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1 : : // SPDX-License-Identifier: GPL-2.0-only
2 : : /*
3 : : * mm/page-writeback.c
4 : : *
5 : : * Copyright (C) 2002, Linus Torvalds.
6 : : * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
7 : : *
8 : : * Contains functions related to writing back dirty pages at the
9 : : * address_space level.
10 : : *
11 : : * 10Apr2002 Andrew Morton
12 : : * Initial version
13 : : */
14 : :
15 : : #include <linux/kernel.h>
16 : : #include <linux/export.h>
17 : : #include <linux/spinlock.h>
18 : : #include <linux/fs.h>
19 : : #include <linux/mm.h>
20 : : #include <linux/swap.h>
21 : : #include <linux/slab.h>
22 : : #include <linux/pagemap.h>
23 : : #include <linux/writeback.h>
24 : : #include <linux/init.h>
25 : : #include <linux/backing-dev.h>
26 : : #include <linux/task_io_accounting_ops.h>
27 : : #include <linux/blkdev.h>
28 : : #include <linux/mpage.h>
29 : : #include <linux/rmap.h>
30 : : #include <linux/percpu.h>
31 : : #include <linux/smp.h>
32 : : #include <linux/sysctl.h>
33 : : #include <linux/cpu.h>
34 : : #include <linux/syscalls.h>
35 : : #include <linux/buffer_head.h> /* __set_page_dirty_buffers */
36 : : #include <linux/pagevec.h>
37 : : #include <linux/timer.h>
38 : : #include <linux/sched/rt.h>
39 : : #include <linux/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 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 : : 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 : : 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 : : int vm_highmem_is_dirtyable;
87 : :
88 : : /*
89 : : * The generator of dirty data starts writeback at this percentage
90 : : */
91 : : 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 : : 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 makes the machine dump writes/reads and block dirtyings.
113 : : */
114 : : int block_dump;
115 : :
116 : : /*
117 : : * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
118 : : * a full sync is triggered after this time elapses without any disk activity.
119 : : */
120 : : int laptop_mode;
121 : :
122 : : EXPORT_SYMBOL(laptop_mode);
123 : :
124 : : /* End of sysctl-exported parameters */
125 : :
126 : : struct wb_domain global_wb_domain;
127 : :
128 : : /* consolidated parameters for balance_dirty_pages() and its subroutines */
129 : : struct dirty_throttle_control {
130 : : #ifdef CONFIG_CGROUP_WRITEBACK
131 : : struct wb_domain *dom;
132 : : struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */
133 : : #endif
134 : : struct bdi_writeback *wb;
135 : : struct fprop_local_percpu *wb_completions;
136 : :
137 : : unsigned long avail; /* dirtyable */
138 : : unsigned long dirty; /* file_dirty + write + nfs */
139 : : unsigned long thresh; /* dirty threshold */
140 : : unsigned long bg_thresh; /* dirty background threshold */
141 : :
142 : : unsigned long wb_dirty; /* per-wb counterparts */
143 : : unsigned long wb_thresh;
144 : : unsigned long wb_bg_thresh;
145 : :
146 : : unsigned long pos_ratio;
147 : : };
148 : :
149 : : /*
150 : : * Length of period for aging writeout fractions of bdis. This is an
151 : : * arbitrarily chosen number. The longer the period, the slower fractions will
152 : : * reflect changes in current writeout rate.
153 : : */
154 : : #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
155 : :
156 : : #ifdef CONFIG_CGROUP_WRITEBACK
157 : :
158 : : #define GDTC_INIT(__wb) .wb = (__wb), \
159 : : .dom = &global_wb_domain, \
160 : : .wb_completions = &(__wb)->completions
161 : :
162 : : #define GDTC_INIT_NO_WB .dom = &global_wb_domain
163 : :
164 : : #define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \
165 : : .dom = mem_cgroup_wb_domain(__wb), \
166 : : .wb_completions = &(__wb)->memcg_completions, \
167 : : .gdtc = __gdtc
168 : :
169 : : static bool mdtc_valid(struct dirty_throttle_control *dtc)
170 : : {
171 : : return dtc->dom;
172 : : }
173 : :
174 : : static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
175 : : {
176 : 4053 : return dtc->dom;
177 : : }
178 : :
179 : : static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
180 : : {
181 : 7510 : return mdtc->gdtc;
182 : : }
183 : :
184 : : static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
185 : : {
186 : 0 : return &wb->memcg_completions;
187 : : }
188 : :
189 : 4053 : static void wb_min_max_ratio(struct bdi_writeback *wb,
190 : : unsigned long *minp, unsigned long *maxp)
191 : : {
192 : 4053 : unsigned long this_bw = wb->avg_write_bandwidth;
193 : 8106 : unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
194 : 4053 : unsigned long long min = wb->bdi->min_ratio;
195 : 4053 : unsigned long long max = wb->bdi->max_ratio;
196 : :
197 : : /*
198 : : * @wb may already be clean by the time control reaches here and
199 : : * the total may not include its bw.
200 : : */
201 [ - + ]: 4053 : if (this_bw < tot_bw) {
202 [ # # ]: 0 : if (min) {
203 : 0 : min *= this_bw;
204 : : min = div64_ul(min, tot_bw);
205 : : }
206 [ # # ]: 0 : if (max < 100) {
207 : 0 : max *= this_bw;
208 : : max = div64_ul(max, tot_bw);
209 : : }
210 : : }
211 : :
212 : 4053 : *minp = min;
213 : 4053 : *maxp = max;
214 : 4053 : }
215 : :
216 : : #else /* CONFIG_CGROUP_WRITEBACK */
217 : :
218 : : #define GDTC_INIT(__wb) .wb = (__wb), \
219 : : .wb_completions = &(__wb)->completions
220 : : #define GDTC_INIT_NO_WB
221 : : #define MDTC_INIT(__wb, __gdtc)
222 : :
223 : : static bool mdtc_valid(struct dirty_throttle_control *dtc)
224 : : {
225 : : return false;
226 : : }
227 : :
228 : : static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
229 : : {
230 : : return &global_wb_domain;
231 : : }
232 : :
233 : : static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
234 : : {
235 : : return NULL;
236 : : }
237 : :
238 : : static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
239 : : {
240 : : return NULL;
241 : : }
242 : :
243 : : static void wb_min_max_ratio(struct bdi_writeback *wb,
244 : : unsigned long *minp, unsigned long *maxp)
245 : : {
246 : : *minp = wb->bdi->min_ratio;
247 : : *maxp = wb->bdi->max_ratio;
248 : : }
249 : :
250 : : #endif /* CONFIG_CGROUP_WRITEBACK */
251 : :
252 : : /*
253 : : * In a memory zone, there is a certain amount of pages we consider
254 : : * available for the page cache, which is essentially the number of
255 : : * free and reclaimable pages, minus some zone reserves to protect
256 : : * lowmem and the ability to uphold the zone's watermarks without
257 : : * requiring writeback.
258 : : *
259 : : * This number of dirtyable pages is the base value of which the
260 : : * user-configurable dirty ratio is the effictive number of pages that
261 : : * are allowed to be actually dirtied. Per individual zone, or
262 : : * globally by using the sum of dirtyable pages over all zones.
263 : : *
264 : : * Because the user is allowed to specify the dirty limit globally as
265 : : * absolute number of bytes, calculating the per-zone dirty limit can
266 : : * require translating the configured limit into a percentage of
267 : : * global dirtyable memory first.
268 : : */
269 : :
270 : : /**
271 : : * node_dirtyable_memory - number of dirtyable pages in a node
272 : : * @pgdat: the node
273 : : *
274 : : * Return: the node's number of pages potentially available for dirty
275 : : * page cache. This is the base value for the per-node dirty limits.
276 : : */
277 : 100774 : static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
278 : : {
279 : : unsigned long nr_pages = 0;
280 : : int z;
281 : :
282 [ + + ]: 302322 : for (z = 0; z < MAX_NR_ZONES; z++) {
283 : 201548 : struct zone *zone = pgdat->node_zones + z;
284 : :
285 [ + + ]: 201548 : if (!populated_zone(zone))
286 : 100774 : continue;
287 : :
288 : 100774 : nr_pages += zone_page_state(zone, NR_FREE_PAGES);
289 : : }
290 : :
291 : : /*
292 : : * Pages reserved for the kernel should not be considered
293 : : * dirtyable, to prevent a situation where reclaim has to
294 : : * clean pages in order to balance the zones.
295 : : */
296 : 100774 : nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
297 : :
298 : 100774 : nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
299 : 100774 : nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
300 : :
301 : 100774 : return nr_pages;
302 : : }
303 : :
304 : : static unsigned long highmem_dirtyable_memory(unsigned long total)
305 : : {
306 : : #ifdef CONFIG_HIGHMEM
307 : : int node;
308 : : unsigned long x = 0;
309 : : int i;
310 : :
311 : : for_each_node_state(node, N_HIGH_MEMORY) {
312 : : for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
313 : : struct zone *z;
314 : : unsigned long nr_pages;
315 : :
316 : : if (!is_highmem_idx(i))
317 : : continue;
318 : :
319 : : z = &NODE_DATA(node)->node_zones[i];
320 : : if (!populated_zone(z))
321 : : continue;
322 : :
323 : : nr_pages = zone_page_state(z, NR_FREE_PAGES);
324 : : /* watch for underflows */
325 : : nr_pages -= min(nr_pages, high_wmark_pages(z));
326 : : nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
327 : : nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
328 : : x += nr_pages;
329 : : }
330 : : }
331 : :
332 : : /*
333 : : * Unreclaimable memory (kernel memory or anonymous memory
334 : : * without swap) can bring down the dirtyable pages below
335 : : * the zone's dirty balance reserve and the above calculation
336 : : * will underflow. However we still want to add in nodes
337 : : * which are below threshold (negative values) to get a more
338 : : * accurate calculation but make sure that the total never
339 : : * underflows.
340 : : */
341 : : if ((long)x < 0)
342 : : x = 0;
343 : :
344 : : /*
345 : : * Make sure that the number of highmem pages is never larger
346 : : * than the number of the total dirtyable memory. This can only
347 : : * occur in very strange VM situations but we want to make sure
348 : : * that this does not occur.
349 : : */
350 : : return min(x, total);
351 : : #else
352 : : return 0;
353 : : #endif
354 : : }
355 : :
356 : : /**
357 : : * global_dirtyable_memory - number of globally dirtyable pages
358 : : *
359 : : * Return: the global number of pages potentially available for dirty
360 : : * page cache. This is the base value for the global dirty limits.
361 : : */
362 : 7510 : static unsigned long global_dirtyable_memory(void)
363 : : {
364 : : unsigned long x;
365 : :
366 : : x = global_zone_page_state(NR_FREE_PAGES);
367 : : /*
368 : : * Pages reserved for the kernel should not be considered
369 : : * dirtyable, to prevent a situation where reclaim has to
370 : : * clean pages in order to balance the zones.
371 : : */
372 : 7510 : x -= min(x, totalreserve_pages);
373 : :
374 : 7510 : x += global_node_page_state(NR_INACTIVE_FILE);
375 : 7510 : x += global_node_page_state(NR_ACTIVE_FILE);
376 : :
377 : : if (!vm_highmem_is_dirtyable)
378 : : x -= highmem_dirtyable_memory(x);
379 : :
380 : 7510 : return x + 1; /* Ensure that we never return 0 */
381 : : }
382 : :
383 : : /**
384 : : * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
385 : : * @dtc: dirty_throttle_control of interest
386 : : *
387 : : * Calculate @dtc->thresh and ->bg_thresh considering
388 : : * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller
389 : : * must ensure that @dtc->avail is set before calling this function. The
390 : : * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
391 : : * real-time tasks.
392 : : */
393 : 7510 : static void domain_dirty_limits(struct dirty_throttle_control *dtc)
394 : : {
395 : 7510 : const unsigned long available_memory = dtc->avail;
396 : : struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
397 : 7510 : unsigned long bytes = vm_dirty_bytes;
398 : 7510 : unsigned long bg_bytes = dirty_background_bytes;
399 : : /* convert ratios to per-PAGE_SIZE for higher precision */
400 : 7510 : unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
401 : 7510 : unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
402 : : unsigned long thresh;
403 : : unsigned long bg_thresh;
404 : : struct task_struct *tsk;
405 : :
406 : : /* gdtc is !NULL iff @dtc is for memcg domain */
407 [ - + ]: 7510 : if (gdtc) {
408 : 0 : unsigned long global_avail = gdtc->avail;
409 : :
410 : : /*
411 : : * The byte settings can't be applied directly to memcg
412 : : * domains. Convert them to ratios by scaling against
413 : : * globally available memory. As the ratios are in
414 : : * per-PAGE_SIZE, they can be obtained by dividing bytes by
415 : : * number of pages.
416 : : */
417 [ # # ]: 0 : if (bytes)
418 : 0 : ratio = min(DIV_ROUND_UP(bytes, global_avail),
419 : : PAGE_SIZE);
420 [ # # ]: 0 : if (bg_bytes)
421 : 0 : bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
422 : : PAGE_SIZE);
423 : : bytes = bg_bytes = 0;
424 : : }
425 : :
426 [ - + ]: 7510 : if (bytes)
427 : 0 : thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
428 : : else
429 : 7510 : thresh = (ratio * available_memory) / PAGE_SIZE;
430 : :
431 [ - + ]: 7510 : if (bg_bytes)
432 : 0 : bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
433 : : else
434 : 7510 : bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
435 : :
436 [ - + ]: 7510 : if (bg_thresh >= thresh)
437 : 0 : bg_thresh = thresh / 2;
438 : 7510 : tsk = current;
439 [ + - - + ]: 15020 : if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
440 : 0 : bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
441 : 0 : thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
442 : : }
443 : 7510 : dtc->thresh = thresh;
444 : 7510 : dtc->bg_thresh = bg_thresh;
445 : :
446 : : /* we should eventually report the domain in the TP */
447 [ + - ]: 7510 : if (!gdtc)
448 : 7510 : trace_global_dirty_state(bg_thresh, thresh);
449 : 7510 : }
450 : :
451 : : /**
452 : : * global_dirty_limits - background-writeback and dirty-throttling thresholds
453 : : * @pbackground: out parameter for bg_thresh
454 : : * @pdirty: out parameter for thresh
455 : : *
456 : : * Calculate bg_thresh and thresh for global_wb_domain. See
457 : : * domain_dirty_limits() for details.
458 : : */
459 : 828 : void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
460 : : {
461 : 828 : struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
462 : :
463 : 828 : gdtc.avail = global_dirtyable_memory();
464 : 828 : domain_dirty_limits(&gdtc);
465 : :
466 : 828 : *pbackground = gdtc.bg_thresh;
467 : 828 : *pdirty = gdtc.thresh;
468 : 828 : }
469 : :
470 : : /**
471 : : * node_dirty_limit - maximum number of dirty pages allowed in a node
472 : : * @pgdat: the node
473 : : *
474 : : * Return: the maximum number of dirty pages allowed in a node, based
475 : : * on the node's dirtyable memory.
476 : : */
477 : 100774 : static unsigned long node_dirty_limit(struct pglist_data *pgdat)
478 : : {
479 : 100774 : unsigned long node_memory = node_dirtyable_memory(pgdat);
480 : 100774 : struct task_struct *tsk = current;
481 : : unsigned long dirty;
482 : :
483 [ - + ]: 100774 : if (vm_dirty_bytes)
484 : 0 : dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
485 : 0 : node_memory / global_dirtyable_memory();
486 : : else
487 : 100774 : dirty = vm_dirty_ratio * node_memory / 100;
488 : :
489 [ + - - + ]: 201548 : if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
490 : 0 : dirty += dirty / 4;
491 : :
492 : 100774 : return dirty;
493 : : }
494 : :
495 : : /**
496 : : * node_dirty_ok - tells whether a node is within its dirty limits
497 : : * @pgdat: the node to check
498 : : *
499 : : * Return: %true when the dirty pages in @pgdat are within the node's
500 : : * dirty limit, %false if the limit is exceeded.
501 : : */
502 : 100774 : bool node_dirty_ok(struct pglist_data *pgdat)
503 : : {
504 : 100774 : unsigned long limit = node_dirty_limit(pgdat);
505 : : unsigned long nr_pages = 0;
506 : :
507 : : nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
508 : 100774 : nr_pages += node_page_state(pgdat, NR_UNSTABLE_NFS);
509 : 100774 : nr_pages += node_page_state(pgdat, NR_WRITEBACK);
510 : :
511 : 100774 : return nr_pages <= limit;
512 : : }
513 : :
514 : 0 : int dirty_background_ratio_handler(struct ctl_table *table, int write,
515 : : void __user *buffer, size_t *lenp,
516 : : loff_t *ppos)
517 : : {
518 : : int ret;
519 : :
520 : 0 : ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
521 [ # # ]: 0 : if (ret == 0 && write)
522 : 0 : dirty_background_bytes = 0;
523 : 0 : return ret;
524 : : }
525 : :
526 : 0 : int dirty_background_bytes_handler(struct ctl_table *table, int write,
527 : : void __user *buffer, size_t *lenp,
528 : : loff_t *ppos)
529 : : {
530 : : int ret;
531 : :
532 : 0 : ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
533 [ # # ]: 0 : if (ret == 0 && write)
534 : 0 : dirty_background_ratio = 0;
535 : 0 : return ret;
536 : : }
537 : :
538 : 0 : int dirty_ratio_handler(struct ctl_table *table, int write,
539 : : void __user *buffer, size_t *lenp,
540 : : loff_t *ppos)
541 : : {
542 : 0 : int old_ratio = vm_dirty_ratio;
543 : : int ret;
544 : :
545 : 0 : ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
546 [ # # # # ]: 0 : if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
547 : 0 : writeback_set_ratelimit();
548 : 0 : vm_dirty_bytes = 0;
549 : : }
550 : 0 : return ret;
551 : : }
552 : :
553 : 0 : int dirty_bytes_handler(struct ctl_table *table, int write,
554 : : void __user *buffer, size_t *lenp,
555 : : loff_t *ppos)
556 : : {
557 : 0 : unsigned long old_bytes = vm_dirty_bytes;
558 : : int ret;
559 : :
560 : 0 : ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
561 [ # # # # ]: 0 : if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
562 : 0 : writeback_set_ratelimit();
563 : 0 : vm_dirty_ratio = 0;
564 : : }
565 : 0 : return ret;
566 : : }
567 : :
568 : : static unsigned long wp_next_time(unsigned long cur_time)
569 : : {
570 : 3297 : cur_time += VM_COMPLETIONS_PERIOD_LEN;
571 : : /* 0 has a special meaning... */
572 [ + - + - ]: 3297 : if (!cur_time)
573 : : return 1;
574 : : return cur_time;
575 : : }
576 : :
577 : 101720 : static void wb_domain_writeout_inc(struct wb_domain *dom,
578 : : struct fprop_local_percpu *completions,
579 : : unsigned int max_prop_frac)
580 : : {
581 : 101720 : __fprop_inc_percpu_max(&dom->completions, completions,
582 : : max_prop_frac);
583 : : /* First event after period switching was turned off? */
584 [ + + ]: 101720 : if (unlikely(!dom->period_time)) {
585 : : /*
586 : : * We can race with other __bdi_writeout_inc calls here but
587 : : * it does not cause any harm since the resulting time when
588 : : * timer will fire and what is in writeout_period_time will be
589 : : * roughly the same.
590 : : */
591 : 1076 : dom->period_time = wp_next_time(jiffies);
592 : 538 : mod_timer(&dom->period_timer, dom->period_time);
593 : : }
594 : 101720 : }
595 : :
596 : : /*
597 : : * Increment @wb's writeout completion count and the global writeout
598 : : * completion count. Called from test_clear_page_writeback().
599 : : */
600 : 101720 : static inline void __wb_writeout_inc(struct bdi_writeback *wb)
601 : : {
602 : : struct wb_domain *cgdom;
603 : :
604 : : inc_wb_stat(wb, WB_WRITTEN);
605 : 203440 : wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
606 : 101720 : wb->bdi->max_prop_frac);
607 : :
608 : 101720 : cgdom = mem_cgroup_wb_domain(wb);
609 [ - + ]: 101720 : if (cgdom)
610 : 0 : wb_domain_writeout_inc(cgdom, wb_memcg_completions(wb),
611 : 0 : wb->bdi->max_prop_frac);
612 : 101720 : }
613 : :
614 : 0 : void wb_writeout_inc(struct bdi_writeback *wb)
615 : : {
616 : : unsigned long flags;
617 : :
618 : 0 : local_irq_save(flags);
619 : 0 : __wb_writeout_inc(wb);
620 [ # # ]: 0 : local_irq_restore(flags);
621 : 0 : }
622 : : EXPORT_SYMBOL_GPL(wb_writeout_inc);
623 : :
624 : : /*
625 : : * On idle system, we can be called long after we scheduled because we use
626 : : * deferred timers so count with missed periods.
627 : : */
628 : 3090 : static void writeout_period(struct timer_list *t)
629 : : {
630 : : struct wb_domain *dom = from_timer(dom, t, period_timer);
631 : 3090 : int miss_periods = (jiffies - dom->period_time) /
632 : : VM_COMPLETIONS_PERIOD_LEN;
633 : :
634 [ + + ]: 3090 : if (fprop_new_period(&dom->completions, miss_periods + 1)) {
635 : 8277 : dom->period_time = wp_next_time(dom->period_time +
636 : 2759 : miss_periods * VM_COMPLETIONS_PERIOD_LEN);
637 : 2759 : mod_timer(&dom->period_timer, dom->period_time);
638 : : } else {
639 : : /*
640 : : * Aging has zeroed all fractions. Stop wasting CPU on period
641 : : * updates.
642 : : */
643 : 331 : dom->period_time = 0;
644 : : }
645 : 3090 : }
646 : :
647 : 414 : int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
648 : : {
649 : 414 : memset(dom, 0, sizeof(*dom));
650 : :
651 : 414 : spin_lock_init(&dom->lock);
652 : :
653 : 414 : timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
654 : :
655 : 414 : dom->dirty_limit_tstamp = jiffies;
656 : :
657 : 414 : return fprop_global_init(&dom->completions, gfp);
658 : : }
659 : :
660 : : #ifdef CONFIG_CGROUP_WRITEBACK
661 : 0 : void wb_domain_exit(struct wb_domain *dom)
662 : : {
663 : 0 : del_timer_sync(&dom->period_timer);
664 : 0 : fprop_global_destroy(&dom->completions);
665 : 0 : }
666 : : #endif
667 : :
668 : : /*
669 : : * bdi_min_ratio keeps the sum of the minimum dirty shares of all
670 : : * registered backing devices, which, for obvious reasons, can not
671 : : * exceed 100%.
672 : : */
673 : : static unsigned int bdi_min_ratio;
674 : :
675 : 0 : int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
676 : : {
677 : : int ret = 0;
678 : :
679 : : spin_lock_bh(&bdi_lock);
680 [ # # ]: 0 : if (min_ratio > bdi->max_ratio) {
681 : : ret = -EINVAL;
682 : : } else {
683 : 0 : min_ratio -= bdi->min_ratio;
684 [ # # ]: 0 : if (bdi_min_ratio + min_ratio < 100) {
685 : 0 : bdi_min_ratio += min_ratio;
686 : 0 : bdi->min_ratio += min_ratio;
687 : : } else {
688 : : ret = -EINVAL;
689 : : }
690 : : }
691 : : spin_unlock_bh(&bdi_lock);
692 : :
693 : 0 : return ret;
694 : : }
695 : :
696 : 207 : int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
697 : : {
698 : : int ret = 0;
699 : :
700 [ + - ]: 207 : if (max_ratio > 100)
701 : : return -EINVAL;
702 : :
703 : : spin_lock_bh(&bdi_lock);
704 [ + - ]: 207 : if (bdi->min_ratio > max_ratio) {
705 : : ret = -EINVAL;
706 : : } else {
707 : 207 : bdi->max_ratio = max_ratio;
708 : 207 : bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
709 : : }
710 : : spin_unlock_bh(&bdi_lock);
711 : :
712 : 207 : return ret;
713 : : }
714 : : EXPORT_SYMBOL(bdi_set_max_ratio);
715 : :
716 : : static unsigned long dirty_freerun_ceiling(unsigned long thresh,
717 : : unsigned long bg_thresh)
718 : : {
719 : 2629 : return (thresh + bg_thresh) / 2;
720 : : }
721 : :
722 : : static unsigned long hard_dirty_limit(struct wb_domain *dom,
723 : : unsigned long thresh)
724 : : {
725 : 0 : return max(thresh, dom->dirty_limit);
726 : : }
727 : :
728 : : /*
729 : : * Memory which can be further allocated to a memcg domain is capped by
730 : : * system-wide clean memory excluding the amount being used in the domain.
731 : : */
732 : : static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
733 : : unsigned long filepages, unsigned long headroom)
734 : : {
735 : : struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
736 : 0 : unsigned long clean = filepages - min(filepages, mdtc->dirty);
737 : 0 : unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
738 : 0 : unsigned long other_clean = global_clean - min(global_clean, clean);
739 : :
740 : 0 : mdtc->avail = filepages + min(headroom, other_clean);
741 : : }
742 : :
743 : : /**
744 : : * __wb_calc_thresh - @wb's share of dirty throttling threshold
745 : : * @dtc: dirty_throttle_context of interest
746 : : *
747 : : * Note that balance_dirty_pages() will only seriously take it as a hard limit
748 : : * when sleeping max_pause per page is not enough to keep the dirty pages under
749 : : * control. For example, when the device is completely stalled due to some error
750 : : * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
751 : : * In the other normal situations, it acts more gently by throttling the tasks
752 : : * more (rather than completely block them) when the wb dirty pages go high.
753 : : *
754 : : * It allocates high/low dirty limits to fast/slow devices, in order to prevent
755 : : * - starving fast devices
756 : : * - piling up dirty pages (that will take long time to sync) on slow devices
757 : : *
758 : : * The wb's share of dirty limit will be adapting to its throughput and
759 : : * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
760 : : *
761 : : * Return: @wb's dirty limit in pages. The term "dirty" in the context of
762 : : * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
763 : : */
764 : 4053 : static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
765 : : {
766 : : struct wb_domain *dom = dtc_dom(dtc);
767 : 4053 : unsigned long thresh = dtc->thresh;
768 : : u64 wb_thresh;
769 : : long numerator, denominator;
770 : : unsigned long wb_min_ratio, wb_max_ratio;
771 : :
772 : : /*
773 : : * Calculate this BDI's share of the thresh ratio.
774 : : */
775 : 4053 : fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
776 : : &numerator, &denominator);
777 : :
778 : 4053 : wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
779 : 4053 : wb_thresh *= numerator;
780 [ - + # # : 4053 : do_div(wb_thresh, denominator);
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781 : :
782 : 4053 : wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
783 : :
784 : 4053 : wb_thresh += (thresh * wb_min_ratio) / 100;
785 [ - + ]: 4053 : if (wb_thresh > (thresh * wb_max_ratio) / 100)
786 : 0 : wb_thresh = thresh * wb_max_ratio / 100;
787 : :
788 : 4053 : return wb_thresh;
789 : : }
790 : :
791 : 4053 : unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
792 : : {
793 : 4053 : struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
794 : : .thresh = thresh };
795 : 4053 : return __wb_calc_thresh(&gdtc);
796 : : }
797 : :
798 : : /*
799 : : * setpoint - dirty 3
800 : : * f(dirty) := 1.0 + (----------------)
801 : : * limit - setpoint
802 : : *
803 : : * it's a 3rd order polynomial that subjects to
804 : : *
805 : : * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
806 : : * (2) f(setpoint) = 1.0 => the balance point
807 : : * (3) f(limit) = 0 => the hard limit
808 : : * (4) df/dx <= 0 => negative feedback control
809 : : * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
810 : : * => fast response on large errors; small oscillation near setpoint
811 : : */
812 : 0 : static long long pos_ratio_polynom(unsigned long setpoint,
813 : : unsigned long dirty,
814 : : unsigned long limit)
815 : : {
816 : : long long pos_ratio;
817 : : long x;
818 : :
819 : 0 : x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
820 : 0 : (limit - setpoint) | 1);
821 : 0 : pos_ratio = x;
822 : 0 : pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
823 : 0 : pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
824 : 0 : pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
825 : :
826 : 0 : return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
827 : : }
828 : :
829 : : /*
830 : : * Dirty position control.
831 : : *
832 : : * (o) global/bdi setpoints
833 : : *
834 : : * We want the dirty pages be balanced around the global/wb setpoints.
835 : : * When the number of dirty pages is higher/lower than the setpoint, the
836 : : * dirty position control ratio (and hence task dirty ratelimit) will be
837 : : * decreased/increased to bring the dirty pages back to the setpoint.
838 : : *
839 : : * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
840 : : *
841 : : * if (dirty < setpoint) scale up pos_ratio
842 : : * if (dirty > setpoint) scale down pos_ratio
843 : : *
844 : : * if (wb_dirty < wb_setpoint) scale up pos_ratio
845 : : * if (wb_dirty > wb_setpoint) scale down pos_ratio
846 : : *
847 : : * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
848 : : *
849 : : * (o) global control line
850 : : *
851 : : * ^ pos_ratio
852 : : * |
853 : : * | |<===== global dirty control scope ======>|
854 : : * 2.0 .............*
855 : : * | .*
856 : : * | . *
857 : : * | . *
858 : : * | . *
859 : : * | . *
860 : : * | . *
861 : : * 1.0 ................................*
862 : : * | . . *
863 : : * | . . *
864 : : * | . . *
865 : : * | . . *
866 : : * | . . *
867 : : * 0 +------------.------------------.----------------------*------------->
868 : : * freerun^ setpoint^ limit^ dirty pages
869 : : *
870 : : * (o) wb control line
871 : : *
872 : : * ^ pos_ratio
873 : : * |
874 : : * | *
875 : : * | *
876 : : * | *
877 : : * | *
878 : : * | * |<=========== span ============>|
879 : : * 1.0 .......................*
880 : : * | . *
881 : : * | . *
882 : : * | . *
883 : : * | . *
884 : : * | . *
885 : : * | . *
886 : : * | . *
887 : : * | . *
888 : : * | . *
889 : : * | . *
890 : : * | . *
891 : : * 1/4 ...............................................* * * * * * * * * * * *
892 : : * | . .
893 : : * | . .
894 : : * | . .
895 : : * 0 +----------------------.-------------------------------.------------->
896 : : * wb_setpoint^ x_intercept^
897 : : *
898 : : * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
899 : : * be smoothly throttled down to normal if it starts high in situations like
900 : : * - start writing to a slow SD card and a fast disk at the same time. The SD
901 : : * card's wb_dirty may rush to many times higher than wb_setpoint.
902 : : * - the wb dirty thresh drops quickly due to change of JBOD workload
903 : : */
904 : 0 : static void wb_position_ratio(struct dirty_throttle_control *dtc)
905 : : {
906 : 0 : struct bdi_writeback *wb = dtc->wb;
907 : 0 : unsigned long write_bw = wb->avg_write_bandwidth;
908 : 0 : unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
909 : : unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
910 : 0 : unsigned long wb_thresh = dtc->wb_thresh;
911 : : unsigned long x_intercept;
912 : : unsigned long setpoint; /* dirty pages' target balance point */
913 : : unsigned long wb_setpoint;
914 : : unsigned long span;
915 : : long long pos_ratio; /* for scaling up/down the rate limit */
916 : : long x;
917 : :
918 : 0 : dtc->pos_ratio = 0;
919 : :
920 [ # # ]: 0 : if (unlikely(dtc->dirty >= limit))
921 : : return;
922 : :
923 : : /*
924 : : * global setpoint
925 : : *
926 : : * See comment for pos_ratio_polynom().
927 : : */
928 : 0 : setpoint = (freerun + limit) / 2;
929 : 0 : pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
930 : :
931 : : /*
932 : : * The strictlimit feature is a tool preventing mistrusted filesystems
933 : : * from growing a large number of dirty pages before throttling. For
934 : : * such filesystems balance_dirty_pages always checks wb counters
935 : : * against wb limits. Even if global "nr_dirty" is under "freerun".
936 : : * This is especially important for fuse which sets bdi->max_ratio to
937 : : * 1% by default. Without strictlimit feature, fuse writeback may
938 : : * consume arbitrary amount of RAM because it is accounted in
939 : : * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
940 : : *
941 : : * Here, in wb_position_ratio(), we calculate pos_ratio based on
942 : : * two values: wb_dirty and wb_thresh. Let's consider an example:
943 : : * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
944 : : * limits are set by default to 10% and 20% (background and throttle).
945 : : * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
946 : : * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
947 : : * about ~6K pages (as the average of background and throttle wb
948 : : * limits). The 3rd order polynomial will provide positive feedback if
949 : : * wb_dirty is under wb_setpoint and vice versa.
950 : : *
951 : : * Note, that we cannot use global counters in these calculations
952 : : * because we want to throttle process writing to a strictlimit wb
953 : : * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
954 : : * in the example above).
955 : : */
956 [ # # ]: 0 : if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
957 : : long long wb_pos_ratio;
958 : :
959 [ # # ]: 0 : if (dtc->wb_dirty < 8) {
960 : 0 : dtc->pos_ratio = min_t(long long, pos_ratio * 2,
961 : : 2 << RATELIMIT_CALC_SHIFT);
962 : 0 : return;
963 : : }
964 : :
965 [ # # ]: 0 : if (dtc->wb_dirty >= wb_thresh)
966 : : return;
967 : :
968 : 0 : wb_setpoint = dirty_freerun_ceiling(wb_thresh,
969 : : dtc->wb_bg_thresh);
970 : :
971 [ # # ]: 0 : if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
972 : : return;
973 : :
974 : 0 : wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
975 : : wb_thresh);
976 : :
977 : : /*
978 : : * Typically, for strictlimit case, wb_setpoint << setpoint
979 : : * and pos_ratio >> wb_pos_ratio. In the other words global
980 : : * state ("dirty") is not limiting factor and we have to
981 : : * make decision based on wb counters. But there is an
982 : : * important case when global pos_ratio should get precedence:
983 : : * global limits are exceeded (e.g. due to activities on other
984 : : * wb's) while given strictlimit wb is below limit.
985 : : *
986 : : * "pos_ratio * wb_pos_ratio" would work for the case above,
987 : : * but it would look too non-natural for the case of all
988 : : * activity in the system coming from a single strictlimit wb
989 : : * with bdi->max_ratio == 100%.
990 : : *
991 : : * Note that min() below somewhat changes the dynamics of the
992 : : * control system. Normally, pos_ratio value can be well over 3
993 : : * (when globally we are at freerun and wb is well below wb
994 : : * setpoint). Now the maximum pos_ratio in the same situation
995 : : * is 2. We might want to tweak this if we observe the control
996 : : * system is too slow to adapt.
997 : : */
998 : 0 : dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
999 : 0 : return;
1000 : : }
1001 : :
1002 : : /*
1003 : : * We have computed basic pos_ratio above based on global situation. If
1004 : : * the wb is over/under its share of dirty pages, we want to scale
1005 : : * pos_ratio further down/up. That is done by the following mechanism.
1006 : : */
1007 : :
1008 : : /*
1009 : : * wb setpoint
1010 : : *
1011 : : * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1012 : : *
1013 : : * x_intercept - wb_dirty
1014 : : * := --------------------------
1015 : : * x_intercept - wb_setpoint
1016 : : *
1017 : : * The main wb control line is a linear function that subjects to
1018 : : *
1019 : : * (1) f(wb_setpoint) = 1.0
1020 : : * (2) k = - 1 / (8 * write_bw) (in single wb case)
1021 : : * or equally: x_intercept = wb_setpoint + 8 * write_bw
1022 : : *
1023 : : * For single wb case, the dirty pages are observed to fluctuate
1024 : : * regularly within range
1025 : : * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1026 : : * for various filesystems, where (2) can yield in a reasonable 12.5%
1027 : : * fluctuation range for pos_ratio.
1028 : : *
1029 : : * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1030 : : * own size, so move the slope over accordingly and choose a slope that
1031 : : * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1032 : : */
1033 [ # # ]: 0 : if (unlikely(wb_thresh > dtc->thresh))
1034 : : wb_thresh = dtc->thresh;
1035 : : /*
1036 : : * It's very possible that wb_thresh is close to 0 not because the
1037 : : * device is slow, but that it has remained inactive for long time.
1038 : : * Honour such devices a reasonable good (hopefully IO efficient)
1039 : : * threshold, so that the occasional writes won't be blocked and active
1040 : : * writes can rampup the threshold quickly.
1041 : : */
1042 : 0 : wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1043 : : /*
1044 : : * scale global setpoint to wb's:
1045 : : * wb_setpoint = setpoint * wb_thresh / thresh
1046 : : */
1047 : 0 : x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1048 : 0 : wb_setpoint = setpoint * (u64)x >> 16;
1049 : : /*
1050 : : * Use span=(8*write_bw) in single wb case as indicated by
1051 : : * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1052 : : *
1053 : : * wb_thresh thresh - wb_thresh
1054 : : * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1055 : : * thresh thresh
1056 : : */
1057 : 0 : span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1058 : 0 : x_intercept = wb_setpoint + span;
1059 : :
1060 [ # # ]: 0 : if (dtc->wb_dirty < x_intercept - span / 4) {
1061 : 0 : pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1062 : 0 : (x_intercept - wb_setpoint) | 1);
1063 : : } else
1064 : 0 : pos_ratio /= 4;
1065 : :
1066 : : /*
1067 : : * wb reserve area, safeguard against dirty pool underrun and disk idle
1068 : : * It may push the desired control point of global dirty pages higher
1069 : : * than setpoint.
1070 : : */
1071 : 0 : x_intercept = wb_thresh / 2;
1072 [ # # ]: 0 : if (dtc->wb_dirty < x_intercept) {
1073 [ # # ]: 0 : if (dtc->wb_dirty > x_intercept / 8)
1074 : 0 : pos_ratio = div_u64(pos_ratio * x_intercept,
1075 : : dtc->wb_dirty);
1076 : : else
1077 : 0 : pos_ratio *= 8;
1078 : : }
1079 : :
1080 : 0 : dtc->pos_ratio = pos_ratio;
1081 : : }
1082 : :
1083 : 1 : static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1084 : : unsigned long elapsed,
1085 : : unsigned long written)
1086 : : {
1087 : : const unsigned long period = roundup_pow_of_two(3 * HZ);
1088 : 1 : unsigned long avg = wb->avg_write_bandwidth;
1089 : 1 : unsigned long old = wb->write_bandwidth;
1090 : : u64 bw;
1091 : :
1092 : : /*
1093 : : * bw = written * HZ / elapsed
1094 : : *
1095 : : * bw * elapsed + write_bandwidth * (period - elapsed)
1096 : : * write_bandwidth = ---------------------------------------------------
1097 : : * period
1098 : : *
1099 : : * @written may have decreased due to account_page_redirty().
1100 : : * Avoid underflowing @bw calculation.
1101 : : */
1102 : 1 : bw = written - min(written, wb->written_stamp);
1103 : 1 : bw *= HZ;
1104 [ - + ]: 1 : if (unlikely(elapsed > period)) {
1105 [ # # # # : 0 : do_div(bw, elapsed);
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# # ]
1106 : 0 : avg = bw;
1107 : 0 : goto out;
1108 : : }
1109 : 1 : bw += (u64)wb->write_bandwidth * (period - elapsed);
1110 : 1 : bw >>= ilog2(period);
1111 : :
1112 : : /*
1113 : : * one more level of smoothing, for filtering out sudden spikes
1114 : : */
1115 [ - + # # ]: 1 : if (avg > old && old >= (unsigned long)bw)
1116 : 0 : avg -= (avg - old) >> 3;
1117 : :
1118 [ - + # # ]: 1 : if (avg < old && old <= (unsigned long)bw)
1119 : 0 : avg += (old - avg) >> 3;
1120 : :
1121 : : out:
1122 : : /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1123 : 1 : avg = max(avg, 1LU);
1124 [ + - ]: 1 : if (wb_has_dirty_io(wb)) {
1125 : 1 : long delta = avg - wb->avg_write_bandwidth;
1126 [ - + # # ]: 2 : WARN_ON_ONCE(atomic_long_add_return(delta,
1127 : : &wb->bdi->tot_write_bandwidth) <= 0);
1128 : : }
1129 : 1 : wb->write_bandwidth = bw;
1130 : 1 : wb->avg_write_bandwidth = avg;
1131 : 1 : }
1132 : :
1133 : : static void update_dirty_limit(struct dirty_throttle_control *dtc)
1134 : : {
1135 : : struct wb_domain *dom = dtc_dom(dtc);
1136 : 0 : unsigned long thresh = dtc->thresh;
1137 : 0 : unsigned long limit = dom->dirty_limit;
1138 : :
1139 : : /*
1140 : : * Follow up in one step.
1141 : : */
1142 [ # # ]: 0 : if (limit < thresh) {
1143 : : limit = thresh;
1144 : : goto update;
1145 : : }
1146 : :
1147 : : /*
1148 : : * Follow down slowly. Use the higher one as the target, because thresh
1149 : : * may drop below dirty. This is exactly the reason to introduce
1150 : : * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1151 : : */
1152 : 0 : thresh = max(thresh, dtc->dirty);
1153 [ # # ]: 0 : if (limit > thresh) {
1154 : 0 : limit -= (limit - thresh) >> 5;
1155 : : goto update;
1156 : : }
1157 : : return;
1158 : : update:
1159 : 0 : dom->dirty_limit = limit;
1160 : : }
1161 : :
1162 : 0 : static void domain_update_bandwidth(struct dirty_throttle_control *dtc,
1163 : : unsigned long now)
1164 : : {
1165 : : struct wb_domain *dom = dtc_dom(dtc);
1166 : :
1167 : : /*
1168 : : * check locklessly first to optimize away locking for the most time
1169 : : */
1170 [ # # ]: 0 : if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1171 : 0 : return;
1172 : :
1173 : : spin_lock(&dom->lock);
1174 [ # # ]: 0 : if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1175 : : update_dirty_limit(dtc);
1176 : 0 : dom->dirty_limit_tstamp = now;
1177 : : }
1178 : : spin_unlock(&dom->lock);
1179 : : }
1180 : :
1181 : : /*
1182 : : * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1183 : : *
1184 : : * Normal wb tasks will be curbed at or below it in long term.
1185 : : * Obviously it should be around (write_bw / N) when there are N dd tasks.
1186 : : */
1187 : 0 : static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1188 : : unsigned long dirtied,
1189 : : unsigned long elapsed)
1190 : : {
1191 : 0 : struct bdi_writeback *wb = dtc->wb;
1192 : 0 : unsigned long dirty = dtc->dirty;
1193 : 0 : unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1194 : : unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1195 : 0 : unsigned long setpoint = (freerun + limit) / 2;
1196 : 0 : unsigned long write_bw = wb->avg_write_bandwidth;
1197 : 0 : unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1198 : : unsigned long dirty_rate;
1199 : : unsigned long task_ratelimit;
1200 : : unsigned long balanced_dirty_ratelimit;
1201 : : unsigned long step;
1202 : : unsigned long x;
1203 : : unsigned long shift;
1204 : :
1205 : : /*
1206 : : * The dirty rate will match the writeout rate in long term, except
1207 : : * when dirty pages are truncated by userspace or re-dirtied by FS.
1208 : : */
1209 : 0 : dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1210 : :
1211 : : /*
1212 : : * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1213 : : */
1214 : 0 : task_ratelimit = (u64)dirty_ratelimit *
1215 : 0 : dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1216 : 0 : task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1217 : :
1218 : : /*
1219 : : * A linear estimation of the "balanced" throttle rate. The theory is,
1220 : : * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1221 : : * dirty_rate will be measured to be (N * task_ratelimit). So the below
1222 : : * formula will yield the balanced rate limit (write_bw / N).
1223 : : *
1224 : : * Note that the expanded form is not a pure rate feedback:
1225 : : * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1226 : : * but also takes pos_ratio into account:
1227 : : * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1228 : : *
1229 : : * (1) is not realistic because pos_ratio also takes part in balancing
1230 : : * the dirty rate. Consider the state
1231 : : * pos_ratio = 0.5 (3)
1232 : : * rate = 2 * (write_bw / N) (4)
1233 : : * If (1) is used, it will stuck in that state! Because each dd will
1234 : : * be throttled at
1235 : : * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1236 : : * yielding
1237 : : * dirty_rate = N * task_ratelimit = write_bw (6)
1238 : : * put (6) into (1) we get
1239 : : * rate_(i+1) = rate_(i) (7)
1240 : : *
1241 : : * So we end up using (2) to always keep
1242 : : * rate_(i+1) ~= (write_bw / N) (8)
1243 : : * regardless of the value of pos_ratio. As long as (8) is satisfied,
1244 : : * pos_ratio is able to drive itself to 1.0, which is not only where
1245 : : * the dirty count meet the setpoint, but also where the slope of
1246 : : * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1247 : : */
1248 : 0 : balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1249 : 0 : dirty_rate | 1);
1250 : : /*
1251 : : * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1252 : : */
1253 [ # # ]: 0 : if (unlikely(balanced_dirty_ratelimit > write_bw))
1254 : : balanced_dirty_ratelimit = write_bw;
1255 : :
1256 : : /*
1257 : : * We could safely do this and return immediately:
1258 : : *
1259 : : * wb->dirty_ratelimit = balanced_dirty_ratelimit;
1260 : : *
1261 : : * However to get a more stable dirty_ratelimit, the below elaborated
1262 : : * code makes use of task_ratelimit to filter out singular points and
1263 : : * limit the step size.
1264 : : *
1265 : : * The below code essentially only uses the relative value of
1266 : : *
1267 : : * task_ratelimit - dirty_ratelimit
1268 : : * = (pos_ratio - 1) * dirty_ratelimit
1269 : : *
1270 : : * which reflects the direction and size of dirty position error.
1271 : : */
1272 : :
1273 : : /*
1274 : : * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1275 : : * task_ratelimit is on the same side of dirty_ratelimit, too.
1276 : : * For example, when
1277 : : * - dirty_ratelimit > balanced_dirty_ratelimit
1278 : : * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1279 : : * lowering dirty_ratelimit will help meet both the position and rate
1280 : : * control targets. Otherwise, don't update dirty_ratelimit if it will
1281 : : * only help meet the rate target. After all, what the users ultimately
1282 : : * feel and care are stable dirty rate and small position error.
1283 : : *
1284 : : * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1285 : : * and filter out the singular points of balanced_dirty_ratelimit. Which
1286 : : * keeps jumping around randomly and can even leap far away at times
1287 : : * due to the small 200ms estimation period of dirty_rate (we want to
1288 : : * keep that period small to reduce time lags).
1289 : : */
1290 : : step = 0;
1291 : :
1292 : : /*
1293 : : * For strictlimit case, calculations above were based on wb counters
1294 : : * and limits (starting from pos_ratio = wb_position_ratio() and up to
1295 : : * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1296 : : * Hence, to calculate "step" properly, we have to use wb_dirty as
1297 : : * "dirty" and wb_setpoint as "setpoint".
1298 : : *
1299 : : * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1300 : : * it's possible that wb_thresh is close to zero due to inactivity
1301 : : * of backing device.
1302 : : */
1303 [ # # ]: 0 : if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1304 : 0 : dirty = dtc->wb_dirty;
1305 [ # # ]: 0 : if (dtc->wb_dirty < 8)
1306 : 0 : setpoint = dtc->wb_dirty + 1;
1307 : : else
1308 : 0 : setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1309 : : }
1310 : :
1311 [ # # ]: 0 : if (dirty < setpoint) {
1312 : 0 : x = min3(wb->balanced_dirty_ratelimit,
1313 : : balanced_dirty_ratelimit, task_ratelimit);
1314 [ # # ]: 0 : if (dirty_ratelimit < x)
1315 : 0 : step = x - dirty_ratelimit;
1316 : : } else {
1317 : 0 : x = max3(wb->balanced_dirty_ratelimit,
1318 : : balanced_dirty_ratelimit, task_ratelimit);
1319 [ # # ]: 0 : if (dirty_ratelimit > x)
1320 : 0 : step = dirty_ratelimit - x;
1321 : : }
1322 : :
1323 : : /*
1324 : : * Don't pursue 100% rate matching. It's impossible since the balanced
1325 : : * rate itself is constantly fluctuating. So decrease the track speed
1326 : : * when it gets close to the target. Helps eliminate pointless tremors.
1327 : : */
1328 : 0 : shift = dirty_ratelimit / (2 * step + 1);
1329 [ # # ]: 0 : if (shift < BITS_PER_LONG)
1330 : 0 : step = DIV_ROUND_UP(step >> shift, 8);
1331 : : else
1332 : : step = 0;
1333 : :
1334 [ # # ]: 0 : if (dirty_ratelimit < balanced_dirty_ratelimit)
1335 : 0 : dirty_ratelimit += step;
1336 : : else
1337 : 0 : dirty_ratelimit -= step;
1338 : :
1339 : 0 : wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1340 : 0 : wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1341 : :
1342 : 0 : trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1343 : 0 : }
1344 : :
1345 : 5212 : static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1346 : : struct dirty_throttle_control *mdtc,
1347 : : unsigned long start_time,
1348 : : bool update_ratelimit)
1349 : : {
1350 : 5212 : struct bdi_writeback *wb = gdtc->wb;
1351 : 5212 : unsigned long now = jiffies;
1352 : 5212 : unsigned long elapsed = now - wb->bw_time_stamp;
1353 : : unsigned long dirtied;
1354 : : unsigned long written;
1355 : :
1356 : : lockdep_assert_held(&wb->list_lock);
1357 : :
1358 : : /*
1359 : : * rate-limit, only update once every 200ms.
1360 : : */
1361 [ + + ]: 5212 : if (elapsed < BANDWIDTH_INTERVAL)
1362 : 5212 : return;
1363 : :
1364 : 3137 : dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1365 : 3137 : written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1366 : :
1367 : : /*
1368 : : * Skip quiet periods when disk bandwidth is under-utilized.
1369 : : * (at least 1s idle time between two flusher runs)
1370 : : */
1371 [ + + - + ]: 3137 : if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
1372 : : goto snapshot;
1373 : :
1374 [ - + ]: 1 : if (update_ratelimit) {
1375 : 0 : domain_update_bandwidth(gdtc, now);
1376 : 0 : wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1377 : :
1378 : : /*
1379 : : * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1380 : : * compiler has no way to figure that out. Help it.
1381 : : */
1382 [ # # ]: 0 : if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1383 : 0 : domain_update_bandwidth(mdtc, now);
1384 : 0 : wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1385 : : }
1386 : : }
1387 : 1 : wb_update_write_bandwidth(wb, elapsed, written);
1388 : :
1389 : : snapshot:
1390 : 3137 : wb->dirtied_stamp = dirtied;
1391 : 3137 : wb->written_stamp = written;
1392 : 3137 : wb->bw_time_stamp = now;
1393 : : }
1394 : :
1395 : 5212 : void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
1396 : : {
1397 : 5212 : struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1398 : :
1399 : 5212 : __wb_update_bandwidth(&gdtc, NULL, start_time, false);
1400 : 5212 : }
1401 : :
1402 : : /*
1403 : : * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1404 : : * will look to see if it needs to start dirty throttling.
1405 : : *
1406 : : * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1407 : : * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1408 : : * (the number of pages we may dirty without exceeding the dirty limits).
1409 : : */
1410 : 2629 : static unsigned long dirty_poll_interval(unsigned long dirty,
1411 : : unsigned long thresh)
1412 : : {
1413 [ + - ]: 2629 : if (thresh > dirty)
1414 [ - + # # : 5258 : return 1UL << (ilog2(thresh - dirty) >> 1);
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1415 : :
1416 : : return 1;
1417 : : }
1418 : :
1419 : : static unsigned long wb_max_pause(struct bdi_writeback *wb,
1420 : : unsigned long wb_dirty)
1421 : : {
1422 : 0 : unsigned long bw = wb->avg_write_bandwidth;
1423 : : unsigned long t;
1424 : :
1425 : : /*
1426 : : * Limit pause time for small memory systems. If sleeping for too long
1427 : : * time, a small pool of dirty/writeback pages may go empty and disk go
1428 : : * idle.
1429 : : *
1430 : : * 8 serves as the safety ratio.
1431 : : */
1432 : 0 : t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1433 : 0 : t++;
1434 : :
1435 : 0 : return min_t(unsigned long, t, MAX_PAUSE);
1436 : : }
1437 : :
1438 : 0 : static long wb_min_pause(struct bdi_writeback *wb,
1439 : : long max_pause,
1440 : : unsigned long task_ratelimit,
1441 : : unsigned long dirty_ratelimit,
1442 : : int *nr_dirtied_pause)
1443 : : {
1444 [ # # # # : 0 : long hi = ilog2(wb->avg_write_bandwidth);
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1445 [ # # # # : 0 : long lo = ilog2(wb->dirty_ratelimit);
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1446 : : long t; /* target pause */
1447 : : long pause; /* estimated next pause */
1448 : : int pages; /* target nr_dirtied_pause */
1449 : :
1450 : : /* target for 10ms pause on 1-dd case */
1451 : : t = max(1, HZ / 100);
1452 : :
1453 : : /*
1454 : : * Scale up pause time for concurrent dirtiers in order to reduce CPU
1455 : : * overheads.
1456 : : *
1457 : : * (N * 10ms) on 2^N concurrent tasks.
1458 : : */
1459 [ # # ]: 0 : if (hi > lo)
1460 : 0 : t += (hi - lo) * (10 * HZ) / 1024;
1461 : :
1462 : : /*
1463 : : * This is a bit convoluted. We try to base the next nr_dirtied_pause
1464 : : * on the much more stable dirty_ratelimit. However the next pause time
1465 : : * will be computed based on task_ratelimit and the two rate limits may
1466 : : * depart considerably at some time. Especially if task_ratelimit goes
1467 : : * below dirty_ratelimit/2 and the target pause is max_pause, the next
1468 : : * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1469 : : * result task_ratelimit won't be executed faithfully, which could
1470 : : * eventually bring down dirty_ratelimit.
1471 : : *
1472 : : * We apply two rules to fix it up:
1473 : : * 1) try to estimate the next pause time and if necessary, use a lower
1474 : : * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1475 : : * nr_dirtied_pause will be "dancing" with task_ratelimit.
1476 : : * 2) limit the target pause time to max_pause/2, so that the normal
1477 : : * small fluctuations of task_ratelimit won't trigger rule (1) and
1478 : : * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1479 : : */
1480 : 0 : t = min(t, 1 + max_pause / 2);
1481 : 0 : pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1482 : :
1483 : : /*
1484 : : * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1485 : : * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1486 : : * When the 16 consecutive reads are often interrupted by some dirty
1487 : : * throttling pause during the async writes, cfq will go into idles
1488 : : * (deadline is fine). So push nr_dirtied_pause as high as possible
1489 : : * until reaches DIRTY_POLL_THRESH=32 pages.
1490 : : */
1491 [ # # ]: 0 : if (pages < DIRTY_POLL_THRESH) {
1492 : : t = max_pause;
1493 : 0 : pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1494 [ # # ]: 0 : if (pages > DIRTY_POLL_THRESH) {
1495 : : pages = DIRTY_POLL_THRESH;
1496 : 0 : t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1497 : : }
1498 : : }
1499 : :
1500 : 0 : pause = HZ * pages / (task_ratelimit + 1);
1501 [ # # ]: 0 : if (pause > max_pause) {
1502 : : t = max_pause;
1503 : 0 : pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1504 : : }
1505 : :
1506 : 0 : *nr_dirtied_pause = pages;
1507 : : /*
1508 : : * The minimal pause time will normally be half the target pause time.
1509 : : */
1510 [ # # ]: 0 : return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1511 : : }
1512 : :
1513 : 0 : static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1514 : : {
1515 : 0 : struct bdi_writeback *wb = dtc->wb;
1516 : : unsigned long wb_reclaimable;
1517 : :
1518 : : /*
1519 : : * wb_thresh is not treated as some limiting factor as
1520 : : * dirty_thresh, due to reasons
1521 : : * - in JBOD setup, wb_thresh can fluctuate a lot
1522 : : * - in a system with HDD and USB key, the USB key may somehow
1523 : : * go into state (wb_dirty >> wb_thresh) either because
1524 : : * wb_dirty starts high, or because wb_thresh drops low.
1525 : : * In this case we don't want to hard throttle the USB key
1526 : : * dirtiers for 100 seconds until wb_dirty drops under
1527 : : * wb_thresh. Instead the auxiliary wb control line in
1528 : : * wb_position_ratio() will let the dirtier task progress
1529 : : * at some rate <= (write_bw / 2) for bringing down wb_dirty.
1530 : : */
1531 : 0 : dtc->wb_thresh = __wb_calc_thresh(dtc);
1532 [ # # ]: 0 : dtc->wb_bg_thresh = dtc->thresh ?
1533 : 0 : div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1534 : :
1535 : : /*
1536 : : * In order to avoid the stacked BDI deadlock we need
1537 : : * to ensure we accurately count the 'dirty' pages when
1538 : : * the threshold is low.
1539 : : *
1540 : : * Otherwise it would be possible to get thresh+n pages
1541 : : * reported dirty, even though there are thresh-m pages
1542 : : * actually dirty; with m+n sitting in the percpu
1543 : : * deltas.
1544 : : */
1545 [ # # ]: 0 : if (dtc->wb_thresh < 2 * wb_stat_error()) {
1546 : 0 : wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1547 : 0 : dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1548 : : } else {
1549 : 0 : wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1550 : 0 : dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1551 : : }
1552 : 0 : }
1553 : :
1554 : : /*
1555 : : * balance_dirty_pages() must be called by processes which are generating dirty
1556 : : * data. It looks at the number of dirty pages in the machine and will force
1557 : : * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1558 : : * If we're over `background_thresh' then the writeback threads are woken to
1559 : : * perform some writeout.
1560 : : */
1561 : 2629 : static void balance_dirty_pages(struct bdi_writeback *wb,
1562 : : unsigned long pages_dirtied)
1563 : : {
1564 : 2629 : struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1565 : 2629 : struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1566 : : struct dirty_throttle_control * const gdtc = &gdtc_stor;
1567 : : struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1568 [ + - ]: 2629 : &mdtc_stor : NULL;
1569 : : struct dirty_throttle_control *sdtc;
1570 : : unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1571 : : long period;
1572 : : long pause;
1573 : : long max_pause;
1574 : : long min_pause;
1575 : : int nr_dirtied_pause;
1576 : : bool dirty_exceeded = false;
1577 : : unsigned long task_ratelimit;
1578 : : unsigned long dirty_ratelimit;
1579 : 2629 : struct backing_dev_info *bdi = wb->bdi;
1580 : 2629 : bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1581 : 2629 : unsigned long start_time = jiffies;
1582 : :
1583 : : for (;;) {
1584 : 2629 : unsigned long now = jiffies;
1585 : : unsigned long dirty, thresh, bg_thresh;
1586 : : unsigned long m_dirty = 0; /* stop bogus uninit warnings */
1587 : : unsigned long m_thresh = 0;
1588 : : unsigned long m_bg_thresh = 0;
1589 : :
1590 : : /*
1591 : : * Unstable writes are a feature of certain networked
1592 : : * filesystems (i.e. NFS) in which data may have been
1593 : : * written to the server's write cache, but has not yet
1594 : : * been flushed to permanent storage.
1595 : : */
1596 : 2629 : nr_reclaimable = global_node_page_state(NR_FILE_DIRTY) +
1597 : : global_node_page_state(NR_UNSTABLE_NFS);
1598 : 2629 : gdtc->avail = global_dirtyable_memory();
1599 : 2629 : gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
1600 : :
1601 : 2629 : domain_dirty_limits(gdtc);
1602 : :
1603 [ - + ]: 2629 : if (unlikely(strictlimit)) {
1604 : 0 : wb_dirty_limits(gdtc);
1605 : :
1606 : 0 : dirty = gdtc->wb_dirty;
1607 : 0 : thresh = gdtc->wb_thresh;
1608 : 0 : bg_thresh = gdtc->wb_bg_thresh;
1609 : : } else {
1610 : 2629 : dirty = gdtc->dirty;
1611 : 2629 : thresh = gdtc->thresh;
1612 : 2629 : bg_thresh = gdtc->bg_thresh;
1613 : : }
1614 : :
1615 [ - + ]: 2629 : if (mdtc) {
1616 : : unsigned long filepages, headroom, writeback;
1617 : :
1618 : : /*
1619 : : * If @wb belongs to !root memcg, repeat the same
1620 : : * basic calculations for the memcg domain.
1621 : : */
1622 : 0 : mem_cgroup_wb_stats(wb, &filepages, &headroom,
1623 : : &mdtc->dirty, &writeback);
1624 : 0 : mdtc->dirty += writeback;
1625 : 0 : mdtc_calc_avail(mdtc, filepages, headroom);
1626 : :
1627 : 0 : domain_dirty_limits(mdtc);
1628 : :
1629 [ # # ]: 0 : if (unlikely(strictlimit)) {
1630 : 0 : wb_dirty_limits(mdtc);
1631 : 0 : m_dirty = mdtc->wb_dirty;
1632 : 0 : m_thresh = mdtc->wb_thresh;
1633 : 0 : m_bg_thresh = mdtc->wb_bg_thresh;
1634 : : } else {
1635 : 0 : m_dirty = mdtc->dirty;
1636 : 0 : m_thresh = mdtc->thresh;
1637 : 0 : m_bg_thresh = mdtc->bg_thresh;
1638 : : }
1639 : : }
1640 : :
1641 : : /*
1642 : : * Throttle it only when the background writeback cannot
1643 : : * catch-up. This avoids (excessively) small writeouts
1644 : : * when the wb limits are ramping up in case of !strictlimit.
1645 : : *
1646 : : * In strictlimit case make decision based on the wb counters
1647 : : * and limits. Small writeouts when the wb limits are ramping
1648 : : * up are the price we consciously pay for strictlimit-ing.
1649 : : *
1650 : : * If memcg domain is in effect, @dirty should be under
1651 : : * both global and memcg freerun ceilings.
1652 : : */
1653 [ + - - + ]: 2629 : if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1654 [ # # ]: 0 : (!mdtc ||
1655 : : m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1656 : 2629 : unsigned long intv = dirty_poll_interval(dirty, thresh);
1657 : : unsigned long m_intv = ULONG_MAX;
1658 : :
1659 : 2629 : current->dirty_paused_when = now;
1660 : 2629 : current->nr_dirtied = 0;
1661 [ - + ]: 2629 : if (mdtc)
1662 : 0 : m_intv = dirty_poll_interval(m_dirty, m_thresh);
1663 : 2629 : current->nr_dirtied_pause = min(intv, m_intv);
1664 : 2629 : break;
1665 : : }
1666 : :
1667 [ # # ]: 0 : if (unlikely(!writeback_in_progress(wb)))
1668 : 0 : wb_start_background_writeback(wb);
1669 : :
1670 : 0 : mem_cgroup_flush_foreign(wb);
1671 : :
1672 : : /*
1673 : : * Calculate global domain's pos_ratio and select the
1674 : : * global dtc by default.
1675 : : */
1676 [ # # ]: 0 : if (!strictlimit)
1677 : 0 : wb_dirty_limits(gdtc);
1678 : :
1679 [ # # # # ]: 0 : dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1680 [ # # ]: 0 : ((gdtc->dirty > gdtc->thresh) || strictlimit);
1681 : :
1682 : 0 : wb_position_ratio(gdtc);
1683 : : sdtc = gdtc;
1684 : :
1685 [ # # ]: 0 : if (mdtc) {
1686 : : /*
1687 : : * If memcg domain is in effect, calculate its
1688 : : * pos_ratio. @wb should satisfy constraints from
1689 : : * both global and memcg domains. Choose the one
1690 : : * w/ lower pos_ratio.
1691 : : */
1692 [ # # ]: 0 : if (!strictlimit)
1693 : 0 : wb_dirty_limits(mdtc);
1694 : :
1695 [ # # # # ]: 0 : dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1696 [ # # ]: 0 : ((mdtc->dirty > mdtc->thresh) || strictlimit);
1697 : :
1698 : 0 : wb_position_ratio(mdtc);
1699 [ # # ]: 0 : if (mdtc->pos_ratio < gdtc->pos_ratio)
1700 : : sdtc = mdtc;
1701 : : }
1702 : :
1703 [ # # # # ]: 0 : if (dirty_exceeded && !wb->dirty_exceeded)
1704 : 0 : wb->dirty_exceeded = 1;
1705 : :
1706 [ # # ]: 0 : if (time_is_before_jiffies(wb->bw_time_stamp +
1707 : : BANDWIDTH_INTERVAL)) {
1708 : : spin_lock(&wb->list_lock);
1709 : 0 : __wb_update_bandwidth(gdtc, mdtc, start_time, true);
1710 : : spin_unlock(&wb->list_lock);
1711 : : }
1712 : :
1713 : : /* throttle according to the chosen dtc */
1714 : 0 : dirty_ratelimit = wb->dirty_ratelimit;
1715 : 0 : task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1716 : : RATELIMIT_CALC_SHIFT;
1717 : 0 : max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1718 : 0 : min_pause = wb_min_pause(wb, max_pause,
1719 : : task_ratelimit, dirty_ratelimit,
1720 : : &nr_dirtied_pause);
1721 : :
1722 [ # # ]: 0 : if (unlikely(task_ratelimit == 0)) {
1723 : : period = max_pause;
1724 : : pause = max_pause;
1725 : : goto pause;
1726 : : }
1727 : 0 : period = HZ * pages_dirtied / task_ratelimit;
1728 : : pause = period;
1729 [ # # ]: 0 : if (current->dirty_paused_when)
1730 : 0 : pause -= now - current->dirty_paused_when;
1731 : : /*
1732 : : * For less than 1s think time (ext3/4 may block the dirtier
1733 : : * for up to 800ms from time to time on 1-HDD; so does xfs,
1734 : : * however at much less frequency), try to compensate it in
1735 : : * future periods by updating the virtual time; otherwise just
1736 : : * do a reset, as it may be a light dirtier.
1737 : : */
1738 [ # # ]: 0 : if (pause < min_pause) {
1739 : 0 : trace_balance_dirty_pages(wb,
1740 : : sdtc->thresh,
1741 : : sdtc->bg_thresh,
1742 : : sdtc->dirty,
1743 : : sdtc->wb_thresh,
1744 : : sdtc->wb_dirty,
1745 : : dirty_ratelimit,
1746 : : task_ratelimit,
1747 : : pages_dirtied,
1748 : : period,
1749 : 0 : min(pause, 0L),
1750 : : start_time);
1751 [ # # ]: 0 : if (pause < -HZ) {
1752 : 0 : current->dirty_paused_when = now;
1753 : 0 : current->nr_dirtied = 0;
1754 [ # # ]: 0 : } else if (period) {
1755 : 0 : current->dirty_paused_when += period;
1756 : 0 : current->nr_dirtied = 0;
1757 [ # # ]: 0 : } else if (current->nr_dirtied_pause <= pages_dirtied)
1758 : 0 : current->nr_dirtied_pause += pages_dirtied;
1759 : : break;
1760 : : }
1761 [ # # ]: 0 : if (unlikely(pause > max_pause)) {
1762 : : /* for occasional dropped task_ratelimit */
1763 : 0 : now += min(pause - max_pause, max_pause);
1764 : : pause = max_pause;
1765 : : }
1766 : :
1767 : : pause:
1768 : 0 : trace_balance_dirty_pages(wb,
1769 : : sdtc->thresh,
1770 : : sdtc->bg_thresh,
1771 : : sdtc->dirty,
1772 : : sdtc->wb_thresh,
1773 : : sdtc->wb_dirty,
1774 : : dirty_ratelimit,
1775 : : task_ratelimit,
1776 : : pages_dirtied,
1777 : : period,
1778 : : pause,
1779 : : start_time);
1780 : 0 : __set_current_state(TASK_KILLABLE);
1781 : 0 : wb->dirty_sleep = now;
1782 : 0 : io_schedule_timeout(pause);
1783 : :
1784 : 0 : current->dirty_paused_when = now + pause;
1785 : 0 : current->nr_dirtied = 0;
1786 : 0 : current->nr_dirtied_pause = nr_dirtied_pause;
1787 : :
1788 : : /*
1789 : : * This is typically equal to (dirty < thresh) and can also
1790 : : * keep "1000+ dd on a slow USB stick" under control.
1791 : : */
1792 [ # # ]: 0 : if (task_ratelimit)
1793 : : break;
1794 : :
1795 : : /*
1796 : : * In the case of an unresponding NFS server and the NFS dirty
1797 : : * pages exceeds dirty_thresh, give the other good wb's a pipe
1798 : : * to go through, so that tasks on them still remain responsive.
1799 : : *
1800 : : * In theory 1 page is enough to keep the consumer-producer
1801 : : * pipe going: the flusher cleans 1 page => the task dirties 1
1802 : : * more page. However wb_dirty has accounting errors. So use
1803 : : * the larger and more IO friendly wb_stat_error.
1804 : : */
1805 [ # # ]: 0 : if (sdtc->wb_dirty <= wb_stat_error())
1806 : : break;
1807 : :
1808 [ # # ]: 0 : if (fatal_signal_pending(current))
1809 : : break;
1810 : : }
1811 : :
1812 [ + - - + ]: 2629 : if (!dirty_exceeded && wb->dirty_exceeded)
1813 : 0 : wb->dirty_exceeded = 0;
1814 : :
1815 [ + + ]: 2629 : if (writeback_in_progress(wb))
1816 : 28 : return;
1817 : :
1818 : : /*
1819 : : * In laptop mode, we wait until hitting the higher threshold before
1820 : : * starting background writeout, and then write out all the way down
1821 : : * to the lower threshold. So slow writers cause minimal disk activity.
1822 : : *
1823 : : * In normal mode, we start background writeout at the lower
1824 : : * background_thresh, to keep the amount of dirty memory low.
1825 : : */
1826 [ + - ]: 2601 : if (laptop_mode)
1827 : : return;
1828 : :
1829 [ - + ]: 2601 : if (nr_reclaimable > gdtc->bg_thresh)
1830 : 0 : wb_start_background_writeback(wb);
1831 : : }
1832 : :
1833 : : static DEFINE_PER_CPU(int, bdp_ratelimits);
1834 : :
1835 : : /*
1836 : : * Normal tasks are throttled by
1837 : : * loop {
1838 : : * dirty tsk->nr_dirtied_pause pages;
1839 : : * take a snap in balance_dirty_pages();
1840 : : * }
1841 : : * However there is a worst case. If every task exit immediately when dirtied
1842 : : * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1843 : : * called to throttle the page dirties. The solution is to save the not yet
1844 : : * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1845 : : * randomly into the running tasks. This works well for the above worst case,
1846 : : * as the new task will pick up and accumulate the old task's leaked dirty
1847 : : * count and eventually get throttled.
1848 : : */
1849 : : DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1850 : :
1851 : : /**
1852 : : * balance_dirty_pages_ratelimited - balance dirty memory state
1853 : : * @mapping: address_space which was dirtied
1854 : : *
1855 : : * Processes which are dirtying memory should call in here once for each page
1856 : : * which was newly dirtied. The function will periodically check the system's
1857 : : * dirty state and will initiate writeback if needed.
1858 : : *
1859 : : * On really big machines, get_writeback_state is expensive, so try to avoid
1860 : : * calling it too often (ratelimiting). But once we're over the dirty memory
1861 : : * limit we decrease the ratelimiting by a lot, to prevent individual processes
1862 : : * from overshooting the limit by (ratelimit_pages) each.
1863 : : */
1864 : 1228661 : void balance_dirty_pages_ratelimited(struct address_space *mapping)
1865 : : {
1866 : 1228661 : struct inode *inode = mapping->host;
1867 : 1228661 : struct backing_dev_info *bdi = inode_to_bdi(inode);
1868 : : struct bdi_writeback *wb = NULL;
1869 : : int ratelimit;
1870 : : int *p;
1871 : :
1872 [ + + ]: 1228906 : if (!bdi_cap_account_dirty(bdi))
1873 : 1228909 : return;
1874 : :
1875 [ - + ]: 335918 : if (inode_cgwb_enabled(inode))
1876 : 0 : wb = wb_get_create_current(bdi, GFP_KERNEL);
1877 [ + - ]: 335908 : if (!wb)
1878 : 335916 : wb = &bdi->wb;
1879 : :
1880 : 335908 : ratelimit = current->nr_dirtied_pause;
1881 [ - + ]: 335908 : if (wb->dirty_exceeded)
1882 : 0 : ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1883 : :
1884 : 335908 : preempt_disable();
1885 : : /*
1886 : : * This prevents one CPU to accumulate too many dirtied pages without
1887 : : * calling into balance_dirty_pages(), which can happen when there are
1888 : : * 1000+ tasks, all of them start dirtying pages at exactly the same
1889 : : * time, hence all honoured too large initial task->nr_dirtied_pause.
1890 : : */
1891 : 671806 : p = this_cpu_ptr(&bdp_ratelimits);
1892 [ + + ]: 335903 : if (unlikely(current->nr_dirtied >= ratelimit))
1893 : 1172 : *p = 0;
1894 [ + + ]: 334731 : else if (unlikely(*p >= ratelimit_pages)) {
1895 : 139 : *p = 0;
1896 : : ratelimit = 0;
1897 : : }
1898 : : /*
1899 : : * Pick up the dirtied pages by the exited tasks. This avoids lots of
1900 : : * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1901 : : * the dirty throttling and livelock other long-run dirtiers.
1902 : : */
1903 : 671806 : p = this_cpu_ptr(&dirty_throttle_leaks);
1904 [ + + + + ]: 385427 : if (*p > 0 && current->nr_dirtied < ratelimit) {
1905 : : unsigned long nr_pages_dirtied;
1906 : 49419 : nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1907 : 49419 : *p -= nr_pages_dirtied;
1908 : 49419 : current->nr_dirtied += nr_pages_dirtied;
1909 : : }
1910 : 335903 : preempt_enable();
1911 : :
1912 [ + + ]: 335898 : if (unlikely(current->nr_dirtied >= ratelimit))
1913 : 2629 : balance_dirty_pages(wb, current->nr_dirtied);
1914 : :
1915 : 335898 : wb_put(wb);
1916 : : }
1917 : : EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1918 : :
1919 : : /**
1920 : : * wb_over_bg_thresh - does @wb need to be written back?
1921 : : * @wb: bdi_writeback of interest
1922 : : *
1923 : : * Determines whether background writeback should keep writing @wb or it's
1924 : : * clean enough.
1925 : : *
1926 : : * Return: %true if writeback should continue.
1927 : : */
1928 : 4053 : bool wb_over_bg_thresh(struct bdi_writeback *wb)
1929 : : {
1930 : 4053 : struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1931 : 4053 : struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1932 : : struct dirty_throttle_control * const gdtc = &gdtc_stor;
1933 : : struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1934 [ + - ]: 4053 : &mdtc_stor : NULL;
1935 : :
1936 : : /*
1937 : : * Similar to balance_dirty_pages() but ignores pages being written
1938 : : * as we're trying to decide whether to put more under writeback.
1939 : : */
1940 : 4053 : gdtc->avail = global_dirtyable_memory();
1941 : 4053 : gdtc->dirty = global_node_page_state(NR_FILE_DIRTY) +
1942 : : global_node_page_state(NR_UNSTABLE_NFS);
1943 : 4053 : domain_dirty_limits(gdtc);
1944 : :
1945 [ + - ]: 4053 : if (gdtc->dirty > gdtc->bg_thresh)
1946 : : return true;
1947 : :
1948 [ + + ]: 4053 : if (wb_stat(wb, WB_RECLAIMABLE) >
1949 : 4053 : wb_calc_thresh(gdtc->wb, gdtc->bg_thresh))
1950 : : return true;
1951 : :
1952 [ - + ]: 3140 : if (mdtc) {
1953 : : unsigned long filepages, headroom, writeback;
1954 : :
1955 : 0 : mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
1956 : : &writeback);
1957 : 0 : mdtc_calc_avail(mdtc, filepages, headroom);
1958 : 0 : domain_dirty_limits(mdtc); /* ditto, ignore writeback */
1959 : :
1960 [ # # ]: 0 : if (mdtc->dirty > mdtc->bg_thresh)
1961 : 0 : return true;
1962 : :
1963 [ # # ]: 0 : if (wb_stat(wb, WB_RECLAIMABLE) >
1964 : 0 : wb_calc_thresh(mdtc->wb, mdtc->bg_thresh))
1965 : : return true;
1966 : : }
1967 : :
1968 : : return false;
1969 : : }
1970 : :
1971 : : /*
1972 : : * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1973 : : */
1974 : 0 : int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
1975 : : void __user *buffer, size_t *length, loff_t *ppos)
1976 : : {
1977 : 0 : unsigned int old_interval = dirty_writeback_interval;
1978 : : int ret;
1979 : :
1980 : 0 : ret = proc_dointvec(table, write, buffer, length, ppos);
1981 : :
1982 : : /*
1983 : : * Writing 0 to dirty_writeback_interval will disable periodic writeback
1984 : : * and a different non-zero value will wakeup the writeback threads.
1985 : : * wb_wakeup_delayed() would be more appropriate, but it's a pain to
1986 : : * iterate over all bdis and wbs.
1987 : : * The reason we do this is to make the change take effect immediately.
1988 : : */
1989 [ # # # # : 0 : if (!ret && write && dirty_writeback_interval &&
# # ]
1990 : : dirty_writeback_interval != old_interval)
1991 : 0 : wakeup_flusher_threads(WB_REASON_PERIODIC);
1992 : :
1993 : 0 : return ret;
1994 : : }
1995 : :
1996 : : #ifdef CONFIG_BLOCK
1997 : 0 : void laptop_mode_timer_fn(struct timer_list *t)
1998 : : {
1999 : : struct backing_dev_info *backing_dev_info =
2000 : 0 : from_timer(backing_dev_info, t, laptop_mode_wb_timer);
2001 : :
2002 : 0 : wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
2003 : 0 : }
2004 : :
2005 : : /*
2006 : : * We've spun up the disk and we're in laptop mode: schedule writeback
2007 : : * of all dirty data a few seconds from now. If the flush is already scheduled
2008 : : * then push it back - the user is still using the disk.
2009 : : */
2010 : 0 : void laptop_io_completion(struct backing_dev_info *info)
2011 : : {
2012 : 0 : mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2013 : 0 : }
2014 : :
2015 : : /*
2016 : : * We're in laptop mode and we've just synced. The sync's writes will have
2017 : : * caused another writeback to be scheduled by laptop_io_completion.
2018 : : * Nothing needs to be written back anymore, so we unschedule the writeback.
2019 : : */
2020 : 0 : void laptop_sync_completion(void)
2021 : : {
2022 : : struct backing_dev_info *bdi;
2023 : :
2024 : : rcu_read_lock();
2025 : :
2026 [ # # ]: 0 : list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2027 : 0 : del_timer(&bdi->laptop_mode_wb_timer);
2028 : :
2029 : : rcu_read_unlock();
2030 : 0 : }
2031 : : #endif
2032 : :
2033 : : /*
2034 : : * If ratelimit_pages is too high then we can get into dirty-data overload
2035 : : * if a large number of processes all perform writes at the same time.
2036 : : * If it is too low then SMP machines will call the (expensive)
2037 : : * get_writeback_state too often.
2038 : : *
2039 : : * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2040 : : * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2041 : : * thresholds.
2042 : : */
2043 : :
2044 : 828 : void writeback_set_ratelimit(void)
2045 : : {
2046 : : struct wb_domain *dom = &global_wb_domain;
2047 : : unsigned long background_thresh;
2048 : : unsigned long dirty_thresh;
2049 : :
2050 : 828 : global_dirty_limits(&background_thresh, &dirty_thresh);
2051 : 828 : dom->dirty_limit = dirty_thresh;
2052 : 828 : ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2053 [ - + ]: 828 : if (ratelimit_pages < 16)
2054 : 0 : ratelimit_pages = 16;
2055 : 828 : }
2056 : :
2057 : 828 : static int page_writeback_cpu_online(unsigned int cpu)
2058 : : {
2059 : 828 : writeback_set_ratelimit();
2060 : 828 : return 0;
2061 : : }
2062 : :
2063 : : /*
2064 : : * Called early on to tune the page writeback dirty limits.
2065 : : *
2066 : : * We used to scale dirty pages according to how total memory
2067 : : * related to pages that could be allocated for buffers (by
2068 : : * comparing nr_free_buffer_pages() to vm_total_pages.
2069 : : *
2070 : : * However, that was when we used "dirty_ratio" to scale with
2071 : : * all memory, and we don't do that any more. "dirty_ratio"
2072 : : * is now applied to total non-HIGHPAGE memory (by subtracting
2073 : : * totalhigh_pages from vm_total_pages), and as such we can't
2074 : : * get into the old insane situation any more where we had
2075 : : * large amounts of dirty pages compared to a small amount of
2076 : : * non-HIGHMEM memory.
2077 : : *
2078 : : * But we might still want to scale the dirty_ratio by how
2079 : : * much memory the box has..
2080 : : */
2081 : 207 : void __init page_writeback_init(void)
2082 : : {
2083 [ - + ]: 207 : BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2084 : :
2085 : : cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2086 : : page_writeback_cpu_online, NULL);
2087 : : cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2088 : : page_writeback_cpu_online);
2089 : 207 : }
2090 : :
2091 : : /**
2092 : : * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2093 : : * @mapping: address space structure to write
2094 : : * @start: starting page index
2095 : : * @end: ending page index (inclusive)
2096 : : *
2097 : : * This function scans the page range from @start to @end (inclusive) and tags
2098 : : * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2099 : : * that write_cache_pages (or whoever calls this function) will then use
2100 : : * TOWRITE tag to identify pages eligible for writeback. This mechanism is
2101 : : * used to avoid livelocking of writeback by a process steadily creating new
2102 : : * dirty pages in the file (thus it is important for this function to be quick
2103 : : * so that it can tag pages faster than a dirtying process can create them).
2104 : : */
2105 : 3355 : void tag_pages_for_writeback(struct address_space *mapping,
2106 : : pgoff_t start, pgoff_t end)
2107 : : {
2108 : 3355 : XA_STATE(xas, &mapping->i_pages, start);
2109 : : unsigned int tagged = 0;
2110 : : void *page;
2111 : :
2112 : : xas_lock_irq(&xas);
2113 [ + + ]: 25453 : xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) {
2114 : 22098 : xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
2115 [ + - ]: 22098 : if (++tagged % XA_CHECK_SCHED)
2116 : 22098 : continue;
2117 : :
2118 : 0 : xas_pause(&xas);
2119 : 0 : xas_unlock_irq(&xas);
2120 : 0 : cond_resched();
2121 : 0 : xas_lock_irq(&xas);
2122 : : }
2123 : 3355 : xas_unlock_irq(&xas);
2124 : 3355 : }
2125 : : EXPORT_SYMBOL(tag_pages_for_writeback);
2126 : :
2127 : : /**
2128 : : * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2129 : : * @mapping: address space structure to write
2130 : : * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2131 : : * @writepage: function called for each page
2132 : : * @data: data passed to writepage function
2133 : : *
2134 : : * If a page is already under I/O, write_cache_pages() skips it, even
2135 : : * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
2136 : : * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
2137 : : * and msync() need to guarantee that all the data which was dirty at the time
2138 : : * the call was made get new I/O started against them. If wbc->sync_mode is
2139 : : * WB_SYNC_ALL then we were called for data integrity and we must wait for
2140 : : * existing IO to complete.
2141 : : *
2142 : : * To avoid livelocks (when other process dirties new pages), we first tag
2143 : : * pages which should be written back with TOWRITE tag and only then start
2144 : : * writing them. For data-integrity sync we have to be careful so that we do
2145 : : * not miss some pages (e.g., because some other process has cleared TOWRITE
2146 : : * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2147 : : * by the process clearing the DIRTY tag (and submitting the page for IO).
2148 : : *
2149 : : * To avoid deadlocks between range_cyclic writeback and callers that hold
2150 : : * pages in PageWriteback to aggregate IO until write_cache_pages() returns,
2151 : : * we do not loop back to the start of the file. Doing so causes a page
2152 : : * lock/page writeback access order inversion - we should only ever lock
2153 : : * multiple pages in ascending page->index order, and looping back to the start
2154 : : * of the file violates that rule and causes deadlocks.
2155 : : *
2156 : : * Return: %0 on success, negative error code otherwise
2157 : : */
2158 : 2027 : int write_cache_pages(struct address_space *mapping,
2159 : : struct writeback_control *wbc, writepage_t writepage,
2160 : : void *data)
2161 : : {
2162 : : int ret = 0;
2163 : : int done = 0;
2164 : : int error;
2165 : : struct pagevec pvec;
2166 : : int nr_pages;
2167 : : pgoff_t uninitialized_var(writeback_index);
2168 : : pgoff_t index;
2169 : : pgoff_t end; /* Inclusive */
2170 : : pgoff_t done_index;
2171 : : int range_whole = 0;
2172 : : xa_mark_t tag;
2173 : :
2174 : : pagevec_init(&pvec);
2175 [ + + ]: 2027 : if (wbc->range_cyclic) {
2176 : 1509 : writeback_index = mapping->writeback_index; /* prev offset */
2177 : 1509 : index = writeback_index;
2178 : : end = -1;
2179 : : } else {
2180 : 518 : index = wbc->range_start >> PAGE_SHIFT;
2181 : 518 : end = wbc->range_end >> PAGE_SHIFT;
2182 [ + - + - ]: 518 : if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2183 : : range_whole = 1;
2184 : : }
2185 [ + + + - ]: 2027 : if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2186 : : tag = PAGECACHE_TAG_TOWRITE;
2187 : : else
2188 : : tag = PAGECACHE_TAG_DIRTY;
2189 [ + + - + ]: 2027 : if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2190 : 518 : tag_pages_for_writeback(mapping, index, end);
2191 : 2027 : done_index = index;
2192 [ + - ]: 10206 : while (!done && (index <= end)) {
2193 : : int i;
2194 : :
2195 : 8179 : nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
2196 : : tag);
2197 [ + + ]: 8179 : if (nr_pages == 0)
2198 : : break;
2199 : :
2200 [ + + ]: 72545 : for (i = 0; i < nr_pages; i++) {
2201 : 72545 : struct page *page = pvec.pages[i];
2202 : :
2203 : 72545 : done_index = page->index;
2204 : :
2205 : 72545 : lock_page(page);
2206 : :
2207 : : /*
2208 : : * Page truncated or invalidated. We can freely skip it
2209 : : * then, even for data integrity operations: the page
2210 : : * has disappeared concurrently, so there could be no
2211 : : * real expectation of this data interity operation
2212 : : * even if there is now a new, dirty page at the same
2213 : : * pagecache address.
2214 : : */
2215 [ - + ]: 72545 : if (unlikely(page->mapping != mapping)) {
2216 : : continue_unlock:
2217 : 0 : unlock_page(page);
2218 : 0 : continue;
2219 : : }
2220 : :
2221 [ - + ]: 72545 : if (!PageDirty(page)) {
2222 : : /* someone wrote it for us */
2223 : : goto continue_unlock;
2224 : : }
2225 : :
2226 [ - + ]: 72545 : if (PageWriteback(page)) {
2227 [ # # ]: 0 : if (wbc->sync_mode != WB_SYNC_NONE)
2228 : 0 : wait_on_page_writeback(page);
2229 : : else
2230 : : goto continue_unlock;
2231 : : }
2232 : :
2233 [ - + ]: 72545 : BUG_ON(PageWriteback(page));
2234 [ - + ]: 72545 : if (!clear_page_dirty_for_io(page))
2235 : : goto continue_unlock;
2236 : :
2237 : 72545 : trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2238 : 72545 : error = (*writepage)(page, wbc, data);
2239 [ - + ]: 72545 : if (unlikely(error)) {
2240 : : /*
2241 : : * Handle errors according to the type of
2242 : : * writeback. There's no need to continue for
2243 : : * background writeback. Just push done_index
2244 : : * past this page so media errors won't choke
2245 : : * writeout for the entire file. For integrity
2246 : : * writeback, we must process the entire dirty
2247 : : * set regardless of errors because the fs may
2248 : : * still have state to clear for each page. In
2249 : : * that case we continue processing and return
2250 : : * the first error.
2251 : : */
2252 [ # # ]: 0 : if (error == AOP_WRITEPAGE_ACTIVATE) {
2253 : 0 : unlock_page(page);
2254 : : error = 0;
2255 [ # # ]: 0 : } else if (wbc->sync_mode != WB_SYNC_ALL) {
2256 : 0 : ret = error;
2257 : 0 : done_index = page->index + 1;
2258 : : done = 1;
2259 : 0 : break;
2260 : : }
2261 [ # # ]: 0 : if (!ret)
2262 : : ret = error;
2263 : : }
2264 : :
2265 : : /*
2266 : : * We stop writing back only if we are not doing
2267 : : * integrity sync. In case of integrity sync we have to
2268 : : * keep going until we have written all the pages
2269 : : * we tagged for writeback prior to entering this loop.
2270 : : */
2271 [ - + # # ]: 72545 : if (--wbc->nr_to_write <= 0 &&
2272 : 0 : wbc->sync_mode == WB_SYNC_NONE) {
2273 : : done = 1;
2274 : : break;
2275 : : }
2276 : : }
2277 : : pagevec_release(&pvec);
2278 : 6152 : cond_resched();
2279 : : }
2280 : :
2281 : : /*
2282 : : * If we hit the last page and there is more work to be done: wrap
2283 : : * back the index back to the start of the file for the next
2284 : : * time we are called.
2285 : : */
2286 [ + + + - ]: 2027 : if (wbc->range_cyclic && !done)
2287 : : done_index = 0;
2288 [ + + + - : 2027 : if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
+ - ]
2289 : 2027 : mapping->writeback_index = done_index;
2290 : :
2291 : 2027 : return ret;
2292 : : }
2293 : : EXPORT_SYMBOL(write_cache_pages);
2294 : :
2295 : : /*
2296 : : * Function used by generic_writepages to call the real writepage
2297 : : * function and set the mapping flags on error
2298 : : */
2299 : 72545 : static int __writepage(struct page *page, struct writeback_control *wbc,
2300 : : void *data)
2301 : : {
2302 : : struct address_space *mapping = data;
2303 : 72545 : int ret = mapping->a_ops->writepage(page, wbc);
2304 : 72545 : mapping_set_error(mapping, ret);
2305 : 72545 : return ret;
2306 : : }
2307 : :
2308 : : /**
2309 : : * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2310 : : * @mapping: address space structure to write
2311 : : * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2312 : : *
2313 : : * This is a library function, which implements the writepages()
2314 : : * address_space_operation.
2315 : : *
2316 : : * Return: %0 on success, negative error code otherwise
2317 : : */
2318 : 24898 : int generic_writepages(struct address_space *mapping,
2319 : : struct writeback_control *wbc)
2320 : : {
2321 : : struct blk_plug plug;
2322 : : int ret;
2323 : :
2324 : : /* deal with chardevs and other special file */
2325 [ + + ]: 24898 : if (!mapping->a_ops->writepage)
2326 : : return 0;
2327 : :
2328 : 2027 : blk_start_plug(&plug);
2329 : 2027 : ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2330 : 2027 : blk_finish_plug(&plug);
2331 : 2027 : return ret;
2332 : : }
2333 : :
2334 : : EXPORT_SYMBOL(generic_writepages);
2335 : :
2336 : 40973 : int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2337 : : {
2338 : : int ret;
2339 : :
2340 [ + - ]: 40973 : if (wbc->nr_to_write <= 0)
2341 : : return 0;
2342 : : while (1) {
2343 [ + + ]: 40973 : if (mapping->a_ops->writepages)
2344 : 18102 : ret = mapping->a_ops->writepages(mapping, wbc);
2345 : : else
2346 : 22871 : ret = generic_writepages(mapping, wbc);
2347 [ - + # # ]: 40972 : if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
2348 : : break;
2349 : 0 : cond_resched();
2350 : 0 : congestion_wait(BLK_RW_ASYNC, HZ/50);
2351 : 0 : }
2352 : 40972 : return ret;
2353 : : }
2354 : :
2355 : : /**
2356 : : * write_one_page - write out a single page and wait on I/O
2357 : : * @page: the page to write
2358 : : *
2359 : : * The page must be locked by the caller and will be unlocked upon return.
2360 : : *
2361 : : * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
2362 : : * function returns.
2363 : : *
2364 : : * Return: %0 on success, negative error code otherwise
2365 : : */
2366 : 0 : int write_one_page(struct page *page)
2367 : : {
2368 : 0 : struct address_space *mapping = page->mapping;
2369 : : int ret = 0;
2370 : 0 : struct writeback_control wbc = {
2371 : : .sync_mode = WB_SYNC_ALL,
2372 : : .nr_to_write = 1,
2373 : : };
2374 : :
2375 [ # # ]: 0 : BUG_ON(!PageLocked(page));
2376 : :
2377 : 0 : wait_on_page_writeback(page);
2378 : :
2379 [ # # ]: 0 : if (clear_page_dirty_for_io(page)) {
2380 : 0 : get_page(page);
2381 : 0 : ret = mapping->a_ops->writepage(page, &wbc);
2382 [ # # ]: 0 : if (ret == 0)
2383 : 0 : wait_on_page_writeback(page);
2384 : 0 : put_page(page);
2385 : : } else {
2386 : 0 : unlock_page(page);
2387 : : }
2388 : :
2389 [ # # ]: 0 : if (!ret)
2390 : 0 : ret = filemap_check_errors(mapping);
2391 : 0 : return ret;
2392 : : }
2393 : : EXPORT_SYMBOL(write_one_page);
2394 : :
2395 : : /*
2396 : : * For address_spaces which do not use buffers nor write back.
2397 : : */
2398 : 2133943 : int __set_page_dirty_no_writeback(struct page *page)
2399 : : {
2400 [ + + ]: 2133815 : if (!PageDirty(page))
2401 : 1249668 : return !TestSetPageDirty(page);
2402 : : return 0;
2403 : : }
2404 : :
2405 : : /*
2406 : : * Helper function for set_page_dirty family.
2407 : : *
2408 : : * Caller must hold lock_page_memcg().
2409 : : *
2410 : : * NOTE: This relies on being atomic wrt interrupts.
2411 : : */
2412 : 187395 : void account_page_dirtied(struct page *page, struct address_space *mapping)
2413 : : {
2414 : 187395 : struct inode *inode = mapping->host;
2415 : :
2416 : 187395 : trace_writeback_dirty_page(page, mapping);
2417 : :
2418 [ + - ]: 187396 : if (mapping_cap_account_dirty(mapping)) {
2419 : : struct bdi_writeback *wb;
2420 : :
2421 : : inode_attach_wb(inode, page);
2422 : : wb = inode_to_wb(inode);
2423 : :
2424 : : __inc_lruvec_page_state(page, NR_FILE_DIRTY);
2425 : 187396 : __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2426 : 187396 : __inc_node_page_state(page, NR_DIRTIED);
2427 : : inc_wb_stat(wb, WB_RECLAIMABLE);
2428 : : inc_wb_stat(wb, WB_DIRTIED);
2429 : : task_io_account_write(PAGE_SIZE);
2430 : 187396 : current->nr_dirtied++;
2431 : 374792 : this_cpu_inc(bdp_ratelimits);
2432 : :
2433 : 187396 : mem_cgroup_track_foreign_dirty(page, wb);
2434 : : }
2435 : 187396 : }
2436 : :
2437 : : /*
2438 : : * Helper function for deaccounting dirty page without writeback.
2439 : : *
2440 : : * Caller must hold lock_page_memcg().
2441 : : */
2442 : 1561 : void account_page_cleaned(struct page *page, struct address_space *mapping,
2443 : : struct bdi_writeback *wb)
2444 : : {
2445 [ + - ]: 1561 : if (mapping_cap_account_dirty(mapping)) {
2446 : : dec_lruvec_page_state(page, NR_FILE_DIRTY);
2447 : 1561 : dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2448 : : dec_wb_stat(wb, WB_RECLAIMABLE);
2449 : : task_io_account_cancelled_write(PAGE_SIZE);
2450 : : }
2451 : 1561 : }
2452 : :
2453 : : /*
2454 : : * For address_spaces which do not use buffers. Just tag the page as dirty in
2455 : : * the xarray.
2456 : : *
2457 : : * This is also used when a single buffer is being dirtied: we want to set the
2458 : : * page dirty in that case, but not all the buffers. This is a "bottom-up"
2459 : : * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2460 : : *
2461 : : * The caller must ensure this doesn't race with truncation. Most will simply
2462 : : * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2463 : : * the pte lock held, which also locks out truncation.
2464 : : */
2465 : 0 : int __set_page_dirty_nobuffers(struct page *page)
2466 : : {
2467 : 0 : lock_page_memcg(page);
2468 [ # # ]: 0 : if (!TestSetPageDirty(page)) {
2469 : 0 : struct address_space *mapping = page_mapping(page);
2470 : : unsigned long flags;
2471 : :
2472 [ # # ]: 0 : if (!mapping) {
2473 : 0 : unlock_page_memcg(page);
2474 : 0 : return 1;
2475 : : }
2476 : :
2477 : 0 : xa_lock_irqsave(&mapping->i_pages, flags);
2478 [ # # ]: 0 : BUG_ON(page_mapping(page) != mapping);
2479 [ # # # # : 0 : WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
# # # # ]
2480 : 0 : account_page_dirtied(page, mapping);
2481 : 0 : __xa_set_mark(&mapping->i_pages, page_index(page),
2482 : : PAGECACHE_TAG_DIRTY);
2483 : : xa_unlock_irqrestore(&mapping->i_pages, flags);
2484 : 0 : unlock_page_memcg(page);
2485 : :
2486 [ # # ]: 0 : if (mapping->host) {
2487 : : /* !PageAnon && !swapper_space */
2488 : 0 : __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2489 : : }
2490 : : return 1;
2491 : : }
2492 : 0 : unlock_page_memcg(page);
2493 : 0 : return 0;
2494 : : }
2495 : : EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2496 : :
2497 : : /*
2498 : : * Call this whenever redirtying a page, to de-account the dirty counters
2499 : : * (NR_DIRTIED, WB_DIRTIED, tsk->nr_dirtied), so that they match the written
2500 : : * counters (NR_WRITTEN, WB_WRITTEN) in long term. The mismatches will lead to
2501 : : * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2502 : : * control.
2503 : : */
2504 : 0 : void account_page_redirty(struct page *page)
2505 : : {
2506 : 0 : struct address_space *mapping = page->mapping;
2507 : :
2508 [ # # # # ]: 0 : if (mapping && mapping_cap_account_dirty(mapping)) {
2509 : 0 : struct inode *inode = mapping->host;
2510 : : struct bdi_writeback *wb;
2511 : 0 : struct wb_lock_cookie cookie = {};
2512 : :
2513 : 0 : wb = unlocked_inode_to_wb_begin(inode, &cookie);
2514 : 0 : current->nr_dirtied--;
2515 : 0 : dec_node_page_state(page, NR_DIRTIED);
2516 : : dec_wb_stat(wb, WB_DIRTIED);
2517 : : unlocked_inode_to_wb_end(inode, &cookie);
2518 : : }
2519 : 0 : }
2520 : : EXPORT_SYMBOL(account_page_redirty);
2521 : :
2522 : : /*
2523 : : * When a writepage implementation decides that it doesn't want to write this
2524 : : * page for some reason, it should redirty the locked page via
2525 : : * redirty_page_for_writepage() and it should then unlock the page and return 0
2526 : : */
2527 : 0 : int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2528 : : {
2529 : : int ret;
2530 : :
2531 : 0 : wbc->pages_skipped++;
2532 : 0 : ret = __set_page_dirty_nobuffers(page);
2533 : 0 : account_page_redirty(page);
2534 : 0 : return ret;
2535 : : }
2536 : : EXPORT_SYMBOL(redirty_page_for_writepage);
2537 : :
2538 : : /*
2539 : : * Dirty a page.
2540 : : *
2541 : : * For pages with a mapping this should be done under the page lock
2542 : : * for the benefit of asynchronous memory errors who prefer a consistent
2543 : : * dirty state. This rule can be broken in some special cases,
2544 : : * but should be better not to.
2545 : : *
2546 : : * If the mapping doesn't provide a set_page_dirty a_op, then
2547 : : * just fall through and assume that it wants buffer_heads.
2548 : : */
2549 : 2138376 : int set_page_dirty(struct page *page)
2550 : : {
2551 : 2138376 : struct address_space *mapping = page_mapping(page);
2552 : :
2553 : : page = compound_head(page);
2554 [ + + ]: 2138225 : if (likely(mapping)) {
2555 : 2136983 : int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2556 : : /*
2557 : : * readahead/lru_deactivate_page could remain
2558 : : * PG_readahead/PG_reclaim due to race with end_page_writeback
2559 : : * About readahead, if the page is written, the flags would be
2560 : : * reset. So no problem.
2561 : : * About lru_deactivate_page, if the page is redirty, the flag
2562 : : * will be reset. So no problem. but if the page is used by readahead
2563 : : * it will confuse readahead and make it restart the size rampup
2564 : : * process. But it's a trivial problem.
2565 : : */
2566 [ - + ]: 2137147 : if (PageReclaim(page))
2567 : : ClearPageReclaim(page);
2568 : : #ifdef CONFIG_BLOCK
2569 [ - + ]: 2137101 : if (!spd)
2570 : : spd = __set_page_dirty_buffers;
2571 : : #endif
2572 : 2137101 : return (*spd)(page);
2573 : : }
2574 [ + + ]: 1242 : if (!PageDirty(page)) {
2575 [ - + ]: 414 : if (!TestSetPageDirty(page))
2576 : : return 1;
2577 : : }
2578 : : return 0;
2579 : : }
2580 : : EXPORT_SYMBOL(set_page_dirty);
2581 : :
2582 : : /*
2583 : : * set_page_dirty() is racy if the caller has no reference against
2584 : : * page->mapping->host, and if the page is unlocked. This is because another
2585 : : * CPU could truncate the page off the mapping and then free the mapping.
2586 : : *
2587 : : * Usually, the page _is_ locked, or the caller is a user-space process which
2588 : : * holds a reference on the inode by having an open file.
2589 : : *
2590 : : * In other cases, the page should be locked before running set_page_dirty().
2591 : : */
2592 : 1242 : int set_page_dirty_lock(struct page *page)
2593 : : {
2594 : : int ret;
2595 : :
2596 : 1242 : lock_page(page);
2597 : 1242 : ret = set_page_dirty(page);
2598 : 1242 : unlock_page(page);
2599 : 1242 : return ret;
2600 : : }
2601 : : EXPORT_SYMBOL(set_page_dirty_lock);
2602 : :
2603 : : /*
2604 : : * This cancels just the dirty bit on the kernel page itself, it does NOT
2605 : : * actually remove dirty bits on any mmap's that may be around. It also
2606 : : * leaves the page tagged dirty, so any sync activity will still find it on
2607 : : * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2608 : : * look at the dirty bits in the VM.
2609 : : *
2610 : : * Doing this should *normally* only ever be done when a page is truncated,
2611 : : * and is not actually mapped anywhere at all. However, fs/buffer.c does
2612 : : * this when it notices that somebody has cleaned out all the buffers on a
2613 : : * page without actually doing it through the VM. Can you say "ext3 is
2614 : : * horribly ugly"? Thought you could.
2615 : : */
2616 : 857480 : void __cancel_dirty_page(struct page *page)
2617 : : {
2618 : 857480 : struct address_space *mapping = page_mapping(page);
2619 : :
2620 [ + + ]: 857480 : if (mapping_cap_account_dirty(mapping)) {
2621 : 1561 : struct inode *inode = mapping->host;
2622 : : struct bdi_writeback *wb;
2623 : 1561 : struct wb_lock_cookie cookie = {};
2624 : :
2625 : 1561 : lock_page_memcg(page);
2626 : 1561 : wb = unlocked_inode_to_wb_begin(inode, &cookie);
2627 : :
2628 [ + - ]: 1561 : if (TestClearPageDirty(page))
2629 : 1561 : account_page_cleaned(page, mapping, wb);
2630 : :
2631 : : unlocked_inode_to_wb_end(inode, &cookie);
2632 : 1561 : unlock_page_memcg(page);
2633 : : } else {
2634 : : ClearPageDirty(page);
2635 : : }
2636 : 857480 : }
2637 : : EXPORT_SYMBOL(__cancel_dirty_page);
2638 : :
2639 : : /*
2640 : : * Clear a page's dirty flag, while caring for dirty memory accounting.
2641 : : * Returns true if the page was previously dirty.
2642 : : *
2643 : : * This is for preparing to put the page under writeout. We leave the page
2644 : : * tagged as dirty in the xarray so that a concurrent write-for-sync
2645 : : * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2646 : : * implementation will run either set_page_writeback() or set_page_dirty(),
2647 : : * at which stage we bring the page's dirty flag and xarray dirty tag
2648 : : * back into sync.
2649 : : *
2650 : : * This incoherency between the page's dirty flag and xarray tag is
2651 : : * unfortunate, but it only exists while the page is locked.
2652 : : */
2653 : 101755 : int clear_page_dirty_for_io(struct page *page)
2654 : : {
2655 : 101755 : struct address_space *mapping = page_mapping(page);
2656 : : int ret = 0;
2657 : :
2658 [ - + ]: 101755 : BUG_ON(!PageLocked(page));
2659 : :
2660 [ + - + - ]: 203510 : if (mapping && mapping_cap_account_dirty(mapping)) {
2661 : 101755 : struct inode *inode = mapping->host;
2662 : : struct bdi_writeback *wb;
2663 : 101755 : struct wb_lock_cookie cookie = {};
2664 : :
2665 : : /*
2666 : : * Yes, Virginia, this is indeed insane.
2667 : : *
2668 : : * We use this sequence to make sure that
2669 : : * (a) we account for dirty stats properly
2670 : : * (b) we tell the low-level filesystem to
2671 : : * mark the whole page dirty if it was
2672 : : * dirty in a pagetable. Only to then
2673 : : * (c) clean the page again and return 1 to
2674 : : * cause the writeback.
2675 : : *
2676 : : * This way we avoid all nasty races with the
2677 : : * dirty bit in multiple places and clearing
2678 : : * them concurrently from different threads.
2679 : : *
2680 : : * Note! Normally the "set_page_dirty(page)"
2681 : : * has no effect on the actual dirty bit - since
2682 : : * that will already usually be set. But we
2683 : : * need the side effects, and it can help us
2684 : : * avoid races.
2685 : : *
2686 : : * We basically use the page "master dirty bit"
2687 : : * as a serialization point for all the different
2688 : : * threads doing their things.
2689 : : */
2690 [ + + ]: 101755 : if (page_mkclean(page))
2691 : 140 : set_page_dirty(page);
2692 : : /*
2693 : : * We carefully synchronise fault handlers against
2694 : : * installing a dirty pte and marking the page dirty
2695 : : * at this point. We do this by having them hold the
2696 : : * page lock while dirtying the page, and pages are
2697 : : * always locked coming in here, so we get the desired
2698 : : * exclusion.
2699 : : */
2700 : 101755 : wb = unlocked_inode_to_wb_begin(inode, &cookie);
2701 [ + - ]: 101755 : if (TestClearPageDirty(page)) {
2702 : : dec_lruvec_page_state(page, NR_FILE_DIRTY);
2703 : 101755 : dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2704 : : dec_wb_stat(wb, WB_RECLAIMABLE);
2705 : : ret = 1;
2706 : : }
2707 : : unlocked_inode_to_wb_end(inode, &cookie);
2708 : : return ret;
2709 : : }
2710 : 0 : return TestClearPageDirty(page);
2711 : : }
2712 : : EXPORT_SYMBOL(clear_page_dirty_for_io);
2713 : :
2714 : 101720 : int test_clear_page_writeback(struct page *page)
2715 : : {
2716 : 101720 : struct address_space *mapping = page_mapping(page);
2717 : : struct mem_cgroup *memcg;
2718 : : struct lruvec *lruvec;
2719 : : int ret;
2720 : :
2721 : 101720 : memcg = lock_page_memcg(page);
2722 : 101720 : lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
2723 [ + - + - ]: 203440 : if (mapping && mapping_use_writeback_tags(mapping)) {
2724 : 101720 : struct inode *inode = mapping->host;
2725 : 101720 : struct backing_dev_info *bdi = inode_to_bdi(inode);
2726 : : unsigned long flags;
2727 : :
2728 : 101720 : xa_lock_irqsave(&mapping->i_pages, flags);
2729 : : ret = TestClearPageWriteback(page);
2730 [ + - ]: 101720 : if (ret) {
2731 : 101720 : __xa_clear_mark(&mapping->i_pages, page_index(page),
2732 : : PAGECACHE_TAG_WRITEBACK);
2733 [ + - ]: 101720 : if (bdi_cap_account_writeback(bdi)) {
2734 : : struct bdi_writeback *wb = inode_to_wb(inode);
2735 : :
2736 : : dec_wb_stat(wb, WB_WRITEBACK);
2737 : 101720 : __wb_writeout_inc(wb);
2738 : : }
2739 : : }
2740 : :
2741 [ + - + + ]: 203440 : if (mapping->host && !mapping_tagged(mapping,
2742 : : PAGECACHE_TAG_WRITEBACK))
2743 : 17330 : sb_clear_inode_writeback(mapping->host);
2744 : :
2745 : : xa_unlock_irqrestore(&mapping->i_pages, flags);
2746 : : } else {
2747 : : ret = TestClearPageWriteback(page);
2748 : : }
2749 : : /*
2750 : : * NOTE: Page might be free now! Writeback doesn't hold a page
2751 : : * reference on its own, it relies on truncation to wait for
2752 : : * the clearing of PG_writeback. The below can only access
2753 : : * page state that is static across allocation cycles.
2754 : : */
2755 [ + - ]: 101720 : if (ret) {
2756 : : dec_lruvec_state(lruvec, NR_WRITEBACK);
2757 : 101720 : dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2758 : 101720 : inc_node_page_state(page, NR_WRITTEN);
2759 : : }
2760 : 101720 : __unlock_page_memcg(memcg);
2761 : 101720 : return ret;
2762 : : }
2763 : :
2764 : 101755 : int __test_set_page_writeback(struct page *page, bool keep_write)
2765 : : {
2766 : 101755 : struct address_space *mapping = page_mapping(page);
2767 : : int ret;
2768 : :
2769 : 101755 : lock_page_memcg(page);
2770 [ + - + - ]: 305265 : if (mapping && mapping_use_writeback_tags(mapping)) {
2771 : 101755 : XA_STATE(xas, &mapping->i_pages, page_index(page));
2772 : 101755 : struct inode *inode = mapping->host;
2773 : 101755 : struct backing_dev_info *bdi = inode_to_bdi(inode);
2774 : : unsigned long flags;
2775 : :
2776 : 203510 : xas_lock_irqsave(&xas, flags);
2777 : 101755 : xas_load(&xas);
2778 : : ret = TestSetPageWriteback(page);
2779 [ + - ]: 101755 : if (!ret) {
2780 : : bool on_wblist;
2781 : :
2782 : : on_wblist = mapping_tagged(mapping,
2783 : : PAGECACHE_TAG_WRITEBACK);
2784 : :
2785 : 101755 : xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
2786 [ + - ]: 101755 : if (bdi_cap_account_writeback(bdi))
2787 : : inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
2788 : :
2789 : : /*
2790 : : * We can come through here when swapping anonymous
2791 : : * pages, so we don't necessarily have an inode to track
2792 : : * for sync.
2793 : : */
2794 [ + - + + ]: 101755 : if (mapping->host && !on_wblist)
2795 : 17351 : sb_mark_inode_writeback(mapping->host);
2796 : : }
2797 [ + - ]: 101755 : if (!PageDirty(page))
2798 : 101755 : xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
2799 [ + - ]: 101755 : if (!keep_write)
2800 : 101755 : xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
2801 : 101755 : xas_unlock_irqrestore(&xas, flags);
2802 : : } else {
2803 : : ret = TestSetPageWriteback(page);
2804 : : }
2805 [ + - ]: 101755 : if (!ret) {
2806 : : inc_lruvec_page_state(page, NR_WRITEBACK);
2807 : 101755 : inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2808 : : }
2809 : 101755 : unlock_page_memcg(page);
2810 : 101755 : return ret;
2811 : :
2812 : : }
2813 : : EXPORT_SYMBOL(__test_set_page_writeback);
2814 : :
2815 : : /*
2816 : : * Wait for a page to complete writeback
2817 : : */
2818 : 73411 : void wait_on_page_writeback(struct page *page)
2819 : : {
2820 [ + + ]: 73411 : if (PageWriteback(page)) {
2821 : 12950 : trace_wait_on_page_writeback(page, page_mapping(page));
2822 : 12950 : wait_on_page_bit(page, PG_writeback);
2823 : : }
2824 : 73411 : }
2825 : : EXPORT_SYMBOL_GPL(wait_on_page_writeback);
2826 : :
2827 : : /**
2828 : : * wait_for_stable_page() - wait for writeback to finish, if necessary.
2829 : : * @page: The page to wait on.
2830 : : *
2831 : : * This function determines if the given page is related to a backing device
2832 : : * that requires page contents to be held stable during writeback. If so, then
2833 : : * it will wait for any pending writeback to complete.
2834 : : */
2835 : 670698 : void wait_for_stable_page(struct page *page)
2836 : : {
2837 [ - + ]: 1341401 : if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host)))
2838 : 0 : wait_on_page_writeback(page);
2839 : 670703 : }
2840 : : EXPORT_SYMBOL_GPL(wait_for_stable_page);
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