1 | /* |
2 | * mm/page-writeback.c |
3 | * |
4 | * Copyright (C) 2002, Linus Torvalds. |
5 | * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra |
6 | * |
7 | * Contains functions related to writing back dirty pages at the |
8 | * address_space level. |
9 | * |
10 | * 10Apr2002 Andrew Morton |
11 | * Initial version |
12 | */ |
13 | |
14 | #include <linux/kernel.h> |
15 | #include <linux/export.h> |
16 | #include <linux/spinlock.h> |
17 | #include <linux/fs.h> |
18 | #include <linux/mm.h> |
19 | #include <linux/swap.h> |
20 | #include <linux/slab.h> |
21 | #include <linux/pagemap.h> |
22 | #include <linux/writeback.h> |
23 | #include <linux/init.h> |
24 | #include <linux/backing-dev.h> |
25 | #include <linux/task_io_accounting_ops.h> |
26 | #include <linux/blkdev.h> |
27 | #include <linux/mpage.h> |
28 | #include <linux/rmap.h> |
29 | #include <linux/percpu.h> |
30 | #include <linux/smp.h> |
31 | #include <linux/sysctl.h> |
32 | #include <linux/cpu.h> |
33 | #include <linux/syscalls.h> |
34 | #include <linux/buffer_head.h> /* __set_page_dirty_buffers */ |
35 | #include <linux/pagevec.h> |
36 | #include <linux/timer.h> |
37 | #include <linux/sched/rt.h> |
38 | #include <linux/sched/signal.h> |
39 | #include <linux/mm_inline.h> |
40 | #include <trace/events/writeback.h> |
41 | |
42 | #include "internal.h" |
43 | |
44 | /* |
45 | * Sleep at most 200ms at a time in balance_dirty_pages(). |
46 | */ |
47 | #define MAX_PAUSE max(HZ/5, 1) |
48 | |
49 | /* |
50 | * Try to keep balance_dirty_pages() call intervals higher than this many pages |
51 | * by raising pause time to max_pause when falls below it. |
52 | */ |
53 | #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10)) |
54 | |
55 | /* |
56 | * Estimate write bandwidth at 200ms intervals. |
57 | */ |
58 | #define BANDWIDTH_INTERVAL max(HZ/5, 1) |
59 | |
60 | #define RATELIMIT_CALC_SHIFT 10 |
61 | |
62 | /* |
63 | * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited |
64 | * will look to see if it needs to force writeback or throttling. |
65 | */ |
66 | static long ratelimit_pages = 32; |
67 | |
68 | /* The following parameters are exported via /proc/sys/vm */ |
69 | |
70 | /* |
71 | * Start background writeback (via writeback threads) at this percentage |
72 | */ |
73 | int dirty_background_ratio = 10; |
74 | |
75 | /* |
76 | * dirty_background_bytes starts at 0 (disabled) so that it is a function of |
77 | * dirty_background_ratio * the amount of dirtyable memory |
78 | */ |
79 | unsigned long dirty_background_bytes; |
80 | |
81 | /* |
82 | * free highmem will not be subtracted from the total free memory |
83 | * for calculating free ratios if vm_highmem_is_dirtyable is true |
84 | */ |
85 | int vm_highmem_is_dirtyable; |
86 | |
87 | /* |
88 | * The generator of dirty data starts writeback at this percentage |
89 | */ |
90 | int vm_dirty_ratio = 20; |
91 | |
92 | /* |
93 | * vm_dirty_bytes starts at 0 (disabled) so that it is a function of |
94 | * vm_dirty_ratio * the amount of dirtyable memory |
95 | */ |
96 | unsigned long vm_dirty_bytes; |
97 | |
98 | /* |
99 | * The interval between `kupdate'-style writebacks |
100 | */ |
101 | unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ |
102 | |
103 | EXPORT_SYMBOL_GPL(dirty_writeback_interval); |
104 | |
105 | /* |
106 | * The longest time for which data is allowed to remain dirty |
107 | */ |
108 | unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ |
109 | |
110 | /* |
111 | * Flag that makes the machine dump writes/reads and block dirtyings. |
112 | */ |
113 | int block_dump; |
114 | |
115 | /* |
116 | * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: |
117 | * a full sync is triggered after this time elapses without any disk activity. |
118 | */ |
119 | int laptop_mode; |
120 | |
121 | EXPORT_SYMBOL(laptop_mode); |
122 | |
123 | /* End of sysctl-exported parameters */ |
124 | |
125 | struct wb_domain global_wb_domain; |
126 | |
127 | /* consolidated parameters for balance_dirty_pages() and its subroutines */ |
128 | struct dirty_throttle_control { |
129 | #ifdef CONFIG_CGROUP_WRITEBACK |
130 | struct wb_domain *dom; |
131 | struct dirty_throttle_control *gdtc; /* only set in memcg dtc's */ |
132 | #endif |
133 | struct bdi_writeback *wb; |
134 | struct fprop_local_percpu *wb_completions; |
135 | |
136 | unsigned long avail; /* dirtyable */ |
137 | unsigned long dirty; /* file_dirty + write + nfs */ |
138 | unsigned long thresh; /* dirty threshold */ |
139 | unsigned long bg_thresh; /* dirty background threshold */ |
140 | |
141 | unsigned long wb_dirty; /* per-wb counterparts */ |
142 | unsigned long wb_thresh; |
143 | unsigned long wb_bg_thresh; |
144 | |
145 | unsigned long pos_ratio; |
146 | }; |
147 | |
148 | /* |
149 | * Length of period for aging writeout fractions of bdis. This is an |
150 | * arbitrarily chosen number. The longer the period, the slower fractions will |
151 | * reflect changes in current writeout rate. |
152 | */ |
153 | #define VM_COMPLETIONS_PERIOD_LEN (3*HZ) |
154 | |
155 | #ifdef CONFIG_CGROUP_WRITEBACK |
156 | |
157 | #define GDTC_INIT(__wb) .wb = (__wb), \ |
158 | .dom = &global_wb_domain, \ |
159 | .wb_completions = &(__wb)->completions |
160 | |
161 | #define GDTC_INIT_NO_WB .dom = &global_wb_domain |
162 | |
163 | #define MDTC_INIT(__wb, __gdtc) .wb = (__wb), \ |
164 | .dom = mem_cgroup_wb_domain(__wb), \ |
165 | .wb_completions = &(__wb)->memcg_completions, \ |
166 | .gdtc = __gdtc |
167 | |
168 | static bool mdtc_valid(struct dirty_throttle_control *dtc) |
169 | { |
170 | return dtc->dom; |
171 | } |
172 | |
173 | static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc) |
174 | { |
175 | return dtc->dom; |
176 | } |
177 | |
178 | static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc) |
179 | { |
180 | return mdtc->gdtc; |
181 | } |
182 | |
183 | static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb) |
184 | { |
185 | return &wb->memcg_completions; |
186 | } |
187 | |
188 | static void wb_min_max_ratio(struct bdi_writeback *wb, |
189 | unsigned long *minp, unsigned long *maxp) |
190 | { |
191 | unsigned long this_bw = wb->avg_write_bandwidth; |
192 | unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth); |
193 | unsigned long long min = wb->bdi->min_ratio; |
194 | unsigned long long max = wb->bdi->max_ratio; |
195 | |
196 | /* |
197 | * @wb may already be clean by the time control reaches here and |
198 | * the total may not include its bw. |
199 | */ |
200 | if (this_bw < tot_bw) { |
201 | if (min) { |
202 | min *= this_bw; |
203 | do_div(min, tot_bw); |
204 | } |
205 | if (max < 100) { |
206 | max *= this_bw; |
207 | do_div(max, tot_bw); |
208 | } |
209 | } |
210 | |
211 | *minp = min; |
212 | *maxp = max; |
213 | } |
214 | |
215 | #else /* CONFIG_CGROUP_WRITEBACK */ |
216 | |
217 | #define GDTC_INIT(__wb) .wb = (__wb), \ |
218 | .wb_completions = &(__wb)->completions |
219 | #define GDTC_INIT_NO_WB |
220 | #define MDTC_INIT(__wb, __gdtc) |
221 | |
222 | static bool mdtc_valid(struct dirty_throttle_control *dtc) |
223 | { |
224 | return false; |
225 | } |
226 | |
227 | static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc) |
228 | { |
229 | return &global_wb_domain; |
230 | } |
231 | |
232 | static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc) |
233 | { |
234 | return NULL; |
235 | } |
236 | |
237 | static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb) |
238 | { |
239 | return NULL; |
240 | } |
241 | |
242 | static void wb_min_max_ratio(struct bdi_writeback *wb, |
243 | unsigned long *minp, unsigned long *maxp) |
244 | { |
245 | *minp = wb->bdi->min_ratio; |
246 | *maxp = wb->bdi->max_ratio; |
247 | } |
248 | |
249 | #endif /* CONFIG_CGROUP_WRITEBACK */ |
250 | |
251 | /* |
252 | * In a memory zone, there is a certain amount of pages we consider |
253 | * available for the page cache, which is essentially the number of |
254 | * free and reclaimable pages, minus some zone reserves to protect |
255 | * lowmem and the ability to uphold the zone's watermarks without |
256 | * requiring writeback. |
257 | * |
258 | * This number of dirtyable pages is the base value of which the |
259 | * user-configurable dirty ratio is the effictive number of pages that |
260 | * are allowed to be actually dirtied. Per individual zone, or |
261 | * globally by using the sum of dirtyable pages over all zones. |
262 | * |
263 | * Because the user is allowed to specify the dirty limit globally as |
264 | * absolute number of bytes, calculating the per-zone dirty limit can |
265 | * require translating the configured limit into a percentage of |
266 | * global dirtyable memory first. |
267 | */ |
268 | |
269 | /** |
270 | * node_dirtyable_memory - number of dirtyable pages in a node |
271 | * @pgdat: the node |
272 | * |
273 | * Return: the node's number of pages potentially available for dirty |
274 | * page cache. This is the base value for the per-node dirty limits. |
275 | */ |
276 | static unsigned long node_dirtyable_memory(struct pglist_data *pgdat) |
277 | { |
278 | unsigned long nr_pages = 0; |
279 | int z; |
280 | |
281 | for (z = 0; z < MAX_NR_ZONES; z++) { |
282 | struct zone *zone = pgdat->node_zones + z; |
283 | |
284 | if (!populated_zone(zone)) |
285 | continue; |
286 | |
287 | nr_pages += zone_page_state(zone, NR_FREE_PAGES); |
288 | } |
289 | |
290 | /* |
291 | * Pages reserved for the kernel should not be considered |
292 | * dirtyable, to prevent a situation where reclaim has to |
293 | * clean pages in order to balance the zones. |
294 | */ |
295 | nr_pages -= min(nr_pages, pgdat->totalreserve_pages); |
296 | |
297 | nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE); |
298 | nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE); |
299 | |
300 | return nr_pages; |
301 | } |
302 | |
303 | static unsigned long highmem_dirtyable_memory(unsigned long total) |
304 | { |
305 | #ifdef CONFIG_HIGHMEM |
306 | int node; |
307 | unsigned long x = 0; |
308 | int i; |
309 | |
310 | for_each_node_state(node, N_HIGH_MEMORY) { |
311 | for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) { |
312 | struct zone *z; |
313 | unsigned long nr_pages; |
314 | |
315 | if (!is_highmem_idx(i)) |
316 | continue; |
317 | |
318 | z = &NODE_DATA(node)->node_zones[i]; |
319 | if (!populated_zone(z)) |
320 | continue; |
321 | |
322 | nr_pages = zone_page_state(z, NR_FREE_PAGES); |
323 | /* watch for underflows */ |
324 | nr_pages -= min(nr_pages, high_wmark_pages(z)); |
325 | nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE); |
326 | nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE); |
327 | x += nr_pages; |
328 | } |
329 | } |
330 | |
331 | /* |
332 | * Unreclaimable memory (kernel memory or anonymous memory |
333 | * without swap) can bring down the dirtyable pages below |
334 | * the zone's dirty balance reserve and the above calculation |
335 | * will underflow. However we still want to add in nodes |
336 | * which are below threshold (negative values) to get a more |
337 | * accurate calculation but make sure that the total never |
338 | * underflows. |
339 | */ |
340 | if ((long)x < 0) |
341 | x = 0; |
342 | |
343 | /* |
344 | * Make sure that the number of highmem pages is never larger |
345 | * than the number of the total dirtyable memory. This can only |
346 | * occur in very strange VM situations but we want to make sure |
347 | * that this does not occur. |
348 | */ |
349 | return min(x, total); |
350 | #else |
351 | return 0; |
352 | #endif |
353 | } |
354 | |
355 | /** |
356 | * global_dirtyable_memory - number of globally dirtyable pages |
357 | * |
358 | * Return: the global number of pages potentially available for dirty |
359 | * page cache. This is the base value for the global dirty limits. |
360 | */ |
361 | static unsigned long global_dirtyable_memory(void) |
362 | { |
363 | unsigned long x; |
364 | |
365 | x = global_zone_page_state(NR_FREE_PAGES); |
366 | /* |
367 | * Pages reserved for the kernel should not be considered |
368 | * dirtyable, to prevent a situation where reclaim has to |
369 | * clean pages in order to balance the zones. |
370 | */ |
371 | x -= min(x, totalreserve_pages); |
372 | |
373 | x += global_node_page_state(NR_INACTIVE_FILE); |
374 | x += global_node_page_state(NR_ACTIVE_FILE); |
375 | |
376 | if (!vm_highmem_is_dirtyable) |
377 | x -= highmem_dirtyable_memory(x); |
378 | |
379 | return x + 1; /* Ensure that we never return 0 */ |
380 | } |
381 | |
382 | /** |
383 | * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain |
384 | * @dtc: dirty_throttle_control of interest |
385 | * |
386 | * Calculate @dtc->thresh and ->bg_thresh considering |
387 | * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller |
388 | * must ensure that @dtc->avail is set before calling this function. The |
389 | * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and |
390 | * real-time tasks. |
391 | */ |
392 | static void domain_dirty_limits(struct dirty_throttle_control *dtc) |
393 | { |
394 | const unsigned long available_memory = dtc->avail; |
395 | struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc); |
396 | unsigned long bytes = vm_dirty_bytes; |
397 | unsigned long bg_bytes = dirty_background_bytes; |
398 | /* convert ratios to per-PAGE_SIZE for higher precision */ |
399 | unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100; |
400 | unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100; |
401 | unsigned long thresh; |
402 | unsigned long bg_thresh; |
403 | struct task_struct *tsk; |
404 | |
405 | /* gdtc is !NULL iff @dtc is for memcg domain */ |
406 | if (gdtc) { |
407 | unsigned long global_avail = gdtc->avail; |
408 | |
409 | /* |
410 | * The byte settings can't be applied directly to memcg |
411 | * domains. Convert them to ratios by scaling against |
412 | * globally available memory. As the ratios are in |
413 | * per-PAGE_SIZE, they can be obtained by dividing bytes by |
414 | * number of pages. |
415 | */ |
416 | if (bytes) |
417 | ratio = min(DIV_ROUND_UP(bytes, global_avail), |
418 | PAGE_SIZE); |
419 | if (bg_bytes) |
420 | bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail), |
421 | PAGE_SIZE); |
422 | bytes = bg_bytes = 0; |
423 | } |
424 | |
425 | if (bytes) |
426 | thresh = DIV_ROUND_UP(bytes, PAGE_SIZE); |
427 | else |
428 | thresh = (ratio * available_memory) / PAGE_SIZE; |
429 | |
430 | if (bg_bytes) |
431 | bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE); |
432 | else |
433 | bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE; |
434 | |
435 | if (bg_thresh >= thresh) |
436 | bg_thresh = thresh / 2; |
437 | tsk = current; |
438 | if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { |
439 | bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32; |
440 | thresh += thresh / 4 + global_wb_domain.dirty_limit / 32; |
441 | } |
442 | dtc->thresh = thresh; |
443 | dtc->bg_thresh = bg_thresh; |
444 | |
445 | /* we should eventually report the domain in the TP */ |
446 | if (!gdtc) |
447 | trace_global_dirty_state(bg_thresh, thresh); |
448 | } |
449 | |
450 | /** |
451 | * global_dirty_limits - background-writeback and dirty-throttling thresholds |
452 | * @pbackground: out parameter for bg_thresh |
453 | * @pdirty: out parameter for thresh |
454 | * |
455 | * Calculate bg_thresh and thresh for global_wb_domain. See |
456 | * domain_dirty_limits() for details. |
457 | */ |
458 | void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) |
459 | { |
460 | struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB }; |
461 | |
462 | gdtc.avail = global_dirtyable_memory(); |
463 | domain_dirty_limits(&gdtc); |
464 | |
465 | *pbackground = gdtc.bg_thresh; |
466 | *pdirty = gdtc.thresh; |
467 | } |
468 | |
469 | /** |
470 | * node_dirty_limit - maximum number of dirty pages allowed in a node |
471 | * @pgdat: the node |
472 | * |
473 | * Return: the maximum number of dirty pages allowed in a node, based |
474 | * on the node's dirtyable memory. |
475 | */ |
476 | static unsigned long node_dirty_limit(struct pglist_data *pgdat) |
477 | { |
478 | unsigned long node_memory = node_dirtyable_memory(pgdat); |
479 | struct task_struct *tsk = current; |
480 | unsigned long dirty; |
481 | |
482 | if (vm_dirty_bytes) |
483 | dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) * |
484 | node_memory / global_dirtyable_memory(); |
485 | else |
486 | dirty = vm_dirty_ratio * node_memory / 100; |
487 | |
488 | if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) |
489 | dirty += dirty / 4; |
490 | |
491 | return dirty; |
492 | } |
493 | |
494 | /** |
495 | * node_dirty_ok - tells whether a node is within its dirty limits |
496 | * @pgdat: the node to check |
497 | * |
498 | * Return: %true when the dirty pages in @pgdat are within the node's |
499 | * dirty limit, %false if the limit is exceeded. |
500 | */ |
501 | bool node_dirty_ok(struct pglist_data *pgdat) |
502 | { |
503 | unsigned long limit = node_dirty_limit(pgdat); |
504 | unsigned long nr_pages = 0; |
505 | |
506 | nr_pages += node_page_state(pgdat, NR_FILE_DIRTY); |
507 | nr_pages += node_page_state(pgdat, NR_UNSTABLE_NFS); |
508 | nr_pages += node_page_state(pgdat, NR_WRITEBACK); |
509 | |
510 | return nr_pages <= limit; |
511 | } |
512 | |
513 | int dirty_background_ratio_handler(struct ctl_table *table, int write, |
514 | void __user *buffer, size_t *lenp, |
515 | loff_t *ppos) |
516 | { |
517 | int ret; |
518 | |
519 | ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
520 | if (ret == 0 && write) |
521 | dirty_background_bytes = 0; |
522 | return ret; |
523 | } |
524 | |
525 | int dirty_background_bytes_handler(struct ctl_table *table, int write, |
526 | void __user *buffer, size_t *lenp, |
527 | loff_t *ppos) |
528 | { |
529 | int ret; |
530 | |
531 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
532 | if (ret == 0 && write) |
533 | dirty_background_ratio = 0; |
534 | return ret; |
535 | } |
536 | |
537 | int dirty_ratio_handler(struct ctl_table *table, int write, |
538 | void __user *buffer, size_t *lenp, |
539 | loff_t *ppos) |
540 | { |
541 | int old_ratio = vm_dirty_ratio; |
542 | int ret; |
543 | |
544 | ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
545 | if (ret == 0 && write && vm_dirty_ratio != old_ratio) { |
546 | writeback_set_ratelimit(); |
547 | vm_dirty_bytes = 0; |
548 | } |
549 | return ret; |
550 | } |
551 | |
552 | int dirty_bytes_handler(struct ctl_table *table, int write, |
553 | void __user *buffer, size_t *lenp, |
554 | loff_t *ppos) |
555 | { |
556 | unsigned long old_bytes = vm_dirty_bytes; |
557 | int ret; |
558 | |
559 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
560 | if (ret == 0 && write && vm_dirty_bytes != old_bytes) { |
561 | writeback_set_ratelimit(); |
562 | vm_dirty_ratio = 0; |
563 | } |
564 | return ret; |
565 | } |
566 | |
567 | static unsigned long wp_next_time(unsigned long cur_time) |
568 | { |
569 | cur_time += VM_COMPLETIONS_PERIOD_LEN; |
570 | /* 0 has a special meaning... */ |
571 | if (!cur_time) |
572 | return 1; |
573 | return cur_time; |
574 | } |
575 | |
576 | static void wb_domain_writeout_inc(struct wb_domain *dom, |
577 | struct fprop_local_percpu *completions, |
578 | unsigned int max_prop_frac) |
579 | { |
580 | __fprop_inc_percpu_max(&dom->completions, completions, |
581 | max_prop_frac); |
582 | /* First event after period switching was turned off? */ |
583 | if (unlikely(!dom->period_time)) { |
584 | /* |
585 | * We can race with other __bdi_writeout_inc calls here but |
586 | * it does not cause any harm since the resulting time when |
587 | * timer will fire and what is in writeout_period_time will be |
588 | * roughly the same. |
589 | */ |
590 | dom->period_time = wp_next_time(jiffies); |
591 | mod_timer(&dom->period_timer, dom->period_time); |
592 | } |
593 | } |
594 | |
595 | /* |
596 | * Increment @wb's writeout completion count and the global writeout |
597 | * completion count. Called from test_clear_page_writeback(). |
598 | */ |
599 | static inline void __wb_writeout_inc(struct bdi_writeback *wb) |
600 | { |
601 | struct wb_domain *cgdom; |
602 | |
603 | inc_wb_stat(wb, WB_WRITTEN); |
604 | wb_domain_writeout_inc(&global_wb_domain, &wb->completions, |
605 | wb->bdi->max_prop_frac); |
606 | |
607 | cgdom = mem_cgroup_wb_domain(wb); |
608 | if (cgdom) |
609 | wb_domain_writeout_inc(cgdom, wb_memcg_completions(wb), |
610 | wb->bdi->max_prop_frac); |
611 | } |
612 | |
613 | void wb_writeout_inc(struct bdi_writeback *wb) |
614 | { |
615 | unsigned long flags; |
616 | |
617 | local_irq_save(flags); |
618 | __wb_writeout_inc(wb); |
619 | local_irq_restore(flags); |
620 | } |
621 | EXPORT_SYMBOL_GPL(wb_writeout_inc); |
622 | |
623 | /* |
624 | * On idle system, we can be called long after we scheduled because we use |
625 | * deferred timers so count with missed periods. |
626 | */ |
627 | static void writeout_period(struct timer_list *t) |
628 | { |
629 | struct wb_domain *dom = from_timer(dom, t, period_timer); |
630 | int miss_periods = (jiffies - dom->period_time) / |
631 | VM_COMPLETIONS_PERIOD_LEN; |
632 | |
633 | if (fprop_new_period(&dom->completions, miss_periods + 1)) { |
634 | dom->period_time = wp_next_time(dom->period_time + |
635 | miss_periods * VM_COMPLETIONS_PERIOD_LEN); |
636 | mod_timer(&dom->period_timer, dom->period_time); |
637 | } else { |
638 | /* |
639 | * Aging has zeroed all fractions. Stop wasting CPU on period |
640 | * updates. |
641 | */ |
642 | dom->period_time = 0; |
643 | } |
644 | } |
645 | |
646 | int wb_domain_init(struct wb_domain *dom, gfp_t gfp) |
647 | { |
648 | memset(dom, 0, sizeof(*dom)); |
649 | |
650 | spin_lock_init(&dom->lock); |
651 | |
652 | timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE); |
653 | |
654 | dom->dirty_limit_tstamp = jiffies; |
655 | |
656 | return fprop_global_init(&dom->completions, gfp); |
657 | } |
658 | |
659 | #ifdef CONFIG_CGROUP_WRITEBACK |
660 | void wb_domain_exit(struct wb_domain *dom) |
661 | { |
662 | del_timer_sync(&dom->period_timer); |
663 | fprop_global_destroy(&dom->completions); |
664 | } |
665 | #endif |
666 | |
667 | /* |
668 | * bdi_min_ratio keeps the sum of the minimum dirty shares of all |
669 | * registered backing devices, which, for obvious reasons, can not |
670 | * exceed 100%. |
671 | */ |
672 | static unsigned int bdi_min_ratio; |
673 | |
674 | int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) |
675 | { |
676 | int ret = 0; |
677 | |
678 | spin_lock_bh(&bdi_lock); |
679 | if (min_ratio > bdi->max_ratio) { |
680 | ret = -EINVAL; |
681 | } else { |
682 | min_ratio -= bdi->min_ratio; |
683 | if (bdi_min_ratio + min_ratio < 100) { |
684 | bdi_min_ratio += min_ratio; |
685 | bdi->min_ratio += min_ratio; |
686 | } else { |
687 | ret = -EINVAL; |
688 | } |
689 | } |
690 | spin_unlock_bh(&bdi_lock); |
691 | |
692 | return ret; |
693 | } |
694 | |
695 | int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) |
696 | { |
697 | int ret = 0; |
698 | |
699 | if (max_ratio > 100) |
700 | return -EINVAL; |
701 | |
702 | spin_lock_bh(&bdi_lock); |
703 | if (bdi->min_ratio > max_ratio) { |
704 | ret = -EINVAL; |
705 | } else { |
706 | bdi->max_ratio = max_ratio; |
707 | bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100; |
708 | } |
709 | spin_unlock_bh(&bdi_lock); |
710 | |
711 | return ret; |
712 | } |
713 | EXPORT_SYMBOL(bdi_set_max_ratio); |
714 | |
715 | static unsigned long dirty_freerun_ceiling(unsigned long thresh, |
716 | unsigned long bg_thresh) |
717 | { |
718 | return (thresh + bg_thresh) / 2; |
719 | } |
720 | |
721 | static unsigned long hard_dirty_limit(struct wb_domain *dom, |
722 | unsigned long thresh) |
723 | { |
724 | return max(thresh, dom->dirty_limit); |
725 | } |
726 | |
727 | /* |
728 | * Memory which can be further allocated to a memcg domain is capped by |
729 | * system-wide clean memory excluding the amount being used in the domain. |
730 | */ |
731 | static void mdtc_calc_avail(struct dirty_throttle_control *mdtc, |
732 | unsigned long filepages, unsigned long headroom) |
733 | { |
734 | struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc); |
735 | unsigned long clean = filepages - min(filepages, mdtc->dirty); |
736 | unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty); |
737 | unsigned long other_clean = global_clean - min(global_clean, clean); |
738 | |
739 | mdtc->avail = filepages + min(headroom, other_clean); |
740 | } |
741 | |
742 | /** |
743 | * __wb_calc_thresh - @wb's share of dirty throttling threshold |
744 | * @dtc: dirty_throttle_context of interest |
745 | * |
746 | * Note that balance_dirty_pages() will only seriously take it as a hard limit |
747 | * when sleeping max_pause per page is not enough to keep the dirty pages under |
748 | * control. For example, when the device is completely stalled due to some error |
749 | * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key. |
750 | * In the other normal situations, it acts more gently by throttling the tasks |
751 | * more (rather than completely block them) when the wb dirty pages go high. |
752 | * |
753 | * It allocates high/low dirty limits to fast/slow devices, in order to prevent |
754 | * - starving fast devices |
755 | * - piling up dirty pages (that will take long time to sync) on slow devices |
756 | * |
757 | * The wb's share of dirty limit will be adapting to its throughput and |
758 | * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. |
759 | * |
760 | * Return: @wb's dirty limit in pages. The term "dirty" in the context of |
761 | * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages. |
762 | */ |
763 | static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc) |
764 | { |
765 | struct wb_domain *dom = dtc_dom(dtc); |
766 | unsigned long thresh = dtc->thresh; |
767 | u64 wb_thresh; |
768 | long numerator, denominator; |
769 | unsigned long wb_min_ratio, wb_max_ratio; |
770 | |
771 | /* |
772 | * Calculate this BDI's share of the thresh ratio. |
773 | */ |
774 | fprop_fraction_percpu(&dom->completions, dtc->wb_completions, |
775 | &numerator, &denominator); |
776 | |
777 | wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100; |
778 | wb_thresh *= numerator; |
779 | do_div(wb_thresh, denominator); |
780 | |
781 | wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio); |
782 | |
783 | wb_thresh += (thresh * wb_min_ratio) / 100; |
784 | if (wb_thresh > (thresh * wb_max_ratio) / 100) |
785 | wb_thresh = thresh * wb_max_ratio / 100; |
786 | |
787 | return wb_thresh; |
788 | } |
789 | |
790 | unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh) |
791 | { |
792 | struct dirty_throttle_control gdtc = { GDTC_INIT(wb), |
793 | .thresh = thresh }; |
794 | return __wb_calc_thresh(&gdtc); |
795 | } |
796 | |
797 | /* |
798 | * setpoint - dirty 3 |
799 | * f(dirty) := 1.0 + (----------------) |
800 | * limit - setpoint |
801 | * |
802 | * it's a 3rd order polynomial that subjects to |
803 | * |
804 | * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast |
805 | * (2) f(setpoint) = 1.0 => the balance point |
806 | * (3) f(limit) = 0 => the hard limit |
807 | * (4) df/dx <= 0 => negative feedback control |
808 | * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) |
809 | * => fast response on large errors; small oscillation near setpoint |
810 | */ |
811 | static long long pos_ratio_polynom(unsigned long setpoint, |
812 | unsigned long dirty, |
813 | unsigned long limit) |
814 | { |
815 | long long pos_ratio; |
816 | long x; |
817 | |
818 | x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, |
819 | (limit - setpoint) | 1); |
820 | pos_ratio = x; |
821 | pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
822 | pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
823 | pos_ratio += 1 << RATELIMIT_CALC_SHIFT; |
824 | |
825 | return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT); |
826 | } |
827 | |
828 | /* |
829 | * Dirty position control. |
830 | * |
831 | * (o) global/bdi setpoints |
832 | * |
833 | * We want the dirty pages be balanced around the global/wb setpoints. |
834 | * When the number of dirty pages is higher/lower than the setpoint, the |
835 | * dirty position control ratio (and hence task dirty ratelimit) will be |
836 | * decreased/increased to bring the dirty pages back to the setpoint. |
837 | * |
838 | * pos_ratio = 1 << RATELIMIT_CALC_SHIFT |
839 | * |
840 | * if (dirty < setpoint) scale up pos_ratio |
841 | * if (dirty > setpoint) scale down pos_ratio |
842 | * |
843 | * if (wb_dirty < wb_setpoint) scale up pos_ratio |
844 | * if (wb_dirty > wb_setpoint) scale down pos_ratio |
845 | * |
846 | * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT |
847 | * |
848 | * (o) global control line |
849 | * |
850 | * ^ pos_ratio |
851 | * | |
852 | * | |<===== global dirty control scope ======>| |
853 | * 2.0 .............* |
854 | * | .* |
855 | * | . * |
856 | * | . * |
857 | * | . * |
858 | * | . * |
859 | * | . * |
860 | * 1.0 ................................* |
861 | * | . . * |
862 | * | . . * |
863 | * | . . * |
864 | * | . . * |
865 | * | . . * |
866 | * 0 +------------.------------------.----------------------*-------------> |
867 | * freerun^ setpoint^ limit^ dirty pages |
868 | * |
869 | * (o) wb control line |
870 | * |
871 | * ^ pos_ratio |
872 | * | |
873 | * | * |
874 | * | * |
875 | * | * |
876 | * | * |
877 | * | * |<=========== span ============>| |
878 | * 1.0 .......................* |
879 | * | . * |
880 | * | . * |
881 | * | . * |
882 | * | . * |
883 | * | . * |
884 | * | . * |
885 | * | . * |
886 | * | . * |
887 | * | . * |
888 | * | . * |
889 | * | . * |
890 | * 1/4 ...............................................* * * * * * * * * * * * |
891 | * | . . |
892 | * | . . |
893 | * | . . |
894 | * 0 +----------------------.-------------------------------.-------------> |
895 | * wb_setpoint^ x_intercept^ |
896 | * |
897 | * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can |
898 | * be smoothly throttled down to normal if it starts high in situations like |
899 | * - start writing to a slow SD card and a fast disk at the same time. The SD |
900 | * card's wb_dirty may rush to many times higher than wb_setpoint. |
901 | * - the wb dirty thresh drops quickly due to change of JBOD workload |
902 | */ |
903 | static void wb_position_ratio(struct dirty_throttle_control *dtc) |
904 | { |
905 | struct bdi_writeback *wb = dtc->wb; |
906 | unsigned long write_bw = wb->avg_write_bandwidth; |
907 | unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh); |
908 | unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); |
909 | unsigned long wb_thresh = dtc->wb_thresh; |
910 | unsigned long x_intercept; |
911 | unsigned long setpoint; /* dirty pages' target balance point */ |
912 | unsigned long wb_setpoint; |
913 | unsigned long span; |
914 | long long pos_ratio; /* for scaling up/down the rate limit */ |
915 | long x; |
916 | |
917 | dtc->pos_ratio = 0; |
918 | |
919 | if (unlikely(dtc->dirty >= limit)) |
920 | return; |
921 | |
922 | /* |
923 | * global setpoint |
924 | * |
925 | * See comment for pos_ratio_polynom(). |
926 | */ |
927 | setpoint = (freerun + limit) / 2; |
928 | pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit); |
929 | |
930 | /* |
931 | * The strictlimit feature is a tool preventing mistrusted filesystems |
932 | * from growing a large number of dirty pages before throttling. For |
933 | * such filesystems balance_dirty_pages always checks wb counters |
934 | * against wb limits. Even if global "nr_dirty" is under "freerun". |
935 | * This is especially important for fuse which sets bdi->max_ratio to |
936 | * 1% by default. Without strictlimit feature, fuse writeback may |
937 | * consume arbitrary amount of RAM because it is accounted in |
938 | * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty". |
939 | * |
940 | * Here, in wb_position_ratio(), we calculate pos_ratio based on |
941 | * two values: wb_dirty and wb_thresh. Let's consider an example: |
942 | * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global |
943 | * limits are set by default to 10% and 20% (background and throttle). |
944 | * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages. |
945 | * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is |
946 | * about ~6K pages (as the average of background and throttle wb |
947 | * limits). The 3rd order polynomial will provide positive feedback if |
948 | * wb_dirty is under wb_setpoint and vice versa. |
949 | * |
950 | * Note, that we cannot use global counters in these calculations |
951 | * because we want to throttle process writing to a strictlimit wb |
952 | * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB |
953 | * in the example above). |
954 | */ |
955 | if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { |
956 | long long wb_pos_ratio; |
957 | |
958 | if (dtc->wb_dirty < 8) { |
959 | dtc->pos_ratio = min_t(long long, pos_ratio * 2, |
960 | 2 << RATELIMIT_CALC_SHIFT); |
961 | return; |
962 | } |
963 | |
964 | if (dtc->wb_dirty >= wb_thresh) |
965 | return; |
966 | |
967 | wb_setpoint = dirty_freerun_ceiling(wb_thresh, |
968 | dtc->wb_bg_thresh); |
969 | |
970 | if (wb_setpoint == 0 || wb_setpoint == wb_thresh) |
971 | return; |
972 | |
973 | wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty, |
974 | wb_thresh); |
975 | |
976 | /* |
977 | * Typically, for strictlimit case, wb_setpoint << setpoint |
978 | * and pos_ratio >> wb_pos_ratio. In the other words global |
979 | * state ("dirty") is not limiting factor and we have to |
980 | * make decision based on wb counters. But there is an |
981 | * important case when global pos_ratio should get precedence: |
982 | * global limits are exceeded (e.g. due to activities on other |
983 | * wb's) while given strictlimit wb is below limit. |
984 | * |
985 | * "pos_ratio * wb_pos_ratio" would work for the case above, |
986 | * but it would look too non-natural for the case of all |
987 | * activity in the system coming from a single strictlimit wb |
988 | * with bdi->max_ratio == 100%. |
989 | * |
990 | * Note that min() below somewhat changes the dynamics of the |
991 | * control system. Normally, pos_ratio value can be well over 3 |
992 | * (when globally we are at freerun and wb is well below wb |
993 | * setpoint). Now the maximum pos_ratio in the same situation |
994 | * is 2. We might want to tweak this if we observe the control |
995 | * system is too slow to adapt. |
996 | */ |
997 | dtc->pos_ratio = min(pos_ratio, wb_pos_ratio); |
998 | return; |
999 | } |
1000 | |
1001 | /* |
1002 | * We have computed basic pos_ratio above based on global situation. If |
1003 | * the wb is over/under its share of dirty pages, we want to scale |
1004 | * pos_ratio further down/up. That is done by the following mechanism. |
1005 | */ |
1006 | |
1007 | /* |
1008 | * wb setpoint |
1009 | * |
1010 | * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint) |
1011 | * |
1012 | * x_intercept - wb_dirty |
1013 | * := -------------------------- |
1014 | * x_intercept - wb_setpoint |
1015 | * |
1016 | * The main wb control line is a linear function that subjects to |
1017 | * |
1018 | * (1) f(wb_setpoint) = 1.0 |
1019 | * (2) k = - 1 / (8 * write_bw) (in single wb case) |
1020 | * or equally: x_intercept = wb_setpoint + 8 * write_bw |
1021 | * |
1022 | * For single wb case, the dirty pages are observed to fluctuate |
1023 | * regularly within range |
1024 | * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2] |
1025 | * for various filesystems, where (2) can yield in a reasonable 12.5% |
1026 | * fluctuation range for pos_ratio. |
1027 | * |
1028 | * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its |
1029 | * own size, so move the slope over accordingly and choose a slope that |
1030 | * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh. |
1031 | */ |
1032 | if (unlikely(wb_thresh > dtc->thresh)) |
1033 | wb_thresh = dtc->thresh; |
1034 | /* |
1035 | * It's very possible that wb_thresh is close to 0 not because the |
1036 | * device is slow, but that it has remained inactive for long time. |
1037 | * Honour such devices a reasonable good (hopefully IO efficient) |
1038 | * threshold, so that the occasional writes won't be blocked and active |
1039 | * writes can rampup the threshold quickly. |
1040 | */ |
1041 | wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8); |
1042 | /* |
1043 | * scale global setpoint to wb's: |
1044 | * wb_setpoint = setpoint * wb_thresh / thresh |
1045 | */ |
1046 | x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1); |
1047 | wb_setpoint = setpoint * (u64)x >> 16; |
1048 | /* |
1049 | * Use span=(8*write_bw) in single wb case as indicated by |
1050 | * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case. |
1051 | * |
1052 | * wb_thresh thresh - wb_thresh |
1053 | * span = --------- * (8 * write_bw) + ------------------ * wb_thresh |
1054 | * thresh thresh |
1055 | */ |
1056 | span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16; |
1057 | x_intercept = wb_setpoint + span; |
1058 | |
1059 | if (dtc->wb_dirty < x_intercept - span / 4) { |
1060 | pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty), |
1061 | (x_intercept - wb_setpoint) | 1); |
1062 | } else |
1063 | pos_ratio /= 4; |
1064 | |
1065 | /* |
1066 | * wb reserve area, safeguard against dirty pool underrun and disk idle |
1067 | * It may push the desired control point of global dirty pages higher |
1068 | * than setpoint. |
1069 | */ |
1070 | x_intercept = wb_thresh / 2; |
1071 | if (dtc->wb_dirty < x_intercept) { |
1072 | if (dtc->wb_dirty > x_intercept / 8) |
1073 | pos_ratio = div_u64(pos_ratio * x_intercept, |
1074 | dtc->wb_dirty); |
1075 | else |
1076 | pos_ratio *= 8; |
1077 | } |
1078 | |
1079 | dtc->pos_ratio = pos_ratio; |
1080 | } |
1081 | |
1082 | static void wb_update_write_bandwidth(struct bdi_writeback *wb, |
1083 | unsigned long elapsed, |
1084 | unsigned long written) |
1085 | { |
1086 | const unsigned long period = roundup_pow_of_two(3 * HZ); |
1087 | unsigned long avg = wb->avg_write_bandwidth; |
1088 | unsigned long old = wb->write_bandwidth; |
1089 | u64 bw; |
1090 | |
1091 | /* |
1092 | * bw = written * HZ / elapsed |
1093 | * |
1094 | * bw * elapsed + write_bandwidth * (period - elapsed) |
1095 | * write_bandwidth = --------------------------------------------------- |
1096 | * period |
1097 | * |
1098 | * @written may have decreased due to account_page_redirty(). |
1099 | * Avoid underflowing @bw calculation. |
1100 | */ |
1101 | bw = written - min(written, wb->written_stamp); |
1102 | bw *= HZ; |
1103 | if (unlikely(elapsed > period)) { |
1104 | do_div(bw, elapsed); |
1105 | avg = bw; |
1106 | goto out; |
1107 | } |
1108 | bw += (u64)wb->write_bandwidth * (period - elapsed); |
1109 | bw >>= ilog2(period); |
1110 | |
1111 | /* |
1112 | * one more level of smoothing, for filtering out sudden spikes |
1113 | */ |
1114 | if (avg > old && old >= (unsigned long)bw) |
1115 | avg -= (avg - old) >> 3; |
1116 | |
1117 | if (avg < old && old <= (unsigned long)bw) |
1118 | avg += (old - avg) >> 3; |
1119 | |
1120 | out: |
1121 | /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */ |
1122 | avg = max(avg, 1LU); |
1123 | if (wb_has_dirty_io(wb)) { |
1124 | long delta = avg - wb->avg_write_bandwidth; |
1125 | WARN_ON_ONCE(atomic_long_add_return(delta, |
1126 | &wb->bdi->tot_write_bandwidth) <= 0); |
1127 | } |
1128 | wb->write_bandwidth = bw; |
1129 | wb->avg_write_bandwidth = avg; |
1130 | } |
1131 | |
1132 | static void update_dirty_limit(struct dirty_throttle_control *dtc) |
1133 | { |
1134 | struct wb_domain *dom = dtc_dom(dtc); |
1135 | unsigned long thresh = dtc->thresh; |
1136 | unsigned long limit = dom->dirty_limit; |
1137 | |
1138 | /* |
1139 | * Follow up in one step. |
1140 | */ |
1141 | if (limit < thresh) { |
1142 | limit = thresh; |
1143 | goto update; |
1144 | } |
1145 | |
1146 | /* |
1147 | * Follow down slowly. Use the higher one as the target, because thresh |
1148 | * may drop below dirty. This is exactly the reason to introduce |
1149 | * dom->dirty_limit which is guaranteed to lie above the dirty pages. |
1150 | */ |
1151 | thresh = max(thresh, dtc->dirty); |
1152 | if (limit > thresh) { |
1153 | limit -= (limit - thresh) >> 5; |
1154 | goto update; |
1155 | } |
1156 | return; |
1157 | update: |
1158 | dom->dirty_limit = limit; |
1159 | } |
1160 | |
1161 | static void domain_update_bandwidth(struct dirty_throttle_control *dtc, |
1162 | unsigned long now) |
1163 | { |
1164 | struct wb_domain *dom = dtc_dom(dtc); |
1165 | |
1166 | /* |
1167 | * check locklessly first to optimize away locking for the most time |
1168 | */ |
1169 | if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) |
1170 | return; |
1171 | |
1172 | spin_lock(&dom->lock); |
1173 | if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) { |
1174 | update_dirty_limit(dtc); |
1175 | dom->dirty_limit_tstamp = now; |
1176 | } |
1177 | spin_unlock(&dom->lock); |
1178 | } |
1179 | |
1180 | /* |
1181 | * Maintain wb->dirty_ratelimit, the base dirty throttle rate. |
1182 | * |
1183 | * Normal wb tasks will be curbed at or below it in long term. |
1184 | * Obviously it should be around (write_bw / N) when there are N dd tasks. |
1185 | */ |
1186 | static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc, |
1187 | unsigned long dirtied, |
1188 | unsigned long elapsed) |
1189 | { |
1190 | struct bdi_writeback *wb = dtc->wb; |
1191 | unsigned long dirty = dtc->dirty; |
1192 | unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh); |
1193 | unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); |
1194 | unsigned long setpoint = (freerun + limit) / 2; |
1195 | unsigned long write_bw = wb->avg_write_bandwidth; |
1196 | unsigned long dirty_ratelimit = wb->dirty_ratelimit; |
1197 | unsigned long dirty_rate; |
1198 | unsigned long task_ratelimit; |
1199 | unsigned long balanced_dirty_ratelimit; |
1200 | unsigned long step; |
1201 | unsigned long x; |
1202 | unsigned long shift; |
1203 | |
1204 | /* |
1205 | * The dirty rate will match the writeout rate in long term, except |
1206 | * when dirty pages are truncated by userspace or re-dirtied by FS. |
1207 | */ |
1208 | dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed; |
1209 | |
1210 | /* |
1211 | * task_ratelimit reflects each dd's dirty rate for the past 200ms. |
1212 | */ |
1213 | task_ratelimit = (u64)dirty_ratelimit * |
1214 | dtc->pos_ratio >> RATELIMIT_CALC_SHIFT; |
1215 | task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */ |
1216 | |
1217 | /* |
1218 | * A linear estimation of the "balanced" throttle rate. The theory is, |
1219 | * if there are N dd tasks, each throttled at task_ratelimit, the wb's |
1220 | * dirty_rate will be measured to be (N * task_ratelimit). So the below |
1221 | * formula will yield the balanced rate limit (write_bw / N). |
1222 | * |
1223 | * Note that the expanded form is not a pure rate feedback: |
1224 | * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1) |
1225 | * but also takes pos_ratio into account: |
1226 | * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2) |
1227 | * |
1228 | * (1) is not realistic because pos_ratio also takes part in balancing |
1229 | * the dirty rate. Consider the state |
1230 | * pos_ratio = 0.5 (3) |
1231 | * rate = 2 * (write_bw / N) (4) |
1232 | * If (1) is used, it will stuck in that state! Because each dd will |
1233 | * be throttled at |
1234 | * task_ratelimit = pos_ratio * rate = (write_bw / N) (5) |
1235 | * yielding |
1236 | * dirty_rate = N * task_ratelimit = write_bw (6) |
1237 | * put (6) into (1) we get |
1238 | * rate_(i+1) = rate_(i) (7) |
1239 | * |
1240 | * So we end up using (2) to always keep |
1241 | * rate_(i+1) ~= (write_bw / N) (8) |
1242 | * regardless of the value of pos_ratio. As long as (8) is satisfied, |
1243 | * pos_ratio is able to drive itself to 1.0, which is not only where |
1244 | * the dirty count meet the setpoint, but also where the slope of |
1245 | * pos_ratio is most flat and hence task_ratelimit is least fluctuated. |
1246 | */ |
1247 | balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw, |
1248 | dirty_rate | 1); |
1249 | /* |
1250 | * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw |
1251 | */ |
1252 | if (unlikely(balanced_dirty_ratelimit > write_bw)) |
1253 | balanced_dirty_ratelimit = write_bw; |
1254 | |
1255 | /* |
1256 | * We could safely do this and return immediately: |
1257 | * |
1258 | * wb->dirty_ratelimit = balanced_dirty_ratelimit; |
1259 | * |
1260 | * However to get a more stable dirty_ratelimit, the below elaborated |
1261 | * code makes use of task_ratelimit to filter out singular points and |
1262 | * limit the step size. |
1263 | * |
1264 | * The below code essentially only uses the relative value of |
1265 | * |
1266 | * task_ratelimit - dirty_ratelimit |
1267 | * = (pos_ratio - 1) * dirty_ratelimit |
1268 | * |
1269 | * which reflects the direction and size of dirty position error. |
1270 | */ |
1271 | |
1272 | /* |
1273 | * dirty_ratelimit will follow balanced_dirty_ratelimit iff |
1274 | * task_ratelimit is on the same side of dirty_ratelimit, too. |
1275 | * For example, when |
1276 | * - dirty_ratelimit > balanced_dirty_ratelimit |
1277 | * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint) |
1278 | * lowering dirty_ratelimit will help meet both the position and rate |
1279 | * control targets. Otherwise, don't update dirty_ratelimit if it will |
1280 | * only help meet the rate target. After all, what the users ultimately |
1281 | * feel and care are stable dirty rate and small position error. |
1282 | * |
1283 | * |task_ratelimit - dirty_ratelimit| is used to limit the step size |
1284 | * and filter out the singular points of balanced_dirty_ratelimit. Which |
1285 | * keeps jumping around randomly and can even leap far away at times |
1286 | * due to the small 200ms estimation period of dirty_rate (we want to |
1287 | * keep that period small to reduce time lags). |
1288 | */ |
1289 | step = 0; |
1290 | |
1291 | /* |
1292 | * For strictlimit case, calculations above were based on wb counters |
1293 | * and limits (starting from pos_ratio = wb_position_ratio() and up to |
1294 | * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate). |
1295 | * Hence, to calculate "step" properly, we have to use wb_dirty as |
1296 | * "dirty" and wb_setpoint as "setpoint". |
1297 | * |
1298 | * We rampup dirty_ratelimit forcibly if wb_dirty is low because |
1299 | * it's possible that wb_thresh is close to zero due to inactivity |
1300 | * of backing device. |
1301 | */ |
1302 | if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { |
1303 | dirty = dtc->wb_dirty; |
1304 | if (dtc->wb_dirty < 8) |
1305 | setpoint = dtc->wb_dirty + 1; |
1306 | else |
1307 | setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2; |
1308 | } |
1309 | |
1310 | if (dirty < setpoint) { |
1311 | x = min3(wb->balanced_dirty_ratelimit, |
1312 | balanced_dirty_ratelimit, task_ratelimit); |
1313 | if (dirty_ratelimit < x) |
1314 | step = x - dirty_ratelimit; |
1315 | } else { |
1316 | x = max3(wb->balanced_dirty_ratelimit, |
1317 | balanced_dirty_ratelimit, task_ratelimit); |
1318 | if (dirty_ratelimit > x) |
1319 | step = dirty_ratelimit - x; |
1320 | } |
1321 | |
1322 | /* |
1323 | * Don't pursue 100% rate matching. It's impossible since the balanced |
1324 | * rate itself is constantly fluctuating. So decrease the track speed |
1325 | * when it gets close to the target. Helps eliminate pointless tremors. |
1326 | */ |
1327 | shift = dirty_ratelimit / (2 * step + 1); |
1328 | if (shift < BITS_PER_LONG) |
1329 | step = DIV_ROUND_UP(step >> shift, 8); |
1330 | else |
1331 | step = 0; |
1332 | |
1333 | if (dirty_ratelimit < balanced_dirty_ratelimit) |
1334 | dirty_ratelimit += step; |
1335 | else |
1336 | dirty_ratelimit -= step; |
1337 | |
1338 | wb->dirty_ratelimit = max(dirty_ratelimit, 1UL); |
1339 | wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit; |
1340 | |
1341 | trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit); |
1342 | } |
1343 | |
1344 | static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc, |
1345 | struct dirty_throttle_control *mdtc, |
1346 | unsigned long start_time, |
1347 | bool update_ratelimit) |
1348 | { |
1349 | struct bdi_writeback *wb = gdtc->wb; |
1350 | unsigned long now = jiffies; |
1351 | unsigned long elapsed = now - wb->bw_time_stamp; |
1352 | unsigned long dirtied; |
1353 | unsigned long written; |
1354 | |
1355 | lockdep_assert_held(&wb->list_lock); |
1356 | |
1357 | /* |
1358 | * rate-limit, only update once every 200ms. |
1359 | */ |
1360 | if (elapsed < BANDWIDTH_INTERVAL) |
1361 | return; |
1362 | |
1363 | dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]); |
1364 | written = percpu_counter_read(&wb->stat[WB_WRITTEN]); |
1365 | |
1366 | /* |
1367 | * Skip quiet periods when disk bandwidth is under-utilized. |
1368 | * (at least 1s idle time between two flusher runs) |
1369 | */ |
1370 | if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time)) |
1371 | goto snapshot; |
1372 | |
1373 | if (update_ratelimit) { |
1374 | domain_update_bandwidth(gdtc, now); |
1375 | wb_update_dirty_ratelimit(gdtc, dirtied, elapsed); |
1376 | |
1377 | /* |
1378 | * @mdtc is always NULL if !CGROUP_WRITEBACK but the |
1379 | * compiler has no way to figure that out. Help it. |
1380 | */ |
1381 | if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) { |
1382 | domain_update_bandwidth(mdtc, now); |
1383 | wb_update_dirty_ratelimit(mdtc, dirtied, elapsed); |
1384 | } |
1385 | } |
1386 | wb_update_write_bandwidth(wb, elapsed, written); |
1387 | |
1388 | snapshot: |
1389 | wb->dirtied_stamp = dirtied; |
1390 | wb->written_stamp = written; |
1391 | wb->bw_time_stamp = now; |
1392 | } |
1393 | |
1394 | void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time) |
1395 | { |
1396 | struct dirty_throttle_control gdtc = { GDTC_INIT(wb) }; |
1397 | |
1398 | __wb_update_bandwidth(&gdtc, NULL, start_time, false); |
1399 | } |
1400 | |
1401 | /* |
1402 | * After a task dirtied this many pages, balance_dirty_pages_ratelimited() |
1403 | * will look to see if it needs to start dirty throttling. |
1404 | * |
1405 | * If dirty_poll_interval is too low, big NUMA machines will call the expensive |
1406 | * global_zone_page_state() too often. So scale it near-sqrt to the safety margin |
1407 | * (the number of pages we may dirty without exceeding the dirty limits). |
1408 | */ |
1409 | static unsigned long dirty_poll_interval(unsigned long dirty, |
1410 | unsigned long thresh) |
1411 | { |
1412 | if (thresh > dirty) |
1413 | return 1UL << (ilog2(thresh - dirty) >> 1); |
1414 | |
1415 | return 1; |
1416 | } |
1417 | |
1418 | static unsigned long wb_max_pause(struct bdi_writeback *wb, |
1419 | unsigned long wb_dirty) |
1420 | { |
1421 | unsigned long bw = wb->avg_write_bandwidth; |
1422 | unsigned long t; |
1423 | |
1424 | /* |
1425 | * Limit pause time for small memory systems. If sleeping for too long |
1426 | * time, a small pool of dirty/writeback pages may go empty and disk go |
1427 | * idle. |
1428 | * |
1429 | * 8 serves as the safety ratio. |
1430 | */ |
1431 | t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8)); |
1432 | t++; |
1433 | |
1434 | return min_t(unsigned long, t, MAX_PAUSE); |
1435 | } |
1436 | |
1437 | static long wb_min_pause(struct bdi_writeback *wb, |
1438 | long max_pause, |
1439 | unsigned long task_ratelimit, |
1440 | unsigned long dirty_ratelimit, |
1441 | int *nr_dirtied_pause) |
1442 | { |
1443 | long hi = ilog2(wb->avg_write_bandwidth); |
1444 | long lo = ilog2(wb->dirty_ratelimit); |
1445 | long t; /* target pause */ |
1446 | long pause; /* estimated next pause */ |
1447 | int pages; /* target nr_dirtied_pause */ |
1448 | |
1449 | /* target for 10ms pause on 1-dd case */ |
1450 | t = max(1, HZ / 100); |
1451 | |
1452 | /* |
1453 | * Scale up pause time for concurrent dirtiers in order to reduce CPU |
1454 | * overheads. |
1455 | * |
1456 | * (N * 10ms) on 2^N concurrent tasks. |
1457 | */ |
1458 | if (hi > lo) |
1459 | t += (hi - lo) * (10 * HZ) / 1024; |
1460 | |
1461 | /* |
1462 | * This is a bit convoluted. We try to base the next nr_dirtied_pause |
1463 | * on the much more stable dirty_ratelimit. However the next pause time |
1464 | * will be computed based on task_ratelimit and the two rate limits may |
1465 | * depart considerably at some time. Especially if task_ratelimit goes |
1466 | * below dirty_ratelimit/2 and the target pause is max_pause, the next |
1467 | * pause time will be max_pause*2 _trimmed down_ to max_pause. As a |
1468 | * result task_ratelimit won't be executed faithfully, which could |
1469 | * eventually bring down dirty_ratelimit. |
1470 | * |
1471 | * We apply two rules to fix it up: |
1472 | * 1) try to estimate the next pause time and if necessary, use a lower |
1473 | * nr_dirtied_pause so as not to exceed max_pause. When this happens, |
1474 | * nr_dirtied_pause will be "dancing" with task_ratelimit. |
1475 | * 2) limit the target pause time to max_pause/2, so that the normal |
1476 | * small fluctuations of task_ratelimit won't trigger rule (1) and |
1477 | * nr_dirtied_pause will remain as stable as dirty_ratelimit. |
1478 | */ |
1479 | t = min(t, 1 + max_pause / 2); |
1480 | pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); |
1481 | |
1482 | /* |
1483 | * Tiny nr_dirtied_pause is found to hurt I/O performance in the test |
1484 | * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}. |
1485 | * When the 16 consecutive reads are often interrupted by some dirty |
1486 | * throttling pause during the async writes, cfq will go into idles |
1487 | * (deadline is fine). So push nr_dirtied_pause as high as possible |
1488 | * until reaches DIRTY_POLL_THRESH=32 pages. |
1489 | */ |
1490 | if (pages < DIRTY_POLL_THRESH) { |
1491 | t = max_pause; |
1492 | pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); |
1493 | if (pages > DIRTY_POLL_THRESH) { |
1494 | pages = DIRTY_POLL_THRESH; |
1495 | t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit; |
1496 | } |
1497 | } |
1498 | |
1499 | pause = HZ * pages / (task_ratelimit + 1); |
1500 | if (pause > max_pause) { |
1501 | t = max_pause; |
1502 | pages = task_ratelimit * t / roundup_pow_of_two(HZ); |
1503 | } |
1504 | |
1505 | *nr_dirtied_pause = pages; |
1506 | /* |
1507 | * The minimal pause time will normally be half the target pause time. |
1508 | */ |
1509 | return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t; |
1510 | } |
1511 | |
1512 | static inline void wb_dirty_limits(struct dirty_throttle_control *dtc) |
1513 | { |
1514 | struct bdi_writeback *wb = dtc->wb; |
1515 | unsigned long wb_reclaimable; |
1516 | |
1517 | /* |
1518 | * wb_thresh is not treated as some limiting factor as |
1519 | * dirty_thresh, due to reasons |
1520 | * - in JBOD setup, wb_thresh can fluctuate a lot |
1521 | * - in a system with HDD and USB key, the USB key may somehow |
1522 | * go into state (wb_dirty >> wb_thresh) either because |
1523 | * wb_dirty starts high, or because wb_thresh drops low. |
1524 | * In this case we don't want to hard throttle the USB key |
1525 | * dirtiers for 100 seconds until wb_dirty drops under |
1526 | * wb_thresh. Instead the auxiliary wb control line in |
1527 | * wb_position_ratio() will let the dirtier task progress |
1528 | * at some rate <= (write_bw / 2) for bringing down wb_dirty. |
1529 | */ |
1530 | dtc->wb_thresh = __wb_calc_thresh(dtc); |
1531 | dtc->wb_bg_thresh = dtc->thresh ? |
1532 | div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0; |
1533 | |
1534 | /* |
1535 | * In order to avoid the stacked BDI deadlock we need |
1536 | * to ensure we accurately count the 'dirty' pages when |
1537 | * the threshold is low. |
1538 | * |
1539 | * Otherwise it would be possible to get thresh+n pages |
1540 | * reported dirty, even though there are thresh-m pages |
1541 | * actually dirty; with m+n sitting in the percpu |
1542 | * deltas. |
1543 | */ |
1544 | if (dtc->wb_thresh < 2 * wb_stat_error()) { |
1545 | wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE); |
1546 | dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK); |
1547 | } else { |
1548 | wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE); |
1549 | dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK); |
1550 | } |
1551 | } |
1552 | |
1553 | /* |
1554 | * balance_dirty_pages() must be called by processes which are generating dirty |
1555 | * data. It looks at the number of dirty pages in the machine and will force |
1556 | * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2. |
1557 | * If we're over `background_thresh' then the writeback threads are woken to |
1558 | * perform some writeout. |
1559 | */ |
1560 | static void balance_dirty_pages(struct bdi_writeback *wb, |
1561 | unsigned long pages_dirtied) |
1562 | { |
1563 | struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) }; |
1564 | struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) }; |
1565 | struct dirty_throttle_control * const gdtc = &gdtc_stor; |
1566 | struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ? |
1567 | &mdtc_stor : NULL; |
1568 | struct dirty_throttle_control *sdtc; |
1569 | unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */ |
1570 | long period; |
1571 | long pause; |
1572 | long max_pause; |
1573 | long min_pause; |
1574 | int nr_dirtied_pause; |
1575 | bool dirty_exceeded = false; |
1576 | unsigned long task_ratelimit; |
1577 | unsigned long dirty_ratelimit; |
1578 | struct backing_dev_info *bdi = wb->bdi; |
1579 | bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT; |
1580 | unsigned long start_time = jiffies; |
1581 | |
1582 | for (;;) { |
1583 | unsigned long now = jiffies; |
1584 | unsigned long dirty, thresh, bg_thresh; |
1585 | unsigned long m_dirty = 0; /* stop bogus uninit warnings */ |
1586 | unsigned long m_thresh = 0; |
1587 | unsigned long m_bg_thresh = 0; |
1588 | |
1589 | /* |
1590 | * Unstable writes are a feature of certain networked |
1591 | * filesystems (i.e. NFS) in which data may have been |
1592 | * written to the server's write cache, but has not yet |
1593 | * been flushed to permanent storage. |
1594 | */ |
1595 | nr_reclaimable = global_node_page_state(NR_FILE_DIRTY) + |
1596 | global_node_page_state(NR_UNSTABLE_NFS); |
1597 | gdtc->avail = global_dirtyable_memory(); |
1598 | gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK); |
1599 | |
1600 | domain_dirty_limits(gdtc); |
1601 | |
1602 | if (unlikely(strictlimit)) { |
1603 | wb_dirty_limits(gdtc); |
1604 | |
1605 | dirty = gdtc->wb_dirty; |
1606 | thresh = gdtc->wb_thresh; |
1607 | bg_thresh = gdtc->wb_bg_thresh; |
1608 | } else { |
1609 | dirty = gdtc->dirty; |
1610 | thresh = gdtc->thresh; |
1611 | bg_thresh = gdtc->bg_thresh; |
1612 | } |
1613 | |
1614 | if (mdtc) { |
1615 | unsigned long filepages, headroom, writeback; |
1616 | |
1617 | /* |
1618 | * If @wb belongs to !root memcg, repeat the same |
1619 | * basic calculations for the memcg domain. |
1620 | */ |
1621 | mem_cgroup_wb_stats(wb, &filepages, &headroom, |
1622 | &mdtc->dirty, &writeback); |
1623 | mdtc->dirty += writeback; |
1624 | mdtc_calc_avail(mdtc, filepages, headroom); |
1625 | |
1626 | domain_dirty_limits(mdtc); |
1627 | |
1628 | if (unlikely(strictlimit)) { |
1629 | wb_dirty_limits(mdtc); |
1630 | m_dirty = mdtc->wb_dirty; |
1631 | m_thresh = mdtc->wb_thresh; |
1632 | m_bg_thresh = mdtc->wb_bg_thresh; |
1633 | } else { |
1634 | m_dirty = mdtc->dirty; |
1635 | m_thresh = mdtc->thresh; |
1636 | m_bg_thresh = mdtc->bg_thresh; |
1637 | } |
1638 | } |
1639 | |
1640 | /* |
1641 | * Throttle it only when the background writeback cannot |
1642 | * catch-up. This avoids (excessively) small writeouts |
1643 | * when the wb limits are ramping up in case of !strictlimit. |
1644 | * |
1645 | * In strictlimit case make decision based on the wb counters |
1646 | * and limits. Small writeouts when the wb limits are ramping |
1647 | * up are the price we consciously pay for strictlimit-ing. |
1648 | * |
1649 | * If memcg domain is in effect, @dirty should be under |
1650 | * both global and memcg freerun ceilings. |
1651 | */ |
1652 | if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) && |
1653 | (!mdtc || |
1654 | m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) { |
1655 | unsigned long intv = dirty_poll_interval(dirty, thresh); |
1656 | unsigned long m_intv = ULONG_MAX; |
1657 | |
1658 | current->dirty_paused_when = now; |
1659 | current->nr_dirtied = 0; |
1660 | if (mdtc) |
1661 | m_intv = dirty_poll_interval(m_dirty, m_thresh); |
1662 | current->nr_dirtied_pause = min(intv, m_intv); |
1663 | break; |
1664 | } |
1665 | |
1666 | if (unlikely(!writeback_in_progress(wb))) |
1667 | wb_start_background_writeback(wb); |
1668 | |
1669 | /* |
1670 | * Calculate global domain's pos_ratio and select the |
1671 | * global dtc by default. |
1672 | */ |
1673 | if (!strictlimit) |
1674 | wb_dirty_limits(gdtc); |
1675 | |
1676 | dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) && |
1677 | ((gdtc->dirty > gdtc->thresh) || strictlimit); |
1678 | |
1679 | wb_position_ratio(gdtc); |
1680 | sdtc = gdtc; |
1681 | |
1682 | if (mdtc) { |
1683 | /* |
1684 | * If memcg domain is in effect, calculate its |
1685 | * pos_ratio. @wb should satisfy constraints from |
1686 | * both global and memcg domains. Choose the one |
1687 | * w/ lower pos_ratio. |
1688 | */ |
1689 | if (!strictlimit) |
1690 | wb_dirty_limits(mdtc); |
1691 | |
1692 | dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) && |
1693 | ((mdtc->dirty > mdtc->thresh) || strictlimit); |
1694 | |
1695 | wb_position_ratio(mdtc); |
1696 | if (mdtc->pos_ratio < gdtc->pos_ratio) |
1697 | sdtc = mdtc; |
1698 | } |
1699 | |
1700 | if (dirty_exceeded && !wb->dirty_exceeded) |
1701 | wb->dirty_exceeded = 1; |
1702 | |
1703 | if (time_is_before_jiffies(wb->bw_time_stamp + |
1704 | BANDWIDTH_INTERVAL)) { |
1705 | spin_lock(&wb->list_lock); |
1706 | __wb_update_bandwidth(gdtc, mdtc, start_time, true); |
1707 | spin_unlock(&wb->list_lock); |
1708 | } |
1709 | |
1710 | /* throttle according to the chosen dtc */ |
1711 | dirty_ratelimit = wb->dirty_ratelimit; |
1712 | task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >> |
1713 | RATELIMIT_CALC_SHIFT; |
1714 | max_pause = wb_max_pause(wb, sdtc->wb_dirty); |
1715 | min_pause = wb_min_pause(wb, max_pause, |
1716 | task_ratelimit, dirty_ratelimit, |
1717 | &nr_dirtied_pause); |
1718 | |
1719 | if (unlikely(task_ratelimit == 0)) { |
1720 | period = max_pause; |
1721 | pause = max_pause; |
1722 | goto pause; |
1723 | } |
1724 | period = HZ * pages_dirtied / task_ratelimit; |
1725 | pause = period; |
1726 | if (current->dirty_paused_when) |
1727 | pause -= now - current->dirty_paused_when; |
1728 | /* |
1729 | * For less than 1s think time (ext3/4 may block the dirtier |
1730 | * for up to 800ms from time to time on 1-HDD; so does xfs, |
1731 | * however at much less frequency), try to compensate it in |
1732 | * future periods by updating the virtual time; otherwise just |
1733 | * do a reset, as it may be a light dirtier. |
1734 | */ |
1735 | if (pause < min_pause) { |
1736 | trace_balance_dirty_pages(wb, |
1737 | sdtc->thresh, |
1738 | sdtc->bg_thresh, |
1739 | sdtc->dirty, |
1740 | sdtc->wb_thresh, |
1741 | sdtc->wb_dirty, |
1742 | dirty_ratelimit, |
1743 | task_ratelimit, |
1744 | pages_dirtied, |
1745 | period, |
1746 | min(pause, 0L), |
1747 | start_time); |
1748 | if (pause < -HZ) { |
1749 | current->dirty_paused_when = now; |
1750 | current->nr_dirtied = 0; |
1751 | } else if (period) { |
1752 | current->dirty_paused_when += period; |
1753 | current->nr_dirtied = 0; |
1754 | } else if (current->nr_dirtied_pause <= pages_dirtied) |
1755 | current->nr_dirtied_pause += pages_dirtied; |
1756 | break; |
1757 | } |
1758 | if (unlikely(pause > max_pause)) { |
1759 | /* for occasional dropped task_ratelimit */ |
1760 | now += min(pause - max_pause, max_pause); |
1761 | pause = max_pause; |
1762 | } |
1763 | |
1764 | pause: |
1765 | trace_balance_dirty_pages(wb, |
1766 | sdtc->thresh, |
1767 | sdtc->bg_thresh, |
1768 | sdtc->dirty, |
1769 | sdtc->wb_thresh, |
1770 | sdtc->wb_dirty, |
1771 | dirty_ratelimit, |
1772 | task_ratelimit, |
1773 | pages_dirtied, |
1774 | period, |
1775 | pause, |
1776 | start_time); |
1777 | __set_current_state(TASK_KILLABLE); |
1778 | wb->dirty_sleep = now; |
1779 | io_schedule_timeout(pause); |
1780 | |
1781 | current->dirty_paused_when = now + pause; |
1782 | current->nr_dirtied = 0; |
1783 | current->nr_dirtied_pause = nr_dirtied_pause; |
1784 | |
1785 | /* |
1786 | * This is typically equal to (dirty < thresh) and can also |
1787 | * keep "1000+ dd on a slow USB stick" under control. |
1788 | */ |
1789 | if (task_ratelimit) |
1790 | break; |
1791 | |
1792 | /* |
1793 | * In the case of an unresponding NFS server and the NFS dirty |
1794 | * pages exceeds dirty_thresh, give the other good wb's a pipe |
1795 | * to go through, so that tasks on them still remain responsive. |
1796 | * |
1797 | * In theory 1 page is enough to keep the consumer-producer |
1798 | * pipe going: the flusher cleans 1 page => the task dirties 1 |
1799 | * more page. However wb_dirty has accounting errors. So use |
1800 | * the larger and more IO friendly wb_stat_error. |
1801 | */ |
1802 | if (sdtc->wb_dirty <= wb_stat_error()) |
1803 | break; |
1804 | |
1805 | if (fatal_signal_pending(current)) |
1806 | break; |
1807 | } |
1808 | |
1809 | if (!dirty_exceeded && wb->dirty_exceeded) |
1810 | wb->dirty_exceeded = 0; |
1811 | |
1812 | if (writeback_in_progress(wb)) |
1813 | return; |
1814 | |
1815 | /* |
1816 | * In laptop mode, we wait until hitting the higher threshold before |
1817 | * starting background writeout, and then write out all the way down |
1818 | * to the lower threshold. So slow writers cause minimal disk activity. |
1819 | * |
1820 | * In normal mode, we start background writeout at the lower |
1821 | * background_thresh, to keep the amount of dirty memory low. |
1822 | */ |
1823 | if (laptop_mode) |
1824 | return; |
1825 | |
1826 | if (nr_reclaimable > gdtc->bg_thresh) |
1827 | wb_start_background_writeback(wb); |
1828 | } |
1829 | |
1830 | static DEFINE_PER_CPU(int, bdp_ratelimits); |
1831 | |
1832 | /* |
1833 | * Normal tasks are throttled by |
1834 | * loop { |
1835 | * dirty tsk->nr_dirtied_pause pages; |
1836 | * take a snap in balance_dirty_pages(); |
1837 | * } |
1838 | * However there is a worst case. If every task exit immediately when dirtied |
1839 | * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be |
1840 | * called to throttle the page dirties. The solution is to save the not yet |
1841 | * throttled page dirties in dirty_throttle_leaks on task exit and charge them |
1842 | * randomly into the running tasks. This works well for the above worst case, |
1843 | * as the new task will pick up and accumulate the old task's leaked dirty |
1844 | * count and eventually get throttled. |
1845 | */ |
1846 | DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0; |
1847 | |
1848 | /** |
1849 | * balance_dirty_pages_ratelimited - balance dirty memory state |
1850 | * @mapping: address_space which was dirtied |
1851 | * |
1852 | * Processes which are dirtying memory should call in here once for each page |
1853 | * which was newly dirtied. The function will periodically check the system's |
1854 | * dirty state and will initiate writeback if needed. |
1855 | * |
1856 | * On really big machines, get_writeback_state is expensive, so try to avoid |
1857 | * calling it too often (ratelimiting). But once we're over the dirty memory |
1858 | * limit we decrease the ratelimiting by a lot, to prevent individual processes |
1859 | * from overshooting the limit by (ratelimit_pages) each. |
1860 | */ |
1861 | void balance_dirty_pages_ratelimited(struct address_space *mapping) |
1862 | { |
1863 | struct inode *inode = mapping->host; |
1864 | struct backing_dev_info *bdi = inode_to_bdi(inode); |
1865 | struct bdi_writeback *wb = NULL; |
1866 | int ratelimit; |
1867 | int *p; |
1868 | |
1869 | if (!bdi_cap_account_dirty(bdi)) |
1870 | return; |
1871 | |
1872 | if (inode_cgwb_enabled(inode)) |
1873 | wb = wb_get_create_current(bdi, GFP_KERNEL); |
1874 | if (!wb) |
1875 | wb = &bdi->wb; |
1876 | |
1877 | ratelimit = current->nr_dirtied_pause; |
1878 | if (wb->dirty_exceeded) |
1879 | ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10)); |
1880 | |
1881 | preempt_disable(); |
1882 | /* |
1883 | * This prevents one CPU to accumulate too many dirtied pages without |
1884 | * calling into balance_dirty_pages(), which can happen when there are |
1885 | * 1000+ tasks, all of them start dirtying pages at exactly the same |
1886 | * time, hence all honoured too large initial task->nr_dirtied_pause. |
1887 | */ |
1888 | p = this_cpu_ptr(&bdp_ratelimits); |
1889 | if (unlikely(current->nr_dirtied >= ratelimit)) |
1890 | *p = 0; |
1891 | else if (unlikely(*p >= ratelimit_pages)) { |
1892 | *p = 0; |
1893 | ratelimit = 0; |
1894 | } |
1895 | /* |
1896 | * Pick up the dirtied pages by the exited tasks. This avoids lots of |
1897 | * short-lived tasks (eg. gcc invocations in a kernel build) escaping |
1898 | * the dirty throttling and livelock other long-run dirtiers. |
1899 | */ |
1900 | p = this_cpu_ptr(&dirty_throttle_leaks); |
1901 | if (*p > 0 && current->nr_dirtied < ratelimit) { |
1902 | unsigned long nr_pages_dirtied; |
1903 | nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied); |
1904 | *p -= nr_pages_dirtied; |
1905 | current->nr_dirtied += nr_pages_dirtied; |
1906 | } |
1907 | preempt_enable(); |
1908 | |
1909 | if (unlikely(current->nr_dirtied >= ratelimit)) |
1910 | balance_dirty_pages(wb, current->nr_dirtied); |
1911 | |
1912 | wb_put(wb); |
1913 | } |
1914 | EXPORT_SYMBOL(balance_dirty_pages_ratelimited); |
1915 | |
1916 | /** |
1917 | * wb_over_bg_thresh - does @wb need to be written back? |
1918 | * @wb: bdi_writeback of interest |
1919 | * |
1920 | * Determines whether background writeback should keep writing @wb or it's |
1921 | * clean enough. |
1922 | * |
1923 | * Return: %true if writeback should continue. |
1924 | */ |
1925 | bool wb_over_bg_thresh(struct bdi_writeback *wb) |
1926 | { |
1927 | struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) }; |
1928 | struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) }; |
1929 | struct dirty_throttle_control * const gdtc = &gdtc_stor; |
1930 | struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ? |
1931 | &mdtc_stor : NULL; |
1932 | |
1933 | /* |
1934 | * Similar to balance_dirty_pages() but ignores pages being written |
1935 | * as we're trying to decide whether to put more under writeback. |
1936 | */ |
1937 | gdtc->avail = global_dirtyable_memory(); |
1938 | gdtc->dirty = global_node_page_state(NR_FILE_DIRTY) + |
1939 | global_node_page_state(NR_UNSTABLE_NFS); |
1940 | domain_dirty_limits(gdtc); |
1941 | |
1942 | if (gdtc->dirty > gdtc->bg_thresh) |
1943 | return true; |
1944 | |
1945 | if (wb_stat(wb, WB_RECLAIMABLE) > |
1946 | wb_calc_thresh(gdtc->wb, gdtc->bg_thresh)) |
1947 | return true; |
1948 | |
1949 | if (mdtc) { |
1950 | unsigned long filepages, headroom, writeback; |
1951 | |
1952 | mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty, |
1953 | &writeback); |
1954 | mdtc_calc_avail(mdtc, filepages, headroom); |
1955 | domain_dirty_limits(mdtc); /* ditto, ignore writeback */ |
1956 | |
1957 | if (mdtc->dirty > mdtc->bg_thresh) |
1958 | return true; |
1959 | |
1960 | if (wb_stat(wb, WB_RECLAIMABLE) > |
1961 | wb_calc_thresh(mdtc->wb, mdtc->bg_thresh)) |
1962 | return true; |
1963 | } |
1964 | |
1965 | return false; |
1966 | } |
1967 | |
1968 | /* |
1969 | * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs |
1970 | */ |
1971 | int dirty_writeback_centisecs_handler(struct ctl_table *table, int write, |
1972 | void __user *buffer, size_t *length, loff_t *ppos) |
1973 | { |
1974 | unsigned int old_interval = dirty_writeback_interval; |
1975 | int ret; |
1976 | |
1977 | ret = proc_dointvec(table, write, buffer, length, ppos); |
1978 | |
1979 | /* |
1980 | * Writing 0 to dirty_writeback_interval will disable periodic writeback |
1981 | * and a different non-zero value will wakeup the writeback threads. |
1982 | * wb_wakeup_delayed() would be more appropriate, but it's a pain to |
1983 | * iterate over all bdis and wbs. |
1984 | * The reason we do this is to make the change take effect immediately. |
1985 | */ |
1986 | if (!ret && write && dirty_writeback_interval && |
1987 | dirty_writeback_interval != old_interval) |
1988 | wakeup_flusher_threads(WB_REASON_PERIODIC); |
1989 | |
1990 | return ret; |
1991 | } |
1992 | |
1993 | #ifdef CONFIG_BLOCK |
1994 | void laptop_mode_timer_fn(struct timer_list *t) |
1995 | { |
1996 | struct backing_dev_info *backing_dev_info = |
1997 | from_timer(backing_dev_info, t, laptop_mode_wb_timer); |
1998 | |
1999 | wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER); |
2000 | } |
2001 | |
2002 | /* |
2003 | * We've spun up the disk and we're in laptop mode: schedule writeback |
2004 | * of all dirty data a few seconds from now. If the flush is already scheduled |
2005 | * then push it back - the user is still using the disk. |
2006 | */ |
2007 | void laptop_io_completion(struct backing_dev_info *info) |
2008 | { |
2009 | mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); |
2010 | } |
2011 | |
2012 | /* |
2013 | * We're in laptop mode and we've just synced. The sync's writes will have |
2014 | * caused another writeback to be scheduled by laptop_io_completion. |
2015 | * Nothing needs to be written back anymore, so we unschedule the writeback. |
2016 | */ |
2017 | void laptop_sync_completion(void) |
2018 | { |
2019 | struct backing_dev_info *bdi; |
2020 | |
2021 | rcu_read_lock(); |
2022 | |
2023 | list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) |
2024 | del_timer(&bdi->laptop_mode_wb_timer); |
2025 | |
2026 | rcu_read_unlock(); |
2027 | } |
2028 | #endif |
2029 | |
2030 | /* |
2031 | * If ratelimit_pages is too high then we can get into dirty-data overload |
2032 | * if a large number of processes all perform writes at the same time. |
2033 | * If it is too low then SMP machines will call the (expensive) |
2034 | * get_writeback_state too often. |
2035 | * |
2036 | * Here we set ratelimit_pages to a level which ensures that when all CPUs are |
2037 | * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory |
2038 | * thresholds. |
2039 | */ |
2040 | |
2041 | void writeback_set_ratelimit(void) |
2042 | { |
2043 | struct wb_domain *dom = &global_wb_domain; |
2044 | unsigned long background_thresh; |
2045 | unsigned long dirty_thresh; |
2046 | |
2047 | global_dirty_limits(&background_thresh, &dirty_thresh); |
2048 | dom->dirty_limit = dirty_thresh; |
2049 | ratelimit_pages = dirty_thresh / (num_online_cpus() * 32); |
2050 | if (ratelimit_pages < 16) |
2051 | ratelimit_pages = 16; |
2052 | } |
2053 | |
2054 | static int page_writeback_cpu_online(unsigned int cpu) |
2055 | { |
2056 | writeback_set_ratelimit(); |
2057 | return 0; |
2058 | } |
2059 | |
2060 | /* |
2061 | * Called early on to tune the page writeback dirty limits. |
2062 | * |
2063 | * We used to scale dirty pages according to how total memory |
2064 | * related to pages that could be allocated for buffers (by |
2065 | * comparing nr_free_buffer_pages() to vm_total_pages. |
2066 | * |
2067 | * However, that was when we used "dirty_ratio" to scale with |
2068 | * all memory, and we don't do that any more. "dirty_ratio" |
2069 | * is now applied to total non-HIGHPAGE memory (by subtracting |
2070 | * totalhigh_pages from vm_total_pages), and as such we can't |
2071 | * get into the old insane situation any more where we had |
2072 | * large amounts of dirty pages compared to a small amount of |
2073 | * non-HIGHMEM memory. |
2074 | * |
2075 | * But we might still want to scale the dirty_ratio by how |
2076 | * much memory the box has.. |
2077 | */ |
2078 | void __init page_writeback_init(void) |
2079 | { |
2080 | BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL)); |
2081 | |
2082 | cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online" , |
2083 | page_writeback_cpu_online, NULL); |
2084 | cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead" , NULL, |
2085 | page_writeback_cpu_online); |
2086 | } |
2087 | |
2088 | /** |
2089 | * tag_pages_for_writeback - tag pages to be written by write_cache_pages |
2090 | * @mapping: address space structure to write |
2091 | * @start: starting page index |
2092 | * @end: ending page index (inclusive) |
2093 | * |
2094 | * This function scans the page range from @start to @end (inclusive) and tags |
2095 | * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is |
2096 | * that write_cache_pages (or whoever calls this function) will then use |
2097 | * TOWRITE tag to identify pages eligible for writeback. This mechanism is |
2098 | * used to avoid livelocking of writeback by a process steadily creating new |
2099 | * dirty pages in the file (thus it is important for this function to be quick |
2100 | * so that it can tag pages faster than a dirtying process can create them). |
2101 | */ |
2102 | void tag_pages_for_writeback(struct address_space *mapping, |
2103 | pgoff_t start, pgoff_t end) |
2104 | { |
2105 | XA_STATE(xas, &mapping->i_pages, start); |
2106 | unsigned int tagged = 0; |
2107 | void *page; |
2108 | |
2109 | xas_lock_irq(&xas); |
2110 | xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) { |
2111 | xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE); |
2112 | if (++tagged % XA_CHECK_SCHED) |
2113 | continue; |
2114 | |
2115 | xas_pause(&xas); |
2116 | xas_unlock_irq(&xas); |
2117 | cond_resched(); |
2118 | xas_lock_irq(&xas); |
2119 | } |
2120 | xas_unlock_irq(&xas); |
2121 | } |
2122 | EXPORT_SYMBOL(tag_pages_for_writeback); |
2123 | |
2124 | /** |
2125 | * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. |
2126 | * @mapping: address space structure to write |
2127 | * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
2128 | * @writepage: function called for each page |
2129 | * @data: data passed to writepage function |
2130 | * |
2131 | * If a page is already under I/O, write_cache_pages() skips it, even |
2132 | * if it's dirty. This is desirable behaviour for memory-cleaning writeback, |
2133 | * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() |
2134 | * and msync() need to guarantee that all the data which was dirty at the time |
2135 | * the call was made get new I/O started against them. If wbc->sync_mode is |
2136 | * WB_SYNC_ALL then we were called for data integrity and we must wait for |
2137 | * existing IO to complete. |
2138 | * |
2139 | * To avoid livelocks (when other process dirties new pages), we first tag |
2140 | * pages which should be written back with TOWRITE tag and only then start |
2141 | * writing them. For data-integrity sync we have to be careful so that we do |
2142 | * not miss some pages (e.g., because some other process has cleared TOWRITE |
2143 | * tag we set). The rule we follow is that TOWRITE tag can be cleared only |
2144 | * by the process clearing the DIRTY tag (and submitting the page for IO). |
2145 | * |
2146 | * To avoid deadlocks between range_cyclic writeback and callers that hold |
2147 | * pages in PageWriteback to aggregate IO until write_cache_pages() returns, |
2148 | * we do not loop back to the start of the file. Doing so causes a page |
2149 | * lock/page writeback access order inversion - we should only ever lock |
2150 | * multiple pages in ascending page->index order, and looping back to the start |
2151 | * of the file violates that rule and causes deadlocks. |
2152 | * |
2153 | * Return: %0 on success, negative error code otherwise |
2154 | */ |
2155 | int write_cache_pages(struct address_space *mapping, |
2156 | struct writeback_control *wbc, writepage_t writepage, |
2157 | void *data) |
2158 | { |
2159 | int ret = 0; |
2160 | int done = 0; |
2161 | int error; |
2162 | struct pagevec pvec; |
2163 | int nr_pages; |
2164 | pgoff_t uninitialized_var(writeback_index); |
2165 | pgoff_t index; |
2166 | pgoff_t end; /* Inclusive */ |
2167 | pgoff_t done_index; |
2168 | int range_whole = 0; |
2169 | xa_mark_t tag; |
2170 | |
2171 | pagevec_init(&pvec); |
2172 | if (wbc->range_cyclic) { |
2173 | writeback_index = mapping->writeback_index; /* prev offset */ |
2174 | index = writeback_index; |
2175 | end = -1; |
2176 | } else { |
2177 | index = wbc->range_start >> PAGE_SHIFT; |
2178 | end = wbc->range_end >> PAGE_SHIFT; |
2179 | if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) |
2180 | range_whole = 1; |
2181 | } |
2182 | if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) |
2183 | tag = PAGECACHE_TAG_TOWRITE; |
2184 | else |
2185 | tag = PAGECACHE_TAG_DIRTY; |
2186 | if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) |
2187 | tag_pages_for_writeback(mapping, index, end); |
2188 | done_index = index; |
2189 | while (!done && (index <= end)) { |
2190 | int i; |
2191 | |
2192 | nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end, |
2193 | tag); |
2194 | if (nr_pages == 0) |
2195 | break; |
2196 | |
2197 | for (i = 0; i < nr_pages; i++) { |
2198 | struct page *page = pvec.pages[i]; |
2199 | |
2200 | done_index = page->index; |
2201 | |
2202 | lock_page(page); |
2203 | |
2204 | /* |
2205 | * Page truncated or invalidated. We can freely skip it |
2206 | * then, even for data integrity operations: the page |
2207 | * has disappeared concurrently, so there could be no |
2208 | * real expectation of this data interity operation |
2209 | * even if there is now a new, dirty page at the same |
2210 | * pagecache address. |
2211 | */ |
2212 | if (unlikely(page->mapping != mapping)) { |
2213 | continue_unlock: |
2214 | unlock_page(page); |
2215 | continue; |
2216 | } |
2217 | |
2218 | if (!PageDirty(page)) { |
2219 | /* someone wrote it for us */ |
2220 | goto continue_unlock; |
2221 | } |
2222 | |
2223 | if (PageWriteback(page)) { |
2224 | if (wbc->sync_mode != WB_SYNC_NONE) |
2225 | wait_on_page_writeback(page); |
2226 | else |
2227 | goto continue_unlock; |
2228 | } |
2229 | |
2230 | BUG_ON(PageWriteback(page)); |
2231 | if (!clear_page_dirty_for_io(page)) |
2232 | goto continue_unlock; |
2233 | |
2234 | trace_wbc_writepage(wbc, inode_to_bdi(mapping->host)); |
2235 | error = (*writepage)(page, wbc, data); |
2236 | if (unlikely(error)) { |
2237 | /* |
2238 | * Handle errors according to the type of |
2239 | * writeback. There's no need to continue for |
2240 | * background writeback. Just push done_index |
2241 | * past this page so media errors won't choke |
2242 | * writeout for the entire file. For integrity |
2243 | * writeback, we must process the entire dirty |
2244 | * set regardless of errors because the fs may |
2245 | * still have state to clear for each page. In |
2246 | * that case we continue processing and return |
2247 | * the first error. |
2248 | */ |
2249 | if (error == AOP_WRITEPAGE_ACTIVATE) { |
2250 | unlock_page(page); |
2251 | error = 0; |
2252 | } else if (wbc->sync_mode != WB_SYNC_ALL) { |
2253 | ret = error; |
2254 | done_index = page->index + 1; |
2255 | done = 1; |
2256 | break; |
2257 | } |
2258 | if (!ret) |
2259 | ret = error; |
2260 | } |
2261 | |
2262 | /* |
2263 | * We stop writing back only if we are not doing |
2264 | * integrity sync. In case of integrity sync we have to |
2265 | * keep going until we have written all the pages |
2266 | * we tagged for writeback prior to entering this loop. |
2267 | */ |
2268 | if (--wbc->nr_to_write <= 0 && |
2269 | wbc->sync_mode == WB_SYNC_NONE) { |
2270 | done = 1; |
2271 | break; |
2272 | } |
2273 | } |
2274 | pagevec_release(&pvec); |
2275 | cond_resched(); |
2276 | } |
2277 | |
2278 | /* |
2279 | * If we hit the last page and there is more work to be done: wrap |
2280 | * back the index back to the start of the file for the next |
2281 | * time we are called. |
2282 | */ |
2283 | if (wbc->range_cyclic && !done) |
2284 | done_index = 0; |
2285 | if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) |
2286 | mapping->writeback_index = done_index; |
2287 | |
2288 | return ret; |
2289 | } |
2290 | EXPORT_SYMBOL(write_cache_pages); |
2291 | |
2292 | /* |
2293 | * Function used by generic_writepages to call the real writepage |
2294 | * function and set the mapping flags on error |
2295 | */ |
2296 | static int __writepage(struct page *page, struct writeback_control *wbc, |
2297 | void *data) |
2298 | { |
2299 | struct address_space *mapping = data; |
2300 | int ret = mapping->a_ops->writepage(page, wbc); |
2301 | mapping_set_error(mapping, ret); |
2302 | return ret; |
2303 | } |
2304 | |
2305 | /** |
2306 | * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. |
2307 | * @mapping: address space structure to write |
2308 | * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
2309 | * |
2310 | * This is a library function, which implements the writepages() |
2311 | * address_space_operation. |
2312 | * |
2313 | * Return: %0 on success, negative error code otherwise |
2314 | */ |
2315 | int generic_writepages(struct address_space *mapping, |
2316 | struct writeback_control *wbc) |
2317 | { |
2318 | struct blk_plug plug; |
2319 | int ret; |
2320 | |
2321 | /* deal with chardevs and other special file */ |
2322 | if (!mapping->a_ops->writepage) |
2323 | return 0; |
2324 | |
2325 | blk_start_plug(&plug); |
2326 | ret = write_cache_pages(mapping, wbc, __writepage, mapping); |
2327 | blk_finish_plug(&plug); |
2328 | return ret; |
2329 | } |
2330 | |
2331 | EXPORT_SYMBOL(generic_writepages); |
2332 | |
2333 | int do_writepages(struct address_space *mapping, struct writeback_control *wbc) |
2334 | { |
2335 | int ret; |
2336 | |
2337 | if (wbc->nr_to_write <= 0) |
2338 | return 0; |
2339 | while (1) { |
2340 | if (mapping->a_ops->writepages) |
2341 | ret = mapping->a_ops->writepages(mapping, wbc); |
2342 | else |
2343 | ret = generic_writepages(mapping, wbc); |
2344 | if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL)) |
2345 | break; |
2346 | cond_resched(); |
2347 | congestion_wait(BLK_RW_ASYNC, HZ/50); |
2348 | } |
2349 | return ret; |
2350 | } |
2351 | |
2352 | /** |
2353 | * write_one_page - write out a single page and wait on I/O |
2354 | * @page: the page to write |
2355 | * |
2356 | * The page must be locked by the caller and will be unlocked upon return. |
2357 | * |
2358 | * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this |
2359 | * function returns. |
2360 | * |
2361 | * Return: %0 on success, negative error code otherwise |
2362 | */ |
2363 | int write_one_page(struct page *page) |
2364 | { |
2365 | struct address_space *mapping = page->mapping; |
2366 | int ret = 0; |
2367 | struct writeback_control wbc = { |
2368 | .sync_mode = WB_SYNC_ALL, |
2369 | .nr_to_write = 1, |
2370 | }; |
2371 | |
2372 | BUG_ON(!PageLocked(page)); |
2373 | |
2374 | wait_on_page_writeback(page); |
2375 | |
2376 | if (clear_page_dirty_for_io(page)) { |
2377 | get_page(page); |
2378 | ret = mapping->a_ops->writepage(page, &wbc); |
2379 | if (ret == 0) |
2380 | wait_on_page_writeback(page); |
2381 | put_page(page); |
2382 | } else { |
2383 | unlock_page(page); |
2384 | } |
2385 | |
2386 | if (!ret) |
2387 | ret = filemap_check_errors(mapping); |
2388 | return ret; |
2389 | } |
2390 | EXPORT_SYMBOL(write_one_page); |
2391 | |
2392 | /* |
2393 | * For address_spaces which do not use buffers nor write back. |
2394 | */ |
2395 | int __set_page_dirty_no_writeback(struct page *page) |
2396 | { |
2397 | if (!PageDirty(page)) |
2398 | return !TestSetPageDirty(page); |
2399 | return 0; |
2400 | } |
2401 | |
2402 | /* |
2403 | * Helper function for set_page_dirty family. |
2404 | * |
2405 | * Caller must hold lock_page_memcg(). |
2406 | * |
2407 | * NOTE: This relies on being atomic wrt interrupts. |
2408 | */ |
2409 | void account_page_dirtied(struct page *page, struct address_space *mapping) |
2410 | { |
2411 | struct inode *inode = mapping->host; |
2412 | |
2413 | trace_writeback_dirty_page(page, mapping); |
2414 | |
2415 | if (mapping_cap_account_dirty(mapping)) { |
2416 | struct bdi_writeback *wb; |
2417 | |
2418 | inode_attach_wb(inode, page); |
2419 | wb = inode_to_wb(inode); |
2420 | |
2421 | __inc_lruvec_page_state(page, NR_FILE_DIRTY); |
2422 | __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING); |
2423 | __inc_node_page_state(page, NR_DIRTIED); |
2424 | inc_wb_stat(wb, WB_RECLAIMABLE); |
2425 | inc_wb_stat(wb, WB_DIRTIED); |
2426 | task_io_account_write(PAGE_SIZE); |
2427 | current->nr_dirtied++; |
2428 | this_cpu_inc(bdp_ratelimits); |
2429 | } |
2430 | } |
2431 | EXPORT_SYMBOL(account_page_dirtied); |
2432 | |
2433 | /* |
2434 | * Helper function for deaccounting dirty page without writeback. |
2435 | * |
2436 | * Caller must hold lock_page_memcg(). |
2437 | */ |
2438 | void account_page_cleaned(struct page *page, struct address_space *mapping, |
2439 | struct bdi_writeback *wb) |
2440 | { |
2441 | if (mapping_cap_account_dirty(mapping)) { |
2442 | dec_lruvec_page_state(page, NR_FILE_DIRTY); |
2443 | dec_zone_page_state(page, NR_ZONE_WRITE_PENDING); |
2444 | dec_wb_stat(wb, WB_RECLAIMABLE); |
2445 | task_io_account_cancelled_write(PAGE_SIZE); |
2446 | } |
2447 | } |
2448 | |
2449 | /* |
2450 | * For address_spaces which do not use buffers. Just tag the page as dirty in |
2451 | * the xarray. |
2452 | * |
2453 | * This is also used when a single buffer is being dirtied: we want to set the |
2454 | * page dirty in that case, but not all the buffers. This is a "bottom-up" |
2455 | * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. |
2456 | * |
2457 | * The caller must ensure this doesn't race with truncation. Most will simply |
2458 | * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and |
2459 | * the pte lock held, which also locks out truncation. |
2460 | */ |
2461 | int __set_page_dirty_nobuffers(struct page *page) |
2462 | { |
2463 | lock_page_memcg(page); |
2464 | if (!TestSetPageDirty(page)) { |
2465 | struct address_space *mapping = page_mapping(page); |
2466 | unsigned long flags; |
2467 | |
2468 | if (!mapping) { |
2469 | unlock_page_memcg(page); |
2470 | return 1; |
2471 | } |
2472 | |
2473 | xa_lock_irqsave(&mapping->i_pages, flags); |
2474 | BUG_ON(page_mapping(page) != mapping); |
2475 | WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); |
2476 | account_page_dirtied(page, mapping); |
2477 | __xa_set_mark(&mapping->i_pages, page_index(page), |
2478 | PAGECACHE_TAG_DIRTY); |
2479 | xa_unlock_irqrestore(&mapping->i_pages, flags); |
2480 | unlock_page_memcg(page); |
2481 | |
2482 | if (mapping->host) { |
2483 | /* !PageAnon && !swapper_space */ |
2484 | __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); |
2485 | } |
2486 | return 1; |
2487 | } |
2488 | unlock_page_memcg(page); |
2489 | return 0; |
2490 | } |
2491 | EXPORT_SYMBOL(__set_page_dirty_nobuffers); |
2492 | |
2493 | /* |
2494 | * Call this whenever redirtying a page, to de-account the dirty counters |
2495 | * (NR_DIRTIED, WB_DIRTIED, tsk->nr_dirtied), so that they match the written |
2496 | * counters (NR_WRITTEN, WB_WRITTEN) in long term. The mismatches will lead to |
2497 | * systematic errors in balanced_dirty_ratelimit and the dirty pages position |
2498 | * control. |
2499 | */ |
2500 | void account_page_redirty(struct page *page) |
2501 | { |
2502 | struct address_space *mapping = page->mapping; |
2503 | |
2504 | if (mapping && mapping_cap_account_dirty(mapping)) { |
2505 | struct inode *inode = mapping->host; |
2506 | struct bdi_writeback *wb; |
2507 | struct wb_lock_cookie cookie = {}; |
2508 | |
2509 | wb = unlocked_inode_to_wb_begin(inode, &cookie); |
2510 | current->nr_dirtied--; |
2511 | dec_node_page_state(page, NR_DIRTIED); |
2512 | dec_wb_stat(wb, WB_DIRTIED); |
2513 | unlocked_inode_to_wb_end(inode, &cookie); |
2514 | } |
2515 | } |
2516 | EXPORT_SYMBOL(account_page_redirty); |
2517 | |
2518 | /* |
2519 | * When a writepage implementation decides that it doesn't want to write this |
2520 | * page for some reason, it should redirty the locked page via |
2521 | * redirty_page_for_writepage() and it should then unlock the page and return 0 |
2522 | */ |
2523 | int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) |
2524 | { |
2525 | int ret; |
2526 | |
2527 | wbc->pages_skipped++; |
2528 | ret = __set_page_dirty_nobuffers(page); |
2529 | account_page_redirty(page); |
2530 | return ret; |
2531 | } |
2532 | EXPORT_SYMBOL(redirty_page_for_writepage); |
2533 | |
2534 | /* |
2535 | * Dirty a page. |
2536 | * |
2537 | * For pages with a mapping this should be done under the page lock |
2538 | * for the benefit of asynchronous memory errors who prefer a consistent |
2539 | * dirty state. This rule can be broken in some special cases, |
2540 | * but should be better not to. |
2541 | * |
2542 | * If the mapping doesn't provide a set_page_dirty a_op, then |
2543 | * just fall through and assume that it wants buffer_heads. |
2544 | */ |
2545 | int set_page_dirty(struct page *page) |
2546 | { |
2547 | struct address_space *mapping = page_mapping(page); |
2548 | |
2549 | page = compound_head(page); |
2550 | if (likely(mapping)) { |
2551 | int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; |
2552 | /* |
2553 | * readahead/lru_deactivate_page could remain |
2554 | * PG_readahead/PG_reclaim due to race with end_page_writeback |
2555 | * About readahead, if the page is written, the flags would be |
2556 | * reset. So no problem. |
2557 | * About lru_deactivate_page, if the page is redirty, the flag |
2558 | * will be reset. So no problem. but if the page is used by readahead |
2559 | * it will confuse readahead and make it restart the size rampup |
2560 | * process. But it's a trivial problem. |
2561 | */ |
2562 | if (PageReclaim(page)) |
2563 | ClearPageReclaim(page); |
2564 | #ifdef CONFIG_BLOCK |
2565 | if (!spd) |
2566 | spd = __set_page_dirty_buffers; |
2567 | #endif |
2568 | return (*spd)(page); |
2569 | } |
2570 | if (!PageDirty(page)) { |
2571 | if (!TestSetPageDirty(page)) |
2572 | return 1; |
2573 | } |
2574 | return 0; |
2575 | } |
2576 | EXPORT_SYMBOL(set_page_dirty); |
2577 | |
2578 | /* |
2579 | * set_page_dirty() is racy if the caller has no reference against |
2580 | * page->mapping->host, and if the page is unlocked. This is because another |
2581 | * CPU could truncate the page off the mapping and then free the mapping. |
2582 | * |
2583 | * Usually, the page _is_ locked, or the caller is a user-space process which |
2584 | * holds a reference on the inode by having an open file. |
2585 | * |
2586 | * In other cases, the page should be locked before running set_page_dirty(). |
2587 | */ |
2588 | int set_page_dirty_lock(struct page *page) |
2589 | { |
2590 | int ret; |
2591 | |
2592 | lock_page(page); |
2593 | ret = set_page_dirty(page); |
2594 | unlock_page(page); |
2595 | return ret; |
2596 | } |
2597 | EXPORT_SYMBOL(set_page_dirty_lock); |
2598 | |
2599 | /* |
2600 | * This cancels just the dirty bit on the kernel page itself, it does NOT |
2601 | * actually remove dirty bits on any mmap's that may be around. It also |
2602 | * leaves the page tagged dirty, so any sync activity will still find it on |
2603 | * the dirty lists, and in particular, clear_page_dirty_for_io() will still |
2604 | * look at the dirty bits in the VM. |
2605 | * |
2606 | * Doing this should *normally* only ever be done when a page is truncated, |
2607 | * and is not actually mapped anywhere at all. However, fs/buffer.c does |
2608 | * this when it notices that somebody has cleaned out all the buffers on a |
2609 | * page without actually doing it through the VM. Can you say "ext3 is |
2610 | * horribly ugly"? Thought you could. |
2611 | */ |
2612 | void __cancel_dirty_page(struct page *page) |
2613 | { |
2614 | struct address_space *mapping = page_mapping(page); |
2615 | |
2616 | if (mapping_cap_account_dirty(mapping)) { |
2617 | struct inode *inode = mapping->host; |
2618 | struct bdi_writeback *wb; |
2619 | struct wb_lock_cookie cookie = {}; |
2620 | |
2621 | lock_page_memcg(page); |
2622 | wb = unlocked_inode_to_wb_begin(inode, &cookie); |
2623 | |
2624 | if (TestClearPageDirty(page)) |
2625 | account_page_cleaned(page, mapping, wb); |
2626 | |
2627 | unlocked_inode_to_wb_end(inode, &cookie); |
2628 | unlock_page_memcg(page); |
2629 | } else { |
2630 | ClearPageDirty(page); |
2631 | } |
2632 | } |
2633 | EXPORT_SYMBOL(__cancel_dirty_page); |
2634 | |
2635 | /* |
2636 | * Clear a page's dirty flag, while caring for dirty memory accounting. |
2637 | * Returns true if the page was previously dirty. |
2638 | * |
2639 | * This is for preparing to put the page under writeout. We leave the page |
2640 | * tagged as dirty in the xarray so that a concurrent write-for-sync |
2641 | * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage |
2642 | * implementation will run either set_page_writeback() or set_page_dirty(), |
2643 | * at which stage we bring the page's dirty flag and xarray dirty tag |
2644 | * back into sync. |
2645 | * |
2646 | * This incoherency between the page's dirty flag and xarray tag is |
2647 | * unfortunate, but it only exists while the page is locked. |
2648 | */ |
2649 | int clear_page_dirty_for_io(struct page *page) |
2650 | { |
2651 | struct address_space *mapping = page_mapping(page); |
2652 | int ret = 0; |
2653 | |
2654 | BUG_ON(!PageLocked(page)); |
2655 | |
2656 | if (mapping && mapping_cap_account_dirty(mapping)) { |
2657 | struct inode *inode = mapping->host; |
2658 | struct bdi_writeback *wb; |
2659 | struct wb_lock_cookie cookie = {}; |
2660 | |
2661 | /* |
2662 | * Yes, Virginia, this is indeed insane. |
2663 | * |
2664 | * We use this sequence to make sure that |
2665 | * (a) we account for dirty stats properly |
2666 | * (b) we tell the low-level filesystem to |
2667 | * mark the whole page dirty if it was |
2668 | * dirty in a pagetable. Only to then |
2669 | * (c) clean the page again and return 1 to |
2670 | * cause the writeback. |
2671 | * |
2672 | * This way we avoid all nasty races with the |
2673 | * dirty bit in multiple places and clearing |
2674 | * them concurrently from different threads. |
2675 | * |
2676 | * Note! Normally the "set_page_dirty(page)" |
2677 | * has no effect on the actual dirty bit - since |
2678 | * that will already usually be set. But we |
2679 | * need the side effects, and it can help us |
2680 | * avoid races. |
2681 | * |
2682 | * We basically use the page "master dirty bit" |
2683 | * as a serialization point for all the different |
2684 | * threads doing their things. |
2685 | */ |
2686 | if (page_mkclean(page)) |
2687 | set_page_dirty(page); |
2688 | /* |
2689 | * We carefully synchronise fault handlers against |
2690 | * installing a dirty pte and marking the page dirty |
2691 | * at this point. We do this by having them hold the |
2692 | * page lock while dirtying the page, and pages are |
2693 | * always locked coming in here, so we get the desired |
2694 | * exclusion. |
2695 | */ |
2696 | wb = unlocked_inode_to_wb_begin(inode, &cookie); |
2697 | if (TestClearPageDirty(page)) { |
2698 | dec_lruvec_page_state(page, NR_FILE_DIRTY); |
2699 | dec_zone_page_state(page, NR_ZONE_WRITE_PENDING); |
2700 | dec_wb_stat(wb, WB_RECLAIMABLE); |
2701 | ret = 1; |
2702 | } |
2703 | unlocked_inode_to_wb_end(inode, &cookie); |
2704 | return ret; |
2705 | } |
2706 | return TestClearPageDirty(page); |
2707 | } |
2708 | EXPORT_SYMBOL(clear_page_dirty_for_io); |
2709 | |
2710 | int test_clear_page_writeback(struct page *page) |
2711 | { |
2712 | struct address_space *mapping = page_mapping(page); |
2713 | struct mem_cgroup *memcg; |
2714 | struct lruvec *lruvec; |
2715 | int ret; |
2716 | |
2717 | memcg = lock_page_memcg(page); |
2718 | lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page)); |
2719 | if (mapping && mapping_use_writeback_tags(mapping)) { |
2720 | struct inode *inode = mapping->host; |
2721 | struct backing_dev_info *bdi = inode_to_bdi(inode); |
2722 | unsigned long flags; |
2723 | |
2724 | xa_lock_irqsave(&mapping->i_pages, flags); |
2725 | ret = TestClearPageWriteback(page); |
2726 | if (ret) { |
2727 | __xa_clear_mark(&mapping->i_pages, page_index(page), |
2728 | PAGECACHE_TAG_WRITEBACK); |
2729 | if (bdi_cap_account_writeback(bdi)) { |
2730 | struct bdi_writeback *wb = inode_to_wb(inode); |
2731 | |
2732 | dec_wb_stat(wb, WB_WRITEBACK); |
2733 | __wb_writeout_inc(wb); |
2734 | } |
2735 | } |
2736 | |
2737 | if (mapping->host && !mapping_tagged(mapping, |
2738 | PAGECACHE_TAG_WRITEBACK)) |
2739 | sb_clear_inode_writeback(mapping->host); |
2740 | |
2741 | xa_unlock_irqrestore(&mapping->i_pages, flags); |
2742 | } else { |
2743 | ret = TestClearPageWriteback(page); |
2744 | } |
2745 | /* |
2746 | * NOTE: Page might be free now! Writeback doesn't hold a page |
2747 | * reference on its own, it relies on truncation to wait for |
2748 | * the clearing of PG_writeback. The below can only access |
2749 | * page state that is static across allocation cycles. |
2750 | */ |
2751 | if (ret) { |
2752 | dec_lruvec_state(lruvec, NR_WRITEBACK); |
2753 | dec_zone_page_state(page, NR_ZONE_WRITE_PENDING); |
2754 | inc_node_page_state(page, NR_WRITTEN); |
2755 | } |
2756 | __unlock_page_memcg(memcg); |
2757 | return ret; |
2758 | } |
2759 | |
2760 | int __test_set_page_writeback(struct page *page, bool keep_write) |
2761 | { |
2762 | struct address_space *mapping = page_mapping(page); |
2763 | int ret; |
2764 | |
2765 | lock_page_memcg(page); |
2766 | if (mapping && mapping_use_writeback_tags(mapping)) { |
2767 | XA_STATE(xas, &mapping->i_pages, page_index(page)); |
2768 | struct inode *inode = mapping->host; |
2769 | struct backing_dev_info *bdi = inode_to_bdi(inode); |
2770 | unsigned long flags; |
2771 | |
2772 | xas_lock_irqsave(&xas, flags); |
2773 | xas_load(&xas); |
2774 | ret = TestSetPageWriteback(page); |
2775 | if (!ret) { |
2776 | bool on_wblist; |
2777 | |
2778 | on_wblist = mapping_tagged(mapping, |
2779 | PAGECACHE_TAG_WRITEBACK); |
2780 | |
2781 | xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK); |
2782 | if (bdi_cap_account_writeback(bdi)) |
2783 | inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK); |
2784 | |
2785 | /* |
2786 | * We can come through here when swapping anonymous |
2787 | * pages, so we don't necessarily have an inode to track |
2788 | * for sync. |
2789 | */ |
2790 | if (mapping->host && !on_wblist) |
2791 | sb_mark_inode_writeback(mapping->host); |
2792 | } |
2793 | if (!PageDirty(page)) |
2794 | xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY); |
2795 | if (!keep_write) |
2796 | xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE); |
2797 | xas_unlock_irqrestore(&xas, flags); |
2798 | } else { |
2799 | ret = TestSetPageWriteback(page); |
2800 | } |
2801 | if (!ret) { |
2802 | inc_lruvec_page_state(page, NR_WRITEBACK); |
2803 | inc_zone_page_state(page, NR_ZONE_WRITE_PENDING); |
2804 | } |
2805 | unlock_page_memcg(page); |
2806 | return ret; |
2807 | |
2808 | } |
2809 | EXPORT_SYMBOL(__test_set_page_writeback); |
2810 | |
2811 | /** |
2812 | * wait_for_stable_page() - wait for writeback to finish, if necessary. |
2813 | * @page: The page to wait on. |
2814 | * |
2815 | * This function determines if the given page is related to a backing device |
2816 | * that requires page contents to be held stable during writeback. If so, then |
2817 | * it will wait for any pending writeback to complete. |
2818 | */ |
2819 | void wait_for_stable_page(struct page *page) |
2820 | { |
2821 | if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host))) |
2822 | wait_on_page_writeback(page); |
2823 | } |
2824 | EXPORT_SYMBOL_GPL(wait_for_stable_page); |
2825 | |