ret && time_before_eq(inode->dirtied_when, jiffies);
1375#endif
1376 return ret;
1377}
1378
1379#define EXPIRE_DIRTY_ATIME 0x0001
1380
1381/*
1382 * Move expired (dirtied before dirtied_before) dirty inodes from
1383 * @delaying_queue to @dispatch_queue.
1384 */
1385static int move_expired_inodes(struct list_head *delaying_queue,
1386 struct list_head *dispatch_queue,
1387 unsigned long dirtied_before)
1388{
1389 LIST_HEAD(tmp);
1390 struct list_head *pos, *node;
1391 struct super_block *sb = NULL;
1392 struct inode *inode;
1393 int do_sb_sort = 0;
1394 int moved = 0;
1395
1396 while (!list_empty(delaying_queue)) {
1397 inode = wb_inode(delaying_queue->prev);
1398 if (inode_dirtied_after(inode, dirtied_before))
1399 break;
1400 list_move(&inode->i_io_list, &tmp);
1401 moved++;
1402 spin_lock(&inode->i_lock);
1403 inode->i_state |= I_SYNC_QUEUED;
1404 spin_unlock(&inode->i_lock);
1405 if (sb_is_blkdev_sb(inode->i_sb))
1406 continue;
1407 if (sb && sb != inode->i_sb)
1408 do_sb_sort = 1;
1409 sb = inode->i_sb;
1410 }
1411
1412 /* just one sb in list, splice to dispatch_queue and we're done */
1413 if (!do_sb_sort) {
1414 list_splice(&tmp, dispatch_queue);
1415 goto out;
1416 }
1417
1418 /* Move inodes from one superblock together */
1419 while (!list_empty(&tmp)) {
1420 sb = wb_inode(tmp.prev)->i_sb;
1421 list_for_each_prev_safe(pos, node, &tmp) {
1422 inode = wb_inode(pos);
1423 if (inode->i_sb == sb)
1424 list_move(&inode->i_io_list, dispatch_queue);
1425 }
1426 }
1427out:
1428 return moved;
1429}
1430
1431/*
1432 * Queue all expired dirty inodes for io, eldest first.
1433 * Before
1434 * newly dirtied b_dirty b_io b_more_io
1435 * =============> gf edc BA
1436 * After
1437 * newly dirtied b_dirty b_io b_more_io
1438 * =============> g fBAedc
1439 * |
1440 * +--> dequeue for IO
1441 */
1442static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
1443 unsigned long dirtied_before)
1444{
1445 int moved;
1446 unsigned long time_expire_jif = dirtied_before;
1447
1448 assert_spin_locked(&wb->list_lock);
1449 list_splice_init(&wb->b_more_io, &wb->b_io);
1450 moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, dirtied_before);
1451 if (!work->for_sync)
1452 time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
1453 moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
1454 time_expire_jif);
1455 if (moved)
1456 wb_io_lists_populated(wb);
1457 trace_writeback_queue_io(wb, work, dirtied_before, moved);
1458}
1459
1460static int write_inode(struct inode *inode, struct writeback_control *wbc)
1461{
1462 int ret;
1463
1464 if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1465 trace_writeback_write_inode_start(inode, wbc);
1466 ret = inode->i_sb->s_op->write_inode(inode, wbc);
1467 trace_writeback_write_inode(inode, wbc);
1468 return ret;
1469 }
1470 return 0;
1471}
1472
1473/*
1474 * Wait for writeback on an inode to complete. Called with i_lock held.
1475 * Caller must make sure inode cannot go away when we drop i_lock.
1476 */
1477static void __inode_wait_for_writeback(struct inode *inode)
1478 __releases(inode->i_lock)
1479 __acquires(inode->i_lock)
1480{
1481 DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1482 wait_queue_head_t *wqh;
1483
1484 wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1485 while (inode->i_state & I_SYNC) {
1486 spin_unlock(&inode->i_lock);
1487 __wait_on_bit(wqh, &wq, bit_wait,
1488 TASK_UNINTERRUPTIBLE);
1489 spin_lock(&inode->i_lock);
1490 }
1491}
1492
1493/*
1494 * Wait for writeback on an inode to complete. Caller must have inode pinned.
1495 */
1496void inode_wait_for_writeback(struct inode *inode)
1497{
1498 spin_lock(&inode->i_lock);
1499 __inode_wait_for_writeback(inode);
1500 spin_unlock(&inode->i_lock);
1501}
1502
1503/*
1504 * Sleep until I_SYNC is cleared. This function must be called with i_lock
1505 * held and drops it. It is aimed for callers not holding any inode reference
1506 * so once i_lock is dropped, inode can go away.
1507 */
1508static void inode_sleep_on_writeback(struct inode *inode)
1509 __releases(inode->i_lock)
1510{
1511 DEFINE_WAIT(wait);
1512 wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1513 int sleep;
1514
1515 prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1516 sleep = inode->i_state & I_SYNC;
1517 spin_unlock(&inode->i_lock);
1518 if (sleep)
1519 schedule();
1520 finish_wait(wqh, &wait);
1521}
1522
1523/*
1524 * Find proper writeback list for the inode depending on its current state and
1525 * possibly also change of its state while we were doing writeback. Here we
1526 * handle things such as livelock prevention or fairness of writeback among
1527 * inodes. This function can be called only by flusher thread - noone else
1528 * processes all inodes in writeback lists and requeueing inodes behind flusher
1529 * thread's back can have unexpected consequences.
1530 */
1531static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1532 struct writeback_control *wbc)
1533{
1534 if (inode->i_state & I_FREEING)
1535 return;
1536
1537 /*
1538 * Sync livelock prevention. Each inode is tagged and synced in one
1539 * shot. If still dirty, it will be redirty_tail()'ed below. Update
1540 * the dirty time to prevent enqueue and sync it again.
1541 */
1542 if ((inode->i_state & I_DIRTY) &&
1543 (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1544 inode->dirtied_when = jiffies;
1545
1546 if (wbc->pages_skipped) {
1547 /*
1548 * writeback is not making progress due to locked
1549 * buffers. Skip this inode for now.
1550 */
1551 redirty_tail_locked(inode, wb);
1552 return;
1553 }
1554
1555 if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1556 /*
1557 * We didn't write back all the pages. nfs_writepages()
1558 * sometimes bales out without doing anything.
1559 */
1560 if (wbc->nr_to_write <= 0) {
1561 /* Slice used up. Queue for next turn. */
1562 requeue_io(inode, wb);
1563 } else {
1564 /*
1565 * Writeback blocked by something other than
1566 * congestion. Delay the inode for some time to
1567 * avoid spinning on the CPU (100% iowait)
1568 * retrying writeback of the dirty page/inode
1569 * that cannot be performed immediately.
1570 */
1571 redirty_tail_locked(inode, wb);
1572 }
1573 } else if (inode->i_state & I_DIRTY) {
1574 /*
1575 * Filesystems can dirty the inode during writeback operations,
1576 * such as delayed allocation during submission or metadata
1577 * updates after data IO completion.
1578 */
1579 redirty_tail_locked(inode, wb);
1580 } else if (inode->i_state & I_DIRTY_TIME) {
1581 inode->dirtied_when = jiffies;
1582 inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
1583 inode->i_state &= ~I_SYNC_QUEUED;
1584 } else {
1585 /* The inode is clean. Remove from writeback lists. */
1586 inode_cgwb_move_to_attached(inode, wb);
1587 }
1588}
1589
1590/*
1591 * Write out an inode and its dirty pages (or some of its dirty pages, depending
1592 * on @wbc->nr_to_write), and clear the relevant dirty flags from i_state.
1593 *
1594 * This doesn't remove the inode from the writeback list it is on, except
1595 * potentially to move it from b_dirty_time to b_dirty due to timestamp
1596 * expiration. The caller is otherwise responsible for writeback list handling.
1597 *
1598 * The caller is also responsible for setting the I_SYNC flag beforehand and
1599 * calling inode_sync_complete() to clear it afterwards.
1600 */
1601static int
1602__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1603{
1604 struct address_space *mapping = inode->i_mapping;
1605 long nr_to_write = wbc->nr_to_write;
1606 unsigned dirty;
1607 int ret;
1608
1609 WARN_ON(!(inode->i_state & I_SYNC));
1610
1611 trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1612
1613 ret = do_writepages(mapping, wbc);
1614
1615 /*
1616 * Make sure to wait on the data before writing out the metadata.
1617 * This is important for filesystems that modify metadata on data
1618 * I/O completion. We don't do it for sync(2) writeback because it has a
1619 * separate, external IO completion path and ->sync_fs for guaranteeing
1620 * inode metadata is written back correctly.
1621 */
1622 if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
1623 int err = filemap_fdatawait(mapping);
1624 if (ret == 0)
1625 ret = err;
1626 }
1627
1628 /*
1629 * If the inode has dirty timestamps and we need to write them, call
1630 * mark_inode_dirty_sync() to notify the filesystem about it and to
1631 * change I_DIRTY_TIME into I_DIRTY_SYNC.
1632 */
1633 if ((inode->i_state & I_DIRTY_TIME) &&
1634 (wbc->sync_mode == WB_SYNC_ALL ||
1635 time_after(jiffies, inode->dirtied_time_when +
1636 dirtytime_expire_interval * HZ))) {
1637 trace_writeback_lazytime(inode);
1638 mark_inode_dirty_sync(inode);
1639 }
1640
1641 /*
1642 * Get and clear the dirty flags from i_state. This needs to be done
1643 * after calling writepages because some filesystems may redirty the
1644 * inode during writepages due to delalloc. It also needs to be done
1645 * after handling timestamp expiration, as that may dirty the inode too.
1646 */
1647 spin_lock(&inode->i_lock);
1648 dirty = inode->i_state & I_DIRTY;
1649 inode->i_state &= ~dirty;
1650
1651 /*
1652 * Paired with smp_mb() in __mark_inode_dirty(). This allows
1653 * __mark_inode_dirty() to test i_state without grabbing i_lock -
1654 * either they see the I_DIRTY bits cleared or we see the dirtied
1655 * inode.
1656 *
1657 * I_DIRTY_PAGES is always cleared together above even if @mapping
1658 * still has dirty pages. The flag is reinstated after smp_mb() if
1659 * necessary. This guarantees that either __mark_inode_dirty()
1660 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1661 */
1662 smp_mb();
1663
1664 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1665 inode->i_state |= I_DIRTY_PAGES;
1666
1667 spin_unlock(&inode->i_lock);
1668
1669 /* Don't write the inode if only I_DIRTY_PAGES was set */
1670 if (dirty & ~I_DIRTY_PAGES) {
1671 int err = write_inode(inode, wbc);
1672 if (ret == 0)
1673 ret = err;
1674 }
1675 trace_writeback_single_inode(inode, wbc, nr_to_write);
1676 return ret;
1677}
1678
1679/*
1680 * Write out an inode's dirty data and metadata on-demand, i.e. separately from
1681 * the regular batched writeback done by the flusher threads in
1682 * writeback_sb_inodes(). @wbc controls various aspects of the write, such as
1683 * whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE).
1684 *
1685 * To prevent the inode from going away, either the caller must have a reference
1686 * to the inode, or the inode must have I_WILL_FREE or I_FREEING set.
1687 */
1688static int writeback_single_inode(struct inode *inode,
1689 struct writeback_control *wbc)
1690{
1691 struct bdi_writeback *wb;
1692 int ret = 0;
1693
1694 spin_lock(&inode->i_lock);
1695 if (!atomic_read(&inode->i_count))
1696 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1697 else
1698 WARN_ON(inode->i_state & I_WILL_FREE);
1699
1700 if (inode->i_state & I_SYNC) {
1701 /*
1702 * Writeback is already running on the inode. For WB_SYNC_NONE,
1703 * that's enough and we can just return. For WB_SYNC_ALL, we
1704 * must wait for the existing writeback to complete, then do
1705 * writeback again if there's anything left.
1706 */
1707 if (wbc->sync_mode != WB_SYNC_ALL)
1708 goto out;
1709 __inode_wait_for_writeback(inode);
1710 }
1711 WARN_ON(inode->i_state & I_SYNC);
1712 /*
1713 * If the inode is already fully clean, then there's nothing to do.
1714 *
1715 * For data-integrity syncs we also need to check whether any pages are
1716 * still under writeback, e.g. due to prior WB_SYNC_NONE writeback. If
1717 * there are any such pages, we'll need to wait for them.
1718 */
1719 if (!(inode->i_state & I_DIRTY_ALL) &&
1720 (wbc->sync_mode != WB_SYNC_ALL ||
1721 !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
1722 goto out;
1723 inode->i_state |= I_SYNC;
1724 wbc_attach_and_unlock_inode(wbc, inode);
1725
1726 ret = __writeback_single_inode(inode, wbc);
1727
1728 wbc_detach_inode(wbc);
1729
1730 wb = inode_to_wb_and_lock_list(inode);
1731 spin_lock(&inode->i_lock);
1732 /*
1733 * If the inode is now fully clean, then it can be safely removed from
1734 * its writeback list (if any). Otherwise the flusher threads are
1735 * responsible for the writeback lists.
1736 */
1737 if (!(inode->i_state & I_DIRTY_ALL))
1738 inode_cgwb_move_to_attached(inode, wb);
1739 spin_unlock(&wb->list_lock);
1740 inode_sync_complete(inode);
1741out:
1742 spin_unlock(&inode->i_lock);
1743 return ret;
1744}
1745
1746static long writeback_chunk_size(struct bdi_writeback *wb,
1747 struct wb_writeback_work *work)
1748{
1749 long pages;
1750
1751 /*
1752 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1753 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1754 * here avoids calling into writeback_inodes_wb() more than once.
1755 *
1756 * The intended call sequence for WB_SYNC_ALL writeback is:
1757 *
1758 * wb_writeback()
1759 * writeback_sb_inodes() <== called only once
1760 * write_cache_pages() <== called once for each inode
1761 * (quickly) tag currently dirty pages
1762 * (maybe slowly) sync all tagged pages
1763 */
1764 if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1765 pages = LONG_MAX;
1766 else {
1767 pages = min(wb->avg_write_bandwidth / 2,
1768 global_wb_domain.dirty_limit / DIRTY_SCOPE);
1769 pages = min(pages, work->nr_pages);
1770 pages = round_down(pages + MIN_WRITEBACK_PAGES,
1771 MIN_WRITEBACK_PAGES);
1772 }
1773
1774 return pages;
1775}
1776
1777/*
1778 * Write a portion of b_io inodes which belong to @sb.
1779 *
1780 * Return the number of pages and/or inodes written.
1781 *
1782 * NOTE! This is called with wb->list_lock held, and will
1783 * unlock and relock that for each inode it ends up doing
1784 * IO for.
1785 */
1786static long writeback_sb_inodes(struct super_block *sb,
1787 struct bdi_writeback *wb,
1788 struct wb_writeback_work *work)
1789{
1790 struct writeback_control wbc = {
1791 .sync_mode = work->sync_mode,
1792 .tagged_writepages = work->tagged_writepages,
1793 .for_kupdate = work->for_kupdate,
1794 .for_background = work->for_background,
1795 .for_sync = work->for_sync,
1796 .range_cyclic = work->range_cyclic,
1797 .range_start = 0,
1798 .range_end = LLONG_MAX,
1799 };
1800 unsigned long start_time = jiffies;
1801 long write_chunk;
1802 long wrote = 0; /* count both pages and inodes */
1803
1804 while (!list_empty(&wb->b_io)) {
1805 struct inode *inode = wb_inode(wb->b_io.prev);
1806 struct bdi_writeback *tmp_wb;
1807
1808 if (inode->i_sb != sb) {
1809 if (work->sb) {
1810 /*
1811 * We only want to write back data for this
1812 * superblock, move all inodes not belonging
1813 * to it back onto the dirty list.
1814 */
1815 redirty_tail(inode, wb);
1816 continue;
1817 }
1818
1819 /*
1820 * The inode belongs to a different superblock.
1821 * Bounce back to the caller to unpin this and
1822 * pin the next superblock.
1823 */
1824 break;
1825 }
1826
1827 /*
1828 * Don't bother with new inodes or inodes being freed, first
1829 * kind does not need periodic writeout yet, and for the latter
1830 * kind writeout is handled by the freer.
1831 */
1832 spin_lock(&inode->i_lock);
1833 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
1834 redirty_tail_locked(inode, wb);
1835 spin_unlock(&inode->i_lock);
1836 continue;
1837 }
1838 if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1839 /*
1840 * If this inode is locked for writeback and we are not
1841 * doing writeback-for-data-integrity, move it to
1842 * b_more_io so that writeback can proceed with the
1843 * other inodes on s_io.
1844 *
1845 * We'll have another go at writing back this inode
1846 * when we completed a full scan of b_io.
1847 */
1848 spin_unlock(&inode->i_lock);
1849 requeue_io(inode, wb);
1850 trace_writeback_sb_inodes_requeue(inode);
1851 continue;
1852 }
1853 spin_unlock(&wb->list_lock);
1854
1855 /*
1856 * We already requeued the inode if it had I_SYNC set and we
1857 * are doing WB_SYNC_NONE writeback. So this catches only the
1858 * WB_SYNC_ALL case.
1859 */
1860 if (inode->i_state & I_SYNC) {
1861 /* Wait for I_SYNC. This function drops i_lock... */
1862 inode_sleep_on_writeback(inode);
1863 /* Inode may be gone, start again */
1864 spin_lock(&wb->list_lock);
1865 continue;
1866 }
1867 inode->i_state |= I_SYNC;
1868 wbc_attach_and_unlock_inode(&wbc, inode);
1869
1870 write_chunk = writeback_chunk_size(wb, work);
1871 wbc.nr_to_write = write_chunk;
1872 wbc.pages_skipped = 0;
1873
1874 /*
1875 * We use I_SYNC to pin the inode in memory. While it is set
1876 * evict_inode() will wait so the inode cannot be freed.
1877 */
1878 __writeback_single_inode(inode, &wbc);
1879
1880 wbc_detach_inode(&wbc);
1881 work->nr_pages -= write_chunk - wbc.nr_to_write;
1882 wrote += write_chunk - wbc.nr_to_write;
1883
1884 if (need_resched()) {
1885 /*
1886 * We're trying to balance between building up a nice
1887 * long list of IOs to improve our merge rate, and
1888 * getting those IOs out quickly for anyone throttling
1889 * in balance_dirty_pages(). cond_resched() doesn't
1890 * unplug, so get our IOs out the door before we
1891 * give up the CPU.
1892 */
1893 blk_flush_plug(current);
1894 cond_resched();
1895 }
1896
1897 /*
1898 * Requeue @inode if still dirty. Be careful as @inode may
1899 * have been switched to another wb in the meantime.
1900 */
1901 tmp_wb = inode_to_wb_and_lock_list(inode);
1902 spin_lock(&inode->i_lock);
1903 if (!(inode->i_state & I_DIRTY_ALL))
1904 wrote++;
1905 requeue_inode(inode, tmp_wb, &wbc);
1906 inode_sync_complete(inode);
1907 spin_unlock(&inode->i_lock);
1908
1909 if (unlikely(tmp_wb != wb)) {
1910 spin_unlock(&tmp_wb->list_lock);
1911 spin_lock(&wb->list_lock);
1912 }
1913
1914 /*
1915 * bail out to wb_writeback() often enough to check
1916 * background threshold and other termination conditions.
1917 */
1918 if (wrote) {
1919 if (time_is_before_jiffies(start_time + HZ / 10UL))
1920 break;
1921 if (work->nr_pages <= 0)
1922 break;
1923 }
1924 }
1925 return wrote;
1926}
1927
1928static long __writeback_inodes_wb(struct bdi_writeback *wb,
1929 struct wb_writeback_work *work)
1930{
1931 unsigned long start_time = jiffies;
1932 long wrote = 0;
1933
1934 while (!list_empty(&wb->b_io)) {
1935 struct inode *inode = wb_inode(wb->b_io.prev);
1936 struct super_block *sb = inode->i_sb;
1937
1938 if (!trylock_super(sb)) {
1939 /*
1940 * trylock_super() may fail consistently due to
1941 * s_umount being grabbed by someone else. Don't use
1942 * requeue_io() to avoid busy retrying the inode/sb.
1943 */
1944 redirty_tail(inode, wb);
1945 continue;
1946 }
1947 wrote += writeback_sb_inodes(sb, wb, work);
1948 up_read(&sb->s_umount);
1949
1950 /* refer to the same tests at the end of writeback_sb_inodes */
1951 if (wrote) {
1952 if (time_is_before_jiffies(start_time + HZ / 10UL))
1953 break;
1954 if (work->nr_pages <= 0)
1955 break;
1956 }
1957 }
1958 /* Leave any unwritten inodes on b_io */
1959 return wrote;
1960}
1961
1962static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
1963 enum wb_reason reason)
1964{
1965 struct wb_writeback_work work = {
1966 .nr_pages = nr_pages,
1967 .sync_mode = WB_SYNC_NONE,
1968 .range_cyclic = 1,
1969 .reason = reason,
1970 };
1971 struct blk_plug plug;
1972
1973 blk_start_plug(&plug);
1974 spin_lock(&wb->list_lock);
1975 if (list_empty(&wb->b_io))
1976 queue_io(wb, &work, jiffies);
1977 __writeback_inodes_wb(wb, &work);
1978 spin_unlock(&wb->list_lock);
1979 blk_finish_plug(&plug);
1980
1981 return nr_pages - work.nr_pages;
1982}
1983
1984/*
1985 * Explicit flushing or periodic writeback of "old" data.
1986 *
1987 * Define "old": the first time one of an inode's pages is dirtied, we mark the
1988 * dirtying-time in the inode's address_space. So this periodic writeback code
1989 * just walks the superblock inode list, writing back any inodes which are
1990 * older than a specific point in time.
1991 *
1992 * Try to run once per dirty_writeback_interval. But if a writeback event
1993 * takes longer than a dirty_writeback_interval interval, then leave a
1994 * one-second gap.
1995 *
1996 * dirtied_before takes precedence over nr_to_write. So we'll only write back
1997 * all dirty pages if they are all attached to "old" mappings.
1998 */
1999static long wb_writeback(struct bdi_writeback *wb,
2000 struct wb_writeback_work *work)
2001{
2002 unsigned long wb_start = jiffies;
2003 long nr_pages = work->nr_pages;
2004 unsigned long dirtied_before = jiffies;
2005 struct inode *inode;
2006 long progress;
2007 struct blk_plug plug;
2008
2009 blk_start_plug(&plug);
2010 spin_lock(&wb->list_lock);
2011 for (;;) {
2012 /*
2013 * Stop writeback when nr_pages has been consumed
2014 */
2015 if (work->nr_pages <= 0)
2016 break;
2017
2018 /*
2019 * Background writeout and kupdate-style writeback may
2020 * run forever. Stop them if there is other work to do
2021 * so that e.g. sync can proceed. They'll be restarted
2022 * after the other works are all done.
2023 */
2024 if ((work->for_background || work->for_kupdate) &&
2025 !list_empty(&wb->work_list))
2026 break;
2027
2028 /*
2029 * For background writeout, stop when we are below the
2030 * background dirty threshold
2031 */
2032 if (work->for_background && !wb_over_bg_thresh(wb))
2033 break;
2034
2035 /*
2036 * Kupdate and background works are special and we want to
2037 * include all inodes that need writing. Livelock avoidance is
2038 * handled by these works yielding to any other work so we are
2039 * safe.
2040 */
2041 if (work->for_kupdate) {
2042 dirtied_before = jiffies -
2043 msecs_to_jiffies(dirty_expire_interval * 10);
2044 } else if (work->for_background)
2045 dirtied_before = jiffies;
2046
2047 trace_writeback_start(wb, work);
2048 if (list_empty(&wb->b_io))
2049 queue_io(wb, work, dirtied_before);
2050 if (work->sb)
2051 progress = writeback_sb_inodes(work->sb, wb, work);
2052 else
2053 progress = __writeback_inodes_wb(wb, work);
2054 trace_writeback_written(wb, work);
2055
2056 wb_update_bandwidth(wb, wb_start);
2057
2058 /*
2059 * Did we write something? Try for more
2060 *
2061 * Dirty inodes are moved to b_io for writeback in batches.
2062 * The completion of the current batch does not necessarily
2063 * mean the overall work is done. So we keep looping as long
2064 * as made some progress on cleaning pages or inodes.
2065 */
2066 if (progress)
2067 continue;
2068 /*
2069 * No more inodes for IO, bail
2070 */
2071 if (list_empty(&wb->b_more_io))
2072 break;
2073 /*
2074 * Nothing written. Wait for some inode to
2075 * become available for writeback. Otherwise
2076 * we'll just busyloop.
2077 */
2078 trace_writeback_wait(wb, work);
2079 inode = wb_inode(wb->b_more_io.prev);
2080 spin_lock(&inode->i_lock);
2081 spin_unlock(&wb->list_lock);
2082 /* This function drops i_lock... */
2083 inode_sleep_on_writeback(inode);
2084 spin_lock(&wb->list_lock);
2085 }
2086 spin_unlock(&wb->list_lock);
2087 blk_finish_plug(&plug);
2088
2089 return nr_pages - work->nr_pages;
2090}
2091
2092/*
2093 * Return the next wb_writeback_work struct that hasn't been processed yet.
2094 */
2095static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
2096{
2097 struct wb_writeback_work *work = NULL;
2098
2099 spin_lock_bh(&wb->work_lock);
2100 if (!list_empty(&wb->work_list)) {
2101 work = list_entry(wb->work_list.next,
2102 struct wb_writeback_work, list);
2103 list_del_init(&work->list);
2104 }
2105 spin_unlock_bh(&wb->work_lock);
2106 return work;
2107}
2108
2109static long wb_check_background_flush(struct bdi_writeback *wb)
2110{
2111 if (wb_over_bg_thresh(wb)) {
2112
2113 struct wb_writeback_work work = {
2114 .nr_pages = LONG_MAX,
2115 .sync_mode = WB_SYNC_NONE,
2116 .for_background = 1,
2117 .range_cyclic = 1,
2118 .reason = WB_REASON_BACKGROUND,
2119 };
2120
2121 return wb_writeback(wb, &work);
2122 }
2123
2124 return 0;
2125}
2126
2127static long wb_check_old_data_flush(struct bdi_writeback *wb)
2128{
2129 unsigned long expired;
2130 long nr_pages;
2131
2132 /*
2133 * When set to zero, disable periodic writeback
2134 */
2135 if (!dirty_writeback_interval)
2136 return 0;
2137
2138 expired = wb->last_old_flush +
2139 msecs_to_jiffies(dirty_writeback_interval * 10);
2140 if (time_before(jiffies, expired))
2141 return 0;
2142
2143 wb->last_old_flush = jiffies;
2144 nr_pages = get_nr_dirty_pages();
2145
2146 if (nr_pages) {
2147 struct wb_writeback_work work = {
2148 .nr_pages = nr_pages,
2149 .sync_mode = WB_SYNC_NONE,
2150 .for_kupdate = 1,
2151 .range_cyclic = 1,
2152 .reason = WB_REASON_PERIODIC,
2153 };
2154
2155 return wb_writeback(wb, &work);
2156 }
2157
2158 return 0;
2159}
2160
2161static long wb_check_start_all(struct bdi_writeback *wb)
2162{
2163 long nr_pages;
2164
2165 if (!test_bit(WB_start_all, &wb->state))
2166 return 0;
2167
2168 nr_pages = get_nr_dirty_pages();
2169 if (nr_pages) {
2170 struct wb_writeback_work work = {
2171 .nr_pages = wb_split_bdi_pages(wb, nr_pages),
2172 .sync_mode = WB_SYNC_NONE,
2173 .range_cyclic = 1,
2174 .reason = wb->start_all_reason,
2175 };
2176
2177 nr_pages = wb_writeback(wb, &work);
2178 }
2179
2180 clear_bit(WB_start_all, &wb->state);
2181 return nr_pages;
2182}
2183
2184
2185/*
2186 * Retrieve work items and do the writeback they describe
2187 */
2188static long wb_do_writeback(struct bdi_writeback *wb)
2189{
2190 struct wb_writeback_work *work;
2191 long wrote = 0;
2192
2193 set_bit(WB_writeback_running, &wb->state);
2194 while ((work = get_next_work_item(wb)) != NULL) {
2195 trace_writeback_exec(wb, work);
2196 wrote += wb_writeback(wb, work);
2197 finish_writeback_work(wb, work);
2198 }
2199
2200 /*
2201 * Check for a flush-everything request
2202 */
2203 wrote += wb_check_start_all(wb);
2204
2205 /*
2206 * Check for periodic writeback, kupdated() style
2207 */
2208 wrote += wb_check_old_data_flush(wb);
2209 wrote += wb_check_background_flush(wb);
2210 clear_bit(WB_writeback_running, &wb->state);
2211
2212 return wrote;
2213}
2214
2215/*
2216 * Handle writeback of dirty data for the device backed by this bdi. Also
2217 * reschedules periodically and does kupdated style flushing.
2218 */
2219void wb_workfn(struct work_struct *work)
2220{
2221 struct bdi_writeback *wb = container_of(to_delayed_work(work),
2222 struct bdi_writeback, dwork);
2223 long pages_written;
2224
2225 set_worker_desc("flush-%s", bdi_dev_name(wb->bdi));
2226 current->flags |= PF_SWAPWRITE;
2227
2228 if (likely(!current_is_workqueue_rescuer() ||
2229 !test_bit(WB_registered, &wb->state))) {
2230 /*
2231 * The normal path. Keep writing back @wb until its
2232 * work_list is empty. Note that this path is also taken
2233 * if @wb is shutting down even when we're running off the
2234 * rescuer as work_list needs to be drained.
2235 */
2236 do {
2237 pages_written = wb_do_writeback(wb);
2238 trace_writeback_pages_written(pages_written);
2239 } while (!list_empty(&wb->work_list));
2240 } else {
2241 /*
2242 * bdi_wq can't get enough workers and we're running off
2243 * the emergency worker. Don't hog it. Hopefully, 1024 is
2244 * enough for efficient IO.
2245 */
2246 pages_written = writeback_inodes_wb(wb, 1024,
2247 WB_REASON_FORKER_THREAD);
2248 trace_writeback_pages_written(pages_written);
2249 }
2250
2251 if (!list_empty(&wb->work_list))
2252 wb_wakeup(wb);
2253 else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
2254 wb_wakeup_delayed(wb);
2255
2256 current->flags &= ~PF_SWAPWRITE;
2257}
2258
2259/*
2260 * Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
2261 * write back the whole world.
2262 */
2263static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2264 enum wb_reason reason)
2265{
2266 struct bdi_writeback *wb;
2267
2268 if (!bdi_has_dirty_io(bdi))
2269 return;
2270
2271 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2272 wb_start_writeback(wb, reason);
2273}
2274
2275void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2276 enum wb_reason reason)
2277{
2278 rcu_read_lock();
2279 __wakeup_flusher_threads_bdi(bdi, reason);
2280 rcu_read_unlock();
2281}
2282
2283/*
2284 * Wakeup the flusher threads to start writeback of all currently dirty pages
2285 */
2286void wakeup_flusher_threads(enum wb_reason reason)
2287{
2288 struct backing_dev_info *bdi;
2289
2290 /*
2291 * If we are expecting writeback progress we must submit plugged IO.
2292 */
2293 if (blk_needs_flush_plug(current))
2294 blk_schedule_flush_plug(current);
2295
2296 rcu_read_lock();
2297 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2298 __wakeup_flusher_threads_bdi(bdi, reason);
2299 rcu_read_unlock();
2300}
2301
2302/*
2303 * Wake up bdi's periodically to make sure dirtytime inodes gets
2304 * written back periodically. We deliberately do *not* check the
2305 * b_dirtytime list in wb_has_dirty_io(), since this would cause the
2306 * kernel to be constantly waking up once there are any dirtytime
2307 * inodes on the system. So instead we define a separate delayed work
2308 * function which gets called much more rarely. (By default, only
2309 * once every 12 hours.)
2310 *
2311 * If there is any other write activity going on in the file system,
2312 * this function won't be necessary. But if the only thing that has
2313 * happened on the file system is a dirtytime inode caused by an atime
2314 * update, we need this infrastructure below to make sure that inode
2315 * eventually gets pushed out to disk.
2316 */
2317static void wakeup_dirtytime_writeback(struct work_struct *w);
2318static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
2319
2320static void wakeup_dirtytime_writeback(struct work_struct *w)
2321{
2322 struct backing_dev_info *bdi;
2323
2324 rcu_read_lock();
2325 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
2326 struct bdi_writeback *wb;
2327
2328 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2329 if (!list_empty(&wb->b_dirty_time))
2330 wb_wakeup(wb);
2331 }
2332 rcu_read_unlock();
2333 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2334}
2335
2336static int __init start_dirtytime_writeback(void)
2337{
2338 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2339 return 0;
2340}
2341__initcall(start_dirtytime_writeback);
2342
2343int dirtytime_interval_handler(struct ctl_table *table, int write,
2344 void *buffer, size_t *lenp, loff_t *ppos)
2345{
2346 int ret;
2347
2348 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
2349 if (ret == 0 && write)
2350 mod_delayed_work(system_wq, &dirtytime_work, 0);
2351 return ret;
2352}
2353
2354/**
2355 * __mark_inode_dirty - internal function to mark an inode dirty
2356 *
2357 * @inode: inode to mark
2358 * @flags: what kind of dirty, e.g. I_DIRTY_SYNC. This can be a combination of
2359 * multiple I_DIRTY_* flags, except that I_DIRTY_TIME can't be combined
2360 * with I_DIRTY_PAGES.
2361 *
2362 * Mark an inode as dirty. We notify the filesystem, then update the inode's
2363 * dirty flags. Then, if needed we add the inode to the appropriate dirty list.
2364 *
2365 * Most callers should use mark_inode_dirty() or mark_inode_dirty_sync()
2366 * instead of calling this directly.
2367 *
2368 * CAREFUL! We only add the inode to the dirty list if it is hashed or if it
2369 * refers to a blockdev. Unhashed inodes will never be added to the dirty list
2370 * even if they are later hashed, as they will have been marked dirty already.
2371 *
2372 * In short, ensure you hash any inodes _before_ you start marking them dirty.
2373 *
2374 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2375 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
2376 * the kernel-internal blockdev inode represents the dirtying time of the
2377 * blockdev's pages. This is why for I_DIRTY_PAGES we always use
2378 * page->mapping->host, so the page-dirtying time is recorded in the internal
2379 * blockdev inode.
2380 */
2381void __mark_inode_dirty(struct inode *inode, int flags)
2382{
2383 struct super_block *sb = inode->i_sb;
2384 int dirtytime = 0;
2385
2386 trace_writeback_mark_inode_dirty(inode, flags);
2387
2388 if (flags & I_DIRTY_INODE) {
2389 /*
2390 * Notify the filesystem about the inode being dirtied, so that
2391 * (if needed) it can update on-disk fields and journal the
2392 * inode. This is only needed when the inode itself is being
2393 * dirtied now. I.e. it's only needed for I_DIRTY_INODE, not
2394 * for just I_DIRTY_PAGES or I_DIRTY_TIME.
2395 */
2396 trace_writeback_dirty_inode_start(inode, flags);
2397 if (sb->s_op->dirty_inode)
2398 sb->s_op->dirty_inode(inode, flags & I_DIRTY_INODE);
2399 trace_writeback_dirty_inode(inode, flags);
2400
2401 /* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
2402 flags &= ~I_DIRTY_TIME;
2403 } else {
2404 /*
2405 * Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
2406 * (We don't support setting both I_DIRTY_PAGES and I_DIRTY_TIME
2407 * in one call to __mark_inode_dirty().)
2408 */
2409 dirtytime = flags & I_DIRTY_TIME;
2410 WARN_ON_ONCE(dirtytime && flags != I_DIRTY_TIME);
2411 }
2412
2413 /*
2414 * Paired with smp_mb() in __writeback_single_inode() for the
2415 * following lockless i_state test. See there for details.
2416 */
2417 smp_mb();
2418
2419 if (((inode->i_state & flags) == flags) ||
2420 (dirtytime && (inode->i_state & I_DIRTY_INODE)))
2421 return;
2422
2423 spin_lock(&inode->i_lock);
2424 if (dirtytime && (inode->i_state & I_DIRTY_INODE))
2425 goto out_unlock_inode;
2426 if ((inode->i_state & flags) != flags) {
2427 const int was_dirty = inode->i_state & I_DIRTY;
2428
2429 inode_attach_wb(inode, NULL);
2430
2431 /* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
2432 if (flags & I_DIRTY_INODE)
2433 inode->i_state &= ~I_DIRTY_TIME;
2434 inode->i_state |= flags;
2435
2436 /*
2437 * If the inode is queued for writeback by flush worker, just
2438 * update its dirty state. Once the flush worker is done with
2439 * the inode it will place it on the appropriate superblock
2440 * list, based upon its state.
2441 */
2442 if (inode->i_state & I_SYNC_QUEUED)
2443 goto out_unlock_inode;
2444
2445 /*
2446 * Only add valid (hashed) inodes to the superblock's
2447 * dirty list. Add blockdev inodes as well.
2448 */
2449 if (!S_ISBLK(inode->i_mode)) {
2450 if (inode_unhashed(inode))
2451 goto out_unlock_inode;
2452 }
2453 if (inode->i_state & I_FREEING)
2454 goto out_unlock_inode;
2455
2456 /*
2457 * If the inode was already on b_dirty/b_io/b_more_io, don't
2458 * reposition it (that would break b_dirty time-ordering).
2459 */
2460 if (!was_dirty) {
2461 struct bdi_writeback *wb;
2462 struct list_head *dirty_list;
2463 bool wakeup_bdi = false;
2464
2465 wb = locked_inode_to_wb_and_lock_list(inode);
2466
2467 inode->dirtied_when = jiffies;
2468 if (dirtytime)
2469 inode->dirtied_time_when = jiffies;
2470
2471 if (inode->i_state & I_DIRTY)
2472 dirty_list = &wb->b_dirty;
2473 else
2474 dirty_list = &wb->b_dirty_time;
2475
2476 wakeup_bdi = inode_io_list_move_locked(inode, wb,
2477 dirty_list);
2478
2479 spin_unlock(&wb->list_lock);
2480 trace_writeback_dirty_inode_enqueue(inode);
2481
2482 /*
2483 * If this is the first dirty inode for this bdi,
2484 * we have to wake-up the corresponding bdi thread
2485 * to make sure background write-back happens
2486 * later.
2487 */
2488 if (wakeup_bdi &&
2489 (wb->bdi->capabilities & BDI_CAP_WRITEBACK))
2490 wb_wakeup_delayed(wb);
2491 return;
2492 }
2493 }
2494out_unlock_inode:
2495 spin_unlock(&inode->i_lock);
2496}
2497EXPORT_SYMBOL(__mark_inode_dirty);
2498
2499/*
2500 * The @s_sync_lock is used to serialise concurrent sync operations
2501 * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2502 * Concurrent callers will block on the s_sync_lock rather than doing contending
2503 * walks. The queueing maintains sync(2) required behaviour as all the IO that
2504 * has been issued up to the time this function is enter is guaranteed to be
2505 * completed by the time we have gained the lock and waited for all IO that is
2506 * in progress regardless of the order callers are granted the lock.
2507 */
2508static void wait_sb_inodes(struct super_block *sb)
2509{
2510 LIST_HEAD(sync_list);
2511
2512 /*
2513 * We need to be protected against the filesystem going from
2514 * r/o to r/w or vice versa.
2515 */
2516 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2517
2518 mutex_lock(&sb->s_sync_lock);
2519
2520 /*
2521 * Splice the writeback list onto a temporary list to avoid waiting on
2522 * inodes that have started writeback after this point.
2523 *
2524 * Use rcu_read_lock() to keep the inodes around until we have a
2525 * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2526 * the local list because inodes can be dropped from either by writeback
2527 * completion.
2528 */
2529 rcu_read_lock();
2530 spin_lock_irq(&sb->s_inode_wblist_lock);
2531 list_splice_init(&sb->s_inodes_wb, &sync_list);
2532
2533 /*
2534 * Data integrity sync. Must wait for all pages under writeback, because
2535 * there may have been pages dirtied before our sync call, but which had
2536 * writeout started before we write it out. In which case, the inode
2537 * may not be on the dirty list, but we still have to wait for that
2538 * writeout.
2539 */
2540 while (!list_empty(&sync_list)) {
2541 struct inode *inode = list_first_entry(&sync_list, struct inode,
2542 i_wb_list);
2543 struct address_space *mapping = inode->i_mapping;
2544
2545 /*
2546 * Move each inode back to the wb list before we drop the lock
2547 * to preserve consistency between i_wb_list and the mapping
2548 * writeback tag. Writeback completion is responsible to remove
2549 * the inode from either list once the writeback tag is cleared.
2550 */
2551 list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
2552
2553 /*
2554 * The mapping can appear untagged while still on-list since we
2555 * do not have the mapping lock. Skip it here, wb completion
2556 * will remove it.
2557 */
2558 if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2559 continue;
2560
2561 spin_unlock_irq(&sb->s_inode_wblist_lock);
2562
2563 spin_lock(&inode->i_lock);
2564 if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
2565 spin_unlock(&inode->i_lock);
2566
2567 spin_lock_irq(&sb->s_inode_wblist_lock);
2568 continue;
2569 }
2570 __iget(inode);
2571 spin_unlock(&inode->i_lock);
2572 rcu_read_unlock();
2573
2574 /*
2575 * We keep the error status of individual mapping so that
2576 * applications can catch the writeback error using fsync(2).
2577 * See filemap_fdatawait_keep_errors() for details.
2578 */
2579 filemap_fdatawait_keep_errors(mapping);
2580
2581 cond_resched();
2582
2583 iput(inode);
2584
2585 rcu_read_lock();
2586 spin_lock_irq(&sb->s_inode_wblist_lock);
2587 }
2588 spin_unlock_irq(&sb->s_inode_wblist_lock);
2589 rcu_read_unlock();
2590 mutex_unlock(&sb->s_sync_lock);
2591}
2592
2593static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2594 enum wb_reason reason, bool skip_if_busy)
2595{
2596 struct backing_dev_info *bdi = sb->s_bdi;
2597 DEFINE_WB_COMPLETION(done, bdi);
2598 struct wb_writeback_work work = {
2599 .sb = sb,
2600 .sync_mode = WB_SYNC_NONE,
2601 .tagged_writepages = 1,
2602 .done = &done,
2603 .nr_pages = nr,
2604 .reason = reason,
2605 };
2606
2607 if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
2608 return;
2609 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2610
2611 bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
2612 wb_wait_for_completion(&done);
2613}
2614
2615/**
2616 * writeback_inodes_sb_nr - writeback dirty inodes from given super_block
2617 * @sb: the superblock
2618 * @nr: the number of pages to write
2619 * @reason: reason why some writeback work initiated
2620 *
2621 * Start writeback on some inodes on this super_block. No guarantees are made
2622 * on how many (if any) will be written, and this function does not wait
2623 * for IO completion of submitted IO.
2624 */
2625void writeback_inodes_sb_nr(struct super_block *sb,
2626 unsigned long nr,
2627 enum wb_reason reason)
2628{
2629 __writeback_inodes_sb_nr(sb, nr, reason, false);
2630}
2631EXPORT_SYMBOL(writeback_inodes_sb_nr);
2632
2633/**
2634 * writeback_inodes_sb - writeback dirty inodes from given super_block
2635 * @sb: the superblock
2636 * @reason: reason why some writeback work was initiated
2637 *
2638 * Start writeback on some inodes on this super_block. No guarantees are made
2639 * on how many (if any) will be written, and this function does not wait
2640 * for IO completion of submitted IO.
2641 */
2642void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2643{
2644 return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2645}
2646EXPORT_SYMBOL(writeback_inodes_sb);
2647
2648/**
2649 * try_to_writeback_inodes_sb - try to start writeback if none underway
2650 * @sb: the superblock
2651 * @reason: reason why some writeback work was initiated
2652 *
2653 * Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
2654 */
2655void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2656{
2657 if (!down_read_trylock(&sb->s_umount))
2658 return;
2659
2660 __writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason, true);
2661 up_read(&sb->s_umount);
2662}
2663EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2664
2665/**
2666 * sync_inodes_sb - sync sb inode pages
2667 * @sb: the superblock
2668 *
2669 * This function writes and waits on any dirty inode belonging to this
2670 * super_block.
2671 */
2672void sync_inodes_sb(struct super_block *sb)
2673{
2674 struct backing_dev_info *bdi = sb->s_bdi;
2675 DEFINE_WB_COMPLETION(done, bdi);
2676 struct wb_writeback_work work = {
2677 .sb = sb,
2678 .sync_mode = WB_SYNC_ALL,
2679 .nr_pages = LONG_MAX,
2680 .range_cyclic = 0,
2681 .done = &done,
2682 .reason = WB_REASON_SYNC,
2683 .for_sync = 1,
2684 };
2685
2686 /*
2687 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
2688 * inodes under writeback and I_DIRTY_TIME inodes ignored by
2689 * bdi_has_dirty() need to be written out too.
2690 */
2691 if (bdi == &noop_backing_dev_info)
2692 return;
2693 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2694
2695 /* protect against inode wb switch, see inode_switch_wbs_work_fn() */
2696 bdi_down_write_wb_switch_rwsem(bdi);
2697 bdi_split_work_to_wbs(bdi, &work, false);
2698 wb_wait_for_completion(&done);
2699 bdi_up_write_wb_switch_rwsem(bdi);
2700
2701 wait_sb_inodes(sb);
2702}
2703EXPORT_SYMBOL(sync_inodes_sb);
2704
2705/**
2706 * write_inode_now - write an inode to disk
2707 * @inode: inode to write to disk
2708 * @sync: whether the write should be synchronous or not
2709 *
2710 * This function commits an inode to disk immediately if it is dirty. This is
2711 * primarily needed by knfsd.
2712 *
2713 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
2714 */
2715int write_inode_now(struct inode *inode, int sync)
2716{
2717 struct writeback_control wbc = {
2718 .nr_to_write = LONG_MAX,
2719 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2720 .range_start = 0,
2721 .range_end = LLONG_MAX,
2722 };
2723
2724 if (!mapping_can_writeback(inode->i_mapping))
2725 wbc.nr_to_write = 0;
2726
2727 might_sleep();
2728 return writeback_single_inode(inode, &wbc);
2729}
2730EXPORT_SYMBOL(write_inode_now);
2731
2732/**
2733 * sync_inode - write an inode and its pages to disk.
2734 * @inode: the inode to sync
2735 * @wbc: controls the writeback mode
2736 *
2737 * sync_inode() will write an inode and its pages to disk. It will also
2738 * correctly update the inode on its superblock's dirty inode lists and will
2739 * update inode->i_state.
2740 *
2741 * The caller must have a ref on the inode.
2742 */
2743int sync_inode(struct inode *inode, struct writeback_control *wbc)
2744{
2745 return writeback_single_inode(inode, wbc);
2746}
2747EXPORT_SYMBOL(sync_inode);
2748
2749/**
2750 * sync_inode_metadata - write an inode to disk
2751 * @inode: the inode to sync
2752 * @wait: wait for I/O to complete.
2753 *
2754 * Write an inode to disk and adjust its dirty state after completion.
2755 *
2756 * Note: only writes the actual inode, no associated data or other metadata.
2757 */
2758int sync_inode_metadata(struct inode *inode, int wait)
2759{
2760 struct writeback_control wbc = {
2761 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2762 .nr_to_write = 0, /* metadata-only */
2763 };
2764
2765 return sync_inode(inode, &wbc);
2766}
2767EXPORT_SYMBOL(sync_inode_metadata);