xref: /linux/mm/page-writeback.c (revision 2c1ed907520c50326b8f604907a8478b27881a2e)
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/math64.h>
17 #include <linux/export.h>
18 #include <linux/spinlock.h>
19 #include <linux/fs.h>
20 #include <linux/mm.h>
21 #include <linux/swap.h>
22 #include <linux/slab.h>
23 #include <linux/pagemap.h>
24 #include <linux/writeback.h>
25 #include <linux/init.h>
26 #include <linux/backing-dev.h>
27 #include <linux/task_io_accounting_ops.h>
28 #include <linux/blkdev.h>
29 #include <linux/mpage.h>
30 #include <linux/rmap.h>
31 #include <linux/percpu.h>
32 #include <linux/smp.h>
33 #include <linux/sysctl.h>
34 #include <linux/cpu.h>
35 #include <linux/syscalls.h>
36 #include <linux/pagevec.h>
37 #include <linux/timer.h>
38 #include <linux/sched/rt.h>
39 #include <linux/sched/signal.h>
40 #include <linux/mm_inline.h>
41 #include <trace/events/writeback.h>
42 
43 #include "internal.h"
44 
45 /*
46  * Sleep at most 200ms at a time in balance_dirty_pages().
47  */
48 #define MAX_PAUSE		max(HZ/5, 1)
49 
50 /*
51  * Try to keep balance_dirty_pages() call intervals higher than this many pages
52  * by raising pause time to max_pause when falls below it.
53  */
54 #define DIRTY_POLL_THRESH	(128 >> (PAGE_SHIFT - 10))
55 
56 /*
57  * Estimate write bandwidth or update dirty limit at 200ms intervals.
58  */
59 #define BANDWIDTH_INTERVAL	max(HZ/5, 1)
60 
61 #define RATELIMIT_CALC_SHIFT	10
62 
63 /*
64  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
65  * will look to see if it needs to force writeback or throttling.
66  */
67 static long ratelimit_pages = 32;
68 
69 /* The following parameters are exported via /proc/sys/vm */
70 
71 /*
72  * Start background writeback (via writeback threads) at this percentage
73  */
74 static int dirty_background_ratio = 10;
75 
76 /*
77  * dirty_background_bytes starts at 0 (disabled) so that it is a function of
78  * dirty_background_ratio * the amount of dirtyable memory
79  */
80 static unsigned long dirty_background_bytes;
81 
82 /*
83  * free highmem will not be subtracted from the total free memory
84  * for calculating free ratios if vm_highmem_is_dirtyable is true
85  */
86 static int vm_highmem_is_dirtyable;
87 
88 /*
89  * The generator of dirty data starts writeback at this percentage
90  */
91 static int vm_dirty_ratio = 20;
92 
93 /*
94  * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
95  * vm_dirty_ratio * the amount of dirtyable memory
96  */
97 static unsigned long vm_dirty_bytes;
98 
99 /*
100  * The interval between `kupdate'-style writebacks
101  */
102 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
103 
104 EXPORT_SYMBOL_GPL(dirty_writeback_interval);
105 
106 /*
107  * The longest time for which data is allowed to remain dirty
108  */
109 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
110 
111 /*
112  * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
113  * a full sync is triggered after this time elapses without any disk activity.
114  */
115 int laptop_mode;
116 
117 EXPORT_SYMBOL(laptop_mode);
118 
119 /* End of sysctl-exported parameters */
120 
121 struct wb_domain global_wb_domain;
122 
123 /* consolidated parameters for balance_dirty_pages() and its subroutines */
124 struct dirty_throttle_control {
125 #ifdef CONFIG_CGROUP_WRITEBACK
126 	struct wb_domain	*dom;
127 	struct dirty_throttle_control *gdtc;	/* only set in memcg dtc's */
128 #endif
129 	struct bdi_writeback	*wb;
130 	struct fprop_local_percpu *wb_completions;
131 
132 	unsigned long		avail;		/* dirtyable */
133 	unsigned long		dirty;		/* file_dirty + write + nfs */
134 	unsigned long		thresh;		/* dirty threshold */
135 	unsigned long		bg_thresh;	/* dirty background threshold */
136 
137 	unsigned long		wb_dirty;	/* per-wb counterparts */
138 	unsigned long		wb_thresh;
139 	unsigned long		wb_bg_thresh;
140 
141 	unsigned long		pos_ratio;
142 	bool			freerun;
143 	bool			dirty_exceeded;
144 };
145 
146 /*
147  * Length of period for aging writeout fractions of bdis. This is an
148  * arbitrarily chosen number. The longer the period, the slower fractions will
149  * reflect changes in current writeout rate.
150  */
151 #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
152 
153 #ifdef CONFIG_CGROUP_WRITEBACK
154 
155 #define GDTC_INIT(__wb)		.wb = (__wb),				\
156 				.dom = &global_wb_domain,		\
157 				.wb_completions = &(__wb)->completions
158 
159 #define GDTC_INIT_NO_WB		.dom = &global_wb_domain
160 
161 #define MDTC_INIT(__wb, __gdtc)	.wb = (__wb),				\
162 				.dom = mem_cgroup_wb_domain(__wb),	\
163 				.wb_completions = &(__wb)->memcg_completions, \
164 				.gdtc = __gdtc
165 
mdtc_valid(struct dirty_throttle_control * dtc)166 static bool mdtc_valid(struct dirty_throttle_control *dtc)
167 {
168 	return dtc->dom;
169 }
170 
dtc_dom(struct dirty_throttle_control * dtc)171 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
172 {
173 	return dtc->dom;
174 }
175 
mdtc_gdtc(struct dirty_throttle_control * mdtc)176 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
177 {
178 	return mdtc->gdtc;
179 }
180 
wb_memcg_completions(struct bdi_writeback * wb)181 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
182 {
183 	return &wb->memcg_completions;
184 }
185 
wb_min_max_ratio(struct bdi_writeback * wb,unsigned long * minp,unsigned long * maxp)186 static void wb_min_max_ratio(struct bdi_writeback *wb,
187 			     unsigned long *minp, unsigned long *maxp)
188 {
189 	unsigned long this_bw = READ_ONCE(wb->avg_write_bandwidth);
190 	unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
191 	unsigned long long min = wb->bdi->min_ratio;
192 	unsigned long long max = wb->bdi->max_ratio;
193 
194 	/*
195 	 * @wb may already be clean by the time control reaches here and
196 	 * the total may not include its bw.
197 	 */
198 	if (this_bw < tot_bw) {
199 		if (min) {
200 			min *= this_bw;
201 			min = div64_ul(min, tot_bw);
202 		}
203 		if (max < 100 * BDI_RATIO_SCALE) {
204 			max *= this_bw;
205 			max = div64_ul(max, tot_bw);
206 		}
207 	}
208 
209 	*minp = min;
210 	*maxp = max;
211 }
212 
213 #else	/* CONFIG_CGROUP_WRITEBACK */
214 
215 #define GDTC_INIT(__wb)		.wb = (__wb),                           \
216 				.wb_completions = &(__wb)->completions
217 #define GDTC_INIT_NO_WB
218 #define MDTC_INIT(__wb, __gdtc)
219 
mdtc_valid(struct dirty_throttle_control * dtc)220 static bool mdtc_valid(struct dirty_throttle_control *dtc)
221 {
222 	return false;
223 }
224 
dtc_dom(struct dirty_throttle_control * dtc)225 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
226 {
227 	return &global_wb_domain;
228 }
229 
mdtc_gdtc(struct dirty_throttle_control * mdtc)230 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
231 {
232 	return NULL;
233 }
234 
wb_memcg_completions(struct bdi_writeback * wb)235 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
236 {
237 	return NULL;
238 }
239 
wb_min_max_ratio(struct bdi_writeback * wb,unsigned long * minp,unsigned long * maxp)240 static void wb_min_max_ratio(struct bdi_writeback *wb,
241 			     unsigned long *minp, unsigned long *maxp)
242 {
243 	*minp = wb->bdi->min_ratio;
244 	*maxp = wb->bdi->max_ratio;
245 }
246 
247 #endif	/* CONFIG_CGROUP_WRITEBACK */
248 
249 /*
250  * In a memory zone, there is a certain amount of pages we consider
251  * available for the page cache, which is essentially the number of
252  * free and reclaimable pages, minus some zone reserves to protect
253  * lowmem and the ability to uphold the zone's watermarks without
254  * requiring writeback.
255  *
256  * This number of dirtyable pages is the base value of which the
257  * user-configurable dirty ratio is the effective number of pages that
258  * are allowed to be actually dirtied.  Per individual zone, or
259  * globally by using the sum of dirtyable pages over all zones.
260  *
261  * Because the user is allowed to specify the dirty limit globally as
262  * absolute number of bytes, calculating the per-zone dirty limit can
263  * require translating the configured limit into a percentage of
264  * global dirtyable memory first.
265  */
266 
267 /**
268  * node_dirtyable_memory - number of dirtyable pages in a node
269  * @pgdat: the node
270  *
271  * Return: the node's number of pages potentially available for dirty
272  * page cache.  This is the base value for the per-node dirty limits.
273  */
node_dirtyable_memory(struct pglist_data * pgdat)274 static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
275 {
276 	unsigned long nr_pages = 0;
277 	int z;
278 
279 	for (z = 0; z < MAX_NR_ZONES; z++) {
280 		struct zone *zone = pgdat->node_zones + z;
281 
282 		if (!populated_zone(zone))
283 			continue;
284 
285 		nr_pages += zone_page_state(zone, NR_FREE_PAGES);
286 	}
287 
288 	/*
289 	 * Pages reserved for the kernel should not be considered
290 	 * dirtyable, to prevent a situation where reclaim has to
291 	 * clean pages in order to balance the zones.
292 	 */
293 	nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
294 
295 	nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
296 	nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
297 
298 	return nr_pages;
299 }
300 
highmem_dirtyable_memory(unsigned long total)301 static unsigned long highmem_dirtyable_memory(unsigned long total)
302 {
303 #ifdef CONFIG_HIGHMEM
304 	int node;
305 	unsigned long x = 0;
306 	int i;
307 
308 	for_each_node_state(node, N_HIGH_MEMORY) {
309 		for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
310 			struct zone *z;
311 			unsigned long nr_pages;
312 
313 			if (!is_highmem_idx(i))
314 				continue;
315 
316 			z = &NODE_DATA(node)->node_zones[i];
317 			if (!populated_zone(z))
318 				continue;
319 
320 			nr_pages = zone_page_state(z, NR_FREE_PAGES);
321 			/* watch for underflows */
322 			nr_pages -= min(nr_pages, high_wmark_pages(z));
323 			nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
324 			nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
325 			x += nr_pages;
326 		}
327 	}
328 
329 	/*
330 	 * Make sure that the number of highmem pages is never larger
331 	 * than the number of the total dirtyable memory. This can only
332 	 * occur in very strange VM situations but we want to make sure
333 	 * that this does not occur.
334 	 */
335 	return min(x, total);
336 #else
337 	return 0;
338 #endif
339 }
340 
341 /**
342  * global_dirtyable_memory - number of globally dirtyable pages
343  *
344  * Return: the global number of pages potentially available for dirty
345  * page cache.  This is the base value for the global dirty limits.
346  */
global_dirtyable_memory(void)347 static unsigned long global_dirtyable_memory(void)
348 {
349 	unsigned long x;
350 
351 	x = global_zone_page_state(NR_FREE_PAGES);
352 	/*
353 	 * Pages reserved for the kernel should not be considered
354 	 * dirtyable, to prevent a situation where reclaim has to
355 	 * clean pages in order to balance the zones.
356 	 */
357 	x -= min(x, totalreserve_pages);
358 
359 	x += global_node_page_state(NR_INACTIVE_FILE);
360 	x += global_node_page_state(NR_ACTIVE_FILE);
361 
362 	if (!vm_highmem_is_dirtyable)
363 		x -= highmem_dirtyable_memory(x);
364 
365 	return x + 1;	/* Ensure that we never return 0 */
366 }
367 
368 /**
369  * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
370  * @dtc: dirty_throttle_control of interest
371  *
372  * Calculate @dtc->thresh and ->bg_thresh considering
373  * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}.  The caller
374  * must ensure that @dtc->avail is set before calling this function.  The
375  * dirty limits will be lifted by 1/4 for real-time tasks.
376  */
domain_dirty_limits(struct dirty_throttle_control * dtc)377 static void domain_dirty_limits(struct dirty_throttle_control *dtc)
378 {
379 	const unsigned long available_memory = dtc->avail;
380 	struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
381 	unsigned long bytes = vm_dirty_bytes;
382 	unsigned long bg_bytes = dirty_background_bytes;
383 	/* convert ratios to per-PAGE_SIZE for higher precision */
384 	unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
385 	unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
386 	unsigned long thresh;
387 	unsigned long bg_thresh;
388 	struct task_struct *tsk;
389 
390 	/* gdtc is !NULL iff @dtc is for memcg domain */
391 	if (gdtc) {
392 		unsigned long global_avail = gdtc->avail;
393 
394 		/*
395 		 * The byte settings can't be applied directly to memcg
396 		 * domains.  Convert them to ratios by scaling against
397 		 * globally available memory.  As the ratios are in
398 		 * per-PAGE_SIZE, they can be obtained by dividing bytes by
399 		 * number of pages.
400 		 */
401 		if (bytes)
402 			ratio = min(DIV_ROUND_UP(bytes, global_avail),
403 				    PAGE_SIZE);
404 		if (bg_bytes)
405 			bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
406 				       PAGE_SIZE);
407 		bytes = bg_bytes = 0;
408 	}
409 
410 	if (bytes)
411 		thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
412 	else
413 		thresh = (ratio * available_memory) / PAGE_SIZE;
414 
415 	if (bg_bytes)
416 		bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
417 	else
418 		bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
419 
420 	tsk = current;
421 	if (rt_or_dl_task(tsk)) {
422 		bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
423 		thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
424 	}
425 	/*
426 	 * Dirty throttling logic assumes the limits in page units fit into
427 	 * 32-bits. This gives 16TB dirty limits max which is hopefully enough.
428 	 */
429 	if (thresh > UINT_MAX)
430 		thresh = UINT_MAX;
431 	/* This makes sure bg_thresh is within 32-bits as well */
432 	if (bg_thresh >= thresh)
433 		bg_thresh = thresh / 2;
434 	dtc->thresh = thresh;
435 	dtc->bg_thresh = bg_thresh;
436 
437 	/* we should eventually report the domain in the TP */
438 	if (!gdtc)
439 		trace_global_dirty_state(bg_thresh, thresh);
440 }
441 
442 /**
443  * global_dirty_limits - background-writeback and dirty-throttling thresholds
444  * @pbackground: out parameter for bg_thresh
445  * @pdirty: out parameter for thresh
446  *
447  * Calculate bg_thresh and thresh for global_wb_domain.  See
448  * domain_dirty_limits() for details.
449  */
global_dirty_limits(unsigned long * pbackground,unsigned long * pdirty)450 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
451 {
452 	struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
453 
454 	gdtc.avail = global_dirtyable_memory();
455 	domain_dirty_limits(&gdtc);
456 
457 	*pbackground = gdtc.bg_thresh;
458 	*pdirty = gdtc.thresh;
459 }
460 
461 /**
462  * node_dirty_limit - maximum number of dirty pages allowed in a node
463  * @pgdat: the node
464  *
465  * Return: the maximum number of dirty pages allowed in a node, based
466  * on the node's dirtyable memory.
467  */
node_dirty_limit(struct pglist_data * pgdat)468 static unsigned long node_dirty_limit(struct pglist_data *pgdat)
469 {
470 	unsigned long node_memory = node_dirtyable_memory(pgdat);
471 	struct task_struct *tsk = current;
472 	unsigned long dirty;
473 
474 	if (vm_dirty_bytes)
475 		dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
476 			node_memory / global_dirtyable_memory();
477 	else
478 		dirty = vm_dirty_ratio * node_memory / 100;
479 
480 	if (rt_or_dl_task(tsk))
481 		dirty += dirty / 4;
482 
483 	/*
484 	 * Dirty throttling logic assumes the limits in page units fit into
485 	 * 32-bits. This gives 16TB dirty limits max which is hopefully enough.
486 	 */
487 	return min_t(unsigned long, dirty, UINT_MAX);
488 }
489 
490 /**
491  * node_dirty_ok - tells whether a node is within its dirty limits
492  * @pgdat: the node to check
493  *
494  * Return: %true when the dirty pages in @pgdat are within the node's
495  * dirty limit, %false if the limit is exceeded.
496  */
node_dirty_ok(struct pglist_data * pgdat)497 bool node_dirty_ok(struct pglist_data *pgdat)
498 {
499 	unsigned long limit = node_dirty_limit(pgdat);
500 	unsigned long nr_pages = 0;
501 
502 	nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
503 	nr_pages += node_page_state(pgdat, NR_WRITEBACK);
504 
505 	return nr_pages <= limit;
506 }
507 
508 #ifdef CONFIG_SYSCTL
dirty_background_ratio_handler(const struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)509 static int dirty_background_ratio_handler(const struct ctl_table *table, int write,
510 		void *buffer, size_t *lenp, loff_t *ppos)
511 {
512 	int ret;
513 
514 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
515 	if (ret == 0 && write)
516 		dirty_background_bytes = 0;
517 	return ret;
518 }
519 
dirty_background_bytes_handler(const struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)520 static int dirty_background_bytes_handler(const struct ctl_table *table, int write,
521 		void *buffer, size_t *lenp, loff_t *ppos)
522 {
523 	int ret;
524 	unsigned long old_bytes = dirty_background_bytes;
525 
526 	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
527 	if (ret == 0 && write) {
528 		if (DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE) >
529 								UINT_MAX) {
530 			dirty_background_bytes = old_bytes;
531 			return -ERANGE;
532 		}
533 		dirty_background_ratio = 0;
534 	}
535 	return ret;
536 }
537 
dirty_ratio_handler(const struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)538 static int dirty_ratio_handler(const struct ctl_table *table, int write, void *buffer,
539 		size_t *lenp, loff_t *ppos)
540 {
541 	int old_ratio = vm_dirty_ratio;
542 	int ret;
543 
544 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
545 	if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
546 		writeback_set_ratelimit();
547 		vm_dirty_bytes = 0;
548 	}
549 	return ret;
550 }
551 
dirty_bytes_handler(const struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)552 static int dirty_bytes_handler(const struct ctl_table *table, int write,
553 		void *buffer, size_t *lenp, loff_t *ppos)
554 {
555 	unsigned long old_bytes = vm_dirty_bytes;
556 	int ret;
557 
558 	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
559 	if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
560 		if (DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) > UINT_MAX) {
561 			vm_dirty_bytes = old_bytes;
562 			return -ERANGE;
563 		}
564 		writeback_set_ratelimit();
565 		vm_dirty_ratio = 0;
566 	}
567 	return ret;
568 }
569 #endif
570 
wp_next_time(unsigned long cur_time)571 static unsigned long wp_next_time(unsigned long cur_time)
572 {
573 	cur_time += VM_COMPLETIONS_PERIOD_LEN;
574 	/* 0 has a special meaning... */
575 	if (!cur_time)
576 		return 1;
577 	return cur_time;
578 }
579 
wb_domain_writeout_add(struct wb_domain * dom,struct fprop_local_percpu * completions,unsigned int max_prop_frac,long nr)580 static void wb_domain_writeout_add(struct wb_domain *dom,
581 				   struct fprop_local_percpu *completions,
582 				   unsigned int max_prop_frac, long nr)
583 {
584 	__fprop_add_percpu_max(&dom->completions, completions,
585 			       max_prop_frac, nr);
586 	/* First event after period switching was turned off? */
587 	if (unlikely(!dom->period_time)) {
588 		/*
589 		 * We can race with other wb_domain_writeout_add calls here but
590 		 * it does not cause any harm since the resulting time when
591 		 * timer will fire and what is in writeout_period_time will be
592 		 * roughly the same.
593 		 */
594 		dom->period_time = wp_next_time(jiffies);
595 		mod_timer(&dom->period_timer, dom->period_time);
596 	}
597 }
598 
599 /*
600  * Increment @wb's writeout completion count and the global writeout
601  * completion count. Called from __folio_end_writeback().
602  */
__wb_writeout_add(struct bdi_writeback * wb,long nr)603 static inline void __wb_writeout_add(struct bdi_writeback *wb, long nr)
604 {
605 	struct wb_domain *cgdom;
606 
607 	wb_stat_mod(wb, WB_WRITTEN, nr);
608 	wb_domain_writeout_add(&global_wb_domain, &wb->completions,
609 			       wb->bdi->max_prop_frac, nr);
610 
611 	cgdom = mem_cgroup_wb_domain(wb);
612 	if (cgdom)
613 		wb_domain_writeout_add(cgdom, wb_memcg_completions(wb),
614 				       wb->bdi->max_prop_frac, nr);
615 }
616 
wb_writeout_inc(struct bdi_writeback * wb)617 void wb_writeout_inc(struct bdi_writeback *wb)
618 {
619 	unsigned long flags;
620 
621 	local_irq_save(flags);
622 	__wb_writeout_add(wb, 1);
623 	local_irq_restore(flags);
624 }
625 EXPORT_SYMBOL_GPL(wb_writeout_inc);
626 
627 /*
628  * On idle system, we can be called long after we scheduled because we use
629  * deferred timers so count with missed periods.
630  */
writeout_period(struct timer_list * t)631 static void writeout_period(struct timer_list *t)
632 {
633 	struct wb_domain *dom = from_timer(dom, t, period_timer);
634 	int miss_periods = (jiffies - dom->period_time) /
635 						 VM_COMPLETIONS_PERIOD_LEN;
636 
637 	if (fprop_new_period(&dom->completions, miss_periods + 1)) {
638 		dom->period_time = wp_next_time(dom->period_time +
639 				miss_periods * VM_COMPLETIONS_PERIOD_LEN);
640 		mod_timer(&dom->period_timer, dom->period_time);
641 	} else {
642 		/*
643 		 * Aging has zeroed all fractions. Stop wasting CPU on period
644 		 * updates.
645 		 */
646 		dom->period_time = 0;
647 	}
648 }
649 
wb_domain_init(struct wb_domain * dom,gfp_t gfp)650 int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
651 {
652 	memset(dom, 0, sizeof(*dom));
653 
654 	spin_lock_init(&dom->lock);
655 
656 	timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
657 
658 	dom->dirty_limit_tstamp = jiffies;
659 
660 	return fprop_global_init(&dom->completions, gfp);
661 }
662 
663 #ifdef CONFIG_CGROUP_WRITEBACK
wb_domain_exit(struct wb_domain * dom)664 void wb_domain_exit(struct wb_domain *dom)
665 {
666 	del_timer_sync(&dom->period_timer);
667 	fprop_global_destroy(&dom->completions);
668 }
669 #endif
670 
671 /*
672  * bdi_min_ratio keeps the sum of the minimum dirty shares of all
673  * registered backing devices, which, for obvious reasons, can not
674  * exceed 100%.
675  */
676 static unsigned int bdi_min_ratio;
677 
bdi_check_pages_limit(unsigned long pages)678 static int bdi_check_pages_limit(unsigned long pages)
679 {
680 	unsigned long max_dirty_pages = global_dirtyable_memory();
681 
682 	if (pages > max_dirty_pages)
683 		return -EINVAL;
684 
685 	return 0;
686 }
687 
bdi_ratio_from_pages(unsigned long pages)688 static unsigned long bdi_ratio_from_pages(unsigned long pages)
689 {
690 	unsigned long background_thresh;
691 	unsigned long dirty_thresh;
692 	unsigned long ratio;
693 
694 	global_dirty_limits(&background_thresh, &dirty_thresh);
695 	if (!dirty_thresh)
696 		return -EINVAL;
697 	ratio = div64_u64(pages * 100ULL * BDI_RATIO_SCALE, dirty_thresh);
698 
699 	return ratio;
700 }
701 
bdi_get_bytes(unsigned int ratio)702 static u64 bdi_get_bytes(unsigned int ratio)
703 {
704 	unsigned long background_thresh;
705 	unsigned long dirty_thresh;
706 	u64 bytes;
707 
708 	global_dirty_limits(&background_thresh, &dirty_thresh);
709 	bytes = (dirty_thresh * PAGE_SIZE * ratio) / BDI_RATIO_SCALE / 100;
710 
711 	return bytes;
712 }
713 
__bdi_set_min_ratio(struct backing_dev_info * bdi,unsigned int min_ratio)714 static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
715 {
716 	unsigned int delta;
717 	int ret = 0;
718 
719 	if (min_ratio > 100 * BDI_RATIO_SCALE)
720 		return -EINVAL;
721 
722 	spin_lock_bh(&bdi_lock);
723 	if (min_ratio > bdi->max_ratio) {
724 		ret = -EINVAL;
725 	} else {
726 		if (min_ratio < bdi->min_ratio) {
727 			delta = bdi->min_ratio - min_ratio;
728 			bdi_min_ratio -= delta;
729 			bdi->min_ratio = min_ratio;
730 		} else {
731 			delta = min_ratio - bdi->min_ratio;
732 			if (bdi_min_ratio + delta < 100 * BDI_RATIO_SCALE) {
733 				bdi_min_ratio += delta;
734 				bdi->min_ratio = min_ratio;
735 			} else {
736 				ret = -EINVAL;
737 			}
738 		}
739 	}
740 	spin_unlock_bh(&bdi_lock);
741 
742 	return ret;
743 }
744 
__bdi_set_max_ratio(struct backing_dev_info * bdi,unsigned int max_ratio)745 static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
746 {
747 	int ret = 0;
748 
749 	if (max_ratio > 100 * BDI_RATIO_SCALE)
750 		return -EINVAL;
751 
752 	spin_lock_bh(&bdi_lock);
753 	if (bdi->min_ratio > max_ratio) {
754 		ret = -EINVAL;
755 	} else {
756 		bdi->max_ratio = max_ratio;
757 		bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) /
758 						(100 * BDI_RATIO_SCALE);
759 	}
760 	spin_unlock_bh(&bdi_lock);
761 
762 	return ret;
763 }
764 
bdi_set_min_ratio_no_scale(struct backing_dev_info * bdi,unsigned int min_ratio)765 int bdi_set_min_ratio_no_scale(struct backing_dev_info *bdi, unsigned int min_ratio)
766 {
767 	return __bdi_set_min_ratio(bdi, min_ratio);
768 }
769 
bdi_set_max_ratio_no_scale(struct backing_dev_info * bdi,unsigned int max_ratio)770 int bdi_set_max_ratio_no_scale(struct backing_dev_info *bdi, unsigned int max_ratio)
771 {
772 	return __bdi_set_max_ratio(bdi, max_ratio);
773 }
774 
bdi_set_min_ratio(struct backing_dev_info * bdi,unsigned int min_ratio)775 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
776 {
777 	return __bdi_set_min_ratio(bdi, min_ratio * BDI_RATIO_SCALE);
778 }
779 
bdi_set_max_ratio(struct backing_dev_info * bdi,unsigned int max_ratio)780 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
781 {
782 	return __bdi_set_max_ratio(bdi, max_ratio * BDI_RATIO_SCALE);
783 }
784 EXPORT_SYMBOL(bdi_set_max_ratio);
785 
bdi_get_min_bytes(struct backing_dev_info * bdi)786 u64 bdi_get_min_bytes(struct backing_dev_info *bdi)
787 {
788 	return bdi_get_bytes(bdi->min_ratio);
789 }
790 
bdi_set_min_bytes(struct backing_dev_info * bdi,u64 min_bytes)791 int bdi_set_min_bytes(struct backing_dev_info *bdi, u64 min_bytes)
792 {
793 	int ret;
794 	unsigned long pages = min_bytes >> PAGE_SHIFT;
795 	long min_ratio;
796 
797 	ret = bdi_check_pages_limit(pages);
798 	if (ret)
799 		return ret;
800 
801 	min_ratio = bdi_ratio_from_pages(pages);
802 	if (min_ratio < 0)
803 		return min_ratio;
804 	return __bdi_set_min_ratio(bdi, min_ratio);
805 }
806 
bdi_get_max_bytes(struct backing_dev_info * bdi)807 u64 bdi_get_max_bytes(struct backing_dev_info *bdi)
808 {
809 	return bdi_get_bytes(bdi->max_ratio);
810 }
811 
bdi_set_max_bytes(struct backing_dev_info * bdi,u64 max_bytes)812 int bdi_set_max_bytes(struct backing_dev_info *bdi, u64 max_bytes)
813 {
814 	int ret;
815 	unsigned long pages = max_bytes >> PAGE_SHIFT;
816 	long max_ratio;
817 
818 	ret = bdi_check_pages_limit(pages);
819 	if (ret)
820 		return ret;
821 
822 	max_ratio = bdi_ratio_from_pages(pages);
823 	if (max_ratio < 0)
824 		return max_ratio;
825 	return __bdi_set_max_ratio(bdi, max_ratio);
826 }
827 
bdi_set_strict_limit(struct backing_dev_info * bdi,unsigned int strict_limit)828 int bdi_set_strict_limit(struct backing_dev_info *bdi, unsigned int strict_limit)
829 {
830 	if (strict_limit > 1)
831 		return -EINVAL;
832 
833 	spin_lock_bh(&bdi_lock);
834 	if (strict_limit)
835 		bdi->capabilities |= BDI_CAP_STRICTLIMIT;
836 	else
837 		bdi->capabilities &= ~BDI_CAP_STRICTLIMIT;
838 	spin_unlock_bh(&bdi_lock);
839 
840 	return 0;
841 }
842 
dirty_freerun_ceiling(unsigned long thresh,unsigned long bg_thresh)843 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
844 					   unsigned long bg_thresh)
845 {
846 	return (thresh + bg_thresh) / 2;
847 }
848 
hard_dirty_limit(struct wb_domain * dom,unsigned long thresh)849 static unsigned long hard_dirty_limit(struct wb_domain *dom,
850 				      unsigned long thresh)
851 {
852 	return max(thresh, dom->dirty_limit);
853 }
854 
855 /*
856  * Memory which can be further allocated to a memcg domain is capped by
857  * system-wide clean memory excluding the amount being used in the domain.
858  */
mdtc_calc_avail(struct dirty_throttle_control * mdtc,unsigned long filepages,unsigned long headroom)859 static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
860 			    unsigned long filepages, unsigned long headroom)
861 {
862 	struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
863 	unsigned long clean = filepages - min(filepages, mdtc->dirty);
864 	unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
865 	unsigned long other_clean = global_clean - min(global_clean, clean);
866 
867 	mdtc->avail = filepages + min(headroom, other_clean);
868 }
869 
dtc_is_global(struct dirty_throttle_control * dtc)870 static inline bool dtc_is_global(struct dirty_throttle_control *dtc)
871 {
872 	return mdtc_gdtc(dtc) == NULL;
873 }
874 
875 /*
876  * Dirty background will ignore pages being written as we're trying to
877  * decide whether to put more under writeback.
878  */
domain_dirty_avail(struct dirty_throttle_control * dtc,bool include_writeback)879 static void domain_dirty_avail(struct dirty_throttle_control *dtc,
880 			       bool include_writeback)
881 {
882 	if (dtc_is_global(dtc)) {
883 		dtc->avail = global_dirtyable_memory();
884 		dtc->dirty = global_node_page_state(NR_FILE_DIRTY);
885 		if (include_writeback)
886 			dtc->dirty += global_node_page_state(NR_WRITEBACK);
887 	} else {
888 		unsigned long filepages = 0, headroom = 0, writeback = 0;
889 
890 		mem_cgroup_wb_stats(dtc->wb, &filepages, &headroom, &dtc->dirty,
891 				    &writeback);
892 		if (include_writeback)
893 			dtc->dirty += writeback;
894 		mdtc_calc_avail(dtc, filepages, headroom);
895 	}
896 }
897 
898 /**
899  * __wb_calc_thresh - @wb's share of dirty threshold
900  * @dtc: dirty_throttle_context of interest
901  * @thresh: dirty throttling or dirty background threshold of wb_domain in @dtc
902  *
903  * Note that balance_dirty_pages() will only seriously take dirty throttling
904  * threshold as a hard limit when sleeping max_pause per page is not enough
905  * to keep the dirty pages under control. For example, when the device is
906  * completely stalled due to some error conditions, or when there are 1000
907  * dd tasks writing to a slow 10MB/s USB key.
908  * In the other normal situations, it acts more gently by throttling the tasks
909  * more (rather than completely block them) when the wb dirty pages go high.
910  *
911  * It allocates high/low dirty limits to fast/slow devices, in order to prevent
912  * - starving fast devices
913  * - piling up dirty pages (that will take long time to sync) on slow devices
914  *
915  * The wb's share of dirty limit will be adapting to its throughput and
916  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
917  *
918  * Return: @wb's dirty limit in pages. For dirty throttling limit, the term
919  * "dirty" in the context of dirty balancing includes all PG_dirty and
920  * PG_writeback pages.
921  */
__wb_calc_thresh(struct dirty_throttle_control * dtc,unsigned long thresh)922 static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc,
923 				      unsigned long thresh)
924 {
925 	struct wb_domain *dom = dtc_dom(dtc);
926 	struct bdi_writeback *wb = dtc->wb;
927 	u64 wb_thresh;
928 	u64 wb_max_thresh;
929 	unsigned long numerator, denominator;
930 	unsigned long wb_min_ratio, wb_max_ratio;
931 
932 	/*
933 	 * Calculate this wb's share of the thresh ratio.
934 	 */
935 	fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
936 			      &numerator, &denominator);
937 
938 	wb_thresh = (thresh * (100 * BDI_RATIO_SCALE - bdi_min_ratio)) / (100 * BDI_RATIO_SCALE);
939 	wb_thresh *= numerator;
940 	wb_thresh = div64_ul(wb_thresh, denominator);
941 
942 	wb_min_max_ratio(wb, &wb_min_ratio, &wb_max_ratio);
943 
944 	wb_thresh += (thresh * wb_min_ratio) / (100 * BDI_RATIO_SCALE);
945 
946 	/*
947 	 * It's very possible that wb_thresh is close to 0 not because the
948 	 * device is slow, but that it has remained inactive for long time.
949 	 * Honour such devices a reasonable good (hopefully IO efficient)
950 	 * threshold, so that the occasional writes won't be blocked and active
951 	 * writes can rampup the threshold quickly.
952 	 */
953 	if (thresh > dtc->dirty) {
954 		if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT))
955 			wb_thresh = max(wb_thresh, (thresh - dtc->dirty) / 100);
956 		else
957 			wb_thresh = max(wb_thresh, (thresh - dtc->dirty) / 8);
958 	}
959 
960 	wb_max_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE);
961 	if (wb_thresh > wb_max_thresh)
962 		wb_thresh = wb_max_thresh;
963 
964 	return wb_thresh;
965 }
966 
wb_calc_thresh(struct bdi_writeback * wb,unsigned long thresh)967 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
968 {
969 	struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
970 
971 	domain_dirty_avail(&gdtc, true);
972 	return __wb_calc_thresh(&gdtc, thresh);
973 }
974 
cgwb_calc_thresh(struct bdi_writeback * wb)975 unsigned long cgwb_calc_thresh(struct bdi_writeback *wb)
976 {
977 	struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
978 	struct dirty_throttle_control mdtc = { MDTC_INIT(wb, &gdtc) };
979 
980 	domain_dirty_avail(&gdtc, true);
981 	domain_dirty_avail(&mdtc, true);
982 	domain_dirty_limits(&mdtc);
983 
984 	return __wb_calc_thresh(&mdtc, mdtc.thresh);
985 }
986 
987 /*
988  *                           setpoint - dirty 3
989  *        f(dirty) := 1.0 + (----------------)
990  *                           limit - setpoint
991  *
992  * it's a 3rd order polynomial that subjects to
993  *
994  * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
995  * (2) f(setpoint) = 1.0 => the balance point
996  * (3) f(limit)    = 0   => the hard limit
997  * (4) df/dx      <= 0	 => negative feedback control
998  * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
999  *     => fast response on large errors; small oscillation near setpoint
1000  */
pos_ratio_polynom(unsigned long setpoint,unsigned long dirty,unsigned long limit)1001 static long long pos_ratio_polynom(unsigned long setpoint,
1002 					  unsigned long dirty,
1003 					  unsigned long limit)
1004 {
1005 	long long pos_ratio;
1006 	long x;
1007 
1008 	x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
1009 		      (limit - setpoint) | 1);
1010 	pos_ratio = x;
1011 	pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
1012 	pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
1013 	pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
1014 
1015 	return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
1016 }
1017 
1018 /*
1019  * Dirty position control.
1020  *
1021  * (o) global/bdi setpoints
1022  *
1023  * We want the dirty pages be balanced around the global/wb setpoints.
1024  * When the number of dirty pages is higher/lower than the setpoint, the
1025  * dirty position control ratio (and hence task dirty ratelimit) will be
1026  * decreased/increased to bring the dirty pages back to the setpoint.
1027  *
1028  *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
1029  *
1030  *     if (dirty < setpoint) scale up   pos_ratio
1031  *     if (dirty > setpoint) scale down pos_ratio
1032  *
1033  *     if (wb_dirty < wb_setpoint) scale up   pos_ratio
1034  *     if (wb_dirty > wb_setpoint) scale down pos_ratio
1035  *
1036  *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
1037  *
1038  * (o) global control line
1039  *
1040  *     ^ pos_ratio
1041  *     |
1042  *     |            |<===== global dirty control scope ======>|
1043  * 2.0  * * * * * * *
1044  *     |            .*
1045  *     |            . *
1046  *     |            .   *
1047  *     |            .     *
1048  *     |            .        *
1049  *     |            .            *
1050  * 1.0 ................................*
1051  *     |            .                  .     *
1052  *     |            .                  .          *
1053  *     |            .                  .              *
1054  *     |            .                  .                 *
1055  *     |            .                  .                    *
1056  *   0 +------------.------------------.----------------------*------------->
1057  *           freerun^          setpoint^                 limit^   dirty pages
1058  *
1059  * (o) wb control line
1060  *
1061  *     ^ pos_ratio
1062  *     |
1063  *     |            *
1064  *     |              *
1065  *     |                *
1066  *     |                  *
1067  *     |                    * |<=========== span ============>|
1068  * 1.0 .......................*
1069  *     |                      . *
1070  *     |                      .   *
1071  *     |                      .     *
1072  *     |                      .       *
1073  *     |                      .         *
1074  *     |                      .           *
1075  *     |                      .             *
1076  *     |                      .               *
1077  *     |                      .                 *
1078  *     |                      .                   *
1079  *     |                      .                     *
1080  * 1/4 ...............................................* * * * * * * * * * * *
1081  *     |                      .                         .
1082  *     |                      .                           .
1083  *     |                      .                             .
1084  *   0 +----------------------.-------------------------------.------------->
1085  *                wb_setpoint^                    x_intercept^
1086  *
1087  * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
1088  * be smoothly throttled down to normal if it starts high in situations like
1089  * - start writing to a slow SD card and a fast disk at the same time. The SD
1090  *   card's wb_dirty may rush to many times higher than wb_setpoint.
1091  * - the wb dirty thresh drops quickly due to change of JBOD workload
1092  */
wb_position_ratio(struct dirty_throttle_control * dtc)1093 static void wb_position_ratio(struct dirty_throttle_control *dtc)
1094 {
1095 	struct bdi_writeback *wb = dtc->wb;
1096 	unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth);
1097 	unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1098 	unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1099 	unsigned long wb_thresh = dtc->wb_thresh;
1100 	unsigned long x_intercept;
1101 	unsigned long setpoint;		/* dirty pages' target balance point */
1102 	unsigned long wb_setpoint;
1103 	unsigned long span;
1104 	long long pos_ratio;		/* for scaling up/down the rate limit */
1105 	long x;
1106 
1107 	dtc->pos_ratio = 0;
1108 
1109 	if (unlikely(dtc->dirty >= limit))
1110 		return;
1111 
1112 	/*
1113 	 * global setpoint
1114 	 *
1115 	 * See comment for pos_ratio_polynom().
1116 	 */
1117 	setpoint = (freerun + limit) / 2;
1118 	pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
1119 
1120 	/*
1121 	 * The strictlimit feature is a tool preventing mistrusted filesystems
1122 	 * from growing a large number of dirty pages before throttling. For
1123 	 * such filesystems balance_dirty_pages always checks wb counters
1124 	 * against wb limits. Even if global "nr_dirty" is under "freerun".
1125 	 * This is especially important for fuse which sets bdi->max_ratio to
1126 	 * 1% by default. Without strictlimit feature, fuse writeback may
1127 	 * consume arbitrary amount of RAM because it is accounted in
1128 	 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
1129 	 *
1130 	 * Here, in wb_position_ratio(), we calculate pos_ratio based on
1131 	 * two values: wb_dirty and wb_thresh. Let's consider an example:
1132 	 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
1133 	 * limits are set by default to 10% and 20% (background and throttle).
1134 	 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
1135 	 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
1136 	 * about ~6K pages (as the average of background and throttle wb
1137 	 * limits). The 3rd order polynomial will provide positive feedback if
1138 	 * wb_dirty is under wb_setpoint and vice versa.
1139 	 *
1140 	 * Note, that we cannot use global counters in these calculations
1141 	 * because we want to throttle process writing to a strictlimit wb
1142 	 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
1143 	 * in the example above).
1144 	 */
1145 	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1146 		long long wb_pos_ratio;
1147 
1148 		if (dtc->wb_dirty >= wb_thresh)
1149 			return;
1150 
1151 		wb_setpoint = dirty_freerun_ceiling(wb_thresh,
1152 						    dtc->wb_bg_thresh);
1153 
1154 		if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
1155 			return;
1156 
1157 		wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
1158 						 wb_thresh);
1159 
1160 		/*
1161 		 * Typically, for strictlimit case, wb_setpoint << setpoint
1162 		 * and pos_ratio >> wb_pos_ratio. In the other words global
1163 		 * state ("dirty") is not limiting factor and we have to
1164 		 * make decision based on wb counters. But there is an
1165 		 * important case when global pos_ratio should get precedence:
1166 		 * global limits are exceeded (e.g. due to activities on other
1167 		 * wb's) while given strictlimit wb is below limit.
1168 		 *
1169 		 * "pos_ratio * wb_pos_ratio" would work for the case above,
1170 		 * but it would look too non-natural for the case of all
1171 		 * activity in the system coming from a single strictlimit wb
1172 		 * with bdi->max_ratio == 100%.
1173 		 *
1174 		 * Note that min() below somewhat changes the dynamics of the
1175 		 * control system. Normally, pos_ratio value can be well over 3
1176 		 * (when globally we are at freerun and wb is well below wb
1177 		 * setpoint). Now the maximum pos_ratio in the same situation
1178 		 * is 2. We might want to tweak this if we observe the control
1179 		 * system is too slow to adapt.
1180 		 */
1181 		dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
1182 		return;
1183 	}
1184 
1185 	/*
1186 	 * We have computed basic pos_ratio above based on global situation. If
1187 	 * the wb is over/under its share of dirty pages, we want to scale
1188 	 * pos_ratio further down/up. That is done by the following mechanism.
1189 	 */
1190 
1191 	/*
1192 	 * wb setpoint
1193 	 *
1194 	 *        f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1195 	 *
1196 	 *                        x_intercept - wb_dirty
1197 	 *                     := --------------------------
1198 	 *                        x_intercept - wb_setpoint
1199 	 *
1200 	 * The main wb control line is a linear function that subjects to
1201 	 *
1202 	 * (1) f(wb_setpoint) = 1.0
1203 	 * (2) k = - 1 / (8 * write_bw)  (in single wb case)
1204 	 *     or equally: x_intercept = wb_setpoint + 8 * write_bw
1205 	 *
1206 	 * For single wb case, the dirty pages are observed to fluctuate
1207 	 * regularly within range
1208 	 *        [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1209 	 * for various filesystems, where (2) can yield in a reasonable 12.5%
1210 	 * fluctuation range for pos_ratio.
1211 	 *
1212 	 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1213 	 * own size, so move the slope over accordingly and choose a slope that
1214 	 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1215 	 */
1216 	if (unlikely(wb_thresh > dtc->thresh))
1217 		wb_thresh = dtc->thresh;
1218 	/*
1219 	 * scale global setpoint to wb's:
1220 	 *	wb_setpoint = setpoint * wb_thresh / thresh
1221 	 */
1222 	x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1223 	wb_setpoint = setpoint * (u64)x >> 16;
1224 	/*
1225 	 * Use span=(8*write_bw) in single wb case as indicated by
1226 	 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1227 	 *
1228 	 *        wb_thresh                    thresh - wb_thresh
1229 	 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1230 	 *         thresh                           thresh
1231 	 */
1232 	span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1233 	x_intercept = wb_setpoint + span;
1234 
1235 	if (dtc->wb_dirty < x_intercept - span / 4) {
1236 		pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1237 				      (x_intercept - wb_setpoint) | 1);
1238 	} else
1239 		pos_ratio /= 4;
1240 
1241 	/*
1242 	 * wb reserve area, safeguard against dirty pool underrun and disk idle
1243 	 * It may push the desired control point of global dirty pages higher
1244 	 * than setpoint.
1245 	 */
1246 	x_intercept = wb_thresh / 2;
1247 	if (dtc->wb_dirty < x_intercept) {
1248 		if (dtc->wb_dirty > x_intercept / 8)
1249 			pos_ratio = div_u64(pos_ratio * x_intercept,
1250 					    dtc->wb_dirty);
1251 		else
1252 			pos_ratio *= 8;
1253 	}
1254 
1255 	dtc->pos_ratio = pos_ratio;
1256 }
1257 
wb_update_write_bandwidth(struct bdi_writeback * wb,unsigned long elapsed,unsigned long written)1258 static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1259 				      unsigned long elapsed,
1260 				      unsigned long written)
1261 {
1262 	const unsigned long period = roundup_pow_of_two(3 * HZ);
1263 	unsigned long avg = wb->avg_write_bandwidth;
1264 	unsigned long old = wb->write_bandwidth;
1265 	u64 bw;
1266 
1267 	/*
1268 	 * bw = written * HZ / elapsed
1269 	 *
1270 	 *                   bw * elapsed + write_bandwidth * (period - elapsed)
1271 	 * write_bandwidth = ---------------------------------------------------
1272 	 *                                          period
1273 	 *
1274 	 * @written may have decreased due to folio_redirty_for_writepage().
1275 	 * Avoid underflowing @bw calculation.
1276 	 */
1277 	bw = written - min(written, wb->written_stamp);
1278 	bw *= HZ;
1279 	if (unlikely(elapsed > period)) {
1280 		bw = div64_ul(bw, elapsed);
1281 		avg = bw;
1282 		goto out;
1283 	}
1284 	bw += (u64)wb->write_bandwidth * (period - elapsed);
1285 	bw >>= ilog2(period);
1286 
1287 	/*
1288 	 * one more level of smoothing, for filtering out sudden spikes
1289 	 */
1290 	if (avg > old && old >= (unsigned long)bw)
1291 		avg -= (avg - old) >> 3;
1292 
1293 	if (avg < old && old <= (unsigned long)bw)
1294 		avg += (old - avg) >> 3;
1295 
1296 out:
1297 	/* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1298 	avg = max(avg, 1LU);
1299 	if (wb_has_dirty_io(wb)) {
1300 		long delta = avg - wb->avg_write_bandwidth;
1301 		WARN_ON_ONCE(atomic_long_add_return(delta,
1302 					&wb->bdi->tot_write_bandwidth) <= 0);
1303 	}
1304 	wb->write_bandwidth = bw;
1305 	WRITE_ONCE(wb->avg_write_bandwidth, avg);
1306 }
1307 
update_dirty_limit(struct dirty_throttle_control * dtc)1308 static void update_dirty_limit(struct dirty_throttle_control *dtc)
1309 {
1310 	struct wb_domain *dom = dtc_dom(dtc);
1311 	unsigned long thresh = dtc->thresh;
1312 	unsigned long limit = dom->dirty_limit;
1313 
1314 	/*
1315 	 * Follow up in one step.
1316 	 */
1317 	if (limit < thresh) {
1318 		limit = thresh;
1319 		goto update;
1320 	}
1321 
1322 	/*
1323 	 * Follow down slowly. Use the higher one as the target, because thresh
1324 	 * may drop below dirty. This is exactly the reason to introduce
1325 	 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1326 	 */
1327 	thresh = max(thresh, dtc->dirty);
1328 	if (limit > thresh) {
1329 		limit -= (limit - thresh) >> 5;
1330 		goto update;
1331 	}
1332 	return;
1333 update:
1334 	dom->dirty_limit = limit;
1335 }
1336 
domain_update_dirty_limit(struct dirty_throttle_control * dtc,unsigned long now)1337 static void domain_update_dirty_limit(struct dirty_throttle_control *dtc,
1338 				      unsigned long now)
1339 {
1340 	struct wb_domain *dom = dtc_dom(dtc);
1341 
1342 	/*
1343 	 * check locklessly first to optimize away locking for the most time
1344 	 */
1345 	if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1346 		return;
1347 
1348 	spin_lock(&dom->lock);
1349 	if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1350 		update_dirty_limit(dtc);
1351 		dom->dirty_limit_tstamp = now;
1352 	}
1353 	spin_unlock(&dom->lock);
1354 }
1355 
1356 /*
1357  * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1358  *
1359  * Normal wb tasks will be curbed at or below it in long term.
1360  * Obviously it should be around (write_bw / N) when there are N dd tasks.
1361  */
wb_update_dirty_ratelimit(struct dirty_throttle_control * dtc,unsigned long dirtied,unsigned long elapsed)1362 static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1363 				      unsigned long dirtied,
1364 				      unsigned long elapsed)
1365 {
1366 	struct bdi_writeback *wb = dtc->wb;
1367 	unsigned long dirty = dtc->dirty;
1368 	unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1369 	unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1370 	unsigned long setpoint = (freerun + limit) / 2;
1371 	unsigned long write_bw = wb->avg_write_bandwidth;
1372 	unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1373 	unsigned long dirty_rate;
1374 	unsigned long task_ratelimit;
1375 	unsigned long balanced_dirty_ratelimit;
1376 	unsigned long step;
1377 	unsigned long x;
1378 	unsigned long shift;
1379 
1380 	/*
1381 	 * The dirty rate will match the writeout rate in long term, except
1382 	 * when dirty pages are truncated by userspace or re-dirtied by FS.
1383 	 */
1384 	dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1385 
1386 	/*
1387 	 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1388 	 */
1389 	task_ratelimit = (u64)dirty_ratelimit *
1390 					dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1391 	task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1392 
1393 	/*
1394 	 * A linear estimation of the "balanced" throttle rate. The theory is,
1395 	 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1396 	 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1397 	 * formula will yield the balanced rate limit (write_bw / N).
1398 	 *
1399 	 * Note that the expanded form is not a pure rate feedback:
1400 	 *	rate_(i+1) = rate_(i) * (write_bw / dirty_rate)		     (1)
1401 	 * but also takes pos_ratio into account:
1402 	 *	rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
1403 	 *
1404 	 * (1) is not realistic because pos_ratio also takes part in balancing
1405 	 * the dirty rate.  Consider the state
1406 	 *	pos_ratio = 0.5						     (3)
1407 	 *	rate = 2 * (write_bw / N)				     (4)
1408 	 * If (1) is used, it will stuck in that state! Because each dd will
1409 	 * be throttled at
1410 	 *	task_ratelimit = pos_ratio * rate = (write_bw / N)	     (5)
1411 	 * yielding
1412 	 *	dirty_rate = N * task_ratelimit = write_bw		     (6)
1413 	 * put (6) into (1) we get
1414 	 *	rate_(i+1) = rate_(i)					     (7)
1415 	 *
1416 	 * So we end up using (2) to always keep
1417 	 *	rate_(i+1) ~= (write_bw / N)				     (8)
1418 	 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1419 	 * pos_ratio is able to drive itself to 1.0, which is not only where
1420 	 * the dirty count meet the setpoint, but also where the slope of
1421 	 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1422 	 */
1423 	balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1424 					   dirty_rate | 1);
1425 	/*
1426 	 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1427 	 */
1428 	if (unlikely(balanced_dirty_ratelimit > write_bw))
1429 		balanced_dirty_ratelimit = write_bw;
1430 
1431 	/*
1432 	 * We could safely do this and return immediately:
1433 	 *
1434 	 *	wb->dirty_ratelimit = balanced_dirty_ratelimit;
1435 	 *
1436 	 * However to get a more stable dirty_ratelimit, the below elaborated
1437 	 * code makes use of task_ratelimit to filter out singular points and
1438 	 * limit the step size.
1439 	 *
1440 	 * The below code essentially only uses the relative value of
1441 	 *
1442 	 *	task_ratelimit - dirty_ratelimit
1443 	 *	= (pos_ratio - 1) * dirty_ratelimit
1444 	 *
1445 	 * which reflects the direction and size of dirty position error.
1446 	 */
1447 
1448 	/*
1449 	 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1450 	 * task_ratelimit is on the same side of dirty_ratelimit, too.
1451 	 * For example, when
1452 	 * - dirty_ratelimit > balanced_dirty_ratelimit
1453 	 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1454 	 * lowering dirty_ratelimit will help meet both the position and rate
1455 	 * control targets. Otherwise, don't update dirty_ratelimit if it will
1456 	 * only help meet the rate target. After all, what the users ultimately
1457 	 * feel and care are stable dirty rate and small position error.
1458 	 *
1459 	 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1460 	 * and filter out the singular points of balanced_dirty_ratelimit. Which
1461 	 * keeps jumping around randomly and can even leap far away at times
1462 	 * due to the small 200ms estimation period of dirty_rate (we want to
1463 	 * keep that period small to reduce time lags).
1464 	 */
1465 	step = 0;
1466 
1467 	/*
1468 	 * For strictlimit case, calculations above were based on wb counters
1469 	 * and limits (starting from pos_ratio = wb_position_ratio() and up to
1470 	 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1471 	 * Hence, to calculate "step" properly, we have to use wb_dirty as
1472 	 * "dirty" and wb_setpoint as "setpoint".
1473 	 */
1474 	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1475 		dirty = dtc->wb_dirty;
1476 		setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1477 	}
1478 
1479 	if (dirty < setpoint) {
1480 		x = min3(wb->balanced_dirty_ratelimit,
1481 			 balanced_dirty_ratelimit, task_ratelimit);
1482 		if (dirty_ratelimit < x)
1483 			step = x - dirty_ratelimit;
1484 	} else {
1485 		x = max3(wb->balanced_dirty_ratelimit,
1486 			 balanced_dirty_ratelimit, task_ratelimit);
1487 		if (dirty_ratelimit > x)
1488 			step = dirty_ratelimit - x;
1489 	}
1490 
1491 	/*
1492 	 * Don't pursue 100% rate matching. It's impossible since the balanced
1493 	 * rate itself is constantly fluctuating. So decrease the track speed
1494 	 * when it gets close to the target. Helps eliminate pointless tremors.
1495 	 */
1496 	shift = dirty_ratelimit / (2 * step + 1);
1497 	if (shift < BITS_PER_LONG)
1498 		step = DIV_ROUND_UP(step >> shift, 8);
1499 	else
1500 		step = 0;
1501 
1502 	if (dirty_ratelimit < balanced_dirty_ratelimit)
1503 		dirty_ratelimit += step;
1504 	else
1505 		dirty_ratelimit -= step;
1506 
1507 	WRITE_ONCE(wb->dirty_ratelimit, max(dirty_ratelimit, 1UL));
1508 	wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1509 
1510 	trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1511 }
1512 
__wb_update_bandwidth(struct dirty_throttle_control * gdtc,struct dirty_throttle_control * mdtc,bool update_ratelimit)1513 static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1514 				  struct dirty_throttle_control *mdtc,
1515 				  bool update_ratelimit)
1516 {
1517 	struct bdi_writeback *wb = gdtc->wb;
1518 	unsigned long now = jiffies;
1519 	unsigned long elapsed;
1520 	unsigned long dirtied;
1521 	unsigned long written;
1522 
1523 	spin_lock(&wb->list_lock);
1524 
1525 	/*
1526 	 * Lockless checks for elapsed time are racy and delayed update after
1527 	 * IO completion doesn't do it at all (to make sure written pages are
1528 	 * accounted reasonably quickly). Make sure elapsed >= 1 to avoid
1529 	 * division errors.
1530 	 */
1531 	elapsed = max(now - wb->bw_time_stamp, 1UL);
1532 	dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1533 	written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1534 
1535 	if (update_ratelimit) {
1536 		domain_update_dirty_limit(gdtc, now);
1537 		wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1538 
1539 		/*
1540 		 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1541 		 * compiler has no way to figure that out.  Help it.
1542 		 */
1543 		if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1544 			domain_update_dirty_limit(mdtc, now);
1545 			wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1546 		}
1547 	}
1548 	wb_update_write_bandwidth(wb, elapsed, written);
1549 
1550 	wb->dirtied_stamp = dirtied;
1551 	wb->written_stamp = written;
1552 	WRITE_ONCE(wb->bw_time_stamp, now);
1553 	spin_unlock(&wb->list_lock);
1554 }
1555 
wb_update_bandwidth(struct bdi_writeback * wb)1556 void wb_update_bandwidth(struct bdi_writeback *wb)
1557 {
1558 	struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1559 
1560 	__wb_update_bandwidth(&gdtc, NULL, false);
1561 }
1562 
1563 /* Interval after which we consider wb idle and don't estimate bandwidth */
1564 #define WB_BANDWIDTH_IDLE_JIF (HZ)
1565 
wb_bandwidth_estimate_start(struct bdi_writeback * wb)1566 static void wb_bandwidth_estimate_start(struct bdi_writeback *wb)
1567 {
1568 	unsigned long now = jiffies;
1569 	unsigned long elapsed = now - READ_ONCE(wb->bw_time_stamp);
1570 
1571 	if (elapsed > WB_BANDWIDTH_IDLE_JIF &&
1572 	    !atomic_read(&wb->writeback_inodes)) {
1573 		spin_lock(&wb->list_lock);
1574 		wb->dirtied_stamp = wb_stat(wb, WB_DIRTIED);
1575 		wb->written_stamp = wb_stat(wb, WB_WRITTEN);
1576 		WRITE_ONCE(wb->bw_time_stamp, now);
1577 		spin_unlock(&wb->list_lock);
1578 	}
1579 }
1580 
1581 /*
1582  * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1583  * will look to see if it needs to start dirty throttling.
1584  *
1585  * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1586  * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1587  * (the number of pages we may dirty without exceeding the dirty limits).
1588  */
dirty_poll_interval(unsigned long dirty,unsigned long thresh)1589 static unsigned long dirty_poll_interval(unsigned long dirty,
1590 					 unsigned long thresh)
1591 {
1592 	if (thresh > dirty)
1593 		return 1UL << (ilog2(thresh - dirty) >> 1);
1594 
1595 	return 1;
1596 }
1597 
wb_max_pause(struct bdi_writeback * wb,unsigned long wb_dirty)1598 static unsigned long wb_max_pause(struct bdi_writeback *wb,
1599 				  unsigned long wb_dirty)
1600 {
1601 	unsigned long bw = READ_ONCE(wb->avg_write_bandwidth);
1602 	unsigned long t;
1603 
1604 	/*
1605 	 * Limit pause time for small memory systems. If sleeping for too long
1606 	 * time, a small pool of dirty/writeback pages may go empty and disk go
1607 	 * idle.
1608 	 *
1609 	 * 8 serves as the safety ratio.
1610 	 */
1611 	t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1612 	t++;
1613 
1614 	return min_t(unsigned long, t, MAX_PAUSE);
1615 }
1616 
wb_min_pause(struct bdi_writeback * wb,long max_pause,unsigned long task_ratelimit,unsigned long dirty_ratelimit,int * nr_dirtied_pause)1617 static long wb_min_pause(struct bdi_writeback *wb,
1618 			 long max_pause,
1619 			 unsigned long task_ratelimit,
1620 			 unsigned long dirty_ratelimit,
1621 			 int *nr_dirtied_pause)
1622 {
1623 	long hi = ilog2(READ_ONCE(wb->avg_write_bandwidth));
1624 	long lo = ilog2(READ_ONCE(wb->dirty_ratelimit));
1625 	long t;		/* target pause */
1626 	long pause;	/* estimated next pause */
1627 	int pages;	/* target nr_dirtied_pause */
1628 
1629 	/* target for 10ms pause on 1-dd case */
1630 	t = max(1, HZ / 100);
1631 
1632 	/*
1633 	 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1634 	 * overheads.
1635 	 *
1636 	 * (N * 10ms) on 2^N concurrent tasks.
1637 	 */
1638 	if (hi > lo)
1639 		t += (hi - lo) * (10 * HZ) / 1024;
1640 
1641 	/*
1642 	 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1643 	 * on the much more stable dirty_ratelimit. However the next pause time
1644 	 * will be computed based on task_ratelimit and the two rate limits may
1645 	 * depart considerably at some time. Especially if task_ratelimit goes
1646 	 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1647 	 * pause time will be max_pause*2 _trimmed down_ to max_pause.  As a
1648 	 * result task_ratelimit won't be executed faithfully, which could
1649 	 * eventually bring down dirty_ratelimit.
1650 	 *
1651 	 * We apply two rules to fix it up:
1652 	 * 1) try to estimate the next pause time and if necessary, use a lower
1653 	 *    nr_dirtied_pause so as not to exceed max_pause. When this happens,
1654 	 *    nr_dirtied_pause will be "dancing" with task_ratelimit.
1655 	 * 2) limit the target pause time to max_pause/2, so that the normal
1656 	 *    small fluctuations of task_ratelimit won't trigger rule (1) and
1657 	 *    nr_dirtied_pause will remain as stable as dirty_ratelimit.
1658 	 */
1659 	t = min(t, 1 + max_pause / 2);
1660 	pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1661 
1662 	/*
1663 	 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1664 	 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1665 	 * When the 16 consecutive reads are often interrupted by some dirty
1666 	 * throttling pause during the async writes, cfq will go into idles
1667 	 * (deadline is fine). So push nr_dirtied_pause as high as possible
1668 	 * until reaches DIRTY_POLL_THRESH=32 pages.
1669 	 */
1670 	if (pages < DIRTY_POLL_THRESH) {
1671 		t = max_pause;
1672 		pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1673 		if (pages > DIRTY_POLL_THRESH) {
1674 			pages = DIRTY_POLL_THRESH;
1675 			t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1676 		}
1677 	}
1678 
1679 	pause = HZ * pages / (task_ratelimit + 1);
1680 	if (pause > max_pause) {
1681 		t = max_pause;
1682 		pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1683 	}
1684 
1685 	*nr_dirtied_pause = pages;
1686 	/*
1687 	 * The minimal pause time will normally be half the target pause time.
1688 	 */
1689 	return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1690 }
1691 
wb_dirty_limits(struct dirty_throttle_control * dtc)1692 static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1693 {
1694 	struct bdi_writeback *wb = dtc->wb;
1695 	unsigned long wb_reclaimable;
1696 
1697 	/*
1698 	 * wb_thresh is not treated as some limiting factor as
1699 	 * dirty_thresh, due to reasons
1700 	 * - in JBOD setup, wb_thresh can fluctuate a lot
1701 	 * - in a system with HDD and USB key, the USB key may somehow
1702 	 *   go into state (wb_dirty >> wb_thresh) either because
1703 	 *   wb_dirty starts high, or because wb_thresh drops low.
1704 	 *   In this case we don't want to hard throttle the USB key
1705 	 *   dirtiers for 100 seconds until wb_dirty drops under
1706 	 *   wb_thresh. Instead the auxiliary wb control line in
1707 	 *   wb_position_ratio() will let the dirtier task progress
1708 	 *   at some rate <= (write_bw / 2) for bringing down wb_dirty.
1709 	 */
1710 	dtc->wb_thresh = __wb_calc_thresh(dtc, dtc->thresh);
1711 	dtc->wb_bg_thresh = dtc->thresh ?
1712 		div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1713 
1714 	/*
1715 	 * In order to avoid the stacked BDI deadlock we need
1716 	 * to ensure we accurately count the 'dirty' pages when
1717 	 * the threshold is low.
1718 	 *
1719 	 * Otherwise it would be possible to get thresh+n pages
1720 	 * reported dirty, even though there are thresh-m pages
1721 	 * actually dirty; with m+n sitting in the percpu
1722 	 * deltas.
1723 	 */
1724 	if (dtc->wb_thresh < 2 * wb_stat_error()) {
1725 		wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1726 		dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1727 	} else {
1728 		wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1729 		dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1730 	}
1731 }
1732 
domain_poll_intv(struct dirty_throttle_control * dtc,bool strictlimit)1733 static unsigned long domain_poll_intv(struct dirty_throttle_control *dtc,
1734 				      bool strictlimit)
1735 {
1736 	unsigned long dirty, thresh;
1737 
1738 	if (strictlimit) {
1739 		dirty = dtc->wb_dirty;
1740 		thresh = dtc->wb_thresh;
1741 	} else {
1742 		dirty = dtc->dirty;
1743 		thresh = dtc->thresh;
1744 	}
1745 
1746 	return dirty_poll_interval(dirty, thresh);
1747 }
1748 
1749 /*
1750  * Throttle it only when the background writeback cannot catch-up. This avoids
1751  * (excessively) small writeouts when the wb limits are ramping up in case of
1752  * !strictlimit.
1753  *
1754  * In strictlimit case make decision based on the wb counters and limits. Small
1755  * writeouts when the wb limits are ramping up are the price we consciously pay
1756  * for strictlimit-ing.
1757  */
domain_dirty_freerun(struct dirty_throttle_control * dtc,bool strictlimit)1758 static void domain_dirty_freerun(struct dirty_throttle_control *dtc,
1759 				 bool strictlimit)
1760 {
1761 	unsigned long dirty, thresh, bg_thresh;
1762 
1763 	if (unlikely(strictlimit)) {
1764 		wb_dirty_limits(dtc);
1765 		dirty = dtc->wb_dirty;
1766 		thresh = dtc->wb_thresh;
1767 		bg_thresh = dtc->wb_bg_thresh;
1768 	} else {
1769 		dirty = dtc->dirty;
1770 		thresh = dtc->thresh;
1771 		bg_thresh = dtc->bg_thresh;
1772 	}
1773 	dtc->freerun = dirty <= dirty_freerun_ceiling(thresh, bg_thresh);
1774 }
1775 
balance_domain_limits(struct dirty_throttle_control * dtc,bool strictlimit)1776 static void balance_domain_limits(struct dirty_throttle_control *dtc,
1777 				  bool strictlimit)
1778 {
1779 	domain_dirty_avail(dtc, true);
1780 	domain_dirty_limits(dtc);
1781 	domain_dirty_freerun(dtc, strictlimit);
1782 }
1783 
wb_dirty_freerun(struct dirty_throttle_control * dtc,bool strictlimit)1784 static void wb_dirty_freerun(struct dirty_throttle_control *dtc,
1785 			     bool strictlimit)
1786 {
1787 	dtc->freerun = false;
1788 
1789 	/* was already handled in domain_dirty_freerun */
1790 	if (strictlimit)
1791 		return;
1792 
1793 	wb_dirty_limits(dtc);
1794 	/*
1795 	 * LOCAL_THROTTLE tasks must not be throttled when below the per-wb
1796 	 * freerun ceiling.
1797 	 */
1798 	if (!(current->flags & PF_LOCAL_THROTTLE))
1799 		return;
1800 
1801 	dtc->freerun = dtc->wb_dirty <
1802 		       dirty_freerun_ceiling(dtc->wb_thresh, dtc->wb_bg_thresh);
1803 }
1804 
wb_dirty_exceeded(struct dirty_throttle_control * dtc,bool strictlimit)1805 static inline void wb_dirty_exceeded(struct dirty_throttle_control *dtc,
1806 				     bool strictlimit)
1807 {
1808 	dtc->dirty_exceeded = (dtc->wb_dirty > dtc->wb_thresh) &&
1809 		((dtc->dirty > dtc->thresh) || strictlimit);
1810 }
1811 
1812 /*
1813  * The limits fields dirty_exceeded and pos_ratio won't be updated if wb is
1814  * in freerun state. Please don't use these invalid fields in freerun case.
1815  */
balance_wb_limits(struct dirty_throttle_control * dtc,bool strictlimit)1816 static void balance_wb_limits(struct dirty_throttle_control *dtc,
1817 			      bool strictlimit)
1818 {
1819 	wb_dirty_freerun(dtc, strictlimit);
1820 	if (dtc->freerun)
1821 		return;
1822 
1823 	wb_dirty_exceeded(dtc, strictlimit);
1824 	wb_position_ratio(dtc);
1825 }
1826 
1827 /*
1828  * balance_dirty_pages() must be called by processes which are generating dirty
1829  * data.  It looks at the number of dirty pages in the machine and will force
1830  * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1831  * If we're over `background_thresh' then the writeback threads are woken to
1832  * perform some writeout.
1833  */
balance_dirty_pages(struct bdi_writeback * wb,unsigned long pages_dirtied,unsigned int flags)1834 static int balance_dirty_pages(struct bdi_writeback *wb,
1835 			       unsigned long pages_dirtied, unsigned int flags)
1836 {
1837 	struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1838 	struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1839 	struct dirty_throttle_control * const gdtc = &gdtc_stor;
1840 	struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1841 						     &mdtc_stor : NULL;
1842 	struct dirty_throttle_control *sdtc;
1843 	unsigned long nr_dirty;
1844 	long period;
1845 	long pause;
1846 	long max_pause;
1847 	long min_pause;
1848 	int nr_dirtied_pause;
1849 	unsigned long task_ratelimit;
1850 	unsigned long dirty_ratelimit;
1851 	struct backing_dev_info *bdi = wb->bdi;
1852 	bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1853 	unsigned long start_time = jiffies;
1854 	int ret = 0;
1855 
1856 	for (;;) {
1857 		unsigned long now = jiffies;
1858 
1859 		nr_dirty = global_node_page_state(NR_FILE_DIRTY);
1860 
1861 		balance_domain_limits(gdtc, strictlimit);
1862 		if (mdtc) {
1863 			/*
1864 			 * If @wb belongs to !root memcg, repeat the same
1865 			 * basic calculations for the memcg domain.
1866 			 */
1867 			balance_domain_limits(mdtc, strictlimit);
1868 		}
1869 
1870 		/*
1871 		 * In laptop mode, we wait until hitting the higher threshold
1872 		 * before starting background writeout, and then write out all
1873 		 * the way down to the lower threshold.  So slow writers cause
1874 		 * minimal disk activity.
1875 		 *
1876 		 * In normal mode, we start background writeout at the lower
1877 		 * background_thresh, to keep the amount of dirty memory low.
1878 		 */
1879 		if (!laptop_mode && nr_dirty > gdtc->bg_thresh &&
1880 		    !writeback_in_progress(wb))
1881 			wb_start_background_writeback(wb);
1882 
1883 		/*
1884 		 * If memcg domain is in effect, @dirty should be under
1885 		 * both global and memcg freerun ceilings.
1886 		 */
1887 		if (gdtc->freerun && (!mdtc || mdtc->freerun)) {
1888 			unsigned long intv;
1889 			unsigned long m_intv;
1890 
1891 free_running:
1892 			intv = domain_poll_intv(gdtc, strictlimit);
1893 			m_intv = ULONG_MAX;
1894 
1895 			current->dirty_paused_when = now;
1896 			current->nr_dirtied = 0;
1897 			if (mdtc)
1898 				m_intv = domain_poll_intv(mdtc, strictlimit);
1899 			current->nr_dirtied_pause = min(intv, m_intv);
1900 			break;
1901 		}
1902 
1903 		/* Start writeback even when in laptop mode */
1904 		if (unlikely(!writeback_in_progress(wb)))
1905 			wb_start_background_writeback(wb);
1906 
1907 		mem_cgroup_flush_foreign(wb);
1908 
1909 		/*
1910 		 * Calculate global domain's pos_ratio and select the
1911 		 * global dtc by default.
1912 		 */
1913 		balance_wb_limits(gdtc, strictlimit);
1914 		if (gdtc->freerun)
1915 			goto free_running;
1916 		sdtc = gdtc;
1917 
1918 		if (mdtc) {
1919 			/*
1920 			 * If memcg domain is in effect, calculate its
1921 			 * pos_ratio.  @wb should satisfy constraints from
1922 			 * both global and memcg domains.  Choose the one
1923 			 * w/ lower pos_ratio.
1924 			 */
1925 			balance_wb_limits(mdtc, strictlimit);
1926 			if (mdtc->freerun)
1927 				goto free_running;
1928 			if (mdtc->pos_ratio < gdtc->pos_ratio)
1929 				sdtc = mdtc;
1930 		}
1931 
1932 		wb->dirty_exceeded = gdtc->dirty_exceeded ||
1933 				     (mdtc && mdtc->dirty_exceeded);
1934 		if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
1935 					   BANDWIDTH_INTERVAL))
1936 			__wb_update_bandwidth(gdtc, mdtc, true);
1937 
1938 		/* throttle according to the chosen dtc */
1939 		dirty_ratelimit = READ_ONCE(wb->dirty_ratelimit);
1940 		task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1941 							RATELIMIT_CALC_SHIFT;
1942 		max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1943 		min_pause = wb_min_pause(wb, max_pause,
1944 					 task_ratelimit, dirty_ratelimit,
1945 					 &nr_dirtied_pause);
1946 
1947 		if (unlikely(task_ratelimit == 0)) {
1948 			period = max_pause;
1949 			pause = max_pause;
1950 			goto pause;
1951 		}
1952 		period = HZ * pages_dirtied / task_ratelimit;
1953 		pause = period;
1954 		if (current->dirty_paused_when)
1955 			pause -= now - current->dirty_paused_when;
1956 		/*
1957 		 * For less than 1s think time (ext3/4 may block the dirtier
1958 		 * for up to 800ms from time to time on 1-HDD; so does xfs,
1959 		 * however at much less frequency), try to compensate it in
1960 		 * future periods by updating the virtual time; otherwise just
1961 		 * do a reset, as it may be a light dirtier.
1962 		 */
1963 		if (pause < min_pause) {
1964 			trace_balance_dirty_pages(wb,
1965 						  sdtc->thresh,
1966 						  sdtc->bg_thresh,
1967 						  sdtc->dirty,
1968 						  sdtc->wb_thresh,
1969 						  sdtc->wb_dirty,
1970 						  dirty_ratelimit,
1971 						  task_ratelimit,
1972 						  pages_dirtied,
1973 						  period,
1974 						  min(pause, 0L),
1975 						  start_time);
1976 			if (pause < -HZ) {
1977 				current->dirty_paused_when = now;
1978 				current->nr_dirtied = 0;
1979 			} else if (period) {
1980 				current->dirty_paused_when += period;
1981 				current->nr_dirtied = 0;
1982 			} else if (current->nr_dirtied_pause <= pages_dirtied)
1983 				current->nr_dirtied_pause += pages_dirtied;
1984 			break;
1985 		}
1986 		if (unlikely(pause > max_pause)) {
1987 			/* for occasional dropped task_ratelimit */
1988 			now += min(pause - max_pause, max_pause);
1989 			pause = max_pause;
1990 		}
1991 
1992 pause:
1993 		trace_balance_dirty_pages(wb,
1994 					  sdtc->thresh,
1995 					  sdtc->bg_thresh,
1996 					  sdtc->dirty,
1997 					  sdtc->wb_thresh,
1998 					  sdtc->wb_dirty,
1999 					  dirty_ratelimit,
2000 					  task_ratelimit,
2001 					  pages_dirtied,
2002 					  period,
2003 					  pause,
2004 					  start_time);
2005 		if (flags & BDP_ASYNC) {
2006 			ret = -EAGAIN;
2007 			break;
2008 		}
2009 		__set_current_state(TASK_KILLABLE);
2010 		bdi->last_bdp_sleep = jiffies;
2011 		io_schedule_timeout(pause);
2012 
2013 		current->dirty_paused_when = now + pause;
2014 		current->nr_dirtied = 0;
2015 		current->nr_dirtied_pause = nr_dirtied_pause;
2016 
2017 		/*
2018 		 * This is typically equal to (dirty < thresh) and can also
2019 		 * keep "1000+ dd on a slow USB stick" under control.
2020 		 */
2021 		if (task_ratelimit)
2022 			break;
2023 
2024 		/*
2025 		 * In the case of an unresponsive NFS server and the NFS dirty
2026 		 * pages exceeds dirty_thresh, give the other good wb's a pipe
2027 		 * to go through, so that tasks on them still remain responsive.
2028 		 *
2029 		 * In theory 1 page is enough to keep the consumer-producer
2030 		 * pipe going: the flusher cleans 1 page => the task dirties 1
2031 		 * more page. However wb_dirty has accounting errors.  So use
2032 		 * the larger and more IO friendly wb_stat_error.
2033 		 */
2034 		if (sdtc->wb_dirty <= wb_stat_error())
2035 			break;
2036 
2037 		if (fatal_signal_pending(current))
2038 			break;
2039 	}
2040 	return ret;
2041 }
2042 
2043 static DEFINE_PER_CPU(int, bdp_ratelimits);
2044 
2045 /*
2046  * Normal tasks are throttled by
2047  *	loop {
2048  *		dirty tsk->nr_dirtied_pause pages;
2049  *		take a snap in balance_dirty_pages();
2050  *	}
2051  * However there is a worst case. If every task exit immediately when dirtied
2052  * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
2053  * called to throttle the page dirties. The solution is to save the not yet
2054  * throttled page dirties in dirty_throttle_leaks on task exit and charge them
2055  * randomly into the running tasks. This works well for the above worst case,
2056  * as the new task will pick up and accumulate the old task's leaked dirty
2057  * count and eventually get throttled.
2058  */
2059 DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
2060 
2061 /**
2062  * balance_dirty_pages_ratelimited_flags - Balance dirty memory state.
2063  * @mapping: address_space which was dirtied.
2064  * @flags: BDP flags.
2065  *
2066  * Processes which are dirtying memory should call in here once for each page
2067  * which was newly dirtied.  The function will periodically check the system's
2068  * dirty state and will initiate writeback if needed.
2069  *
2070  * See balance_dirty_pages_ratelimited() for details.
2071  *
2072  * Return: If @flags contains BDP_ASYNC, it may return -EAGAIN to
2073  * indicate that memory is out of balance and the caller must wait
2074  * for I/O to complete.  Otherwise, it will return 0 to indicate
2075  * that either memory was already in balance, or it was able to sleep
2076  * until the amount of dirty memory returned to balance.
2077  */
balance_dirty_pages_ratelimited_flags(struct address_space * mapping,unsigned int flags)2078 int balance_dirty_pages_ratelimited_flags(struct address_space *mapping,
2079 					unsigned int flags)
2080 {
2081 	struct inode *inode = mapping->host;
2082 	struct backing_dev_info *bdi = inode_to_bdi(inode);
2083 	struct bdi_writeback *wb = NULL;
2084 	int ratelimit;
2085 	int ret = 0;
2086 	int *p;
2087 
2088 	if (!(bdi->capabilities & BDI_CAP_WRITEBACK))
2089 		return ret;
2090 
2091 	if (inode_cgwb_enabled(inode))
2092 		wb = wb_get_create_current(bdi, GFP_KERNEL);
2093 	if (!wb)
2094 		wb = &bdi->wb;
2095 
2096 	ratelimit = current->nr_dirtied_pause;
2097 	if (wb->dirty_exceeded)
2098 		ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
2099 
2100 	preempt_disable();
2101 	/*
2102 	 * This prevents one CPU to accumulate too many dirtied pages without
2103 	 * calling into balance_dirty_pages(), which can happen when there are
2104 	 * 1000+ tasks, all of them start dirtying pages at exactly the same
2105 	 * time, hence all honoured too large initial task->nr_dirtied_pause.
2106 	 */
2107 	p =  this_cpu_ptr(&bdp_ratelimits);
2108 	if (unlikely(current->nr_dirtied >= ratelimit))
2109 		*p = 0;
2110 	else if (unlikely(*p >= ratelimit_pages)) {
2111 		*p = 0;
2112 		ratelimit = 0;
2113 	}
2114 	/*
2115 	 * Pick up the dirtied pages by the exited tasks. This avoids lots of
2116 	 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
2117 	 * the dirty throttling and livelock other long-run dirtiers.
2118 	 */
2119 	p = this_cpu_ptr(&dirty_throttle_leaks);
2120 	if (*p > 0 && current->nr_dirtied < ratelimit) {
2121 		unsigned long nr_pages_dirtied;
2122 		nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
2123 		*p -= nr_pages_dirtied;
2124 		current->nr_dirtied += nr_pages_dirtied;
2125 	}
2126 	preempt_enable();
2127 
2128 	if (unlikely(current->nr_dirtied >= ratelimit))
2129 		ret = balance_dirty_pages(wb, current->nr_dirtied, flags);
2130 
2131 	wb_put(wb);
2132 	return ret;
2133 }
2134 EXPORT_SYMBOL_GPL(balance_dirty_pages_ratelimited_flags);
2135 
2136 /**
2137  * balance_dirty_pages_ratelimited - balance dirty memory state.
2138  * @mapping: address_space which was dirtied.
2139  *
2140  * Processes which are dirtying memory should call in here once for each page
2141  * which was newly dirtied.  The function will periodically check the system's
2142  * dirty state and will initiate writeback if needed.
2143  *
2144  * Once we're over the dirty memory limit we decrease the ratelimiting
2145  * by a lot, to prevent individual processes from overshooting the limit
2146  * by (ratelimit_pages) each.
2147  */
balance_dirty_pages_ratelimited(struct address_space * mapping)2148 void balance_dirty_pages_ratelimited(struct address_space *mapping)
2149 {
2150 	balance_dirty_pages_ratelimited_flags(mapping, 0);
2151 }
2152 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
2153 
2154 /*
2155  * Similar to wb_dirty_limits, wb_bg_dirty_limits also calculates dirty
2156  * and thresh, but it's for background writeback.
2157  */
wb_bg_dirty_limits(struct dirty_throttle_control * dtc)2158 static void wb_bg_dirty_limits(struct dirty_throttle_control *dtc)
2159 {
2160 	struct bdi_writeback *wb = dtc->wb;
2161 
2162 	dtc->wb_bg_thresh = __wb_calc_thresh(dtc, dtc->bg_thresh);
2163 	if (dtc->wb_bg_thresh < 2 * wb_stat_error())
2164 		dtc->wb_dirty = wb_stat_sum(wb, WB_RECLAIMABLE);
2165 	else
2166 		dtc->wb_dirty = wb_stat(wb, WB_RECLAIMABLE);
2167 }
2168 
domain_over_bg_thresh(struct dirty_throttle_control * dtc)2169 static bool domain_over_bg_thresh(struct dirty_throttle_control *dtc)
2170 {
2171 	domain_dirty_avail(dtc, false);
2172 	domain_dirty_limits(dtc);
2173 	if (dtc->dirty > dtc->bg_thresh)
2174 		return true;
2175 
2176 	wb_bg_dirty_limits(dtc);
2177 	if (dtc->wb_dirty > dtc->wb_bg_thresh)
2178 		return true;
2179 
2180 	return false;
2181 }
2182 
2183 /**
2184  * wb_over_bg_thresh - does @wb need to be written back?
2185  * @wb: bdi_writeback of interest
2186  *
2187  * Determines whether background writeback should keep writing @wb or it's
2188  * clean enough.
2189  *
2190  * Return: %true if writeback should continue.
2191  */
wb_over_bg_thresh(struct bdi_writeback * wb)2192 bool wb_over_bg_thresh(struct bdi_writeback *wb)
2193 {
2194 	struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
2195 	struct dirty_throttle_control mdtc = { MDTC_INIT(wb, &gdtc) };
2196 
2197 	if (domain_over_bg_thresh(&gdtc))
2198 		return true;
2199 
2200 	if (mdtc_valid(&mdtc))
2201 		return domain_over_bg_thresh(&mdtc);
2202 
2203 	return false;
2204 }
2205 
2206 #ifdef CONFIG_SYSCTL
2207 /*
2208  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
2209  */
dirty_writeback_centisecs_handler(const struct ctl_table * table,int write,void * buffer,size_t * length,loff_t * ppos)2210 static int dirty_writeback_centisecs_handler(const struct ctl_table *table, int write,
2211 		void *buffer, size_t *length, loff_t *ppos)
2212 {
2213 	unsigned int old_interval = dirty_writeback_interval;
2214 	int ret;
2215 
2216 	ret = proc_dointvec(table, write, buffer, length, ppos);
2217 
2218 	/*
2219 	 * Writing 0 to dirty_writeback_interval will disable periodic writeback
2220 	 * and a different non-zero value will wakeup the writeback threads.
2221 	 * wb_wakeup_delayed() would be more appropriate, but it's a pain to
2222 	 * iterate over all bdis and wbs.
2223 	 * The reason we do this is to make the change take effect immediately.
2224 	 */
2225 	if (!ret && write && dirty_writeback_interval &&
2226 		dirty_writeback_interval != old_interval)
2227 		wakeup_flusher_threads(WB_REASON_PERIODIC);
2228 
2229 	return ret;
2230 }
2231 #endif
2232 
laptop_mode_timer_fn(struct timer_list * t)2233 void laptop_mode_timer_fn(struct timer_list *t)
2234 {
2235 	struct backing_dev_info *backing_dev_info =
2236 		from_timer(backing_dev_info, t, laptop_mode_wb_timer);
2237 
2238 	wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
2239 }
2240 
2241 /*
2242  * We've spun up the disk and we're in laptop mode: schedule writeback
2243  * of all dirty data a few seconds from now.  If the flush is already scheduled
2244  * then push it back - the user is still using the disk.
2245  */
laptop_io_completion(struct backing_dev_info * info)2246 void laptop_io_completion(struct backing_dev_info *info)
2247 {
2248 	mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2249 }
2250 
2251 /*
2252  * We're in laptop mode and we've just synced. The sync's writes will have
2253  * caused another writeback to be scheduled by laptop_io_completion.
2254  * Nothing needs to be written back anymore, so we unschedule the writeback.
2255  */
laptop_sync_completion(void)2256 void laptop_sync_completion(void)
2257 {
2258 	struct backing_dev_info *bdi;
2259 
2260 	rcu_read_lock();
2261 
2262 	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2263 		del_timer(&bdi->laptop_mode_wb_timer);
2264 
2265 	rcu_read_unlock();
2266 }
2267 
2268 /*
2269  * If ratelimit_pages is too high then we can get into dirty-data overload
2270  * if a large number of processes all perform writes at the same time.
2271  *
2272  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2273  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2274  * thresholds.
2275  */
2276 
writeback_set_ratelimit(void)2277 void writeback_set_ratelimit(void)
2278 {
2279 	struct wb_domain *dom = &global_wb_domain;
2280 	unsigned long background_thresh;
2281 	unsigned long dirty_thresh;
2282 
2283 	global_dirty_limits(&background_thresh, &dirty_thresh);
2284 	dom->dirty_limit = dirty_thresh;
2285 	ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2286 	if (ratelimit_pages < 16)
2287 		ratelimit_pages = 16;
2288 }
2289 
page_writeback_cpu_online(unsigned int cpu)2290 static int page_writeback_cpu_online(unsigned int cpu)
2291 {
2292 	writeback_set_ratelimit();
2293 	return 0;
2294 }
2295 
2296 #ifdef CONFIG_SYSCTL
2297 
2298 /* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
2299 static const unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
2300 
2301 static const struct ctl_table vm_page_writeback_sysctls[] = {
2302 	{
2303 		.procname   = "dirty_background_ratio",
2304 		.data       = &dirty_background_ratio,
2305 		.maxlen     = sizeof(dirty_background_ratio),
2306 		.mode       = 0644,
2307 		.proc_handler   = dirty_background_ratio_handler,
2308 		.extra1     = SYSCTL_ZERO,
2309 		.extra2     = SYSCTL_ONE_HUNDRED,
2310 	},
2311 	{
2312 		.procname   = "dirty_background_bytes",
2313 		.data       = &dirty_background_bytes,
2314 		.maxlen     = sizeof(dirty_background_bytes),
2315 		.mode       = 0644,
2316 		.proc_handler   = dirty_background_bytes_handler,
2317 		.extra1     = SYSCTL_LONG_ONE,
2318 	},
2319 	{
2320 		.procname   = "dirty_ratio",
2321 		.data       = &vm_dirty_ratio,
2322 		.maxlen     = sizeof(vm_dirty_ratio),
2323 		.mode       = 0644,
2324 		.proc_handler   = dirty_ratio_handler,
2325 		.extra1     = SYSCTL_ZERO,
2326 		.extra2     = SYSCTL_ONE_HUNDRED,
2327 	},
2328 	{
2329 		.procname   = "dirty_bytes",
2330 		.data       = &vm_dirty_bytes,
2331 		.maxlen     = sizeof(vm_dirty_bytes),
2332 		.mode       = 0644,
2333 		.proc_handler   = dirty_bytes_handler,
2334 		.extra1     = (void *)&dirty_bytes_min,
2335 	},
2336 	{
2337 		.procname   = "dirty_writeback_centisecs",
2338 		.data       = &dirty_writeback_interval,
2339 		.maxlen     = sizeof(dirty_writeback_interval),
2340 		.mode       = 0644,
2341 		.proc_handler   = dirty_writeback_centisecs_handler,
2342 	},
2343 	{
2344 		.procname   = "dirty_expire_centisecs",
2345 		.data       = &dirty_expire_interval,
2346 		.maxlen     = sizeof(dirty_expire_interval),
2347 		.mode       = 0644,
2348 		.proc_handler   = proc_dointvec_minmax,
2349 		.extra1     = SYSCTL_ZERO,
2350 	},
2351 #ifdef CONFIG_HIGHMEM
2352 	{
2353 		.procname	= "highmem_is_dirtyable",
2354 		.data		= &vm_highmem_is_dirtyable,
2355 		.maxlen		= sizeof(vm_highmem_is_dirtyable),
2356 		.mode		= 0644,
2357 		.proc_handler	= proc_dointvec_minmax,
2358 		.extra1		= SYSCTL_ZERO,
2359 		.extra2		= SYSCTL_ONE,
2360 	},
2361 #endif
2362 	{
2363 		.procname	= "laptop_mode",
2364 		.data		= &laptop_mode,
2365 		.maxlen		= sizeof(laptop_mode),
2366 		.mode		= 0644,
2367 		.proc_handler	= proc_dointvec_jiffies,
2368 	},
2369 };
2370 #endif
2371 
2372 /*
2373  * Called early on to tune the page writeback dirty limits.
2374  *
2375  * We used to scale dirty pages according to how total memory
2376  * related to pages that could be allocated for buffers.
2377  *
2378  * However, that was when we used "dirty_ratio" to scale with
2379  * all memory, and we don't do that any more. "dirty_ratio"
2380  * is now applied to total non-HIGHPAGE memory, and as such we can't
2381  * get into the old insane situation any more where we had
2382  * large amounts of dirty pages compared to a small amount of
2383  * non-HIGHMEM memory.
2384  *
2385  * But we might still want to scale the dirty_ratio by how
2386  * much memory the box has..
2387  */
page_writeback_init(void)2388 void __init page_writeback_init(void)
2389 {
2390 	BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2391 
2392 	cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2393 			  page_writeback_cpu_online, NULL);
2394 	cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2395 			  page_writeback_cpu_online);
2396 #ifdef CONFIG_SYSCTL
2397 	register_sysctl_init("vm", vm_page_writeback_sysctls);
2398 #endif
2399 }
2400 
2401 /**
2402  * tag_pages_for_writeback - tag pages to be written by writeback
2403  * @mapping: address space structure to write
2404  * @start: starting page index
2405  * @end: ending page index (inclusive)
2406  *
2407  * This function scans the page range from @start to @end (inclusive) and tags
2408  * all pages that have DIRTY tag set with a special TOWRITE tag.  The caller
2409  * can then use the TOWRITE tag to identify pages eligible for writeback.
2410  * This mechanism is used to avoid livelocking of writeback by a process
2411  * steadily creating new dirty pages in the file (thus it is important for this
2412  * function to be quick so that it can tag pages faster than a dirtying process
2413  * can create them).
2414  */
tag_pages_for_writeback(struct address_space * mapping,pgoff_t start,pgoff_t end)2415 void tag_pages_for_writeback(struct address_space *mapping,
2416 			     pgoff_t start, pgoff_t end)
2417 {
2418 	XA_STATE(xas, &mapping->i_pages, start);
2419 	unsigned int tagged = 0;
2420 	void *page;
2421 
2422 	xas_lock_irq(&xas);
2423 	xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) {
2424 		xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
2425 		if (++tagged % XA_CHECK_SCHED)
2426 			continue;
2427 
2428 		xas_pause(&xas);
2429 		xas_unlock_irq(&xas);
2430 		cond_resched();
2431 		xas_lock_irq(&xas);
2432 	}
2433 	xas_unlock_irq(&xas);
2434 }
2435 EXPORT_SYMBOL(tag_pages_for_writeback);
2436 
folio_prepare_writeback(struct address_space * mapping,struct writeback_control * wbc,struct folio * folio)2437 static bool folio_prepare_writeback(struct address_space *mapping,
2438 		struct writeback_control *wbc, struct folio *folio)
2439 {
2440 	/*
2441 	 * Folio truncated or invalidated. We can freely skip it then,
2442 	 * even for data integrity operations: the folio has disappeared
2443 	 * concurrently, so there could be no real expectation of this
2444 	 * data integrity operation even if there is now a new, dirty
2445 	 * folio at the same pagecache index.
2446 	 */
2447 	if (unlikely(folio->mapping != mapping))
2448 		return false;
2449 
2450 	/*
2451 	 * Did somebody else write it for us?
2452 	 */
2453 	if (!folio_test_dirty(folio))
2454 		return false;
2455 
2456 	if (folio_test_writeback(folio)) {
2457 		if (wbc->sync_mode == WB_SYNC_NONE)
2458 			return false;
2459 		folio_wait_writeback(folio);
2460 	}
2461 	BUG_ON(folio_test_writeback(folio));
2462 
2463 	if (!folio_clear_dirty_for_io(folio))
2464 		return false;
2465 
2466 	return true;
2467 }
2468 
wbc_to_tag(struct writeback_control * wbc)2469 static xa_mark_t wbc_to_tag(struct writeback_control *wbc)
2470 {
2471 	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2472 		return PAGECACHE_TAG_TOWRITE;
2473 	return PAGECACHE_TAG_DIRTY;
2474 }
2475 
wbc_end(struct writeback_control * wbc)2476 static pgoff_t wbc_end(struct writeback_control *wbc)
2477 {
2478 	if (wbc->range_cyclic)
2479 		return -1;
2480 	return wbc->range_end >> PAGE_SHIFT;
2481 }
2482 
writeback_get_folio(struct address_space * mapping,struct writeback_control * wbc)2483 static struct folio *writeback_get_folio(struct address_space *mapping,
2484 		struct writeback_control *wbc)
2485 {
2486 	struct folio *folio;
2487 
2488 retry:
2489 	folio = folio_batch_next(&wbc->fbatch);
2490 	if (!folio) {
2491 		folio_batch_release(&wbc->fbatch);
2492 		cond_resched();
2493 		filemap_get_folios_tag(mapping, &wbc->index, wbc_end(wbc),
2494 				wbc_to_tag(wbc), &wbc->fbatch);
2495 		folio = folio_batch_next(&wbc->fbatch);
2496 		if (!folio)
2497 			return NULL;
2498 	}
2499 
2500 	folio_lock(folio);
2501 	if (unlikely(!folio_prepare_writeback(mapping, wbc, folio))) {
2502 		folio_unlock(folio);
2503 		goto retry;
2504 	}
2505 
2506 	trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2507 	return folio;
2508 }
2509 
2510 /**
2511  * writeback_iter - iterate folio of a mapping for writeback
2512  * @mapping: address space structure to write
2513  * @wbc: writeback context
2514  * @folio: previously iterated folio (%NULL to start)
2515  * @error: in-out pointer for writeback errors (see below)
2516  *
2517  * This function returns the next folio for the writeback operation described by
2518  * @wbc on @mapping and  should be called in a while loop in the ->writepages
2519  * implementation.
2520  *
2521  * To start the writeback operation, %NULL is passed in the @folio argument, and
2522  * for every subsequent iteration the folio returned previously should be passed
2523  * back in.
2524  *
2525  * If there was an error in the per-folio writeback inside the writeback_iter()
2526  * loop, @error should be set to the error value.
2527  *
2528  * Once the writeback described in @wbc has finished, this function will return
2529  * %NULL and if there was an error in any iteration restore it to @error.
2530  *
2531  * Note: callers should not manually break out of the loop using break or goto
2532  * but must keep calling writeback_iter() until it returns %NULL.
2533  *
2534  * Return: the folio to write or %NULL if the loop is done.
2535  */
writeback_iter(struct address_space * mapping,struct writeback_control * wbc,struct folio * folio,int * error)2536 struct folio *writeback_iter(struct address_space *mapping,
2537 		struct writeback_control *wbc, struct folio *folio, int *error)
2538 {
2539 	if (!folio) {
2540 		folio_batch_init(&wbc->fbatch);
2541 		wbc->saved_err = *error = 0;
2542 
2543 		/*
2544 		 * For range cyclic writeback we remember where we stopped so
2545 		 * that we can continue where we stopped.
2546 		 *
2547 		 * For non-cyclic writeback we always start at the beginning of
2548 		 * the passed in range.
2549 		 */
2550 		if (wbc->range_cyclic)
2551 			wbc->index = mapping->writeback_index;
2552 		else
2553 			wbc->index = wbc->range_start >> PAGE_SHIFT;
2554 
2555 		/*
2556 		 * To avoid livelocks when other processes dirty new pages, we
2557 		 * first tag pages which should be written back and only then
2558 		 * start writing them.
2559 		 *
2560 		 * For data-integrity writeback we have to be careful so that we
2561 		 * do not miss some pages (e.g., because some other process has
2562 		 * cleared the TOWRITE tag we set).  The rule we follow is that
2563 		 * TOWRITE tag can be cleared only by the process clearing the
2564 		 * DIRTY tag (and submitting the page for I/O).
2565 		 */
2566 		if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2567 			tag_pages_for_writeback(mapping, wbc->index,
2568 					wbc_end(wbc));
2569 	} else {
2570 		wbc->nr_to_write -= folio_nr_pages(folio);
2571 
2572 		WARN_ON_ONCE(*error > 0);
2573 
2574 		/*
2575 		 * For integrity writeback we have to keep going until we have
2576 		 * written all the folios we tagged for writeback above, even if
2577 		 * we run past wbc->nr_to_write or encounter errors.
2578 		 * We stash away the first error we encounter in wbc->saved_err
2579 		 * so that it can be retrieved when we're done.  This is because
2580 		 * the file system may still have state to clear for each folio.
2581 		 *
2582 		 * For background writeback we exit as soon as we run past
2583 		 * wbc->nr_to_write or encounter the first error.
2584 		 */
2585 		if (wbc->sync_mode == WB_SYNC_ALL) {
2586 			if (*error && !wbc->saved_err)
2587 				wbc->saved_err = *error;
2588 		} else {
2589 			if (*error || wbc->nr_to_write <= 0)
2590 				goto done;
2591 		}
2592 	}
2593 
2594 	folio = writeback_get_folio(mapping, wbc);
2595 	if (!folio) {
2596 		/*
2597 		 * To avoid deadlocks between range_cyclic writeback and callers
2598 		 * that hold pages in PageWriteback to aggregate I/O until
2599 		 * the writeback iteration finishes, we do not loop back to the
2600 		 * start of the file.  Doing so causes a page lock/page
2601 		 * writeback access order inversion - we should only ever lock
2602 		 * multiple pages in ascending page->index order, and looping
2603 		 * back to the start of the file violates that rule and causes
2604 		 * deadlocks.
2605 		 */
2606 		if (wbc->range_cyclic)
2607 			mapping->writeback_index = 0;
2608 
2609 		/*
2610 		 * Return the first error we encountered (if there was any) to
2611 		 * the caller.
2612 		 */
2613 		*error = wbc->saved_err;
2614 	}
2615 	return folio;
2616 
2617 done:
2618 	if (wbc->range_cyclic)
2619 		mapping->writeback_index = folio_next_index(folio);
2620 	folio_batch_release(&wbc->fbatch);
2621 	return NULL;
2622 }
2623 EXPORT_SYMBOL_GPL(writeback_iter);
2624 
2625 /**
2626  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2627  * @mapping: address space structure to write
2628  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2629  * @writepage: function called for each page
2630  * @data: data passed to writepage function
2631  *
2632  * Return: %0 on success, negative error code otherwise
2633  *
2634  * Note: please use writeback_iter() instead.
2635  */
write_cache_pages(struct address_space * mapping,struct writeback_control * wbc,writepage_t writepage,void * data)2636 int write_cache_pages(struct address_space *mapping,
2637 		      struct writeback_control *wbc, writepage_t writepage,
2638 		      void *data)
2639 {
2640 	struct folio *folio = NULL;
2641 	int error;
2642 
2643 	while ((folio = writeback_iter(mapping, wbc, folio, &error))) {
2644 		error = writepage(folio, wbc, data);
2645 		if (error == AOP_WRITEPAGE_ACTIVATE) {
2646 			folio_unlock(folio);
2647 			error = 0;
2648 		}
2649 	}
2650 
2651 	return error;
2652 }
2653 EXPORT_SYMBOL(write_cache_pages);
2654 
writeback_use_writepage(struct address_space * mapping,struct writeback_control * wbc)2655 static int writeback_use_writepage(struct address_space *mapping,
2656 		struct writeback_control *wbc)
2657 {
2658 	struct folio *folio = NULL;
2659 	struct blk_plug plug;
2660 	int err;
2661 
2662 	blk_start_plug(&plug);
2663 	while ((folio = writeback_iter(mapping, wbc, folio, &err))) {
2664 		err = mapping->a_ops->writepage(&folio->page, wbc);
2665 		if (err == AOP_WRITEPAGE_ACTIVATE) {
2666 			folio_unlock(folio);
2667 			err = 0;
2668 		}
2669 		mapping_set_error(mapping, err);
2670 	}
2671 	blk_finish_plug(&plug);
2672 
2673 	return err;
2674 }
2675 
do_writepages(struct address_space * mapping,struct writeback_control * wbc)2676 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2677 {
2678 	int ret;
2679 	struct bdi_writeback *wb;
2680 
2681 	if (wbc->nr_to_write <= 0)
2682 		return 0;
2683 	wb = inode_to_wb_wbc(mapping->host, wbc);
2684 	wb_bandwidth_estimate_start(wb);
2685 	while (1) {
2686 		if (mapping->a_ops->writepages) {
2687 			ret = mapping->a_ops->writepages(mapping, wbc);
2688 		} else if (mapping->a_ops->writepage) {
2689 			ret = writeback_use_writepage(mapping, wbc);
2690 		} else {
2691 			/* deal with chardevs and other special files */
2692 			ret = 0;
2693 		}
2694 		if (ret != -ENOMEM || wbc->sync_mode != WB_SYNC_ALL)
2695 			break;
2696 
2697 		/*
2698 		 * Lacking an allocation context or the locality or writeback
2699 		 * state of any of the inode's pages, throttle based on
2700 		 * writeback activity on the local node. It's as good a
2701 		 * guess as any.
2702 		 */
2703 		reclaim_throttle(NODE_DATA(numa_node_id()),
2704 			VMSCAN_THROTTLE_WRITEBACK);
2705 	}
2706 	/*
2707 	 * Usually few pages are written by now from those we've just submitted
2708 	 * but if there's constant writeback being submitted, this makes sure
2709 	 * writeback bandwidth is updated once in a while.
2710 	 */
2711 	if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
2712 				   BANDWIDTH_INTERVAL))
2713 		wb_update_bandwidth(wb);
2714 	return ret;
2715 }
2716 
2717 /*
2718  * For address_spaces which do not use buffers nor write back.
2719  */
noop_dirty_folio(struct address_space * mapping,struct folio * folio)2720 bool noop_dirty_folio(struct address_space *mapping, struct folio *folio)
2721 {
2722 	if (!folio_test_dirty(folio))
2723 		return !folio_test_set_dirty(folio);
2724 	return false;
2725 }
2726 EXPORT_SYMBOL(noop_dirty_folio);
2727 
2728 /*
2729  * Helper function for set_page_dirty family.
2730  *
2731  * NOTE: This relies on being atomic wrt interrupts.
2732  */
folio_account_dirtied(struct folio * folio,struct address_space * mapping)2733 static void folio_account_dirtied(struct folio *folio,
2734 		struct address_space *mapping)
2735 {
2736 	struct inode *inode = mapping->host;
2737 
2738 	trace_writeback_dirty_folio(folio, mapping);
2739 
2740 	if (mapping_can_writeback(mapping)) {
2741 		struct bdi_writeback *wb;
2742 		long nr = folio_nr_pages(folio);
2743 
2744 		inode_attach_wb(inode, folio);
2745 		wb = inode_to_wb(inode);
2746 
2747 		__lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, nr);
2748 		__zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
2749 		__node_stat_mod_folio(folio, NR_DIRTIED, nr);
2750 		wb_stat_mod(wb, WB_RECLAIMABLE, nr);
2751 		wb_stat_mod(wb, WB_DIRTIED, nr);
2752 		task_io_account_write(nr * PAGE_SIZE);
2753 		current->nr_dirtied += nr;
2754 		__this_cpu_add(bdp_ratelimits, nr);
2755 
2756 		mem_cgroup_track_foreign_dirty(folio, wb);
2757 	}
2758 }
2759 
2760 /*
2761  * Helper function for deaccounting dirty page without writeback.
2762  *
2763  */
folio_account_cleaned(struct folio * folio,struct bdi_writeback * wb)2764 void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
2765 {
2766 	long nr = folio_nr_pages(folio);
2767 
2768 	lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
2769 	zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
2770 	wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
2771 	task_io_account_cancelled_write(nr * PAGE_SIZE);
2772 }
2773 
2774 /*
2775  * Mark the folio dirty, and set it dirty in the page cache.
2776  *
2777  * If warn is true, then emit a warning if the folio is not uptodate and has
2778  * not been truncated.
2779  *
2780  * It is the caller's responsibility to prevent the folio from being truncated
2781  * while this function is in progress, although it may have been truncated
2782  * before this function is called.  Most callers have the folio locked.
2783  * A few have the folio blocked from truncation through other means (e.g.
2784  * zap_vma_pages() has it mapped and is holding the page table lock).
2785  * When called from mark_buffer_dirty(), the filesystem should hold a
2786  * reference to the buffer_head that is being marked dirty, which causes
2787  * try_to_free_buffers() to fail.
2788  */
__folio_mark_dirty(struct folio * folio,struct address_space * mapping,int warn)2789 void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
2790 			     int warn)
2791 {
2792 	unsigned long flags;
2793 
2794 	xa_lock_irqsave(&mapping->i_pages, flags);
2795 	if (folio->mapping) {	/* Race with truncate? */
2796 		WARN_ON_ONCE(warn && !folio_test_uptodate(folio));
2797 		folio_account_dirtied(folio, mapping);
2798 		__xa_set_mark(&mapping->i_pages, folio_index(folio),
2799 				PAGECACHE_TAG_DIRTY);
2800 	}
2801 	xa_unlock_irqrestore(&mapping->i_pages, flags);
2802 }
2803 
2804 /**
2805  * filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads.
2806  * @mapping: Address space this folio belongs to.
2807  * @folio: Folio to be marked as dirty.
2808  *
2809  * Filesystems which do not use buffer heads should call this function
2810  * from their dirty_folio address space operation.  It ignores the
2811  * contents of folio_get_private(), so if the filesystem marks individual
2812  * blocks as dirty, the filesystem should handle that itself.
2813  *
2814  * This is also sometimes used by filesystems which use buffer_heads when
2815  * a single buffer is being dirtied: we want to set the folio dirty in
2816  * that case, but not all the buffers.  This is a "bottom-up" dirtying,
2817  * whereas block_dirty_folio() is a "top-down" dirtying.
2818  *
2819  * The caller must ensure this doesn't race with truncation.  Most will
2820  * simply hold the folio lock, but e.g. zap_pte_range() calls with the
2821  * folio mapped and the pte lock held, which also locks out truncation.
2822  */
filemap_dirty_folio(struct address_space * mapping,struct folio * folio)2823 bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
2824 {
2825 	if (folio_test_set_dirty(folio))
2826 		return false;
2827 
2828 	__folio_mark_dirty(folio, mapping, !folio_test_private(folio));
2829 
2830 	if (mapping->host) {
2831 		/* !PageAnon && !swapper_space */
2832 		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2833 	}
2834 	return true;
2835 }
2836 EXPORT_SYMBOL(filemap_dirty_folio);
2837 
2838 /**
2839  * folio_redirty_for_writepage - Decline to write a dirty folio.
2840  * @wbc: The writeback control.
2841  * @folio: The folio.
2842  *
2843  * When a writepage implementation decides that it doesn't want to write
2844  * @folio for some reason, it should call this function, unlock @folio and
2845  * return 0.
2846  *
2847  * Return: True if we redirtied the folio.  False if someone else dirtied
2848  * it first.
2849  */
folio_redirty_for_writepage(struct writeback_control * wbc,struct folio * folio)2850 bool folio_redirty_for_writepage(struct writeback_control *wbc,
2851 		struct folio *folio)
2852 {
2853 	struct address_space *mapping = folio->mapping;
2854 	long nr = folio_nr_pages(folio);
2855 	bool ret;
2856 
2857 	wbc->pages_skipped += nr;
2858 	ret = filemap_dirty_folio(mapping, folio);
2859 	if (mapping && mapping_can_writeback(mapping)) {
2860 		struct inode *inode = mapping->host;
2861 		struct bdi_writeback *wb;
2862 		struct wb_lock_cookie cookie = {};
2863 
2864 		wb = unlocked_inode_to_wb_begin(inode, &cookie);
2865 		current->nr_dirtied -= nr;
2866 		node_stat_mod_folio(folio, NR_DIRTIED, -nr);
2867 		wb_stat_mod(wb, WB_DIRTIED, -nr);
2868 		unlocked_inode_to_wb_end(inode, &cookie);
2869 	}
2870 	return ret;
2871 }
2872 EXPORT_SYMBOL(folio_redirty_for_writepage);
2873 
2874 /**
2875  * folio_mark_dirty - Mark a folio as being modified.
2876  * @folio: The folio.
2877  *
2878  * The folio may not be truncated while this function is running.
2879  * Holding the folio lock is sufficient to prevent truncation, but some
2880  * callers cannot acquire a sleeping lock.  These callers instead hold
2881  * the page table lock for a page table which contains at least one page
2882  * in this folio.  Truncation will block on the page table lock as it
2883  * unmaps pages before removing the folio from its mapping.
2884  *
2885  * Return: True if the folio was newly dirtied, false if it was already dirty.
2886  */
folio_mark_dirty(struct folio * folio)2887 bool folio_mark_dirty(struct folio *folio)
2888 {
2889 	struct address_space *mapping = folio_mapping(folio);
2890 
2891 	if (likely(mapping)) {
2892 		/*
2893 		 * readahead/folio_deactivate could remain
2894 		 * PG_readahead/PG_reclaim due to race with folio_end_writeback
2895 		 * About readahead, if the folio is written, the flags would be
2896 		 * reset. So no problem.
2897 		 * About folio_deactivate, if the folio is redirtied,
2898 		 * the flag will be reset. So no problem. but if the
2899 		 * folio is used by readahead it will confuse readahead
2900 		 * and make it restart the size rampup process. But it's
2901 		 * a trivial problem.
2902 		 */
2903 		if (folio_test_reclaim(folio))
2904 			folio_clear_reclaim(folio);
2905 		return mapping->a_ops->dirty_folio(mapping, folio);
2906 	}
2907 
2908 	return noop_dirty_folio(mapping, folio);
2909 }
2910 EXPORT_SYMBOL(folio_mark_dirty);
2911 
2912 /*
2913  * folio_mark_dirty() is racy if the caller has no reference against
2914  * folio->mapping->host, and if the folio is unlocked.  This is because another
2915  * CPU could truncate the folio off the mapping and then free the mapping.
2916  *
2917  * Usually, the folio _is_ locked, or the caller is a user-space process which
2918  * holds a reference on the inode by having an open file.
2919  *
2920  * In other cases, the folio should be locked before running folio_mark_dirty().
2921  */
folio_mark_dirty_lock(struct folio * folio)2922 bool folio_mark_dirty_lock(struct folio *folio)
2923 {
2924 	bool ret;
2925 
2926 	folio_lock(folio);
2927 	ret = folio_mark_dirty(folio);
2928 	folio_unlock(folio);
2929 	return ret;
2930 }
2931 EXPORT_SYMBOL(folio_mark_dirty_lock);
2932 
2933 /*
2934  * This cancels just the dirty bit on the kernel page itself, it does NOT
2935  * actually remove dirty bits on any mmap's that may be around. It also
2936  * leaves the page tagged dirty, so any sync activity will still find it on
2937  * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2938  * look at the dirty bits in the VM.
2939  *
2940  * Doing this should *normally* only ever be done when a page is truncated,
2941  * and is not actually mapped anywhere at all. However, fs/buffer.c does
2942  * this when it notices that somebody has cleaned out all the buffers on a
2943  * page without actually doing it through the VM. Can you say "ext3 is
2944  * horribly ugly"? Thought you could.
2945  */
__folio_cancel_dirty(struct folio * folio)2946 void __folio_cancel_dirty(struct folio *folio)
2947 {
2948 	struct address_space *mapping = folio_mapping(folio);
2949 
2950 	if (mapping_can_writeback(mapping)) {
2951 		struct inode *inode = mapping->host;
2952 		struct bdi_writeback *wb;
2953 		struct wb_lock_cookie cookie = {};
2954 
2955 		wb = unlocked_inode_to_wb_begin(inode, &cookie);
2956 
2957 		if (folio_test_clear_dirty(folio))
2958 			folio_account_cleaned(folio, wb);
2959 
2960 		unlocked_inode_to_wb_end(inode, &cookie);
2961 	} else {
2962 		folio_clear_dirty(folio);
2963 	}
2964 }
2965 EXPORT_SYMBOL(__folio_cancel_dirty);
2966 
2967 /*
2968  * Clear a folio's dirty flag, while caring for dirty memory accounting.
2969  * Returns true if the folio was previously dirty.
2970  *
2971  * This is for preparing to put the folio under writeout.  We leave
2972  * the folio tagged as dirty in the xarray so that a concurrent
2973  * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
2974  * The ->writepage implementation will run either folio_start_writeback()
2975  * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
2976  * and xarray dirty tag back into sync.
2977  *
2978  * This incoherency between the folio's dirty flag and xarray tag is
2979  * unfortunate, but it only exists while the folio is locked.
2980  */
folio_clear_dirty_for_io(struct folio * folio)2981 bool folio_clear_dirty_for_io(struct folio *folio)
2982 {
2983 	struct address_space *mapping = folio_mapping(folio);
2984 	bool ret = false;
2985 
2986 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
2987 
2988 	if (mapping && mapping_can_writeback(mapping)) {
2989 		struct inode *inode = mapping->host;
2990 		struct bdi_writeback *wb;
2991 		struct wb_lock_cookie cookie = {};
2992 
2993 		/*
2994 		 * Yes, Virginia, this is indeed insane.
2995 		 *
2996 		 * We use this sequence to make sure that
2997 		 *  (a) we account for dirty stats properly
2998 		 *  (b) we tell the low-level filesystem to
2999 		 *      mark the whole folio dirty if it was
3000 		 *      dirty in a pagetable. Only to then
3001 		 *  (c) clean the folio again and return 1 to
3002 		 *      cause the writeback.
3003 		 *
3004 		 * This way we avoid all nasty races with the
3005 		 * dirty bit in multiple places and clearing
3006 		 * them concurrently from different threads.
3007 		 *
3008 		 * Note! Normally the "folio_mark_dirty(folio)"
3009 		 * has no effect on the actual dirty bit - since
3010 		 * that will already usually be set. But we
3011 		 * need the side effects, and it can help us
3012 		 * avoid races.
3013 		 *
3014 		 * We basically use the folio "master dirty bit"
3015 		 * as a serialization point for all the different
3016 		 * threads doing their things.
3017 		 */
3018 		if (folio_mkclean(folio))
3019 			folio_mark_dirty(folio);
3020 		/*
3021 		 * We carefully synchronise fault handlers against
3022 		 * installing a dirty pte and marking the folio dirty
3023 		 * at this point.  We do this by having them hold the
3024 		 * page lock while dirtying the folio, and folios are
3025 		 * always locked coming in here, so we get the desired
3026 		 * exclusion.
3027 		 */
3028 		wb = unlocked_inode_to_wb_begin(inode, &cookie);
3029 		if (folio_test_clear_dirty(folio)) {
3030 			long nr = folio_nr_pages(folio);
3031 			lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
3032 			zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
3033 			wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
3034 			ret = true;
3035 		}
3036 		unlocked_inode_to_wb_end(inode, &cookie);
3037 		return ret;
3038 	}
3039 	return folio_test_clear_dirty(folio);
3040 }
3041 EXPORT_SYMBOL(folio_clear_dirty_for_io);
3042 
wb_inode_writeback_start(struct bdi_writeback * wb)3043 static void wb_inode_writeback_start(struct bdi_writeback *wb)
3044 {
3045 	atomic_inc(&wb->writeback_inodes);
3046 }
3047 
wb_inode_writeback_end(struct bdi_writeback * wb)3048 static void wb_inode_writeback_end(struct bdi_writeback *wb)
3049 {
3050 	unsigned long flags;
3051 	atomic_dec(&wb->writeback_inodes);
3052 	/*
3053 	 * Make sure estimate of writeback throughput gets updated after
3054 	 * writeback completed. We delay the update by BANDWIDTH_INTERVAL
3055 	 * (which is the interval other bandwidth updates use for batching) so
3056 	 * that if multiple inodes end writeback at a similar time, they get
3057 	 * batched into one bandwidth update.
3058 	 */
3059 	spin_lock_irqsave(&wb->work_lock, flags);
3060 	if (test_bit(WB_registered, &wb->state))
3061 		queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL);
3062 	spin_unlock_irqrestore(&wb->work_lock, flags);
3063 }
3064 
__folio_end_writeback(struct folio * folio)3065 bool __folio_end_writeback(struct folio *folio)
3066 {
3067 	long nr = folio_nr_pages(folio);
3068 	struct address_space *mapping = folio_mapping(folio);
3069 	bool ret;
3070 
3071 	if (mapping && mapping_use_writeback_tags(mapping)) {
3072 		struct inode *inode = mapping->host;
3073 		struct backing_dev_info *bdi = inode_to_bdi(inode);
3074 		unsigned long flags;
3075 
3076 		xa_lock_irqsave(&mapping->i_pages, flags);
3077 		ret = folio_xor_flags_has_waiters(folio, 1 << PG_writeback);
3078 		__xa_clear_mark(&mapping->i_pages, folio_index(folio),
3079 					PAGECACHE_TAG_WRITEBACK);
3080 		if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
3081 			struct bdi_writeback *wb = inode_to_wb(inode);
3082 
3083 			wb_stat_mod(wb, WB_WRITEBACK, -nr);
3084 			__wb_writeout_add(wb, nr);
3085 			if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
3086 				wb_inode_writeback_end(wb);
3087 		}
3088 
3089 		if (mapping->host && !mapping_tagged(mapping,
3090 						     PAGECACHE_TAG_WRITEBACK))
3091 			sb_clear_inode_writeback(mapping->host);
3092 
3093 		xa_unlock_irqrestore(&mapping->i_pages, flags);
3094 	} else {
3095 		ret = folio_xor_flags_has_waiters(folio, 1 << PG_writeback);
3096 	}
3097 
3098 	lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr);
3099 	zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
3100 	node_stat_mod_folio(folio, NR_WRITTEN, nr);
3101 
3102 	return ret;
3103 }
3104 
__folio_start_writeback(struct folio * folio,bool keep_write)3105 void __folio_start_writeback(struct folio *folio, bool keep_write)
3106 {
3107 	long nr = folio_nr_pages(folio);
3108 	struct address_space *mapping = folio_mapping(folio);
3109 	int access_ret;
3110 
3111 	VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
3112 
3113 	if (mapping && mapping_use_writeback_tags(mapping)) {
3114 		XA_STATE(xas, &mapping->i_pages, folio_index(folio));
3115 		struct inode *inode = mapping->host;
3116 		struct backing_dev_info *bdi = inode_to_bdi(inode);
3117 		unsigned long flags;
3118 		bool on_wblist;
3119 
3120 		xas_lock_irqsave(&xas, flags);
3121 		xas_load(&xas);
3122 		folio_test_set_writeback(folio);
3123 
3124 		on_wblist = mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK);
3125 
3126 		xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
3127 		if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
3128 			struct bdi_writeback *wb = inode_to_wb(inode);
3129 
3130 			wb_stat_mod(wb, WB_WRITEBACK, nr);
3131 			if (!on_wblist)
3132 				wb_inode_writeback_start(wb);
3133 		}
3134 
3135 		/*
3136 		 * We can come through here when swapping anonymous
3137 		 * folios, so we don't necessarily have an inode to
3138 		 * track for sync.
3139 		 */
3140 		if (mapping->host && !on_wblist)
3141 			sb_mark_inode_writeback(mapping->host);
3142 		if (!folio_test_dirty(folio))
3143 			xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
3144 		if (!keep_write)
3145 			xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
3146 		xas_unlock_irqrestore(&xas, flags);
3147 	} else {
3148 		folio_test_set_writeback(folio);
3149 	}
3150 
3151 	lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr);
3152 	zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
3153 
3154 	access_ret = arch_make_folio_accessible(folio);
3155 	/*
3156 	 * If writeback has been triggered on a page that cannot be made
3157 	 * accessible, it is too late to recover here.
3158 	 */
3159 	VM_BUG_ON_FOLIO(access_ret != 0, folio);
3160 }
3161 EXPORT_SYMBOL(__folio_start_writeback);
3162 
3163 /**
3164  * folio_wait_writeback - Wait for a folio to finish writeback.
3165  * @folio: The folio to wait for.
3166  *
3167  * If the folio is currently being written back to storage, wait for the
3168  * I/O to complete.
3169  *
3170  * Context: Sleeps.  Must be called in process context and with
3171  * no spinlocks held.  Caller should hold a reference on the folio.
3172  * If the folio is not locked, writeback may start again after writeback
3173  * has finished.
3174  */
folio_wait_writeback(struct folio * folio)3175 void folio_wait_writeback(struct folio *folio)
3176 {
3177 	while (folio_test_writeback(folio)) {
3178 		trace_folio_wait_writeback(folio, folio_mapping(folio));
3179 		folio_wait_bit(folio, PG_writeback);
3180 	}
3181 }
3182 EXPORT_SYMBOL_GPL(folio_wait_writeback);
3183 
3184 /**
3185  * folio_wait_writeback_killable - Wait for a folio to finish writeback.
3186  * @folio: The folio to wait for.
3187  *
3188  * If the folio is currently being written back to storage, wait for the
3189  * I/O to complete or a fatal signal to arrive.
3190  *
3191  * Context: Sleeps.  Must be called in process context and with
3192  * no spinlocks held.  Caller should hold a reference on the folio.
3193  * If the folio is not locked, writeback may start again after writeback
3194  * has finished.
3195  * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
3196  */
folio_wait_writeback_killable(struct folio * folio)3197 int folio_wait_writeback_killable(struct folio *folio)
3198 {
3199 	while (folio_test_writeback(folio)) {
3200 		trace_folio_wait_writeback(folio, folio_mapping(folio));
3201 		if (folio_wait_bit_killable(folio, PG_writeback))
3202 			return -EINTR;
3203 	}
3204 
3205 	return 0;
3206 }
3207 EXPORT_SYMBOL_GPL(folio_wait_writeback_killable);
3208 
3209 /**
3210  * folio_wait_stable() - wait for writeback to finish, if necessary.
3211  * @folio: The folio to wait on.
3212  *
3213  * This function determines if the given folio is related to a backing
3214  * device that requires folio contents to be held stable during writeback.
3215  * If so, then it will wait for any pending writeback to complete.
3216  *
3217  * Context: Sleeps.  Must be called in process context and with
3218  * no spinlocks held.  Caller should hold a reference on the folio.
3219  * If the folio is not locked, writeback may start again after writeback
3220  * has finished.
3221  */
folio_wait_stable(struct folio * folio)3222 void folio_wait_stable(struct folio *folio)
3223 {
3224 	if (mapping_stable_writes(folio_mapping(folio)))
3225 		folio_wait_writeback(folio);
3226 }
3227 EXPORT_SYMBOL_GPL(folio_wait_stable);
3228