blob: 46e36366a03a79cf444c4b14760392f2ec775ff6
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/notifier.h> |
31 | #include <linux/smp.h> |
32 | #include <linux/sysctl.h> |
33 | #include <linux/cpu.h> |
34 | #include <linux/syscalls.h> |
35 | #include <linux/buffer_head.h> /* __set_page_dirty_buffers */ |
36 | #include <linux/pagevec.h> |
37 | #include <linux/timer.h> |
38 | #include <linux/sched/rt.h> |
39 | #include <linux/mm_inline.h> |
40 | #include <trace/events/writeback.h> |
41 | |
42 | #include "internal.h" |
43 | |
44 | /* |
45 | * Sleep at most 200ms at a time in balance_dirty_pages(). |
46 | */ |
47 | #define MAX_PAUSE max(HZ/5, 1) |
48 | |
49 | /* |
50 | * Try to keep balance_dirty_pages() call intervals higher than this many pages |
51 | * by raising pause time to max_pause when falls below it. |
52 | */ |
53 | #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10)) |
54 | |
55 | /* |
56 | * Estimate write bandwidth at 200ms intervals. |
57 | */ |
58 | #define BANDWIDTH_INTERVAL max(HZ/5, 1) |
59 | |
60 | #define RATELIMIT_CALC_SHIFT 10 |
61 | |
62 | /* |
63 | * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited |
64 | * will look to see if it needs to force writeback or throttling. |
65 | */ |
66 | static long ratelimit_pages = 32; |
67 | |
68 | /* The following parameters are exported via /proc/sys/vm */ |
69 | |
70 | /* |
71 | * Start background writeback (via writeback threads) at this percentage |
72 | */ |
73 | int dirty_background_ratio = 10; |
74 | |
75 | /* |
76 | * dirty_background_bytes starts at 0 (disabled) so that it is a function of |
77 | * dirty_background_ratio * the amount of dirtyable memory |
78 | */ |
79 | unsigned long dirty_background_bytes; |
80 | |
81 | /* |
82 | * free highmem will not be subtracted from the total free memory |
83 | * for calculating free ratios if vm_highmem_is_dirtyable is true |
84 | */ |
85 | int vm_highmem_is_dirtyable; |
86 | |
87 | /* |
88 | * The generator of dirty data starts writeback at this percentage |
89 | */ |
90 | int vm_dirty_ratio = 20; |
91 | |
92 | /* |
93 | * vm_dirty_bytes starts at 0 (disabled) so that it is a function of |
94 | * vm_dirty_ratio * the amount of dirtyable memory |
95 | */ |
96 | unsigned long vm_dirty_bytes; |
97 | |
98 | /* |
99 | * The interval between `kupdate'-style writebacks |
100 | */ |
101 | unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ |
102 | |
103 | EXPORT_SYMBOL_GPL(dirty_writeback_interval); |
104 | |
105 | /* |
106 | * The longest time for which data is allowed to remain dirty |
107 | */ |
108 | unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ |
109 | |
110 | /* |
111 | * Flag that makes the machine dump writes/reads and block dirtyings. |
112 | */ |
113 | int block_dump; |
114 | |
115 | /* |
116 | * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: |
117 | * a full sync is triggered after this time elapses without any disk activity. |
118 | */ |
119 | int laptop_mode; |
120 | |
121 | EXPORT_SYMBOL(laptop_mode); |
122 | |
123 | /* End of sysctl-exported parameters */ |
124 | |
125 | 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 | * Returns 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 | * Returns 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_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 | * Returns 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 | * Returns %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(unsigned long t) |
628 | { |
629 | struct wb_domain *dom = (void *)t; |
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 | init_timer_deferrable(&dom->period_timer); |
653 | dom->period_timer.function = writeout_period; |
654 | dom->period_timer.data = (unsigned long)dom; |
655 | |
656 | dom->dirty_limit_tstamp = jiffies; |
657 | |
658 | return fprop_global_init(&dom->completions, gfp); |
659 | } |
660 | |
661 | #ifdef CONFIG_CGROUP_WRITEBACK |
662 | void wb_domain_exit(struct wb_domain *dom) |
663 | { |
664 | del_timer_sync(&dom->period_timer); |
665 | fprop_global_destroy(&dom->completions); |
666 | } |
667 | #endif |
668 | |
669 | /* |
670 | * bdi_min_ratio keeps the sum of the minimum dirty shares of all |
671 | * registered backing devices, which, for obvious reasons, can not |
672 | * exceed 100%. |
673 | */ |
674 | static unsigned int bdi_min_ratio; |
675 | |
676 | int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) |
677 | { |
678 | int ret = 0; |
679 | |
680 | spin_lock_bh(&bdi_lock); |
681 | if (min_ratio > bdi->max_ratio) { |
682 | ret = -EINVAL; |
683 | } else { |
684 | min_ratio -= bdi->min_ratio; |
685 | if (bdi_min_ratio + min_ratio < 100) { |
686 | bdi_min_ratio += min_ratio; |
687 | bdi->min_ratio += min_ratio; |
688 | } else { |
689 | ret = -EINVAL; |
690 | } |
691 | } |
692 | spin_unlock_bh(&bdi_lock); |
693 | |
694 | return ret; |
695 | } |
696 | |
697 | int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) |
698 | { |
699 | int ret = 0; |
700 | |
701 | if (max_ratio > 100) |
702 | return -EINVAL; |
703 | |
704 | spin_lock_bh(&bdi_lock); |
705 | if (bdi->min_ratio > max_ratio) { |
706 | ret = -EINVAL; |
707 | } else { |
708 | bdi->max_ratio = max_ratio; |
709 | bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100; |
710 | } |
711 | spin_unlock_bh(&bdi_lock); |
712 | |
713 | return ret; |
714 | } |
715 | EXPORT_SYMBOL(bdi_set_max_ratio); |
716 | |
717 | static unsigned long dirty_freerun_ceiling(unsigned long thresh, |
718 | unsigned long bg_thresh) |
719 | { |
720 | return (thresh + bg_thresh) / 2; |
721 | } |
722 | |
723 | static unsigned long hard_dirty_limit(struct wb_domain *dom, |
724 | unsigned long thresh) |
725 | { |
726 | return max(thresh, dom->dirty_limit); |
727 | } |
728 | |
729 | /* |
730 | * Memory which can be further allocated to a memcg domain is capped by |
731 | * system-wide clean memory excluding the amount being used in the domain. |
732 | */ |
733 | static void mdtc_calc_avail(struct dirty_throttle_control *mdtc, |
734 | unsigned long filepages, unsigned long headroom) |
735 | { |
736 | struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc); |
737 | unsigned long clean = filepages - min(filepages, mdtc->dirty); |
738 | unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty); |
739 | unsigned long other_clean = global_clean - min(global_clean, clean); |
740 | |
741 | mdtc->avail = filepages + min(headroom, other_clean); |
742 | } |
743 | |
744 | /** |
745 | * __wb_calc_thresh - @wb's share of dirty throttling threshold |
746 | * @dtc: dirty_throttle_context of interest |
747 | * |
748 | * Returns @wb's dirty limit in pages. The term "dirty" in the context of |
749 | * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages. |
750 | * |
751 | * Note that balance_dirty_pages() will only seriously take it as a hard limit |
752 | * when sleeping max_pause per page is not enough to keep the dirty pages under |
753 | * control. For example, when the device is completely stalled due to some error |
754 | * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key. |
755 | * In the other normal situations, it acts more gently by throttling the tasks |
756 | * more (rather than completely block them) when the wb dirty pages go high. |
757 | * |
758 | * It allocates high/low dirty limits to fast/slow devices, in order to prevent |
759 | * - starving fast devices |
760 | * - piling up dirty pages (that will take long time to sync) on slow devices |
761 | * |
762 | * The wb's share of dirty limit will be adapting to its throughput and |
763 | * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. |
764 | */ |
765 | static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc) |
766 | { |
767 | struct wb_domain *dom = dtc_dom(dtc); |
768 | unsigned long thresh = dtc->thresh; |
769 | u64 wb_thresh; |
770 | long numerator, denominator; |
771 | unsigned long wb_min_ratio, wb_max_ratio; |
772 | |
773 | /* |
774 | * Calculate this BDI's share of the thresh ratio. |
775 | */ |
776 | fprop_fraction_percpu(&dom->completions, dtc->wb_completions, |
777 | &numerator, &denominator); |
778 | |
779 | wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100; |
780 | wb_thresh *= numerator; |
781 | do_div(wb_thresh, denominator); |
782 | |
783 | wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio); |
784 | |
785 | wb_thresh += (thresh * wb_min_ratio) / 100; |
786 | if (wb_thresh > (thresh * wb_max_ratio) / 100) |
787 | wb_thresh = thresh * wb_max_ratio / 100; |
788 | |
789 | return wb_thresh; |
790 | } |
791 | |
792 | unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh) |
793 | { |
794 | struct dirty_throttle_control gdtc = { GDTC_INIT(wb), |
795 | .thresh = thresh }; |
796 | return __wb_calc_thresh(&gdtc); |
797 | } |
798 | |
799 | /* |
800 | * setpoint - dirty 3 |
801 | * f(dirty) := 1.0 + (----------------) |
802 | * limit - setpoint |
803 | * |
804 | * it's a 3rd order polynomial that subjects to |
805 | * |
806 | * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast |
807 | * (2) f(setpoint) = 1.0 => the balance point |
808 | * (3) f(limit) = 0 => the hard limit |
809 | * (4) df/dx <= 0 => negative feedback control |
810 | * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) |
811 | * => fast response on large errors; small oscillation near setpoint |
812 | */ |
813 | static long long pos_ratio_polynom(unsigned long setpoint, |
814 | unsigned long dirty, |
815 | unsigned long limit) |
816 | { |
817 | long long pos_ratio; |
818 | long x; |
819 | |
820 | x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, |
821 | (limit - setpoint) | 1); |
822 | pos_ratio = x; |
823 | pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
824 | pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
825 | pos_ratio += 1 << RATELIMIT_CALC_SHIFT; |
826 | |
827 | return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT); |
828 | } |
829 | |
830 | /* |
831 | * Dirty position control. |
832 | * |
833 | * (o) global/bdi setpoints |
834 | * |
835 | * We want the dirty pages be balanced around the global/wb setpoints. |
836 | * When the number of dirty pages is higher/lower than the setpoint, the |
837 | * dirty position control ratio (and hence task dirty ratelimit) will be |
838 | * decreased/increased to bring the dirty pages back to the setpoint. |
839 | * |
840 | * pos_ratio = 1 << RATELIMIT_CALC_SHIFT |
841 | * |
842 | * if (dirty < setpoint) scale up pos_ratio |
843 | * if (dirty > setpoint) scale down pos_ratio |
844 | * |
845 | * if (wb_dirty < wb_setpoint) scale up pos_ratio |
846 | * if (wb_dirty > wb_setpoint) scale down pos_ratio |
847 | * |
848 | * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT |
849 | * |
850 | * (o) global control line |
851 | * |
852 | * ^ pos_ratio |
853 | * | |
854 | * | |<===== global dirty control scope ======>| |
855 | * 2.0 .............* |
856 | * | .* |
857 | * | . * |
858 | * | . * |
859 | * | . * |
860 | * | . * |
861 | * | . * |
862 | * 1.0 ................................* |
863 | * | . . * |
864 | * | . . * |
865 | * | . . * |
866 | * | . . * |
867 | * | . . * |
868 | * 0 +------------.------------------.----------------------*-------------> |
869 | * freerun^ setpoint^ limit^ dirty pages |
870 | * |
871 | * (o) wb control line |
872 | * |
873 | * ^ pos_ratio |
874 | * | |
875 | * | * |
876 | * | * |
877 | * | * |
878 | * | * |
879 | * | * |<=========== span ============>| |
880 | * 1.0 .......................* |
881 | * | . * |
882 | * | . * |
883 | * | . * |
884 | * | . * |
885 | * | . * |
886 | * | . * |
887 | * | . * |
888 | * | . * |
889 | * | . * |
890 | * | . * |
891 | * | . * |
892 | * 1/4 ...............................................* * * * * * * * * * * * |
893 | * | . . |
894 | * | . . |
895 | * | . . |
896 | * 0 +----------------------.-------------------------------.-------------> |
897 | * wb_setpoint^ x_intercept^ |
898 | * |
899 | * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can |
900 | * be smoothly throttled down to normal if it starts high in situations like |
901 | * - start writing to a slow SD card and a fast disk at the same time. The SD |
902 | * card's wb_dirty may rush to many times higher than wb_setpoint. |
903 | * - the wb dirty thresh drops quickly due to change of JBOD workload |
904 | */ |
905 | static void wb_position_ratio(struct dirty_throttle_control *dtc) |
906 | { |
907 | struct bdi_writeback *wb = dtc->wb; |
908 | unsigned long write_bw = wb->avg_write_bandwidth; |
909 | unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh); |
910 | unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); |
911 | unsigned long wb_thresh = dtc->wb_thresh; |
912 | unsigned long x_intercept; |
913 | unsigned long setpoint; /* dirty pages' target balance point */ |
914 | unsigned long wb_setpoint; |
915 | unsigned long span; |
916 | long long pos_ratio; /* for scaling up/down the rate limit */ |
917 | long x; |
918 | |
919 | dtc->pos_ratio = 0; |
920 | |
921 | if (unlikely(dtc->dirty >= limit)) |
922 | return; |
923 | |
924 | /* |
925 | * global setpoint |
926 | * |
927 | * See comment for pos_ratio_polynom(). |
928 | */ |
929 | setpoint = (freerun + limit) / 2; |
930 | pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit); |
931 | |
932 | /* |
933 | * The strictlimit feature is a tool preventing mistrusted filesystems |
934 | * from growing a large number of dirty pages before throttling. For |
935 | * such filesystems balance_dirty_pages always checks wb counters |
936 | * against wb limits. Even if global "nr_dirty" is under "freerun". |
937 | * This is especially important for fuse which sets bdi->max_ratio to |
938 | * 1% by default. Without strictlimit feature, fuse writeback may |
939 | * consume arbitrary amount of RAM because it is accounted in |
940 | * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty". |
941 | * |
942 | * Here, in wb_position_ratio(), we calculate pos_ratio based on |
943 | * two values: wb_dirty and wb_thresh. Let's consider an example: |
944 | * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global |
945 | * limits are set by default to 10% and 20% (background and throttle). |
946 | * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages. |
947 | * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is |
948 | * about ~6K pages (as the average of background and throttle wb |
949 | * limits). The 3rd order polynomial will provide positive feedback if |
950 | * wb_dirty is under wb_setpoint and vice versa. |
951 | * |
952 | * Note, that we cannot use global counters in these calculations |
953 | * because we want to throttle process writing to a strictlimit wb |
954 | * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB |
955 | * in the example above). |
956 | */ |
957 | if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { |
958 | long long wb_pos_ratio; |
959 | |
960 | if (dtc->wb_dirty < 8) { |
961 | dtc->pos_ratio = min_t(long long, pos_ratio * 2, |
962 | 2 << RATELIMIT_CALC_SHIFT); |
963 | return; |
964 | } |
965 | |
966 | if (dtc->wb_dirty >= wb_thresh) |
967 | return; |
968 | |
969 | wb_setpoint = dirty_freerun_ceiling(wb_thresh, |
970 | dtc->wb_bg_thresh); |
971 | |
972 | if (wb_setpoint == 0 || wb_setpoint == wb_thresh) |
973 | return; |
974 | |
975 | wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty, |
976 | wb_thresh); |
977 | |
978 | /* |
979 | * Typically, for strictlimit case, wb_setpoint << setpoint |
980 | * and pos_ratio >> wb_pos_ratio. In the other words global |
981 | * state ("dirty") is not limiting factor and we have to |
982 | * make decision based on wb counters. But there is an |
983 | * important case when global pos_ratio should get precedence: |
984 | * global limits are exceeded (e.g. due to activities on other |
985 | * wb's) while given strictlimit wb is below limit. |
986 | * |
987 | * "pos_ratio * wb_pos_ratio" would work for the case above, |
988 | * but it would look too non-natural for the case of all |
989 | * activity in the system coming from a single strictlimit wb |
990 | * with bdi->max_ratio == 100%. |
991 | * |
992 | * Note that min() below somewhat changes the dynamics of the |
993 | * control system. Normally, pos_ratio value can be well over 3 |
994 | * (when globally we are at freerun and wb is well below wb |
995 | * setpoint). Now the maximum pos_ratio in the same situation |
996 | * is 2. We might want to tweak this if we observe the control |
997 | * system is too slow to adapt. |
998 | */ |
999 | dtc->pos_ratio = min(pos_ratio, wb_pos_ratio); |
1000 | return; |
1001 | } |
1002 | |
1003 | /* |
1004 | * We have computed basic pos_ratio above based on global situation. If |
1005 | * the wb is over/under its share of dirty pages, we want to scale |
1006 | * pos_ratio further down/up. That is done by the following mechanism. |
1007 | */ |
1008 | |
1009 | /* |
1010 | * wb setpoint |
1011 | * |
1012 | * f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint) |
1013 | * |
1014 | * x_intercept - wb_dirty |
1015 | * := -------------------------- |
1016 | * x_intercept - wb_setpoint |
1017 | * |
1018 | * The main wb control line is a linear function that subjects to |
1019 | * |
1020 | * (1) f(wb_setpoint) = 1.0 |
1021 | * (2) k = - 1 / (8 * write_bw) (in single wb case) |
1022 | * or equally: x_intercept = wb_setpoint + 8 * write_bw |
1023 | * |
1024 | * For single wb case, the dirty pages are observed to fluctuate |
1025 | * regularly within range |
1026 | * [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2] |
1027 | * for various filesystems, where (2) can yield in a reasonable 12.5% |
1028 | * fluctuation range for pos_ratio. |
1029 | * |
1030 | * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its |
1031 | * own size, so move the slope over accordingly and choose a slope that |
1032 | * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh. |
1033 | */ |
1034 | if (unlikely(wb_thresh > dtc->thresh)) |
1035 | wb_thresh = dtc->thresh; |
1036 | /* |
1037 | * It's very possible that wb_thresh is close to 0 not because the |
1038 | * device is slow, but that it has remained inactive for long time. |
1039 | * Honour such devices a reasonable good (hopefully IO efficient) |
1040 | * threshold, so that the occasional writes won't be blocked and active |
1041 | * writes can rampup the threshold quickly. |
1042 | */ |
1043 | wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8); |
1044 | /* |
1045 | * scale global setpoint to wb's: |
1046 | * wb_setpoint = setpoint * wb_thresh / thresh |
1047 | */ |
1048 | x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1); |
1049 | wb_setpoint = setpoint * (u64)x >> 16; |
1050 | /* |
1051 | * Use span=(8*write_bw) in single wb case as indicated by |
1052 | * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case. |
1053 | * |
1054 | * wb_thresh thresh - wb_thresh |
1055 | * span = --------- * (8 * write_bw) + ------------------ * wb_thresh |
1056 | * thresh thresh |
1057 | */ |
1058 | span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16; |
1059 | x_intercept = wb_setpoint + span; |
1060 | |
1061 | if (dtc->wb_dirty < x_intercept - span / 4) { |
1062 | pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty), |
1063 | (x_intercept - wb_setpoint) | 1); |
1064 | } else |
1065 | pos_ratio /= 4; |
1066 | |
1067 | /* |
1068 | * wb reserve area, safeguard against dirty pool underrun and disk idle |
1069 | * It may push the desired control point of global dirty pages higher |
1070 | * than setpoint. |
1071 | */ |
1072 | x_intercept = wb_thresh / 2; |
1073 | if (dtc->wb_dirty < x_intercept) { |
1074 | if (dtc->wb_dirty > x_intercept / 8) |
1075 | pos_ratio = div_u64(pos_ratio * x_intercept, |
1076 | dtc->wb_dirty); |
1077 | else |
1078 | pos_ratio *= 8; |
1079 | } |
1080 | |
1081 | dtc->pos_ratio = pos_ratio; |
1082 | } |
1083 | |
1084 | static void wb_update_write_bandwidth(struct bdi_writeback *wb, |
1085 | unsigned long elapsed, |
1086 | unsigned long written) |
1087 | { |
1088 | const unsigned long period = roundup_pow_of_two(3 * HZ); |
1089 | unsigned long avg = wb->avg_write_bandwidth; |
1090 | unsigned long old = wb->write_bandwidth; |
1091 | u64 bw; |
1092 | |
1093 | /* |
1094 | * bw = written * HZ / elapsed |
1095 | * |
1096 | * bw * elapsed + write_bandwidth * (period - elapsed) |
1097 | * write_bandwidth = --------------------------------------------------- |
1098 | * period |
1099 | * |
1100 | * @written may have decreased due to account_page_redirty(). |
1101 | * Avoid underflowing @bw calculation. |
1102 | */ |
1103 | bw = written - min(written, wb->written_stamp); |
1104 | bw *= HZ; |
1105 | if (unlikely(elapsed > period)) { |
1106 | do_div(bw, elapsed); |
1107 | avg = bw; |
1108 | goto out; |
1109 | } |
1110 | bw += (u64)wb->write_bandwidth * (period - elapsed); |
1111 | bw >>= ilog2(period); |
1112 | |
1113 | /* |
1114 | * one more level of smoothing, for filtering out sudden spikes |
1115 | */ |
1116 | if (avg > old && old >= (unsigned long)bw) |
1117 | avg -= (avg - old) >> 3; |
1118 | |
1119 | if (avg < old && old <= (unsigned long)bw) |
1120 | avg += (old - avg) >> 3; |
1121 | |
1122 | out: |
1123 | /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */ |
1124 | avg = max(avg, 1LU); |
1125 | if (wb_has_dirty_io(wb)) { |
1126 | long delta = avg - wb->avg_write_bandwidth; |
1127 | WARN_ON_ONCE(atomic_long_add_return(delta, |
1128 | &wb->bdi->tot_write_bandwidth) <= 0); |
1129 | } |
1130 | wb->write_bandwidth = bw; |
1131 | wb->avg_write_bandwidth = avg; |
1132 | } |
1133 | |
1134 | static void update_dirty_limit(struct dirty_throttle_control *dtc) |
1135 | { |
1136 | struct wb_domain *dom = dtc_dom(dtc); |
1137 | unsigned long thresh = dtc->thresh; |
1138 | unsigned long limit = dom->dirty_limit; |
1139 | |
1140 | /* |
1141 | * Follow up in one step. |
1142 | */ |
1143 | if (limit < thresh) { |
1144 | limit = thresh; |
1145 | goto update; |
1146 | } |
1147 | |
1148 | /* |
1149 | * Follow down slowly. Use the higher one as the target, because thresh |
1150 | * may drop below dirty. This is exactly the reason to introduce |
1151 | * dom->dirty_limit which is guaranteed to lie above the dirty pages. |
1152 | */ |
1153 | thresh = max(thresh, dtc->dirty); |
1154 | if (limit > thresh) { |
1155 | limit -= (limit - thresh) >> 5; |
1156 | goto update; |
1157 | } |
1158 | return; |
1159 | update: |
1160 | dom->dirty_limit = limit; |
1161 | } |
1162 | |
1163 | static void domain_update_bandwidth(struct dirty_throttle_control *dtc, |
1164 | unsigned long now) |
1165 | { |
1166 | struct wb_domain *dom = dtc_dom(dtc); |
1167 | |
1168 | /* |
1169 | * check locklessly first to optimize away locking for the most time |
1170 | */ |
1171 | if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) |
1172 | return; |
1173 | |
1174 | spin_lock(&dom->lock); |
1175 | if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) { |
1176 | update_dirty_limit(dtc); |
1177 | dom->dirty_limit_tstamp = now; |
1178 | } |
1179 | spin_unlock(&dom->lock); |
1180 | } |
1181 | |
1182 | /* |
1183 | * Maintain wb->dirty_ratelimit, the base dirty throttle rate. |
1184 | * |
1185 | * Normal wb tasks will be curbed at or below it in long term. |
1186 | * Obviously it should be around (write_bw / N) when there are N dd tasks. |
1187 | */ |
1188 | static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc, |
1189 | unsigned long dirtied, |
1190 | unsigned long elapsed) |
1191 | { |
1192 | struct bdi_writeback *wb = dtc->wb; |
1193 | unsigned long dirty = dtc->dirty; |
1194 | unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh); |
1195 | unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); |
1196 | unsigned long setpoint = (freerun + limit) / 2; |
1197 | unsigned long write_bw = wb->avg_write_bandwidth; |
1198 | unsigned long dirty_ratelimit = wb->dirty_ratelimit; |
1199 | unsigned long dirty_rate; |
1200 | unsigned long task_ratelimit; |
1201 | unsigned long balanced_dirty_ratelimit; |
1202 | unsigned long step; |
1203 | unsigned long x; |
1204 | unsigned long shift; |
1205 | |
1206 | /* |
1207 | * The dirty rate will match the writeout rate in long term, except |
1208 | * when dirty pages are truncated by userspace or re-dirtied by FS. |
1209 | */ |
1210 | dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed; |
1211 | |
1212 | /* |
1213 | * task_ratelimit reflects each dd's dirty rate for the past 200ms. |
1214 | */ |
1215 | task_ratelimit = (u64)dirty_ratelimit * |
1216 | dtc->pos_ratio >> RATELIMIT_CALC_SHIFT; |
1217 | task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */ |
1218 | |
1219 | /* |
1220 | * A linear estimation of the "balanced" throttle rate. The theory is, |
1221 | * if there are N dd tasks, each throttled at task_ratelimit, the wb's |
1222 | * dirty_rate will be measured to be (N * task_ratelimit). So the below |
1223 | * formula will yield the balanced rate limit (write_bw / N). |
1224 | * |
1225 | * Note that the expanded form is not a pure rate feedback: |
1226 | * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1) |
1227 | * but also takes pos_ratio into account: |
1228 | * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2) |
1229 | * |
1230 | * (1) is not realistic because pos_ratio also takes part in balancing |
1231 | * the dirty rate. Consider the state |
1232 | * pos_ratio = 0.5 (3) |
1233 | * rate = 2 * (write_bw / N) (4) |
1234 | * If (1) is used, it will stuck in that state! Because each dd will |
1235 | * be throttled at |
1236 | * task_ratelimit = pos_ratio * rate = (write_bw / N) (5) |
1237 | * yielding |
1238 | * dirty_rate = N * task_ratelimit = write_bw (6) |
1239 | * put (6) into (1) we get |
1240 | * rate_(i+1) = rate_(i) (7) |
1241 | * |
1242 | * So we end up using (2) to always keep |
1243 | * rate_(i+1) ~= (write_bw / N) (8) |
1244 | * regardless of the value of pos_ratio. As long as (8) is satisfied, |
1245 | * pos_ratio is able to drive itself to 1.0, which is not only where |
1246 | * the dirty count meet the setpoint, but also where the slope of |
1247 | * pos_ratio is most flat and hence task_ratelimit is least fluctuated. |
1248 | */ |
1249 | balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw, |
1250 | dirty_rate | 1); |
1251 | /* |
1252 | * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw |
1253 | */ |
1254 | if (unlikely(balanced_dirty_ratelimit > write_bw)) |
1255 | balanced_dirty_ratelimit = write_bw; |
1256 | |
1257 | /* |
1258 | * We could safely do this and return immediately: |
1259 | * |
1260 | * wb->dirty_ratelimit = balanced_dirty_ratelimit; |
1261 | * |
1262 | * However to get a more stable dirty_ratelimit, the below elaborated |
1263 | * code makes use of task_ratelimit to filter out singular points and |
1264 | * limit the step size. |
1265 | * |
1266 | * The below code essentially only uses the relative value of |
1267 | * |
1268 | * task_ratelimit - dirty_ratelimit |
1269 | * = (pos_ratio - 1) * dirty_ratelimit |
1270 | * |
1271 | * which reflects the direction and size of dirty position error. |
1272 | */ |
1273 | |
1274 | /* |
1275 | * dirty_ratelimit will follow balanced_dirty_ratelimit iff |
1276 | * task_ratelimit is on the same side of dirty_ratelimit, too. |
1277 | * For example, when |
1278 | * - dirty_ratelimit > balanced_dirty_ratelimit |
1279 | * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint) |
1280 | * lowering dirty_ratelimit will help meet both the position and rate |
1281 | * control targets. Otherwise, don't update dirty_ratelimit if it will |
1282 | * only help meet the rate target. After all, what the users ultimately |
1283 | * feel and care are stable dirty rate and small position error. |
1284 | * |
1285 | * |task_ratelimit - dirty_ratelimit| is used to limit the step size |
1286 | * and filter out the singular points of balanced_dirty_ratelimit. Which |
1287 | * keeps jumping around randomly and can even leap far away at times |
1288 | * due to the small 200ms estimation period of dirty_rate (we want to |
1289 | * keep that period small to reduce time lags). |
1290 | */ |
1291 | step = 0; |
1292 | |
1293 | /* |
1294 | * For strictlimit case, calculations above were based on wb counters |
1295 | * and limits (starting from pos_ratio = wb_position_ratio() and up to |
1296 | * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate). |
1297 | * Hence, to calculate "step" properly, we have to use wb_dirty as |
1298 | * "dirty" and wb_setpoint as "setpoint". |
1299 | * |
1300 | * We rampup dirty_ratelimit forcibly if wb_dirty is low because |
1301 | * it's possible that wb_thresh is close to zero due to inactivity |
1302 | * of backing device. |
1303 | */ |
1304 | if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) { |
1305 | dirty = dtc->wb_dirty; |
1306 | if (dtc->wb_dirty < 8) |
1307 | setpoint = dtc->wb_dirty + 1; |
1308 | else |
1309 | setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2; |
1310 | } |
1311 | |
1312 | if (dirty < setpoint) { |
1313 | x = min3(wb->balanced_dirty_ratelimit, |
1314 | balanced_dirty_ratelimit, task_ratelimit); |
1315 | if (dirty_ratelimit < x) |
1316 | step = x - dirty_ratelimit; |
1317 | } else { |
1318 | x = max3(wb->balanced_dirty_ratelimit, |
1319 | balanced_dirty_ratelimit, task_ratelimit); |
1320 | if (dirty_ratelimit > x) |
1321 | step = dirty_ratelimit - x; |
1322 | } |
1323 | |
1324 | /* |
1325 | * Don't pursue 100% rate matching. It's impossible since the balanced |
1326 | * rate itself is constantly fluctuating. So decrease the track speed |
1327 | * when it gets close to the target. Helps eliminate pointless tremors. |
1328 | */ |
1329 | shift = dirty_ratelimit / (2 * step + 1); |
1330 | if (shift < BITS_PER_LONG) |
1331 | step = DIV_ROUND_UP(step >> shift, 8); |
1332 | else |
1333 | step = 0; |
1334 | |
1335 | if (dirty_ratelimit < balanced_dirty_ratelimit) |
1336 | dirty_ratelimit += step; |
1337 | else |
1338 | dirty_ratelimit -= step; |
1339 | |
1340 | wb->dirty_ratelimit = max(dirty_ratelimit, 1UL); |
1341 | wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit; |
1342 | |
1343 | trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit); |
1344 | } |
1345 | |
1346 | static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc, |
1347 | struct dirty_throttle_control *mdtc, |
1348 | unsigned long start_time, |
1349 | bool update_ratelimit) |
1350 | { |
1351 | struct bdi_writeback *wb = gdtc->wb; |
1352 | unsigned long now = jiffies; |
1353 | unsigned long elapsed = now - wb->bw_time_stamp; |
1354 | unsigned long dirtied; |
1355 | unsigned long written; |
1356 | |
1357 | lockdep_assert_held(&wb->list_lock); |
1358 | |
1359 | /* |
1360 | * rate-limit, only update once every 200ms. |
1361 | */ |
1362 | if (elapsed < BANDWIDTH_INTERVAL) |
1363 | return; |
1364 | |
1365 | dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]); |
1366 | written = percpu_counter_read(&wb->stat[WB_WRITTEN]); |
1367 | |
1368 | /* |
1369 | * Skip quiet periods when disk bandwidth is under-utilized. |
1370 | * (at least 1s idle time between two flusher runs) |
1371 | */ |
1372 | if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time)) |
1373 | goto snapshot; |
1374 | |
1375 | if (update_ratelimit) { |
1376 | domain_update_bandwidth(gdtc, now); |
1377 | wb_update_dirty_ratelimit(gdtc, dirtied, elapsed); |
1378 | |
1379 | /* |
1380 | * @mdtc is always NULL if !CGROUP_WRITEBACK but the |
1381 | * compiler has no way to figure that out. Help it. |
1382 | */ |
1383 | if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) { |
1384 | domain_update_bandwidth(mdtc, now); |
1385 | wb_update_dirty_ratelimit(mdtc, dirtied, elapsed); |
1386 | } |
1387 | } |
1388 | wb_update_write_bandwidth(wb, elapsed, written); |
1389 | |
1390 | snapshot: |
1391 | wb->dirtied_stamp = dirtied; |
1392 | wb->written_stamp = written; |
1393 | wb->bw_time_stamp = now; |
1394 | } |
1395 | |
1396 | void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time) |
1397 | { |
1398 | struct dirty_throttle_control gdtc = { GDTC_INIT(wb) }; |
1399 | |
1400 | __wb_update_bandwidth(&gdtc, NULL, start_time, false); |
1401 | } |
1402 | |
1403 | /* |
1404 | * After a task dirtied this many pages, balance_dirty_pages_ratelimited() |
1405 | * will look to see if it needs to start dirty throttling. |
1406 | * |
1407 | * If dirty_poll_interval is too low, big NUMA machines will call the expensive |
1408 | * global_page_state() too often. So scale it near-sqrt to the safety margin |
1409 | * (the number of pages we may dirty without exceeding the dirty limits). |
1410 | */ |
1411 | static unsigned long dirty_poll_interval(unsigned long dirty, |
1412 | unsigned long thresh) |
1413 | { |
1414 | if (thresh > dirty) |
1415 | return 1UL << (ilog2(thresh - dirty) >> 1); |
1416 | |
1417 | return 1; |
1418 | } |
1419 | |
1420 | static unsigned long wb_max_pause(struct bdi_writeback *wb, |
1421 | unsigned long wb_dirty) |
1422 | { |
1423 | unsigned long bw = wb->avg_write_bandwidth; |
1424 | unsigned long t; |
1425 | |
1426 | /* |
1427 | * Limit pause time for small memory systems. If sleeping for too long |
1428 | * time, a small pool of dirty/writeback pages may go empty and disk go |
1429 | * idle. |
1430 | * |
1431 | * 8 serves as the safety ratio. |
1432 | */ |
1433 | t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8)); |
1434 | t++; |
1435 | |
1436 | return min_t(unsigned long, t, MAX_PAUSE); |
1437 | } |
1438 | |
1439 | static long wb_min_pause(struct bdi_writeback *wb, |
1440 | long max_pause, |
1441 | unsigned long task_ratelimit, |
1442 | unsigned long dirty_ratelimit, |
1443 | int *nr_dirtied_pause) |
1444 | { |
1445 | long hi = ilog2(wb->avg_write_bandwidth); |
1446 | long lo = ilog2(wb->dirty_ratelimit); |
1447 | long t; /* target pause */ |
1448 | long pause; /* estimated next pause */ |
1449 | int pages; /* target nr_dirtied_pause */ |
1450 | |
1451 | /* target for 10ms pause on 1-dd case */ |
1452 | t = max(1, HZ / 100); |
1453 | |
1454 | /* |
1455 | * Scale up pause time for concurrent dirtiers in order to reduce CPU |
1456 | * overheads. |
1457 | * |
1458 | * (N * 10ms) on 2^N concurrent tasks. |
1459 | */ |
1460 | if (hi > lo) |
1461 | t += (hi - lo) * (10 * HZ) / 1024; |
1462 | |
1463 | /* |
1464 | * This is a bit convoluted. We try to base the next nr_dirtied_pause |
1465 | * on the much more stable dirty_ratelimit. However the next pause time |
1466 | * will be computed based on task_ratelimit and the two rate limits may |
1467 | * depart considerably at some time. Especially if task_ratelimit goes |
1468 | * below dirty_ratelimit/2 and the target pause is max_pause, the next |
1469 | * pause time will be max_pause*2 _trimmed down_ to max_pause. As a |
1470 | * result task_ratelimit won't be executed faithfully, which could |
1471 | * eventually bring down dirty_ratelimit. |
1472 | * |
1473 | * We apply two rules to fix it up: |
1474 | * 1) try to estimate the next pause time and if necessary, use a lower |
1475 | * nr_dirtied_pause so as not to exceed max_pause. When this happens, |
1476 | * nr_dirtied_pause will be "dancing" with task_ratelimit. |
1477 | * 2) limit the target pause time to max_pause/2, so that the normal |
1478 | * small fluctuations of task_ratelimit won't trigger rule (1) and |
1479 | * nr_dirtied_pause will remain as stable as dirty_ratelimit. |
1480 | */ |
1481 | t = min(t, 1 + max_pause / 2); |
1482 | pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); |
1483 | |
1484 | /* |
1485 | * Tiny nr_dirtied_pause is found to hurt I/O performance in the test |
1486 | * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}. |
1487 | * When the 16 consecutive reads are often interrupted by some dirty |
1488 | * throttling pause during the async writes, cfq will go into idles |
1489 | * (deadline is fine). So push nr_dirtied_pause as high as possible |
1490 | * until reaches DIRTY_POLL_THRESH=32 pages. |
1491 | */ |
1492 | if (pages < DIRTY_POLL_THRESH) { |
1493 | t = max_pause; |
1494 | pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); |
1495 | if (pages > DIRTY_POLL_THRESH) { |
1496 | pages = DIRTY_POLL_THRESH; |
1497 | t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit; |
1498 | } |
1499 | } |
1500 | |
1501 | pause = HZ * pages / (task_ratelimit + 1); |
1502 | if (pause > max_pause) { |
1503 | t = max_pause; |
1504 | pages = task_ratelimit * t / roundup_pow_of_two(HZ); |
1505 | } |
1506 | |
1507 | *nr_dirtied_pause = pages; |
1508 | /* |
1509 | * The minimal pause time will normally be half the target pause time. |
1510 | */ |
1511 | return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t; |
1512 | } |
1513 | |
1514 | static inline void wb_dirty_limits(struct dirty_throttle_control *dtc) |
1515 | { |
1516 | struct bdi_writeback *wb = dtc->wb; |
1517 | unsigned long wb_reclaimable; |
1518 | |
1519 | /* |
1520 | * wb_thresh is not treated as some limiting factor as |
1521 | * dirty_thresh, due to reasons |
1522 | * - in JBOD setup, wb_thresh can fluctuate a lot |
1523 | * - in a system with HDD and USB key, the USB key may somehow |
1524 | * go into state (wb_dirty >> wb_thresh) either because |
1525 | * wb_dirty starts high, or because wb_thresh drops low. |
1526 | * In this case we don't want to hard throttle the USB key |
1527 | * dirtiers for 100 seconds until wb_dirty drops under |
1528 | * wb_thresh. Instead the auxiliary wb control line in |
1529 | * wb_position_ratio() will let the dirtier task progress |
1530 | * at some rate <= (write_bw / 2) for bringing down wb_dirty. |
1531 | */ |
1532 | dtc->wb_thresh = __wb_calc_thresh(dtc); |
1533 | dtc->wb_bg_thresh = dtc->thresh ? |
1534 | div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0; |
1535 | |
1536 | /* |
1537 | * In order to avoid the stacked BDI deadlock we need |
1538 | * to ensure we accurately count the 'dirty' pages when |
1539 | * the threshold is low. |
1540 | * |
1541 | * Otherwise it would be possible to get thresh+n pages |
1542 | * reported dirty, even though there are thresh-m pages |
1543 | * actually dirty; with m+n sitting in the percpu |
1544 | * deltas. |
1545 | */ |
1546 | if (dtc->wb_thresh < 2 * wb_stat_error(wb)) { |
1547 | wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE); |
1548 | dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK); |
1549 | } else { |
1550 | wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE); |
1551 | dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK); |
1552 | } |
1553 | } |
1554 | |
1555 | /* |
1556 | * balance_dirty_pages() must be called by processes which are generating dirty |
1557 | * data. It looks at the number of dirty pages in the machine and will force |
1558 | * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2. |
1559 | * If we're over `background_thresh' then the writeback threads are woken to |
1560 | * perform some writeout. |
1561 | */ |
1562 | static void balance_dirty_pages(struct address_space *mapping, |
1563 | struct bdi_writeback *wb, |
1564 | unsigned long pages_dirtied) |
1565 | { |
1566 | struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) }; |
1567 | struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) }; |
1568 | struct dirty_throttle_control * const gdtc = &gdtc_stor; |
1569 | struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ? |
1570 | &mdtc_stor : NULL; |
1571 | struct dirty_throttle_control *sdtc; |
1572 | unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */ |
1573 | long period; |
1574 | long pause; |
1575 | long max_pause; |
1576 | long min_pause; |
1577 | int nr_dirtied_pause; |
1578 | bool dirty_exceeded = false; |
1579 | unsigned long task_ratelimit; |
1580 | unsigned long dirty_ratelimit; |
1581 | struct backing_dev_info *bdi = wb->bdi; |
1582 | bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT; |
1583 | unsigned long start_time = jiffies; |
1584 | |
1585 | for (;;) { |
1586 | unsigned long now = jiffies; |
1587 | unsigned long dirty, thresh, bg_thresh; |
1588 | unsigned long m_dirty = 0; /* stop bogus uninit warnings */ |
1589 | unsigned long m_thresh = 0; |
1590 | unsigned long m_bg_thresh = 0; |
1591 | |
1592 | /* |
1593 | * Unstable writes are a feature of certain networked |
1594 | * filesystems (i.e. NFS) in which data may have been |
1595 | * written to the server's write cache, but has not yet |
1596 | * been flushed to permanent storage. |
1597 | */ |
1598 | nr_reclaimable = global_node_page_state(NR_FILE_DIRTY) + |
1599 | global_node_page_state(NR_UNSTABLE_NFS); |
1600 | gdtc->avail = global_dirtyable_memory(); |
1601 | gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK); |
1602 | |
1603 | domain_dirty_limits(gdtc); |
1604 | |
1605 | if (unlikely(strictlimit)) { |
1606 | wb_dirty_limits(gdtc); |
1607 | |
1608 | dirty = gdtc->wb_dirty; |
1609 | thresh = gdtc->wb_thresh; |
1610 | bg_thresh = gdtc->wb_bg_thresh; |
1611 | } else { |
1612 | dirty = gdtc->dirty; |
1613 | thresh = gdtc->thresh; |
1614 | bg_thresh = gdtc->bg_thresh; |
1615 | } |
1616 | |
1617 | if (mdtc) { |
1618 | unsigned long filepages, headroom, writeback; |
1619 | |
1620 | /* |
1621 | * If @wb belongs to !root memcg, repeat the same |
1622 | * basic calculations for the memcg domain. |
1623 | */ |
1624 | mem_cgroup_wb_stats(wb, &filepages, &headroom, |
1625 | &mdtc->dirty, &writeback); |
1626 | mdtc->dirty += writeback; |
1627 | mdtc_calc_avail(mdtc, filepages, headroom); |
1628 | |
1629 | domain_dirty_limits(mdtc); |
1630 | |
1631 | if (unlikely(strictlimit)) { |
1632 | wb_dirty_limits(mdtc); |
1633 | m_dirty = mdtc->wb_dirty; |
1634 | m_thresh = mdtc->wb_thresh; |
1635 | m_bg_thresh = mdtc->wb_bg_thresh; |
1636 | } else { |
1637 | m_dirty = mdtc->dirty; |
1638 | m_thresh = mdtc->thresh; |
1639 | m_bg_thresh = mdtc->bg_thresh; |
1640 | } |
1641 | } |
1642 | |
1643 | /* |
1644 | * Throttle it only when the background writeback cannot |
1645 | * catch-up. This avoids (excessively) small writeouts |
1646 | * when the wb limits are ramping up in case of !strictlimit. |
1647 | * |
1648 | * In strictlimit case make decision based on the wb counters |
1649 | * and limits. Small writeouts when the wb limits are ramping |
1650 | * up are the price we consciously pay for strictlimit-ing. |
1651 | * |
1652 | * If memcg domain is in effect, @dirty should be under |
1653 | * both global and memcg freerun ceilings. |
1654 | */ |
1655 | if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) && |
1656 | (!mdtc || |
1657 | m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) { |
1658 | unsigned long intv = dirty_poll_interval(dirty, thresh); |
1659 | unsigned long m_intv = ULONG_MAX; |
1660 | |
1661 | current->dirty_paused_when = now; |
1662 | current->nr_dirtied = 0; |
1663 | if (mdtc) |
1664 | m_intv = dirty_poll_interval(m_dirty, m_thresh); |
1665 | current->nr_dirtied_pause = min(intv, m_intv); |
1666 | break; |
1667 | } |
1668 | |
1669 | if (unlikely(!writeback_in_progress(wb))) |
1670 | wb_start_background_writeback(wb); |
1671 | |
1672 | /* |
1673 | * Calculate global domain's pos_ratio and select the |
1674 | * global dtc by default. |
1675 | */ |
1676 | if (!strictlimit) |
1677 | wb_dirty_limits(gdtc); |
1678 | |
1679 | dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) && |
1680 | ((gdtc->dirty > gdtc->thresh) || strictlimit); |
1681 | |
1682 | wb_position_ratio(gdtc); |
1683 | sdtc = gdtc; |
1684 | |
1685 | if (mdtc) { |
1686 | /* |
1687 | * If memcg domain is in effect, calculate its |
1688 | * pos_ratio. @wb should satisfy constraints from |
1689 | * both global and memcg domains. Choose the one |
1690 | * w/ lower pos_ratio. |
1691 | */ |
1692 | if (!strictlimit) |
1693 | wb_dirty_limits(mdtc); |
1694 | |
1695 | dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) && |
1696 | ((mdtc->dirty > mdtc->thresh) || strictlimit); |
1697 | |
1698 | wb_position_ratio(mdtc); |
1699 | if (mdtc->pos_ratio < gdtc->pos_ratio) |
1700 | sdtc = mdtc; |
1701 | } |
1702 | |
1703 | if (dirty_exceeded && !wb->dirty_exceeded) |
1704 | wb->dirty_exceeded = 1; |
1705 | |
1706 | if (time_is_before_jiffies(wb->bw_time_stamp + |
1707 | BANDWIDTH_INTERVAL)) { |
1708 | spin_lock(&wb->list_lock); |
1709 | __wb_update_bandwidth(gdtc, mdtc, start_time, true); |
1710 | spin_unlock(&wb->list_lock); |
1711 | } |
1712 | |
1713 | /* throttle according to the chosen dtc */ |
1714 | dirty_ratelimit = wb->dirty_ratelimit; |
1715 | task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >> |
1716 | RATELIMIT_CALC_SHIFT; |
1717 | max_pause = wb_max_pause(wb, sdtc->wb_dirty); |
1718 | min_pause = wb_min_pause(wb, max_pause, |
1719 | task_ratelimit, dirty_ratelimit, |
1720 | &nr_dirtied_pause); |
1721 | |
1722 | if (unlikely(task_ratelimit == 0)) { |
1723 | period = max_pause; |
1724 | pause = max_pause; |
1725 | goto pause; |
1726 | } |
1727 | period = HZ * pages_dirtied / task_ratelimit; |
1728 | pause = period; |
1729 | if (current->dirty_paused_when) |
1730 | pause -= now - current->dirty_paused_when; |
1731 | /* |
1732 | * For less than 1s think time (ext3/4 may block the dirtier |
1733 | * for up to 800ms from time to time on 1-HDD; so does xfs, |
1734 | * however at much less frequency), try to compensate it in |
1735 | * future periods by updating the virtual time; otherwise just |
1736 | * do a reset, as it may be a light dirtier. |
1737 | */ |
1738 | if (pause < min_pause) { |
1739 | trace_balance_dirty_pages(wb, |
1740 | sdtc->thresh, |
1741 | sdtc->bg_thresh, |
1742 | sdtc->dirty, |
1743 | sdtc->wb_thresh, |
1744 | sdtc->wb_dirty, |
1745 | dirty_ratelimit, |
1746 | task_ratelimit, |
1747 | pages_dirtied, |
1748 | period, |
1749 | min(pause, 0L), |
1750 | start_time); |
1751 | if (pause < -HZ) { |
1752 | current->dirty_paused_when = now; |
1753 | current->nr_dirtied = 0; |
1754 | } else if (period) { |
1755 | current->dirty_paused_when += period; |
1756 | current->nr_dirtied = 0; |
1757 | } else if (current->nr_dirtied_pause <= pages_dirtied) |
1758 | current->nr_dirtied_pause += pages_dirtied; |
1759 | break; |
1760 | } |
1761 | if (unlikely(pause > max_pause)) { |
1762 | /* for occasional dropped task_ratelimit */ |
1763 | now += min(pause - max_pause, max_pause); |
1764 | pause = max_pause; |
1765 | } |
1766 | |
1767 | pause: |
1768 | trace_balance_dirty_pages(wb, |
1769 | sdtc->thresh, |
1770 | sdtc->bg_thresh, |
1771 | sdtc->dirty, |
1772 | sdtc->wb_thresh, |
1773 | sdtc->wb_dirty, |
1774 | dirty_ratelimit, |
1775 | task_ratelimit, |
1776 | pages_dirtied, |
1777 | period, |
1778 | pause, |
1779 | start_time); |
1780 | __set_current_state(TASK_KILLABLE); |
1781 | io_schedule_timeout(pause); |
1782 | |
1783 | current->dirty_paused_when = now + pause; |
1784 | current->nr_dirtied = 0; |
1785 | current->nr_dirtied_pause = nr_dirtied_pause; |
1786 | |
1787 | /* |
1788 | * This is typically equal to (dirty < thresh) and can also |
1789 | * keep "1000+ dd on a slow USB stick" under control. |
1790 | */ |
1791 | if (task_ratelimit) |
1792 | break; |
1793 | |
1794 | /* |
1795 | * In the case of an unresponding NFS server and the NFS dirty |
1796 | * pages exceeds dirty_thresh, give the other good wb's a pipe |
1797 | * to go through, so that tasks on them still remain responsive. |
1798 | * |
1799 | * In theory 1 page is enough to keep the comsumer-producer |
1800 | * pipe going: the flusher cleans 1 page => the task dirties 1 |
1801 | * more page. However wb_dirty has accounting errors. So use |
1802 | * the larger and more IO friendly wb_stat_error. |
1803 | */ |
1804 | if (sdtc->wb_dirty <= wb_stat_error(wb)) |
1805 | break; |
1806 | |
1807 | if (fatal_signal_pending(current)) |
1808 | break; |
1809 | } |
1810 | |
1811 | if (!dirty_exceeded && wb->dirty_exceeded) |
1812 | wb->dirty_exceeded = 0; |
1813 | |
1814 | if (writeback_in_progress(wb)) |
1815 | return; |
1816 | |
1817 | /* |
1818 | * In laptop mode, we wait until hitting the higher threshold before |
1819 | * starting background writeout, and then write out all the way down |
1820 | * to the lower threshold. So slow writers cause minimal disk activity. |
1821 | * |
1822 | * In normal mode, we start background writeout at the lower |
1823 | * background_thresh, to keep the amount of dirty memory low. |
1824 | */ |
1825 | if (laptop_mode) |
1826 | return; |
1827 | |
1828 | if (nr_reclaimable > gdtc->bg_thresh) |
1829 | wb_start_background_writeback(wb); |
1830 | } |
1831 | |
1832 | static DEFINE_PER_CPU(int, bdp_ratelimits); |
1833 | |
1834 | /* |
1835 | * Normal tasks are throttled by |
1836 | * loop { |
1837 | * dirty tsk->nr_dirtied_pause pages; |
1838 | * take a snap in balance_dirty_pages(); |
1839 | * } |
1840 | * However there is a worst case. If every task exit immediately when dirtied |
1841 | * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be |
1842 | * called to throttle the page dirties. The solution is to save the not yet |
1843 | * throttled page dirties in dirty_throttle_leaks on task exit and charge them |
1844 | * randomly into the running tasks. This works well for the above worst case, |
1845 | * as the new task will pick up and accumulate the old task's leaked dirty |
1846 | * count and eventually get throttled. |
1847 | */ |
1848 | DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0; |
1849 | |
1850 | /** |
1851 | * balance_dirty_pages_ratelimited - balance dirty memory state |
1852 | * @mapping: address_space which was dirtied |
1853 | * |
1854 | * Processes which are dirtying memory should call in here once for each page |
1855 | * which was newly dirtied. The function will periodically check the system's |
1856 | * dirty state and will initiate writeback if needed. |
1857 | * |
1858 | * On really big machines, get_writeback_state is expensive, so try to avoid |
1859 | * calling it too often (ratelimiting). But once we're over the dirty memory |
1860 | * limit we decrease the ratelimiting by a lot, to prevent individual processes |
1861 | * from overshooting the limit by (ratelimit_pages) each. |
1862 | */ |
1863 | void balance_dirty_pages_ratelimited(struct address_space *mapping) |
1864 | { |
1865 | struct inode *inode = mapping->host; |
1866 | struct backing_dev_info *bdi = inode_to_bdi(inode); |
1867 | struct bdi_writeback *wb = NULL; |
1868 | int ratelimit; |
1869 | int *p; |
1870 | |
1871 | if (!bdi_cap_account_dirty(bdi)) |
1872 | return; |
1873 | |
1874 | if (inode_cgwb_enabled(inode)) |
1875 | wb = wb_get_create_current(bdi, GFP_KERNEL); |
1876 | if (!wb) |
1877 | wb = &bdi->wb; |
1878 | |
1879 | ratelimit = current->nr_dirtied_pause; |
1880 | if (wb->dirty_exceeded) |
1881 | ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10)); |
1882 | |
1883 | preempt_disable(); |
1884 | /* |
1885 | * This prevents one CPU to accumulate too many dirtied pages without |
1886 | * calling into balance_dirty_pages(), which can happen when there are |
1887 | * 1000+ tasks, all of them start dirtying pages at exactly the same |
1888 | * time, hence all honoured too large initial task->nr_dirtied_pause. |
1889 | */ |
1890 | p = this_cpu_ptr(&bdp_ratelimits); |
1891 | if (unlikely(current->nr_dirtied >= ratelimit)) |
1892 | *p = 0; |
1893 | else if (unlikely(*p >= ratelimit_pages)) { |
1894 | *p = 0; |
1895 | ratelimit = 0; |
1896 | } |
1897 | /* |
1898 | * Pick up the dirtied pages by the exited tasks. This avoids lots of |
1899 | * short-lived tasks (eg. gcc invocations in a kernel build) escaping |
1900 | * the dirty throttling and livelock other long-run dirtiers. |
1901 | */ |
1902 | p = this_cpu_ptr(&dirty_throttle_leaks); |
1903 | if (*p > 0 && current->nr_dirtied < ratelimit) { |
1904 | unsigned long nr_pages_dirtied; |
1905 | nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied); |
1906 | *p -= nr_pages_dirtied; |
1907 | current->nr_dirtied += nr_pages_dirtied; |
1908 | } |
1909 | preempt_enable(); |
1910 | |
1911 | if (unlikely(current->nr_dirtied >= ratelimit)) |
1912 | balance_dirty_pages(mapping, wb, current->nr_dirtied); |
1913 | |
1914 | wb_put(wb); |
1915 | } |
1916 | EXPORT_SYMBOL(balance_dirty_pages_ratelimited); |
1917 | |
1918 | /** |
1919 | * wb_over_bg_thresh - does @wb need to be written back? |
1920 | * @wb: bdi_writeback of interest |
1921 | * |
1922 | * Determines whether background writeback should keep writing @wb or it's |
1923 | * clean enough. Returns %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 | proc_dointvec(table, write, buffer, length, ppos); |
1975 | return 0; |
1976 | } |
1977 | |
1978 | #ifdef CONFIG_BLOCK |
1979 | void laptop_mode_timer_fn(unsigned long data) |
1980 | { |
1981 | struct request_queue *q = (struct request_queue *)data; |
1982 | int nr_pages = global_node_page_state(NR_FILE_DIRTY) + |
1983 | global_node_page_state(NR_UNSTABLE_NFS); |
1984 | struct bdi_writeback *wb; |
1985 | |
1986 | /* |
1987 | * We want to write everything out, not just down to the dirty |
1988 | * threshold |
1989 | */ |
1990 | if (!bdi_has_dirty_io(&q->backing_dev_info)) |
1991 | return; |
1992 | |
1993 | rcu_read_lock(); |
1994 | list_for_each_entry_rcu(wb, &q->backing_dev_info.wb_list, bdi_node) |
1995 | if (wb_has_dirty_io(wb)) |
1996 | wb_start_writeback(wb, nr_pages, true, |
1997 | WB_REASON_LAPTOP_TIMER); |
1998 | rcu_read_unlock(); |
1999 | } |
2000 | |
2001 | /* |
2002 | * We've spun up the disk and we're in laptop mode: schedule writeback |
2003 | * of all dirty data a few seconds from now. If the flush is already scheduled |
2004 | * then push it back - the user is still using the disk. |
2005 | */ |
2006 | void laptop_io_completion(struct backing_dev_info *info) |
2007 | { |
2008 | mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); |
2009 | } |
2010 | |
2011 | /* |
2012 | * We're in laptop mode and we've just synced. The sync's writes will have |
2013 | * caused another writeback to be scheduled by laptop_io_completion. |
2014 | * Nothing needs to be written back anymore, so we unschedule the writeback. |
2015 | */ |
2016 | void laptop_sync_completion(void) |
2017 | { |
2018 | struct backing_dev_info *bdi; |
2019 | |
2020 | rcu_read_lock(); |
2021 | |
2022 | list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) |
2023 | del_timer(&bdi->laptop_mode_wb_timer); |
2024 | |
2025 | rcu_read_unlock(); |
2026 | } |
2027 | #endif |
2028 | |
2029 | /* |
2030 | * If ratelimit_pages is too high then we can get into dirty-data overload |
2031 | * if a large number of processes all perform writes at the same time. |
2032 | * If it is too low then SMP machines will call the (expensive) |
2033 | * get_writeback_state too often. |
2034 | * |
2035 | * Here we set ratelimit_pages to a level which ensures that when all CPUs are |
2036 | * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory |
2037 | * thresholds. |
2038 | */ |
2039 | |
2040 | void writeback_set_ratelimit(void) |
2041 | { |
2042 | struct wb_domain *dom = &global_wb_domain; |
2043 | unsigned long background_thresh; |
2044 | unsigned long dirty_thresh; |
2045 | |
2046 | global_dirty_limits(&background_thresh, &dirty_thresh); |
2047 | dom->dirty_limit = dirty_thresh; |
2048 | ratelimit_pages = dirty_thresh / (num_online_cpus() * 32); |
2049 | if (ratelimit_pages < 16) |
2050 | ratelimit_pages = 16; |
2051 | } |
2052 | |
2053 | static int page_writeback_cpu_online(unsigned int cpu) |
2054 | { |
2055 | writeback_set_ratelimit(); |
2056 | return 0; |
2057 | } |
2058 | |
2059 | /* |
2060 | * Called early on to tune the page writeback dirty limits. |
2061 | * |
2062 | * We used to scale dirty pages according to how total memory |
2063 | * related to pages that could be allocated for buffers (by |
2064 | * comparing nr_free_buffer_pages() to vm_total_pages. |
2065 | * |
2066 | * However, that was when we used "dirty_ratio" to scale with |
2067 | * all memory, and we don't do that any more. "dirty_ratio" |
2068 | * is now applied to total non-HIGHPAGE memory (by subtracting |
2069 | * totalhigh_pages from vm_total_pages), and as such we can't |
2070 | * get into the old insane situation any more where we had |
2071 | * large amounts of dirty pages compared to a small amount of |
2072 | * non-HIGHMEM memory. |
2073 | * |
2074 | * But we might still want to scale the dirty_ratio by how |
2075 | * much memory the box has.. |
2076 | */ |
2077 | void __init page_writeback_init(void) |
2078 | { |
2079 | BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL)); |
2080 | |
2081 | cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online", |
2082 | page_writeback_cpu_online, NULL); |
2083 | cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL, |
2084 | page_writeback_cpu_online); |
2085 | } |
2086 | |
2087 | /** |
2088 | * tag_pages_for_writeback - tag pages to be written by write_cache_pages |
2089 | * @mapping: address space structure to write |
2090 | * @start: starting page index |
2091 | * @end: ending page index (inclusive) |
2092 | * |
2093 | * This function scans the page range from @start to @end (inclusive) and tags |
2094 | * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is |
2095 | * that write_cache_pages (or whoever calls this function) will then use |
2096 | * TOWRITE tag to identify pages eligible for writeback. This mechanism is |
2097 | * used to avoid livelocking of writeback by a process steadily creating new |
2098 | * dirty pages in the file (thus it is important for this function to be quick |
2099 | * so that it can tag pages faster than a dirtying process can create them). |
2100 | */ |
2101 | /* |
2102 | * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency. |
2103 | */ |
2104 | void tag_pages_for_writeback(struct address_space *mapping, |
2105 | pgoff_t start, pgoff_t end) |
2106 | { |
2107 | #define WRITEBACK_TAG_BATCH 4096 |
2108 | unsigned long tagged; |
2109 | |
2110 | do { |
2111 | spin_lock_irq(&mapping->tree_lock); |
2112 | tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree, |
2113 | &start, end, WRITEBACK_TAG_BATCH, |
2114 | PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE); |
2115 | spin_unlock_irq(&mapping->tree_lock); |
2116 | WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH); |
2117 | cond_resched(); |
2118 | /* We check 'start' to handle wrapping when end == ~0UL */ |
2119 | } while (tagged >= WRITEBACK_TAG_BATCH && start); |
2120 | } |
2121 | EXPORT_SYMBOL(tag_pages_for_writeback); |
2122 | |
2123 | /** |
2124 | * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. |
2125 | * @mapping: address space structure to write |
2126 | * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
2127 | * @writepage: function called for each page |
2128 | * @data: data passed to writepage function |
2129 | * |
2130 | * If a page is already under I/O, write_cache_pages() skips it, even |
2131 | * if it's dirty. This is desirable behaviour for memory-cleaning writeback, |
2132 | * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() |
2133 | * and msync() need to guarantee that all the data which was dirty at the time |
2134 | * the call was made get new I/O started against them. If wbc->sync_mode is |
2135 | * WB_SYNC_ALL then we were called for data integrity and we must wait for |
2136 | * existing IO to complete. |
2137 | * |
2138 | * To avoid livelocks (when other process dirties new pages), we first tag |
2139 | * pages which should be written back with TOWRITE tag and only then start |
2140 | * writing them. For data-integrity sync we have to be careful so that we do |
2141 | * not miss some pages (e.g., because some other process has cleared TOWRITE |
2142 | * tag we set). The rule we follow is that TOWRITE tag can be cleared only |
2143 | * by the process clearing the DIRTY tag (and submitting the page for IO). |
2144 | */ |
2145 | int write_cache_pages(struct address_space *mapping, |
2146 | struct writeback_control *wbc, writepage_t writepage, |
2147 | void *data) |
2148 | { |
2149 | int ret = 0; |
2150 | int done = 0; |
2151 | int error; |
2152 | struct pagevec pvec; |
2153 | int nr_pages; |
2154 | pgoff_t uninitialized_var(writeback_index); |
2155 | pgoff_t index; |
2156 | pgoff_t end; /* Inclusive */ |
2157 | pgoff_t done_index; |
2158 | int cycled; |
2159 | int range_whole = 0; |
2160 | int tag; |
2161 | |
2162 | pagevec_init(&pvec, 0); |
2163 | if (wbc->range_cyclic) { |
2164 | writeback_index = mapping->writeback_index; /* prev offset */ |
2165 | index = writeback_index; |
2166 | if (index == 0) |
2167 | cycled = 1; |
2168 | else |
2169 | cycled = 0; |
2170 | end = -1; |
2171 | } else { |
2172 | index = wbc->range_start >> PAGE_SHIFT; |
2173 | end = wbc->range_end >> PAGE_SHIFT; |
2174 | if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) |
2175 | range_whole = 1; |
2176 | cycled = 1; /* ignore range_cyclic tests */ |
2177 | } |
2178 | if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) |
2179 | tag = PAGECACHE_TAG_TOWRITE; |
2180 | else |
2181 | tag = PAGECACHE_TAG_DIRTY; |
2182 | retry: |
2183 | if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) |
2184 | tag_pages_for_writeback(mapping, index, end); |
2185 | done_index = index; |
2186 | while (!done && (index <= end)) { |
2187 | int i; |
2188 | |
2189 | nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end, |
2190 | tag); |
2191 | if (nr_pages == 0) |
2192 | break; |
2193 | |
2194 | for (i = 0; i < nr_pages; i++) { |
2195 | struct page *page = pvec.pages[i]; |
2196 | |
2197 | done_index = page->index; |
2198 | |
2199 | lock_page(page); |
2200 | |
2201 | /* |
2202 | * Page truncated or invalidated. We can freely skip it |
2203 | * then, even for data integrity operations: the page |
2204 | * has disappeared concurrently, so there could be no |
2205 | * real expectation of this data interity operation |
2206 | * even if there is now a new, dirty page at the same |
2207 | * pagecache address. |
2208 | */ |
2209 | if (unlikely(page->mapping != mapping)) { |
2210 | continue_unlock: |
2211 | unlock_page(page); |
2212 | continue; |
2213 | } |
2214 | |
2215 | if (!PageDirty(page)) { |
2216 | /* someone wrote it for us */ |
2217 | goto continue_unlock; |
2218 | } |
2219 | |
2220 | if (PageWriteback(page)) { |
2221 | if (wbc->sync_mode != WB_SYNC_NONE) |
2222 | wait_on_page_writeback(page); |
2223 | else |
2224 | goto continue_unlock; |
2225 | } |
2226 | |
2227 | BUG_ON(PageWriteback(page)); |
2228 | if (!clear_page_dirty_for_io(page)) |
2229 | goto continue_unlock; |
2230 | |
2231 | trace_wbc_writepage(wbc, inode_to_bdi(mapping->host)); |
2232 | error = (*writepage)(page, wbc, data); |
2233 | if (unlikely(error)) { |
2234 | /* |
2235 | * Handle errors according to the type of |
2236 | * writeback. There's no need to continue for |
2237 | * background writeback. Just push done_index |
2238 | * past this page so media errors won't choke |
2239 | * writeout for the entire file. For integrity |
2240 | * writeback, we must process the entire dirty |
2241 | * set regardless of errors because the fs may |
2242 | * still have state to clear for each page. In |
2243 | * that case we continue processing and return |
2244 | * the first error. |
2245 | */ |
2246 | if (error == AOP_WRITEPAGE_ACTIVATE) { |
2247 | unlock_page(page); |
2248 | error = 0; |
2249 | } else if (wbc->sync_mode != WB_SYNC_ALL) { |
2250 | ret = error; |
2251 | done_index = page->index + 1; |
2252 | done = 1; |
2253 | break; |
2254 | } |
2255 | if (!ret) |
2256 | ret = error; |
2257 | } |
2258 | |
2259 | /* |
2260 | * We stop writing back only if we are not doing |
2261 | * integrity sync. In case of integrity sync we have to |
2262 | * keep going until we have written all the pages |
2263 | * we tagged for writeback prior to entering this loop. |
2264 | */ |
2265 | if (--wbc->nr_to_write <= 0 && |
2266 | wbc->sync_mode == WB_SYNC_NONE) { |
2267 | done = 1; |
2268 | break; |
2269 | } |
2270 | } |
2271 | pagevec_release(&pvec); |
2272 | cond_resched(); |
2273 | } |
2274 | if (!cycled && !done) { |
2275 | /* |
2276 | * range_cyclic: |
2277 | * We hit the last page and there is more work to be done: wrap |
2278 | * back to the start of the file |
2279 | */ |
2280 | cycled = 1; |
2281 | index = 0; |
2282 | end = writeback_index - 1; |
2283 | goto retry; |
2284 | } |
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 | int generic_writepages(struct address_space *mapping, |
2314 | struct writeback_control *wbc) |
2315 | { |
2316 | struct blk_plug plug; |
2317 | int ret; |
2318 | |
2319 | /* deal with chardevs and other special file */ |
2320 | if (!mapping->a_ops->writepage) |
2321 | return 0; |
2322 | |
2323 | blk_start_plug(&plug); |
2324 | ret = write_cache_pages(mapping, wbc, __writepage, mapping); |
2325 | blk_finish_plug(&plug); |
2326 | return ret; |
2327 | } |
2328 | |
2329 | EXPORT_SYMBOL(generic_writepages); |
2330 | |
2331 | int do_writepages(struct address_space *mapping, struct writeback_control *wbc) |
2332 | { |
2333 | int ret; |
2334 | |
2335 | if (wbc->nr_to_write <= 0) |
2336 | return 0; |
2337 | if (mapping->a_ops->writepages) |
2338 | ret = mapping->a_ops->writepages(mapping, wbc); |
2339 | else |
2340 | ret = generic_writepages(mapping, wbc); |
2341 | return ret; |
2342 | } |
2343 | |
2344 | /** |
2345 | * write_one_page - write out a single page and optionally wait on I/O |
2346 | * @page: the page to write |
2347 | * @wait: if true, wait on writeout |
2348 | * |
2349 | * The page must be locked by the caller and will be unlocked upon return. |
2350 | * |
2351 | * write_one_page() returns a negative error code if I/O failed. |
2352 | */ |
2353 | int write_one_page(struct page *page, int wait) |
2354 | { |
2355 | struct address_space *mapping = page->mapping; |
2356 | int ret = 0; |
2357 | struct writeback_control wbc = { |
2358 | .sync_mode = WB_SYNC_ALL, |
2359 | .nr_to_write = 1, |
2360 | }; |
2361 | |
2362 | BUG_ON(!PageLocked(page)); |
2363 | |
2364 | if (wait) |
2365 | wait_on_page_writeback(page); |
2366 | |
2367 | if (clear_page_dirty_for_io(page)) { |
2368 | get_page(page); |
2369 | ret = mapping->a_ops->writepage(page, &wbc); |
2370 | if (ret == 0 && wait) { |
2371 | wait_on_page_writeback(page); |
2372 | if (PageError(page)) |
2373 | ret = -EIO; |
2374 | } |
2375 | put_page(page); |
2376 | } else { |
2377 | unlock_page(page); |
2378 | } |
2379 | return ret; |
2380 | } |
2381 | EXPORT_SYMBOL(write_one_page); |
2382 | |
2383 | /* |
2384 | * For address_spaces which do not use buffers nor write back. |
2385 | */ |
2386 | int __set_page_dirty_no_writeback(struct page *page) |
2387 | { |
2388 | if (!PageDirty(page)) |
2389 | return !TestSetPageDirty(page); |
2390 | return 0; |
2391 | } |
2392 | |
2393 | /* |
2394 | * Helper function for set_page_dirty family. |
2395 | * |
2396 | * Caller must hold lock_page_memcg(). |
2397 | * |
2398 | * NOTE: This relies on being atomic wrt interrupts. |
2399 | */ |
2400 | void account_page_dirtied(struct page *page, struct address_space *mapping) |
2401 | { |
2402 | struct inode *inode = mapping->host; |
2403 | |
2404 | trace_writeback_dirty_page(page, mapping); |
2405 | |
2406 | if (mapping_cap_account_dirty(mapping)) { |
2407 | struct bdi_writeback *wb; |
2408 | |
2409 | inode_attach_wb(inode, page); |
2410 | wb = inode_to_wb(inode); |
2411 | |
2412 | mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_DIRTY); |
2413 | __inc_node_page_state(page, NR_FILE_DIRTY); |
2414 | __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING); |
2415 | __inc_node_page_state(page, NR_DIRTIED); |
2416 | __inc_wb_stat(wb, WB_RECLAIMABLE); |
2417 | __inc_wb_stat(wb, WB_DIRTIED); |
2418 | task_io_account_write(PAGE_SIZE); |
2419 | current->nr_dirtied++; |
2420 | this_cpu_inc(bdp_ratelimits); |
2421 | } |
2422 | } |
2423 | EXPORT_SYMBOL(account_page_dirtied); |
2424 | |
2425 | /* |
2426 | * Helper function for deaccounting dirty page without writeback. |
2427 | * |
2428 | * Caller must hold lock_page_memcg(). |
2429 | */ |
2430 | void account_page_cleaned(struct page *page, struct address_space *mapping, |
2431 | struct bdi_writeback *wb) |
2432 | { |
2433 | if (mapping_cap_account_dirty(mapping)) { |
2434 | mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY); |
2435 | dec_node_page_state(page, NR_FILE_DIRTY); |
2436 | dec_zone_page_state(page, NR_ZONE_WRITE_PENDING); |
2437 | dec_wb_stat(wb, WB_RECLAIMABLE); |
2438 | task_io_account_cancelled_write(PAGE_SIZE); |
2439 | } |
2440 | } |
2441 | |
2442 | /* |
2443 | * For address_spaces which do not use buffers. Just tag the page as dirty in |
2444 | * its radix tree. |
2445 | * |
2446 | * This is also used when a single buffer is being dirtied: we want to set the |
2447 | * page dirty in that case, but not all the buffers. This is a "bottom-up" |
2448 | * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. |
2449 | * |
2450 | * The caller must ensure this doesn't race with truncation. Most will simply |
2451 | * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and |
2452 | * the pte lock held, which also locks out truncation. |
2453 | */ |
2454 | int __set_page_dirty_nobuffers(struct page *page) |
2455 | { |
2456 | lock_page_memcg(page); |
2457 | if (!TestSetPageDirty(page)) { |
2458 | struct address_space *mapping = page_mapping(page); |
2459 | unsigned long flags; |
2460 | |
2461 | if (!mapping) { |
2462 | unlock_page_memcg(page); |
2463 | return 1; |
2464 | } |
2465 | |
2466 | spin_lock_irqsave(&mapping->tree_lock, flags); |
2467 | BUG_ON(page_mapping(page) != mapping); |
2468 | WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); |
2469 | account_page_dirtied(page, mapping); |
2470 | radix_tree_tag_set(&mapping->page_tree, page_index(page), |
2471 | PAGECACHE_TAG_DIRTY); |
2472 | spin_unlock_irqrestore(&mapping->tree_lock, flags); |
2473 | unlock_page_memcg(page); |
2474 | |
2475 | if (mapping->host) { |
2476 | /* !PageAnon && !swapper_space */ |
2477 | __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); |
2478 | } |
2479 | return 1; |
2480 | } |
2481 | unlock_page_memcg(page); |
2482 | return 0; |
2483 | } |
2484 | EXPORT_SYMBOL(__set_page_dirty_nobuffers); |
2485 | |
2486 | /* |
2487 | * Call this whenever redirtying a page, to de-account the dirty counters |
2488 | * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written |
2489 | * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to |
2490 | * systematic errors in balanced_dirty_ratelimit and the dirty pages position |
2491 | * control. |
2492 | */ |
2493 | void account_page_redirty(struct page *page) |
2494 | { |
2495 | struct address_space *mapping = page->mapping; |
2496 | |
2497 | if (mapping && mapping_cap_account_dirty(mapping)) { |
2498 | struct inode *inode = mapping->host; |
2499 | struct bdi_writeback *wb; |
2500 | struct wb_lock_cookie cookie = {}; |
2501 | |
2502 | wb = unlocked_inode_to_wb_begin(inode, &cookie); |
2503 | current->nr_dirtied--; |
2504 | dec_node_page_state(page, NR_DIRTIED); |
2505 | dec_wb_stat(wb, WB_DIRTIED); |
2506 | unlocked_inode_to_wb_end(inode, &cookie); |
2507 | } |
2508 | } |
2509 | EXPORT_SYMBOL(account_page_redirty); |
2510 | |
2511 | /* |
2512 | * When a writepage implementation decides that it doesn't want to write this |
2513 | * page for some reason, it should redirty the locked page via |
2514 | * redirty_page_for_writepage() and it should then unlock the page and return 0 |
2515 | */ |
2516 | int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) |
2517 | { |
2518 | int ret; |
2519 | |
2520 | wbc->pages_skipped++; |
2521 | ret = __set_page_dirty_nobuffers(page); |
2522 | account_page_redirty(page); |
2523 | return ret; |
2524 | } |
2525 | EXPORT_SYMBOL(redirty_page_for_writepage); |
2526 | |
2527 | /* |
2528 | * Dirty a page. |
2529 | * |
2530 | * For pages with a mapping this should be done under the page lock |
2531 | * for the benefit of asynchronous memory errors who prefer a consistent |
2532 | * dirty state. This rule can be broken in some special cases, |
2533 | * but should be better not to. |
2534 | * |
2535 | * If the mapping doesn't provide a set_page_dirty a_op, then |
2536 | * just fall through and assume that it wants buffer_heads. |
2537 | */ |
2538 | int set_page_dirty(struct page *page) |
2539 | { |
2540 | struct address_space *mapping = page_mapping(page); |
2541 | |
2542 | page = compound_head(page); |
2543 | if (likely(mapping)) { |
2544 | int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; |
2545 | /* |
2546 | * readahead/lru_deactivate_page could remain |
2547 | * PG_readahead/PG_reclaim due to race with end_page_writeback |
2548 | * About readahead, if the page is written, the flags would be |
2549 | * reset. So no problem. |
2550 | * About lru_deactivate_page, if the page is redirty, the flag |
2551 | * will be reset. So no problem. but if the page is used by readahead |
2552 | * it will confuse readahead and make it restart the size rampup |
2553 | * process. But it's a trivial problem. |
2554 | */ |
2555 | if (PageReclaim(page)) |
2556 | ClearPageReclaim(page); |
2557 | #ifdef CONFIG_BLOCK |
2558 | if (!spd) |
2559 | spd = __set_page_dirty_buffers; |
2560 | #endif |
2561 | return (*spd)(page); |
2562 | } |
2563 | if (!PageDirty(page)) { |
2564 | if (!TestSetPageDirty(page)) |
2565 | return 1; |
2566 | } |
2567 | return 0; |
2568 | } |
2569 | EXPORT_SYMBOL(set_page_dirty); |
2570 | |
2571 | /* |
2572 | * set_page_dirty() is racy if the caller has no reference against |
2573 | * page->mapping->host, and if the page is unlocked. This is because another |
2574 | * CPU could truncate the page off the mapping and then free the mapping. |
2575 | * |
2576 | * Usually, the page _is_ locked, or the caller is a user-space process which |
2577 | * holds a reference on the inode by having an open file. |
2578 | * |
2579 | * In other cases, the page should be locked before running set_page_dirty(). |
2580 | */ |
2581 | int set_page_dirty_lock(struct page *page) |
2582 | { |
2583 | int ret; |
2584 | |
2585 | lock_page(page); |
2586 | ret = set_page_dirty(page); |
2587 | unlock_page(page); |
2588 | return ret; |
2589 | } |
2590 | EXPORT_SYMBOL(set_page_dirty_lock); |
2591 | |
2592 | /* |
2593 | * This cancels just the dirty bit on the kernel page itself, it does NOT |
2594 | * actually remove dirty bits on any mmap's that may be around. It also |
2595 | * leaves the page tagged dirty, so any sync activity will still find it on |
2596 | * the dirty lists, and in particular, clear_page_dirty_for_io() will still |
2597 | * look at the dirty bits in the VM. |
2598 | * |
2599 | * Doing this should *normally* only ever be done when a page is truncated, |
2600 | * and is not actually mapped anywhere at all. However, fs/buffer.c does |
2601 | * this when it notices that somebody has cleaned out all the buffers on a |
2602 | * page without actually doing it through the VM. Can you say "ext3 is |
2603 | * horribly ugly"? Thought you could. |
2604 | */ |
2605 | void cancel_dirty_page(struct page *page) |
2606 | { |
2607 | struct address_space *mapping = page_mapping(page); |
2608 | |
2609 | if (mapping_cap_account_dirty(mapping)) { |
2610 | struct inode *inode = mapping->host; |
2611 | struct bdi_writeback *wb; |
2612 | struct wb_lock_cookie cookie = {}; |
2613 | |
2614 | lock_page_memcg(page); |
2615 | wb = unlocked_inode_to_wb_begin(inode, &cookie); |
2616 | |
2617 | if (TestClearPageDirty(page)) |
2618 | account_page_cleaned(page, mapping, wb); |
2619 | |
2620 | unlocked_inode_to_wb_end(inode, &cookie); |
2621 | unlock_page_memcg(page); |
2622 | } else { |
2623 | ClearPageDirty(page); |
2624 | } |
2625 | } |
2626 | EXPORT_SYMBOL(cancel_dirty_page); |
2627 | |
2628 | /* |
2629 | * Clear a page's dirty flag, while caring for dirty memory accounting. |
2630 | * Returns true if the page was previously dirty. |
2631 | * |
2632 | * This is for preparing to put the page under writeout. We leave the page |
2633 | * tagged as dirty in the radix tree so that a concurrent write-for-sync |
2634 | * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage |
2635 | * implementation will run either set_page_writeback() or set_page_dirty(), |
2636 | * at which stage we bring the page's dirty flag and radix-tree dirty tag |
2637 | * back into sync. |
2638 | * |
2639 | * This incoherency between the page's dirty flag and radix-tree tag is |
2640 | * unfortunate, but it only exists while the page is locked. |
2641 | */ |
2642 | int clear_page_dirty_for_io(struct page *page) |
2643 | { |
2644 | struct address_space *mapping = page_mapping(page); |
2645 | int ret = 0; |
2646 | |
2647 | BUG_ON(!PageLocked(page)); |
2648 | |
2649 | if (mapping && mapping_cap_account_dirty(mapping)) { |
2650 | struct inode *inode = mapping->host; |
2651 | struct bdi_writeback *wb; |
2652 | struct wb_lock_cookie cookie = {}; |
2653 | |
2654 | /* |
2655 | * Yes, Virginia, this is indeed insane. |
2656 | * |
2657 | * We use this sequence to make sure that |
2658 | * (a) we account for dirty stats properly |
2659 | * (b) we tell the low-level filesystem to |
2660 | * mark the whole page dirty if it was |
2661 | * dirty in a pagetable. Only to then |
2662 | * (c) clean the page again and return 1 to |
2663 | * cause the writeback. |
2664 | * |
2665 | * This way we avoid all nasty races with the |
2666 | * dirty bit in multiple places and clearing |
2667 | * them concurrently from different threads. |
2668 | * |
2669 | * Note! Normally the "set_page_dirty(page)" |
2670 | * has no effect on the actual dirty bit - since |
2671 | * that will already usually be set. But we |
2672 | * need the side effects, and it can help us |
2673 | * avoid races. |
2674 | * |
2675 | * We basically use the page "master dirty bit" |
2676 | * as a serialization point for all the different |
2677 | * threads doing their things. |
2678 | */ |
2679 | if (page_mkclean(page)) |
2680 | set_page_dirty(page); |
2681 | /* |
2682 | * We carefully synchronise fault handlers against |
2683 | * installing a dirty pte and marking the page dirty |
2684 | * at this point. We do this by having them hold the |
2685 | * page lock while dirtying the page, and pages are |
2686 | * always locked coming in here, so we get the desired |
2687 | * exclusion. |
2688 | */ |
2689 | wb = unlocked_inode_to_wb_begin(inode, &cookie); |
2690 | if (TestClearPageDirty(page)) { |
2691 | mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY); |
2692 | dec_node_page_state(page, NR_FILE_DIRTY); |
2693 | dec_zone_page_state(page, NR_ZONE_WRITE_PENDING); |
2694 | dec_wb_stat(wb, WB_RECLAIMABLE); |
2695 | ret = 1; |
2696 | } |
2697 | unlocked_inode_to_wb_end(inode, &cookie); |
2698 | return ret; |
2699 | } |
2700 | return TestClearPageDirty(page); |
2701 | } |
2702 | EXPORT_SYMBOL(clear_page_dirty_for_io); |
2703 | |
2704 | int test_clear_page_writeback(struct page *page) |
2705 | { |
2706 | struct address_space *mapping = page_mapping(page); |
2707 | int ret; |
2708 | |
2709 | lock_page_memcg(page); |
2710 | if (mapping && mapping_use_writeback_tags(mapping)) { |
2711 | struct inode *inode = mapping->host; |
2712 | struct backing_dev_info *bdi = inode_to_bdi(inode); |
2713 | unsigned long flags; |
2714 | |
2715 | spin_lock_irqsave(&mapping->tree_lock, flags); |
2716 | ret = TestClearPageWriteback(page); |
2717 | if (ret) { |
2718 | radix_tree_tag_clear(&mapping->page_tree, |
2719 | page_index(page), |
2720 | PAGECACHE_TAG_WRITEBACK); |
2721 | if (bdi_cap_account_writeback(bdi)) { |
2722 | struct bdi_writeback *wb = inode_to_wb(inode); |
2723 | |
2724 | __dec_wb_stat(wb, WB_WRITEBACK); |
2725 | __wb_writeout_inc(wb); |
2726 | } |
2727 | } |
2728 | |
2729 | if (mapping->host && !mapping_tagged(mapping, |
2730 | PAGECACHE_TAG_WRITEBACK)) |
2731 | sb_clear_inode_writeback(mapping->host); |
2732 | |
2733 | spin_unlock_irqrestore(&mapping->tree_lock, flags); |
2734 | } else { |
2735 | ret = TestClearPageWriteback(page); |
2736 | } |
2737 | if (ret) { |
2738 | mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK); |
2739 | dec_node_page_state(page, NR_WRITEBACK); |
2740 | dec_zone_page_state(page, NR_ZONE_WRITE_PENDING); |
2741 | inc_node_page_state(page, NR_WRITTEN); |
2742 | } |
2743 | unlock_page_memcg(page); |
2744 | return ret; |
2745 | } |
2746 | |
2747 | int __test_set_page_writeback(struct page *page, bool keep_write) |
2748 | { |
2749 | struct address_space *mapping = page_mapping(page); |
2750 | int ret; |
2751 | |
2752 | lock_page_memcg(page); |
2753 | if (mapping && mapping_use_writeback_tags(mapping)) { |
2754 | struct inode *inode = mapping->host; |
2755 | struct backing_dev_info *bdi = inode_to_bdi(inode); |
2756 | unsigned long flags; |
2757 | |
2758 | spin_lock_irqsave(&mapping->tree_lock, flags); |
2759 | ret = TestSetPageWriteback(page); |
2760 | if (!ret) { |
2761 | bool on_wblist; |
2762 | |
2763 | on_wblist = mapping_tagged(mapping, |
2764 | PAGECACHE_TAG_WRITEBACK); |
2765 | |
2766 | radix_tree_tag_set(&mapping->page_tree, |
2767 | page_index(page), |
2768 | PAGECACHE_TAG_WRITEBACK); |
2769 | if (bdi_cap_account_writeback(bdi)) |
2770 | __inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK); |
2771 | |
2772 | /* |
2773 | * We can come through here when swapping anonymous |
2774 | * pages, so we don't necessarily have an inode to track |
2775 | * for sync. |
2776 | */ |
2777 | if (mapping->host && !on_wblist) |
2778 | sb_mark_inode_writeback(mapping->host); |
2779 | } |
2780 | if (!PageDirty(page)) |
2781 | radix_tree_tag_clear(&mapping->page_tree, |
2782 | page_index(page), |
2783 | PAGECACHE_TAG_DIRTY); |
2784 | if (!keep_write) |
2785 | radix_tree_tag_clear(&mapping->page_tree, |
2786 | page_index(page), |
2787 | PAGECACHE_TAG_TOWRITE); |
2788 | spin_unlock_irqrestore(&mapping->tree_lock, flags); |
2789 | } else { |
2790 | ret = TestSetPageWriteback(page); |
2791 | } |
2792 | if (!ret) { |
2793 | mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK); |
2794 | inc_node_page_state(page, NR_WRITEBACK); |
2795 | inc_zone_page_state(page, NR_ZONE_WRITE_PENDING); |
2796 | } |
2797 | unlock_page_memcg(page); |
2798 | return ret; |
2799 | |
2800 | } |
2801 | EXPORT_SYMBOL(__test_set_page_writeback); |
2802 | |
2803 | /* |
2804 | * Return true if any of the pages in the mapping are marked with the |
2805 | * passed tag. |
2806 | */ |
2807 | int mapping_tagged(struct address_space *mapping, int tag) |
2808 | { |
2809 | return radix_tree_tagged(&mapping->page_tree, tag); |
2810 | } |
2811 | EXPORT_SYMBOL(mapping_tagged); |
2812 | |
2813 | /** |
2814 | * wait_for_stable_page() - wait for writeback to finish, if necessary. |
2815 | * @page: The page to wait on. |
2816 | * |
2817 | * This function determines if the given page is related to a backing device |
2818 | * that requires page contents to be held stable during writeback. If so, then |
2819 | * it will wait for any pending writeback to complete. |
2820 | */ |
2821 | void wait_for_stable_page(struct page *page) |
2822 | { |
2823 | if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host))) |
2824 | wait_on_page_writeback(page); |
2825 | } |
2826 | EXPORT_SYMBOL_GPL(wait_for_stable_page); |
2827 |