1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * mm/page-writeback.c
4  *
5  * Copyright (C) 2002, Linus Torvalds.
6  * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
7  *
8  * Contains functions related to writing back dirty pages at the
9  * address_space level.
10  *
11  * 10Apr2002	Andrew Morton
12  *		Initial version
13  */
14 
15 #include <linux/kernel.h>
16 #include <linux/export.h>
17 #include <linux/spinlock.h>
18 #include <linux/fs.h>
19 #include <linux/mm.h>
20 #include <linux/swap.h>
21 #include <linux/slab.h>
22 #include <linux/pagemap.h>
23 #include <linux/writeback.h>
24 #include <linux/init.h>
25 #include <linux/backing-dev.h>
26 #include <linux/task_io_accounting_ops.h>
27 #include <linux/blkdev.h>
28 #include <linux/mpage.h>
29 #include <linux/rmap.h>
30 #include <linux/percpu.h>
31 #include <linux/smp.h>
32 #include <linux/sysctl.h>
33 #include <linux/cpu.h>
34 #include <linux/syscalls.h>
35 #include <linux/pagevec.h>
36 #include <linux/timer.h>
37 #include <linux/sched/rt.h>
38 #include <linux/sched/signal.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 static 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 static 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 static int vm_highmem_is_dirtyable;
86 
87 /*
88  * The generator of dirty data starts writeback at this percentage
89  */
90 static 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 static 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 puts the machine in "laptop mode". Doubles as a timeout in jiffies:
112  * a full sync is triggered after this time elapses without any disk activity.
113  */
114 int laptop_mode;
115 
116 EXPORT_SYMBOL(laptop_mode);
117 
118 /* End of sysctl-exported parameters */
119 
120 struct wb_domain global_wb_domain;
121 
122 /* consolidated parameters for balance_dirty_pages() and its subroutines */
123 struct dirty_throttle_control {
124 #ifdef CONFIG_CGROUP_WRITEBACK
125 	struct wb_domain	*dom;
126 	struct dirty_throttle_control *gdtc;	/* only set in memcg dtc's */
127 #endif
128 	struct bdi_writeback	*wb;
129 	struct fprop_local_percpu *wb_completions;
130 
131 	unsigned long		avail;		/* dirtyable */
132 	unsigned long		dirty;		/* file_dirty + write + nfs */
133 	unsigned long		thresh;		/* dirty threshold */
134 	unsigned long		bg_thresh;	/* dirty background threshold */
135 
136 	unsigned long		wb_dirty;	/* per-wb counterparts */
137 	unsigned long		wb_thresh;
138 	unsigned long		wb_bg_thresh;
139 
140 	unsigned long		pos_ratio;
141 };
142 
143 /*
144  * Length of period for aging writeout fractions of bdis. This is an
145  * arbitrarily chosen number. The longer the period, the slower fractions will
146  * reflect changes in current writeout rate.
147  */
148 #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
149 
150 #ifdef CONFIG_CGROUP_WRITEBACK
151 
152 #define GDTC_INIT(__wb)		.wb = (__wb),				\
153 				.dom = &global_wb_domain,		\
154 				.wb_completions = &(__wb)->completions
155 
156 #define GDTC_INIT_NO_WB		.dom = &global_wb_domain
157 
158 #define MDTC_INIT(__wb, __gdtc)	.wb = (__wb),				\
159 				.dom = mem_cgroup_wb_domain(__wb),	\
160 				.wb_completions = &(__wb)->memcg_completions, \
161 				.gdtc = __gdtc
162 
mdtc_valid(struct dirty_throttle_control * dtc)163 static bool mdtc_valid(struct dirty_throttle_control *dtc)
164 {
165 	return dtc->dom;
166 }
167 
dtc_dom(struct dirty_throttle_control * dtc)168 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
169 {
170 	return dtc->dom;
171 }
172 
mdtc_gdtc(struct dirty_throttle_control * mdtc)173 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
174 {
175 	return mdtc->gdtc;
176 }
177 
wb_memcg_completions(struct bdi_writeback * wb)178 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
179 {
180 	return &wb->memcg_completions;
181 }
182 
wb_min_max_ratio(struct bdi_writeback * wb,unsigned long * minp,unsigned long * maxp)183 static void wb_min_max_ratio(struct bdi_writeback *wb,
184 			     unsigned long *minp, unsigned long *maxp)
185 {
186 	unsigned long this_bw = READ_ONCE(wb->avg_write_bandwidth);
187 	unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
188 	unsigned long long min = wb->bdi->min_ratio;
189 	unsigned long long max = wb->bdi->max_ratio;
190 
191 	/*
192 	 * @wb may already be clean by the time control reaches here and
193 	 * the total may not include its bw.
194 	 */
195 	if (this_bw < tot_bw) {
196 		if (min) {
197 			min *= this_bw;
198 			min = div64_ul(min, tot_bw);
199 		}
200 		if (max < 100) {
201 			max *= this_bw;
202 			max = div64_ul(max, tot_bw);
203 		}
204 	}
205 
206 	*minp = min;
207 	*maxp = max;
208 }
209 
210 #else	/* CONFIG_CGROUP_WRITEBACK */
211 
212 #define GDTC_INIT(__wb)		.wb = (__wb),                           \
213 				.wb_completions = &(__wb)->completions
214 #define GDTC_INIT_NO_WB
215 #define MDTC_INIT(__wb, __gdtc)
216 
mdtc_valid(struct dirty_throttle_control * dtc)217 static bool mdtc_valid(struct dirty_throttle_control *dtc)
218 {
219 	return false;
220 }
221 
dtc_dom(struct dirty_throttle_control * dtc)222 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
223 {
224 	return &global_wb_domain;
225 }
226 
mdtc_gdtc(struct dirty_throttle_control * mdtc)227 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
228 {
229 	return NULL;
230 }
231 
wb_memcg_completions(struct bdi_writeback * wb)232 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
233 {
234 	return NULL;
235 }
236 
wb_min_max_ratio(struct bdi_writeback * wb,unsigned long * minp,unsigned long * maxp)237 static void wb_min_max_ratio(struct bdi_writeback *wb,
238 			     unsigned long *minp, unsigned long *maxp)
239 {
240 	*minp = wb->bdi->min_ratio;
241 	*maxp = wb->bdi->max_ratio;
242 }
243 
244 #endif	/* CONFIG_CGROUP_WRITEBACK */
245 
246 /*
247  * In a memory zone, there is a certain amount of pages we consider
248  * available for the page cache, which is essentially the number of
249  * free and reclaimable pages, minus some zone reserves to protect
250  * lowmem and the ability to uphold the zone's watermarks without
251  * requiring writeback.
252  *
253  * This number of dirtyable pages is the base value of which the
254  * user-configurable dirty ratio is the effective number of pages that
255  * are allowed to be actually dirtied.  Per individual zone, or
256  * globally by using the sum of dirtyable pages over all zones.
257  *
258  * Because the user is allowed to specify the dirty limit globally as
259  * absolute number of bytes, calculating the per-zone dirty limit can
260  * require translating the configured limit into a percentage of
261  * global dirtyable memory first.
262  */
263 
264 /**
265  * node_dirtyable_memory - number of dirtyable pages in a node
266  * @pgdat: the node
267  *
268  * Return: the node's number of pages potentially available for dirty
269  * page cache.  This is the base value for the per-node dirty limits.
270  */
node_dirtyable_memory(struct pglist_data * pgdat)271 static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
272 {
273 	unsigned long nr_pages = 0;
274 	int z;
275 
276 	for (z = 0; z < MAX_NR_ZONES; z++) {
277 		struct zone *zone = pgdat->node_zones + z;
278 
279 		if (!populated_zone(zone))
280 			continue;
281 
282 		nr_pages += zone_page_state(zone, NR_FREE_PAGES);
283 	}
284 
285 	/*
286 	 * Pages reserved for the kernel should not be considered
287 	 * dirtyable, to prevent a situation where reclaim has to
288 	 * clean pages in order to balance the zones.
289 	 */
290 	nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
291 
292 	nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
293 	nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
294 
295 	return nr_pages;
296 }
297 
highmem_dirtyable_memory(unsigned long total)298 static unsigned long highmem_dirtyable_memory(unsigned long total)
299 {
300 #ifdef CONFIG_HIGHMEM
301 	int node;
302 	unsigned long x = 0;
303 	int i;
304 
305 	for_each_node_state(node, N_HIGH_MEMORY) {
306 		for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
307 			struct zone *z;
308 			unsigned long nr_pages;
309 
310 			if (!is_highmem_idx(i))
311 				continue;
312 
313 			z = &NODE_DATA(node)->node_zones[i];
314 			if (!populated_zone(z))
315 				continue;
316 
317 			nr_pages = zone_page_state(z, NR_FREE_PAGES);
318 			/* watch for underflows */
319 			nr_pages -= min(nr_pages, high_wmark_pages(z));
320 			nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
321 			nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
322 			x += nr_pages;
323 		}
324 	}
325 
326 	/*
327 	 * Make sure that the number of highmem pages is never larger
328 	 * than the number of the total dirtyable memory. This can only
329 	 * occur in very strange VM situations but we want to make sure
330 	 * that this does not occur.
331 	 */
332 	return min(x, total);
333 #else
334 	return 0;
335 #endif
336 }
337 
338 /**
339  * global_dirtyable_memory - number of globally dirtyable pages
340  *
341  * Return: the global number of pages potentially available for dirty
342  * page cache.  This is the base value for the global dirty limits.
343  */
global_dirtyable_memory(void)344 static unsigned long global_dirtyable_memory(void)
345 {
346 	unsigned long x;
347 
348 	x = global_zone_page_state(NR_FREE_PAGES);
349 	/*
350 	 * Pages reserved for the kernel should not be considered
351 	 * dirtyable, to prevent a situation where reclaim has to
352 	 * clean pages in order to balance the zones.
353 	 */
354 	x -= min(x, totalreserve_pages);
355 
356 	x += global_node_page_state(NR_INACTIVE_FILE);
357 	x += global_node_page_state(NR_ACTIVE_FILE);
358 
359 	if (!vm_highmem_is_dirtyable)
360 		x -= highmem_dirtyable_memory(x);
361 
362 	return x + 1;	/* Ensure that we never return 0 */
363 }
364 
365 /**
366  * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
367  * @dtc: dirty_throttle_control of interest
368  *
369  * Calculate @dtc->thresh and ->bg_thresh considering
370  * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}.  The caller
371  * must ensure that @dtc->avail is set before calling this function.  The
372  * dirty limits will be lifted by 1/4 for real-time tasks.
373  */
domain_dirty_limits(struct dirty_throttle_control * dtc)374 static void domain_dirty_limits(struct dirty_throttle_control *dtc)
375 {
376 	const unsigned long available_memory = dtc->avail;
377 	struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
378 	unsigned long bytes = vm_dirty_bytes;
379 	unsigned long bg_bytes = dirty_background_bytes;
380 	/* convert ratios to per-PAGE_SIZE for higher precision */
381 	unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
382 	unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
383 	unsigned long thresh;
384 	unsigned long bg_thresh;
385 	struct task_struct *tsk;
386 
387 	/* gdtc is !NULL iff @dtc is for memcg domain */
388 	if (gdtc) {
389 		unsigned long global_avail = gdtc->avail;
390 
391 		/*
392 		 * The byte settings can't be applied directly to memcg
393 		 * domains.  Convert them to ratios by scaling against
394 		 * globally available memory.  As the ratios are in
395 		 * per-PAGE_SIZE, they can be obtained by dividing bytes by
396 		 * number of pages.
397 		 */
398 		if (bytes)
399 			ratio = min(DIV_ROUND_UP(bytes, global_avail),
400 				    PAGE_SIZE);
401 		if (bg_bytes)
402 			bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
403 				       PAGE_SIZE);
404 		bytes = bg_bytes = 0;
405 	}
406 
407 	if (bytes)
408 		thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
409 	else
410 		thresh = (ratio * available_memory) / PAGE_SIZE;
411 
412 	if (bg_bytes)
413 		bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
414 	else
415 		bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
416 
417 	if (bg_thresh >= thresh)
418 		bg_thresh = thresh / 2;
419 	tsk = current;
420 	if (rt_task(tsk)) {
421 		bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
422 		thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
423 	}
424 	dtc->thresh = thresh;
425 	dtc->bg_thresh = bg_thresh;
426 
427 	/* we should eventually report the domain in the TP */
428 	if (!gdtc)
429 		trace_global_dirty_state(bg_thresh, thresh);
430 }
431 
432 /**
433  * global_dirty_limits - background-writeback and dirty-throttling thresholds
434  * @pbackground: out parameter for bg_thresh
435  * @pdirty: out parameter for thresh
436  *
437  * Calculate bg_thresh and thresh for global_wb_domain.  See
438  * domain_dirty_limits() for details.
439  */
global_dirty_limits(unsigned long * pbackground,unsigned long * pdirty)440 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
441 {
442 	struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
443 
444 	gdtc.avail = global_dirtyable_memory();
445 	domain_dirty_limits(&gdtc);
446 
447 	*pbackground = gdtc.bg_thresh;
448 	*pdirty = gdtc.thresh;
449 }
450 
451 /**
452  * node_dirty_limit - maximum number of dirty pages allowed in a node
453  * @pgdat: the node
454  *
455  * Return: the maximum number of dirty pages allowed in a node, based
456  * on the node's dirtyable memory.
457  */
node_dirty_limit(struct pglist_data * pgdat)458 static unsigned long node_dirty_limit(struct pglist_data *pgdat)
459 {
460 	unsigned long node_memory = node_dirtyable_memory(pgdat);
461 	struct task_struct *tsk = current;
462 	unsigned long dirty;
463 
464 	if (vm_dirty_bytes)
465 		dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
466 			node_memory / global_dirtyable_memory();
467 	else
468 		dirty = vm_dirty_ratio * node_memory / 100;
469 
470 	if (rt_task(tsk))
471 		dirty += dirty / 4;
472 
473 	return dirty;
474 }
475 
476 /**
477  * node_dirty_ok - tells whether a node is within its dirty limits
478  * @pgdat: the node to check
479  *
480  * Return: %true when the dirty pages in @pgdat are within the node's
481  * dirty limit, %false if the limit is exceeded.
482  */
node_dirty_ok(struct pglist_data * pgdat)483 bool node_dirty_ok(struct pglist_data *pgdat)
484 {
485 	unsigned long limit = node_dirty_limit(pgdat);
486 	unsigned long nr_pages = 0;
487 
488 	nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
489 	nr_pages += node_page_state(pgdat, NR_WRITEBACK);
490 
491 	return nr_pages <= limit;
492 }
493 
494 #ifdef CONFIG_SYSCTL
dirty_background_ratio_handler(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)495 static int dirty_background_ratio_handler(struct ctl_table *table, int write,
496 		void *buffer, size_t *lenp, loff_t *ppos)
497 {
498 	int ret;
499 
500 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
501 	if (ret == 0 && write)
502 		dirty_background_bytes = 0;
503 	return ret;
504 }
505 
dirty_background_bytes_handler(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)506 static int dirty_background_bytes_handler(struct ctl_table *table, int write,
507 		void *buffer, size_t *lenp, loff_t *ppos)
508 {
509 	int ret;
510 
511 	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
512 	if (ret == 0 && write)
513 		dirty_background_ratio = 0;
514 	return ret;
515 }
516 
dirty_ratio_handler(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)517 static int dirty_ratio_handler(struct ctl_table *table, int write, void *buffer,
518 		size_t *lenp, loff_t *ppos)
519 {
520 	int old_ratio = vm_dirty_ratio;
521 	int ret;
522 
523 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
524 	if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
525 		writeback_set_ratelimit();
526 		vm_dirty_bytes = 0;
527 	}
528 	return ret;
529 }
530 
dirty_bytes_handler(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)531 static int dirty_bytes_handler(struct ctl_table *table, int write,
532 		void *buffer, size_t *lenp, loff_t *ppos)
533 {
534 	unsigned long old_bytes = vm_dirty_bytes;
535 	int ret;
536 
537 	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
538 	if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
539 		writeback_set_ratelimit();
540 		vm_dirty_ratio = 0;
541 	}
542 	return ret;
543 }
544 #endif
545 
wp_next_time(unsigned long cur_time)546 static unsigned long wp_next_time(unsigned long cur_time)
547 {
548 	cur_time += VM_COMPLETIONS_PERIOD_LEN;
549 	/* 0 has a special meaning... */
550 	if (!cur_time)
551 		return 1;
552 	return cur_time;
553 }
554 
wb_domain_writeout_add(struct wb_domain * dom,struct fprop_local_percpu * completions,unsigned int max_prop_frac,long nr)555 static void wb_domain_writeout_add(struct wb_domain *dom,
556 				   struct fprop_local_percpu *completions,
557 				   unsigned int max_prop_frac, long nr)
558 {
559 	__fprop_add_percpu_max(&dom->completions, completions,
560 			       max_prop_frac, nr);
561 	/* First event after period switching was turned off? */
562 	if (unlikely(!dom->period_time)) {
563 		/*
564 		 * We can race with other __bdi_writeout_inc calls here but
565 		 * it does not cause any harm since the resulting time when
566 		 * timer will fire and what is in writeout_period_time will be
567 		 * roughly the same.
568 		 */
569 		dom->period_time = wp_next_time(jiffies);
570 		mod_timer(&dom->period_timer, dom->period_time);
571 	}
572 }
573 
574 /*
575  * Increment @wb's writeout completion count and the global writeout
576  * completion count. Called from __folio_end_writeback().
577  */
__wb_writeout_add(struct bdi_writeback * wb,long nr)578 static inline void __wb_writeout_add(struct bdi_writeback *wb, long nr)
579 {
580 	struct wb_domain *cgdom;
581 
582 	wb_stat_mod(wb, WB_WRITTEN, nr);
583 	wb_domain_writeout_add(&global_wb_domain, &wb->completions,
584 			       wb->bdi->max_prop_frac, nr);
585 
586 	cgdom = mem_cgroup_wb_domain(wb);
587 	if (cgdom)
588 		wb_domain_writeout_add(cgdom, wb_memcg_completions(wb),
589 				       wb->bdi->max_prop_frac, nr);
590 }
591 
wb_writeout_inc(struct bdi_writeback * wb)592 void wb_writeout_inc(struct bdi_writeback *wb)
593 {
594 	unsigned long flags;
595 
596 	local_irq_save(flags);
597 	__wb_writeout_add(wb, 1);
598 	local_irq_restore(flags);
599 }
600 EXPORT_SYMBOL_GPL(wb_writeout_inc);
601 
602 /*
603  * On idle system, we can be called long after we scheduled because we use
604  * deferred timers so count with missed periods.
605  */
writeout_period(struct timer_list * t)606 static void writeout_period(struct timer_list *t)
607 {
608 	struct wb_domain *dom = from_timer(dom, t, period_timer);
609 	int miss_periods = (jiffies - dom->period_time) /
610 						 VM_COMPLETIONS_PERIOD_LEN;
611 
612 	if (fprop_new_period(&dom->completions, miss_periods + 1)) {
613 		dom->period_time = wp_next_time(dom->period_time +
614 				miss_periods * VM_COMPLETIONS_PERIOD_LEN);
615 		mod_timer(&dom->period_timer, dom->period_time);
616 	} else {
617 		/*
618 		 * Aging has zeroed all fractions. Stop wasting CPU on period
619 		 * updates.
620 		 */
621 		dom->period_time = 0;
622 	}
623 }
624 
wb_domain_init(struct wb_domain * dom,gfp_t gfp)625 int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
626 {
627 	memset(dom, 0, sizeof(*dom));
628 
629 	spin_lock_init(&dom->lock);
630 
631 	timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
632 
633 	dom->dirty_limit_tstamp = jiffies;
634 
635 	return fprop_global_init(&dom->completions, gfp);
636 }
637 
638 #ifdef CONFIG_CGROUP_WRITEBACK
wb_domain_exit(struct wb_domain * dom)639 void wb_domain_exit(struct wb_domain *dom)
640 {
641 	del_timer_sync(&dom->period_timer);
642 	fprop_global_destroy(&dom->completions);
643 }
644 #endif
645 
646 /*
647  * bdi_min_ratio keeps the sum of the minimum dirty shares of all
648  * registered backing devices, which, for obvious reasons, can not
649  * exceed 100%.
650  */
651 static unsigned int bdi_min_ratio;
652 
bdi_set_min_ratio(struct backing_dev_info * bdi,unsigned int min_ratio)653 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
654 {
655 	unsigned int delta;
656 	int ret = 0;
657 
658 	spin_lock_bh(&bdi_lock);
659 	if (min_ratio > bdi->max_ratio) {
660 		ret = -EINVAL;
661 	} else {
662 		if (min_ratio < bdi->min_ratio) {
663 			delta = bdi->min_ratio - min_ratio;
664 			bdi_min_ratio -= delta;
665 			bdi->min_ratio = min_ratio;
666 		} else {
667 			delta = min_ratio - bdi->min_ratio;
668 			if (bdi_min_ratio + delta < 100) {
669 				bdi_min_ratio += delta;
670 				bdi->min_ratio = min_ratio;
671 			} else {
672 				ret = -EINVAL;
673 			}
674 		}
675 	}
676 	spin_unlock_bh(&bdi_lock);
677 
678 	return ret;
679 }
680 
bdi_set_max_ratio(struct backing_dev_info * bdi,unsigned max_ratio)681 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
682 {
683 	int ret = 0;
684 
685 	if (max_ratio > 100)
686 		return -EINVAL;
687 
688 	spin_lock_bh(&bdi_lock);
689 	if (bdi->min_ratio > max_ratio) {
690 		ret = -EINVAL;
691 	} else {
692 		bdi->max_ratio = max_ratio;
693 		bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
694 	}
695 	spin_unlock_bh(&bdi_lock);
696 
697 	return ret;
698 }
699 EXPORT_SYMBOL(bdi_set_max_ratio);
700 
dirty_freerun_ceiling(unsigned long thresh,unsigned long bg_thresh)701 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
702 					   unsigned long bg_thresh)
703 {
704 	return (thresh + bg_thresh) / 2;
705 }
706 
hard_dirty_limit(struct wb_domain * dom,unsigned long thresh)707 static unsigned long hard_dirty_limit(struct wb_domain *dom,
708 				      unsigned long thresh)
709 {
710 	return max(thresh, dom->dirty_limit);
711 }
712 
713 /*
714  * Memory which can be further allocated to a memcg domain is capped by
715  * system-wide clean memory excluding the amount being used in the domain.
716  */
mdtc_calc_avail(struct dirty_throttle_control * mdtc,unsigned long filepages,unsigned long headroom)717 static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
718 			    unsigned long filepages, unsigned long headroom)
719 {
720 	struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
721 	unsigned long clean = filepages - min(filepages, mdtc->dirty);
722 	unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
723 	unsigned long other_clean = global_clean - min(global_clean, clean);
724 
725 	mdtc->avail = filepages + min(headroom, other_clean);
726 }
727 
728 /**
729  * __wb_calc_thresh - @wb's share of dirty throttling threshold
730  * @dtc: dirty_throttle_context of interest
731  *
732  * Note that balance_dirty_pages() will only seriously take it as a hard limit
733  * when sleeping max_pause per page is not enough to keep the dirty pages under
734  * control. For example, when the device is completely stalled due to some error
735  * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
736  * In the other normal situations, it acts more gently by throttling the tasks
737  * more (rather than completely block them) when the wb dirty pages go high.
738  *
739  * It allocates high/low dirty limits to fast/slow devices, in order to prevent
740  * - starving fast devices
741  * - piling up dirty pages (that will take long time to sync) on slow devices
742  *
743  * The wb's share of dirty limit will be adapting to its throughput and
744  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
745  *
746  * Return: @wb's dirty limit in pages. The term "dirty" in the context of
747  * dirty balancing includes all PG_dirty and PG_writeback pages.
748  */
__wb_calc_thresh(struct dirty_throttle_control * dtc)749 static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
750 {
751 	struct wb_domain *dom = dtc_dom(dtc);
752 	unsigned long thresh = dtc->thresh;
753 	u64 wb_thresh;
754 	unsigned long numerator, denominator;
755 	unsigned long wb_min_ratio, wb_max_ratio;
756 
757 	/*
758 	 * Calculate this BDI's share of the thresh ratio.
759 	 */
760 	fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
761 			      &numerator, &denominator);
762 
763 	wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
764 	wb_thresh *= numerator;
765 	wb_thresh = div64_ul(wb_thresh, denominator);
766 
767 	wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
768 
769 	wb_thresh += (thresh * wb_min_ratio) / 100;
770 	if (wb_thresh > (thresh * wb_max_ratio) / 100)
771 		wb_thresh = thresh * wb_max_ratio / 100;
772 
773 	return wb_thresh;
774 }
775 
wb_calc_thresh(struct bdi_writeback * wb,unsigned long thresh)776 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
777 {
778 	struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
779 					       .thresh = thresh };
780 	return __wb_calc_thresh(&gdtc);
781 }
782 
783 /*
784  *                           setpoint - dirty 3
785  *        f(dirty) := 1.0 + (----------------)
786  *                           limit - setpoint
787  *
788  * it's a 3rd order polynomial that subjects to
789  *
790  * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
791  * (2) f(setpoint) = 1.0 => the balance point
792  * (3) f(limit)    = 0   => the hard limit
793  * (4) df/dx      <= 0	 => negative feedback control
794  * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
795  *     => fast response on large errors; small oscillation near setpoint
796  */
pos_ratio_polynom(unsigned long setpoint,unsigned long dirty,unsigned long limit)797 static long long pos_ratio_polynom(unsigned long setpoint,
798 					  unsigned long dirty,
799 					  unsigned long limit)
800 {
801 	long long pos_ratio;
802 	long x;
803 
804 	x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
805 		      (limit - setpoint) | 1);
806 	pos_ratio = x;
807 	pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
808 	pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
809 	pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
810 
811 	return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
812 }
813 
814 /*
815  * Dirty position control.
816  *
817  * (o) global/bdi setpoints
818  *
819  * We want the dirty pages be balanced around the global/wb setpoints.
820  * When the number of dirty pages is higher/lower than the setpoint, the
821  * dirty position control ratio (and hence task dirty ratelimit) will be
822  * decreased/increased to bring the dirty pages back to the setpoint.
823  *
824  *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
825  *
826  *     if (dirty < setpoint) scale up   pos_ratio
827  *     if (dirty > setpoint) scale down pos_ratio
828  *
829  *     if (wb_dirty < wb_setpoint) scale up   pos_ratio
830  *     if (wb_dirty > wb_setpoint) scale down pos_ratio
831  *
832  *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
833  *
834  * (o) global control line
835  *
836  *     ^ pos_ratio
837  *     |
838  *     |            |<===== global dirty control scope ======>|
839  * 2.0  * * * * * * *
840  *     |            .*
841  *     |            . *
842  *     |            .   *
843  *     |            .     *
844  *     |            .        *
845  *     |            .            *
846  * 1.0 ................................*
847  *     |            .                  .     *
848  *     |            .                  .          *
849  *     |            .                  .              *
850  *     |            .                  .                 *
851  *     |            .                  .                    *
852  *   0 +------------.------------------.----------------------*------------->
853  *           freerun^          setpoint^                 limit^   dirty pages
854  *
855  * (o) wb control line
856  *
857  *     ^ pos_ratio
858  *     |
859  *     |            *
860  *     |              *
861  *     |                *
862  *     |                  *
863  *     |                    * |<=========== span ============>|
864  * 1.0 .......................*
865  *     |                      . *
866  *     |                      .   *
867  *     |                      .     *
868  *     |                      .       *
869  *     |                      .         *
870  *     |                      .           *
871  *     |                      .             *
872  *     |                      .               *
873  *     |                      .                 *
874  *     |                      .                   *
875  *     |                      .                     *
876  * 1/4 ...............................................* * * * * * * * * * * *
877  *     |                      .                         .
878  *     |                      .                           .
879  *     |                      .                             .
880  *   0 +----------------------.-------------------------------.------------->
881  *                wb_setpoint^                    x_intercept^
882  *
883  * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
884  * be smoothly throttled down to normal if it starts high in situations like
885  * - start writing to a slow SD card and a fast disk at the same time. The SD
886  *   card's wb_dirty may rush to many times higher than wb_setpoint.
887  * - the wb dirty thresh drops quickly due to change of JBOD workload
888  */
wb_position_ratio(struct dirty_throttle_control * dtc)889 static void wb_position_ratio(struct dirty_throttle_control *dtc)
890 {
891 	struct bdi_writeback *wb = dtc->wb;
892 	unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth);
893 	unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
894 	unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
895 	unsigned long wb_thresh = dtc->wb_thresh;
896 	unsigned long x_intercept;
897 	unsigned long setpoint;		/* dirty pages' target balance point */
898 	unsigned long wb_setpoint;
899 	unsigned long span;
900 	long long pos_ratio;		/* for scaling up/down the rate limit */
901 	long x;
902 
903 	dtc->pos_ratio = 0;
904 
905 	if (unlikely(dtc->dirty >= limit))
906 		return;
907 
908 	/*
909 	 * global setpoint
910 	 *
911 	 * See comment for pos_ratio_polynom().
912 	 */
913 	setpoint = (freerun + limit) / 2;
914 	pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
915 
916 	/*
917 	 * The strictlimit feature is a tool preventing mistrusted filesystems
918 	 * from growing a large number of dirty pages before throttling. For
919 	 * such filesystems balance_dirty_pages always checks wb counters
920 	 * against wb limits. Even if global "nr_dirty" is under "freerun".
921 	 * This is especially important for fuse which sets bdi->max_ratio to
922 	 * 1% by default. Without strictlimit feature, fuse writeback may
923 	 * consume arbitrary amount of RAM because it is accounted in
924 	 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
925 	 *
926 	 * Here, in wb_position_ratio(), we calculate pos_ratio based on
927 	 * two values: wb_dirty and wb_thresh. Let's consider an example:
928 	 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
929 	 * limits are set by default to 10% and 20% (background and throttle).
930 	 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
931 	 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
932 	 * about ~6K pages (as the average of background and throttle wb
933 	 * limits). The 3rd order polynomial will provide positive feedback if
934 	 * wb_dirty is under wb_setpoint and vice versa.
935 	 *
936 	 * Note, that we cannot use global counters in these calculations
937 	 * because we want to throttle process writing to a strictlimit wb
938 	 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
939 	 * in the example above).
940 	 */
941 	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
942 		long long wb_pos_ratio;
943 
944 		if (dtc->wb_dirty < 8) {
945 			dtc->pos_ratio = min_t(long long, pos_ratio * 2,
946 					   2 << RATELIMIT_CALC_SHIFT);
947 			return;
948 		}
949 
950 		if (dtc->wb_dirty >= wb_thresh)
951 			return;
952 
953 		wb_setpoint = dirty_freerun_ceiling(wb_thresh,
954 						    dtc->wb_bg_thresh);
955 
956 		if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
957 			return;
958 
959 		wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
960 						 wb_thresh);
961 
962 		/*
963 		 * Typically, for strictlimit case, wb_setpoint << setpoint
964 		 * and pos_ratio >> wb_pos_ratio. In the other words global
965 		 * state ("dirty") is not limiting factor and we have to
966 		 * make decision based on wb counters. But there is an
967 		 * important case when global pos_ratio should get precedence:
968 		 * global limits are exceeded (e.g. due to activities on other
969 		 * wb's) while given strictlimit wb is below limit.
970 		 *
971 		 * "pos_ratio * wb_pos_ratio" would work for the case above,
972 		 * but it would look too non-natural for the case of all
973 		 * activity in the system coming from a single strictlimit wb
974 		 * with bdi->max_ratio == 100%.
975 		 *
976 		 * Note that min() below somewhat changes the dynamics of the
977 		 * control system. Normally, pos_ratio value can be well over 3
978 		 * (when globally we are at freerun and wb is well below wb
979 		 * setpoint). Now the maximum pos_ratio in the same situation
980 		 * is 2. We might want to tweak this if we observe the control
981 		 * system is too slow to adapt.
982 		 */
983 		dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
984 		return;
985 	}
986 
987 	/*
988 	 * We have computed basic pos_ratio above based on global situation. If
989 	 * the wb is over/under its share of dirty pages, we want to scale
990 	 * pos_ratio further down/up. That is done by the following mechanism.
991 	 */
992 
993 	/*
994 	 * wb setpoint
995 	 *
996 	 *        f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
997 	 *
998 	 *                        x_intercept - wb_dirty
999 	 *                     := --------------------------
1000 	 *                        x_intercept - wb_setpoint
1001 	 *
1002 	 * The main wb control line is a linear function that subjects to
1003 	 *
1004 	 * (1) f(wb_setpoint) = 1.0
1005 	 * (2) k = - 1 / (8 * write_bw)  (in single wb case)
1006 	 *     or equally: x_intercept = wb_setpoint + 8 * write_bw
1007 	 *
1008 	 * For single wb case, the dirty pages are observed to fluctuate
1009 	 * regularly within range
1010 	 *        [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1011 	 * for various filesystems, where (2) can yield in a reasonable 12.5%
1012 	 * fluctuation range for pos_ratio.
1013 	 *
1014 	 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1015 	 * own size, so move the slope over accordingly and choose a slope that
1016 	 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1017 	 */
1018 	if (unlikely(wb_thresh > dtc->thresh))
1019 		wb_thresh = dtc->thresh;
1020 	/*
1021 	 * It's very possible that wb_thresh is close to 0 not because the
1022 	 * device is slow, but that it has remained inactive for long time.
1023 	 * Honour such devices a reasonable good (hopefully IO efficient)
1024 	 * threshold, so that the occasional writes won't be blocked and active
1025 	 * writes can rampup the threshold quickly.
1026 	 */
1027 	wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1028 	/*
1029 	 * scale global setpoint to wb's:
1030 	 *	wb_setpoint = setpoint * wb_thresh / thresh
1031 	 */
1032 	x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1033 	wb_setpoint = setpoint * (u64)x >> 16;
1034 	/*
1035 	 * Use span=(8*write_bw) in single wb case as indicated by
1036 	 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1037 	 *
1038 	 *        wb_thresh                    thresh - wb_thresh
1039 	 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1040 	 *         thresh                           thresh
1041 	 */
1042 	span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1043 	x_intercept = wb_setpoint + span;
1044 
1045 	if (dtc->wb_dirty < x_intercept - span / 4) {
1046 		pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1047 				      (x_intercept - wb_setpoint) | 1);
1048 	} else
1049 		pos_ratio /= 4;
1050 
1051 	/*
1052 	 * wb reserve area, safeguard against dirty pool underrun and disk idle
1053 	 * It may push the desired control point of global dirty pages higher
1054 	 * than setpoint.
1055 	 */
1056 	x_intercept = wb_thresh / 2;
1057 	if (dtc->wb_dirty < x_intercept) {
1058 		if (dtc->wb_dirty > x_intercept / 8)
1059 			pos_ratio = div_u64(pos_ratio * x_intercept,
1060 					    dtc->wb_dirty);
1061 		else
1062 			pos_ratio *= 8;
1063 	}
1064 
1065 	dtc->pos_ratio = pos_ratio;
1066 }
1067 
wb_update_write_bandwidth(struct bdi_writeback * wb,unsigned long elapsed,unsigned long written)1068 static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1069 				      unsigned long elapsed,
1070 				      unsigned long written)
1071 {
1072 	const unsigned long period = roundup_pow_of_two(3 * HZ);
1073 	unsigned long avg = wb->avg_write_bandwidth;
1074 	unsigned long old = wb->write_bandwidth;
1075 	u64 bw;
1076 
1077 	/*
1078 	 * bw = written * HZ / elapsed
1079 	 *
1080 	 *                   bw * elapsed + write_bandwidth * (period - elapsed)
1081 	 * write_bandwidth = ---------------------------------------------------
1082 	 *                                          period
1083 	 *
1084 	 * @written may have decreased due to folio_account_redirty().
1085 	 * Avoid underflowing @bw calculation.
1086 	 */
1087 	bw = written - min(written, wb->written_stamp);
1088 	bw *= HZ;
1089 	if (unlikely(elapsed > period)) {
1090 		bw = div64_ul(bw, elapsed);
1091 		avg = bw;
1092 		goto out;
1093 	}
1094 	bw += (u64)wb->write_bandwidth * (period - elapsed);
1095 	bw >>= ilog2(period);
1096 
1097 	/*
1098 	 * one more level of smoothing, for filtering out sudden spikes
1099 	 */
1100 	if (avg > old && old >= (unsigned long)bw)
1101 		avg -= (avg - old) >> 3;
1102 
1103 	if (avg < old && old <= (unsigned long)bw)
1104 		avg += (old - avg) >> 3;
1105 
1106 out:
1107 	/* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1108 	avg = max(avg, 1LU);
1109 	if (wb_has_dirty_io(wb)) {
1110 		long delta = avg - wb->avg_write_bandwidth;
1111 		WARN_ON_ONCE(atomic_long_add_return(delta,
1112 					&wb->bdi->tot_write_bandwidth) <= 0);
1113 	}
1114 	wb->write_bandwidth = bw;
1115 	WRITE_ONCE(wb->avg_write_bandwidth, avg);
1116 }
1117 
update_dirty_limit(struct dirty_throttle_control * dtc)1118 static void update_dirty_limit(struct dirty_throttle_control *dtc)
1119 {
1120 	struct wb_domain *dom = dtc_dom(dtc);
1121 	unsigned long thresh = dtc->thresh;
1122 	unsigned long limit = dom->dirty_limit;
1123 
1124 	/*
1125 	 * Follow up in one step.
1126 	 */
1127 	if (limit < thresh) {
1128 		limit = thresh;
1129 		goto update;
1130 	}
1131 
1132 	/*
1133 	 * Follow down slowly. Use the higher one as the target, because thresh
1134 	 * may drop below dirty. This is exactly the reason to introduce
1135 	 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1136 	 */
1137 	thresh = max(thresh, dtc->dirty);
1138 	if (limit > thresh) {
1139 		limit -= (limit - thresh) >> 5;
1140 		goto update;
1141 	}
1142 	return;
1143 update:
1144 	dom->dirty_limit = limit;
1145 }
1146 
domain_update_dirty_limit(struct dirty_throttle_control * dtc,unsigned long now)1147 static void domain_update_dirty_limit(struct dirty_throttle_control *dtc,
1148 				      unsigned long now)
1149 {
1150 	struct wb_domain *dom = dtc_dom(dtc);
1151 
1152 	/*
1153 	 * check locklessly first to optimize away locking for the most time
1154 	 */
1155 	if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1156 		return;
1157 
1158 	spin_lock(&dom->lock);
1159 	if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1160 		update_dirty_limit(dtc);
1161 		dom->dirty_limit_tstamp = now;
1162 	}
1163 	spin_unlock(&dom->lock);
1164 }
1165 
1166 /*
1167  * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1168  *
1169  * Normal wb tasks will be curbed at or below it in long term.
1170  * Obviously it should be around (write_bw / N) when there are N dd tasks.
1171  */
wb_update_dirty_ratelimit(struct dirty_throttle_control * dtc,unsigned long dirtied,unsigned long elapsed)1172 static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1173 				      unsigned long dirtied,
1174 				      unsigned long elapsed)
1175 {
1176 	struct bdi_writeback *wb = dtc->wb;
1177 	unsigned long dirty = dtc->dirty;
1178 	unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1179 	unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1180 	unsigned long setpoint = (freerun + limit) / 2;
1181 	unsigned long write_bw = wb->avg_write_bandwidth;
1182 	unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1183 	unsigned long dirty_rate;
1184 	unsigned long task_ratelimit;
1185 	unsigned long balanced_dirty_ratelimit;
1186 	unsigned long step;
1187 	unsigned long x;
1188 	unsigned long shift;
1189 
1190 	/*
1191 	 * The dirty rate will match the writeout rate in long term, except
1192 	 * when dirty pages are truncated by userspace or re-dirtied by FS.
1193 	 */
1194 	dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1195 
1196 	/*
1197 	 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1198 	 */
1199 	task_ratelimit = (u64)dirty_ratelimit *
1200 					dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1201 	task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1202 
1203 	/*
1204 	 * A linear estimation of the "balanced" throttle rate. The theory is,
1205 	 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1206 	 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1207 	 * formula will yield the balanced rate limit (write_bw / N).
1208 	 *
1209 	 * Note that the expanded form is not a pure rate feedback:
1210 	 *	rate_(i+1) = rate_(i) * (write_bw / dirty_rate)		     (1)
1211 	 * but also takes pos_ratio into account:
1212 	 *	rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
1213 	 *
1214 	 * (1) is not realistic because pos_ratio also takes part in balancing
1215 	 * the dirty rate.  Consider the state
1216 	 *	pos_ratio = 0.5						     (3)
1217 	 *	rate = 2 * (write_bw / N)				     (4)
1218 	 * If (1) is used, it will stuck in that state! Because each dd will
1219 	 * be throttled at
1220 	 *	task_ratelimit = pos_ratio * rate = (write_bw / N)	     (5)
1221 	 * yielding
1222 	 *	dirty_rate = N * task_ratelimit = write_bw		     (6)
1223 	 * put (6) into (1) we get
1224 	 *	rate_(i+1) = rate_(i)					     (7)
1225 	 *
1226 	 * So we end up using (2) to always keep
1227 	 *	rate_(i+1) ~= (write_bw / N)				     (8)
1228 	 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1229 	 * pos_ratio is able to drive itself to 1.0, which is not only where
1230 	 * the dirty count meet the setpoint, but also where the slope of
1231 	 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1232 	 */
1233 	balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1234 					   dirty_rate | 1);
1235 	/*
1236 	 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1237 	 */
1238 	if (unlikely(balanced_dirty_ratelimit > write_bw))
1239 		balanced_dirty_ratelimit = write_bw;
1240 
1241 	/*
1242 	 * We could safely do this and return immediately:
1243 	 *
1244 	 *	wb->dirty_ratelimit = balanced_dirty_ratelimit;
1245 	 *
1246 	 * However to get a more stable dirty_ratelimit, the below elaborated
1247 	 * code makes use of task_ratelimit to filter out singular points and
1248 	 * limit the step size.
1249 	 *
1250 	 * The below code essentially only uses the relative value of
1251 	 *
1252 	 *	task_ratelimit - dirty_ratelimit
1253 	 *	= (pos_ratio - 1) * dirty_ratelimit
1254 	 *
1255 	 * which reflects the direction and size of dirty position error.
1256 	 */
1257 
1258 	/*
1259 	 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1260 	 * task_ratelimit is on the same side of dirty_ratelimit, too.
1261 	 * For example, when
1262 	 * - dirty_ratelimit > balanced_dirty_ratelimit
1263 	 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1264 	 * lowering dirty_ratelimit will help meet both the position and rate
1265 	 * control targets. Otherwise, don't update dirty_ratelimit if it will
1266 	 * only help meet the rate target. After all, what the users ultimately
1267 	 * feel and care are stable dirty rate and small position error.
1268 	 *
1269 	 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1270 	 * and filter out the singular points of balanced_dirty_ratelimit. Which
1271 	 * keeps jumping around randomly and can even leap far away at times
1272 	 * due to the small 200ms estimation period of dirty_rate (we want to
1273 	 * keep that period small to reduce time lags).
1274 	 */
1275 	step = 0;
1276 
1277 	/*
1278 	 * For strictlimit case, calculations above were based on wb counters
1279 	 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1280 	 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1281 	 * Hence, to calculate "step" properly, we have to use wb_dirty as
1282 	 * "dirty" and wb_setpoint as "setpoint".
1283 	 *
1284 	 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1285 	 * it's possible that wb_thresh is close to zero due to inactivity
1286 	 * of backing device.
1287 	 */
1288 	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1289 		dirty = dtc->wb_dirty;
1290 		if (dtc->wb_dirty < 8)
1291 			setpoint = dtc->wb_dirty + 1;
1292 		else
1293 			setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1294 	}
1295 
1296 	if (dirty < setpoint) {
1297 		x = min3(wb->balanced_dirty_ratelimit,
1298 			 balanced_dirty_ratelimit, task_ratelimit);
1299 		if (dirty_ratelimit < x)
1300 			step = x - dirty_ratelimit;
1301 	} else {
1302 		x = max3(wb->balanced_dirty_ratelimit,
1303 			 balanced_dirty_ratelimit, task_ratelimit);
1304 		if (dirty_ratelimit > x)
1305 			step = dirty_ratelimit - x;
1306 	}
1307 
1308 	/*
1309 	 * Don't pursue 100% rate matching. It's impossible since the balanced
1310 	 * rate itself is constantly fluctuating. So decrease the track speed
1311 	 * when it gets close to the target. Helps eliminate pointless tremors.
1312 	 */
1313 	shift = dirty_ratelimit / (2 * step + 1);
1314 	if (shift < BITS_PER_LONG)
1315 		step = DIV_ROUND_UP(step >> shift, 8);
1316 	else
1317 		step = 0;
1318 
1319 	if (dirty_ratelimit < balanced_dirty_ratelimit)
1320 		dirty_ratelimit += step;
1321 	else
1322 		dirty_ratelimit -= step;
1323 
1324 	WRITE_ONCE(wb->dirty_ratelimit, max(dirty_ratelimit, 1UL));
1325 	wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1326 
1327 	trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1328 }
1329 
__wb_update_bandwidth(struct dirty_throttle_control * gdtc,struct dirty_throttle_control * mdtc,bool update_ratelimit)1330 static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1331 				  struct dirty_throttle_control *mdtc,
1332 				  bool update_ratelimit)
1333 {
1334 	struct bdi_writeback *wb = gdtc->wb;
1335 	unsigned long now = jiffies;
1336 	unsigned long elapsed;
1337 	unsigned long dirtied;
1338 	unsigned long written;
1339 
1340 	spin_lock(&wb->list_lock);
1341 
1342 	/*
1343 	 * Lockless checks for elapsed time are racy and delayed update after
1344 	 * IO completion doesn't do it at all (to make sure written pages are
1345 	 * accounted reasonably quickly). Make sure elapsed >= 1 to avoid
1346 	 * division errors.
1347 	 */
1348 	elapsed = max(now - wb->bw_time_stamp, 1UL);
1349 	dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1350 	written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1351 
1352 	if (update_ratelimit) {
1353 		domain_update_dirty_limit(gdtc, now);
1354 		wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1355 
1356 		/*
1357 		 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1358 		 * compiler has no way to figure that out.  Help it.
1359 		 */
1360 		if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1361 			domain_update_dirty_limit(mdtc, now);
1362 			wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1363 		}
1364 	}
1365 	wb_update_write_bandwidth(wb, elapsed, written);
1366 
1367 	wb->dirtied_stamp = dirtied;
1368 	wb->written_stamp = written;
1369 	WRITE_ONCE(wb->bw_time_stamp, now);
1370 	spin_unlock(&wb->list_lock);
1371 }
1372 
wb_update_bandwidth(struct bdi_writeback * wb)1373 void wb_update_bandwidth(struct bdi_writeback *wb)
1374 {
1375 	struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1376 
1377 	__wb_update_bandwidth(&gdtc, NULL, false);
1378 }
1379 
1380 /* Interval after which we consider wb idle and don't estimate bandwidth */
1381 #define WB_BANDWIDTH_IDLE_JIF (HZ)
1382 
wb_bandwidth_estimate_start(struct bdi_writeback * wb)1383 static void wb_bandwidth_estimate_start(struct bdi_writeback *wb)
1384 {
1385 	unsigned long now = jiffies;
1386 	unsigned long elapsed = now - READ_ONCE(wb->bw_time_stamp);
1387 
1388 	if (elapsed > WB_BANDWIDTH_IDLE_JIF &&
1389 	    !atomic_read(&wb->writeback_inodes)) {
1390 		spin_lock(&wb->list_lock);
1391 		wb->dirtied_stamp = wb_stat(wb, WB_DIRTIED);
1392 		wb->written_stamp = wb_stat(wb, WB_WRITTEN);
1393 		WRITE_ONCE(wb->bw_time_stamp, now);
1394 		spin_unlock(&wb->list_lock);
1395 	}
1396 }
1397 
1398 /*
1399  * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1400  * will look to see if it needs to start dirty throttling.
1401  *
1402  * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1403  * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1404  * (the number of pages we may dirty without exceeding the dirty limits).
1405  */
dirty_poll_interval(unsigned long dirty,unsigned long thresh)1406 static unsigned long dirty_poll_interval(unsigned long dirty,
1407 					 unsigned long thresh)
1408 {
1409 	if (thresh > dirty)
1410 		return 1UL << (ilog2(thresh - dirty) >> 1);
1411 
1412 	return 1;
1413 }
1414 
wb_max_pause(struct bdi_writeback * wb,unsigned long wb_dirty)1415 static unsigned long wb_max_pause(struct bdi_writeback *wb,
1416 				  unsigned long wb_dirty)
1417 {
1418 	unsigned long bw = READ_ONCE(wb->avg_write_bandwidth);
1419 	unsigned long t;
1420 
1421 	/*
1422 	 * Limit pause time for small memory systems. If sleeping for too long
1423 	 * time, a small pool of dirty/writeback pages may go empty and disk go
1424 	 * idle.
1425 	 *
1426 	 * 8 serves as the safety ratio.
1427 	 */
1428 	t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1429 	t++;
1430 
1431 	return min_t(unsigned long, t, MAX_PAUSE);
1432 }
1433 
wb_min_pause(struct bdi_writeback * wb,long max_pause,unsigned long task_ratelimit,unsigned long dirty_ratelimit,int * nr_dirtied_pause)1434 static long wb_min_pause(struct bdi_writeback *wb,
1435 			 long max_pause,
1436 			 unsigned long task_ratelimit,
1437 			 unsigned long dirty_ratelimit,
1438 			 int *nr_dirtied_pause)
1439 {
1440 	long hi = ilog2(READ_ONCE(wb->avg_write_bandwidth));
1441 	long lo = ilog2(READ_ONCE(wb->dirty_ratelimit));
1442 	long t;		/* target pause */
1443 	long pause;	/* estimated next pause */
1444 	int pages;	/* target nr_dirtied_pause */
1445 
1446 	/* target for 10ms pause on 1-dd case */
1447 	t = max(1, HZ / 100);
1448 
1449 	/*
1450 	 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1451 	 * overheads.
1452 	 *
1453 	 * (N * 10ms) on 2^N concurrent tasks.
1454 	 */
1455 	if (hi > lo)
1456 		t += (hi - lo) * (10 * HZ) / 1024;
1457 
1458 	/*
1459 	 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1460 	 * on the much more stable dirty_ratelimit. However the next pause time
1461 	 * will be computed based on task_ratelimit and the two rate limits may
1462 	 * depart considerably at some time. Especially if task_ratelimit goes
1463 	 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1464 	 * pause time will be max_pause*2 _trimmed down_ to max_pause.  As a
1465 	 * result task_ratelimit won't be executed faithfully, which could
1466 	 * eventually bring down dirty_ratelimit.
1467 	 *
1468 	 * We apply two rules to fix it up:
1469 	 * 1) try to estimate the next pause time and if necessary, use a lower
1470 	 *    nr_dirtied_pause so as not to exceed max_pause. When this happens,
1471 	 *    nr_dirtied_pause will be "dancing" with task_ratelimit.
1472 	 * 2) limit the target pause time to max_pause/2, so that the normal
1473 	 *    small fluctuations of task_ratelimit won't trigger rule (1) and
1474 	 *    nr_dirtied_pause will remain as stable as dirty_ratelimit.
1475 	 */
1476 	t = min(t, 1 + max_pause / 2);
1477 	pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1478 
1479 	/*
1480 	 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1481 	 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1482 	 * When the 16 consecutive reads are often interrupted by some dirty
1483 	 * throttling pause during the async writes, cfq will go into idles
1484 	 * (deadline is fine). So push nr_dirtied_pause as high as possible
1485 	 * until reaches DIRTY_POLL_THRESH=32 pages.
1486 	 */
1487 	if (pages < DIRTY_POLL_THRESH) {
1488 		t = max_pause;
1489 		pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1490 		if (pages > DIRTY_POLL_THRESH) {
1491 			pages = DIRTY_POLL_THRESH;
1492 			t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1493 		}
1494 	}
1495 
1496 	pause = HZ * pages / (task_ratelimit + 1);
1497 	if (pause > max_pause) {
1498 		t = max_pause;
1499 		pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1500 	}
1501 
1502 	*nr_dirtied_pause = pages;
1503 	/*
1504 	 * The minimal pause time will normally be half the target pause time.
1505 	 */
1506 	return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1507 }
1508 
wb_dirty_limits(struct dirty_throttle_control * dtc)1509 static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1510 {
1511 	struct bdi_writeback *wb = dtc->wb;
1512 	unsigned long wb_reclaimable;
1513 
1514 	/*
1515 	 * wb_thresh is not treated as some limiting factor as
1516 	 * dirty_thresh, due to reasons
1517 	 * - in JBOD setup, wb_thresh can fluctuate a lot
1518 	 * - in a system with HDD and USB key, the USB key may somehow
1519 	 *   go into state (wb_dirty >> wb_thresh) either because
1520 	 *   wb_dirty starts high, or because wb_thresh drops low.
1521 	 *   In this case we don't want to hard throttle the USB key
1522 	 *   dirtiers for 100 seconds until wb_dirty drops under
1523 	 *   wb_thresh. Instead the auxiliary wb control line in
1524 	 *   wb_position_ratio() will let the dirtier task progress
1525 	 *   at some rate <= (write_bw / 2) for bringing down wb_dirty.
1526 	 */
1527 	dtc->wb_thresh = __wb_calc_thresh(dtc);
1528 	dtc->wb_bg_thresh = dtc->thresh ?
1529 		div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1530 
1531 	/*
1532 	 * In order to avoid the stacked BDI deadlock we need
1533 	 * to ensure we accurately count the 'dirty' pages when
1534 	 * the threshold is low.
1535 	 *
1536 	 * Otherwise it would be possible to get thresh+n pages
1537 	 * reported dirty, even though there are thresh-m pages
1538 	 * actually dirty; with m+n sitting in the percpu
1539 	 * deltas.
1540 	 */
1541 	if (dtc->wb_thresh < 2 * wb_stat_error()) {
1542 		wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1543 		dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1544 	} else {
1545 		wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1546 		dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1547 	}
1548 }
1549 
1550 /*
1551  * balance_dirty_pages() must be called by processes which are generating dirty
1552  * data.  It looks at the number of dirty pages in the machine and will force
1553  * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1554  * If we're over `background_thresh' then the writeback threads are woken to
1555  * perform some writeout.
1556  */
balance_dirty_pages(struct bdi_writeback * wb,unsigned long pages_dirtied)1557 static void balance_dirty_pages(struct bdi_writeback *wb,
1558 				unsigned long pages_dirtied)
1559 {
1560 	struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1561 	struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1562 	struct dirty_throttle_control * const gdtc = &gdtc_stor;
1563 	struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1564 						     &mdtc_stor : NULL;
1565 	struct dirty_throttle_control *sdtc;
1566 	unsigned long nr_reclaimable;	/* = file_dirty */
1567 	long period;
1568 	long pause;
1569 	long max_pause;
1570 	long min_pause;
1571 	int nr_dirtied_pause;
1572 	bool dirty_exceeded = false;
1573 	unsigned long task_ratelimit;
1574 	unsigned long dirty_ratelimit;
1575 	struct backing_dev_info *bdi = wb->bdi;
1576 	bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1577 	unsigned long start_time = jiffies;
1578 
1579 	for (;;) {
1580 		unsigned long now = jiffies;
1581 		unsigned long dirty, thresh, bg_thresh;
1582 		unsigned long m_dirty = 0;	/* stop bogus uninit warnings */
1583 		unsigned long m_thresh = 0;
1584 		unsigned long m_bg_thresh = 0;
1585 
1586 		nr_reclaimable = global_node_page_state(NR_FILE_DIRTY);
1587 		gdtc->avail = global_dirtyable_memory();
1588 		gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
1589 
1590 		domain_dirty_limits(gdtc);
1591 
1592 		if (unlikely(strictlimit)) {
1593 			wb_dirty_limits(gdtc);
1594 
1595 			dirty = gdtc->wb_dirty;
1596 			thresh = gdtc->wb_thresh;
1597 			bg_thresh = gdtc->wb_bg_thresh;
1598 		} else {
1599 			dirty = gdtc->dirty;
1600 			thresh = gdtc->thresh;
1601 			bg_thresh = gdtc->bg_thresh;
1602 		}
1603 
1604 		if (mdtc) {
1605 			unsigned long filepages, headroom, writeback;
1606 
1607 			/*
1608 			 * If @wb belongs to !root memcg, repeat the same
1609 			 * basic calculations for the memcg domain.
1610 			 */
1611 			mem_cgroup_wb_stats(wb, &filepages, &headroom,
1612 					    &mdtc->dirty, &writeback);
1613 			mdtc->dirty += writeback;
1614 			mdtc_calc_avail(mdtc, filepages, headroom);
1615 
1616 			domain_dirty_limits(mdtc);
1617 
1618 			if (unlikely(strictlimit)) {
1619 				wb_dirty_limits(mdtc);
1620 				m_dirty = mdtc->wb_dirty;
1621 				m_thresh = mdtc->wb_thresh;
1622 				m_bg_thresh = mdtc->wb_bg_thresh;
1623 			} else {
1624 				m_dirty = mdtc->dirty;
1625 				m_thresh = mdtc->thresh;
1626 				m_bg_thresh = mdtc->bg_thresh;
1627 			}
1628 		}
1629 
1630 		/*
1631 		 * Throttle it only when the background writeback cannot
1632 		 * catch-up. This avoids (excessively) small writeouts
1633 		 * when the wb limits are ramping up in case of !strictlimit.
1634 		 *
1635 		 * In strictlimit case make decision based on the wb counters
1636 		 * and limits. Small writeouts when the wb limits are ramping
1637 		 * up are the price we consciously pay for strictlimit-ing.
1638 		 *
1639 		 * If memcg domain is in effect, @dirty should be under
1640 		 * both global and memcg freerun ceilings.
1641 		 */
1642 		if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1643 		    (!mdtc ||
1644 		     m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1645 			unsigned long intv;
1646 			unsigned long m_intv;
1647 
1648 free_running:
1649 			intv = dirty_poll_interval(dirty, thresh);
1650 			m_intv = ULONG_MAX;
1651 
1652 			current->dirty_paused_when = now;
1653 			current->nr_dirtied = 0;
1654 			if (mdtc)
1655 				m_intv = dirty_poll_interval(m_dirty, m_thresh);
1656 			current->nr_dirtied_pause = min(intv, m_intv);
1657 			break;
1658 		}
1659 
1660 		if (unlikely(!writeback_in_progress(wb)))
1661 			wb_start_background_writeback(wb);
1662 
1663 		mem_cgroup_flush_foreign(wb);
1664 
1665 		/*
1666 		 * Calculate global domain's pos_ratio and select the
1667 		 * global dtc by default.
1668 		 */
1669 		if (!strictlimit) {
1670 			wb_dirty_limits(gdtc);
1671 
1672 			if ((current->flags & PF_LOCAL_THROTTLE) &&
1673 			    gdtc->wb_dirty <
1674 			    dirty_freerun_ceiling(gdtc->wb_thresh,
1675 						  gdtc->wb_bg_thresh))
1676 				/*
1677 				 * LOCAL_THROTTLE tasks must not be throttled
1678 				 * when below the per-wb freerun ceiling.
1679 				 */
1680 				goto free_running;
1681 		}
1682 
1683 		dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1684 			((gdtc->dirty > gdtc->thresh) || strictlimit);
1685 
1686 		wb_position_ratio(gdtc);
1687 		sdtc = gdtc;
1688 
1689 		if (mdtc) {
1690 			/*
1691 			 * If memcg domain is in effect, calculate its
1692 			 * pos_ratio.  @wb should satisfy constraints from
1693 			 * both global and memcg domains.  Choose the one
1694 			 * w/ lower pos_ratio.
1695 			 */
1696 			if (!strictlimit) {
1697 				wb_dirty_limits(mdtc);
1698 
1699 				if ((current->flags & PF_LOCAL_THROTTLE) &&
1700 				    mdtc->wb_dirty <
1701 				    dirty_freerun_ceiling(mdtc->wb_thresh,
1702 							  mdtc->wb_bg_thresh))
1703 					/*
1704 					 * LOCAL_THROTTLE tasks must not be
1705 					 * throttled when below the per-wb
1706 					 * freerun ceiling.
1707 					 */
1708 					goto free_running;
1709 			}
1710 			dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1711 				((mdtc->dirty > mdtc->thresh) || strictlimit);
1712 
1713 			wb_position_ratio(mdtc);
1714 			if (mdtc->pos_ratio < gdtc->pos_ratio)
1715 				sdtc = mdtc;
1716 		}
1717 
1718 		if (dirty_exceeded && !wb->dirty_exceeded)
1719 			wb->dirty_exceeded = 1;
1720 
1721 		if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
1722 					   BANDWIDTH_INTERVAL))
1723 			__wb_update_bandwidth(gdtc, mdtc, true);
1724 
1725 		/* throttle according to the chosen dtc */
1726 		dirty_ratelimit = READ_ONCE(wb->dirty_ratelimit);
1727 		task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1728 							RATELIMIT_CALC_SHIFT;
1729 		max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1730 		min_pause = wb_min_pause(wb, max_pause,
1731 					 task_ratelimit, dirty_ratelimit,
1732 					 &nr_dirtied_pause);
1733 
1734 		if (unlikely(task_ratelimit == 0)) {
1735 			period = max_pause;
1736 			pause = max_pause;
1737 			goto pause;
1738 		}
1739 		period = HZ * pages_dirtied / task_ratelimit;
1740 		pause = period;
1741 		if (current->dirty_paused_when)
1742 			pause -= now - current->dirty_paused_when;
1743 		/*
1744 		 * For less than 1s think time (ext3/4 may block the dirtier
1745 		 * for up to 800ms from time to time on 1-HDD; so does xfs,
1746 		 * however at much less frequency), try to compensate it in
1747 		 * future periods by updating the virtual time; otherwise just
1748 		 * do a reset, as it may be a light dirtier.
1749 		 */
1750 		if (pause < min_pause) {
1751 			trace_balance_dirty_pages(wb,
1752 						  sdtc->thresh,
1753 						  sdtc->bg_thresh,
1754 						  sdtc->dirty,
1755 						  sdtc->wb_thresh,
1756 						  sdtc->wb_dirty,
1757 						  dirty_ratelimit,
1758 						  task_ratelimit,
1759 						  pages_dirtied,
1760 						  period,
1761 						  min(pause, 0L),
1762 						  start_time);
1763 			if (pause < -HZ) {
1764 				current->dirty_paused_when = now;
1765 				current->nr_dirtied = 0;
1766 			} else if (period) {
1767 				current->dirty_paused_when += period;
1768 				current->nr_dirtied = 0;
1769 			} else if (current->nr_dirtied_pause <= pages_dirtied)
1770 				current->nr_dirtied_pause += pages_dirtied;
1771 			break;
1772 		}
1773 		if (unlikely(pause > max_pause)) {
1774 			/* for occasional dropped task_ratelimit */
1775 			now += min(pause - max_pause, max_pause);
1776 			pause = max_pause;
1777 		}
1778 
1779 pause:
1780 		trace_balance_dirty_pages(wb,
1781 					  sdtc->thresh,
1782 					  sdtc->bg_thresh,
1783 					  sdtc->dirty,
1784 					  sdtc->wb_thresh,
1785 					  sdtc->wb_dirty,
1786 					  dirty_ratelimit,
1787 					  task_ratelimit,
1788 					  pages_dirtied,
1789 					  period,
1790 					  pause,
1791 					  start_time);
1792 		__set_current_state(TASK_KILLABLE);
1793 		wb->dirty_sleep = now;
1794 		io_schedule_timeout(pause);
1795 
1796 		current->dirty_paused_when = now + pause;
1797 		current->nr_dirtied = 0;
1798 		current->nr_dirtied_pause = nr_dirtied_pause;
1799 
1800 		/*
1801 		 * This is typically equal to (dirty < thresh) and can also
1802 		 * keep "1000+ dd on a slow USB stick" under control.
1803 		 */
1804 		if (task_ratelimit)
1805 			break;
1806 
1807 		/*
1808 		 * In the case of an unresponsive NFS server and the NFS dirty
1809 		 * pages exceeds dirty_thresh, give the other good wb's a pipe
1810 		 * to go through, so that tasks on them still remain responsive.
1811 		 *
1812 		 * In theory 1 page is enough to keep the consumer-producer
1813 		 * pipe going: the flusher cleans 1 page => the task dirties 1
1814 		 * more page. However wb_dirty has accounting errors.  So use
1815 		 * the larger and more IO friendly wb_stat_error.
1816 		 */
1817 		if (sdtc->wb_dirty <= wb_stat_error())
1818 			break;
1819 
1820 		if (fatal_signal_pending(current))
1821 			break;
1822 	}
1823 
1824 	if (!dirty_exceeded && wb->dirty_exceeded)
1825 		wb->dirty_exceeded = 0;
1826 
1827 	if (writeback_in_progress(wb))
1828 		return;
1829 
1830 	/*
1831 	 * In laptop mode, we wait until hitting the higher threshold before
1832 	 * starting background writeout, and then write out all the way down
1833 	 * to the lower threshold.  So slow writers cause minimal disk activity.
1834 	 *
1835 	 * In normal mode, we start background writeout at the lower
1836 	 * background_thresh, to keep the amount of dirty memory low.
1837 	 */
1838 	if (laptop_mode)
1839 		return;
1840 
1841 	if (nr_reclaimable > gdtc->bg_thresh)
1842 		wb_start_background_writeback(wb);
1843 }
1844 
1845 static DEFINE_PER_CPU(int, bdp_ratelimits);
1846 
1847 /*
1848  * Normal tasks are throttled by
1849  *	loop {
1850  *		dirty tsk->nr_dirtied_pause pages;
1851  *		take a snap in balance_dirty_pages();
1852  *	}
1853  * However there is a worst case. If every task exit immediately when dirtied
1854  * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1855  * called to throttle the page dirties. The solution is to save the not yet
1856  * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1857  * randomly into the running tasks. This works well for the above worst case,
1858  * as the new task will pick up and accumulate the old task's leaked dirty
1859  * count and eventually get throttled.
1860  */
1861 DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1862 
1863 /**
1864  * balance_dirty_pages_ratelimited - balance dirty memory state
1865  * @mapping: address_space which was dirtied
1866  *
1867  * Processes which are dirtying memory should call in here once for each page
1868  * which was newly dirtied.  The function will periodically check the system's
1869  * dirty state and will initiate writeback if needed.
1870  *
1871  * Once we're over the dirty memory limit we decrease the ratelimiting
1872  * by a lot, to prevent individual processes from overshooting the limit
1873  * by (ratelimit_pages) each.
1874  */
balance_dirty_pages_ratelimited(struct address_space * mapping)1875 void balance_dirty_pages_ratelimited(struct address_space *mapping)
1876 {
1877 	struct inode *inode = mapping->host;
1878 	struct backing_dev_info *bdi = inode_to_bdi(inode);
1879 	struct bdi_writeback *wb = NULL;
1880 	int ratelimit;
1881 	int *p;
1882 
1883 	if (!(bdi->capabilities & BDI_CAP_WRITEBACK))
1884 		return;
1885 
1886 	if (inode_cgwb_enabled(inode))
1887 		wb = wb_get_create_current(bdi, GFP_KERNEL);
1888 	if (!wb)
1889 		wb = &bdi->wb;
1890 
1891 	ratelimit = current->nr_dirtied_pause;
1892 	if (wb->dirty_exceeded)
1893 		ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1894 
1895 	preempt_disable();
1896 	/*
1897 	 * This prevents one CPU to accumulate too many dirtied pages without
1898 	 * calling into balance_dirty_pages(), which can happen when there are
1899 	 * 1000+ tasks, all of them start dirtying pages at exactly the same
1900 	 * time, hence all honoured too large initial task->nr_dirtied_pause.
1901 	 */
1902 	p =  this_cpu_ptr(&bdp_ratelimits);
1903 	if (unlikely(current->nr_dirtied >= ratelimit))
1904 		*p = 0;
1905 	else if (unlikely(*p >= ratelimit_pages)) {
1906 		*p = 0;
1907 		ratelimit = 0;
1908 	}
1909 	/*
1910 	 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1911 	 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1912 	 * the dirty throttling and livelock other long-run dirtiers.
1913 	 */
1914 	p = this_cpu_ptr(&dirty_throttle_leaks);
1915 	if (*p > 0 && current->nr_dirtied < ratelimit) {
1916 		unsigned long nr_pages_dirtied;
1917 		nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1918 		*p -= nr_pages_dirtied;
1919 		current->nr_dirtied += nr_pages_dirtied;
1920 	}
1921 	preempt_enable();
1922 
1923 	if (unlikely(current->nr_dirtied >= ratelimit))
1924 		balance_dirty_pages(wb, current->nr_dirtied);
1925 
1926 	wb_put(wb);
1927 }
1928 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1929 
1930 /**
1931  * wb_over_bg_thresh - does @wb need to be written back?
1932  * @wb: bdi_writeback of interest
1933  *
1934  * Determines whether background writeback should keep writing @wb or it's
1935  * clean enough.
1936  *
1937  * Return: %true if writeback should continue.
1938  */
wb_over_bg_thresh(struct bdi_writeback * wb)1939 bool wb_over_bg_thresh(struct bdi_writeback *wb)
1940 {
1941 	struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1942 	struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1943 	struct dirty_throttle_control * const gdtc = &gdtc_stor;
1944 	struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1945 						     &mdtc_stor : NULL;
1946 	unsigned long reclaimable;
1947 	unsigned long thresh;
1948 
1949 	/*
1950 	 * Similar to balance_dirty_pages() but ignores pages being written
1951 	 * as we're trying to decide whether to put more under writeback.
1952 	 */
1953 	gdtc->avail = global_dirtyable_memory();
1954 	gdtc->dirty = global_node_page_state(NR_FILE_DIRTY);
1955 	domain_dirty_limits(gdtc);
1956 
1957 	if (gdtc->dirty > gdtc->bg_thresh)
1958 		return true;
1959 
1960 	thresh = wb_calc_thresh(gdtc->wb, gdtc->bg_thresh);
1961 	if (thresh < 2 * wb_stat_error())
1962 		reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1963 	else
1964 		reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1965 
1966 	if (reclaimable > thresh)
1967 		return true;
1968 
1969 	if (mdtc) {
1970 		unsigned long filepages, headroom, writeback;
1971 
1972 		mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
1973 				    &writeback);
1974 		mdtc_calc_avail(mdtc, filepages, headroom);
1975 		domain_dirty_limits(mdtc);	/* ditto, ignore writeback */
1976 
1977 		if (mdtc->dirty > mdtc->bg_thresh)
1978 			return true;
1979 
1980 		thresh = wb_calc_thresh(mdtc->wb, mdtc->bg_thresh);
1981 		if (thresh < 2 * wb_stat_error())
1982 			reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1983 		else
1984 			reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1985 
1986 		if (reclaimable > thresh)
1987 			return true;
1988 	}
1989 
1990 	return false;
1991 }
1992 
1993 #ifdef CONFIG_SYSCTL
1994 /*
1995  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1996  */
dirty_writeback_centisecs_handler(struct ctl_table * table,int write,void * buffer,size_t * length,loff_t * ppos)1997 static int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
1998 		void *buffer, size_t *length, loff_t *ppos)
1999 {
2000 	unsigned int old_interval = dirty_writeback_interval;
2001 	int ret;
2002 
2003 	ret = proc_dointvec(table, write, buffer, length, ppos);
2004 
2005 	/*
2006 	 * Writing 0 to dirty_writeback_interval will disable periodic writeback
2007 	 * and a different non-zero value will wakeup the writeback threads.
2008 	 * wb_wakeup_delayed() would be more appropriate, but it's a pain to
2009 	 * iterate over all bdis and wbs.
2010 	 * The reason we do this is to make the change take effect immediately.
2011 	 */
2012 	if (!ret && write && dirty_writeback_interval &&
2013 		dirty_writeback_interval != old_interval)
2014 		wakeup_flusher_threads(WB_REASON_PERIODIC);
2015 
2016 	return ret;
2017 }
2018 #endif
2019 
laptop_mode_timer_fn(struct timer_list * t)2020 void laptop_mode_timer_fn(struct timer_list *t)
2021 {
2022 	struct backing_dev_info *backing_dev_info =
2023 		from_timer(backing_dev_info, t, laptop_mode_wb_timer);
2024 
2025 	wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
2026 }
2027 
2028 /*
2029  * We've spun up the disk and we're in laptop mode: schedule writeback
2030  * of all dirty data a few seconds from now.  If the flush is already scheduled
2031  * then push it back - the user is still using the disk.
2032  */
laptop_io_completion(struct backing_dev_info * info)2033 void laptop_io_completion(struct backing_dev_info *info)
2034 {
2035 	mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2036 }
2037 
2038 /*
2039  * We're in laptop mode and we've just synced. The sync's writes will have
2040  * caused another writeback to be scheduled by laptop_io_completion.
2041  * Nothing needs to be written back anymore, so we unschedule the writeback.
2042  */
laptop_sync_completion(void)2043 void laptop_sync_completion(void)
2044 {
2045 	struct backing_dev_info *bdi;
2046 
2047 	rcu_read_lock();
2048 
2049 	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2050 		del_timer(&bdi->laptop_mode_wb_timer);
2051 
2052 	rcu_read_unlock();
2053 }
2054 
2055 /*
2056  * If ratelimit_pages is too high then we can get into dirty-data overload
2057  * if a large number of processes all perform writes at the same time.
2058  *
2059  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2060  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2061  * thresholds.
2062  */
2063 
writeback_set_ratelimit(void)2064 void writeback_set_ratelimit(void)
2065 {
2066 	struct wb_domain *dom = &global_wb_domain;
2067 	unsigned long background_thresh;
2068 	unsigned long dirty_thresh;
2069 
2070 	global_dirty_limits(&background_thresh, &dirty_thresh);
2071 	dom->dirty_limit = dirty_thresh;
2072 	ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2073 	if (ratelimit_pages < 16)
2074 		ratelimit_pages = 16;
2075 }
2076 
page_writeback_cpu_online(unsigned int cpu)2077 static int page_writeback_cpu_online(unsigned int cpu)
2078 {
2079 	writeback_set_ratelimit();
2080 	return 0;
2081 }
2082 
2083 #ifdef CONFIG_SYSCTL
2084 
2085 /* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
2086 static const unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
2087 
2088 static struct ctl_table vm_page_writeback_sysctls[] = {
2089 	{
2090 		.procname   = "dirty_background_ratio",
2091 		.data       = &dirty_background_ratio,
2092 		.maxlen     = sizeof(dirty_background_ratio),
2093 		.mode       = 0644,
2094 		.proc_handler   = dirty_background_ratio_handler,
2095 		.extra1     = SYSCTL_ZERO,
2096 		.extra2     = SYSCTL_ONE_HUNDRED,
2097 	},
2098 	{
2099 		.procname   = "dirty_background_bytes",
2100 		.data       = &dirty_background_bytes,
2101 		.maxlen     = sizeof(dirty_background_bytes),
2102 		.mode       = 0644,
2103 		.proc_handler   = dirty_background_bytes_handler,
2104 		.extra1     = SYSCTL_LONG_ONE,
2105 	},
2106 	{
2107 		.procname   = "dirty_ratio",
2108 		.data       = &vm_dirty_ratio,
2109 		.maxlen     = sizeof(vm_dirty_ratio),
2110 		.mode       = 0644,
2111 		.proc_handler   = dirty_ratio_handler,
2112 		.extra1     = SYSCTL_ZERO,
2113 		.extra2     = SYSCTL_ONE_HUNDRED,
2114 	},
2115 	{
2116 		.procname   = "dirty_bytes",
2117 		.data       = &vm_dirty_bytes,
2118 		.maxlen     = sizeof(vm_dirty_bytes),
2119 		.mode       = 0644,
2120 		.proc_handler   = dirty_bytes_handler,
2121 		.extra1     = (void *)&dirty_bytes_min,
2122 	},
2123 	{
2124 		.procname   = "dirty_writeback_centisecs",
2125 		.data       = &dirty_writeback_interval,
2126 		.maxlen     = sizeof(dirty_writeback_interval),
2127 		.mode       = 0644,
2128 		.proc_handler   = dirty_writeback_centisecs_handler,
2129 	},
2130 	{
2131 		.procname   = "dirty_expire_centisecs",
2132 		.data       = &dirty_expire_interval,
2133 		.maxlen     = sizeof(dirty_expire_interval),
2134 		.mode       = 0644,
2135 		.proc_handler   = proc_dointvec_minmax,
2136 		.extra1     = SYSCTL_ZERO,
2137 	},
2138 #ifdef CONFIG_HIGHMEM
2139 	{
2140 		.procname	= "highmem_is_dirtyable",
2141 		.data		= &vm_highmem_is_dirtyable,
2142 		.maxlen		= sizeof(vm_highmem_is_dirtyable),
2143 		.mode		= 0644,
2144 		.proc_handler	= proc_dointvec_minmax,
2145 		.extra1		= SYSCTL_ZERO,
2146 		.extra2		= SYSCTL_ONE,
2147 	},
2148 #endif
2149 	{
2150 		.procname	= "laptop_mode",
2151 		.data		= &laptop_mode,
2152 		.maxlen		= sizeof(laptop_mode),
2153 		.mode		= 0644,
2154 		.proc_handler	= proc_dointvec_jiffies,
2155 	},
2156 	{}
2157 };
2158 #endif
2159 
2160 /*
2161  * Called early on to tune the page writeback dirty limits.
2162  *
2163  * We used to scale dirty pages according to how total memory
2164  * related to pages that could be allocated for buffers.
2165  *
2166  * However, that was when we used "dirty_ratio" to scale with
2167  * all memory, and we don't do that any more. "dirty_ratio"
2168  * is now applied to total non-HIGHPAGE memory, and as such we can't
2169  * get into the old insane situation any more where we had
2170  * large amounts of dirty pages compared to a small amount of
2171  * non-HIGHMEM memory.
2172  *
2173  * But we might still want to scale the dirty_ratio by how
2174  * much memory the box has..
2175  */
page_writeback_init(void)2176 void __init page_writeback_init(void)
2177 {
2178 	BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2179 
2180 	cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2181 			  page_writeback_cpu_online, NULL);
2182 	cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2183 			  page_writeback_cpu_online);
2184 #ifdef CONFIG_SYSCTL
2185 	register_sysctl_init("vm", vm_page_writeback_sysctls);
2186 #endif
2187 }
2188 
2189 /**
2190  * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2191  * @mapping: address space structure to write
2192  * @start: starting page index
2193  * @end: ending page index (inclusive)
2194  *
2195  * This function scans the page range from @start to @end (inclusive) and tags
2196  * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2197  * that write_cache_pages (or whoever calls this function) will then use
2198  * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
2199  * used to avoid livelocking of writeback by a process steadily creating new
2200  * dirty pages in the file (thus it is important for this function to be quick
2201  * so that it can tag pages faster than a dirtying process can create them).
2202  */
tag_pages_for_writeback(struct address_space * mapping,pgoff_t start,pgoff_t end)2203 void tag_pages_for_writeback(struct address_space *mapping,
2204 			     pgoff_t start, pgoff_t end)
2205 {
2206 	XA_STATE(xas, &mapping->i_pages, start);
2207 	unsigned int tagged = 0;
2208 	void *page;
2209 
2210 	xas_lock_irq(&xas);
2211 	xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) {
2212 		xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
2213 		if (++tagged % XA_CHECK_SCHED)
2214 			continue;
2215 
2216 		xas_pause(&xas);
2217 		xas_unlock_irq(&xas);
2218 		cond_resched();
2219 		xas_lock_irq(&xas);
2220 	}
2221 	xas_unlock_irq(&xas);
2222 }
2223 EXPORT_SYMBOL(tag_pages_for_writeback);
2224 
2225 /**
2226  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2227  * @mapping: address space structure to write
2228  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2229  * @writepage: function called for each page
2230  * @data: data passed to writepage function
2231  *
2232  * If a page is already under I/O, write_cache_pages() skips it, even
2233  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
2234  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
2235  * and msync() need to guarantee that all the data which was dirty at the time
2236  * the call was made get new I/O started against them.  If wbc->sync_mode is
2237  * WB_SYNC_ALL then we were called for data integrity and we must wait for
2238  * existing IO to complete.
2239  *
2240  * To avoid livelocks (when other process dirties new pages), we first tag
2241  * pages which should be written back with TOWRITE tag and only then start
2242  * writing them. For data-integrity sync we have to be careful so that we do
2243  * not miss some pages (e.g., because some other process has cleared TOWRITE
2244  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2245  * by the process clearing the DIRTY tag (and submitting the page for IO).
2246  *
2247  * To avoid deadlocks between range_cyclic writeback and callers that hold
2248  * pages in PageWriteback to aggregate IO until write_cache_pages() returns,
2249  * we do not loop back to the start of the file. Doing so causes a page
2250  * lock/page writeback access order inversion - we should only ever lock
2251  * multiple pages in ascending page->index order, and looping back to the start
2252  * of the file violates that rule and causes deadlocks.
2253  *
2254  * Return: %0 on success, negative error code otherwise
2255  */
write_cache_pages(struct address_space * mapping,struct writeback_control * wbc,writepage_t writepage,void * data)2256 int write_cache_pages(struct address_space *mapping,
2257 		      struct writeback_control *wbc, writepage_t writepage,
2258 		      void *data)
2259 {
2260 	int ret = 0;
2261 	int done = 0;
2262 	int error;
2263 	struct pagevec pvec;
2264 	int nr_pages;
2265 	pgoff_t index;
2266 	pgoff_t end;		/* Inclusive */
2267 	pgoff_t done_index;
2268 	int range_whole = 0;
2269 	xa_mark_t tag;
2270 
2271 	pagevec_init(&pvec);
2272 	if (wbc->range_cyclic) {
2273 		index = mapping->writeback_index; /* prev offset */
2274 		end = -1;
2275 	} else {
2276 		index = wbc->range_start >> PAGE_SHIFT;
2277 		end = wbc->range_end >> PAGE_SHIFT;
2278 		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2279 			range_whole = 1;
2280 	}
2281 	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
2282 		tag_pages_for_writeback(mapping, index, end);
2283 		tag = PAGECACHE_TAG_TOWRITE;
2284 	} else {
2285 		tag = PAGECACHE_TAG_DIRTY;
2286 	}
2287 	done_index = index;
2288 	while (!done && (index <= end)) {
2289 		int i;
2290 
2291 		nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
2292 				tag);
2293 		if (nr_pages == 0)
2294 			break;
2295 
2296 		for (i = 0; i < nr_pages; i++) {
2297 			struct page *page = pvec.pages[i];
2298 
2299 			done_index = page->index;
2300 
2301 			lock_page(page);
2302 
2303 			/*
2304 			 * Page truncated or invalidated. We can freely skip it
2305 			 * then, even for data integrity operations: the page
2306 			 * has disappeared concurrently, so there could be no
2307 			 * real expectation of this data integrity operation
2308 			 * even if there is now a new, dirty page at the same
2309 			 * pagecache address.
2310 			 */
2311 			if (unlikely(page->mapping != mapping)) {
2312 continue_unlock:
2313 				unlock_page(page);
2314 				continue;
2315 			}
2316 
2317 			if (!PageDirty(page)) {
2318 				/* someone wrote it for us */
2319 				goto continue_unlock;
2320 			}
2321 
2322 			if (PageWriteback(page)) {
2323 				if (wbc->sync_mode != WB_SYNC_NONE)
2324 					wait_on_page_writeback(page);
2325 				else
2326 					goto continue_unlock;
2327 			}
2328 
2329 			BUG_ON(PageWriteback(page));
2330 			if (!clear_page_dirty_for_io(page))
2331 				goto continue_unlock;
2332 
2333 			trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2334 			error = (*writepage)(page, wbc, data);
2335 			if (unlikely(error)) {
2336 				/*
2337 				 * Handle errors according to the type of
2338 				 * writeback. There's no need to continue for
2339 				 * background writeback. Just push done_index
2340 				 * past this page so media errors won't choke
2341 				 * writeout for the entire file. For integrity
2342 				 * writeback, we must process the entire dirty
2343 				 * set regardless of errors because the fs may
2344 				 * still have state to clear for each page. In
2345 				 * that case we continue processing and return
2346 				 * the first error.
2347 				 */
2348 				if (error == AOP_WRITEPAGE_ACTIVATE) {
2349 					unlock_page(page);
2350 					error = 0;
2351 				} else if (wbc->sync_mode != WB_SYNC_ALL) {
2352 					ret = error;
2353 					done_index = page->index + 1;
2354 					done = 1;
2355 					break;
2356 				}
2357 				if (!ret)
2358 					ret = error;
2359 			}
2360 
2361 			/*
2362 			 * We stop writing back only if we are not doing
2363 			 * integrity sync. In case of integrity sync we have to
2364 			 * keep going until we have written all the pages
2365 			 * we tagged for writeback prior to entering this loop.
2366 			 */
2367 			if (--wbc->nr_to_write <= 0 &&
2368 			    wbc->sync_mode == WB_SYNC_NONE) {
2369 				done = 1;
2370 				break;
2371 			}
2372 		}
2373 		pagevec_release(&pvec);
2374 		cond_resched();
2375 	}
2376 
2377 	/*
2378 	 * If we hit the last page and there is more work to be done: wrap
2379 	 * back the index back to the start of the file for the next
2380 	 * time we are called.
2381 	 */
2382 	if (wbc->range_cyclic && !done)
2383 		done_index = 0;
2384 	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2385 		mapping->writeback_index = done_index;
2386 
2387 	return ret;
2388 }
2389 EXPORT_SYMBOL(write_cache_pages);
2390 
2391 /*
2392  * Function used by generic_writepages to call the real writepage
2393  * function and set the mapping flags on error
2394  */
__writepage(struct page * page,struct writeback_control * wbc,void * data)2395 static int __writepage(struct page *page, struct writeback_control *wbc,
2396 		       void *data)
2397 {
2398 	struct address_space *mapping = data;
2399 	int ret = mapping->a_ops->writepage(page, wbc);
2400 	mapping_set_error(mapping, ret);
2401 	return ret;
2402 }
2403 
2404 /**
2405  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2406  * @mapping: address space structure to write
2407  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2408  *
2409  * This is a library function, which implements the writepages()
2410  * address_space_operation.
2411  *
2412  * Return: %0 on success, negative error code otherwise
2413  */
generic_writepages(struct address_space * mapping,struct writeback_control * wbc)2414 int generic_writepages(struct address_space *mapping,
2415 		       struct writeback_control *wbc)
2416 {
2417 	struct blk_plug plug;
2418 	int ret;
2419 
2420 	/* deal with chardevs and other special file */
2421 	if (!mapping->a_ops->writepage)
2422 		return 0;
2423 
2424 	blk_start_plug(&plug);
2425 	ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2426 	blk_finish_plug(&plug);
2427 	return ret;
2428 }
2429 
2430 EXPORT_SYMBOL(generic_writepages);
2431 
do_writepages(struct address_space * mapping,struct writeback_control * wbc)2432 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2433 {
2434 	int ret;
2435 	struct bdi_writeback *wb;
2436 
2437 	if (wbc->nr_to_write <= 0)
2438 		return 0;
2439 	wb = inode_to_wb_wbc(mapping->host, wbc);
2440 	wb_bandwidth_estimate_start(wb);
2441 	while (1) {
2442 		if (mapping->a_ops->writepages)
2443 			ret = mapping->a_ops->writepages(mapping, wbc);
2444 		else
2445 			ret = generic_writepages(mapping, wbc);
2446 		if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
2447 			break;
2448 
2449 		/*
2450 		 * Lacking an allocation context or the locality or writeback
2451 		 * state of any of the inode's pages, throttle based on
2452 		 * writeback activity on the local node. It's as good a
2453 		 * guess as any.
2454 		 */
2455 		reclaim_throttle(NODE_DATA(numa_node_id()),
2456 			VMSCAN_THROTTLE_WRITEBACK);
2457 	}
2458 	/*
2459 	 * Usually few pages are written by now from those we've just submitted
2460 	 * but if there's constant writeback being submitted, this makes sure
2461 	 * writeback bandwidth is updated once in a while.
2462 	 */
2463 	if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
2464 				   BANDWIDTH_INTERVAL))
2465 		wb_update_bandwidth(wb);
2466 	return ret;
2467 }
2468 
2469 /**
2470  * folio_write_one - write out a single folio and wait on I/O.
2471  * @folio: The folio to write.
2472  *
2473  * The folio must be locked by the caller and will be unlocked upon return.
2474  *
2475  * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
2476  * function returns.
2477  *
2478  * Return: %0 on success, negative error code otherwise
2479  */
folio_write_one(struct folio * folio)2480 int folio_write_one(struct folio *folio)
2481 {
2482 	struct address_space *mapping = folio->mapping;
2483 	int ret = 0;
2484 	struct writeback_control wbc = {
2485 		.sync_mode = WB_SYNC_ALL,
2486 		.nr_to_write = folio_nr_pages(folio),
2487 	};
2488 
2489 	BUG_ON(!folio_test_locked(folio));
2490 
2491 	folio_wait_writeback(folio);
2492 
2493 	if (folio_clear_dirty_for_io(folio)) {
2494 		folio_get(folio);
2495 		ret = mapping->a_ops->writepage(&folio->page, &wbc);
2496 		if (ret == 0)
2497 			folio_wait_writeback(folio);
2498 		folio_put(folio);
2499 	} else {
2500 		folio_unlock(folio);
2501 	}
2502 
2503 	if (!ret)
2504 		ret = filemap_check_errors(mapping);
2505 	return ret;
2506 }
2507 EXPORT_SYMBOL(folio_write_one);
2508 
2509 /*
2510  * For address_spaces which do not use buffers nor write back.
2511  */
noop_dirty_folio(struct address_space * mapping,struct folio * folio)2512 bool noop_dirty_folio(struct address_space *mapping, struct folio *folio)
2513 {
2514 	if (!folio_test_dirty(folio))
2515 		return !folio_test_set_dirty(folio);
2516 	return false;
2517 }
2518 EXPORT_SYMBOL(noop_dirty_folio);
2519 
2520 /*
2521  * Helper function for set_page_dirty family.
2522  *
2523  * Caller must hold lock_page_memcg().
2524  *
2525  * NOTE: This relies on being atomic wrt interrupts.
2526  */
folio_account_dirtied(struct folio * folio,struct address_space * mapping)2527 static void folio_account_dirtied(struct folio *folio,
2528 		struct address_space *mapping)
2529 {
2530 	struct inode *inode = mapping->host;
2531 
2532 	trace_writeback_dirty_folio(folio, mapping);
2533 
2534 	if (mapping_can_writeback(mapping)) {
2535 		struct bdi_writeback *wb;
2536 		long nr = folio_nr_pages(folio);
2537 
2538 		inode_attach_wb(inode, &folio->page);
2539 		wb = inode_to_wb(inode);
2540 
2541 		__lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, nr);
2542 		__zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
2543 		__node_stat_mod_folio(folio, NR_DIRTIED, nr);
2544 		wb_stat_mod(wb, WB_RECLAIMABLE, nr);
2545 		wb_stat_mod(wb, WB_DIRTIED, nr);
2546 		task_io_account_write(nr * PAGE_SIZE);
2547 		current->nr_dirtied += nr;
2548 		__this_cpu_add(bdp_ratelimits, nr);
2549 
2550 		mem_cgroup_track_foreign_dirty(folio, wb);
2551 	}
2552 }
2553 
2554 /*
2555  * Helper function for deaccounting dirty page without writeback.
2556  *
2557  * Caller must hold lock_page_memcg().
2558  */
folio_account_cleaned(struct folio * folio,struct bdi_writeback * wb)2559 void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
2560 {
2561 	long nr = folio_nr_pages(folio);
2562 
2563 	lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
2564 	zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2565 	wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
2566 	task_io_account_cancelled_write(nr * PAGE_SIZE);
2567 }
2568 
2569 /*
2570  * Mark the folio dirty, and set it dirty in the page cache, and mark
2571  * the inode dirty.
2572  *
2573  * If warn is true, then emit a warning if the folio is not uptodate and has
2574  * not been truncated.
2575  *
2576  * The caller must hold lock_page_memcg().  Most callers have the folio
2577  * locked.  A few have the folio blocked from truncation through other
2578  * means (eg zap_page_range() has it mapped and is holding the page table
2579  * lock).  This can also be called from mark_buffer_dirty(), which I
2580  * cannot prove is always protected against truncate.
2581  */
__folio_mark_dirty(struct folio * folio,struct address_space * mapping,int warn)2582 void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
2583 			     int warn)
2584 {
2585 	unsigned long flags;
2586 
2587 	xa_lock_irqsave(&mapping->i_pages, flags);
2588 	if (folio->mapping) {	/* Race with truncate? */
2589 		WARN_ON_ONCE(warn && !folio_test_uptodate(folio));
2590 		folio_account_dirtied(folio, mapping);
2591 		__xa_set_mark(&mapping->i_pages, folio_index(folio),
2592 				PAGECACHE_TAG_DIRTY);
2593 	}
2594 	xa_unlock_irqrestore(&mapping->i_pages, flags);
2595 }
2596 
2597 /**
2598  * filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads.
2599  * @mapping: Address space this folio belongs to.
2600  * @folio: Folio to be marked as dirty.
2601  *
2602  * Filesystems which do not use buffer heads should call this function
2603  * from their set_page_dirty address space operation.  It ignores the
2604  * contents of folio_get_private(), so if the filesystem marks individual
2605  * blocks as dirty, the filesystem should handle that itself.
2606  *
2607  * This is also sometimes used by filesystems which use buffer_heads when
2608  * a single buffer is being dirtied: we want to set the folio dirty in
2609  * that case, but not all the buffers.  This is a "bottom-up" dirtying,
2610  * whereas block_dirty_folio() is a "top-down" dirtying.
2611  *
2612  * The caller must ensure this doesn't race with truncation.  Most will
2613  * simply hold the folio lock, but e.g. zap_pte_range() calls with the
2614  * folio mapped and the pte lock held, which also locks out truncation.
2615  */
filemap_dirty_folio(struct address_space * mapping,struct folio * folio)2616 bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
2617 {
2618 	folio_memcg_lock(folio);
2619 	if (folio_test_set_dirty(folio)) {
2620 		folio_memcg_unlock(folio);
2621 		return false;
2622 	}
2623 
2624 	__folio_mark_dirty(folio, mapping, !folio_test_private(folio));
2625 	folio_memcg_unlock(folio);
2626 
2627 	if (mapping->host) {
2628 		/* !PageAnon && !swapper_space */
2629 		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2630 	}
2631 	return true;
2632 }
2633 EXPORT_SYMBOL(filemap_dirty_folio);
2634 
2635 /**
2636  * folio_account_redirty - Manually account for redirtying a page.
2637  * @folio: The folio which is being redirtied.
2638  *
2639  * Most filesystems should call folio_redirty_for_writepage() instead
2640  * of this fuction.  If your filesystem is doing writeback outside the
2641  * context of a writeback_control(), it can call this when redirtying
2642  * a folio, to de-account the dirty counters (NR_DIRTIED, WB_DIRTIED,
2643  * tsk->nr_dirtied), so that they match the written counters (NR_WRITTEN,
2644  * WB_WRITTEN) in long term. The mismatches will lead to systematic errors
2645  * in balanced_dirty_ratelimit and the dirty pages position control.
2646  */
folio_account_redirty(struct folio * folio)2647 void folio_account_redirty(struct folio *folio)
2648 {
2649 	struct address_space *mapping = folio->mapping;
2650 
2651 	if (mapping && mapping_can_writeback(mapping)) {
2652 		struct inode *inode = mapping->host;
2653 		struct bdi_writeback *wb;
2654 		struct wb_lock_cookie cookie = {};
2655 		long nr = folio_nr_pages(folio);
2656 
2657 		wb = unlocked_inode_to_wb_begin(inode, &cookie);
2658 		current->nr_dirtied -= nr;
2659 		node_stat_mod_folio(folio, NR_DIRTIED, -nr);
2660 		wb_stat_mod(wb, WB_DIRTIED, -nr);
2661 		unlocked_inode_to_wb_end(inode, &cookie);
2662 	}
2663 }
2664 EXPORT_SYMBOL(folio_account_redirty);
2665 
2666 /**
2667  * folio_redirty_for_writepage - Decline to write a dirty folio.
2668  * @wbc: The writeback control.
2669  * @folio: The folio.
2670  *
2671  * When a writepage implementation decides that it doesn't want to write
2672  * @folio for some reason, it should call this function, unlock @folio and
2673  * return 0.
2674  *
2675  * Return: True if we redirtied the folio.  False if someone else dirtied
2676  * it first.
2677  */
folio_redirty_for_writepage(struct writeback_control * wbc,struct folio * folio)2678 bool folio_redirty_for_writepage(struct writeback_control *wbc,
2679 		struct folio *folio)
2680 {
2681 	bool ret;
2682 	long nr = folio_nr_pages(folio);
2683 
2684 	wbc->pages_skipped += nr;
2685 	ret = filemap_dirty_folio(folio->mapping, folio);
2686 	folio_account_redirty(folio);
2687 
2688 	return ret;
2689 }
2690 EXPORT_SYMBOL(folio_redirty_for_writepage);
2691 
2692 /**
2693  * folio_mark_dirty - Mark a folio as being modified.
2694  * @folio: The folio.
2695  *
2696  * The folio may not be truncated while this function is running.
2697  * Holding the folio lock is sufficient to prevent truncation, but some
2698  * callers cannot acquire a sleeping lock.  These callers instead hold
2699  * the page table lock for a page table which contains at least one page
2700  * in this folio.  Truncation will block on the page table lock as it
2701  * unmaps pages before removing the folio from its mapping.
2702  *
2703  * Return: True if the folio was newly dirtied, false if it was already dirty.
2704  */
folio_mark_dirty(struct folio * folio)2705 bool folio_mark_dirty(struct folio *folio)
2706 {
2707 	struct address_space *mapping = folio_mapping(folio);
2708 
2709 	if (likely(mapping)) {
2710 		/*
2711 		 * readahead/lru_deactivate_page could remain
2712 		 * PG_readahead/PG_reclaim due to race with folio_end_writeback
2713 		 * About readahead, if the folio is written, the flags would be
2714 		 * reset. So no problem.
2715 		 * About lru_deactivate_page, if the folio is redirtied,
2716 		 * the flag will be reset. So no problem. but if the
2717 		 * folio is used by readahead it will confuse readahead
2718 		 * and make it restart the size rampup process. But it's
2719 		 * a trivial problem.
2720 		 */
2721 		if (folio_test_reclaim(folio))
2722 			folio_clear_reclaim(folio);
2723 		return mapping->a_ops->dirty_folio(mapping, folio);
2724 	}
2725 
2726 	return noop_dirty_folio(mapping, folio);
2727 }
2728 EXPORT_SYMBOL(folio_mark_dirty);
2729 
2730 /*
2731  * set_page_dirty() is racy if the caller has no reference against
2732  * page->mapping->host, and if the page is unlocked.  This is because another
2733  * CPU could truncate the page off the mapping and then free the mapping.
2734  *
2735  * Usually, the page _is_ locked, or the caller is a user-space process which
2736  * holds a reference on the inode by having an open file.
2737  *
2738  * In other cases, the page should be locked before running set_page_dirty().
2739  */
set_page_dirty_lock(struct page * page)2740 int set_page_dirty_lock(struct page *page)
2741 {
2742 	int ret;
2743 
2744 	lock_page(page);
2745 	ret = set_page_dirty(page);
2746 	unlock_page(page);
2747 	return ret;
2748 }
2749 EXPORT_SYMBOL(set_page_dirty_lock);
2750 
2751 /*
2752  * This cancels just the dirty bit on the kernel page itself, it does NOT
2753  * actually remove dirty bits on any mmap's that may be around. It also
2754  * leaves the page tagged dirty, so any sync activity will still find it on
2755  * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2756  * look at the dirty bits in the VM.
2757  *
2758  * Doing this should *normally* only ever be done when a page is truncated,
2759  * and is not actually mapped anywhere at all. However, fs/buffer.c does
2760  * this when it notices that somebody has cleaned out all the buffers on a
2761  * page without actually doing it through the VM. Can you say "ext3 is
2762  * horribly ugly"? Thought you could.
2763  */
__folio_cancel_dirty(struct folio * folio)2764 void __folio_cancel_dirty(struct folio *folio)
2765 {
2766 	struct address_space *mapping = folio_mapping(folio);
2767 
2768 	if (mapping_can_writeback(mapping)) {
2769 		struct inode *inode = mapping->host;
2770 		struct bdi_writeback *wb;
2771 		struct wb_lock_cookie cookie = {};
2772 
2773 		folio_memcg_lock(folio);
2774 		wb = unlocked_inode_to_wb_begin(inode, &cookie);
2775 
2776 		if (folio_test_clear_dirty(folio))
2777 			folio_account_cleaned(folio, wb);
2778 
2779 		unlocked_inode_to_wb_end(inode, &cookie);
2780 		folio_memcg_unlock(folio);
2781 	} else {
2782 		folio_clear_dirty(folio);
2783 	}
2784 }
2785 EXPORT_SYMBOL(__folio_cancel_dirty);
2786 
2787 /*
2788  * Clear a folio's dirty flag, while caring for dirty memory accounting.
2789  * Returns true if the folio was previously dirty.
2790  *
2791  * This is for preparing to put the folio under writeout.  We leave
2792  * the folio tagged as dirty in the xarray so that a concurrent
2793  * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
2794  * The ->writepage implementation will run either folio_start_writeback()
2795  * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
2796  * and xarray dirty tag back into sync.
2797  *
2798  * This incoherency between the folio's dirty flag and xarray tag is
2799  * unfortunate, but it only exists while the folio is locked.
2800  */
folio_clear_dirty_for_io(struct folio * folio)2801 bool folio_clear_dirty_for_io(struct folio *folio)
2802 {
2803 	struct address_space *mapping = folio_mapping(folio);
2804 	bool ret = false;
2805 
2806 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
2807 
2808 	if (mapping && mapping_can_writeback(mapping)) {
2809 		struct inode *inode = mapping->host;
2810 		struct bdi_writeback *wb;
2811 		struct wb_lock_cookie cookie = {};
2812 
2813 		/*
2814 		 * Yes, Virginia, this is indeed insane.
2815 		 *
2816 		 * We use this sequence to make sure that
2817 		 *  (a) we account for dirty stats properly
2818 		 *  (b) we tell the low-level filesystem to
2819 		 *      mark the whole folio dirty if it was
2820 		 *      dirty in a pagetable. Only to then
2821 		 *  (c) clean the folio again and return 1 to
2822 		 *      cause the writeback.
2823 		 *
2824 		 * This way we avoid all nasty races with the
2825 		 * dirty bit in multiple places and clearing
2826 		 * them concurrently from different threads.
2827 		 *
2828 		 * Note! Normally the "folio_mark_dirty(folio)"
2829 		 * has no effect on the actual dirty bit - since
2830 		 * that will already usually be set. But we
2831 		 * need the side effects, and it can help us
2832 		 * avoid races.
2833 		 *
2834 		 * We basically use the folio "master dirty bit"
2835 		 * as a serialization point for all the different
2836 		 * threads doing their things.
2837 		 */
2838 		if (folio_mkclean(folio))
2839 			folio_mark_dirty(folio);
2840 		/*
2841 		 * We carefully synchronise fault handlers against
2842 		 * installing a dirty pte and marking the folio dirty
2843 		 * at this point.  We do this by having them hold the
2844 		 * page lock while dirtying the folio, and folios are
2845 		 * always locked coming in here, so we get the desired
2846 		 * exclusion.
2847 		 */
2848 		wb = unlocked_inode_to_wb_begin(inode, &cookie);
2849 		if (folio_test_clear_dirty(folio)) {
2850 			long nr = folio_nr_pages(folio);
2851 			lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
2852 			zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2853 			wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
2854 			ret = true;
2855 		}
2856 		unlocked_inode_to_wb_end(inode, &cookie);
2857 		return ret;
2858 	}
2859 	return folio_test_clear_dirty(folio);
2860 }
2861 EXPORT_SYMBOL(folio_clear_dirty_for_io);
2862 
wb_inode_writeback_start(struct bdi_writeback * wb)2863 static void wb_inode_writeback_start(struct bdi_writeback *wb)
2864 {
2865 	atomic_inc(&wb->writeback_inodes);
2866 }
2867 
wb_inode_writeback_end(struct bdi_writeback * wb)2868 static void wb_inode_writeback_end(struct bdi_writeback *wb)
2869 {
2870 	unsigned long flags;
2871 	atomic_dec(&wb->writeback_inodes);
2872 	/*
2873 	 * Make sure estimate of writeback throughput gets updated after
2874 	 * writeback completed. We delay the update by BANDWIDTH_INTERVAL
2875 	 * (which is the interval other bandwidth updates use for batching) so
2876 	 * that if multiple inodes end writeback at a similar time, they get
2877 	 * batched into one bandwidth update.
2878 	 */
2879 	spin_lock_irqsave(&wb->work_lock, flags);
2880 	if (test_bit(WB_registered, &wb->state))
2881 		queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL);
2882 	spin_unlock_irqrestore(&wb->work_lock, flags);
2883 }
2884 
__folio_end_writeback(struct folio * folio)2885 bool __folio_end_writeback(struct folio *folio)
2886 {
2887 	long nr = folio_nr_pages(folio);
2888 	struct address_space *mapping = folio_mapping(folio);
2889 	bool ret;
2890 
2891 	folio_memcg_lock(folio);
2892 	if (mapping && mapping_use_writeback_tags(mapping)) {
2893 		struct inode *inode = mapping->host;
2894 		struct backing_dev_info *bdi = inode_to_bdi(inode);
2895 		unsigned long flags;
2896 
2897 		xa_lock_irqsave(&mapping->i_pages, flags);
2898 		ret = folio_test_clear_writeback(folio);
2899 		if (ret) {
2900 			__xa_clear_mark(&mapping->i_pages, folio_index(folio),
2901 						PAGECACHE_TAG_WRITEBACK);
2902 			if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
2903 				struct bdi_writeback *wb = inode_to_wb(inode);
2904 
2905 				wb_stat_mod(wb, WB_WRITEBACK, -nr);
2906 				__wb_writeout_add(wb, nr);
2907 				if (!mapping_tagged(mapping,
2908 						    PAGECACHE_TAG_WRITEBACK))
2909 					wb_inode_writeback_end(wb);
2910 			}
2911 		}
2912 
2913 		if (mapping->host && !mapping_tagged(mapping,
2914 						     PAGECACHE_TAG_WRITEBACK))
2915 			sb_clear_inode_writeback(mapping->host);
2916 
2917 		xa_unlock_irqrestore(&mapping->i_pages, flags);
2918 	} else {
2919 		ret = folio_test_clear_writeback(folio);
2920 	}
2921 	if (ret) {
2922 		lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr);
2923 		zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2924 		node_stat_mod_folio(folio, NR_WRITTEN, nr);
2925 	}
2926 	folio_memcg_unlock(folio);
2927 	return ret;
2928 }
2929 
__folio_start_writeback(struct folio * folio,bool keep_write)2930 bool __folio_start_writeback(struct folio *folio, bool keep_write)
2931 {
2932 	long nr = folio_nr_pages(folio);
2933 	struct address_space *mapping = folio_mapping(folio);
2934 	bool ret;
2935 	int access_ret;
2936 
2937 	folio_memcg_lock(folio);
2938 	if (mapping && mapping_use_writeback_tags(mapping)) {
2939 		XA_STATE(xas, &mapping->i_pages, folio_index(folio));
2940 		struct inode *inode = mapping->host;
2941 		struct backing_dev_info *bdi = inode_to_bdi(inode);
2942 		unsigned long flags;
2943 
2944 		xas_lock_irqsave(&xas, flags);
2945 		xas_load(&xas);
2946 		ret = folio_test_set_writeback(folio);
2947 		if (!ret) {
2948 			bool on_wblist;
2949 
2950 			on_wblist = mapping_tagged(mapping,
2951 						   PAGECACHE_TAG_WRITEBACK);
2952 
2953 			xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
2954 			if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
2955 				struct bdi_writeback *wb = inode_to_wb(inode);
2956 
2957 				wb_stat_mod(wb, WB_WRITEBACK, nr);
2958 				if (!on_wblist)
2959 					wb_inode_writeback_start(wb);
2960 			}
2961 
2962 			/*
2963 			 * We can come through here when swapping
2964 			 * anonymous folios, so we don't necessarily
2965 			 * have an inode to track for sync.
2966 			 */
2967 			if (mapping->host && !on_wblist)
2968 				sb_mark_inode_writeback(mapping->host);
2969 		}
2970 		if (!folio_test_dirty(folio))
2971 			xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
2972 		if (!keep_write)
2973 			xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
2974 		xas_unlock_irqrestore(&xas, flags);
2975 	} else {
2976 		ret = folio_test_set_writeback(folio);
2977 	}
2978 	if (!ret) {
2979 		lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr);
2980 		zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
2981 	}
2982 	folio_memcg_unlock(folio);
2983 	access_ret = arch_make_folio_accessible(folio);
2984 	/*
2985 	 * If writeback has been triggered on a page that cannot be made
2986 	 * accessible, it is too late to recover here.
2987 	 */
2988 	VM_BUG_ON_FOLIO(access_ret != 0, folio);
2989 
2990 	return ret;
2991 }
2992 EXPORT_SYMBOL(__folio_start_writeback);
2993 
2994 /**
2995  * folio_wait_writeback - Wait for a folio to finish writeback.
2996  * @folio: The folio to wait for.
2997  *
2998  * If the folio is currently being written back to storage, wait for the
2999  * I/O to complete.
3000  *
3001  * Context: Sleeps.  Must be called in process context and with
3002  * no spinlocks held.  Caller should hold a reference on the folio.
3003  * If the folio is not locked, writeback may start again after writeback
3004  * has finished.
3005  */
folio_wait_writeback(struct folio * folio)3006 void folio_wait_writeback(struct folio *folio)
3007 {
3008 	while (folio_test_writeback(folio)) {
3009 		trace_folio_wait_writeback(folio, folio_mapping(folio));
3010 		folio_wait_bit(folio, PG_writeback);
3011 	}
3012 }
3013 EXPORT_SYMBOL_GPL(folio_wait_writeback);
3014 
3015 /**
3016  * folio_wait_writeback_killable - Wait for a folio to finish writeback.
3017  * @folio: The folio to wait for.
3018  *
3019  * If the folio is currently being written back to storage, wait for the
3020  * I/O to complete or a fatal signal to arrive.
3021  *
3022  * Context: Sleeps.  Must be called in process context and with
3023  * no spinlocks held.  Caller should hold a reference on the folio.
3024  * If the folio is not locked, writeback may start again after writeback
3025  * has finished.
3026  * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
3027  */
folio_wait_writeback_killable(struct folio * folio)3028 int folio_wait_writeback_killable(struct folio *folio)
3029 {
3030 	while (folio_test_writeback(folio)) {
3031 		trace_folio_wait_writeback(folio, folio_mapping(folio));
3032 		if (folio_wait_bit_killable(folio, PG_writeback))
3033 			return -EINTR;
3034 	}
3035 
3036 	return 0;
3037 }
3038 EXPORT_SYMBOL_GPL(folio_wait_writeback_killable);
3039 
3040 /**
3041  * folio_wait_stable() - wait for writeback to finish, if necessary.
3042  * @folio: The folio to wait on.
3043  *
3044  * This function determines if the given folio is related to a backing
3045  * device that requires folio contents to be held stable during writeback.
3046  * If so, then it will wait for any pending writeback to complete.
3047  *
3048  * Context: Sleeps.  Must be called in process context and with
3049  * no spinlocks held.  Caller should hold a reference on the folio.
3050  * If the folio is not locked, writeback may start again after writeback
3051  * has finished.
3052  */
folio_wait_stable(struct folio * folio)3053 void folio_wait_stable(struct folio *folio)
3054 {
3055 	if (folio_inode(folio)->i_sb->s_iflags & SB_I_STABLE_WRITES)
3056 		folio_wait_writeback(folio);
3057 }
3058 EXPORT_SYMBOL_GPL(folio_wait_stable);
3059