Merge tag 'seccomp-v4.16-rc3' of https://git.kernel.org/pub/scm/linux/kernel/git...
[linux-2.6-block.git] / fs / fs-writeback.c
CommitLineData
1da177e4
LT
1/*
2 * fs/fs-writeback.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 *
6 * Contains all the functions related to writing back and waiting
7 * upon dirty inodes against superblocks, and writing back dirty
8 * pages against inodes. ie: data writeback. Writeout of the
9 * inode itself is not handled here.
10 *
e1f8e874 11 * 10Apr2002 Andrew Morton
1da177e4
LT
12 * Split out of fs/inode.c
13 * Additions for address_space-based writeback
14 */
15
16#include <linux/kernel.h>
630d9c47 17#include <linux/export.h>
1da177e4 18#include <linux/spinlock.h>
5a0e3ad6 19#include <linux/slab.h>
1da177e4
LT
20#include <linux/sched.h>
21#include <linux/fs.h>
22#include <linux/mm.h>
bc31b86a 23#include <linux/pagemap.h>
03ba3782 24#include <linux/kthread.h>
1da177e4
LT
25#include <linux/writeback.h>
26#include <linux/blkdev.h>
27#include <linux/backing-dev.h>
455b2864 28#include <linux/tracepoint.h>
719ea2fb 29#include <linux/device.h>
21c6321f 30#include <linux/memcontrol.h>
07f3f05c 31#include "internal.h"
1da177e4 32
bc31b86a
WF
33/*
34 * 4MB minimal write chunk size
35 */
09cbfeaf 36#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_SHIFT - 10))
bc31b86a 37
cc395d7f
TH
38struct wb_completion {
39 atomic_t cnt;
40};
41
c4a77a6c
JA
42/*
43 * Passed into wb_writeback(), essentially a subset of writeback_control
44 */
83ba7b07 45struct wb_writeback_work {
c4a77a6c
JA
46 long nr_pages;
47 struct super_block *sb;
0dc83bd3 48 unsigned long *older_than_this;
c4a77a6c 49 enum writeback_sync_modes sync_mode;
6e6938b6 50 unsigned int tagged_writepages:1;
52957fe1
HS
51 unsigned int for_kupdate:1;
52 unsigned int range_cyclic:1;
53 unsigned int for_background:1;
7747bd4b 54 unsigned int for_sync:1; /* sync(2) WB_SYNC_ALL writeback */
ac7b19a3 55 unsigned int auto_free:1; /* free on completion */
0e175a18 56 enum wb_reason reason; /* why was writeback initiated? */
c4a77a6c 57
8010c3b6 58 struct list_head list; /* pending work list */
cc395d7f 59 struct wb_completion *done; /* set if the caller waits */
03ba3782
JA
60};
61
cc395d7f
TH
62/*
63 * If one wants to wait for one or more wb_writeback_works, each work's
64 * ->done should be set to a wb_completion defined using the following
65 * macro. Once all work items are issued with wb_queue_work(), the caller
66 * can wait for the completion of all using wb_wait_for_completion(). Work
67 * items which are waited upon aren't freed automatically on completion.
68 */
69#define DEFINE_WB_COMPLETION_ONSTACK(cmpl) \
70 struct wb_completion cmpl = { \
71 .cnt = ATOMIC_INIT(1), \
72 }
73
74
a2f48706
TT
75/*
76 * If an inode is constantly having its pages dirtied, but then the
77 * updates stop dirtytime_expire_interval seconds in the past, it's
78 * possible for the worst case time between when an inode has its
79 * timestamps updated and when they finally get written out to be two
80 * dirtytime_expire_intervals. We set the default to 12 hours (in
81 * seconds), which means most of the time inodes will have their
82 * timestamps written to disk after 12 hours, but in the worst case a
83 * few inodes might not their timestamps updated for 24 hours.
84 */
85unsigned int dirtytime_expire_interval = 12 * 60 * 60;
86
7ccf19a8
NP
87static inline struct inode *wb_inode(struct list_head *head)
88{
c7f54084 89 return list_entry(head, struct inode, i_io_list);
7ccf19a8
NP
90}
91
15eb77a0
WF
92/*
93 * Include the creation of the trace points after defining the
94 * wb_writeback_work structure and inline functions so that the definition
95 * remains local to this file.
96 */
97#define CREATE_TRACE_POINTS
98#include <trace/events/writeback.h>
99
774016b2
SW
100EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
101
d6c10f1f
TH
102static bool wb_io_lists_populated(struct bdi_writeback *wb)
103{
104 if (wb_has_dirty_io(wb)) {
105 return false;
106 } else {
107 set_bit(WB_has_dirty_io, &wb->state);
95a46c65 108 WARN_ON_ONCE(!wb->avg_write_bandwidth);
766a9d6e
TH
109 atomic_long_add(wb->avg_write_bandwidth,
110 &wb->bdi->tot_write_bandwidth);
d6c10f1f
TH
111 return true;
112 }
113}
114
115static void wb_io_lists_depopulated(struct bdi_writeback *wb)
116{
117 if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
766a9d6e 118 list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
d6c10f1f 119 clear_bit(WB_has_dirty_io, &wb->state);
95a46c65
TH
120 WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
121 &wb->bdi->tot_write_bandwidth) < 0);
766a9d6e 122 }
d6c10f1f
TH
123}
124
125/**
c7f54084 126 * inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
d6c10f1f
TH
127 * @inode: inode to be moved
128 * @wb: target bdi_writeback
bbbc3c1c 129 * @head: one of @wb->b_{dirty|io|more_io|dirty_time}
d6c10f1f 130 *
c7f54084 131 * Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
d6c10f1f
TH
132 * Returns %true if @inode is the first occupant of the !dirty_time IO
133 * lists; otherwise, %false.
134 */
c7f54084 135static bool inode_io_list_move_locked(struct inode *inode,
d6c10f1f
TH
136 struct bdi_writeback *wb,
137 struct list_head *head)
138{
139 assert_spin_locked(&wb->list_lock);
140
c7f54084 141 list_move(&inode->i_io_list, head);
d6c10f1f
TH
142
143 /* dirty_time doesn't count as dirty_io until expiration */
144 if (head != &wb->b_dirty_time)
145 return wb_io_lists_populated(wb);
146
147 wb_io_lists_depopulated(wb);
148 return false;
149}
150
151/**
c7f54084 152 * inode_io_list_del_locked - remove an inode from its bdi_writeback IO list
d6c10f1f
TH
153 * @inode: inode to be removed
154 * @wb: bdi_writeback @inode is being removed from
155 *
156 * Remove @inode which may be on one of @wb->b_{dirty|io|more_io} lists and
157 * clear %WB_has_dirty_io if all are empty afterwards.
158 */
c7f54084 159static void inode_io_list_del_locked(struct inode *inode,
d6c10f1f
TH
160 struct bdi_writeback *wb)
161{
162 assert_spin_locked(&wb->list_lock);
163
c7f54084 164 list_del_init(&inode->i_io_list);
d6c10f1f
TH
165 wb_io_lists_depopulated(wb);
166}
167
f0054bb1 168static void wb_wakeup(struct bdi_writeback *wb)
5acda9d1 169{
f0054bb1
TH
170 spin_lock_bh(&wb->work_lock);
171 if (test_bit(WB_registered, &wb->state))
172 mod_delayed_work(bdi_wq, &wb->dwork, 0);
173 spin_unlock_bh(&wb->work_lock);
5acda9d1
JK
174}
175
4a3a485b
TE
176static void finish_writeback_work(struct bdi_writeback *wb,
177 struct wb_writeback_work *work)
178{
179 struct wb_completion *done = work->done;
180
181 if (work->auto_free)
182 kfree(work);
183 if (done && atomic_dec_and_test(&done->cnt))
184 wake_up_all(&wb->bdi->wb_waitq);
185}
186
f0054bb1
TH
187static void wb_queue_work(struct bdi_writeback *wb,
188 struct wb_writeback_work *work)
6585027a 189{
5634cc2a 190 trace_writeback_queue(wb, work);
6585027a 191
cc395d7f
TH
192 if (work->done)
193 atomic_inc(&work->done->cnt);
4a3a485b
TE
194
195 spin_lock_bh(&wb->work_lock);
196
197 if (test_bit(WB_registered, &wb->state)) {
198 list_add_tail(&work->list, &wb->work_list);
199 mod_delayed_work(bdi_wq, &wb->dwork, 0);
200 } else
201 finish_writeback_work(wb, work);
202
f0054bb1 203 spin_unlock_bh(&wb->work_lock);
1da177e4
LT
204}
205
cc395d7f
TH
206/**
207 * wb_wait_for_completion - wait for completion of bdi_writeback_works
208 * @bdi: bdi work items were issued to
209 * @done: target wb_completion
210 *
211 * Wait for one or more work items issued to @bdi with their ->done field
212 * set to @done, which should have been defined with
213 * DEFINE_WB_COMPLETION_ONSTACK(). This function returns after all such
214 * work items are completed. Work items which are waited upon aren't freed
215 * automatically on completion.
216 */
217static void wb_wait_for_completion(struct backing_dev_info *bdi,
218 struct wb_completion *done)
219{
220 atomic_dec(&done->cnt); /* put down the initial count */
221 wait_event(bdi->wb_waitq, !atomic_read(&done->cnt));
222}
223
703c2708
TH
224#ifdef CONFIG_CGROUP_WRITEBACK
225
2a814908
TH
226/* parameters for foreign inode detection, see wb_detach_inode() */
227#define WB_FRN_TIME_SHIFT 13 /* 1s = 2^13, upto 8 secs w/ 16bit */
228#define WB_FRN_TIME_AVG_SHIFT 3 /* avg = avg * 7/8 + new * 1/8 */
229#define WB_FRN_TIME_CUT_DIV 2 /* ignore rounds < avg / 2 */
230#define WB_FRN_TIME_PERIOD (2 * (1 << WB_FRN_TIME_SHIFT)) /* 2s */
231
232#define WB_FRN_HIST_SLOTS 16 /* inode->i_wb_frn_history is 16bit */
233#define WB_FRN_HIST_UNIT (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
234 /* each slot's duration is 2s / 16 */
235#define WB_FRN_HIST_THR_SLOTS (WB_FRN_HIST_SLOTS / 2)
236 /* if foreign slots >= 8, switch */
237#define WB_FRN_HIST_MAX_SLOTS (WB_FRN_HIST_THR_SLOTS / 2 + 1)
238 /* one round can affect upto 5 slots */
239
a1a0e23e
TH
240static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
241static struct workqueue_struct *isw_wq;
242
21c6321f
TH
243void __inode_attach_wb(struct inode *inode, struct page *page)
244{
245 struct backing_dev_info *bdi = inode_to_bdi(inode);
246 struct bdi_writeback *wb = NULL;
247
248 if (inode_cgwb_enabled(inode)) {
249 struct cgroup_subsys_state *memcg_css;
250
251 if (page) {
252 memcg_css = mem_cgroup_css_from_page(page);
253 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
254 } else {
255 /* must pin memcg_css, see wb_get_create() */
256 memcg_css = task_get_css(current, memory_cgrp_id);
257 wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
258 css_put(memcg_css);
259 }
260 }
261
262 if (!wb)
263 wb = &bdi->wb;
264
265 /*
266 * There may be multiple instances of this function racing to
267 * update the same inode. Use cmpxchg() to tell the winner.
268 */
269 if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
270 wb_put(wb);
271}
272
87e1d789
TH
273/**
274 * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
275 * @inode: inode of interest with i_lock held
276 *
277 * Returns @inode's wb with its list_lock held. @inode->i_lock must be
278 * held on entry and is released on return. The returned wb is guaranteed
279 * to stay @inode's associated wb until its list_lock is released.
280 */
281static struct bdi_writeback *
282locked_inode_to_wb_and_lock_list(struct inode *inode)
283 __releases(&inode->i_lock)
284 __acquires(&wb->list_lock)
285{
286 while (true) {
287 struct bdi_writeback *wb = inode_to_wb(inode);
288
289 /*
290 * inode_to_wb() association is protected by both
291 * @inode->i_lock and @wb->list_lock but list_lock nests
292 * outside i_lock. Drop i_lock and verify that the
293 * association hasn't changed after acquiring list_lock.
294 */
295 wb_get(wb);
296 spin_unlock(&inode->i_lock);
297 spin_lock(&wb->list_lock);
87e1d789 298
aaa2cacf 299 /* i_wb may have changed inbetween, can't use inode_to_wb() */
614a4e37
TH
300 if (likely(wb == inode->i_wb)) {
301 wb_put(wb); /* @inode already has ref */
302 return wb;
303 }
87e1d789
TH
304
305 spin_unlock(&wb->list_lock);
614a4e37 306 wb_put(wb);
87e1d789
TH
307 cpu_relax();
308 spin_lock(&inode->i_lock);
309 }
310}
311
312/**
313 * inode_to_wb_and_lock_list - determine an inode's wb and lock it
314 * @inode: inode of interest
315 *
316 * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
317 * on entry.
318 */
319static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
320 __acquires(&wb->list_lock)
321{
322 spin_lock(&inode->i_lock);
323 return locked_inode_to_wb_and_lock_list(inode);
324}
325
682aa8e1
TH
326struct inode_switch_wbs_context {
327 struct inode *inode;
328 struct bdi_writeback *new_wb;
329
330 struct rcu_head rcu_head;
331 struct work_struct work;
332};
333
334static void inode_switch_wbs_work_fn(struct work_struct *work)
335{
336 struct inode_switch_wbs_context *isw =
337 container_of(work, struct inode_switch_wbs_context, work);
338 struct inode *inode = isw->inode;
d10c8095
TH
339 struct address_space *mapping = inode->i_mapping;
340 struct bdi_writeback *old_wb = inode->i_wb;
682aa8e1 341 struct bdi_writeback *new_wb = isw->new_wb;
d10c8095
TH
342 struct radix_tree_iter iter;
343 bool switched = false;
344 void **slot;
682aa8e1
TH
345
346 /*
347 * By the time control reaches here, RCU grace period has passed
348 * since I_WB_SWITCH assertion and all wb stat update transactions
349 * between unlocked_inode_to_wb_begin/end() are guaranteed to be
350 * synchronizing against mapping->tree_lock.
d10c8095
TH
351 *
352 * Grabbing old_wb->list_lock, inode->i_lock and mapping->tree_lock
353 * gives us exclusion against all wb related operations on @inode
354 * including IO list manipulations and stat updates.
682aa8e1 355 */
d10c8095
TH
356 if (old_wb < new_wb) {
357 spin_lock(&old_wb->list_lock);
358 spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
359 } else {
360 spin_lock(&new_wb->list_lock);
361 spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
362 }
682aa8e1 363 spin_lock(&inode->i_lock);
d10c8095
TH
364 spin_lock_irq(&mapping->tree_lock);
365
366 /*
367 * Once I_FREEING is visible under i_lock, the eviction path owns
c7f54084 368 * the inode and we shouldn't modify ->i_io_list.
d10c8095
TH
369 */
370 if (unlikely(inode->i_state & I_FREEING))
371 goto skip_switch;
372
373 /*
374 * Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
375 * to possibly dirty pages while PAGECACHE_TAG_WRITEBACK points to
376 * pages actually under underwriteback.
377 */
378 radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, 0,
379 PAGECACHE_TAG_DIRTY) {
380 struct page *page = radix_tree_deref_slot_protected(slot,
381 &mapping->tree_lock);
382 if (likely(page) && PageDirty(page)) {
3e8f399d
NB
383 dec_wb_stat(old_wb, WB_RECLAIMABLE);
384 inc_wb_stat(new_wb, WB_RECLAIMABLE);
d10c8095
TH
385 }
386 }
387
388 radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, 0,
389 PAGECACHE_TAG_WRITEBACK) {
390 struct page *page = radix_tree_deref_slot_protected(slot,
391 &mapping->tree_lock);
392 if (likely(page)) {
393 WARN_ON_ONCE(!PageWriteback(page));
3e8f399d
NB
394 dec_wb_stat(old_wb, WB_WRITEBACK);
395 inc_wb_stat(new_wb, WB_WRITEBACK);
d10c8095
TH
396 }
397 }
398
399 wb_get(new_wb);
400
401 /*
402 * Transfer to @new_wb's IO list if necessary. The specific list
403 * @inode was on is ignored and the inode is put on ->b_dirty which
404 * is always correct including from ->b_dirty_time. The transfer
405 * preserves @inode->dirtied_when ordering.
406 */
c7f54084 407 if (!list_empty(&inode->i_io_list)) {
d10c8095
TH
408 struct inode *pos;
409
c7f54084 410 inode_io_list_del_locked(inode, old_wb);
d10c8095 411 inode->i_wb = new_wb;
c7f54084 412 list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
d10c8095
TH
413 if (time_after_eq(inode->dirtied_when,
414 pos->dirtied_when))
415 break;
c7f54084 416 inode_io_list_move_locked(inode, new_wb, pos->i_io_list.prev);
d10c8095
TH
417 } else {
418 inode->i_wb = new_wb;
419 }
682aa8e1 420
d10c8095 421 /* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
682aa8e1
TH
422 inode->i_wb_frn_winner = 0;
423 inode->i_wb_frn_avg_time = 0;
424 inode->i_wb_frn_history = 0;
d10c8095
TH
425 switched = true;
426skip_switch:
682aa8e1
TH
427 /*
428 * Paired with load_acquire in unlocked_inode_to_wb_begin() and
429 * ensures that the new wb is visible if they see !I_WB_SWITCH.
430 */
431 smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
432
d10c8095 433 spin_unlock_irq(&mapping->tree_lock);
682aa8e1 434 spin_unlock(&inode->i_lock);
d10c8095
TH
435 spin_unlock(&new_wb->list_lock);
436 spin_unlock(&old_wb->list_lock);
682aa8e1 437
d10c8095
TH
438 if (switched) {
439 wb_wakeup(new_wb);
440 wb_put(old_wb);
441 }
682aa8e1 442 wb_put(new_wb);
d10c8095
TH
443
444 iput(inode);
682aa8e1 445 kfree(isw);
a1a0e23e
TH
446
447 atomic_dec(&isw_nr_in_flight);
682aa8e1
TH
448}
449
450static void inode_switch_wbs_rcu_fn(struct rcu_head *rcu_head)
451{
452 struct inode_switch_wbs_context *isw = container_of(rcu_head,
453 struct inode_switch_wbs_context, rcu_head);
454
455 /* needs to grab bh-unsafe locks, bounce to work item */
456 INIT_WORK(&isw->work, inode_switch_wbs_work_fn);
a1a0e23e 457 queue_work(isw_wq, &isw->work);
682aa8e1
TH
458}
459
460/**
461 * inode_switch_wbs - change the wb association of an inode
462 * @inode: target inode
463 * @new_wb_id: ID of the new wb
464 *
465 * Switch @inode's wb association to the wb identified by @new_wb_id. The
466 * switching is performed asynchronously and may fail silently.
467 */
468static void inode_switch_wbs(struct inode *inode, int new_wb_id)
469{
470 struct backing_dev_info *bdi = inode_to_bdi(inode);
471 struct cgroup_subsys_state *memcg_css;
472 struct inode_switch_wbs_context *isw;
473
474 /* noop if seems to be already in progress */
475 if (inode->i_state & I_WB_SWITCH)
476 return;
477
478 isw = kzalloc(sizeof(*isw), GFP_ATOMIC);
479 if (!isw)
480 return;
481
482 /* find and pin the new wb */
483 rcu_read_lock();
484 memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
485 if (memcg_css)
486 isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
487 rcu_read_unlock();
488 if (!isw->new_wb)
489 goto out_free;
490
491 /* while holding I_WB_SWITCH, no one else can update the association */
492 spin_lock(&inode->i_lock);
1751e8a6 493 if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
a1a0e23e
TH
494 inode->i_state & (I_WB_SWITCH | I_FREEING) ||
495 inode_to_wb(inode) == isw->new_wb) {
496 spin_unlock(&inode->i_lock);
497 goto out_free;
498 }
682aa8e1 499 inode->i_state |= I_WB_SWITCH;
74524955 500 __iget(inode);
682aa8e1
TH
501 spin_unlock(&inode->i_lock);
502
682aa8e1
TH
503 isw->inode = inode;
504
a1a0e23e
TH
505 atomic_inc(&isw_nr_in_flight);
506
682aa8e1
TH
507 /*
508 * In addition to synchronizing among switchers, I_WB_SWITCH tells
509 * the RCU protected stat update paths to grab the mapping's
510 * tree_lock so that stat transfer can synchronize against them.
511 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
512 */
513 call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn);
514 return;
515
516out_free:
517 if (isw->new_wb)
518 wb_put(isw->new_wb);
519 kfree(isw);
520}
521
b16b1deb
TH
522/**
523 * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
524 * @wbc: writeback_control of interest
525 * @inode: target inode
526 *
527 * @inode is locked and about to be written back under the control of @wbc.
528 * Record @inode's writeback context into @wbc and unlock the i_lock. On
529 * writeback completion, wbc_detach_inode() should be called. This is used
530 * to track the cgroup writeback context.
531 */
532void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
533 struct inode *inode)
534{
dd73e4b7
TH
535 if (!inode_cgwb_enabled(inode)) {
536 spin_unlock(&inode->i_lock);
537 return;
538 }
539
b16b1deb 540 wbc->wb = inode_to_wb(inode);
2a814908
TH
541 wbc->inode = inode;
542
543 wbc->wb_id = wbc->wb->memcg_css->id;
544 wbc->wb_lcand_id = inode->i_wb_frn_winner;
545 wbc->wb_tcand_id = 0;
546 wbc->wb_bytes = 0;
547 wbc->wb_lcand_bytes = 0;
548 wbc->wb_tcand_bytes = 0;
549
b16b1deb
TH
550 wb_get(wbc->wb);
551 spin_unlock(&inode->i_lock);
e8a7abf5
TH
552
553 /*
554 * A dying wb indicates that the memcg-blkcg mapping has changed
555 * and a new wb is already serving the memcg. Switch immediately.
556 */
557 if (unlikely(wb_dying(wbc->wb)))
558 inode_switch_wbs(inode, wbc->wb_id);
b16b1deb
TH
559}
560
561/**
2a814908
TH
562 * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
563 * @wbc: writeback_control of the just finished writeback
b16b1deb
TH
564 *
565 * To be called after a writeback attempt of an inode finishes and undoes
566 * wbc_attach_and_unlock_inode(). Can be called under any context.
2a814908
TH
567 *
568 * As concurrent write sharing of an inode is expected to be very rare and
569 * memcg only tracks page ownership on first-use basis severely confining
570 * the usefulness of such sharing, cgroup writeback tracks ownership
571 * per-inode. While the support for concurrent write sharing of an inode
572 * is deemed unnecessary, an inode being written to by different cgroups at
573 * different points in time is a lot more common, and, more importantly,
574 * charging only by first-use can too readily lead to grossly incorrect
575 * behaviors (single foreign page can lead to gigabytes of writeback to be
576 * incorrectly attributed).
577 *
578 * To resolve this issue, cgroup writeback detects the majority dirtier of
579 * an inode and transfers the ownership to it. To avoid unnnecessary
580 * oscillation, the detection mechanism keeps track of history and gives
581 * out the switch verdict only if the foreign usage pattern is stable over
582 * a certain amount of time and/or writeback attempts.
583 *
584 * On each writeback attempt, @wbc tries to detect the majority writer
585 * using Boyer-Moore majority vote algorithm. In addition to the byte
586 * count from the majority voting, it also counts the bytes written for the
587 * current wb and the last round's winner wb (max of last round's current
588 * wb, the winner from two rounds ago, and the last round's majority
589 * candidate). Keeping track of the historical winner helps the algorithm
590 * to semi-reliably detect the most active writer even when it's not the
591 * absolute majority.
592 *
593 * Once the winner of the round is determined, whether the winner is
594 * foreign or not and how much IO time the round consumed is recorded in
595 * inode->i_wb_frn_history. If the amount of recorded foreign IO time is
596 * over a certain threshold, the switch verdict is given.
b16b1deb
TH
597 */
598void wbc_detach_inode(struct writeback_control *wbc)
599{
2a814908
TH
600 struct bdi_writeback *wb = wbc->wb;
601 struct inode *inode = wbc->inode;
dd73e4b7
TH
602 unsigned long avg_time, max_bytes, max_time;
603 u16 history;
2a814908
TH
604 int max_id;
605
dd73e4b7
TH
606 if (!wb)
607 return;
608
609 history = inode->i_wb_frn_history;
610 avg_time = inode->i_wb_frn_avg_time;
611
2a814908
TH
612 /* pick the winner of this round */
613 if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
614 wbc->wb_bytes >= wbc->wb_tcand_bytes) {
615 max_id = wbc->wb_id;
616 max_bytes = wbc->wb_bytes;
617 } else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
618 max_id = wbc->wb_lcand_id;
619 max_bytes = wbc->wb_lcand_bytes;
620 } else {
621 max_id = wbc->wb_tcand_id;
622 max_bytes = wbc->wb_tcand_bytes;
623 }
624
625 /*
626 * Calculate the amount of IO time the winner consumed and fold it
627 * into the running average kept per inode. If the consumed IO
628 * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
629 * deciding whether to switch or not. This is to prevent one-off
630 * small dirtiers from skewing the verdict.
631 */
632 max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
633 wb->avg_write_bandwidth);
634 if (avg_time)
635 avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
636 (avg_time >> WB_FRN_TIME_AVG_SHIFT);
637 else
638 avg_time = max_time; /* immediate catch up on first run */
639
640 if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
641 int slots;
642
643 /*
644 * The switch verdict is reached if foreign wb's consume
645 * more than a certain proportion of IO time in a
646 * WB_FRN_TIME_PERIOD. This is loosely tracked by 16 slot
647 * history mask where each bit represents one sixteenth of
648 * the period. Determine the number of slots to shift into
649 * history from @max_time.
650 */
651 slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
652 (unsigned long)WB_FRN_HIST_MAX_SLOTS);
653 history <<= slots;
654 if (wbc->wb_id != max_id)
655 history |= (1U << slots) - 1;
656
657 /*
658 * Switch if the current wb isn't the consistent winner.
659 * If there are multiple closely competing dirtiers, the
660 * inode may switch across them repeatedly over time, which
661 * is okay. The main goal is avoiding keeping an inode on
662 * the wrong wb for an extended period of time.
663 */
682aa8e1
TH
664 if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
665 inode_switch_wbs(inode, max_id);
2a814908
TH
666 }
667
668 /*
669 * Multiple instances of this function may race to update the
670 * following fields but we don't mind occassional inaccuracies.
671 */
672 inode->i_wb_frn_winner = max_id;
673 inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
674 inode->i_wb_frn_history = history;
675
b16b1deb
TH
676 wb_put(wbc->wb);
677 wbc->wb = NULL;
678}
679
2a814908
TH
680/**
681 * wbc_account_io - account IO issued during writeback
682 * @wbc: writeback_control of the writeback in progress
683 * @page: page being written out
684 * @bytes: number of bytes being written out
685 *
686 * @bytes from @page are about to written out during the writeback
687 * controlled by @wbc. Keep the book for foreign inode detection. See
688 * wbc_detach_inode().
689 */
690void wbc_account_io(struct writeback_control *wbc, struct page *page,
691 size_t bytes)
692{
693 int id;
694
695 /*
696 * pageout() path doesn't attach @wbc to the inode being written
697 * out. This is intentional as we don't want the function to block
698 * behind a slow cgroup. Ultimately, we want pageout() to kick off
699 * regular writeback instead of writing things out itself.
700 */
701 if (!wbc->wb)
702 return;
703
2a814908 704 id = mem_cgroup_css_from_page(page)->id;
2a814908
TH
705
706 if (id == wbc->wb_id) {
707 wbc->wb_bytes += bytes;
708 return;
709 }
710
711 if (id == wbc->wb_lcand_id)
712 wbc->wb_lcand_bytes += bytes;
713
714 /* Boyer-Moore majority vote algorithm */
715 if (!wbc->wb_tcand_bytes)
716 wbc->wb_tcand_id = id;
717 if (id == wbc->wb_tcand_id)
718 wbc->wb_tcand_bytes += bytes;
719 else
720 wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
721}
5aa2a96b 722EXPORT_SYMBOL_GPL(wbc_account_io);
2a814908 723
703c2708
TH
724/**
725 * inode_congested - test whether an inode is congested
60292bcc 726 * @inode: inode to test for congestion (may be NULL)
703c2708
TH
727 * @cong_bits: mask of WB_[a]sync_congested bits to test
728 *
729 * Tests whether @inode is congested. @cong_bits is the mask of congestion
730 * bits to test and the return value is the mask of set bits.
731 *
732 * If cgroup writeback is enabled for @inode, the congestion state is
733 * determined by whether the cgwb (cgroup bdi_writeback) for the blkcg
734 * associated with @inode is congested; otherwise, the root wb's congestion
735 * state is used.
60292bcc
TH
736 *
737 * @inode is allowed to be NULL as this function is often called on
738 * mapping->host which is NULL for the swapper space.
703c2708
TH
739 */
740int inode_congested(struct inode *inode, int cong_bits)
741{
5cb8b824
TH
742 /*
743 * Once set, ->i_wb never becomes NULL while the inode is alive.
744 * Start transaction iff ->i_wb is visible.
745 */
aaa2cacf 746 if (inode && inode_to_wb_is_valid(inode)) {
5cb8b824
TH
747 struct bdi_writeback *wb;
748 bool locked, congested;
749
750 wb = unlocked_inode_to_wb_begin(inode, &locked);
751 congested = wb_congested(wb, cong_bits);
752 unlocked_inode_to_wb_end(inode, locked);
753 return congested;
703c2708
TH
754 }
755
756 return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
757}
758EXPORT_SYMBOL_GPL(inode_congested);
759
f2b65121
TH
760/**
761 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
762 * @wb: target bdi_writeback to split @nr_pages to
763 * @nr_pages: number of pages to write for the whole bdi
764 *
765 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
766 * relation to the total write bandwidth of all wb's w/ dirty inodes on
767 * @wb->bdi.
768 */
769static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
770{
771 unsigned long this_bw = wb->avg_write_bandwidth;
772 unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
773
774 if (nr_pages == LONG_MAX)
775 return LONG_MAX;
776
777 /*
778 * This may be called on clean wb's and proportional distribution
779 * may not make sense, just use the original @nr_pages in those
780 * cases. In general, we wanna err on the side of writing more.
781 */
782 if (!tot_bw || this_bw >= tot_bw)
783 return nr_pages;
784 else
785 return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
786}
787
db125360
TH
788/**
789 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
790 * @bdi: target backing_dev_info
791 * @base_work: wb_writeback_work to issue
792 * @skip_if_busy: skip wb's which already have writeback in progress
793 *
794 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
795 * have dirty inodes. If @base_work->nr_page isn't %LONG_MAX, it's
796 * distributed to the busy wbs according to each wb's proportion in the
797 * total active write bandwidth of @bdi.
798 */
799static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
800 struct wb_writeback_work *base_work,
801 bool skip_if_busy)
802{
b817525a 803 struct bdi_writeback *last_wb = NULL;
b33e18f6
TH
804 struct bdi_writeback *wb = list_entry(&bdi->wb_list,
805 struct bdi_writeback, bdi_node);
db125360
TH
806
807 might_sleep();
db125360
TH
808restart:
809 rcu_read_lock();
b817525a 810 list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
8a1270cd
TH
811 DEFINE_WB_COMPLETION_ONSTACK(fallback_work_done);
812 struct wb_writeback_work fallback_work;
813 struct wb_writeback_work *work;
814 long nr_pages;
815
b817525a
TH
816 if (last_wb) {
817 wb_put(last_wb);
818 last_wb = NULL;
819 }
820
006a0973
TH
821 /* SYNC_ALL writes out I_DIRTY_TIME too */
822 if (!wb_has_dirty_io(wb) &&
823 (base_work->sync_mode == WB_SYNC_NONE ||
824 list_empty(&wb->b_dirty_time)))
825 continue;
826 if (skip_if_busy && writeback_in_progress(wb))
db125360
TH
827 continue;
828
8a1270cd
TH
829 nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
830
831 work = kmalloc(sizeof(*work), GFP_ATOMIC);
832 if (work) {
833 *work = *base_work;
834 work->nr_pages = nr_pages;
835 work->auto_free = 1;
836 wb_queue_work(wb, work);
837 continue;
db125360 838 }
8a1270cd
TH
839
840 /* alloc failed, execute synchronously using on-stack fallback */
841 work = &fallback_work;
842 *work = *base_work;
843 work->nr_pages = nr_pages;
844 work->auto_free = 0;
845 work->done = &fallback_work_done;
846
847 wb_queue_work(wb, work);
848
b817525a
TH
849 /*
850 * Pin @wb so that it stays on @bdi->wb_list. This allows
851 * continuing iteration from @wb after dropping and
852 * regrabbing rcu read lock.
853 */
854 wb_get(wb);
855 last_wb = wb;
856
8a1270cd
TH
857 rcu_read_unlock();
858 wb_wait_for_completion(bdi, &fallback_work_done);
859 goto restart;
db125360
TH
860 }
861 rcu_read_unlock();
b817525a
TH
862
863 if (last_wb)
864 wb_put(last_wb);
db125360
TH
865}
866
a1a0e23e
TH
867/**
868 * cgroup_writeback_umount - flush inode wb switches for umount
869 *
870 * This function is called when a super_block is about to be destroyed and
871 * flushes in-flight inode wb switches. An inode wb switch goes through
872 * RCU and then workqueue, so the two need to be flushed in order to ensure
873 * that all previously scheduled switches are finished. As wb switches are
874 * rare occurrences and synchronize_rcu() can take a while, perform
875 * flushing iff wb switches are in flight.
876 */
877void cgroup_writeback_umount(void)
878{
879 if (atomic_read(&isw_nr_in_flight)) {
880 synchronize_rcu();
881 flush_workqueue(isw_wq);
882 }
883}
884
885static int __init cgroup_writeback_init(void)
886{
887 isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
888 if (!isw_wq)
889 return -ENOMEM;
890 return 0;
891}
892fs_initcall(cgroup_writeback_init);
893
f2b65121
TH
894#else /* CONFIG_CGROUP_WRITEBACK */
895
87e1d789
TH
896static struct bdi_writeback *
897locked_inode_to_wb_and_lock_list(struct inode *inode)
898 __releases(&inode->i_lock)
899 __acquires(&wb->list_lock)
900{
901 struct bdi_writeback *wb = inode_to_wb(inode);
902
903 spin_unlock(&inode->i_lock);
904 spin_lock(&wb->list_lock);
905 return wb;
906}
907
908static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
909 __acquires(&wb->list_lock)
910{
911 struct bdi_writeback *wb = inode_to_wb(inode);
912
913 spin_lock(&wb->list_lock);
914 return wb;
915}
916
f2b65121
TH
917static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
918{
919 return nr_pages;
920}
921
db125360
TH
922static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
923 struct wb_writeback_work *base_work,
924 bool skip_if_busy)
925{
926 might_sleep();
927
006a0973 928 if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
db125360 929 base_work->auto_free = 0;
db125360
TH
930 wb_queue_work(&bdi->wb, base_work);
931 }
932}
933
703c2708
TH
934#endif /* CONFIG_CGROUP_WRITEBACK */
935
e8e8a0c6
JA
936/*
937 * Add in the number of potentially dirty inodes, because each inode
938 * write can dirty pagecache in the underlying blockdev.
939 */
940static unsigned long get_nr_dirty_pages(void)
941{
942 return global_node_page_state(NR_FILE_DIRTY) +
943 global_node_page_state(NR_UNSTABLE_NFS) +
944 get_nr_dirty_inodes();
945}
946
947static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
b6e51316 948{
c00ddad3
TH
949 if (!wb_has_dirty_io(wb))
950 return;
951
aac8d41c
JA
952 /*
953 * All callers of this function want to start writeback of all
954 * dirty pages. Places like vmscan can call this at a very
955 * high frequency, causing pointless allocations of tons of
956 * work items and keeping the flusher threads busy retrieving
957 * that work. Ensure that we only allow one of them pending and
85009b4f 958 * inflight at the time.
aac8d41c 959 */
85009b4f
JA
960 if (test_bit(WB_start_all, &wb->state) ||
961 test_and_set_bit(WB_start_all, &wb->state))
aac8d41c
JA
962 return;
963
85009b4f
JA
964 wb->start_all_reason = reason;
965 wb_wakeup(wb);
c5444198 966}
d3ddec76 967
c5444198 968/**
9ecf4866
TH
969 * wb_start_background_writeback - start background writeback
970 * @wb: bdi_writback to write from
c5444198
CH
971 *
972 * Description:
6585027a 973 * This makes sure WB_SYNC_NONE background writeback happens. When
9ecf4866 974 * this function returns, it is only guaranteed that for given wb
6585027a
JK
975 * some IO is happening if we are over background dirty threshold.
976 * Caller need not hold sb s_umount semaphore.
c5444198 977 */
9ecf4866 978void wb_start_background_writeback(struct bdi_writeback *wb)
c5444198 979{
6585027a
JK
980 /*
981 * We just wake up the flusher thread. It will perform background
982 * writeback as soon as there is no other work to do.
983 */
5634cc2a 984 trace_writeback_wake_background(wb);
9ecf4866 985 wb_wakeup(wb);
1da177e4
LT
986}
987
a66979ab
DC
988/*
989 * Remove the inode from the writeback list it is on.
990 */
c7f54084 991void inode_io_list_del(struct inode *inode)
a66979ab 992{
87e1d789 993 struct bdi_writeback *wb;
f758eeab 994
87e1d789 995 wb = inode_to_wb_and_lock_list(inode);
c7f54084 996 inode_io_list_del_locked(inode, wb);
52ebea74 997 spin_unlock(&wb->list_lock);
a66979ab
DC
998}
999
6c60d2b5
DC
1000/*
1001 * mark an inode as under writeback on the sb
1002 */
1003void sb_mark_inode_writeback(struct inode *inode)
1004{
1005 struct super_block *sb = inode->i_sb;
1006 unsigned long flags;
1007
1008 if (list_empty(&inode->i_wb_list)) {
1009 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
9a46b04f 1010 if (list_empty(&inode->i_wb_list)) {
6c60d2b5 1011 list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
9a46b04f
BF
1012 trace_sb_mark_inode_writeback(inode);
1013 }
6c60d2b5
DC
1014 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1015 }
1016}
1017
1018/*
1019 * clear an inode as under writeback on the sb
1020 */
1021void sb_clear_inode_writeback(struct inode *inode)
1022{
1023 struct super_block *sb = inode->i_sb;
1024 unsigned long flags;
1025
1026 if (!list_empty(&inode->i_wb_list)) {
1027 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
9a46b04f
BF
1028 if (!list_empty(&inode->i_wb_list)) {
1029 list_del_init(&inode->i_wb_list);
1030 trace_sb_clear_inode_writeback(inode);
1031 }
6c60d2b5
DC
1032 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1033 }
1034}
1035
6610a0bc
AM
1036/*
1037 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1038 * furthest end of its superblock's dirty-inode list.
1039 *
1040 * Before stamping the inode's ->dirtied_when, we check to see whether it is
66f3b8e2 1041 * already the most-recently-dirtied inode on the b_dirty list. If that is
6610a0bc
AM
1042 * the case then the inode must have been redirtied while it was being written
1043 * out and we don't reset its dirtied_when.
1044 */
f758eeab 1045static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
6610a0bc 1046{
03ba3782 1047 if (!list_empty(&wb->b_dirty)) {
66f3b8e2 1048 struct inode *tail;
6610a0bc 1049
7ccf19a8 1050 tail = wb_inode(wb->b_dirty.next);
66f3b8e2 1051 if (time_before(inode->dirtied_when, tail->dirtied_when))
6610a0bc
AM
1052 inode->dirtied_when = jiffies;
1053 }
c7f54084 1054 inode_io_list_move_locked(inode, wb, &wb->b_dirty);
6610a0bc
AM
1055}
1056
c986d1e2 1057/*
66f3b8e2 1058 * requeue inode for re-scanning after bdi->b_io list is exhausted.
c986d1e2 1059 */
f758eeab 1060static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
c986d1e2 1061{
c7f54084 1062 inode_io_list_move_locked(inode, wb, &wb->b_more_io);
c986d1e2
AM
1063}
1064
1c0eeaf5
JE
1065static void inode_sync_complete(struct inode *inode)
1066{
365b94ae 1067 inode->i_state &= ~I_SYNC;
4eff96dd
JK
1068 /* If inode is clean an unused, put it into LRU now... */
1069 inode_add_lru(inode);
365b94ae 1070 /* Waiters must see I_SYNC cleared before being woken up */
1c0eeaf5
JE
1071 smp_mb();
1072 wake_up_bit(&inode->i_state, __I_SYNC);
1073}
1074
d2caa3c5
JL
1075static bool inode_dirtied_after(struct inode *inode, unsigned long t)
1076{
1077 bool ret = time_after(inode->dirtied_when, t);
1078#ifndef CONFIG_64BIT
1079 /*
1080 * For inodes being constantly redirtied, dirtied_when can get stuck.
1081 * It _appears_ to be in the future, but is actually in distant past.
1082 * This test is necessary to prevent such wrapped-around relative times
5b0830cb 1083 * from permanently stopping the whole bdi writeback.
d2caa3c5
JL
1084 */
1085 ret = ret && time_before_eq(inode->dirtied_when, jiffies);
1086#endif
1087 return ret;
1088}
1089
0ae45f63
TT
1090#define EXPIRE_DIRTY_ATIME 0x0001
1091
2c136579 1092/*
0e2f2b23 1093 * Move expired (dirtied before work->older_than_this) dirty inodes from
697e6fed 1094 * @delaying_queue to @dispatch_queue.
2c136579 1095 */
e84d0a4f 1096static int move_expired_inodes(struct list_head *delaying_queue,
2c136579 1097 struct list_head *dispatch_queue,
0ae45f63 1098 int flags,
ad4e38dd 1099 struct wb_writeback_work *work)
2c136579 1100{
0ae45f63
TT
1101 unsigned long *older_than_this = NULL;
1102 unsigned long expire_time;
5c03449d
SL
1103 LIST_HEAD(tmp);
1104 struct list_head *pos, *node;
cf137307 1105 struct super_block *sb = NULL;
5c03449d 1106 struct inode *inode;
cf137307 1107 int do_sb_sort = 0;
e84d0a4f 1108 int moved = 0;
5c03449d 1109
0ae45f63
TT
1110 if ((flags & EXPIRE_DIRTY_ATIME) == 0)
1111 older_than_this = work->older_than_this;
a2f48706
TT
1112 else if (!work->for_sync) {
1113 expire_time = jiffies - (dirtytime_expire_interval * HZ);
0ae45f63
TT
1114 older_than_this = &expire_time;
1115 }
2c136579 1116 while (!list_empty(delaying_queue)) {
7ccf19a8 1117 inode = wb_inode(delaying_queue->prev);
0ae45f63
TT
1118 if (older_than_this &&
1119 inode_dirtied_after(inode, *older_than_this))
2c136579 1120 break;
c7f54084 1121 list_move(&inode->i_io_list, &tmp);
a8855990 1122 moved++;
0ae45f63
TT
1123 if (flags & EXPIRE_DIRTY_ATIME)
1124 set_bit(__I_DIRTY_TIME_EXPIRED, &inode->i_state);
a8855990
JK
1125 if (sb_is_blkdev_sb(inode->i_sb))
1126 continue;
cf137307
JA
1127 if (sb && sb != inode->i_sb)
1128 do_sb_sort = 1;
1129 sb = inode->i_sb;
5c03449d
SL
1130 }
1131
cf137307
JA
1132 /* just one sb in list, splice to dispatch_queue and we're done */
1133 if (!do_sb_sort) {
1134 list_splice(&tmp, dispatch_queue);
e84d0a4f 1135 goto out;
cf137307
JA
1136 }
1137
5c03449d
SL
1138 /* Move inodes from one superblock together */
1139 while (!list_empty(&tmp)) {
7ccf19a8 1140 sb = wb_inode(tmp.prev)->i_sb;
5c03449d 1141 list_for_each_prev_safe(pos, node, &tmp) {
7ccf19a8 1142 inode = wb_inode(pos);
5c03449d 1143 if (inode->i_sb == sb)
c7f54084 1144 list_move(&inode->i_io_list, dispatch_queue);
5c03449d 1145 }
2c136579 1146 }
e84d0a4f
WF
1147out:
1148 return moved;
2c136579
FW
1149}
1150
1151/*
1152 * Queue all expired dirty inodes for io, eldest first.
4ea879b9
WF
1153 * Before
1154 * newly dirtied b_dirty b_io b_more_io
1155 * =============> gf edc BA
1156 * After
1157 * newly dirtied b_dirty b_io b_more_io
1158 * =============> g fBAedc
1159 * |
1160 * +--> dequeue for IO
2c136579 1161 */
ad4e38dd 1162static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
66f3b8e2 1163{
e84d0a4f 1164 int moved;
0ae45f63 1165
f758eeab 1166 assert_spin_locked(&wb->list_lock);
4ea879b9 1167 list_splice_init(&wb->b_more_io, &wb->b_io);
0ae45f63
TT
1168 moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, 0, work);
1169 moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
1170 EXPIRE_DIRTY_ATIME, work);
d6c10f1f
TH
1171 if (moved)
1172 wb_io_lists_populated(wb);
ad4e38dd 1173 trace_writeback_queue_io(wb, work, moved);
66f3b8e2
JA
1174}
1175
a9185b41 1176static int write_inode(struct inode *inode, struct writeback_control *wbc)
08d8e974 1177{
9fb0a7da
TH
1178 int ret;
1179
1180 if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1181 trace_writeback_write_inode_start(inode, wbc);
1182 ret = inode->i_sb->s_op->write_inode(inode, wbc);
1183 trace_writeback_write_inode(inode, wbc);
1184 return ret;
1185 }
03ba3782 1186 return 0;
08d8e974 1187}
08d8e974 1188
1da177e4 1189/*
169ebd90
JK
1190 * Wait for writeback on an inode to complete. Called with i_lock held.
1191 * Caller must make sure inode cannot go away when we drop i_lock.
01c03194 1192 */
169ebd90
JK
1193static void __inode_wait_for_writeback(struct inode *inode)
1194 __releases(inode->i_lock)
1195 __acquires(inode->i_lock)
01c03194
CH
1196{
1197 DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1198 wait_queue_head_t *wqh;
1199
1200 wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
250df6ed
DC
1201 while (inode->i_state & I_SYNC) {
1202 spin_unlock(&inode->i_lock);
74316201
N
1203 __wait_on_bit(wqh, &wq, bit_wait,
1204 TASK_UNINTERRUPTIBLE);
250df6ed 1205 spin_lock(&inode->i_lock);
58a9d3d8 1206 }
01c03194
CH
1207}
1208
169ebd90
JK
1209/*
1210 * Wait for writeback on an inode to complete. Caller must have inode pinned.
1211 */
1212void inode_wait_for_writeback(struct inode *inode)
1213{
1214 spin_lock(&inode->i_lock);
1215 __inode_wait_for_writeback(inode);
1216 spin_unlock(&inode->i_lock);
1217}
1218
1219/*
1220 * Sleep until I_SYNC is cleared. This function must be called with i_lock
1221 * held and drops it. It is aimed for callers not holding any inode reference
1222 * so once i_lock is dropped, inode can go away.
1223 */
1224static void inode_sleep_on_writeback(struct inode *inode)
1225 __releases(inode->i_lock)
1226{
1227 DEFINE_WAIT(wait);
1228 wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1229 int sleep;
1230
1231 prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1232 sleep = inode->i_state & I_SYNC;
1233 spin_unlock(&inode->i_lock);
1234 if (sleep)
1235 schedule();
1236 finish_wait(wqh, &wait);
1237}
1238
ccb26b5a
JK
1239/*
1240 * Find proper writeback list for the inode depending on its current state and
1241 * possibly also change of its state while we were doing writeback. Here we
1242 * handle things such as livelock prevention or fairness of writeback among
1243 * inodes. This function can be called only by flusher thread - noone else
1244 * processes all inodes in writeback lists and requeueing inodes behind flusher
1245 * thread's back can have unexpected consequences.
1246 */
1247static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1248 struct writeback_control *wbc)
1249{
1250 if (inode->i_state & I_FREEING)
1251 return;
1252
1253 /*
1254 * Sync livelock prevention. Each inode is tagged and synced in one
1255 * shot. If still dirty, it will be redirty_tail()'ed below. Update
1256 * the dirty time to prevent enqueue and sync it again.
1257 */
1258 if ((inode->i_state & I_DIRTY) &&
1259 (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1260 inode->dirtied_when = jiffies;
1261
4f8ad655
JK
1262 if (wbc->pages_skipped) {
1263 /*
1264 * writeback is not making progress due to locked
1265 * buffers. Skip this inode for now.
1266 */
1267 redirty_tail(inode, wb);
1268 return;
1269 }
1270
ccb26b5a
JK
1271 if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1272 /*
1273 * We didn't write back all the pages. nfs_writepages()
1274 * sometimes bales out without doing anything.
1275 */
1276 if (wbc->nr_to_write <= 0) {
1277 /* Slice used up. Queue for next turn. */
1278 requeue_io(inode, wb);
1279 } else {
1280 /*
1281 * Writeback blocked by something other than
1282 * congestion. Delay the inode for some time to
1283 * avoid spinning on the CPU (100% iowait)
1284 * retrying writeback of the dirty page/inode
1285 * that cannot be performed immediately.
1286 */
1287 redirty_tail(inode, wb);
1288 }
1289 } else if (inode->i_state & I_DIRTY) {
1290 /*
1291 * Filesystems can dirty the inode during writeback operations,
1292 * such as delayed allocation during submission or metadata
1293 * updates after data IO completion.
1294 */
1295 redirty_tail(inode, wb);
0ae45f63 1296 } else if (inode->i_state & I_DIRTY_TIME) {
a2f48706 1297 inode->dirtied_when = jiffies;
c7f54084 1298 inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
ccb26b5a
JK
1299 } else {
1300 /* The inode is clean. Remove from writeback lists. */
c7f54084 1301 inode_io_list_del_locked(inode, wb);
ccb26b5a
JK
1302 }
1303}
1304
01c03194 1305/*
4f8ad655
JK
1306 * Write out an inode and its dirty pages. Do not update the writeback list
1307 * linkage. That is left to the caller. The caller is also responsible for
1308 * setting I_SYNC flag and calling inode_sync_complete() to clear it.
1da177e4
LT
1309 */
1310static int
cd8ed2a4 1311__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1da177e4 1312{
1da177e4 1313 struct address_space *mapping = inode->i_mapping;
251d6a47 1314 long nr_to_write = wbc->nr_to_write;
01c03194 1315 unsigned dirty;
1da177e4
LT
1316 int ret;
1317
4f8ad655 1318 WARN_ON(!(inode->i_state & I_SYNC));
1da177e4 1319
9fb0a7da
TH
1320 trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1321
1da177e4
LT
1322 ret = do_writepages(mapping, wbc);
1323
26821ed4
CH
1324 /*
1325 * Make sure to wait on the data before writing out the metadata.
1326 * This is important for filesystems that modify metadata on data
7747bd4b
DC
1327 * I/O completion. We don't do it for sync(2) writeback because it has a
1328 * separate, external IO completion path and ->sync_fs for guaranteeing
1329 * inode metadata is written back correctly.
26821ed4 1330 */
7747bd4b 1331 if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
26821ed4 1332 int err = filemap_fdatawait(mapping);
1da177e4
LT
1333 if (ret == 0)
1334 ret = err;
1335 }
1336
5547e8aa
DM
1337 /*
1338 * Some filesystems may redirty the inode during the writeback
1339 * due to delalloc, clear dirty metadata flags right before
1340 * write_inode()
1341 */
250df6ed 1342 spin_lock(&inode->i_lock);
9c6ac78e 1343
5547e8aa 1344 dirty = inode->i_state & I_DIRTY;
a2f48706
TT
1345 if (inode->i_state & I_DIRTY_TIME) {
1346 if ((dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) ||
dc5ff2b1 1347 wbc->sync_mode == WB_SYNC_ALL ||
a2f48706
TT
1348 unlikely(inode->i_state & I_DIRTY_TIME_EXPIRED) ||
1349 unlikely(time_after(jiffies,
1350 (inode->dirtied_time_when +
1351 dirtytime_expire_interval * HZ)))) {
1352 dirty |= I_DIRTY_TIME | I_DIRTY_TIME_EXPIRED;
1353 trace_writeback_lazytime(inode);
1354 }
1355 } else
1356 inode->i_state &= ~I_DIRTY_TIME_EXPIRED;
0ae45f63 1357 inode->i_state &= ~dirty;
9c6ac78e
TH
1358
1359 /*
1360 * Paired with smp_mb() in __mark_inode_dirty(). This allows
1361 * __mark_inode_dirty() to test i_state without grabbing i_lock -
1362 * either they see the I_DIRTY bits cleared or we see the dirtied
1363 * inode.
1364 *
1365 * I_DIRTY_PAGES is always cleared together above even if @mapping
1366 * still has dirty pages. The flag is reinstated after smp_mb() if
1367 * necessary. This guarantees that either __mark_inode_dirty()
1368 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1369 */
1370 smp_mb();
1371
1372 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1373 inode->i_state |= I_DIRTY_PAGES;
1374
250df6ed 1375 spin_unlock(&inode->i_lock);
9c6ac78e 1376
0ae45f63
TT
1377 if (dirty & I_DIRTY_TIME)
1378 mark_inode_dirty_sync(inode);
26821ed4 1379 /* Don't write the inode if only I_DIRTY_PAGES was set */
0ae45f63 1380 if (dirty & ~I_DIRTY_PAGES) {
a9185b41 1381 int err = write_inode(inode, wbc);
1da177e4
LT
1382 if (ret == 0)
1383 ret = err;
1384 }
4f8ad655
JK
1385 trace_writeback_single_inode(inode, wbc, nr_to_write);
1386 return ret;
1387}
1388
1389/*
1390 * Write out an inode's dirty pages. Either the caller has an active reference
1391 * on the inode or the inode has I_WILL_FREE set.
1392 *
1393 * This function is designed to be called for writing back one inode which
1394 * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
1395 * and does more profound writeback list handling in writeback_sb_inodes().
1396 */
aaf25593
TH
1397static int writeback_single_inode(struct inode *inode,
1398 struct writeback_control *wbc)
4f8ad655 1399{
aaf25593 1400 struct bdi_writeback *wb;
4f8ad655
JK
1401 int ret = 0;
1402
1403 spin_lock(&inode->i_lock);
1404 if (!atomic_read(&inode->i_count))
1405 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1406 else
1407 WARN_ON(inode->i_state & I_WILL_FREE);
1408
1409 if (inode->i_state & I_SYNC) {
1410 if (wbc->sync_mode != WB_SYNC_ALL)
1411 goto out;
1412 /*
169ebd90
JK
1413 * It's a data-integrity sync. We must wait. Since callers hold
1414 * inode reference or inode has I_WILL_FREE set, it cannot go
1415 * away under us.
4f8ad655 1416 */
169ebd90 1417 __inode_wait_for_writeback(inode);
4f8ad655
JK
1418 }
1419 WARN_ON(inode->i_state & I_SYNC);
1420 /*
f9b0e058
JK
1421 * Skip inode if it is clean and we have no outstanding writeback in
1422 * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
1423 * function since flusher thread may be doing for example sync in
1424 * parallel and if we move the inode, it could get skipped. So here we
1425 * make sure inode is on some writeback list and leave it there unless
1426 * we have completely cleaned the inode.
4f8ad655 1427 */
0ae45f63 1428 if (!(inode->i_state & I_DIRTY_ALL) &&
f9b0e058
JK
1429 (wbc->sync_mode != WB_SYNC_ALL ||
1430 !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
4f8ad655
JK
1431 goto out;
1432 inode->i_state |= I_SYNC;
b16b1deb 1433 wbc_attach_and_unlock_inode(wbc, inode);
4f8ad655 1434
cd8ed2a4 1435 ret = __writeback_single_inode(inode, wbc);
1da177e4 1436
b16b1deb 1437 wbc_detach_inode(wbc);
aaf25593
TH
1438
1439 wb = inode_to_wb_and_lock_list(inode);
250df6ed 1440 spin_lock(&inode->i_lock);
4f8ad655
JK
1441 /*
1442 * If inode is clean, remove it from writeback lists. Otherwise don't
1443 * touch it. See comment above for explanation.
1444 */
0ae45f63 1445 if (!(inode->i_state & I_DIRTY_ALL))
c7f54084 1446 inode_io_list_del_locked(inode, wb);
4f8ad655 1447 spin_unlock(&wb->list_lock);
1c0eeaf5 1448 inode_sync_complete(inode);
4f8ad655
JK
1449out:
1450 spin_unlock(&inode->i_lock);
1da177e4
LT
1451 return ret;
1452}
1453
a88a341a 1454static long writeback_chunk_size(struct bdi_writeback *wb,
1a12d8bd 1455 struct wb_writeback_work *work)
d46db3d5
WF
1456{
1457 long pages;
1458
1459 /*
1460 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1461 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1462 * here avoids calling into writeback_inodes_wb() more than once.
1463 *
1464 * The intended call sequence for WB_SYNC_ALL writeback is:
1465 *
1466 * wb_writeback()
1467 * writeback_sb_inodes() <== called only once
1468 * write_cache_pages() <== called once for each inode
1469 * (quickly) tag currently dirty pages
1470 * (maybe slowly) sync all tagged pages
1471 */
1472 if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1473 pages = LONG_MAX;
1a12d8bd 1474 else {
a88a341a 1475 pages = min(wb->avg_write_bandwidth / 2,
dcc25ae7 1476 global_wb_domain.dirty_limit / DIRTY_SCOPE);
1a12d8bd
WF
1477 pages = min(pages, work->nr_pages);
1478 pages = round_down(pages + MIN_WRITEBACK_PAGES,
1479 MIN_WRITEBACK_PAGES);
1480 }
d46db3d5
WF
1481
1482 return pages;
1483}
1484
f11c9c5c
ES
1485/*
1486 * Write a portion of b_io inodes which belong to @sb.
edadfb10 1487 *
d46db3d5 1488 * Return the number of pages and/or inodes written.
0ba13fd1
LT
1489 *
1490 * NOTE! This is called with wb->list_lock held, and will
1491 * unlock and relock that for each inode it ends up doing
1492 * IO for.
f11c9c5c 1493 */
d46db3d5
WF
1494static long writeback_sb_inodes(struct super_block *sb,
1495 struct bdi_writeback *wb,
1496 struct wb_writeback_work *work)
1da177e4 1497{
d46db3d5
WF
1498 struct writeback_control wbc = {
1499 .sync_mode = work->sync_mode,
1500 .tagged_writepages = work->tagged_writepages,
1501 .for_kupdate = work->for_kupdate,
1502 .for_background = work->for_background,
7747bd4b 1503 .for_sync = work->for_sync,
d46db3d5
WF
1504 .range_cyclic = work->range_cyclic,
1505 .range_start = 0,
1506 .range_end = LLONG_MAX,
1507 };
1508 unsigned long start_time = jiffies;
1509 long write_chunk;
1510 long wrote = 0; /* count both pages and inodes */
1511
03ba3782 1512 while (!list_empty(&wb->b_io)) {
7ccf19a8 1513 struct inode *inode = wb_inode(wb->b_io.prev);
aaf25593 1514 struct bdi_writeback *tmp_wb;
edadfb10
CH
1515
1516 if (inode->i_sb != sb) {
d46db3d5 1517 if (work->sb) {
edadfb10
CH
1518 /*
1519 * We only want to write back data for this
1520 * superblock, move all inodes not belonging
1521 * to it back onto the dirty list.
1522 */
f758eeab 1523 redirty_tail(inode, wb);
edadfb10
CH
1524 continue;
1525 }
1526
1527 /*
1528 * The inode belongs to a different superblock.
1529 * Bounce back to the caller to unpin this and
1530 * pin the next superblock.
1531 */
d46db3d5 1532 break;
edadfb10
CH
1533 }
1534
9843b76a 1535 /*
331cbdee
WL
1536 * Don't bother with new inodes or inodes being freed, first
1537 * kind does not need periodic writeout yet, and for the latter
9843b76a
CH
1538 * kind writeout is handled by the freer.
1539 */
250df6ed 1540 spin_lock(&inode->i_lock);
9843b76a 1541 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
250df6ed 1542 spin_unlock(&inode->i_lock);
fcc5c222 1543 redirty_tail(inode, wb);
7ef0d737
NP
1544 continue;
1545 }
cc1676d9
JK
1546 if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1547 /*
1548 * If this inode is locked for writeback and we are not
1549 * doing writeback-for-data-integrity, move it to
1550 * b_more_io so that writeback can proceed with the
1551 * other inodes on s_io.
1552 *
1553 * We'll have another go at writing back this inode
1554 * when we completed a full scan of b_io.
1555 */
1556 spin_unlock(&inode->i_lock);
1557 requeue_io(inode, wb);
1558 trace_writeback_sb_inodes_requeue(inode);
1559 continue;
1560 }
f0d07b7f
JK
1561 spin_unlock(&wb->list_lock);
1562
4f8ad655
JK
1563 /*
1564 * We already requeued the inode if it had I_SYNC set and we
1565 * are doing WB_SYNC_NONE writeback. So this catches only the
1566 * WB_SYNC_ALL case.
1567 */
169ebd90
JK
1568 if (inode->i_state & I_SYNC) {
1569 /* Wait for I_SYNC. This function drops i_lock... */
1570 inode_sleep_on_writeback(inode);
1571 /* Inode may be gone, start again */
ead188f9 1572 spin_lock(&wb->list_lock);
169ebd90
JK
1573 continue;
1574 }
4f8ad655 1575 inode->i_state |= I_SYNC;
b16b1deb 1576 wbc_attach_and_unlock_inode(&wbc, inode);
169ebd90 1577
a88a341a 1578 write_chunk = writeback_chunk_size(wb, work);
d46db3d5
WF
1579 wbc.nr_to_write = write_chunk;
1580 wbc.pages_skipped = 0;
250df6ed 1581
169ebd90
JK
1582 /*
1583 * We use I_SYNC to pin the inode in memory. While it is set
1584 * evict_inode() will wait so the inode cannot be freed.
1585 */
cd8ed2a4 1586 __writeback_single_inode(inode, &wbc);
250df6ed 1587
b16b1deb 1588 wbc_detach_inode(&wbc);
d46db3d5
WF
1589 work->nr_pages -= write_chunk - wbc.nr_to_write;
1590 wrote += write_chunk - wbc.nr_to_write;
590dca3a
CM
1591
1592 if (need_resched()) {
1593 /*
1594 * We're trying to balance between building up a nice
1595 * long list of IOs to improve our merge rate, and
1596 * getting those IOs out quickly for anyone throttling
1597 * in balance_dirty_pages(). cond_resched() doesn't
1598 * unplug, so get our IOs out the door before we
1599 * give up the CPU.
1600 */
1601 blk_flush_plug(current);
1602 cond_resched();
1603 }
1604
aaf25593
TH
1605 /*
1606 * Requeue @inode if still dirty. Be careful as @inode may
1607 * have been switched to another wb in the meantime.
1608 */
1609 tmp_wb = inode_to_wb_and_lock_list(inode);
4f8ad655 1610 spin_lock(&inode->i_lock);
0ae45f63 1611 if (!(inode->i_state & I_DIRTY_ALL))
d46db3d5 1612 wrote++;
aaf25593 1613 requeue_inode(inode, tmp_wb, &wbc);
4f8ad655 1614 inode_sync_complete(inode);
0f1b1fd8 1615 spin_unlock(&inode->i_lock);
590dca3a 1616
aaf25593
TH
1617 if (unlikely(tmp_wb != wb)) {
1618 spin_unlock(&tmp_wb->list_lock);
1619 spin_lock(&wb->list_lock);
1620 }
1621
d46db3d5
WF
1622 /*
1623 * bail out to wb_writeback() often enough to check
1624 * background threshold and other termination conditions.
1625 */
1626 if (wrote) {
1627 if (time_is_before_jiffies(start_time + HZ / 10UL))
1628 break;
1629 if (work->nr_pages <= 0)
1630 break;
8bc3be27 1631 }
1da177e4 1632 }
d46db3d5 1633 return wrote;
f11c9c5c
ES
1634}
1635
d46db3d5
WF
1636static long __writeback_inodes_wb(struct bdi_writeback *wb,
1637 struct wb_writeback_work *work)
f11c9c5c 1638{
d46db3d5
WF
1639 unsigned long start_time = jiffies;
1640 long wrote = 0;
38f21977 1641
f11c9c5c 1642 while (!list_empty(&wb->b_io)) {
7ccf19a8 1643 struct inode *inode = wb_inode(wb->b_io.prev);
f11c9c5c 1644 struct super_block *sb = inode->i_sb;
9ecc2738 1645
eb6ef3df 1646 if (!trylock_super(sb)) {
0e995816 1647 /*
eb6ef3df 1648 * trylock_super() may fail consistently due to
0e995816
WF
1649 * s_umount being grabbed by someone else. Don't use
1650 * requeue_io() to avoid busy retrying the inode/sb.
1651 */
1652 redirty_tail(inode, wb);
edadfb10 1653 continue;
f11c9c5c 1654 }
d46db3d5 1655 wrote += writeback_sb_inodes(sb, wb, work);
eb6ef3df 1656 up_read(&sb->s_umount);
f11c9c5c 1657
d46db3d5
WF
1658 /* refer to the same tests at the end of writeback_sb_inodes */
1659 if (wrote) {
1660 if (time_is_before_jiffies(start_time + HZ / 10UL))
1661 break;
1662 if (work->nr_pages <= 0)
1663 break;
1664 }
f11c9c5c 1665 }
66f3b8e2 1666 /* Leave any unwritten inodes on b_io */
d46db3d5 1667 return wrote;
66f3b8e2
JA
1668}
1669
7d9f073b 1670static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
0e175a18 1671 enum wb_reason reason)
edadfb10 1672{
d46db3d5
WF
1673 struct wb_writeback_work work = {
1674 .nr_pages = nr_pages,
1675 .sync_mode = WB_SYNC_NONE,
1676 .range_cyclic = 1,
0e175a18 1677 .reason = reason,
d46db3d5 1678 };
505a666e 1679 struct blk_plug plug;
edadfb10 1680
505a666e 1681 blk_start_plug(&plug);
f758eeab 1682 spin_lock(&wb->list_lock);
424b351f 1683 if (list_empty(&wb->b_io))
ad4e38dd 1684 queue_io(wb, &work);
d46db3d5 1685 __writeback_inodes_wb(wb, &work);
f758eeab 1686 spin_unlock(&wb->list_lock);
505a666e 1687 blk_finish_plug(&plug);
edadfb10 1688
d46db3d5
WF
1689 return nr_pages - work.nr_pages;
1690}
03ba3782 1691
03ba3782
JA
1692/*
1693 * Explicit flushing or periodic writeback of "old" data.
66f3b8e2 1694 *
03ba3782
JA
1695 * Define "old": the first time one of an inode's pages is dirtied, we mark the
1696 * dirtying-time in the inode's address_space. So this periodic writeback code
1697 * just walks the superblock inode list, writing back any inodes which are
1698 * older than a specific point in time.
66f3b8e2 1699 *
03ba3782
JA
1700 * Try to run once per dirty_writeback_interval. But if a writeback event
1701 * takes longer than a dirty_writeback_interval interval, then leave a
1702 * one-second gap.
66f3b8e2 1703 *
03ba3782
JA
1704 * older_than_this takes precedence over nr_to_write. So we'll only write back
1705 * all dirty pages if they are all attached to "old" mappings.
66f3b8e2 1706 */
c4a77a6c 1707static long wb_writeback(struct bdi_writeback *wb,
83ba7b07 1708 struct wb_writeback_work *work)
66f3b8e2 1709{
e98be2d5 1710 unsigned long wb_start = jiffies;
d46db3d5 1711 long nr_pages = work->nr_pages;
0dc83bd3 1712 unsigned long oldest_jif;
a5989bdc 1713 struct inode *inode;
d46db3d5 1714 long progress;
505a666e 1715 struct blk_plug plug;
66f3b8e2 1716
0dc83bd3
JK
1717 oldest_jif = jiffies;
1718 work->older_than_this = &oldest_jif;
38f21977 1719
505a666e 1720 blk_start_plug(&plug);
e8dfc305 1721 spin_lock(&wb->list_lock);
03ba3782
JA
1722 for (;;) {
1723 /*
d3ddec76 1724 * Stop writeback when nr_pages has been consumed
03ba3782 1725 */
83ba7b07 1726 if (work->nr_pages <= 0)
03ba3782 1727 break;
66f3b8e2 1728
aa373cf5
JK
1729 /*
1730 * Background writeout and kupdate-style writeback may
1731 * run forever. Stop them if there is other work to do
1732 * so that e.g. sync can proceed. They'll be restarted
1733 * after the other works are all done.
1734 */
1735 if ((work->for_background || work->for_kupdate) &&
f0054bb1 1736 !list_empty(&wb->work_list))
aa373cf5
JK
1737 break;
1738
38f21977 1739 /*
d3ddec76
WF
1740 * For background writeout, stop when we are below the
1741 * background dirty threshold
38f21977 1742 */
aa661bbe 1743 if (work->for_background && !wb_over_bg_thresh(wb))
03ba3782 1744 break;
38f21977 1745
1bc36b64
JK
1746 /*
1747 * Kupdate and background works are special and we want to
1748 * include all inodes that need writing. Livelock avoidance is
1749 * handled by these works yielding to any other work so we are
1750 * safe.
1751 */
ba9aa839 1752 if (work->for_kupdate) {
0dc83bd3 1753 oldest_jif = jiffies -
ba9aa839 1754 msecs_to_jiffies(dirty_expire_interval * 10);
1bc36b64 1755 } else if (work->for_background)
0dc83bd3 1756 oldest_jif = jiffies;
028c2dd1 1757
5634cc2a 1758 trace_writeback_start(wb, work);
e8dfc305 1759 if (list_empty(&wb->b_io))
ad4e38dd 1760 queue_io(wb, work);
83ba7b07 1761 if (work->sb)
d46db3d5 1762 progress = writeback_sb_inodes(work->sb, wb, work);
edadfb10 1763 else
d46db3d5 1764 progress = __writeback_inodes_wb(wb, work);
5634cc2a 1765 trace_writeback_written(wb, work);
028c2dd1 1766
e98be2d5 1767 wb_update_bandwidth(wb, wb_start);
03ba3782
JA
1768
1769 /*
e6fb6da2
WF
1770 * Did we write something? Try for more
1771 *
1772 * Dirty inodes are moved to b_io for writeback in batches.
1773 * The completion of the current batch does not necessarily
1774 * mean the overall work is done. So we keep looping as long
1775 * as made some progress on cleaning pages or inodes.
03ba3782 1776 */
d46db3d5 1777 if (progress)
71fd05a8
JA
1778 continue;
1779 /*
e6fb6da2 1780 * No more inodes for IO, bail
71fd05a8 1781 */
b7a2441f 1782 if (list_empty(&wb->b_more_io))
03ba3782 1783 break;
71fd05a8
JA
1784 /*
1785 * Nothing written. Wait for some inode to
1786 * become available for writeback. Otherwise
1787 * we'll just busyloop.
1788 */
bace9248
TE
1789 trace_writeback_wait(wb, work);
1790 inode = wb_inode(wb->b_more_io.prev);
1791 spin_lock(&inode->i_lock);
1792 spin_unlock(&wb->list_lock);
1793 /* This function drops i_lock... */
1794 inode_sleep_on_writeback(inode);
1795 spin_lock(&wb->list_lock);
03ba3782 1796 }
e8dfc305 1797 spin_unlock(&wb->list_lock);
505a666e 1798 blk_finish_plug(&plug);
03ba3782 1799
d46db3d5 1800 return nr_pages - work->nr_pages;
03ba3782
JA
1801}
1802
1803/*
83ba7b07 1804 * Return the next wb_writeback_work struct that hasn't been processed yet.
03ba3782 1805 */
f0054bb1 1806static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
03ba3782 1807{
83ba7b07 1808 struct wb_writeback_work *work = NULL;
03ba3782 1809
f0054bb1
TH
1810 spin_lock_bh(&wb->work_lock);
1811 if (!list_empty(&wb->work_list)) {
1812 work = list_entry(wb->work_list.next,
83ba7b07
CH
1813 struct wb_writeback_work, list);
1814 list_del_init(&work->list);
03ba3782 1815 }
f0054bb1 1816 spin_unlock_bh(&wb->work_lock);
83ba7b07 1817 return work;
03ba3782
JA
1818}
1819
6585027a
JK
1820static long wb_check_background_flush(struct bdi_writeback *wb)
1821{
aa661bbe 1822 if (wb_over_bg_thresh(wb)) {
6585027a
JK
1823
1824 struct wb_writeback_work work = {
1825 .nr_pages = LONG_MAX,
1826 .sync_mode = WB_SYNC_NONE,
1827 .for_background = 1,
1828 .range_cyclic = 1,
0e175a18 1829 .reason = WB_REASON_BACKGROUND,
6585027a
JK
1830 };
1831
1832 return wb_writeback(wb, &work);
1833 }
1834
1835 return 0;
1836}
1837
03ba3782
JA
1838static long wb_check_old_data_flush(struct bdi_writeback *wb)
1839{
1840 unsigned long expired;
1841 long nr_pages;
1842
69b62d01
JA
1843 /*
1844 * When set to zero, disable periodic writeback
1845 */
1846 if (!dirty_writeback_interval)
1847 return 0;
1848
03ba3782
JA
1849 expired = wb->last_old_flush +
1850 msecs_to_jiffies(dirty_writeback_interval * 10);
1851 if (time_before(jiffies, expired))
1852 return 0;
1853
1854 wb->last_old_flush = jiffies;
cdf01dd5 1855 nr_pages = get_nr_dirty_pages();
03ba3782 1856
c4a77a6c 1857 if (nr_pages) {
83ba7b07 1858 struct wb_writeback_work work = {
c4a77a6c
JA
1859 .nr_pages = nr_pages,
1860 .sync_mode = WB_SYNC_NONE,
1861 .for_kupdate = 1,
1862 .range_cyclic = 1,
0e175a18 1863 .reason = WB_REASON_PERIODIC,
c4a77a6c
JA
1864 };
1865
83ba7b07 1866 return wb_writeback(wb, &work);
c4a77a6c 1867 }
03ba3782
JA
1868
1869 return 0;
1870}
1871
85009b4f
JA
1872static long wb_check_start_all(struct bdi_writeback *wb)
1873{
1874 long nr_pages;
1875
1876 if (!test_bit(WB_start_all, &wb->state))
1877 return 0;
1878
1879 nr_pages = get_nr_dirty_pages();
1880 if (nr_pages) {
1881 struct wb_writeback_work work = {
1882 .nr_pages = wb_split_bdi_pages(wb, nr_pages),
1883 .sync_mode = WB_SYNC_NONE,
1884 .range_cyclic = 1,
1885 .reason = wb->start_all_reason,
1886 };
1887
1888 nr_pages = wb_writeback(wb, &work);
1889 }
1890
1891 clear_bit(WB_start_all, &wb->state);
1892 return nr_pages;
1893}
1894
1895
03ba3782
JA
1896/*
1897 * Retrieve work items and do the writeback they describe
1898 */
25d130ba 1899static long wb_do_writeback(struct bdi_writeback *wb)
03ba3782 1900{
83ba7b07 1901 struct wb_writeback_work *work;
c4a77a6c 1902 long wrote = 0;
03ba3782 1903
4452226e 1904 set_bit(WB_writeback_running, &wb->state);
f0054bb1 1905 while ((work = get_next_work_item(wb)) != NULL) {
5634cc2a 1906 trace_writeback_exec(wb, work);
83ba7b07 1907 wrote += wb_writeback(wb, work);
4a3a485b 1908 finish_writeback_work(wb, work);
03ba3782
JA
1909 }
1910
85009b4f
JA
1911 /*
1912 * Check for a flush-everything request
1913 */
1914 wrote += wb_check_start_all(wb);
1915
03ba3782
JA
1916 /*
1917 * Check for periodic writeback, kupdated() style
1918 */
1919 wrote += wb_check_old_data_flush(wb);
6585027a 1920 wrote += wb_check_background_flush(wb);
4452226e 1921 clear_bit(WB_writeback_running, &wb->state);
03ba3782
JA
1922
1923 return wrote;
1924}
1925
1926/*
1927 * Handle writeback of dirty data for the device backed by this bdi. Also
839a8e86 1928 * reschedules periodically and does kupdated style flushing.
03ba3782 1929 */
f0054bb1 1930void wb_workfn(struct work_struct *work)
03ba3782 1931{
839a8e86
TH
1932 struct bdi_writeback *wb = container_of(to_delayed_work(work),
1933 struct bdi_writeback, dwork);
03ba3782
JA
1934 long pages_written;
1935
f0054bb1 1936 set_worker_desc("flush-%s", dev_name(wb->bdi->dev));
766f9164 1937 current->flags |= PF_SWAPWRITE;
455b2864 1938
839a8e86 1939 if (likely(!current_is_workqueue_rescuer() ||
4452226e 1940 !test_bit(WB_registered, &wb->state))) {
6467716a 1941 /*
f0054bb1 1942 * The normal path. Keep writing back @wb until its
839a8e86 1943 * work_list is empty. Note that this path is also taken
f0054bb1 1944 * if @wb is shutting down even when we're running off the
839a8e86 1945 * rescuer as work_list needs to be drained.
6467716a 1946 */
839a8e86 1947 do {
25d130ba 1948 pages_written = wb_do_writeback(wb);
839a8e86 1949 trace_writeback_pages_written(pages_written);
f0054bb1 1950 } while (!list_empty(&wb->work_list));
839a8e86
TH
1951 } else {
1952 /*
1953 * bdi_wq can't get enough workers and we're running off
1954 * the emergency worker. Don't hog it. Hopefully, 1024 is
1955 * enough for efficient IO.
1956 */
f0054bb1 1957 pages_written = writeback_inodes_wb(wb, 1024,
839a8e86 1958 WB_REASON_FORKER_THREAD);
455b2864 1959 trace_writeback_pages_written(pages_written);
03ba3782
JA
1960 }
1961
f0054bb1 1962 if (!list_empty(&wb->work_list))
6ca738d6
DB
1963 mod_delayed_work(bdi_wq, &wb->dwork, 0);
1964 else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
f0054bb1 1965 wb_wakeup_delayed(wb);
455b2864 1966
839a8e86 1967 current->flags &= ~PF_SWAPWRITE;
03ba3782
JA
1968}
1969
595043e5
JA
1970/*
1971 * Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
1972 * write back the whole world.
1973 */
1974static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
e8e8a0c6 1975 enum wb_reason reason)
595043e5
JA
1976{
1977 struct bdi_writeback *wb;
1978
1979 if (!bdi_has_dirty_io(bdi))
1980 return;
1981
1982 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
e8e8a0c6 1983 wb_start_writeback(wb, reason);
595043e5
JA
1984}
1985
1986void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
1987 enum wb_reason reason)
1988{
595043e5 1989 rcu_read_lock();
e8e8a0c6 1990 __wakeup_flusher_threads_bdi(bdi, reason);
595043e5
JA
1991 rcu_read_unlock();
1992}
1993
03ba3782 1994/*
9ba4b2df 1995 * Wakeup the flusher threads to start writeback of all currently dirty pages
03ba3782 1996 */
9ba4b2df 1997void wakeup_flusher_threads(enum wb_reason reason)
03ba3782 1998{
b8c2f347 1999 struct backing_dev_info *bdi;
03ba3782 2000
51350ea0
KK
2001 /*
2002 * If we are expecting writeback progress we must submit plugged IO.
2003 */
2004 if (blk_needs_flush_plug(current))
2005 blk_schedule_flush_plug(current);
2006
b8c2f347 2007 rcu_read_lock();
595043e5 2008 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
e8e8a0c6 2009 __wakeup_flusher_threads_bdi(bdi, reason);
cfc4ba53 2010 rcu_read_unlock();
1da177e4
LT
2011}
2012
a2f48706
TT
2013/*
2014 * Wake up bdi's periodically to make sure dirtytime inodes gets
2015 * written back periodically. We deliberately do *not* check the
2016 * b_dirtytime list in wb_has_dirty_io(), since this would cause the
2017 * kernel to be constantly waking up once there are any dirtytime
2018 * inodes on the system. So instead we define a separate delayed work
2019 * function which gets called much more rarely. (By default, only
2020 * once every 12 hours.)
2021 *
2022 * If there is any other write activity going on in the file system,
2023 * this function won't be necessary. But if the only thing that has
2024 * happened on the file system is a dirtytime inode caused by an atime
2025 * update, we need this infrastructure below to make sure that inode
2026 * eventually gets pushed out to disk.
2027 */
2028static void wakeup_dirtytime_writeback(struct work_struct *w);
2029static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
2030
2031static void wakeup_dirtytime_writeback(struct work_struct *w)
2032{
2033 struct backing_dev_info *bdi;
2034
2035 rcu_read_lock();
2036 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
001fe6f6 2037 struct bdi_writeback *wb;
001fe6f6 2038
b817525a 2039 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
6fdf860f
TH
2040 if (!list_empty(&wb->b_dirty_time))
2041 wb_wakeup(wb);
a2f48706
TT
2042 }
2043 rcu_read_unlock();
2044 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2045}
2046
2047static int __init start_dirtytime_writeback(void)
2048{
2049 schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2050 return 0;
2051}
2052__initcall(start_dirtytime_writeback);
2053
1efff914
TT
2054int dirtytime_interval_handler(struct ctl_table *table, int write,
2055 void __user *buffer, size_t *lenp, loff_t *ppos)
2056{
2057 int ret;
2058
2059 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
2060 if (ret == 0 && write)
2061 mod_delayed_work(system_wq, &dirtytime_work, 0);
2062 return ret;
2063}
2064
03ba3782
JA
2065static noinline void block_dump___mark_inode_dirty(struct inode *inode)
2066{
2067 if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
2068 struct dentry *dentry;
2069 const char *name = "?";
2070
2071 dentry = d_find_alias(inode);
2072 if (dentry) {
2073 spin_lock(&dentry->d_lock);
2074 name = (const char *) dentry->d_name.name;
2075 }
2076 printk(KERN_DEBUG
2077 "%s(%d): dirtied inode %lu (%s) on %s\n",
2078 current->comm, task_pid_nr(current), inode->i_ino,
2079 name, inode->i_sb->s_id);
2080 if (dentry) {
2081 spin_unlock(&dentry->d_lock);
2082 dput(dentry);
2083 }
2084 }
2085}
2086
2087/**
0117d427
MCC
2088 * __mark_inode_dirty - internal function
2089 *
2090 * @inode: inode to mark
2091 * @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
2092 *
2093 * Mark an inode as dirty. Callers should use mark_inode_dirty or
2094 * mark_inode_dirty_sync.
1da177e4 2095 *
03ba3782
JA
2096 * Put the inode on the super block's dirty list.
2097 *
2098 * CAREFUL! We mark it dirty unconditionally, but move it onto the
2099 * dirty list only if it is hashed or if it refers to a blockdev.
2100 * If it was not hashed, it will never be added to the dirty list
2101 * even if it is later hashed, as it will have been marked dirty already.
2102 *
2103 * In short, make sure you hash any inodes _before_ you start marking
2104 * them dirty.
1da177e4 2105 *
03ba3782
JA
2106 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2107 * the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
2108 * the kernel-internal blockdev inode represents the dirtying time of the
2109 * blockdev's pages. This is why for I_DIRTY_PAGES we always use
2110 * page->mapping->host, so the page-dirtying time is recorded in the internal
2111 * blockdev inode.
1da177e4 2112 */
03ba3782 2113void __mark_inode_dirty(struct inode *inode, int flags)
1da177e4 2114{
dbce03b9 2115#define I_DIRTY_INODE (I_DIRTY_SYNC | I_DIRTY_DATASYNC)
03ba3782 2116 struct super_block *sb = inode->i_sb;
0ae45f63
TT
2117 int dirtytime;
2118
2119 trace_writeback_mark_inode_dirty(inode, flags);
1da177e4 2120
03ba3782
JA
2121 /*
2122 * Don't do this for I_DIRTY_PAGES - that doesn't actually
2123 * dirty the inode itself
2124 */
0ae45f63 2125 if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_TIME)) {
9fb0a7da
TH
2126 trace_writeback_dirty_inode_start(inode, flags);
2127
03ba3782 2128 if (sb->s_op->dirty_inode)
aa385729 2129 sb->s_op->dirty_inode(inode, flags);
9fb0a7da
TH
2130
2131 trace_writeback_dirty_inode(inode, flags);
03ba3782 2132 }
0ae45f63
TT
2133 if (flags & I_DIRTY_INODE)
2134 flags &= ~I_DIRTY_TIME;
2135 dirtytime = flags & I_DIRTY_TIME;
03ba3782
JA
2136
2137 /*
9c6ac78e
TH
2138 * Paired with smp_mb() in __writeback_single_inode() for the
2139 * following lockless i_state test. See there for details.
03ba3782
JA
2140 */
2141 smp_mb();
2142
0ae45f63
TT
2143 if (((inode->i_state & flags) == flags) ||
2144 (dirtytime && (inode->i_state & I_DIRTY_INODE)))
03ba3782
JA
2145 return;
2146
2147 if (unlikely(block_dump))
2148 block_dump___mark_inode_dirty(inode);
2149
250df6ed 2150 spin_lock(&inode->i_lock);
0ae45f63
TT
2151 if (dirtytime && (inode->i_state & I_DIRTY_INODE))
2152 goto out_unlock_inode;
03ba3782
JA
2153 if ((inode->i_state & flags) != flags) {
2154 const int was_dirty = inode->i_state & I_DIRTY;
2155
52ebea74
TH
2156 inode_attach_wb(inode, NULL);
2157
0ae45f63
TT
2158 if (flags & I_DIRTY_INODE)
2159 inode->i_state &= ~I_DIRTY_TIME;
03ba3782
JA
2160 inode->i_state |= flags;
2161
2162 /*
2163 * If the inode is being synced, just update its dirty state.
2164 * The unlocker will place the inode on the appropriate
2165 * superblock list, based upon its state.
2166 */
2167 if (inode->i_state & I_SYNC)
250df6ed 2168 goto out_unlock_inode;
03ba3782
JA
2169
2170 /*
2171 * Only add valid (hashed) inodes to the superblock's
2172 * dirty list. Add blockdev inodes as well.
2173 */
2174 if (!S_ISBLK(inode->i_mode)) {
1d3382cb 2175 if (inode_unhashed(inode))
250df6ed 2176 goto out_unlock_inode;
03ba3782 2177 }
a4ffdde6 2178 if (inode->i_state & I_FREEING)
250df6ed 2179 goto out_unlock_inode;
03ba3782
JA
2180
2181 /*
2182 * If the inode was already on b_dirty/b_io/b_more_io, don't
2183 * reposition it (that would break b_dirty time-ordering).
2184 */
2185 if (!was_dirty) {
87e1d789 2186 struct bdi_writeback *wb;
d6c10f1f 2187 struct list_head *dirty_list;
a66979ab 2188 bool wakeup_bdi = false;
253c34e9 2189
87e1d789 2190 wb = locked_inode_to_wb_and_lock_list(inode);
253c34e9 2191
0747259d
TH
2192 WARN(bdi_cap_writeback_dirty(wb->bdi) &&
2193 !test_bit(WB_registered, &wb->state),
2194 "bdi-%s not registered\n", wb->bdi->name);
03ba3782
JA
2195
2196 inode->dirtied_when = jiffies;
a2f48706
TT
2197 if (dirtytime)
2198 inode->dirtied_time_when = jiffies;
d6c10f1f 2199
a2f48706 2200 if (inode->i_state & (I_DIRTY_INODE | I_DIRTY_PAGES))
0747259d 2201 dirty_list = &wb->b_dirty;
a2f48706 2202 else
0747259d 2203 dirty_list = &wb->b_dirty_time;
d6c10f1f 2204
c7f54084 2205 wakeup_bdi = inode_io_list_move_locked(inode, wb,
d6c10f1f
TH
2206 dirty_list);
2207
0747259d 2208 spin_unlock(&wb->list_lock);
0ae45f63 2209 trace_writeback_dirty_inode_enqueue(inode);
a66979ab 2210
d6c10f1f
TH
2211 /*
2212 * If this is the first dirty inode for this bdi,
2213 * we have to wake-up the corresponding bdi thread
2214 * to make sure background write-back happens
2215 * later.
2216 */
0747259d
TH
2217 if (bdi_cap_writeback_dirty(wb->bdi) && wakeup_bdi)
2218 wb_wakeup_delayed(wb);
a66979ab 2219 return;
1da177e4 2220 }
1da177e4 2221 }
250df6ed
DC
2222out_unlock_inode:
2223 spin_unlock(&inode->i_lock);
253c34e9 2224
dbce03b9 2225#undef I_DIRTY_INODE
03ba3782
JA
2226}
2227EXPORT_SYMBOL(__mark_inode_dirty);
2228
e97fedb9
DC
2229/*
2230 * The @s_sync_lock is used to serialise concurrent sync operations
2231 * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2232 * Concurrent callers will block on the s_sync_lock rather than doing contending
2233 * walks. The queueing maintains sync(2) required behaviour as all the IO that
2234 * has been issued up to the time this function is enter is guaranteed to be
2235 * completed by the time we have gained the lock and waited for all IO that is
2236 * in progress regardless of the order callers are granted the lock.
2237 */
b6e51316 2238static void wait_sb_inodes(struct super_block *sb)
03ba3782 2239{
6c60d2b5 2240 LIST_HEAD(sync_list);
03ba3782
JA
2241
2242 /*
2243 * We need to be protected against the filesystem going from
2244 * r/o to r/w or vice versa.
2245 */
b6e51316 2246 WARN_ON(!rwsem_is_locked(&sb->s_umount));
03ba3782 2247
e97fedb9 2248 mutex_lock(&sb->s_sync_lock);
03ba3782
JA
2249
2250 /*
6c60d2b5
DC
2251 * Splice the writeback list onto a temporary list to avoid waiting on
2252 * inodes that have started writeback after this point.
2253 *
2254 * Use rcu_read_lock() to keep the inodes around until we have a
2255 * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2256 * the local list because inodes can be dropped from either by writeback
2257 * completion.
2258 */
2259 rcu_read_lock();
2260 spin_lock_irq(&sb->s_inode_wblist_lock);
2261 list_splice_init(&sb->s_inodes_wb, &sync_list);
2262
2263 /*
2264 * Data integrity sync. Must wait for all pages under writeback, because
2265 * there may have been pages dirtied before our sync call, but which had
2266 * writeout started before we write it out. In which case, the inode
2267 * may not be on the dirty list, but we still have to wait for that
2268 * writeout.
03ba3782 2269 */
6c60d2b5
DC
2270 while (!list_empty(&sync_list)) {
2271 struct inode *inode = list_first_entry(&sync_list, struct inode,
2272 i_wb_list);
250df6ed 2273 struct address_space *mapping = inode->i_mapping;
03ba3782 2274
6c60d2b5
DC
2275 /*
2276 * Move each inode back to the wb list before we drop the lock
2277 * to preserve consistency between i_wb_list and the mapping
2278 * writeback tag. Writeback completion is responsible to remove
2279 * the inode from either list once the writeback tag is cleared.
2280 */
2281 list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
2282
2283 /*
2284 * The mapping can appear untagged while still on-list since we
2285 * do not have the mapping lock. Skip it here, wb completion
2286 * will remove it.
2287 */
2288 if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2289 continue;
2290
2291 spin_unlock_irq(&sb->s_inode_wblist_lock);
2292
250df6ed 2293 spin_lock(&inode->i_lock);
6c60d2b5 2294 if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
250df6ed 2295 spin_unlock(&inode->i_lock);
6c60d2b5
DC
2296
2297 spin_lock_irq(&sb->s_inode_wblist_lock);
03ba3782 2298 continue;
250df6ed 2299 }
03ba3782 2300 __iget(inode);
250df6ed 2301 spin_unlock(&inode->i_lock);
6c60d2b5 2302 rcu_read_unlock();
03ba3782 2303
aa750fd7
JN
2304 /*
2305 * We keep the error status of individual mapping so that
2306 * applications can catch the writeback error using fsync(2).
2307 * See filemap_fdatawait_keep_errors() for details.
2308 */
2309 filemap_fdatawait_keep_errors(mapping);
03ba3782
JA
2310
2311 cond_resched();
2312
6c60d2b5
DC
2313 iput(inode);
2314
2315 rcu_read_lock();
2316 spin_lock_irq(&sb->s_inode_wblist_lock);
03ba3782 2317 }
6c60d2b5
DC
2318 spin_unlock_irq(&sb->s_inode_wblist_lock);
2319 rcu_read_unlock();
e97fedb9 2320 mutex_unlock(&sb->s_sync_lock);
1da177e4
LT
2321}
2322
f30a7d0c
TH
2323static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2324 enum wb_reason reason, bool skip_if_busy)
1da177e4 2325{
cc395d7f 2326 DEFINE_WB_COMPLETION_ONSTACK(done);
83ba7b07 2327 struct wb_writeback_work work = {
6e6938b6
WF
2328 .sb = sb,
2329 .sync_mode = WB_SYNC_NONE,
2330 .tagged_writepages = 1,
2331 .done = &done,
2332 .nr_pages = nr,
0e175a18 2333 .reason = reason,
3c4d7165 2334 };
e7972912 2335 struct backing_dev_info *bdi = sb->s_bdi;
d8a8559c 2336
e7972912 2337 if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
6eedc701 2338 return;
cf37e972 2339 WARN_ON(!rwsem_is_locked(&sb->s_umount));
f30a7d0c 2340
db125360 2341 bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
cc395d7f 2342 wb_wait_for_completion(bdi, &done);
e913fc82 2343}
f30a7d0c
TH
2344
2345/**
2346 * writeback_inodes_sb_nr - writeback dirty inodes from given super_block
2347 * @sb: the superblock
2348 * @nr: the number of pages to write
2349 * @reason: reason why some writeback work initiated
2350 *
2351 * Start writeback on some inodes on this super_block. No guarantees are made
2352 * on how many (if any) will be written, and this function does not wait
2353 * for IO completion of submitted IO.
2354 */
2355void writeback_inodes_sb_nr(struct super_block *sb,
2356 unsigned long nr,
2357 enum wb_reason reason)
2358{
2359 __writeback_inodes_sb_nr(sb, nr, reason, false);
2360}
3259f8be
CM
2361EXPORT_SYMBOL(writeback_inodes_sb_nr);
2362
2363/**
2364 * writeback_inodes_sb - writeback dirty inodes from given super_block
2365 * @sb: the superblock
786228ab 2366 * @reason: reason why some writeback work was initiated
3259f8be
CM
2367 *
2368 * Start writeback on some inodes on this super_block. No guarantees are made
2369 * on how many (if any) will be written, and this function does not wait
2370 * for IO completion of submitted IO.
2371 */
0e175a18 2372void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
3259f8be 2373{
0e175a18 2374 return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
3259f8be 2375}
0e3c9a22 2376EXPORT_SYMBOL(writeback_inodes_sb);
e913fc82 2377
17bd55d0 2378/**
8264c321 2379 * try_to_writeback_inodes_sb - try to start writeback if none underway
17bd55d0 2380 * @sb: the superblock
8264c321 2381 * @reason: reason why some writeback work was initiated
17bd55d0 2382 *
8264c321 2383 * Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
17bd55d0 2384 */
8264c321 2385void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
17bd55d0 2386{
10ee27a0 2387 if (!down_read_trylock(&sb->s_umount))
8264c321 2388 return;
10ee27a0 2389
8264c321 2390 __writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason, true);
10ee27a0 2391 up_read(&sb->s_umount);
3259f8be 2392}
10ee27a0 2393EXPORT_SYMBOL(try_to_writeback_inodes_sb);
3259f8be 2394
d8a8559c
JA
2395/**
2396 * sync_inodes_sb - sync sb inode pages
0dc83bd3 2397 * @sb: the superblock
d8a8559c
JA
2398 *
2399 * This function writes and waits on any dirty inode belonging to this
0dc83bd3 2400 * super_block.
d8a8559c 2401 */
0dc83bd3 2402void sync_inodes_sb(struct super_block *sb)
d8a8559c 2403{
cc395d7f 2404 DEFINE_WB_COMPLETION_ONSTACK(done);
83ba7b07 2405 struct wb_writeback_work work = {
3c4d7165
CH
2406 .sb = sb,
2407 .sync_mode = WB_SYNC_ALL,
2408 .nr_pages = LONG_MAX,
2409 .range_cyclic = 0,
83ba7b07 2410 .done = &done,
0e175a18 2411 .reason = WB_REASON_SYNC,
7747bd4b 2412 .for_sync = 1,
3c4d7165 2413 };
e7972912 2414 struct backing_dev_info *bdi = sb->s_bdi;
3c4d7165 2415
006a0973
TH
2416 /*
2417 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
2418 * inodes under writeback and I_DIRTY_TIME inodes ignored by
2419 * bdi_has_dirty() need to be written out too.
2420 */
2421 if (bdi == &noop_backing_dev_info)
6eedc701 2422 return;
cf37e972
CH
2423 WARN_ON(!rwsem_is_locked(&sb->s_umount));
2424
db125360 2425 bdi_split_work_to_wbs(bdi, &work, false);
cc395d7f 2426 wb_wait_for_completion(bdi, &done);
83ba7b07 2427
b6e51316 2428 wait_sb_inodes(sb);
1da177e4 2429}
d8a8559c 2430EXPORT_SYMBOL(sync_inodes_sb);
1da177e4 2431
1da177e4 2432/**
7f04c26d
AA
2433 * write_inode_now - write an inode to disk
2434 * @inode: inode to write to disk
2435 * @sync: whether the write should be synchronous or not
2436 *
2437 * This function commits an inode to disk immediately if it is dirty. This is
2438 * primarily needed by knfsd.
1da177e4 2439 *
7f04c26d 2440 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1da177e4 2441 */
1da177e4
LT
2442int write_inode_now(struct inode *inode, int sync)
2443{
1da177e4
LT
2444 struct writeback_control wbc = {
2445 .nr_to_write = LONG_MAX,
18914b18 2446 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
111ebb6e
OH
2447 .range_start = 0,
2448 .range_end = LLONG_MAX,
1da177e4
LT
2449 };
2450
2451 if (!mapping_cap_writeback_dirty(inode->i_mapping))
49364ce2 2452 wbc.nr_to_write = 0;
1da177e4
LT
2453
2454 might_sleep();
aaf25593 2455 return writeback_single_inode(inode, &wbc);
1da177e4
LT
2456}
2457EXPORT_SYMBOL(write_inode_now);
2458
2459/**
2460 * sync_inode - write an inode and its pages to disk.
2461 * @inode: the inode to sync
2462 * @wbc: controls the writeback mode
2463 *
2464 * sync_inode() will write an inode and its pages to disk. It will also
2465 * correctly update the inode on its superblock's dirty inode lists and will
2466 * update inode->i_state.
2467 *
2468 * The caller must have a ref on the inode.
2469 */
2470int sync_inode(struct inode *inode, struct writeback_control *wbc)
2471{
aaf25593 2472 return writeback_single_inode(inode, wbc);
1da177e4
LT
2473}
2474EXPORT_SYMBOL(sync_inode);
c3765016
CH
2475
2476/**
c691b9d9 2477 * sync_inode_metadata - write an inode to disk
c3765016
CH
2478 * @inode: the inode to sync
2479 * @wait: wait for I/O to complete.
2480 *
c691b9d9 2481 * Write an inode to disk and adjust its dirty state after completion.
c3765016
CH
2482 *
2483 * Note: only writes the actual inode, no associated data or other metadata.
2484 */
2485int sync_inode_metadata(struct inode *inode, int wait)
2486{
2487 struct writeback_control wbc = {
2488 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2489 .nr_to_write = 0, /* metadata-only */
2490 };
2491
2492 return sync_inode(inode, &wbc);
2493}
2494EXPORT_SYMBOL(sync_inode_metadata);