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Root/mm/page-writeback.c

1	/*
2	* mm/page-writeback.c
3	*
4	* Copyright (C) 2002, Linus Torvalds.
5	* Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
6	*
7	* Contains functions related to writing back dirty pages at the
8	* address_space level.
9	*
10	* 10Apr2002 Andrew Morton
11	* Initial version
12	*/
13
14	#include <linux/kernel.h>
15	#include <linux/export.h>
16	#include <linux/spinlock.h>
17	#include <linux/fs.h>
18	#include <linux/mm.h>
19	#include <linux/swap.h>
20	#include <linux/slab.h>
21	#include <linux/pagemap.h>
22	#include <linux/writeback.h>
23	#include <linux/init.h>
24	#include <linux/backing-dev.h>
25	#include <linux/task_io_accounting_ops.h>
26	#include <linux/blkdev.h>
27	#include <linux/mpage.h>
28	#include <linux/rmap.h>
29	#include <linux/percpu.h>
30	#include <linux/notifier.h>
31	#include <linux/smp.h>
32	#include <linux/sysctl.h>
33	#include <linux/cpu.h>
34	#include <linux/syscalls.h>
35	#include <linux/buffer_head.h> /* __set_page_dirty_buffers */
36	#include <linux/pagevec.h>
37	#include <linux/timer.h>
38	#include <linux/sched/rt.h>
39	#include <linux/mm_inline.h>
40	#include <trace/events/writeback.h>
41
42	#include "internal.h"
43
44	/*
45	* Sleep at most 200ms at a time in balance_dirty_pages().
46	*/
47	#define MAX_PAUSE max(HZ/5, 1)
48
49	/*
50	* Try to keep balance_dirty_pages() call intervals higher than this many pages
51	* by raising pause time to max_pause when falls below it.
52	*/
53	#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
54
55	/*
56	* Estimate write bandwidth at 200ms intervals.
57	*/
58	#define BANDWIDTH_INTERVAL max(HZ/5, 1)
59
60	#define RATELIMIT_CALC_SHIFT 10
61
62	/*
63	* After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
64	* will look to see if it needs to force writeback or throttling.
65	*/
66	static long ratelimit_pages = 32;
67
68	/* The following parameters are exported via /proc/sys/vm */
69
70	/*
71	* Start background writeback (via writeback threads) at this percentage
72	*/
73	int dirty_background_ratio = 10;
74
75	/*
76	* dirty_background_bytes starts at 0 (disabled) so that it is a function of
77	* dirty_background_ratio * the amount of dirtyable memory
78	*/
79	unsigned long dirty_background_bytes;
80
81	/*
82	* free highmem will not be subtracted from the total free memory
83	* for calculating free ratios if vm_highmem_is_dirtyable is true
84	*/
85	int vm_highmem_is_dirtyable;
86
87	/*
88	* The generator of dirty data starts writeback at this percentage
89	*/
90	int vm_dirty_ratio = 20;
91
92	/*
93	* vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94	* vm_dirty_ratio * the amount of dirtyable memory
95	*/
96	unsigned long vm_dirty_bytes;
97
98	/*
99	* The interval between `kupdate'-style writebacks
100	*/
101	unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
102
103	EXPORT_SYMBOL_GPL(dirty_writeback_interval);
104
105	/*
106	* The longest time for which data is allowed to remain dirty
107	*/
108	unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
109
110	/*
111	* Flag that makes the machine dump writes/reads and block dirtyings.
112	*/
113	int block_dump;
114
115	/*
116	* Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
117	* a full sync is triggered after this time elapses without any disk activity.
118	*/
119	int laptop_mode;
120
121	EXPORT_SYMBOL(laptop_mode);
122
123	/* End of sysctl-exported parameters */
124
125	unsigned long global_dirty_limit;
126
127	/*
128	* Scale the writeback cache size proportional to the relative writeout speeds.
129	*
130	* We do this by keeping a floating proportion between BDIs, based on page
131	* writeback completions [end_page_writeback()]. Those devices that write out
132	* pages fastest will get the larger share, while the slower will get a smaller
133	* share.
134	*
135	* We use page writeout completions because we are interested in getting rid of
136	* dirty pages. Having them written out is the primary goal.
137	*
138	* We introduce a concept of time, a period over which we measure these events,
139	* because demand can/will vary over time. The length of this period itself is
140	* measured in page writeback completions.
141	*
142	*/
143	static struct fprop_global writeout_completions;
144
145	static void writeout_period(unsigned long t);
146	/* Timer for aging of writeout_completions */
147	static struct timer_list writeout_period_timer =
148	TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0);
149	static unsigned long writeout_period_time = 0;
150
151	/*
152	* Length of period for aging writeout fractions of bdis. This is an
153	* arbitrarily chosen number. The longer the period, the slower fractions will
154	* reflect changes in current writeout rate.
155	*/
156	#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
157
158	/*
159	* Work out the current dirty-memory clamping and background writeout
160	* thresholds.
161	*
162	* The main aim here is to lower them aggressively if there is a lot of mapped
163	* memory around. To avoid stressing page reclaim with lots of unreclaimable
164	* pages. It is better to clamp down on writers than to start swapping, and
165	* performing lots of scanning.
166	*
167	* We only allow 1/2 of the currently-unmapped memory to be dirtied.
168	*
169	* We don't permit the clamping level to fall below 5% - that is getting rather
170	* excessive.
171	*
172	* We make sure that the background writeout level is below the adjusted
173	* clamping level.
174	*/
175
176	/*
177	* In a memory zone, there is a certain amount of pages we consider
178	* available for the page cache, which is essentially the number of
179	* free and reclaimable pages, minus some zone reserves to protect
180	* lowmem and the ability to uphold the zone's watermarks without
181	* requiring writeback.
182	*
183	* This number of dirtyable pages is the base value of which the
184	* user-configurable dirty ratio is the effictive number of pages that
185	* are allowed to be actually dirtied. Per individual zone, or
186	* globally by using the sum of dirtyable pages over all zones.
187	*
188	* Because the user is allowed to specify the dirty limit globally as
189	* absolute number of bytes, calculating the per-zone dirty limit can
190	* require translating the configured limit into a percentage of
191	* global dirtyable memory first.
192	*/
193
194	static unsigned long highmem_dirtyable_memory(unsigned long total)
195	{
196	#ifdef CONFIG_HIGHMEM
197	int node;
198	unsigned long x = 0;
199
200	for_each_node_state(node, N_HIGH_MEMORY) {
201	struct zone *z =
202	&NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
203
204	x += zone_page_state(z, NR_FREE_PAGES) +
205	zone_reclaimable_pages(z) - z->dirty_balance_reserve;
206	}
207	/*
208	* Unreclaimable memory (kernel memory or anonymous memory
209	* without swap) can bring down the dirtyable pages below
210	* the zone's dirty balance reserve and the above calculation
211	* will underflow. However we still want to add in nodes
212	* which are below threshold (negative values) to get a more
213	* accurate calculation but make sure that the total never
214	* underflows.
215	*/
216	if ((long)x < 0)
217	x = 0;
218
219	/*
220	* Make sure that the number of highmem pages is never larger
221	* than the number of the total dirtyable memory. This can only
222	* occur in very strange VM situations but we want to make sure
223	* that this does not occur.
224	*/
225	return min(x, total);
226	#else
227	return 0;
228	#endif
229	}
230
231	/**
232	* global_dirtyable_memory - number of globally dirtyable pages
233	*
234	* Returns the global number of pages potentially available for dirty
235	* page cache. This is the base value for the global dirty limits.
236	*/
237	static unsigned long global_dirtyable_memory(void)
238	{
239	unsigned long x;
240
241	x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
242	x -= min(x, dirty_balance_reserve);
243
244	if (!vm_highmem_is_dirtyable)
245	x -= highmem_dirtyable_memory(x);
246
247	return x + 1; /* Ensure that we never return 0 */
248	}
249
250	/*
251	* global_dirty_limits - background-writeback and dirty-throttling thresholds
252	*
253	* Calculate the dirty thresholds based on sysctl parameters
254	* - vm.dirty_background_ratio or vm.dirty_background_bytes
255	* - vm.dirty_ratio or vm.dirty_bytes
256	* The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
257	* real-time tasks.
258	*/
259	void global_dirty_limits(unsigned long pbackground, unsigned long pdirty)
260	{
261	unsigned long background;
262	unsigned long dirty;
263	unsigned long uninitialized_var(available_memory);
264	struct task_struct *tsk;
265
266	if (!vm_dirty_bytes \|\| !dirty_background_bytes)
267	available_memory = global_dirtyable_memory();
268
269	if (vm_dirty_bytes)
270	dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
271	else
272	dirty = (vm_dirty_ratio * available_memory) / 100;
273
274	if (dirty_background_bytes)
275	background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
276	else
277	background = (dirty_background_ratio * available_memory) / 100;
278
279	if (background >= dirty)
280	background = dirty / 2;
281	tsk = current;
282	if (tsk->flags & PF_LESS_THROTTLE \|\| rt_task(tsk)) {
283	background += background / 4;
284	dirty += dirty / 4;
285	}
286	*pbackground = background;
287	*pdirty = dirty;
288	trace_global_dirty_state(background, dirty);
289	}
290
291	/**
292	* zone_dirtyable_memory - number of dirtyable pages in a zone
293	* @zone: the zone
294	*
295	* Returns the zone's number of pages potentially available for dirty
296	* page cache. This is the base value for the per-zone dirty limits.
297	*/
298	static unsigned long zone_dirtyable_memory(struct zone *zone)
299	{
300	/*
301	* The effective global number of dirtyable pages may exclude
302	* highmem as a big-picture measure to keep the ratio between
303	* dirty memory and lowmem reasonable.
304	*
305	* But this function is purely about the individual zone and a
306	* highmem zone can hold its share of dirty pages, so we don't
307	* care about vm_highmem_is_dirtyable here.
308	*/
309	unsigned long nr_pages = zone_page_state(zone, NR_FREE_PAGES) +
310	zone_reclaimable_pages(zone);
311
312	/* don't allow this to underflow */
313	nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
314	return nr_pages;
315	}
316
317	/**
318	* zone_dirty_limit - maximum number of dirty pages allowed in a zone
319	* @zone: the zone
320	*
321	* Returns the maximum number of dirty pages allowed in a zone, based
322	* on the zone's dirtyable memory.
323	*/
324	static unsigned long zone_dirty_limit(struct zone *zone)
325	{
326	unsigned long zone_memory = zone_dirtyable_memory(zone);
327	struct task_struct *tsk = current;
328	unsigned long dirty;
329
330	if (vm_dirty_bytes)
331	dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
332	zone_memory / global_dirtyable_memory();
333	else
334	dirty = vm_dirty_ratio * zone_memory / 100;
335
336	if (tsk->flags & PF_LESS_THROTTLE \|\| rt_task(tsk))
337	dirty += dirty / 4;
338
339	return dirty;
340	}
341
342	/**
343	* zone_dirty_ok - tells whether a zone is within its dirty limits
344	* @zone: the zone to check
345	*
346	* Returns %true when the dirty pages in @zone are within the zone's
347	* dirty limit, %false if the limit is exceeded.
348	*/
349	bool zone_dirty_ok(struct zone *zone)
350	{
351	unsigned long limit = zone_dirty_limit(zone);
352
353	return zone_page_state(zone, NR_FILE_DIRTY) +
354	zone_page_state(zone, NR_UNSTABLE_NFS) +
355	zone_page_state(zone, NR_WRITEBACK) <= limit;
356	}
357
358	int dirty_background_ratio_handler(struct ctl_table *table, int write,
359	void __user buffer, size_t lenp,
360	loff_t *ppos)
361	{
362	int ret;
363
364	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
365	if (ret == 0 && write)
366	dirty_background_bytes = 0;
367	return ret;
368	}
369
370	int dirty_background_bytes_handler(struct ctl_table *table, int write,
371	void __user buffer, size_t lenp,
372	loff_t *ppos)
373	{
374	int ret;
375
376	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
377	if (ret == 0 && write)
378	dirty_background_ratio = 0;
379	return ret;
380	}
381
382	int dirty_ratio_handler(struct ctl_table *table, int write,
383	void __user buffer, size_t lenp,
384	loff_t *ppos)
385	{
386	int old_ratio = vm_dirty_ratio;
387	int ret;
388
389	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
390	if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
391	writeback_set_ratelimit();
392	vm_dirty_bytes = 0;
393	}
394	return ret;
395	}
396
397	int dirty_bytes_handler(struct ctl_table *table, int write,
398	void __user buffer, size_t lenp,
399	loff_t *ppos)
400	{
401	unsigned long old_bytes = vm_dirty_bytes;
402	int ret;
403
404	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
405	if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
406	writeback_set_ratelimit();
407	vm_dirty_ratio = 0;
408	}
409	return ret;
410	}
411
412	static unsigned long wp_next_time(unsigned long cur_time)
413	{
414	cur_time += VM_COMPLETIONS_PERIOD_LEN;
415	/* 0 has a special meaning... */
416	if (!cur_time)
417	return 1;
418	return cur_time;
419	}
420
421	/*
422	* Increment the BDI's writeout completion count and the global writeout
423	* completion count. Called from test_clear_page_writeback().
424	*/
425	static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
426	{
427	__inc_bdi_stat(bdi, BDI_WRITTEN);
428	__fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
429	bdi->max_prop_frac);
430	/* First event after period switching was turned off? */
431	if (!unlikely(writeout_period_time)) {
432	/*
433	* We can race with other __bdi_writeout_inc calls here but
434	* it does not cause any harm since the resulting time when
435	* timer will fire and what is in writeout_period_time will be
436	* roughly the same.
437	*/
438	writeout_period_time = wp_next_time(jiffies);
439	mod_timer(&writeout_period_timer, writeout_period_time);
440	}
441	}
442
443	void bdi_writeout_inc(struct backing_dev_info *bdi)
444	{
445	unsigned long flags;
446
447	local_irq_save(flags);
448	__bdi_writeout_inc(bdi);
449	local_irq_restore(flags);
450	}
451	EXPORT_SYMBOL_GPL(bdi_writeout_inc);
452
453	/*
454	* Obtain an accurate fraction of the BDI's portion.
455	*/
456	static void bdi_writeout_fraction(struct backing_dev_info *bdi,
457	long numerator, long denominator)
458	{
459	fprop_fraction_percpu(&writeout_completions, &bdi->completions,
460	numerator, denominator);
461	}
462
463	/*
464	* On idle system, we can be called long after we scheduled because we use
465	* deferred timers so count with missed periods.
466	*/
467	static void writeout_period(unsigned long t)
468	{
469	int miss_periods = (jiffies - writeout_period_time) /
470	VM_COMPLETIONS_PERIOD_LEN;
471
472	if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
473	writeout_period_time = wp_next_time(writeout_period_time +
474	miss_periods * VM_COMPLETIONS_PERIOD_LEN);
475	mod_timer(&writeout_period_timer, writeout_period_time);
476	} else {
477	/*
478	* Aging has zeroed all fractions. Stop wasting CPU on period
479	* updates.
480	*/
481	writeout_period_time = 0;
482	}
483	}
484
485	/*
486	* bdi_min_ratio keeps the sum of the minimum dirty shares of all
487	* registered backing devices, which, for obvious reasons, can not
488	* exceed 100%.
489	*/
490	static unsigned int bdi_min_ratio;
491
492	int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
493	{
494	int ret = 0;
495
496	spin_lock_bh(&bdi_lock);
497	if (min_ratio > bdi->max_ratio) {
498	ret = -EINVAL;
499	} else {
500	min_ratio -= bdi->min_ratio;
501	if (bdi_min_ratio + min_ratio < 100) {
502	bdi_min_ratio += min_ratio;
503	bdi->min_ratio += min_ratio;
504	} else {
505	ret = -EINVAL;
506	}
507	}
508	spin_unlock_bh(&bdi_lock);
509
510	return ret;
511	}
512
513	int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
514	{
515	int ret = 0;
516
517	if (max_ratio > 100)
518	return -EINVAL;
519
520	spin_lock_bh(&bdi_lock);
521	if (bdi->min_ratio > max_ratio) {
522	ret = -EINVAL;
523	} else {
524	bdi->max_ratio = max_ratio;
525	bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
526	}
527	spin_unlock_bh(&bdi_lock);
528
529	return ret;
530	}
531	EXPORT_SYMBOL(bdi_set_max_ratio);
532
533	static unsigned long dirty_freerun_ceiling(unsigned long thresh,
534	unsigned long bg_thresh)
535	{
536	return (thresh + bg_thresh) / 2;
537	}
538
539	static unsigned long hard_dirty_limit(unsigned long thresh)
540	{
541	return max(thresh, global_dirty_limit);
542	}
543
544	/**
545	* bdi_dirty_limit - @bdi's share of dirty throttling threshold
546	* @bdi: the backing_dev_info to query
547	* @dirty: global dirty limit in pages
548	*
549	* Returns @bdi's dirty limit in pages. The term "dirty" in the context of
550	* dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
551	*
552	* Note that balance_dirty_pages() will only seriously take it as a hard limit
553	* when sleeping max_pause per page is not enough to keep the dirty pages under
554	* control. For example, when the device is completely stalled due to some error
555	* conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
556	* In the other normal situations, it acts more gently by throttling the tasks
557	* more (rather than completely block them) when the bdi dirty pages go high.
558	*
559	* It allocates high/low dirty limits to fast/slow devices, in order to prevent
560	* - starving fast devices
561	* - piling up dirty pages (that will take long time to sync) on slow devices
562	*
563	* The bdi's share of dirty limit will be adapting to its throughput and
564	* bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
565	*/
566	unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
567	{
568	u64 bdi_dirty;
569	long numerator, denominator;
570
571	/*
572	* Calculate this BDI's share of the dirty ratio.
573	*/
574	bdi_writeout_fraction(bdi, &numerator, &denominator);
575
576	bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
577	bdi_dirty *= numerator;
578	do_div(bdi_dirty, denominator);
579
580	bdi_dirty += (dirty * bdi->min_ratio) / 100;
581	if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
582	bdi_dirty = dirty * bdi->max_ratio / 100;
583
584	return bdi_dirty;
585	}
586
587	/*
588	* setpoint - dirty 3
589	* f(dirty) := 1.0 + (----------------)
590	* limit - setpoint
591	*
592	* it's a 3rd order polynomial that subjects to
593	*
594	* (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
595	* (2) f(setpoint) = 1.0 => the balance point
596	* (3) f(limit) = 0 => the hard limit
597	* (4) df/dx <= 0 => negative feedback control
598	* (5) the closer to setpoint, the smaller \|df/dx\| (and the reverse)
599	* => fast response on large errors; small oscillation near setpoint
600	*/
601	static inline long long pos_ratio_polynom(unsigned long setpoint,
602	unsigned long dirty,
603	unsigned long limit)
604	{
605	long long pos_ratio;
606	long x;
607
608	x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
609	limit - setpoint + 1);
610	pos_ratio = x;
611	pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
612	pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
613	pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
614
615	return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
616	}
617
618	/*
619	* Dirty position control.
620	*
621	* (o) global/bdi setpoints
622	*
623	* We want the dirty pages be balanced around the global/bdi setpoints.
624	* When the number of dirty pages is higher/lower than the setpoint, the
625	* dirty position control ratio (and hence task dirty ratelimit) will be
626	* decreased/increased to bring the dirty pages back to the setpoint.
627	*
628	* pos_ratio = 1 << RATELIMIT_CALC_SHIFT
629	*
630	* if (dirty < setpoint) scale up pos_ratio
631	* if (dirty > setpoint) scale down pos_ratio
632	*
633	* if (bdi_dirty < bdi_setpoint) scale up pos_ratio
634	* if (bdi_dirty > bdi_setpoint) scale down pos_ratio
635	*
636	* task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
637	*
638	* (o) global control line
639	*
640	* ^ pos_ratio
641	* \|
642	* \| \|<===== global dirty control scope ======>\|
643	* 2.0 .............*
644	* \| .*
645	* \| . *
646	* \| . *
647	* \| . *
648	* \| . *
649	* \| . *
650	* 1.0 ................................*
651	* \| . . *
652	* \| . . *
653	* \| . . *
654	* \| . . *
655	* \| . . *
656	* 0 +------------.------------------.----------------------*------------->
657	* freerun^ setpoint^ limit^ dirty pages
658	*
659	* (o) bdi control line
660	*
661	* ^ pos_ratio
662	* \|
663	* \| *
664	* \| *
665	* \| *
666	* \| *
667	* \| * \|<=========== span ============>\|
668	* 1.0 .......................*
669	* \| . *
670	* \| . *
671	* \| . *
672	* \| . *
673	* \| . *
674	* \| . *
675	* \| . *
676	* \| . *
677	* \| . *
678	* \| . *
679	* \| . *
680	* 1/4 ...............................................* * * * * * * * * * * *
681	* \| . .
682	* \| . .
683	* \| . .
684	* 0 +----------------------.-------------------------------.------------->
685	* bdi_setpoint^ x_intercept^
686	*
687	* The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
688	* be smoothly throttled down to normal if it starts high in situations like
689	* - start writing to a slow SD card and a fast disk at the same time. The SD
690	* card's bdi_dirty may rush to many times higher than bdi_setpoint.
691	* - the bdi dirty thresh drops quickly due to change of JBOD workload
692	*/
693	static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
694	unsigned long thresh,
695	unsigned long bg_thresh,
696	unsigned long dirty,
697	unsigned long bdi_thresh,
698	unsigned long bdi_dirty)
699	{
700	unsigned long write_bw = bdi->avg_write_bandwidth;
701	unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
702	unsigned long limit = hard_dirty_limit(thresh);
703	unsigned long x_intercept;
704	unsigned long setpoint; /* dirty pages' target balance point */
705	unsigned long bdi_setpoint;
706	unsigned long span;
707	long long pos_ratio; /* for scaling up/down the rate limit */
708	long x;
709
710	if (unlikely(dirty >= limit))
711	return 0;
712
713	/*
714	* global setpoint
715	*
716	* See comment for pos_ratio_polynom().
717	*/
718	setpoint = (freerun + limit) / 2;
719	pos_ratio = pos_ratio_polynom(setpoint, dirty, limit);
720
721	/*
722	* The strictlimit feature is a tool preventing mistrusted filesystems
723	* from growing a large number of dirty pages before throttling. For
724	* such filesystems balance_dirty_pages always checks bdi counters
725	* against bdi limits. Even if global "nr_dirty" is under "freerun".
726	* This is especially important for fuse which sets bdi->max_ratio to
727	* 1% by default. Without strictlimit feature, fuse writeback may
728	* consume arbitrary amount of RAM because it is accounted in
729	* NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
730	*
731	* Here, in bdi_position_ratio(), we calculate pos_ratio based on
732	* two values: bdi_dirty and bdi_thresh. Let's consider an example:
733	* total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
734	* limits are set by default to 10% and 20% (background and throttle).
735	* Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
736	* bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
737	* about ~6K pages (as the average of background and throttle bdi
738	* limits). The 3rd order polynomial will provide positive feedback if
739	* bdi_dirty is under bdi_setpoint and vice versa.
740	*
741	* Note, that we cannot use global counters in these calculations
742	* because we want to throttle process writing to a strictlimit BDI
743	* much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
744	* in the example above).
745	*/
746	if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
747	long long bdi_pos_ratio;
748	unsigned long bdi_bg_thresh;
749
750	if (bdi_dirty < 8)
751	return min_t(long long, pos_ratio * 2,
752	2 << RATELIMIT_CALC_SHIFT);
753
754	if (bdi_dirty >= bdi_thresh)
755	return 0;
756
757	bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh);
758	bdi_setpoint = dirty_freerun_ceiling(bdi_thresh,
759	bdi_bg_thresh);
760
761	if (bdi_setpoint == 0 \|\| bdi_setpoint == bdi_thresh)
762	return 0;
763
764	bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
765	bdi_thresh);
766
767	/*
768	* Typically, for strictlimit case, bdi_setpoint << setpoint
769	* and pos_ratio >> bdi_pos_ratio. In the other words global
770	* state ("dirty") is not limiting factor and we have to
771	* make decision based on bdi counters. But there is an
772	* important case when global pos_ratio should get precedence:
773	* global limits are exceeded (e.g. due to activities on other
774	* BDIs) while given strictlimit BDI is below limit.
775	*
776	* "pos_ratio * bdi_pos_ratio" would work for the case above,
777	* but it would look too non-natural for the case of all
778	* activity in the system coming from a single strictlimit BDI
779	* with bdi->max_ratio == 100%.
780	*
781	* Note that min() below somewhat changes the dynamics of the
782	* control system. Normally, pos_ratio value can be well over 3
783	* (when globally we are at freerun and bdi is well below bdi
784	* setpoint). Now the maximum pos_ratio in the same situation
785	* is 2. We might want to tweak this if we observe the control
786	* system is too slow to adapt.
787	*/
788	return min(pos_ratio, bdi_pos_ratio);
789	}
790
791	/*
792	* We have computed basic pos_ratio above based on global situation. If
793	* the bdi is over/under its share of dirty pages, we want to scale
794	* pos_ratio further down/up. That is done by the following mechanism.
795	*/
796
797	/*
798	* bdi setpoint
799	*
800	* f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
801	*
802	* x_intercept - bdi_dirty
803	* := --------------------------
804	* x_intercept - bdi_setpoint
805	*
806	* The main bdi control line is a linear function that subjects to
807	*
808	* (1) f(bdi_setpoint) = 1.0
809	* (2) k = - 1 / (8 * write_bw) (in single bdi case)
810	* or equally: x_intercept = bdi_setpoint + 8 * write_bw
811	*
812	* For single bdi case, the dirty pages are observed to fluctuate
813	* regularly within range
814	* [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
815	* for various filesystems, where (2) can yield in a reasonable 12.5%
816	* fluctuation range for pos_ratio.
817	*
818	* For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
819	* own size, so move the slope over accordingly and choose a slope that
820	* yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
821	*/
822	if (unlikely(bdi_thresh > thresh))
823	bdi_thresh = thresh;
824	/*
825	* It's very possible that bdi_thresh is close to 0 not because the
826	* device is slow, but that it has remained inactive for long time.
827	* Honour such devices a reasonable good (hopefully IO efficient)
828	* threshold, so that the occasional writes won't be blocked and active
829	* writes can rampup the threshold quickly.
830	*/
831	bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
832	/*
833	* scale global setpoint to bdi's:
834	* bdi_setpoint = setpoint * bdi_thresh / thresh
835	*/
836	x = div_u64((u64)bdi_thresh << 16, thresh + 1);
837	bdi_setpoint = setpoint * (u64)x >> 16;
838	/*
839	* Use span=(8*write_bw) in single bdi case as indicated by
840	* (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
841	*
842	* bdi_thresh thresh - bdi_thresh
843	* span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
844	* thresh thresh
845	*/
846	span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
847	x_intercept = bdi_setpoint + span;
848
849	if (bdi_dirty < x_intercept - span / 4) {
850	pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
851	x_intercept - bdi_setpoint + 1);
852	} else
853	pos_ratio /= 4;
854
855	/*
856	* bdi reserve area, safeguard against dirty pool underrun and disk idle
857	* It may push the desired control point of global dirty pages higher
858	* than setpoint.
859	*/
860	x_intercept = bdi_thresh / 2;
861	if (bdi_dirty < x_intercept) {
862	if (bdi_dirty > x_intercept / 8)
863	pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
864	else
865	pos_ratio *= 8;
866	}
867
868	return pos_ratio;
869	}
870
871	static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
872	unsigned long elapsed,
873	unsigned long written)
874	{
875	const unsigned long period = roundup_pow_of_two(3 * HZ);
876	unsigned long avg = bdi->avg_write_bandwidth;
877	unsigned long old = bdi->write_bandwidth;
878	u64 bw;
879
880	/*
881	* bw = written * HZ / elapsed
882	*
883	* bw * elapsed + write_bandwidth * (period - elapsed)
884	* write_bandwidth = ---------------------------------------------------
885	* period
886	*/
887	bw = written - bdi->written_stamp;
888	bw *= HZ;
889	if (unlikely(elapsed > period)) {
890	do_div(bw, elapsed);
891	avg = bw;
892	goto out;
893	}
894	bw += (u64)bdi->write_bandwidth * (period - elapsed);
895	bw >>= ilog2(period);
896
897	/*
898	* one more level of smoothing, for filtering out sudden spikes
899	*/
900	if (avg > old && old >= (unsigned long)bw)
901	avg -= (avg - old) >> 3;
902
903	if (avg < old && old <= (unsigned long)bw)
904	avg += (old - avg) >> 3;
905
906	out:
907	bdi->write_bandwidth = bw;
908	bdi->avg_write_bandwidth = avg;
909	}
910
911	/*
912	* The global dirtyable memory and dirty threshold could be suddenly knocked
913	* down by a large amount (eg. on the startup of KVM in a swapless system).
914	* This may throw the system into deep dirty exceeded state and throttle
915	* heavy/light dirtiers alike. To retain good responsiveness, maintain
916	* global_dirty_limit for tracking slowly down to the knocked down dirty
917	* threshold.
918	*/
919	static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
920	{
921	unsigned long limit = global_dirty_limit;
922
923	/*
924	* Follow up in one step.
925	*/
926	if (limit < thresh) {
927	limit = thresh;
928	goto update;
929	}
930
931	/*
932	* Follow down slowly. Use the higher one as the target, because thresh
933	* may drop below dirty. This is exactly the reason to introduce
934	* global_dirty_limit which is guaranteed to lie above the dirty pages.
935	*/
936	thresh = max(thresh, dirty);
937	if (limit > thresh) {
938	limit -= (limit - thresh) >> 5;
939	goto update;
940	}
941	return;
942	update:
943	global_dirty_limit = limit;
944	}
945
946	static void global_update_bandwidth(unsigned long thresh,
947	unsigned long dirty,
948	unsigned long now)
949	{
950	static DEFINE_SPINLOCK(dirty_lock);
951	static unsigned long update_time;
952
953	/*
954	* check locklessly first to optimize away locking for the most time
955	*/
956	if (time_before(now, update_time + BANDWIDTH_INTERVAL))
957	return;
958
959	spin_lock(&dirty_lock);
960	if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
961	update_dirty_limit(thresh, dirty);
962	update_time = now;
963	}
964	spin_unlock(&dirty_lock);
965	}
966
967	/*
968	* Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
969	*
970	* Normal bdi tasks will be curbed at or below it in long term.
971	* Obviously it should be around (write_bw / N) when there are N dd tasks.
972	*/
973	static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
974	unsigned long thresh,
975	unsigned long bg_thresh,
976	unsigned long dirty,
977	unsigned long bdi_thresh,
978	unsigned long bdi_dirty,
979	unsigned long dirtied,
980	unsigned long elapsed)
981	{
982	unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
983	unsigned long limit = hard_dirty_limit(thresh);
984	unsigned long setpoint = (freerun + limit) / 2;
985	unsigned long write_bw = bdi->avg_write_bandwidth;
986	unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
987	unsigned long dirty_rate;
988	unsigned long task_ratelimit;
989	unsigned long balanced_dirty_ratelimit;
990	unsigned long pos_ratio;
991	unsigned long step;
992	unsigned long x;
993
994	/*
995	* The dirty rate will match the writeout rate in long term, except
996	* when dirty pages are truncated by userspace or re-dirtied by FS.
997	*/
998	dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
999
1000	pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
1001	bdi_thresh, bdi_dirty);
1002	/*
1003	* task_ratelimit reflects each dd's dirty rate for the past 200ms.
1004	*/
1005	task_ratelimit = (u64)dirty_ratelimit *
1006	pos_ratio >> RATELIMIT_CALC_SHIFT;
1007	task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1008
1009	/*
1010	* A linear estimation of the "balanced" throttle rate. The theory is,
1011	* if there are N dd tasks, each throttled at task_ratelimit, the bdi's
1012	* dirty_rate will be measured to be (N * task_ratelimit). So the below
1013	* formula will yield the balanced rate limit (write_bw / N).
1014	*
1015	* Note that the expanded form is not a pure rate feedback:
1016	* rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1017	* but also takes pos_ratio into account:
1018	* rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1019	*
1020	* (1) is not realistic because pos_ratio also takes part in balancing
1021	* the dirty rate. Consider the state
1022	* pos_ratio = 0.5 (3)
1023	* rate = 2 * (write_bw / N) (4)
1024	* If (1) is used, it will stuck in that state! Because each dd will
1025	* be throttled at
1026	* task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1027	* yielding
1028	* dirty_rate = N * task_ratelimit = write_bw (6)
1029	* put (6) into (1) we get
1030	* rate_(i+1) = rate_(i) (7)
1031	*
1032	* So we end up using (2) to always keep
1033	* rate_(i+1) ~= (write_bw / N) (8)
1034	* regardless of the value of pos_ratio. As long as (8) is satisfied,
1035	* pos_ratio is able to drive itself to 1.0, which is not only where
1036	* the dirty count meet the setpoint, but also where the slope of
1037	* pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1038	*/
1039	balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1040	dirty_rate \| 1);
1041	/*
1042	* balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1043	*/
1044	if (unlikely(balanced_dirty_ratelimit > write_bw))
1045	balanced_dirty_ratelimit = write_bw;
1046
1047	/*
1048	* We could safely do this and return immediately:
1049	*
1050	* bdi->dirty_ratelimit = balanced_dirty_ratelimit;
1051	*
1052	* However to get a more stable dirty_ratelimit, the below elaborated
1053	* code makes use of task_ratelimit to filter out singular points and
1054	* limit the step size.
1055	*
1056	* The below code essentially only uses the relative value of
1057	*
1058	* task_ratelimit - dirty_ratelimit
1059	* = (pos_ratio - 1) * dirty_ratelimit
1060	*
1061	* which reflects the direction and size of dirty position error.
1062	*/
1063
1064	/*
1065	* dirty_ratelimit will follow balanced_dirty_ratelimit iff
1066	* task_ratelimit is on the same side of dirty_ratelimit, too.
1067	* For example, when
1068	* - dirty_ratelimit > balanced_dirty_ratelimit
1069	* - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1070	* lowering dirty_ratelimit will help meet both the position and rate
1071	* control targets. Otherwise, don't update dirty_ratelimit if it will
1072	* only help meet the rate target. After all, what the users ultimately
1073	* feel and care are stable dirty rate and small position error.
1074	*
1075	* \|task_ratelimit - dirty_ratelimit\| is used to limit the step size
1076	* and filter out the singular points of balanced_dirty_ratelimit. Which
1077	* keeps jumping around randomly and can even leap far away at times
1078	* due to the small 200ms estimation period of dirty_rate (we want to
1079	* keep that period small to reduce time lags).
1080	*/
1081	step = 0;
1082
1083	/*
1084	* For strictlimit case, calculations above were based on bdi counters
1085	* and limits (starting from pos_ratio = bdi_position_ratio() and up to
1086	* balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1087	* Hence, to calculate "step" properly, we have to use bdi_dirty as
1088	* "dirty" and bdi_setpoint as "setpoint".
1089	*
1090	* We rampup dirty_ratelimit forcibly if bdi_dirty is low because
1091	* it's possible that bdi_thresh is close to zero due to inactivity
1092	* of backing device (see the implementation of bdi_dirty_limit()).
1093	*/
1094	if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1095	dirty = bdi_dirty;
1096	if (bdi_dirty < 8)
1097	setpoint = bdi_dirty + 1;
1098	else
1099	setpoint = (bdi_thresh +
1100	bdi_dirty_limit(bdi, bg_thresh)) / 2;
1101	}
1102
1103	if (dirty < setpoint) {
1104	x = min(bdi->balanced_dirty_ratelimit,
1105	min(balanced_dirty_ratelimit, task_ratelimit));
1106	if (dirty_ratelimit < x)
1107	step = x - dirty_ratelimit;
1108	} else {
1109	x = max(bdi->balanced_dirty_ratelimit,
1110	max(balanced_dirty_ratelimit, task_ratelimit));
1111	if (dirty_ratelimit > x)
1112	step = dirty_ratelimit - x;
1113	}
1114
1115	/*
1116	* Don't pursue 100% rate matching. It's impossible since the balanced
1117	* rate itself is constantly fluctuating. So decrease the track speed
1118	* when it gets close to the target. Helps eliminate pointless tremors.
1119	*/
1120	step >>= dirty_ratelimit / (2 * step + 1);
1121	/*
1122	* Limit the tracking speed to avoid overshooting.
1123	*/
1124	step = (step + 7) / 8;
1125
1126	if (dirty_ratelimit < balanced_dirty_ratelimit)
1127	dirty_ratelimit += step;
1128	else
1129	dirty_ratelimit -= step;
1130
1131	bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1132	bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1133
1134	trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
1135	}
1136
1137	void __bdi_update_bandwidth(struct backing_dev_info *bdi,
1138	unsigned long thresh,
1139	unsigned long bg_thresh,
1140	unsigned long dirty,
1141	unsigned long bdi_thresh,
1142	unsigned long bdi_dirty,
1143	unsigned long start_time)
1144	{
1145	unsigned long now = jiffies;
1146	unsigned long elapsed = now - bdi->bw_time_stamp;
1147	unsigned long dirtied;
1148	unsigned long written;
1149
1150	/*
1151	* rate-limit, only update once every 200ms.
1152	*/
1153	if (elapsed < BANDWIDTH_INTERVAL)
1154	return;
1155
1156	dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
1157	written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1158
1159	/*
1160	* Skip quiet periods when disk bandwidth is under-utilized.
1161	* (at least 1s idle time between two flusher runs)
1162	*/
1163	if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1164	goto snapshot;
1165
1166	if (thresh) {
1167	global_update_bandwidth(thresh, dirty, now);
1168	bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1169	bdi_thresh, bdi_dirty,
1170	dirtied, elapsed);
1171	}
1172	bdi_update_write_bandwidth(bdi, elapsed, written);
1173
1174	snapshot:
1175	bdi->dirtied_stamp = dirtied;
1176	bdi->written_stamp = written;
1177	bdi->bw_time_stamp = now;
1178	}
1179
1180	static void bdi_update_bandwidth(struct backing_dev_info *bdi,
1181	unsigned long thresh,
1182	unsigned long bg_thresh,
1183	unsigned long dirty,
1184	unsigned long bdi_thresh,
1185	unsigned long bdi_dirty,
1186	unsigned long start_time)
1187	{
1188	if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1189	return;
1190	spin_lock(&bdi->wb.list_lock);
1191	__bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1192	bdi_thresh, bdi_dirty, start_time);
1193	spin_unlock(&bdi->wb.list_lock);
1194	}
1195
1196	/*
1197	* After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1198	* will look to see if it needs to start dirty throttling.
1199	*
1200	* If dirty_poll_interval is too low, big NUMA machines will call the expensive
1201	* global_page_state() too often. So scale it near-sqrt to the safety margin
1202	* (the number of pages we may dirty without exceeding the dirty limits).
1203	*/
1204	static unsigned long dirty_poll_interval(unsigned long dirty,
1205	unsigned long thresh)
1206	{
1207	if (thresh > dirty)
1208	return 1UL << (ilog2(thresh - dirty) >> 1);
1209
1210	return 1;
1211	}
1212
1213	static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
1214	unsigned long bdi_dirty)
1215	{
1216	unsigned long bw = bdi->avg_write_bandwidth;
1217	unsigned long t;
1218
1219	/*
1220	* Limit pause time for small memory systems. If sleeping for too long
1221	* time, a small pool of dirty/writeback pages may go empty and disk go
1222	* idle.
1223	*
1224	* 8 serves as the safety ratio.
1225	*/
1226	t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1227	t++;
1228
1229	return min_t(unsigned long, t, MAX_PAUSE);
1230	}
1231
1232	static long bdi_min_pause(struct backing_dev_info *bdi,
1233	long max_pause,
1234	unsigned long task_ratelimit,
1235	unsigned long dirty_ratelimit,
1236	int *nr_dirtied_pause)
1237	{
1238	long hi = ilog2(bdi->avg_write_bandwidth);
1239	long lo = ilog2(bdi->dirty_ratelimit);
1240	long t; /* target pause */
1241	long pause; /* estimated next pause */
1242	int pages; /* target nr_dirtied_pause */
1243
1244	/* target for 10ms pause on 1-dd case */
1245	t = max(1, HZ / 100);
1246
1247	/*
1248	* Scale up pause time for concurrent dirtiers in order to reduce CPU
1249	* overheads.
1250	*
1251	* (N * 10ms) on 2^N concurrent tasks.
1252	*/
1253	if (hi > lo)
1254	t += (hi - lo) * (10 * HZ) / 1024;
1255
1256	/*
1257	* This is a bit convoluted. We try to base the next nr_dirtied_pause
1258	* on the much more stable dirty_ratelimit. However the next pause time
1259	* will be computed based on task_ratelimit and the two rate limits may
1260	* depart considerably at some time. Especially if task_ratelimit goes
1261	* below dirty_ratelimit/2 and the target pause is max_pause, the next
1262	* pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1263	* result task_ratelimit won't be executed faithfully, which could
1264	* eventually bring down dirty_ratelimit.
1265	*
1266	* We apply two rules to fix it up:
1267	* 1) try to estimate the next pause time and if necessary, use a lower
1268	* nr_dirtied_pause so as not to exceed max_pause. When this happens,
1269	* nr_dirtied_pause will be "dancing" with task_ratelimit.
1270	* 2) limit the target pause time to max_pause/2, so that the normal
1271	* small fluctuations of task_ratelimit won't trigger rule (1) and
1272	* nr_dirtied_pause will remain as stable as dirty_ratelimit.
1273	*/
1274	t = min(t, 1 + max_pause / 2);
1275	pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1276
1277	/*
1278	* Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1279	* case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1280	* When the 16 consecutive reads are often interrupted by some dirty
1281	* throttling pause during the async writes, cfq will go into idles
1282	* (deadline is fine). So push nr_dirtied_pause as high as possible
1283	* until reaches DIRTY_POLL_THRESH=32 pages.
1284	*/
1285	if (pages < DIRTY_POLL_THRESH) {
1286	t = max_pause;
1287	pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1288	if (pages > DIRTY_POLL_THRESH) {
1289	pages = DIRTY_POLL_THRESH;
1290	t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1291	}
1292	}
1293
1294	pause = HZ * pages / (task_ratelimit + 1);
1295	if (pause > max_pause) {
1296	t = max_pause;
1297	pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1298	}
1299
1300	*nr_dirtied_pause = pages;
1301	/*
1302	* The minimal pause time will normally be half the target pause time.
1303	*/
1304	return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1305	}
1306
1307	static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
1308	unsigned long dirty_thresh,
1309	unsigned long background_thresh,
1310	unsigned long *bdi_dirty,
1311	unsigned long *bdi_thresh,
1312	unsigned long *bdi_bg_thresh)
1313	{
1314	unsigned long bdi_reclaimable;
1315
1316	/*
1317	* bdi_thresh is not treated as some limiting factor as
1318	* dirty_thresh, due to reasons
1319	* - in JBOD setup, bdi_thresh can fluctuate a lot
1320	* - in a system with HDD and USB key, the USB key may somehow
1321	* go into state (bdi_dirty >> bdi_thresh) either because
1322	* bdi_dirty starts high, or because bdi_thresh drops low.
1323	* In this case we don't want to hard throttle the USB key
1324	* dirtiers for 100 seconds until bdi_dirty drops under
1325	* bdi_thresh. Instead the auxiliary bdi control line in
1326	* bdi_position_ratio() will let the dirtier task progress
1327	* at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1328	*/
1329	*bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1330
1331	if (bdi_bg_thresh)
1332	bdi_bg_thresh = div_u64((u64)bdi_thresh *
1333	background_thresh,
1334	dirty_thresh);
1335
1336	/*
1337	* In order to avoid the stacked BDI deadlock we need
1338	* to ensure we accurately count the 'dirty' pages when
1339	* the threshold is low.
1340	*
1341	* Otherwise it would be possible to get thresh+n pages
1342	* reported dirty, even though there are thresh-m pages
1343	* actually dirty; with m+n sitting in the percpu
1344	* deltas.
1345	*/
1346	if (bdi_thresh < 2 bdi_stat_error(bdi)) {
1347	bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1348	*bdi_dirty = bdi_reclaimable +
1349	bdi_stat_sum(bdi, BDI_WRITEBACK);
1350	} else {
1351	bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1352	*bdi_dirty = bdi_reclaimable +
1353	bdi_stat(bdi, BDI_WRITEBACK);
1354	}
1355	}
1356
1357	/*
1358	* balance_dirty_pages() must be called by processes which are generating dirty
1359	* data. It looks at the number of dirty pages in the machine and will force
1360	* the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1361	* If we're over `background_thresh' then the writeback threads are woken to
1362	* perform some writeout.
1363	*/
1364	static void balance_dirty_pages(struct address_space *mapping,
1365	unsigned long pages_dirtied)
1366	{
1367	unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1368	unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
1369	unsigned long background_thresh;
1370	unsigned long dirty_thresh;
1371	long period;
1372	long pause;
1373	long max_pause;
1374	long min_pause;
1375	int nr_dirtied_pause;
1376	bool dirty_exceeded = false;
1377	unsigned long task_ratelimit;
1378	unsigned long dirty_ratelimit;
1379	unsigned long pos_ratio;
1380	struct backing_dev_info *bdi = mapping->backing_dev_info;
1381	bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1382	unsigned long start_time = jiffies;
1383
1384	for (;;) {
1385	unsigned long now = jiffies;
1386	unsigned long uninitialized_var(bdi_thresh);
1387	unsigned long thresh;
1388	unsigned long uninitialized_var(bdi_dirty);
1389	unsigned long dirty;
1390	unsigned long bg_thresh;
1391
1392	/*
1393	* Unstable writes are a feature of certain networked
1394	* filesystems (i.e. NFS) in which data may have been
1395	* written to the server's write cache, but has not yet
1396	* been flushed to permanent storage.
1397	*/
1398	nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1399	global_page_state(NR_UNSTABLE_NFS);
1400	nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1401
1402	global_dirty_limits(&background_thresh, &dirty_thresh);
1403
1404	if (unlikely(strictlimit)) {
1405	bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1406	&bdi_dirty, &bdi_thresh, &bg_thresh);
1407
1408	dirty = bdi_dirty;
1409	thresh = bdi_thresh;
1410	} else {
1411	dirty = nr_dirty;
1412	thresh = dirty_thresh;
1413	bg_thresh = background_thresh;
1414	}
1415
1416	/*
1417	* Throttle it only when the background writeback cannot
1418	* catch-up. This avoids (excessively) small writeouts
1419	* when the bdi limits are ramping up in case of !strictlimit.
1420	*
1421	* In strictlimit case make decision based on the bdi counters
1422	* and limits. Small writeouts when the bdi limits are ramping
1423	* up are the price we consciously pay for strictlimit-ing.
1424	*/
1425	if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh)) {
1426	current->dirty_paused_when = now;
1427	current->nr_dirtied = 0;
1428	current->nr_dirtied_pause =
1429	dirty_poll_interval(dirty, thresh);
1430	break;
1431	}
1432
1433	if (unlikely(!writeback_in_progress(bdi)))
1434	bdi_start_background_writeback(bdi);
1435
1436	if (!strictlimit)
1437	bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1438	&bdi_dirty, &bdi_thresh, NULL);
1439
1440	dirty_exceeded = (bdi_dirty > bdi_thresh) &&
1441	((nr_dirty > dirty_thresh) \|\| strictlimit);
1442	if (dirty_exceeded && !bdi->dirty_exceeded)
1443	bdi->dirty_exceeded = 1;
1444
1445	bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1446	nr_dirty, bdi_thresh, bdi_dirty,
1447	start_time);
1448
1449	dirty_ratelimit = bdi->dirty_ratelimit;
1450	pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1451	background_thresh, nr_dirty,
1452	bdi_thresh, bdi_dirty);
1453	task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1454	RATELIMIT_CALC_SHIFT;
1455	max_pause = bdi_max_pause(bdi, bdi_dirty);
1456	min_pause = bdi_min_pause(bdi, max_pause,
1457	task_ratelimit, dirty_ratelimit,
1458	&nr_dirtied_pause);
1459
1460	if (unlikely(task_ratelimit == 0)) {
1461	period = max_pause;
1462	pause = max_pause;
1463	goto pause;
1464	}
1465	period = HZ * pages_dirtied / task_ratelimit;
1466	pause = period;
1467	if (current->dirty_paused_when)
1468	pause -= now - current->dirty_paused_when;
1469	/*
1470	* For less than 1s think time (ext3/4 may block the dirtier
1471	* for up to 800ms from time to time on 1-HDD; so does xfs,
1472	* however at much less frequency), try to compensate it in
1473	* future periods by updating the virtual time; otherwise just
1474	* do a reset, as it may be a light dirtier.
1475	*/
1476	if (pause < min_pause) {
1477	trace_balance_dirty_pages(bdi,
1478	dirty_thresh,
1479	background_thresh,
1480	nr_dirty,
1481	bdi_thresh,
1482	bdi_dirty,
1483	dirty_ratelimit,
1484	task_ratelimit,
1485	pages_dirtied,
1486	period,
1487	min(pause, 0L),
1488	start_time);
1489	if (pause < -HZ) {
1490	current->dirty_paused_when = now;
1491	current->nr_dirtied = 0;
1492	} else if (period) {
1493	current->dirty_paused_when += period;
1494	current->nr_dirtied = 0;
1495	} else if (current->nr_dirtied_pause <= pages_dirtied)
1496	current->nr_dirtied_pause += pages_dirtied;
1497	break;
1498	}
1499	if (unlikely(pause > max_pause)) {
1500	/* for occasional dropped task_ratelimit */
1501	now += min(pause - max_pause, max_pause);
1502	pause = max_pause;
1503	}
1504
1505	pause:
1506	trace_balance_dirty_pages(bdi,
1507	dirty_thresh,
1508	background_thresh,
1509	nr_dirty,
1510	bdi_thresh,
1511	bdi_dirty,
1512	dirty_ratelimit,
1513	task_ratelimit,
1514	pages_dirtied,
1515	period,
1516	pause,
1517	start_time);
1518	__set_current_state(TASK_KILLABLE);
1519	io_schedule_timeout(pause);
1520
1521	current->dirty_paused_when = now + pause;
1522	current->nr_dirtied = 0;
1523	current->nr_dirtied_pause = nr_dirtied_pause;
1524
1525	/*
1526	* This is typically equal to (nr_dirty < dirty_thresh) and can
1527	* also keep "1000+ dd on a slow USB stick" under control.
1528	*/
1529	if (task_ratelimit)
1530	break;
1531
1532	/*
1533	* In the case of an unresponding NFS server and the NFS dirty
1534	* pages exceeds dirty_thresh, give the other good bdi's a pipe
1535	* to go through, so that tasks on them still remain responsive.
1536	*
1537	* In theory 1 page is enough to keep the comsumer-producer
1538	* pipe going: the flusher cleans 1 page => the task dirties 1
1539	* more page. However bdi_dirty has accounting errors. So use
1540	* the larger and more IO friendly bdi_stat_error.
1541	*/
1542	if (bdi_dirty <= bdi_stat_error(bdi))
1543	break;
1544
1545	if (fatal_signal_pending(current))
1546	break;
1547	}
1548
1549	if (!dirty_exceeded && bdi->dirty_exceeded)
1550	bdi->dirty_exceeded = 0;
1551
1552	if (writeback_in_progress(bdi))
1553	return;
1554
1555	/*
1556	* In laptop mode, we wait until hitting the higher threshold before
1557	* starting background writeout, and then write out all the way down
1558	* to the lower threshold. So slow writers cause minimal disk activity.
1559	*
1560	* In normal mode, we start background writeout at the lower
1561	* background_thresh, to keep the amount of dirty memory low.
1562	*/
1563	if (laptop_mode)
1564	return;
1565
1566	if (nr_reclaimable > background_thresh)
1567	bdi_start_background_writeback(bdi);
1568	}
1569
1570	void set_page_dirty_balance(struct page *page, int page_mkwrite)
1571	{
1572	if (set_page_dirty(page) \|\| page_mkwrite) {
1573	struct address_space *mapping = page_mapping(page);
1574
1575	if (mapping)
1576	balance_dirty_pages_ratelimited(mapping);
1577	}
1578	}
1579
1580	static DEFINE_PER_CPU(int, bdp_ratelimits);
1581
1582	/*
1583	* Normal tasks are throttled by
1584	* loop {
1585	* dirty tsk->nr_dirtied_pause pages;
1586	* take a snap in balance_dirty_pages();
1587	* }
1588	* However there is a worst case. If every task exit immediately when dirtied
1589	* (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1590	* called to throttle the page dirties. The solution is to save the not yet
1591	* throttled page dirties in dirty_throttle_leaks on task exit and charge them
1592	* randomly into the running tasks. This works well for the above worst case,
1593	* as the new task will pick up and accumulate the old task's leaked dirty
1594	* count and eventually get throttled.
1595	*/
1596	DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1597
1598	/**
1599	* balance_dirty_pages_ratelimited - balance dirty memory state
1600	* @mapping: address_space which was dirtied
1601	*
1602	* Processes which are dirtying memory should call in here once for each page
1603	* which was newly dirtied. The function will periodically check the system's
1604	* dirty state and will initiate writeback if needed.
1605	*
1606	* On really big machines, get_writeback_state is expensive, so try to avoid
1607	* calling it too often (ratelimiting). But once we're over the dirty memory
1608	* limit we decrease the ratelimiting by a lot, to prevent individual processes
1609	* from overshooting the limit by (ratelimit_pages) each.
1610	*/
1611	void balance_dirty_pages_ratelimited(struct address_space *mapping)
1612	{
1613	struct backing_dev_info *bdi = mapping->backing_dev_info;
1614	int ratelimit;
1615	int *p;
1616
1617	if (!bdi_cap_account_dirty(bdi))
1618	return;
1619
1620	ratelimit = current->nr_dirtied_pause;
1621	if (bdi->dirty_exceeded)
1622	ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1623
1624	preempt_disable();
1625	/*
1626	* This prevents one CPU to accumulate too many dirtied pages without
1627	* calling into balance_dirty_pages(), which can happen when there are
1628	* 1000+ tasks, all of them start dirtying pages at exactly the same
1629	* time, hence all honoured too large initial task->nr_dirtied_pause.
1630	*/
1631	p = &__get_cpu_var(bdp_ratelimits);
1632	if (unlikely(current->nr_dirtied >= ratelimit))
1633	*p = 0;
1634	else if (unlikely(*p >= ratelimit_pages)) {
1635	*p = 0;
1636	ratelimit = 0;
1637	}
1638	/*
1639	* Pick up the dirtied pages by the exited tasks. This avoids lots of
1640	* short-lived tasks (eg. gcc invocations in a kernel build) escaping
1641	* the dirty throttling and livelock other long-run dirtiers.
1642	*/
1643	p = &__get_cpu_var(dirty_throttle_leaks);
1644	if (*p > 0 && current->nr_dirtied < ratelimit) {
1645	unsigned long nr_pages_dirtied;
1646	nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1647	*p -= nr_pages_dirtied;
1648	current->nr_dirtied += nr_pages_dirtied;
1649	}
1650	preempt_enable();
1651
1652	if (unlikely(current->nr_dirtied >= ratelimit))
1653	balance_dirty_pages(mapping, current->nr_dirtied);
1654	}
1655	EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1656
1657	void throttle_vm_writeout(gfp_t gfp_mask)
1658	{
1659	unsigned long background_thresh;
1660	unsigned long dirty_thresh;
1661
1662	for ( ; ; ) {
1663	global_dirty_limits(&background_thresh, &dirty_thresh);
1664	dirty_thresh = hard_dirty_limit(dirty_thresh);
1665
1666	/*
1667	* Boost the allowable dirty threshold a bit for page
1668	* allocators so they don't get DoS'ed by heavy writers
1669	*/
1670	dirty_thresh += dirty_thresh / 10; /* wheeee... */
1671
1672	if (global_page_state(NR_UNSTABLE_NFS) +
1673	global_page_state(NR_WRITEBACK) <= dirty_thresh)
1674	break;
1675	congestion_wait(BLK_RW_ASYNC, HZ/10);
1676
1677	/*
1678	* The caller might hold locks which can prevent IO completion
1679	* or progress in the filesystem. So we cannot just sit here
1680	* waiting for IO to complete.
1681	*/
1682	if ((gfp_mask & (__GFP_FS\|__GFP_IO)) != (__GFP_FS\|__GFP_IO))
1683	break;
1684	}
1685	}
1686
1687	/*
1688	* sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1689	*/
1690	int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1691	void __user buffer, size_t length, loff_t *ppos)
1692	{
1693	proc_dointvec(table, write, buffer, length, ppos);
1694	return 0;
1695	}
1696
1697	#ifdef CONFIG_BLOCK
1698	void laptop_mode_timer_fn(unsigned long data)
1699	{
1700	struct request_queue q = (struct request_queue )data;
1701	int nr_pages = global_page_state(NR_FILE_DIRTY) +
1702	global_page_state(NR_UNSTABLE_NFS);
1703
1704	/*
1705	* We want to write everything out, not just down to the dirty
1706	* threshold
1707	*/
1708	if (bdi_has_dirty_io(&q->backing_dev_info))
1709	bdi_start_writeback(&q->backing_dev_info, nr_pages,
1710	WB_REASON_LAPTOP_TIMER);
1711	}
1712
1713	/*
1714	* We've spun up the disk and we're in laptop mode: schedule writeback
1715	* of all dirty data a few seconds from now. If the flush is already scheduled
1716	* then push it back - the user is still using the disk.
1717	*/
1718	void laptop_io_completion(struct backing_dev_info *info)
1719	{
1720	mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1721	}
1722
1723	/*
1724	* We're in laptop mode and we've just synced. The sync's writes will have
1725	* caused another writeback to be scheduled by laptop_io_completion.
1726	* Nothing needs to be written back anymore, so we unschedule the writeback.
1727	*/
1728	void laptop_sync_completion(void)
1729	{
1730	struct backing_dev_info *bdi;
1731
1732	rcu_read_lock();
1733
1734	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1735	del_timer(&bdi->laptop_mode_wb_timer);
1736
1737	rcu_read_unlock();
1738	}
1739	#endif
1740
1741	/*
1742	* If ratelimit_pages is too high then we can get into dirty-data overload
1743	* if a large number of processes all perform writes at the same time.
1744	* If it is too low then SMP machines will call the (expensive)
1745	* get_writeback_state too often.
1746	*
1747	* Here we set ratelimit_pages to a level which ensures that when all CPUs are
1748	* dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1749	* thresholds.
1750	*/
1751
1752	void writeback_set_ratelimit(void)
1753	{
1754	unsigned long background_thresh;
1755	unsigned long dirty_thresh;
1756	global_dirty_limits(&background_thresh, &dirty_thresh);
1757	global_dirty_limit = dirty_thresh;
1758	ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1759	if (ratelimit_pages < 16)
1760	ratelimit_pages = 16;
1761	}
1762
1763	static int
1764	ratelimit_handler(struct notifier_block *self, unsigned long action,
1765	void *hcpu)
1766	{
1767
1768	switch (action & ~CPU_TASKS_FROZEN) {
1769	case CPU_ONLINE:
1770	case CPU_DEAD:
1771	writeback_set_ratelimit();
1772	return NOTIFY_OK;
1773	default:
1774	return NOTIFY_DONE;
1775	}
1776	}
1777
1778	static struct notifier_block ratelimit_nb = {
1779	.notifier_call = ratelimit_handler,
1780	.next = NULL,
1781	};
1782
1783	/*
1784	* Called early on to tune the page writeback dirty limits.
1785	*
1786	* We used to scale dirty pages according to how total memory
1787	* related to pages that could be allocated for buffers (by
1788	* comparing nr_free_buffer_pages() to vm_total_pages.
1789	*
1790	* However, that was when we used "dirty_ratio" to scale with
1791	* all memory, and we don't do that any more. "dirty_ratio"
1792	* is now applied to total non-HIGHPAGE memory (by subtracting
1793	* totalhigh_pages from vm_total_pages), and as such we can't
1794	* get into the old insane situation any more where we had
1795	* large amounts of dirty pages compared to a small amount of
1796	* non-HIGHMEM memory.
1797	*
1798	* But we might still want to scale the dirty_ratio by how
1799	* much memory the box has..
1800	*/
1801	void __init page_writeback_init(void)
1802	{
1803	writeback_set_ratelimit();
1804	register_cpu_notifier(&ratelimit_nb);
1805
1806	fprop_global_init(&writeout_completions);
1807	}
1808
1809	/**
1810	* tag_pages_for_writeback - tag pages to be written by write_cache_pages
1811	* @mapping: address space structure to write
1812	* @start: starting page index
1813	* @end: ending page index (inclusive)
1814	*
1815	* This function scans the page range from @start to @end (inclusive) and tags
1816	* all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1817	* that write_cache_pages (or whoever calls this function) will then use
1818	* TOWRITE tag to identify pages eligible for writeback. This mechanism is
1819	* used to avoid livelocking of writeback by a process steadily creating new
1820	* dirty pages in the file (thus it is important for this function to be quick
1821	* so that it can tag pages faster than a dirtying process can create them).
1822	*/
1823	/*
1824	* We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1825	*/
1826	void tag_pages_for_writeback(struct address_space *mapping,
1827	pgoff_t start, pgoff_t end)
1828	{
1829	#define WRITEBACK_TAG_BATCH 4096
1830	unsigned long tagged;
1831
1832	do {
1833	spin_lock_irq(&mapping->tree_lock);
1834	tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1835	&start, end, WRITEBACK_TAG_BATCH,
1836	PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1837	spin_unlock_irq(&mapping->tree_lock);
1838	WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1839	cond_resched();
1840	/* We check 'start' to handle wrapping when end == ~0UL */
1841	} while (tagged >= WRITEBACK_TAG_BATCH && start);
1842	}
1843	EXPORT_SYMBOL(tag_pages_for_writeback);
1844
1845	/**
1846	* write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1847	* @mapping: address space structure to write
1848	* @wbc: subtract the number of written pages from *@wbc->nr_to_write
1849	* @writepage: function called for each page
1850	* @data: data passed to writepage function
1851	*
1852	* If a page is already under I/O, write_cache_pages() skips it, even
1853	* if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1854	* but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1855	* and msync() need to guarantee that all the data which was dirty at the time
1856	* the call was made get new I/O started against them. If wbc->sync_mode is
1857	* WB_SYNC_ALL then we were called for data integrity and we must wait for
1858	* existing IO to complete.
1859	*
1860	* To avoid livelocks (when other process dirties new pages), we first tag
1861	* pages which should be written back with TOWRITE tag and only then start
1862	* writing them. For data-integrity sync we have to be careful so that we do
1863	* not miss some pages (e.g., because some other process has cleared TOWRITE
1864	* tag we set). The rule we follow is that TOWRITE tag can be cleared only
1865	* by the process clearing the DIRTY tag (and submitting the page for IO).
1866	*/
1867	int write_cache_pages(struct address_space *mapping,
1868	struct writeback_control *wbc, writepage_t writepage,
1869	void *data)
1870	{
1871	int ret = 0;
1872	int done = 0;
1873	struct pagevec pvec;
1874	int nr_pages;
1875	pgoff_t uninitialized_var(writeback_index);
1876	pgoff_t index;
1877	pgoff_t end; /* Inclusive */
1878	pgoff_t done_index;
1879	int cycled;
1880	int range_whole = 0;
1881	int tag;
1882
1883	pagevec_init(&pvec, 0);
1884	if (wbc->range_cyclic) {
1885	writeback_index = mapping->writeback_index; /* prev offset */
1886	index = writeback_index;
1887	if (index == 0)
1888	cycled = 1;
1889	else
1890	cycled = 0;
1891	end = -1;
1892	} else {
1893	index = wbc->range_start >> PAGE_CACHE_SHIFT;
1894	end = wbc->range_end >> PAGE_CACHE_SHIFT;
1895	if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1896	range_whole = 1;
1897	cycled = 1; /* ignore range_cyclic tests */
1898	}
1899	if (wbc->sync_mode == WB_SYNC_ALL \|\| wbc->tagged_writepages)
1900	tag = PAGECACHE_TAG_TOWRITE;
1901	else
1902	tag = PAGECACHE_TAG_DIRTY;
1903	retry:
1904	if (wbc->sync_mode == WB_SYNC_ALL \|\| wbc->tagged_writepages)
1905	tag_pages_for_writeback(mapping, index, end);
1906	done_index = index;
1907	while (!done && (index <= end)) {
1908	int i;
1909
1910	nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1911	min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1912	if (nr_pages == 0)
1913	break;
1914
1915	for (i = 0; i < nr_pages; i++) {
1916	struct page *page = pvec.pages[i];
1917
1918	/*
1919	* At this point, the page may be truncated or
1920	* invalidated (changing page->mapping to NULL), or
1921	* even swizzled back from swapper_space to tmpfs file
1922	* mapping. However, page->index will not change
1923	* because we have a reference on the page.
1924	*/
1925	if (page->index > end) {
1926	/*
1927	* can't be range_cyclic (1st pass) because
1928	* end == -1 in that case.
1929	*/
1930	done = 1;
1931	break;
1932	}
1933
1934	done_index = page->index;
1935
1936	lock_page(page);
1937
1938	/*
1939	* Page truncated or invalidated. We can freely skip it
1940	* then, even for data integrity operations: the page
1941	* has disappeared concurrently, so there could be no
1942	* real expectation of this data interity operation
1943	* even if there is now a new, dirty page at the same
1944	* pagecache address.
1945	*/
1946	if (unlikely(page->mapping != mapping)) {
1947	continue_unlock:
1948	unlock_page(page);
1949	continue;
1950	}
1951
1952	if (!PageDirty(page)) {
1953	/* someone wrote it for us */
1954	goto continue_unlock;
1955	}
1956
1957	if (PageWriteback(page)) {
1958	if (wbc->sync_mode != WB_SYNC_NONE)
1959	wait_on_page_writeback(page);
1960	else
1961	goto continue_unlock;
1962	}
1963
1964	BUG_ON(PageWriteback(page));
1965	if (!clear_page_dirty_for_io(page))
1966	goto continue_unlock;
1967
1968	trace_wbc_writepage(wbc, mapping->backing_dev_info);
1969	ret = (*writepage)(page, wbc, data);
1970	if (unlikely(ret)) {
1971	if (ret == AOP_WRITEPAGE_ACTIVATE) {
1972	unlock_page(page);
1973	ret = 0;
1974	} else {
1975	/*
1976	* done_index is set past this page,
1977	* so media errors will not choke
1978	* background writeout for the entire
1979	* file. This has consequences for
1980	* range_cyclic semantics (ie. it may
1981	* not be suitable for data integrity
1982	* writeout).
1983	*/
1984	done_index = page->index + 1;
1985	done = 1;
1986	break;
1987	}
1988	}
1989
1990	/*
1991	* We stop writing back only if we are not doing
1992	* integrity sync. In case of integrity sync we have to
1993	* keep going until we have written all the pages
1994	* we tagged for writeback prior to entering this loop.
1995	*/
1996	if (--wbc->nr_to_write <= 0 &&
1997	wbc->sync_mode == WB_SYNC_NONE) {
1998	done = 1;
1999	break;
2000	}
2001	}
2002	pagevec_release(&pvec);
2003	cond_resched();
2004	}
2005	if (!cycled && !done) {
2006	/*
2007	* range_cyclic:
2008	* We hit the last page and there is more work to be done: wrap
2009	* back to the start of the file
2010	*/
2011	cycled = 1;
2012	index = 0;
2013	end = writeback_index - 1;
2014	goto retry;
2015	}
2016	if (wbc->range_cyclic \|\| (range_whole && wbc->nr_to_write > 0))
2017	mapping->writeback_index = done_index;
2018
2019	return ret;
2020	}
2021	EXPORT_SYMBOL(write_cache_pages);
2022
2023	/*
2024	* Function used by generic_writepages to call the real writepage
2025	* function and set the mapping flags on error
2026	*/
2027	static int __writepage(struct page page, struct writeback_control wbc,
2028	void *data)
2029	{
2030	struct address_space *mapping = data;
2031	int ret = mapping->a_ops->writepage(page, wbc);
2032	mapping_set_error(mapping, ret);
2033	return ret;
2034	}
2035
2036	/**
2037	* generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2038	* @mapping: address space structure to write
2039	* @wbc: subtract the number of written pages from *@wbc->nr_to_write
2040	*
2041	* This is a library function, which implements the writepages()
2042	* address_space_operation.
2043	*/
2044	int generic_writepages(struct address_space *mapping,
2045	struct writeback_control *wbc)
2046	{
2047	struct blk_plug plug;
2048	int ret;
2049
2050	/* deal with chardevs and other special file */
2051	if (!mapping->a_ops->writepage)
2052	return 0;
2053
2054	blk_start_plug(&plug);
2055	ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2056	blk_finish_plug(&plug);
2057	return ret;
2058	}
2059
2060	EXPORT_SYMBOL(generic_writepages);
2061
2062	int do_writepages(struct address_space mapping, struct writeback_control wbc)
2063	{
2064	int ret;
2065
2066	if (wbc->nr_to_write <= 0)
2067	return 0;
2068	if (mapping->a_ops->writepages)
2069	ret = mapping->a_ops->writepages(mapping, wbc);
2070	else
2071	ret = generic_writepages(mapping, wbc);
2072	return ret;
2073	}
2074
2075	/**
2076	* write_one_page - write out a single page and optionally wait on I/O
2077	* @page: the page to write
2078	* @wait: if true, wait on writeout
2079	*
2080	* The page must be locked by the caller and will be unlocked upon return.
2081	*
2082	* write_one_page() returns a negative error code if I/O failed.
2083	*/
2084	int write_one_page(struct page *page, int wait)
2085	{
2086	struct address_space *mapping = page->mapping;
2087	int ret = 0;
2088	struct writeback_control wbc = {
2089	.sync_mode = WB_SYNC_ALL,
2090	.nr_to_write = 1,
2091	};
2092
2093	BUG_ON(!PageLocked(page));
2094
2095	if (wait)
2096	wait_on_page_writeback(page);
2097
2098	if (clear_page_dirty_for_io(page)) {
2099	page_cache_get(page);
2100	ret = mapping->a_ops->writepage(page, &wbc);
2101	if (ret == 0 && wait) {
2102	wait_on_page_writeback(page);
2103	if (PageError(page))
2104	ret = -EIO;
2105	}
2106	page_cache_release(page);
2107	} else {
2108	unlock_page(page);
2109	}
2110	return ret;
2111	}
2112	EXPORT_SYMBOL(write_one_page);
2113
2114	/*
2115	* For address_spaces which do not use buffers nor write back.
2116	*/
2117	int __set_page_dirty_no_writeback(struct page *page)
2118	{
2119	if (!PageDirty(page))
2120	return !TestSetPageDirty(page);
2121	return 0;
2122	}
2123
2124	/*
2125	* Helper function for set_page_dirty family.
2126	* NOTE: This relies on being atomic wrt interrupts.
2127	*/
2128	void account_page_dirtied(struct page page, struct address_space mapping)
2129	{
2130	trace_writeback_dirty_page(page, mapping);
2131
2132	if (mapping_cap_account_dirty(mapping)) {
2133	__inc_zone_page_state(page, NR_FILE_DIRTY);
2134	__inc_zone_page_state(page, NR_DIRTIED);
2135	__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
2136	__inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2137	task_io_account_write(PAGE_CACHE_SIZE);
2138	current->nr_dirtied++;
2139	this_cpu_inc(bdp_ratelimits);
2140	}
2141	}
2142	EXPORT_SYMBOL(account_page_dirtied);
2143
2144	/*
2145	* Helper function for set_page_writeback family.
2146	*
2147	* The caller must hold mem_cgroup_begin/end_update_page_stat() lock
2148	* while calling this function.
2149	* See test_set_page_writeback for example.
2150	*
2151	* NOTE: Unlike account_page_dirtied this does not rely on being atomic
2152	* wrt interrupts.
2153	*/
2154	void account_page_writeback(struct page *page)
2155	{
2156	mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2157	inc_zone_page_state(page, NR_WRITEBACK);
2158	}
2159	EXPORT_SYMBOL(account_page_writeback);
2160
2161	/*
2162	* For address_spaces which do not use buffers. Just tag the page as dirty in
2163	* its radix tree.
2164	*
2165	* This is also used when a single buffer is being dirtied: we want to set the
2166	* page dirty in that case, but not all the buffers. This is a "bottom-up"
2167	* dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2168	*
2169	* Most callers have locked the page, which pins the address_space in memory.
2170	* But zap_pte_range() does not lock the page, however in that case the
2171	* mapping is pinned by the vma's ->vm_file reference.
2172	*
2173	* We take care to handle the case where the page was truncated from the
2174	* mapping by re-checking page_mapping() inside tree_lock.
2175	*/
2176	int __set_page_dirty_nobuffers(struct page *page)
2177	{
2178	if (!TestSetPageDirty(page)) {
2179	struct address_space *mapping = page_mapping(page);
2180	struct address_space *mapping2;
2181
2182	if (!mapping)
2183	return 1;
2184
2185	spin_lock_irq(&mapping->tree_lock);
2186	mapping2 = page_mapping(page);
2187	if (mapping2) { /* Race with truncate? */
2188	BUG_ON(mapping2 != mapping);
2189	WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2190	account_page_dirtied(page, mapping);
2191	radix_tree_tag_set(&mapping->page_tree,
2192	page_index(page), PAGECACHE_TAG_DIRTY);
2193	}
2194	spin_unlock_irq(&mapping->tree_lock);
2195	if (mapping->host) {
2196	/* !PageAnon && !swapper_space */
2197	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2198	}
2199	return 1;
2200	}
2201	return 0;
2202	}
2203	EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2204
2205	/*
2206	* Call this whenever redirtying a page, to de-account the dirty counters
2207	* (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2208	* counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2209	* systematic errors in balanced_dirty_ratelimit and the dirty pages position
2210	* control.
2211	*/
2212	void account_page_redirty(struct page *page)
2213	{
2214	struct address_space *mapping = page->mapping;
2215	if (mapping && mapping_cap_account_dirty(mapping)) {
2216	current->nr_dirtied--;
2217	dec_zone_page_state(page, NR_DIRTIED);
2218	dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2219	}
2220	}
2221	EXPORT_SYMBOL(account_page_redirty);
2222
2223	/*
2224	* When a writepage implementation decides that it doesn't want to write this
2225	* page for some reason, it should redirty the locked page via
2226	* redirty_page_for_writepage() and it should then unlock the page and return 0
2227	*/
2228	int redirty_page_for_writepage(struct writeback_control wbc, struct page page)
2229	{
2230	wbc->pages_skipped++;
2231	account_page_redirty(page);
2232	return __set_page_dirty_nobuffers(page);
2233	}
2234	EXPORT_SYMBOL(redirty_page_for_writepage);
2235
2236	/*
2237	* Dirty a page.
2238	*
2239	* For pages with a mapping this should be done under the page lock
2240	* for the benefit of asynchronous memory errors who prefer a consistent
2241	* dirty state. This rule can be broken in some special cases,
2242	* but should be better not to.
2243	*
2244	* If the mapping doesn't provide a set_page_dirty a_op, then
2245	* just fall through and assume that it wants buffer_heads.
2246	*/
2247	int set_page_dirty(struct page *page)
2248	{
2249	struct address_space *mapping = page_mapping(page);
2250
2251	if (likely(mapping)) {
2252	int (spd)(struct page ) = mapping->a_ops->set_page_dirty;
2253	/*
2254	* readahead/lru_deactivate_page could remain
2255	* PG_readahead/PG_reclaim due to race with end_page_writeback
2256	* About readahead, if the page is written, the flags would be
2257	* reset. So no problem.
2258	* About lru_deactivate_page, if the page is redirty, the flag
2259	* will be reset. So no problem. but if the page is used by readahead
2260	* it will confuse readahead and make it restart the size rampup
2261	* process. But it's a trivial problem.
2262	*/
2263	ClearPageReclaim(page);
2264	#ifdef CONFIG_BLOCK
2265	if (!spd)
2266	spd = __set_page_dirty_buffers;
2267	#endif
2268	return (*spd)(page);
2269	}
2270	if (!PageDirty(page)) {
2271	if (!TestSetPageDirty(page))
2272	return 1;
2273	}
2274	return 0;
2275	}
2276	EXPORT_SYMBOL(set_page_dirty);
2277
2278	/*
2279	* set_page_dirty() is racy if the caller has no reference against
2280	* page->mapping->host, and if the page is unlocked. This is because another
2281	* CPU could truncate the page off the mapping and then free the mapping.
2282	*
2283	* Usually, the page _is_ locked, or the caller is a user-space process which
2284	* holds a reference on the inode by having an open file.
2285	*
2286	* In other cases, the page should be locked before running set_page_dirty().
2287	*/
2288	int set_page_dirty_lock(struct page *page)
2289	{
2290	int ret;
2291
2292	lock_page(page);
2293	ret = set_page_dirty(page);
2294	unlock_page(page);
2295	return ret;
2296	}
2297	EXPORT_SYMBOL(set_page_dirty_lock);
2298
2299	/*
2300	* Clear a page's dirty flag, while caring for dirty memory accounting.
2301	* Returns true if the page was previously dirty.
2302	*
2303	* This is for preparing to put the page under writeout. We leave the page
2304	* tagged as dirty in the radix tree so that a concurrent write-for-sync
2305	* can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2306	* implementation will run either set_page_writeback() or set_page_dirty(),
2307	* at which stage we bring the page's dirty flag and radix-tree dirty tag
2308	* back into sync.
2309	*
2310	* This incoherency between the page's dirty flag and radix-tree tag is
2311	* unfortunate, but it only exists while the page is locked.
2312	*/
2313	int clear_page_dirty_for_io(struct page *page)
2314	{
2315	struct address_space *mapping = page_mapping(page);
2316
2317	BUG_ON(!PageLocked(page));
2318
2319	if (mapping && mapping_cap_account_dirty(mapping)) {
2320	/*
2321	* Yes, Virginia, this is indeed insane.
2322	*
2323	* We use this sequence to make sure that
2324	* (a) we account for dirty stats properly
2325	* (b) we tell the low-level filesystem to
2326	* mark the whole page dirty if it was
2327	* dirty in a pagetable. Only to then
2328	* (c) clean the page again and return 1 to
2329	* cause the writeback.
2330	*
2331	* This way we avoid all nasty races with the
2332	* dirty bit in multiple places and clearing
2333	* them concurrently from different threads.
2334	*
2335	* Note! Normally the "set_page_dirty(page)"
2336	* has no effect on the actual dirty bit - since
2337	* that will already usually be set. But we
2338	* need the side effects, and it can help us
2339	* avoid races.
2340	*
2341	* We basically use the page "master dirty bit"
2342	* as a serialization point for all the different
2343	* threads doing their things.
2344	*/
2345	if (page_mkclean(page))
2346	set_page_dirty(page);
2347	/*
2348	* We carefully synchronise fault handlers against
2349	* installing a dirty pte and marking the page dirty
2350	* at this point. We do this by having them hold the
2351	* page lock at some point after installing their
2352	* pte, but before marking the page dirty.
2353	* Pages are always locked coming in here, so we get
2354	* the desired exclusion. See mm/memory.c:do_wp_page()
2355	* for more comments.
2356	*/
2357	if (TestClearPageDirty(page)) {
2358	dec_zone_page_state(page, NR_FILE_DIRTY);
2359	dec_bdi_stat(mapping->backing_dev_info,
2360	BDI_RECLAIMABLE);
2361	return 1;
2362	}
2363	return 0;
2364	}
2365	return TestClearPageDirty(page);
2366	}
2367	EXPORT_SYMBOL(clear_page_dirty_for_io);
2368
2369	int test_clear_page_writeback(struct page *page)
2370	{
2371	struct address_space *mapping = page_mapping(page);
2372	int ret;
2373	bool locked;
2374	unsigned long memcg_flags;
2375
2376	mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
2377	if (mapping) {
2378	struct backing_dev_info *bdi = mapping->backing_dev_info;
2379	unsigned long flags;
2380
2381	spin_lock_irqsave(&mapping->tree_lock, flags);
2382	ret = TestClearPageWriteback(page);
2383	if (ret) {
2384	radix_tree_tag_clear(&mapping->page_tree,
2385	page_index(page),
2386	PAGECACHE_TAG_WRITEBACK);
2387	if (bdi_cap_account_writeback(bdi)) {
2388	__dec_bdi_stat(bdi, BDI_WRITEBACK);
2389	__bdi_writeout_inc(bdi);
2390	}
2391	}
2392	spin_unlock_irqrestore(&mapping->tree_lock, flags);
2393	} else {
2394	ret = TestClearPageWriteback(page);
2395	}
2396	if (ret) {
2397	mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2398	dec_zone_page_state(page, NR_WRITEBACK);
2399	inc_zone_page_state(page, NR_WRITTEN);
2400	}
2401	mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
2402	return ret;
2403	}
2404
2405	int test_set_page_writeback(struct page *page)
2406	{
2407	struct address_space *mapping = page_mapping(page);
2408	int ret;
2409	bool locked;
2410	unsigned long memcg_flags;
2411
2412	mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
2413	if (mapping) {
2414	struct backing_dev_info *bdi = mapping->backing_dev_info;
2415	unsigned long flags;
2416
2417	spin_lock_irqsave(&mapping->tree_lock, flags);
2418	ret = TestSetPageWriteback(page);
2419	if (!ret) {
2420	radix_tree_tag_set(&mapping->page_tree,
2421	page_index(page),
2422	PAGECACHE_TAG_WRITEBACK);
2423	if (bdi_cap_account_writeback(bdi))
2424	__inc_bdi_stat(bdi, BDI_WRITEBACK);
2425	}
2426	if (!PageDirty(page))
2427	radix_tree_tag_clear(&mapping->page_tree,
2428	page_index(page),
2429	PAGECACHE_TAG_DIRTY);
2430	radix_tree_tag_clear(&mapping->page_tree,
2431	page_index(page),
2432	PAGECACHE_TAG_TOWRITE);
2433	spin_unlock_irqrestore(&mapping->tree_lock, flags);
2434	} else {
2435	ret = TestSetPageWriteback(page);
2436	}
2437	if (!ret)
2438	account_page_writeback(page);
2439	mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
2440	return ret;
2441
2442	}
2443	EXPORT_SYMBOL(test_set_page_writeback);
2444
2445	/*
2446	* Return true if any of the pages in the mapping are marked with the
2447	* passed tag.
2448	*/
2449	int mapping_tagged(struct address_space *mapping, int tag)
2450	{
2451	return radix_tree_tagged(&mapping->page_tree, tag);
2452	}
2453	EXPORT_SYMBOL(mapping_tagged);
2454
2455	/**
2456	* wait_for_stable_page() - wait for writeback to finish, if necessary.
2457	* @page: The page to wait on.
2458	*
2459	* This function determines if the given page is related to a backing device
2460	* that requires page contents to be held stable during writeback. If so, then
2461	* it will wait for any pending writeback to complete.
2462	*/
2463	void wait_for_stable_page(struct page *page)
2464	{
2465	struct address_space *mapping = page_mapping(page);
2466	struct backing_dev_info *bdi = mapping->backing_dev_info;
2467
2468	if (!bdi_cap_stable_pages_required(bdi))
2469	return;
2470
2471	wait_on_page_writeback(page);
2472	}
2473	EXPORT_SYMBOL_GPL(wait_for_stable_page);
2474

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jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master

Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9

Kernel

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Root/mm/page-writeback.c

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