linux - fs/fs-writeback.c

2628 lines · 74.8 KiB

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	*/
42	struct 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	*/
68	unsigned int dirtytime_expire_interval = 12 * 60 * 60;
69
70	static 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
83	EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
84
85	static 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
98	static 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	*/
118	static 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	*/
142	static 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
153	static 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
161	static 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
177	static 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	*/
206	void 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
247	static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
248	static struct workqueue_struct *isw_wq;
249
250	void __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	}
279	EXPORT_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	*/
289	static struct bdi_writeback *
290	locked_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	*/
327	static 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
334	struct 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
342	static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
343	{
344	down_write(&bdi->wb_switch_rwsem);
345	}
346
347	static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
348	{
349	up_write(&bdi->wb_switch_rwsem);
350	}
351
352	static 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;
446	skip_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
472	static 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	*/
490	static 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
542	out_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	*/
558	void 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	}
589	EXPORT_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	*/
628	void 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	}
712	EXPORT_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	*/
724	void 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	}
762	EXPORT_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	*/
780	int 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	}
799	EXPORT_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	*/
810	static 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	*/
840	static 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();
849	restart:
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	*/
919	int 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);
984	out_css_put:
985	css_put(memcg_css);
986	out_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	*/
1001	void 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
1013	static 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	}
1020	fs_initcall(cgroup_writeback_init);
1021
1022	#else /* CONFIG_CGROUP_WRITEBACK */
1023
1024	static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1025	static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1026
1027	static struct bdi_writeback *
1028	locked_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
1039	static 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
1048	static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
1049	{
1050	return nr_pages;
1051	}
1052
1053	static 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	*/
1071	static unsigned long get_nr_dirty_pages(void)
1072	{
1073	return global_node_page_state(NR_FILE_DIRTY) +
1074	get_nr_dirty_inodes();
1075	}
1076
1077	static 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	*/
1108	void 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	*/
1121	void 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	}
1131	EXPORT_SYMBOL(inode_io_list_del);
1132
1133	/*
1134	* mark an inode as under writeback on the sb
1135	*/
1136	void 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	*/
1154	void 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	*/
1178	static 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
1193	static 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	*/
1203	static 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
1208	static 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
1218	static 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	*/
1239	static 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	}
1281	out:
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	*/
1296	static 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
1314	static 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	*/
1331	static 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	*/
1350	void 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	*/
1362	static 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	*/
1385	static 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	*/
1449	static 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	*/
1532	static 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);
1584	out:
1585	spin_unlock(&inode->i_lock);
1586	return ret;
1587	}
1588
1589	static 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	*/
1629	static 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
1771	static 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
1805	static 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	*/
1842	static 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	*/
1938	static 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
1952	static 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
1970	static 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
2004	static 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	*/
2031	static 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	*/
2062	void 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	*/
2106	static 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
2118	void 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	*/
2129	void 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	*/
2160	static void wakeup_dirtytime_writeback(struct work_struct *w);
2161	static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
2162
2163	static 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
2179	static 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
2186	int 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
2197	static 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	*/
2245	void __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((wb->bdi->capabilities & BDI_CAP_WRITEBACK) &&
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 (wakeup_bdi &&
2350	(wb->bdi->capabilities & BDI_CAP_WRITEBACK))
2351	wb_wakeup_delayed(wb);
2352	return;
2353	}
2354	}
2355	out_unlock_inode:
2356	spin_unlock(&inode->i_lock);
2357	}
2358	EXPORT_SYMBOL(__mark_inode_dirty);
2359
2360	/*
2361	* The @s_sync_lock is used to serialise concurrent sync operations
2362	* to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2363	* Concurrent callers will block on the s_sync_lock rather than doing contending
2364	* walks. The queueing maintains sync(2) required behaviour as all the IO that
2365	* has been issued up to the time this function is enter is guaranteed to be
2366	* completed by the time we have gained the lock and waited for all IO that is
2367	* in progress regardless of the order callers are granted the lock.
2368	*/
2369	static void wait_sb_inodes(struct super_block *sb)
2370	{
2371	LIST_HEAD(sync_list);
2372
2373	/*
2374	* We need to be protected against the filesystem going from
2375	* r/o to r/w or vice versa.
2376	*/
2377	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2378
2379	mutex_lock(&sb->s_sync_lock);
2380
2381	/*
2382	* Splice the writeback list onto a temporary list to avoid waiting on
2383	* inodes that have started writeback after this point.
2384	*
2385	* Use rcu_read_lock() to keep the inodes around until we have a
2386	* reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2387	* the local list because inodes can be dropped from either by writeback
2388	* completion.
2389	*/
2390	rcu_read_lock();
2391	spin_lock_irq(&sb->s_inode_wblist_lock);
2392	list_splice_init(&sb->s_inodes_wb, &sync_list);
2393
2394	/*
2395	* Data integrity sync. Must wait for all pages under writeback, because
2396	* there may have been pages dirtied before our sync call, but which had
2397	* writeout started before we write it out. In which case, the inode
2398	* may not be on the dirty list, but we still have to wait for that
2399	* writeout.
2400	*/
2401	while (!list_empty(&sync_list)) {
2402	struct inode *inode = list_first_entry(&sync_list, struct inode,
2403	i_wb_list);
2404	struct address_space *mapping = inode->i_mapping;
2405
2406	/*
2407	* Move each inode back to the wb list before we drop the lock
2408	* to preserve consistency between i_wb_list and the mapping
2409	* writeback tag. Writeback completion is responsible to remove
2410	* the inode from either list once the writeback tag is cleared.
2411	*/
2412	list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
2413
2414	/*
2415	* The mapping can appear untagged while still on-list since we
2416	* do not have the mapping lock. Skip it here, wb completion
2417	* will remove it.
2418	*/
2419	if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2420	continue;
2421
2422	spin_unlock_irq(&sb->s_inode_wblist_lock);
2423
2424	spin_lock(&inode->i_lock);
2425	if (inode->i_state & (I_FREEING\|I_WILL_FREE\|I_NEW)) {
2426	spin_unlock(&inode->i_lock);
2427
2428	spin_lock_irq(&sb->s_inode_wblist_lock);
2429	continue;
2430	}
2431	__iget(inode);
2432	spin_unlock(&inode->i_lock);
2433	rcu_read_unlock();
2434
2435	/*
2436	* We keep the error status of individual mapping so that
2437	* applications can catch the writeback error using fsync(2).
2438	* See filemap_fdatawait_keep_errors() for details.
2439	*/
2440	filemap_fdatawait_keep_errors(mapping);
2441
2442	cond_resched();
2443
2444	iput(inode);
2445
2446	rcu_read_lock();
2447	spin_lock_irq(&sb->s_inode_wblist_lock);
2448	}
2449	spin_unlock_irq(&sb->s_inode_wblist_lock);
2450	rcu_read_unlock();
2451	mutex_unlock(&sb->s_sync_lock);
2452	}
2453
2454	static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2455	enum wb_reason reason, bool skip_if_busy)
2456	{
2457	struct backing_dev_info *bdi = sb->s_bdi;
2458	DEFINE_WB_COMPLETION(done, bdi);
2459	struct wb_writeback_work work = {
2460	.sb = sb,
2461	.sync_mode = WB_SYNC_NONE,
2462	.tagged_writepages = 1,
2463	.done = &done,
2464	.nr_pages = nr,
2465	.reason = reason,
2466	};
2467
2468	if (!bdi_has_dirty_io(bdi) \|\| bdi == &noop_backing_dev_info)
2469	return;
2470	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2471
2472	bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
2473	wb_wait_for_completion(&done);
2474	}
2475
2476	/**
2477	* writeback_inodes_sb_nr - writeback dirty inodes from given super_block
2478	* @sb: the superblock
2479	* @nr: the number of pages to write
2480	* @reason: reason why some writeback work initiated
2481	*
2482	* Start writeback on some inodes on this super_block. No guarantees are made
2483	* on how many (if any) will be written, and this function does not wait
2484	* for IO completion of submitted IO.
2485	*/
2486	void writeback_inodes_sb_nr(struct super_block *sb,
2487	unsigned long nr,
2488	enum wb_reason reason)
2489	{
2490	__writeback_inodes_sb_nr(sb, nr, reason, false);
2491	}
2492	EXPORT_SYMBOL(writeback_inodes_sb_nr);
2493
2494	/**
2495	* writeback_inodes_sb - writeback dirty inodes from given super_block
2496	* @sb: the superblock
2497	* @reason: reason why some writeback work was initiated
2498	*
2499	* Start writeback on some inodes on this super_block. No guarantees are made
2500	* on how many (if any) will be written, and this function does not wait
2501	* for IO completion of submitted IO.
2502	*/
2503	void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2504	{
2505	return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2506	}
2507	EXPORT_SYMBOL(writeback_inodes_sb);
2508
2509	/**
2510	* try_to_writeback_inodes_sb - try to start writeback if none underway
2511	* @sb: the superblock
2512	* @reason: reason why some writeback work was initiated
2513	*
2514	* Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
2515	*/
2516	void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2517	{
2518	if (!down_read_trylock(&sb->s_umount))
2519	return;
2520
2521	__writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason, true);
2522	up_read(&sb->s_umount);
2523	}
2524	EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2525
2526	/**
2527	* sync_inodes_sb - sync sb inode pages
2528	* @sb: the superblock
2529	*
2530	* This function writes and waits on any dirty inode belonging to this
2531	* super_block.
2532	*/
2533	void sync_inodes_sb(struct super_block *sb)
2534	{
2535	struct backing_dev_info *bdi = sb->s_bdi;
2536	DEFINE_WB_COMPLETION(done, bdi);
2537	struct wb_writeback_work work = {
2538	.sb = sb,
2539	.sync_mode = WB_SYNC_ALL,
2540	.nr_pages = LONG_MAX,
2541	.range_cyclic = 0,
2542	.done = &done,
2543	.reason = WB_REASON_SYNC,
2544	.for_sync = 1,
2545	};
2546
2547	/*
2548	* Can't skip on !bdi_has_dirty() because we should wait for !dirty
2549	* inodes under writeback and I_DIRTY_TIME inodes ignored by
2550	* bdi_has_dirty() need to be written out too.
2551	*/
2552	if (bdi == &noop_backing_dev_info)
2553	return;
2554	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2555
2556	/* protect against inode wb switch, see inode_switch_wbs_work_fn() */
2557	bdi_down_write_wb_switch_rwsem(bdi);
2558	bdi_split_work_to_wbs(bdi, &work, false);
2559	wb_wait_for_completion(&done);
2560	bdi_up_write_wb_switch_rwsem(bdi);
2561
2562	wait_sb_inodes(sb);
2563	}
2564	EXPORT_SYMBOL(sync_inodes_sb);
2565
2566	/**
2567	* write_inode_now - write an inode to disk
2568	* @inode: inode to write to disk
2569	* @sync: whether the write should be synchronous or not
2570	*
2571	* This function commits an inode to disk immediately if it is dirty. This is
2572	* primarily needed by knfsd.
2573	*
2574	* The caller must either have a ref on the inode or must have set I_WILL_FREE.
2575	*/
2576	int write_inode_now(struct inode *inode, int sync)
2577	{
2578	struct writeback_control wbc = {
2579	.nr_to_write = LONG_MAX,
2580	.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2581	.range_start = 0,
2582	.range_end = LLONG_MAX,
2583	};
2584
2585	if (!mapping_can_writeback(inode->i_mapping))
2586	wbc.nr_to_write = 0;
2587
2588	might_sleep();
2589	return writeback_single_inode(inode, &wbc);
2590	}
2591	EXPORT_SYMBOL(write_inode_now);
2592
2593	/**
2594	* sync_inode - write an inode and its pages to disk.
2595	* @inode: the inode to sync
2596	* @wbc: controls the writeback mode
2597	*
2598	* sync_inode() will write an inode and its pages to disk. It will also
2599	* correctly update the inode on its superblock's dirty inode lists and will
2600	* update inode->i_state.
2601	*
2602	* The caller must have a ref on the inode.
2603	*/
2604	int sync_inode(struct inode inode, struct writeback_control wbc)
2605	{
2606	return writeback_single_inode(inode, wbc);
2607	}
2608	EXPORT_SYMBOL(sync_inode);
2609
2610	/**
2611	* sync_inode_metadata - write an inode to disk
2612	* @inode: the inode to sync
2613	* @wait: wait for I/O to complete.
2614	*
2615	* Write an inode to disk and adjust its dirty state after completion.
2616	*
2617	* Note: only writes the actual inode, no associated data or other metadata.
2618	*/
2619	int sync_inode_metadata(struct inode *inode, int wait)
2620	{
2621	struct writeback_control wbc = {
2622	.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2623	.nr_to_write = 0, /* metadata-only */
2624	};
2625
2626	return sync_inode(inode, &wbc);
2627	}
2628	EXPORT_SYMBOL(sync_inode_metadata);