Root/
1 | /* |
2 | * mm/page-writeback.c |
3 | * |
4 | * Copyright (C) 2002, Linus Torvalds. |
5 | * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> |
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 <trace/events/writeback.h> |
40 | |
41 | /* |
42 | * Sleep at most 200ms at a time in balance_dirty_pages(). |
43 | */ |
44 | #define MAX_PAUSE max(HZ/5, 1) |
45 | |
46 | /* |
47 | * Try to keep balance_dirty_pages() call intervals higher than this many pages |
48 | * by raising pause time to max_pause when falls below it. |
49 | */ |
50 | #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10)) |
51 | |
52 | /* |
53 | * Estimate write bandwidth at 200ms intervals. |
54 | */ |
55 | #define BANDWIDTH_INTERVAL max(HZ/5, 1) |
56 | |
57 | #define RATELIMIT_CALC_SHIFT 10 |
58 | |
59 | /* |
60 | * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited |
61 | * will look to see if it needs to force writeback or throttling. |
62 | */ |
63 | static long ratelimit_pages = 32; |
64 | |
65 | /* The following parameters are exported via /proc/sys/vm */ |
66 | |
67 | /* |
68 | * Start background writeback (via writeback threads) at this percentage |
69 | */ |
70 | int dirty_background_ratio = 10; |
71 | |
72 | /* |
73 | * dirty_background_bytes starts at 0 (disabled) so that it is a function of |
74 | * dirty_background_ratio * the amount of dirtyable memory |
75 | */ |
76 | unsigned long dirty_background_bytes; |
77 | |
78 | /* |
79 | * free highmem will not be subtracted from the total free memory |
80 | * for calculating free ratios if vm_highmem_is_dirtyable is true |
81 | */ |
82 | int vm_highmem_is_dirtyable; |
83 | |
84 | /* |
85 | * The generator of dirty data starts writeback at this percentage |
86 | */ |
87 | int vm_dirty_ratio = 20; |
88 | |
89 | /* |
90 | * vm_dirty_bytes starts at 0 (disabled) so that it is a function of |
91 | * vm_dirty_ratio * the amount of dirtyable memory |
92 | */ |
93 | unsigned long vm_dirty_bytes; |
94 | |
95 | /* |
96 | * The interval between `kupdate'-style writebacks |
97 | */ |
98 | unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ |
99 | |
100 | EXPORT_SYMBOL_GPL(dirty_writeback_interval); |
101 | |
102 | /* |
103 | * The longest time for which data is allowed to remain dirty |
104 | */ |
105 | unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ |
106 | |
107 | /* |
108 | * Flag that makes the machine dump writes/reads and block dirtyings. |
109 | */ |
110 | int block_dump; |
111 | |
112 | /* |
113 | * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: |
114 | * a full sync is triggered after this time elapses without any disk activity. |
115 | */ |
116 | int laptop_mode; |
117 | |
118 | EXPORT_SYMBOL(laptop_mode); |
119 | |
120 | /* End of sysctl-exported parameters */ |
121 | |
122 | unsigned long global_dirty_limit; |
123 | |
124 | /* |
125 | * Scale the writeback cache size proportional to the relative writeout speeds. |
126 | * |
127 | * We do this by keeping a floating proportion between BDIs, based on page |
128 | * writeback completions [end_page_writeback()]. Those devices that write out |
129 | * pages fastest will get the larger share, while the slower will get a smaller |
130 | * share. |
131 | * |
132 | * We use page writeout completions because we are interested in getting rid of |
133 | * dirty pages. Having them written out is the primary goal. |
134 | * |
135 | * We introduce a concept of time, a period over which we measure these events, |
136 | * because demand can/will vary over time. The length of this period itself is |
137 | * measured in page writeback completions. |
138 | * |
139 | */ |
140 | static struct fprop_global writeout_completions; |
141 | |
142 | static void writeout_period(unsigned long t); |
143 | /* Timer for aging of writeout_completions */ |
144 | static struct timer_list writeout_period_timer = |
145 | TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0); |
146 | static unsigned long writeout_period_time = 0; |
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 | /* |
156 | * Work out the current dirty-memory clamping and background writeout |
157 | * thresholds. |
158 | * |
159 | * The main aim here is to lower them aggressively if there is a lot of mapped |
160 | * memory around. To avoid stressing page reclaim with lots of unreclaimable |
161 | * pages. It is better to clamp down on writers than to start swapping, and |
162 | * performing lots of scanning. |
163 | * |
164 | * We only allow 1/2 of the currently-unmapped memory to be dirtied. |
165 | * |
166 | * We don't permit the clamping level to fall below 5% - that is getting rather |
167 | * excessive. |
168 | * |
169 | * We make sure that the background writeout level is below the adjusted |
170 | * clamping level. |
171 | */ |
172 | |
173 | /* |
174 | * In a memory zone, there is a certain amount of pages we consider |
175 | * available for the page cache, which is essentially the number of |
176 | * free and reclaimable pages, minus some zone reserves to protect |
177 | * lowmem and the ability to uphold the zone's watermarks without |
178 | * requiring writeback. |
179 | * |
180 | * This number of dirtyable pages is the base value of which the |
181 | * user-configurable dirty ratio is the effictive number of pages that |
182 | * are allowed to be actually dirtied. Per individual zone, or |
183 | * globally by using the sum of dirtyable pages over all zones. |
184 | * |
185 | * Because the user is allowed to specify the dirty limit globally as |
186 | * absolute number of bytes, calculating the per-zone dirty limit can |
187 | * require translating the configured limit into a percentage of |
188 | * global dirtyable memory first. |
189 | */ |
190 | |
191 | static unsigned long highmem_dirtyable_memory(unsigned long total) |
192 | { |
193 | #ifdef CONFIG_HIGHMEM |
194 | int node; |
195 | unsigned long x = 0; |
196 | |
197 | for_each_node_state(node, N_HIGH_MEMORY) { |
198 | struct zone *z = |
199 | &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; |
200 | |
201 | x += zone_page_state(z, NR_FREE_PAGES) + |
202 | zone_reclaimable_pages(z) - z->dirty_balance_reserve; |
203 | } |
204 | /* |
205 | * Unreclaimable memory (kernel memory or anonymous memory |
206 | * without swap) can bring down the dirtyable pages below |
207 | * the zone's dirty balance reserve and the above calculation |
208 | * will underflow. However we still want to add in nodes |
209 | * which are below threshold (negative values) to get a more |
210 | * accurate calculation but make sure that the total never |
211 | * underflows. |
212 | */ |
213 | if ((long)x < 0) |
214 | x = 0; |
215 | |
216 | /* |
217 | * Make sure that the number of highmem pages is never larger |
218 | * than the number of the total dirtyable memory. This can only |
219 | * occur in very strange VM situations but we want to make sure |
220 | * that this does not occur. |
221 | */ |
222 | return min(x, total); |
223 | #else |
224 | return 0; |
225 | #endif |
226 | } |
227 | |
228 | /** |
229 | * global_dirtyable_memory - number of globally dirtyable pages |
230 | * |
231 | * Returns the global number of pages potentially available for dirty |
232 | * page cache. This is the base value for the global dirty limits. |
233 | */ |
234 | static unsigned long global_dirtyable_memory(void) |
235 | { |
236 | unsigned long x; |
237 | |
238 | x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages(); |
239 | x -= min(x, dirty_balance_reserve); |
240 | |
241 | if (!vm_highmem_is_dirtyable) |
242 | x -= highmem_dirtyable_memory(x); |
243 | |
244 | /* Subtract min_free_kbytes */ |
245 | x -= min_t(unsigned long, x, min_free_kbytes >> (PAGE_SHIFT - 10)); |
246 | |
247 | return x + 1; /* Ensure that we never return 0 */ |
248 | } |
249 | |
250 | /* |
251 | * global_dirty_limits - background-writeback and dirty-throttling thresholds |
252 | * |
253 | * Calculate the dirty thresholds based on sysctl parameters |
254 | * - vm.dirty_background_ratio or vm.dirty_background_bytes |
255 | * - vm.dirty_ratio or vm.dirty_bytes |
256 | * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and |
257 | * real-time tasks. |
258 | */ |
259 | void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) |
260 | { |
261 | unsigned long background; |
262 | unsigned long dirty; |
263 | unsigned long uninitialized_var(available_memory); |
264 | struct task_struct *tsk; |
265 | |
266 | if (!vm_dirty_bytes || !dirty_background_bytes) |
267 | available_memory = global_dirtyable_memory(); |
268 | |
269 | if (vm_dirty_bytes) |
270 | dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); |
271 | else |
272 | dirty = (vm_dirty_ratio * available_memory) / 100; |
273 | |
274 | if (dirty_background_bytes) |
275 | background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE); |
276 | else |
277 | background = (dirty_background_ratio * available_memory) / 100; |
278 | |
279 | if (background >= dirty) |
280 | background = dirty / 2; |
281 | tsk = current; |
282 | if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { |
283 | background += background / 4; |
284 | dirty += dirty / 4; |
285 | } |
286 | *pbackground = background; |
287 | *pdirty = dirty; |
288 | trace_global_dirty_state(background, dirty); |
289 | } |
290 | |
291 | /** |
292 | * zone_dirtyable_memory - number of dirtyable pages in a zone |
293 | * @zone: the zone |
294 | * |
295 | * Returns the zone's number of pages potentially available for dirty |
296 | * page cache. This is the base value for the per-zone dirty limits. |
297 | */ |
298 | static unsigned long zone_dirtyable_memory(struct zone *zone) |
299 | { |
300 | /* |
301 | * The effective global number of dirtyable pages may exclude |
302 | * highmem as a big-picture measure to keep the ratio between |
303 | * dirty memory and lowmem reasonable. |
304 | * |
305 | * But this function is purely about the individual zone and a |
306 | * highmem zone can hold its share of dirty pages, so we don't |
307 | * care about vm_highmem_is_dirtyable here. |
308 | */ |
309 | unsigned long nr_pages = zone_page_state(zone, NR_FREE_PAGES) + |
310 | zone_reclaimable_pages(zone); |
311 | |
312 | /* don't allow this to underflow */ |
313 | nr_pages -= min(nr_pages, zone->dirty_balance_reserve); |
314 | return nr_pages; |
315 | } |
316 | |
317 | /** |
318 | * zone_dirty_limit - maximum number of dirty pages allowed in a zone |
319 | * @zone: the zone |
320 | * |
321 | * Returns the maximum number of dirty pages allowed in a zone, based |
322 | * on the zone's dirtyable memory. |
323 | */ |
324 | static unsigned long zone_dirty_limit(struct zone *zone) |
325 | { |
326 | unsigned long zone_memory = zone_dirtyable_memory(zone); |
327 | struct task_struct *tsk = current; |
328 | unsigned long dirty; |
329 | |
330 | if (vm_dirty_bytes) |
331 | dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) * |
332 | zone_memory / global_dirtyable_memory(); |
333 | else |
334 | dirty = vm_dirty_ratio * zone_memory / 100; |
335 | |
336 | if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) |
337 | dirty += dirty / 4; |
338 | |
339 | return dirty; |
340 | } |
341 | |
342 | /** |
343 | * zone_dirty_ok - tells whether a zone is within its dirty limits |
344 | * @zone: the zone to check |
345 | * |
346 | * Returns %true when the dirty pages in @zone are within the zone's |
347 | * dirty limit, %false if the limit is exceeded. |
348 | */ |
349 | bool zone_dirty_ok(struct zone *zone) |
350 | { |
351 | unsigned long limit = zone_dirty_limit(zone); |
352 | |
353 | return zone_page_state(zone, NR_FILE_DIRTY) + |
354 | zone_page_state(zone, NR_UNSTABLE_NFS) + |
355 | zone_page_state(zone, NR_WRITEBACK) <= limit; |
356 | } |
357 | |
358 | int dirty_background_ratio_handler(struct ctl_table *table, int write, |
359 | void __user *buffer, size_t *lenp, |
360 | loff_t *ppos) |
361 | { |
362 | int ret; |
363 | |
364 | ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
365 | if (ret == 0 && write) |
366 | dirty_background_bytes = 0; |
367 | return ret; |
368 | } |
369 | |
370 | int dirty_background_bytes_handler(struct ctl_table *table, int write, |
371 | void __user *buffer, size_t *lenp, |
372 | loff_t *ppos) |
373 | { |
374 | int ret; |
375 | |
376 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
377 | if (ret == 0 && write) |
378 | dirty_background_ratio = 0; |
379 | return ret; |
380 | } |
381 | |
382 | int dirty_ratio_handler(struct ctl_table *table, int write, |
383 | void __user *buffer, size_t *lenp, |
384 | loff_t *ppos) |
385 | { |
386 | int old_ratio = vm_dirty_ratio; |
387 | int ret; |
388 | |
389 | ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
390 | if (ret == 0 && write && vm_dirty_ratio != old_ratio) { |
391 | writeback_set_ratelimit(); |
392 | vm_dirty_bytes = 0; |
393 | } |
394 | return ret; |
395 | } |
396 | |
397 | int dirty_bytes_handler(struct ctl_table *table, int write, |
398 | void __user *buffer, size_t *lenp, |
399 | loff_t *ppos) |
400 | { |
401 | unsigned long old_bytes = vm_dirty_bytes; |
402 | int ret; |
403 | |
404 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
405 | if (ret == 0 && write && vm_dirty_bytes != old_bytes) { |
406 | writeback_set_ratelimit(); |
407 | vm_dirty_ratio = 0; |
408 | } |
409 | return ret; |
410 | } |
411 | |
412 | static unsigned long wp_next_time(unsigned long cur_time) |
413 | { |
414 | cur_time += VM_COMPLETIONS_PERIOD_LEN; |
415 | /* 0 has a special meaning... */ |
416 | if (!cur_time) |
417 | return 1; |
418 | return cur_time; |
419 | } |
420 | |
421 | /* |
422 | * Increment the BDI's writeout completion count and the global writeout |
423 | * completion count. Called from test_clear_page_writeback(). |
424 | */ |
425 | static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) |
426 | { |
427 | __inc_bdi_stat(bdi, BDI_WRITTEN); |
428 | __fprop_inc_percpu_max(&writeout_completions, &bdi->completions, |
429 | bdi->max_prop_frac); |
430 | /* First event after period switching was turned off? */ |
431 | if (!unlikely(writeout_period_time)) { |
432 | /* |
433 | * We can race with other __bdi_writeout_inc calls here but |
434 | * it does not cause any harm since the resulting time when |
435 | * timer will fire and what is in writeout_period_time will be |
436 | * roughly the same. |
437 | */ |
438 | writeout_period_time = wp_next_time(jiffies); |
439 | mod_timer(&writeout_period_timer, writeout_period_time); |
440 | } |
441 | } |
442 | |
443 | void bdi_writeout_inc(struct backing_dev_info *bdi) |
444 | { |
445 | unsigned long flags; |
446 | |
447 | local_irq_save(flags); |
448 | __bdi_writeout_inc(bdi); |
449 | local_irq_restore(flags); |
450 | } |
451 | EXPORT_SYMBOL_GPL(bdi_writeout_inc); |
452 | |
453 | /* |
454 | * Obtain an accurate fraction of the BDI's portion. |
455 | */ |
456 | static void bdi_writeout_fraction(struct backing_dev_info *bdi, |
457 | long *numerator, long *denominator) |
458 | { |
459 | fprop_fraction_percpu(&writeout_completions, &bdi->completions, |
460 | numerator, denominator); |
461 | } |
462 | |
463 | /* |
464 | * On idle system, we can be called long after we scheduled because we use |
465 | * deferred timers so count with missed periods. |
466 | */ |
467 | static void writeout_period(unsigned long t) |
468 | { |
469 | int miss_periods = (jiffies - writeout_period_time) / |
470 | VM_COMPLETIONS_PERIOD_LEN; |
471 | |
472 | if (fprop_new_period(&writeout_completions, miss_periods + 1)) { |
473 | writeout_period_time = wp_next_time(writeout_period_time + |
474 | miss_periods * VM_COMPLETIONS_PERIOD_LEN); |
475 | mod_timer(&writeout_period_timer, writeout_period_time); |
476 | } else { |
477 | /* |
478 | * Aging has zeroed all fractions. Stop wasting CPU on period |
479 | * updates. |
480 | */ |
481 | writeout_period_time = 0; |
482 | } |
483 | } |
484 | |
485 | /* |
486 | * bdi_min_ratio keeps the sum of the minimum dirty shares of all |
487 | * registered backing devices, which, for obvious reasons, can not |
488 | * exceed 100%. |
489 | */ |
490 | static unsigned int bdi_min_ratio; |
491 | |
492 | int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) |
493 | { |
494 | int ret = 0; |
495 | |
496 | spin_lock_bh(&bdi_lock); |
497 | if (min_ratio > bdi->max_ratio) { |
498 | ret = -EINVAL; |
499 | } else { |
500 | min_ratio -= bdi->min_ratio; |
501 | if (bdi_min_ratio + min_ratio < 100) { |
502 | bdi_min_ratio += min_ratio; |
503 | bdi->min_ratio += min_ratio; |
504 | } else { |
505 | ret = -EINVAL; |
506 | } |
507 | } |
508 | spin_unlock_bh(&bdi_lock); |
509 | |
510 | return ret; |
511 | } |
512 | |
513 | int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) |
514 | { |
515 | int ret = 0; |
516 | |
517 | if (max_ratio > 100) |
518 | return -EINVAL; |
519 | |
520 | spin_lock_bh(&bdi_lock); |
521 | if (bdi->min_ratio > max_ratio) { |
522 | ret = -EINVAL; |
523 | } else { |
524 | bdi->max_ratio = max_ratio; |
525 | bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100; |
526 | } |
527 | spin_unlock_bh(&bdi_lock); |
528 | |
529 | return ret; |
530 | } |
531 | EXPORT_SYMBOL(bdi_set_max_ratio); |
532 | |
533 | static unsigned long dirty_freerun_ceiling(unsigned long thresh, |
534 | unsigned long bg_thresh) |
535 | { |
536 | return (thresh + bg_thresh) / 2; |
537 | } |
538 | |
539 | static unsigned long hard_dirty_limit(unsigned long thresh) |
540 | { |
541 | return max(thresh, global_dirty_limit); |
542 | } |
543 | |
544 | /** |
545 | * bdi_dirty_limit - @bdi's share of dirty throttling threshold |
546 | * @bdi: the backing_dev_info to query |
547 | * @dirty: global dirty limit in pages |
548 | * |
549 | * Returns @bdi's dirty limit in pages. The term "dirty" in the context of |
550 | * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages. |
551 | * |
552 | * Note that balance_dirty_pages() will only seriously take it as a hard limit |
553 | * when sleeping max_pause per page is not enough to keep the dirty pages under |
554 | * control. For example, when the device is completely stalled due to some error |
555 | * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key. |
556 | * In the other normal situations, it acts more gently by throttling the tasks |
557 | * more (rather than completely block them) when the bdi dirty pages go high. |
558 | * |
559 | * It allocates high/low dirty limits to fast/slow devices, in order to prevent |
560 | * - starving fast devices |
561 | * - piling up dirty pages (that will take long time to sync) on slow devices |
562 | * |
563 | * The bdi's share of dirty limit will be adapting to its throughput and |
564 | * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. |
565 | */ |
566 | unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) |
567 | { |
568 | u64 bdi_dirty; |
569 | long numerator, denominator; |
570 | |
571 | /* |
572 | * Calculate this BDI's share of the dirty ratio. |
573 | */ |
574 | bdi_writeout_fraction(bdi, &numerator, &denominator); |
575 | |
576 | bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; |
577 | bdi_dirty *= numerator; |
578 | do_div(bdi_dirty, denominator); |
579 | |
580 | bdi_dirty += (dirty * bdi->min_ratio) / 100; |
581 | if (bdi_dirty > (dirty * bdi->max_ratio) / 100) |
582 | bdi_dirty = dirty * bdi->max_ratio / 100; |
583 | |
584 | return bdi_dirty; |
585 | } |
586 | |
587 | /* |
588 | * Dirty position control. |
589 | * |
590 | * (o) global/bdi setpoints |
591 | * |
592 | * We want the dirty pages be balanced around the global/bdi setpoints. |
593 | * When the number of dirty pages is higher/lower than the setpoint, the |
594 | * dirty position control ratio (and hence task dirty ratelimit) will be |
595 | * decreased/increased to bring the dirty pages back to the setpoint. |
596 | * |
597 | * pos_ratio = 1 << RATELIMIT_CALC_SHIFT |
598 | * |
599 | * if (dirty < setpoint) scale up pos_ratio |
600 | * if (dirty > setpoint) scale down pos_ratio |
601 | * |
602 | * if (bdi_dirty < bdi_setpoint) scale up pos_ratio |
603 | * if (bdi_dirty > bdi_setpoint) scale down pos_ratio |
604 | * |
605 | * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT |
606 | * |
607 | * (o) global control line |
608 | * |
609 | * ^ pos_ratio |
610 | * | |
611 | * | |<===== global dirty control scope ======>| |
612 | * 2.0 .............* |
613 | * | .* |
614 | * | . * |
615 | * | . * |
616 | * | . * |
617 | * | . * |
618 | * | . * |
619 | * 1.0 ................................* |
620 | * | . . * |
621 | * | . . * |
622 | * | . . * |
623 | * | . . * |
624 | * | . . * |
625 | * 0 +------------.------------------.----------------------*-------------> |
626 | * freerun^ setpoint^ limit^ dirty pages |
627 | * |
628 | * (o) bdi control line |
629 | * |
630 | * ^ pos_ratio |
631 | * | |
632 | * | * |
633 | * | * |
634 | * | * |
635 | * | * |
636 | * | * |<=========== span ============>| |
637 | * 1.0 .......................* |
638 | * | . * |
639 | * | . * |
640 | * | . * |
641 | * | . * |
642 | * | . * |
643 | * | . * |
644 | * | . * |
645 | * | . * |
646 | * | . * |
647 | * | . * |
648 | * | . * |
649 | * 1/4 ...............................................* * * * * * * * * * * * |
650 | * | . . |
651 | * | . . |
652 | * | . . |
653 | * 0 +----------------------.-------------------------------.-------------> |
654 | * bdi_setpoint^ x_intercept^ |
655 | * |
656 | * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can |
657 | * be smoothly throttled down to normal if it starts high in situations like |
658 | * - start writing to a slow SD card and a fast disk at the same time. The SD |
659 | * card's bdi_dirty may rush to many times higher than bdi_setpoint. |
660 | * - the bdi dirty thresh drops quickly due to change of JBOD workload |
661 | */ |
662 | static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, |
663 | unsigned long thresh, |
664 | unsigned long bg_thresh, |
665 | unsigned long dirty, |
666 | unsigned long bdi_thresh, |
667 | unsigned long bdi_dirty) |
668 | { |
669 | unsigned long write_bw = bdi->avg_write_bandwidth; |
670 | unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); |
671 | unsigned long limit = hard_dirty_limit(thresh); |
672 | unsigned long x_intercept; |
673 | unsigned long setpoint; /* dirty pages' target balance point */ |
674 | unsigned long bdi_setpoint; |
675 | unsigned long span; |
676 | long long pos_ratio; /* for scaling up/down the rate limit */ |
677 | long x; |
678 | |
679 | if (unlikely(dirty >= limit)) |
680 | return 0; |
681 | |
682 | /* |
683 | * global setpoint |
684 | * |
685 | * setpoint - dirty 3 |
686 | * f(dirty) := 1.0 + (----------------) |
687 | * limit - setpoint |
688 | * |
689 | * it's a 3rd order polynomial that subjects to |
690 | * |
691 | * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast |
692 | * (2) f(setpoint) = 1.0 => the balance point |
693 | * (3) f(limit) = 0 => the hard limit |
694 | * (4) df/dx <= 0 => negative feedback control |
695 | * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) |
696 | * => fast response on large errors; small oscillation near setpoint |
697 | */ |
698 | setpoint = (freerun + limit) / 2; |
699 | x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, |
700 | limit - setpoint + 1); |
701 | pos_ratio = x; |
702 | pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
703 | pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
704 | pos_ratio += 1 << RATELIMIT_CALC_SHIFT; |
705 | |
706 | /* |
707 | * We have computed basic pos_ratio above based on global situation. If |
708 | * the bdi is over/under its share of dirty pages, we want to scale |
709 | * pos_ratio further down/up. That is done by the following mechanism. |
710 | */ |
711 | |
712 | /* |
713 | * bdi setpoint |
714 | * |
715 | * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint) |
716 | * |
717 | * x_intercept - bdi_dirty |
718 | * := -------------------------- |
719 | * x_intercept - bdi_setpoint |
720 | * |
721 | * The main bdi control line is a linear function that subjects to |
722 | * |
723 | * (1) f(bdi_setpoint) = 1.0 |
724 | * (2) k = - 1 / (8 * write_bw) (in single bdi case) |
725 | * or equally: x_intercept = bdi_setpoint + 8 * write_bw |
726 | * |
727 | * For single bdi case, the dirty pages are observed to fluctuate |
728 | * regularly within range |
729 | * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2] |
730 | * for various filesystems, where (2) can yield in a reasonable 12.5% |
731 | * fluctuation range for pos_ratio. |
732 | * |
733 | * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its |
734 | * own size, so move the slope over accordingly and choose a slope that |
735 | * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh. |
736 | */ |
737 | if (unlikely(bdi_thresh > thresh)) |
738 | bdi_thresh = thresh; |
739 | /* |
740 | * It's very possible that bdi_thresh is close to 0 not because the |
741 | * device is slow, but that it has remained inactive for long time. |
742 | * Honour such devices a reasonable good (hopefully IO efficient) |
743 | * threshold, so that the occasional writes won't be blocked and active |
744 | * writes can rampup the threshold quickly. |
745 | */ |
746 | bdi_thresh = max(bdi_thresh, (limit - dirty) / 8); |
747 | /* |
748 | * scale global setpoint to bdi's: |
749 | * bdi_setpoint = setpoint * bdi_thresh / thresh |
750 | */ |
751 | x = div_u64((u64)bdi_thresh << 16, thresh + 1); |
752 | bdi_setpoint = setpoint * (u64)x >> 16; |
753 | /* |
754 | * Use span=(8*write_bw) in single bdi case as indicated by |
755 | * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case. |
756 | * |
757 | * bdi_thresh thresh - bdi_thresh |
758 | * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh |
759 | * thresh thresh |
760 | */ |
761 | span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16; |
762 | x_intercept = bdi_setpoint + span; |
763 | |
764 | if (bdi_dirty < x_intercept - span / 4) { |
765 | pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty), |
766 | x_intercept - bdi_setpoint + 1); |
767 | } else |
768 | pos_ratio /= 4; |
769 | |
770 | /* |
771 | * bdi reserve area, safeguard against dirty pool underrun and disk idle |
772 | * It may push the desired control point of global dirty pages higher |
773 | * than setpoint. |
774 | */ |
775 | x_intercept = bdi_thresh / 2; |
776 | if (bdi_dirty < x_intercept) { |
777 | if (bdi_dirty > x_intercept / 8) |
778 | pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty); |
779 | else |
780 | pos_ratio *= 8; |
781 | } |
782 | |
783 | return pos_ratio; |
784 | } |
785 | |
786 | static void bdi_update_write_bandwidth(struct backing_dev_info *bdi, |
787 | unsigned long elapsed, |
788 | unsigned long written) |
789 | { |
790 | const unsigned long period = roundup_pow_of_two(3 * HZ); |
791 | unsigned long avg = bdi->avg_write_bandwidth; |
792 | unsigned long old = bdi->write_bandwidth; |
793 | u64 bw; |
794 | |
795 | /* |
796 | * bw = written * HZ / elapsed |
797 | * |
798 | * bw * elapsed + write_bandwidth * (period - elapsed) |
799 | * write_bandwidth = --------------------------------------------------- |
800 | * period |
801 | */ |
802 | bw = written - bdi->written_stamp; |
803 | bw *= HZ; |
804 | if (unlikely(elapsed > period)) { |
805 | do_div(bw, elapsed); |
806 | avg = bw; |
807 | goto out; |
808 | } |
809 | bw += (u64)bdi->write_bandwidth * (period - elapsed); |
810 | bw >>= ilog2(period); |
811 | |
812 | /* |
813 | * one more level of smoothing, for filtering out sudden spikes |
814 | */ |
815 | if (avg > old && old >= (unsigned long)bw) |
816 | avg -= (avg - old) >> 3; |
817 | |
818 | if (avg < old && old <= (unsigned long)bw) |
819 | avg += (old - avg) >> 3; |
820 | |
821 | out: |
822 | bdi->write_bandwidth = bw; |
823 | bdi->avg_write_bandwidth = avg; |
824 | } |
825 | |
826 | /* |
827 | * The global dirtyable memory and dirty threshold could be suddenly knocked |
828 | * down by a large amount (eg. on the startup of KVM in a swapless system). |
829 | * This may throw the system into deep dirty exceeded state and throttle |
830 | * heavy/light dirtiers alike. To retain good responsiveness, maintain |
831 | * global_dirty_limit for tracking slowly down to the knocked down dirty |
832 | * threshold. |
833 | */ |
834 | static void update_dirty_limit(unsigned long thresh, unsigned long dirty) |
835 | { |
836 | unsigned long limit = global_dirty_limit; |
837 | |
838 | /* |
839 | * Follow up in one step. |
840 | */ |
841 | if (limit < thresh) { |
842 | limit = thresh; |
843 | goto update; |
844 | } |
845 | |
846 | /* |
847 | * Follow down slowly. Use the higher one as the target, because thresh |
848 | * may drop below dirty. This is exactly the reason to introduce |
849 | * global_dirty_limit which is guaranteed to lie above the dirty pages. |
850 | */ |
851 | thresh = max(thresh, dirty); |
852 | if (limit > thresh) { |
853 | limit -= (limit - thresh) >> 5; |
854 | goto update; |
855 | } |
856 | return; |
857 | update: |
858 | global_dirty_limit = limit; |
859 | } |
860 | |
861 | static void global_update_bandwidth(unsigned long thresh, |
862 | unsigned long dirty, |
863 | unsigned long now) |
864 | { |
865 | static DEFINE_SPINLOCK(dirty_lock); |
866 | static unsigned long update_time; |
867 | |
868 | /* |
869 | * check locklessly first to optimize away locking for the most time |
870 | */ |
871 | if (time_before(now, update_time + BANDWIDTH_INTERVAL)) |
872 | return; |
873 | |
874 | spin_lock(&dirty_lock); |
875 | if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) { |
876 | update_dirty_limit(thresh, dirty); |
877 | update_time = now; |
878 | } |
879 | spin_unlock(&dirty_lock); |
880 | } |
881 | |
882 | /* |
883 | * Maintain bdi->dirty_ratelimit, the base dirty throttle rate. |
884 | * |
885 | * Normal bdi tasks will be curbed at or below it in long term. |
886 | * Obviously it should be around (write_bw / N) when there are N dd tasks. |
887 | */ |
888 | static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi, |
889 | unsigned long thresh, |
890 | unsigned long bg_thresh, |
891 | unsigned long dirty, |
892 | unsigned long bdi_thresh, |
893 | unsigned long bdi_dirty, |
894 | unsigned long dirtied, |
895 | unsigned long elapsed) |
896 | { |
897 | unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); |
898 | unsigned long limit = hard_dirty_limit(thresh); |
899 | unsigned long setpoint = (freerun + limit) / 2; |
900 | unsigned long write_bw = bdi->avg_write_bandwidth; |
901 | unsigned long dirty_ratelimit = bdi->dirty_ratelimit; |
902 | unsigned long dirty_rate; |
903 | unsigned long task_ratelimit; |
904 | unsigned long balanced_dirty_ratelimit; |
905 | unsigned long pos_ratio; |
906 | unsigned long step; |
907 | unsigned long x; |
908 | |
909 | /* |
910 | * The dirty rate will match the writeout rate in long term, except |
911 | * when dirty pages are truncated by userspace or re-dirtied by FS. |
912 | */ |
913 | dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed; |
914 | |
915 | pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty, |
916 | bdi_thresh, bdi_dirty); |
917 | /* |
918 | * task_ratelimit reflects each dd's dirty rate for the past 200ms. |
919 | */ |
920 | task_ratelimit = (u64)dirty_ratelimit * |
921 | pos_ratio >> RATELIMIT_CALC_SHIFT; |
922 | task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */ |
923 | |
924 | /* |
925 | * A linear estimation of the "balanced" throttle rate. The theory is, |
926 | * if there are N dd tasks, each throttled at task_ratelimit, the bdi's |
927 | * dirty_rate will be measured to be (N * task_ratelimit). So the below |
928 | * formula will yield the balanced rate limit (write_bw / N). |
929 | * |
930 | * Note that the expanded form is not a pure rate feedback: |
931 | * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1) |
932 | * but also takes pos_ratio into account: |
933 | * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2) |
934 | * |
935 | * (1) is not realistic because pos_ratio also takes part in balancing |
936 | * the dirty rate. Consider the state |
937 | * pos_ratio = 0.5 (3) |
938 | * rate = 2 * (write_bw / N) (4) |
939 | * If (1) is used, it will stuck in that state! Because each dd will |
940 | * be throttled at |
941 | * task_ratelimit = pos_ratio * rate = (write_bw / N) (5) |
942 | * yielding |
943 | * dirty_rate = N * task_ratelimit = write_bw (6) |
944 | * put (6) into (1) we get |
945 | * rate_(i+1) = rate_(i) (7) |
946 | * |
947 | * So we end up using (2) to always keep |
948 | * rate_(i+1) ~= (write_bw / N) (8) |
949 | * regardless of the value of pos_ratio. As long as (8) is satisfied, |
950 | * pos_ratio is able to drive itself to 1.0, which is not only where |
951 | * the dirty count meet the setpoint, but also where the slope of |
952 | * pos_ratio is most flat and hence task_ratelimit is least fluctuated. |
953 | */ |
954 | balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw, |
955 | dirty_rate | 1); |
956 | /* |
957 | * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw |
958 | */ |
959 | if (unlikely(balanced_dirty_ratelimit > write_bw)) |
960 | balanced_dirty_ratelimit = write_bw; |
961 | |
962 | /* |
963 | * We could safely do this and return immediately: |
964 | * |
965 | * bdi->dirty_ratelimit = balanced_dirty_ratelimit; |
966 | * |
967 | * However to get a more stable dirty_ratelimit, the below elaborated |
968 | * code makes use of task_ratelimit to filter out singular points and |
969 | * limit the step size. |
970 | * |
971 | * The below code essentially only uses the relative value of |
972 | * |
973 | * task_ratelimit - dirty_ratelimit |
974 | * = (pos_ratio - 1) * dirty_ratelimit |
975 | * |
976 | * which reflects the direction and size of dirty position error. |
977 | */ |
978 | |
979 | /* |
980 | * dirty_ratelimit will follow balanced_dirty_ratelimit iff |
981 | * task_ratelimit is on the same side of dirty_ratelimit, too. |
982 | * For example, when |
983 | * - dirty_ratelimit > balanced_dirty_ratelimit |
984 | * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint) |
985 | * lowering dirty_ratelimit will help meet both the position and rate |
986 | * control targets. Otherwise, don't update dirty_ratelimit if it will |
987 | * only help meet the rate target. After all, what the users ultimately |
988 | * feel and care are stable dirty rate and small position error. |
989 | * |
990 | * |task_ratelimit - dirty_ratelimit| is used to limit the step size |
991 | * and filter out the singular points of balanced_dirty_ratelimit. Which |
992 | * keeps jumping around randomly and can even leap far away at times |
993 | * due to the small 200ms estimation period of dirty_rate (we want to |
994 | * keep that period small to reduce time lags). |
995 | */ |
996 | step = 0; |
997 | if (dirty < setpoint) { |
998 | x = min(bdi->balanced_dirty_ratelimit, |
999 | min(balanced_dirty_ratelimit, task_ratelimit)); |
1000 | if (dirty_ratelimit < x) |
1001 | step = x - dirty_ratelimit; |
1002 | } else { |
1003 | x = max(bdi->balanced_dirty_ratelimit, |
1004 | max(balanced_dirty_ratelimit, task_ratelimit)); |
1005 | if (dirty_ratelimit > x) |
1006 | step = dirty_ratelimit - x; |
1007 | } |
1008 | |
1009 | /* |
1010 | * Don't pursue 100% rate matching. It's impossible since the balanced |
1011 | * rate itself is constantly fluctuating. So decrease the track speed |
1012 | * when it gets close to the target. Helps eliminate pointless tremors. |
1013 | */ |
1014 | step >>= dirty_ratelimit / (2 * step + 1); |
1015 | /* |
1016 | * Limit the tracking speed to avoid overshooting. |
1017 | */ |
1018 | step = (step + 7) / 8; |
1019 | |
1020 | if (dirty_ratelimit < balanced_dirty_ratelimit) |
1021 | dirty_ratelimit += step; |
1022 | else |
1023 | dirty_ratelimit -= step; |
1024 | |
1025 | bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL); |
1026 | bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit; |
1027 | |
1028 | trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit); |
1029 | } |
1030 | |
1031 | void __bdi_update_bandwidth(struct backing_dev_info *bdi, |
1032 | unsigned long thresh, |
1033 | unsigned long bg_thresh, |
1034 | unsigned long dirty, |
1035 | unsigned long bdi_thresh, |
1036 | unsigned long bdi_dirty, |
1037 | unsigned long start_time) |
1038 | { |
1039 | unsigned long now = jiffies; |
1040 | unsigned long elapsed = now - bdi->bw_time_stamp; |
1041 | unsigned long dirtied; |
1042 | unsigned long written; |
1043 | |
1044 | /* |
1045 | * rate-limit, only update once every 200ms. |
1046 | */ |
1047 | if (elapsed < BANDWIDTH_INTERVAL) |
1048 | return; |
1049 | |
1050 | dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]); |
1051 | written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]); |
1052 | |
1053 | /* |
1054 | * Skip quiet periods when disk bandwidth is under-utilized. |
1055 | * (at least 1s idle time between two flusher runs) |
1056 | */ |
1057 | if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time)) |
1058 | goto snapshot; |
1059 | |
1060 | if (thresh) { |
1061 | global_update_bandwidth(thresh, dirty, now); |
1062 | bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty, |
1063 | bdi_thresh, bdi_dirty, |
1064 | dirtied, elapsed); |
1065 | } |
1066 | bdi_update_write_bandwidth(bdi, elapsed, written); |
1067 | |
1068 | snapshot: |
1069 | bdi->dirtied_stamp = dirtied; |
1070 | bdi->written_stamp = written; |
1071 | bdi->bw_time_stamp = now; |
1072 | } |
1073 | |
1074 | static void bdi_update_bandwidth(struct backing_dev_info *bdi, |
1075 | unsigned long thresh, |
1076 | unsigned long bg_thresh, |
1077 | unsigned long dirty, |
1078 | unsigned long bdi_thresh, |
1079 | unsigned long bdi_dirty, |
1080 | unsigned long start_time) |
1081 | { |
1082 | if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL)) |
1083 | return; |
1084 | spin_lock(&bdi->wb.list_lock); |
1085 | __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty, |
1086 | bdi_thresh, bdi_dirty, start_time); |
1087 | spin_unlock(&bdi->wb.list_lock); |
1088 | } |
1089 | |
1090 | /* |
1091 | * After a task dirtied this many pages, balance_dirty_pages_ratelimited() |
1092 | * will look to see if it needs to start dirty throttling. |
1093 | * |
1094 | * If dirty_poll_interval is too low, big NUMA machines will call the expensive |
1095 | * global_page_state() too often. So scale it near-sqrt to the safety margin |
1096 | * (the number of pages we may dirty without exceeding the dirty limits). |
1097 | */ |
1098 | static unsigned long dirty_poll_interval(unsigned long dirty, |
1099 | unsigned long thresh) |
1100 | { |
1101 | if (thresh > dirty) |
1102 | return 1UL << (ilog2(thresh - dirty) >> 1); |
1103 | |
1104 | return 1; |
1105 | } |
1106 | |
1107 | static long bdi_max_pause(struct backing_dev_info *bdi, |
1108 | unsigned long bdi_dirty) |
1109 | { |
1110 | long bw = bdi->avg_write_bandwidth; |
1111 | long t; |
1112 | |
1113 | /* |
1114 | * Limit pause time for small memory systems. If sleeping for too long |
1115 | * time, a small pool of dirty/writeback pages may go empty and disk go |
1116 | * idle. |
1117 | * |
1118 | * 8 serves as the safety ratio. |
1119 | */ |
1120 | t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8)); |
1121 | t++; |
1122 | |
1123 | return min_t(long, t, MAX_PAUSE); |
1124 | } |
1125 | |
1126 | static long bdi_min_pause(struct backing_dev_info *bdi, |
1127 | long max_pause, |
1128 | unsigned long task_ratelimit, |
1129 | unsigned long dirty_ratelimit, |
1130 | int *nr_dirtied_pause) |
1131 | { |
1132 | long hi = ilog2(bdi->avg_write_bandwidth); |
1133 | long lo = ilog2(bdi->dirty_ratelimit); |
1134 | long t; /* target pause */ |
1135 | long pause; /* estimated next pause */ |
1136 | int pages; /* target nr_dirtied_pause */ |
1137 | |
1138 | /* target for 10ms pause on 1-dd case */ |
1139 | t = max(1, HZ / 100); |
1140 | |
1141 | /* |
1142 | * Scale up pause time for concurrent dirtiers in order to reduce CPU |
1143 | * overheads. |
1144 | * |
1145 | * (N * 10ms) on 2^N concurrent tasks. |
1146 | */ |
1147 | if (hi > lo) |
1148 | t += (hi - lo) * (10 * HZ) / 1024; |
1149 | |
1150 | /* |
1151 | * This is a bit convoluted. We try to base the next nr_dirtied_pause |
1152 | * on the much more stable dirty_ratelimit. However the next pause time |
1153 | * will be computed based on task_ratelimit and the two rate limits may |
1154 | * depart considerably at some time. Especially if task_ratelimit goes |
1155 | * below dirty_ratelimit/2 and the target pause is max_pause, the next |
1156 | * pause time will be max_pause*2 _trimmed down_ to max_pause. As a |
1157 | * result task_ratelimit won't be executed faithfully, which could |
1158 | * eventually bring down dirty_ratelimit. |
1159 | * |
1160 | * We apply two rules to fix it up: |
1161 | * 1) try to estimate the next pause time and if necessary, use a lower |
1162 | * nr_dirtied_pause so as not to exceed max_pause. When this happens, |
1163 | * nr_dirtied_pause will be "dancing" with task_ratelimit. |
1164 | * 2) limit the target pause time to max_pause/2, so that the normal |
1165 | * small fluctuations of task_ratelimit won't trigger rule (1) and |
1166 | * nr_dirtied_pause will remain as stable as dirty_ratelimit. |
1167 | */ |
1168 | t = min(t, 1 + max_pause / 2); |
1169 | pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); |
1170 | |
1171 | /* |
1172 | * Tiny nr_dirtied_pause is found to hurt I/O performance in the test |
1173 | * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}. |
1174 | * When the 16 consecutive reads are often interrupted by some dirty |
1175 | * throttling pause during the async writes, cfq will go into idles |
1176 | * (deadline is fine). So push nr_dirtied_pause as high as possible |
1177 | * until reaches DIRTY_POLL_THRESH=32 pages. |
1178 | */ |
1179 | if (pages < DIRTY_POLL_THRESH) { |
1180 | t = max_pause; |
1181 | pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); |
1182 | if (pages > DIRTY_POLL_THRESH) { |
1183 | pages = DIRTY_POLL_THRESH; |
1184 | t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit; |
1185 | } |
1186 | } |
1187 | |
1188 | pause = HZ * pages / (task_ratelimit + 1); |
1189 | if (pause > max_pause) { |
1190 | t = max_pause; |
1191 | pages = task_ratelimit * t / roundup_pow_of_two(HZ); |
1192 | } |
1193 | |
1194 | *nr_dirtied_pause = pages; |
1195 | /* |
1196 | * The minimal pause time will normally be half the target pause time. |
1197 | */ |
1198 | return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t; |
1199 | } |
1200 | |
1201 | /* |
1202 | * balance_dirty_pages() must be called by processes which are generating dirty |
1203 | * data. It looks at the number of dirty pages in the machine and will force |
1204 | * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2. |
1205 | * If we're over `background_thresh' then the writeback threads are woken to |
1206 | * perform some writeout. |
1207 | */ |
1208 | static void balance_dirty_pages(struct address_space *mapping, |
1209 | unsigned long pages_dirtied) |
1210 | { |
1211 | unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */ |
1212 | unsigned long bdi_reclaimable; |
1213 | unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */ |
1214 | unsigned long bdi_dirty; |
1215 | unsigned long freerun; |
1216 | unsigned long background_thresh; |
1217 | unsigned long dirty_thresh; |
1218 | unsigned long bdi_thresh; |
1219 | long period; |
1220 | long pause; |
1221 | long max_pause; |
1222 | long min_pause; |
1223 | int nr_dirtied_pause; |
1224 | bool dirty_exceeded = false; |
1225 | unsigned long task_ratelimit; |
1226 | unsigned long dirty_ratelimit; |
1227 | unsigned long pos_ratio; |
1228 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
1229 | unsigned long start_time = jiffies; |
1230 | |
1231 | for (;;) { |
1232 | unsigned long now = jiffies; |
1233 | |
1234 | /* |
1235 | * Unstable writes are a feature of certain networked |
1236 | * filesystems (i.e. NFS) in which data may have been |
1237 | * written to the server's write cache, but has not yet |
1238 | * been flushed to permanent storage. |
1239 | */ |
1240 | nr_reclaimable = global_page_state(NR_FILE_DIRTY) + |
1241 | global_page_state(NR_UNSTABLE_NFS); |
1242 | nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK); |
1243 | |
1244 | global_dirty_limits(&background_thresh, &dirty_thresh); |
1245 | |
1246 | /* |
1247 | * Throttle it only when the background writeback cannot |
1248 | * catch-up. This avoids (excessively) small writeouts |
1249 | * when the bdi limits are ramping up. |
1250 | */ |
1251 | freerun = dirty_freerun_ceiling(dirty_thresh, |
1252 | background_thresh); |
1253 | if (nr_dirty <= freerun) { |
1254 | current->dirty_paused_when = now; |
1255 | current->nr_dirtied = 0; |
1256 | current->nr_dirtied_pause = |
1257 | dirty_poll_interval(nr_dirty, dirty_thresh); |
1258 | break; |
1259 | } |
1260 | |
1261 | if (unlikely(!writeback_in_progress(bdi))) |
1262 | bdi_start_background_writeback(bdi); |
1263 | |
1264 | /* |
1265 | * bdi_thresh is not treated as some limiting factor as |
1266 | * dirty_thresh, due to reasons |
1267 | * - in JBOD setup, bdi_thresh can fluctuate a lot |
1268 | * - in a system with HDD and USB key, the USB key may somehow |
1269 | * go into state (bdi_dirty >> bdi_thresh) either because |
1270 | * bdi_dirty starts high, or because bdi_thresh drops low. |
1271 | * In this case we don't want to hard throttle the USB key |
1272 | * dirtiers for 100 seconds until bdi_dirty drops under |
1273 | * bdi_thresh. Instead the auxiliary bdi control line in |
1274 | * bdi_position_ratio() will let the dirtier task progress |
1275 | * at some rate <= (write_bw / 2) for bringing down bdi_dirty. |
1276 | */ |
1277 | bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); |
1278 | |
1279 | /* |
1280 | * In order to avoid the stacked BDI deadlock we need |
1281 | * to ensure we accurately count the 'dirty' pages when |
1282 | * the threshold is low. |
1283 | * |
1284 | * Otherwise it would be possible to get thresh+n pages |
1285 | * reported dirty, even though there are thresh-m pages |
1286 | * actually dirty; with m+n sitting in the percpu |
1287 | * deltas. |
1288 | */ |
1289 | if (bdi_thresh < 2 * bdi_stat_error(bdi)) { |
1290 | bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); |
1291 | bdi_dirty = bdi_reclaimable + |
1292 | bdi_stat_sum(bdi, BDI_WRITEBACK); |
1293 | } else { |
1294 | bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); |
1295 | bdi_dirty = bdi_reclaimable + |
1296 | bdi_stat(bdi, BDI_WRITEBACK); |
1297 | } |
1298 | |
1299 | dirty_exceeded = (bdi_dirty > bdi_thresh) && |
1300 | (nr_dirty > dirty_thresh); |
1301 | if (dirty_exceeded && !bdi->dirty_exceeded) |
1302 | bdi->dirty_exceeded = 1; |
1303 | |
1304 | bdi_update_bandwidth(bdi, dirty_thresh, background_thresh, |
1305 | nr_dirty, bdi_thresh, bdi_dirty, |
1306 | start_time); |
1307 | |
1308 | dirty_ratelimit = bdi->dirty_ratelimit; |
1309 | pos_ratio = bdi_position_ratio(bdi, dirty_thresh, |
1310 | background_thresh, nr_dirty, |
1311 | bdi_thresh, bdi_dirty); |
1312 | task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >> |
1313 | RATELIMIT_CALC_SHIFT; |
1314 | max_pause = bdi_max_pause(bdi, bdi_dirty); |
1315 | min_pause = bdi_min_pause(bdi, max_pause, |
1316 | task_ratelimit, dirty_ratelimit, |
1317 | &nr_dirtied_pause); |
1318 | |
1319 | if (unlikely(task_ratelimit == 0)) { |
1320 | period = max_pause; |
1321 | pause = max_pause; |
1322 | goto pause; |
1323 | } |
1324 | period = HZ * pages_dirtied / task_ratelimit; |
1325 | pause = period; |
1326 | if (current->dirty_paused_when) |
1327 | pause -= now - current->dirty_paused_when; |
1328 | /* |
1329 | * For less than 1s think time (ext3/4 may block the dirtier |
1330 | * for up to 800ms from time to time on 1-HDD; so does xfs, |
1331 | * however at much less frequency), try to compensate it in |
1332 | * future periods by updating the virtual time; otherwise just |
1333 | * do a reset, as it may be a light dirtier. |
1334 | */ |
1335 | if (pause < min_pause) { |
1336 | trace_balance_dirty_pages(bdi, |
1337 | dirty_thresh, |
1338 | background_thresh, |
1339 | nr_dirty, |
1340 | bdi_thresh, |
1341 | bdi_dirty, |
1342 | dirty_ratelimit, |
1343 | task_ratelimit, |
1344 | pages_dirtied, |
1345 | period, |
1346 | min(pause, 0L), |
1347 | start_time); |
1348 | if (pause < -HZ) { |
1349 | current->dirty_paused_when = now; |
1350 | current->nr_dirtied = 0; |
1351 | } else if (period) { |
1352 | current->dirty_paused_when += period; |
1353 | current->nr_dirtied = 0; |
1354 | } else if (current->nr_dirtied_pause <= pages_dirtied) |
1355 | current->nr_dirtied_pause += pages_dirtied; |
1356 | break; |
1357 | } |
1358 | if (unlikely(pause > max_pause)) { |
1359 | /* for occasional dropped task_ratelimit */ |
1360 | now += min(pause - max_pause, max_pause); |
1361 | pause = max_pause; |
1362 | } |
1363 | |
1364 | pause: |
1365 | trace_balance_dirty_pages(bdi, |
1366 | dirty_thresh, |
1367 | background_thresh, |
1368 | nr_dirty, |
1369 | bdi_thresh, |
1370 | bdi_dirty, |
1371 | dirty_ratelimit, |
1372 | task_ratelimit, |
1373 | pages_dirtied, |
1374 | period, |
1375 | pause, |
1376 | start_time); |
1377 | __set_current_state(TASK_KILLABLE); |
1378 | io_schedule_timeout(pause); |
1379 | |
1380 | current->dirty_paused_when = now + pause; |
1381 | current->nr_dirtied = 0; |
1382 | current->nr_dirtied_pause = nr_dirtied_pause; |
1383 | |
1384 | /* |
1385 | * This is typically equal to (nr_dirty < dirty_thresh) and can |
1386 | * also keep "1000+ dd on a slow USB stick" under control. |
1387 | */ |
1388 | if (task_ratelimit) |
1389 | break; |
1390 | |
1391 | /* |
1392 | * In the case of an unresponding NFS server and the NFS dirty |
1393 | * pages exceeds dirty_thresh, give the other good bdi's a pipe |
1394 | * to go through, so that tasks on them still remain responsive. |
1395 | * |
1396 | * In theory 1 page is enough to keep the comsumer-producer |
1397 | * pipe going: the flusher cleans 1 page => the task dirties 1 |
1398 | * more page. However bdi_dirty has accounting errors. So use |
1399 | * the larger and more IO friendly bdi_stat_error. |
1400 | */ |
1401 | if (bdi_dirty <= bdi_stat_error(bdi)) |
1402 | break; |
1403 | |
1404 | if (fatal_signal_pending(current)) |
1405 | break; |
1406 | } |
1407 | |
1408 | if (!dirty_exceeded && bdi->dirty_exceeded) |
1409 | bdi->dirty_exceeded = 0; |
1410 | |
1411 | if (writeback_in_progress(bdi)) |
1412 | return; |
1413 | |
1414 | /* |
1415 | * In laptop mode, we wait until hitting the higher threshold before |
1416 | * starting background writeout, and then write out all the way down |
1417 | * to the lower threshold. So slow writers cause minimal disk activity. |
1418 | * |
1419 | * In normal mode, we start background writeout at the lower |
1420 | * background_thresh, to keep the amount of dirty memory low. |
1421 | */ |
1422 | if (laptop_mode) |
1423 | return; |
1424 | |
1425 | if (nr_reclaimable > background_thresh) |
1426 | bdi_start_background_writeback(bdi); |
1427 | } |
1428 | |
1429 | void set_page_dirty_balance(struct page *page, int page_mkwrite) |
1430 | { |
1431 | if (set_page_dirty(page) || page_mkwrite) { |
1432 | struct address_space *mapping = page_mapping(page); |
1433 | |
1434 | if (mapping) |
1435 | balance_dirty_pages_ratelimited(mapping); |
1436 | } |
1437 | } |
1438 | |
1439 | static DEFINE_PER_CPU(int, bdp_ratelimits); |
1440 | |
1441 | /* |
1442 | * Normal tasks are throttled by |
1443 | * loop { |
1444 | * dirty tsk->nr_dirtied_pause pages; |
1445 | * take a snap in balance_dirty_pages(); |
1446 | * } |
1447 | * However there is a worst case. If every task exit immediately when dirtied |
1448 | * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be |
1449 | * called to throttle the page dirties. The solution is to save the not yet |
1450 | * throttled page dirties in dirty_throttle_leaks on task exit and charge them |
1451 | * randomly into the running tasks. This works well for the above worst case, |
1452 | * as the new task will pick up and accumulate the old task's leaked dirty |
1453 | * count and eventually get throttled. |
1454 | */ |
1455 | DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0; |
1456 | |
1457 | /** |
1458 | * balance_dirty_pages_ratelimited - balance dirty memory state |
1459 | * @mapping: address_space which was dirtied |
1460 | * |
1461 | * Processes which are dirtying memory should call in here once for each page |
1462 | * which was newly dirtied. The function will periodically check the system's |
1463 | * dirty state and will initiate writeback if needed. |
1464 | * |
1465 | * On really big machines, get_writeback_state is expensive, so try to avoid |
1466 | * calling it too often (ratelimiting). But once we're over the dirty memory |
1467 | * limit we decrease the ratelimiting by a lot, to prevent individual processes |
1468 | * from overshooting the limit by (ratelimit_pages) each. |
1469 | */ |
1470 | void balance_dirty_pages_ratelimited(struct address_space *mapping) |
1471 | { |
1472 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
1473 | int ratelimit; |
1474 | int *p; |
1475 | |
1476 | if (!bdi_cap_account_dirty(bdi)) |
1477 | return; |
1478 | |
1479 | ratelimit = current->nr_dirtied_pause; |
1480 | if (bdi->dirty_exceeded) |
1481 | ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10)); |
1482 | |
1483 | preempt_disable(); |
1484 | /* |
1485 | * This prevents one CPU to accumulate too many dirtied pages without |
1486 | * calling into balance_dirty_pages(), which can happen when there are |
1487 | * 1000+ tasks, all of them start dirtying pages at exactly the same |
1488 | * time, hence all honoured too large initial task->nr_dirtied_pause. |
1489 | */ |
1490 | p = &__get_cpu_var(bdp_ratelimits); |
1491 | if (unlikely(current->nr_dirtied >= ratelimit)) |
1492 | *p = 0; |
1493 | else if (unlikely(*p >= ratelimit_pages)) { |
1494 | *p = 0; |
1495 | ratelimit = 0; |
1496 | } |
1497 | /* |
1498 | * Pick up the dirtied pages by the exited tasks. This avoids lots of |
1499 | * short-lived tasks (eg. gcc invocations in a kernel build) escaping |
1500 | * the dirty throttling and livelock other long-run dirtiers. |
1501 | */ |
1502 | p = &__get_cpu_var(dirty_throttle_leaks); |
1503 | if (*p > 0 && current->nr_dirtied < ratelimit) { |
1504 | unsigned long nr_pages_dirtied; |
1505 | nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied); |
1506 | *p -= nr_pages_dirtied; |
1507 | current->nr_dirtied += nr_pages_dirtied; |
1508 | } |
1509 | preempt_enable(); |
1510 | |
1511 | if (unlikely(current->nr_dirtied >= ratelimit)) |
1512 | balance_dirty_pages(mapping, current->nr_dirtied); |
1513 | } |
1514 | EXPORT_SYMBOL(balance_dirty_pages_ratelimited); |
1515 | |
1516 | void throttle_vm_writeout(gfp_t gfp_mask) |
1517 | { |
1518 | unsigned long background_thresh; |
1519 | unsigned long dirty_thresh; |
1520 | |
1521 | for ( ; ; ) { |
1522 | global_dirty_limits(&background_thresh, &dirty_thresh); |
1523 | dirty_thresh = hard_dirty_limit(dirty_thresh); |
1524 | |
1525 | /* |
1526 | * Boost the allowable dirty threshold a bit for page |
1527 | * allocators so they don't get DoS'ed by heavy writers |
1528 | */ |
1529 | dirty_thresh += dirty_thresh / 10; /* wheeee... */ |
1530 | |
1531 | if (global_page_state(NR_UNSTABLE_NFS) + |
1532 | global_page_state(NR_WRITEBACK) <= dirty_thresh) |
1533 | break; |
1534 | congestion_wait(BLK_RW_ASYNC, HZ/10); |
1535 | |
1536 | /* |
1537 | * The caller might hold locks which can prevent IO completion |
1538 | * or progress in the filesystem. So we cannot just sit here |
1539 | * waiting for IO to complete. |
1540 | */ |
1541 | if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) |
1542 | break; |
1543 | } |
1544 | } |
1545 | |
1546 | /* |
1547 | * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs |
1548 | */ |
1549 | int dirty_writeback_centisecs_handler(ctl_table *table, int write, |
1550 | void __user *buffer, size_t *length, loff_t *ppos) |
1551 | { |
1552 | proc_dointvec(table, write, buffer, length, ppos); |
1553 | return 0; |
1554 | } |
1555 | |
1556 | #ifdef CONFIG_BLOCK |
1557 | void laptop_mode_timer_fn(unsigned long data) |
1558 | { |
1559 | struct request_queue *q = (struct request_queue *)data; |
1560 | int nr_pages = global_page_state(NR_FILE_DIRTY) + |
1561 | global_page_state(NR_UNSTABLE_NFS); |
1562 | |
1563 | /* |
1564 | * We want to write everything out, not just down to the dirty |
1565 | * threshold |
1566 | */ |
1567 | if (bdi_has_dirty_io(&q->backing_dev_info)) |
1568 | bdi_start_writeback(&q->backing_dev_info, nr_pages, |
1569 | WB_REASON_LAPTOP_TIMER); |
1570 | } |
1571 | |
1572 | /* |
1573 | * We've spun up the disk and we're in laptop mode: schedule writeback |
1574 | * of all dirty data a few seconds from now. If the flush is already scheduled |
1575 | * then push it back - the user is still using the disk. |
1576 | */ |
1577 | void laptop_io_completion(struct backing_dev_info *info) |
1578 | { |
1579 | mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); |
1580 | } |
1581 | |
1582 | /* |
1583 | * We're in laptop mode and we've just synced. The sync's writes will have |
1584 | * caused another writeback to be scheduled by laptop_io_completion. |
1585 | * Nothing needs to be written back anymore, so we unschedule the writeback. |
1586 | */ |
1587 | void laptop_sync_completion(void) |
1588 | { |
1589 | struct backing_dev_info *bdi; |
1590 | |
1591 | rcu_read_lock(); |
1592 | |
1593 | list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) |
1594 | del_timer(&bdi->laptop_mode_wb_timer); |
1595 | |
1596 | rcu_read_unlock(); |
1597 | } |
1598 | #endif |
1599 | |
1600 | /* |
1601 | * If ratelimit_pages is too high then we can get into dirty-data overload |
1602 | * if a large number of processes all perform writes at the same time. |
1603 | * If it is too low then SMP machines will call the (expensive) |
1604 | * get_writeback_state too often. |
1605 | * |
1606 | * Here we set ratelimit_pages to a level which ensures that when all CPUs are |
1607 | * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory |
1608 | * thresholds. |
1609 | */ |
1610 | |
1611 | void writeback_set_ratelimit(void) |
1612 | { |
1613 | unsigned long background_thresh; |
1614 | unsigned long dirty_thresh; |
1615 | global_dirty_limits(&background_thresh, &dirty_thresh); |
1616 | global_dirty_limit = dirty_thresh; |
1617 | ratelimit_pages = dirty_thresh / (num_online_cpus() * 32); |
1618 | if (ratelimit_pages < 16) |
1619 | ratelimit_pages = 16; |
1620 | } |
1621 | |
1622 | static int __cpuinit |
1623 | ratelimit_handler(struct notifier_block *self, unsigned long action, |
1624 | void *hcpu) |
1625 | { |
1626 | |
1627 | switch (action & ~CPU_TASKS_FROZEN) { |
1628 | case CPU_ONLINE: |
1629 | case CPU_DEAD: |
1630 | writeback_set_ratelimit(); |
1631 | return NOTIFY_OK; |
1632 | default: |
1633 | return NOTIFY_DONE; |
1634 | } |
1635 | } |
1636 | |
1637 | static struct notifier_block __cpuinitdata ratelimit_nb = { |
1638 | .notifier_call = ratelimit_handler, |
1639 | .next = NULL, |
1640 | }; |
1641 | |
1642 | /* |
1643 | * Called early on to tune the page writeback dirty limits. |
1644 | * |
1645 | * We used to scale dirty pages according to how total memory |
1646 | * related to pages that could be allocated for buffers (by |
1647 | * comparing nr_free_buffer_pages() to vm_total_pages. |
1648 | * |
1649 | * However, that was when we used "dirty_ratio" to scale with |
1650 | * all memory, and we don't do that any more. "dirty_ratio" |
1651 | * is now applied to total non-HIGHPAGE memory (by subtracting |
1652 | * totalhigh_pages from vm_total_pages), and as such we can't |
1653 | * get into the old insane situation any more where we had |
1654 | * large amounts of dirty pages compared to a small amount of |
1655 | * non-HIGHMEM memory. |
1656 | * |
1657 | * But we might still want to scale the dirty_ratio by how |
1658 | * much memory the box has.. |
1659 | */ |
1660 | void __init page_writeback_init(void) |
1661 | { |
1662 | writeback_set_ratelimit(); |
1663 | register_cpu_notifier(&ratelimit_nb); |
1664 | |
1665 | fprop_global_init(&writeout_completions); |
1666 | } |
1667 | |
1668 | /** |
1669 | * tag_pages_for_writeback - tag pages to be written by write_cache_pages |
1670 | * @mapping: address space structure to write |
1671 | * @start: starting page index |
1672 | * @end: ending page index (inclusive) |
1673 | * |
1674 | * This function scans the page range from @start to @end (inclusive) and tags |
1675 | * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is |
1676 | * that write_cache_pages (or whoever calls this function) will then use |
1677 | * TOWRITE tag to identify pages eligible for writeback. This mechanism is |
1678 | * used to avoid livelocking of writeback by a process steadily creating new |
1679 | * dirty pages in the file (thus it is important for this function to be quick |
1680 | * so that it can tag pages faster than a dirtying process can create them). |
1681 | */ |
1682 | /* |
1683 | * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency. |
1684 | */ |
1685 | void tag_pages_for_writeback(struct address_space *mapping, |
1686 | pgoff_t start, pgoff_t end) |
1687 | { |
1688 | #define WRITEBACK_TAG_BATCH 4096 |
1689 | unsigned long tagged; |
1690 | |
1691 | do { |
1692 | spin_lock_irq(&mapping->tree_lock); |
1693 | tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree, |
1694 | &start, end, WRITEBACK_TAG_BATCH, |
1695 | PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE); |
1696 | spin_unlock_irq(&mapping->tree_lock); |
1697 | WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH); |
1698 | cond_resched(); |
1699 | /* We check 'start' to handle wrapping when end == ~0UL */ |
1700 | } while (tagged >= WRITEBACK_TAG_BATCH && start); |
1701 | } |
1702 | EXPORT_SYMBOL(tag_pages_for_writeback); |
1703 | |
1704 | /** |
1705 | * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. |
1706 | * @mapping: address space structure to write |
1707 | * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
1708 | * @writepage: function called for each page |
1709 | * @data: data passed to writepage function |
1710 | * |
1711 | * If a page is already under I/O, write_cache_pages() skips it, even |
1712 | * if it's dirty. This is desirable behaviour for memory-cleaning writeback, |
1713 | * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() |
1714 | * and msync() need to guarantee that all the data which was dirty at the time |
1715 | * the call was made get new I/O started against them. If wbc->sync_mode is |
1716 | * WB_SYNC_ALL then we were called for data integrity and we must wait for |
1717 | * existing IO to complete. |
1718 | * |
1719 | * To avoid livelocks (when other process dirties new pages), we first tag |
1720 | * pages which should be written back with TOWRITE tag and only then start |
1721 | * writing them. For data-integrity sync we have to be careful so that we do |
1722 | * not miss some pages (e.g., because some other process has cleared TOWRITE |
1723 | * tag we set). The rule we follow is that TOWRITE tag can be cleared only |
1724 | * by the process clearing the DIRTY tag (and submitting the page for IO). |
1725 | */ |
1726 | int write_cache_pages(struct address_space *mapping, |
1727 | struct writeback_control *wbc, writepage_t writepage, |
1728 | void *data) |
1729 | { |
1730 | int ret = 0; |
1731 | int done = 0; |
1732 | struct pagevec pvec; |
1733 | int nr_pages; |
1734 | pgoff_t uninitialized_var(writeback_index); |
1735 | pgoff_t index; |
1736 | pgoff_t end; /* Inclusive */ |
1737 | pgoff_t done_index; |
1738 | int cycled; |
1739 | int range_whole = 0; |
1740 | int tag; |
1741 | |
1742 | pagevec_init(&pvec, 0); |
1743 | if (wbc->range_cyclic) { |
1744 | writeback_index = mapping->writeback_index; /* prev offset */ |
1745 | index = writeback_index; |
1746 | if (index == 0) |
1747 | cycled = 1; |
1748 | else |
1749 | cycled = 0; |
1750 | end = -1; |
1751 | } else { |
1752 | index = wbc->range_start >> PAGE_CACHE_SHIFT; |
1753 | end = wbc->range_end >> PAGE_CACHE_SHIFT; |
1754 | if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) |
1755 | range_whole = 1; |
1756 | cycled = 1; /* ignore range_cyclic tests */ |
1757 | } |
1758 | if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) |
1759 | tag = PAGECACHE_TAG_TOWRITE; |
1760 | else |
1761 | tag = PAGECACHE_TAG_DIRTY; |
1762 | retry: |
1763 | if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) |
1764 | tag_pages_for_writeback(mapping, index, end); |
1765 | done_index = index; |
1766 | while (!done && (index <= end)) { |
1767 | int i; |
1768 | |
1769 | nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag, |
1770 | min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); |
1771 | if (nr_pages == 0) |
1772 | break; |
1773 | |
1774 | for (i = 0; i < nr_pages; i++) { |
1775 | struct page *page = pvec.pages[i]; |
1776 | |
1777 | /* |
1778 | * At this point, the page may be truncated or |
1779 | * invalidated (changing page->mapping to NULL), or |
1780 | * even swizzled back from swapper_space to tmpfs file |
1781 | * mapping. However, page->index will not change |
1782 | * because we have a reference on the page. |
1783 | */ |
1784 | if (page->index > end) { |
1785 | /* |
1786 | * can't be range_cyclic (1st pass) because |
1787 | * end == -1 in that case. |
1788 | */ |
1789 | done = 1; |
1790 | break; |
1791 | } |
1792 | |
1793 | done_index = page->index; |
1794 | |
1795 | lock_page(page); |
1796 | |
1797 | /* |
1798 | * Page truncated or invalidated. We can freely skip it |
1799 | * then, even for data integrity operations: the page |
1800 | * has disappeared concurrently, so there could be no |
1801 | * real expectation of this data interity operation |
1802 | * even if there is now a new, dirty page at the same |
1803 | * pagecache address. |
1804 | */ |
1805 | if (unlikely(page->mapping != mapping)) { |
1806 | continue_unlock: |
1807 | unlock_page(page); |
1808 | continue; |
1809 | } |
1810 | |
1811 | if (!PageDirty(page)) { |
1812 | /* someone wrote it for us */ |
1813 | goto continue_unlock; |
1814 | } |
1815 | |
1816 | if (PageWriteback(page)) { |
1817 | if (wbc->sync_mode != WB_SYNC_NONE) |
1818 | wait_on_page_writeback(page); |
1819 | else |
1820 | goto continue_unlock; |
1821 | } |
1822 | |
1823 | BUG_ON(PageWriteback(page)); |
1824 | if (!clear_page_dirty_for_io(page)) |
1825 | goto continue_unlock; |
1826 | |
1827 | trace_wbc_writepage(wbc, mapping->backing_dev_info); |
1828 | ret = (*writepage)(page, wbc, data); |
1829 | if (unlikely(ret)) { |
1830 | if (ret == AOP_WRITEPAGE_ACTIVATE) { |
1831 | unlock_page(page); |
1832 | ret = 0; |
1833 | } else { |
1834 | /* |
1835 | * done_index is set past this page, |
1836 | * so media errors will not choke |
1837 | * background writeout for the entire |
1838 | * file. This has consequences for |
1839 | * range_cyclic semantics (ie. it may |
1840 | * not be suitable for data integrity |
1841 | * writeout). |
1842 | */ |
1843 | done_index = page->index + 1; |
1844 | done = 1; |
1845 | break; |
1846 | } |
1847 | } |
1848 | |
1849 | /* |
1850 | * We stop writing back only if we are not doing |
1851 | * integrity sync. In case of integrity sync we have to |
1852 | * keep going until we have written all the pages |
1853 | * we tagged for writeback prior to entering this loop. |
1854 | */ |
1855 | if (--wbc->nr_to_write <= 0 && |
1856 | wbc->sync_mode == WB_SYNC_NONE) { |
1857 | done = 1; |
1858 | break; |
1859 | } |
1860 | } |
1861 | pagevec_release(&pvec); |
1862 | cond_resched(); |
1863 | } |
1864 | if (!cycled && !done) { |
1865 | /* |
1866 | * range_cyclic: |
1867 | * We hit the last page and there is more work to be done: wrap |
1868 | * back to the start of the file |
1869 | */ |
1870 | cycled = 1; |
1871 | index = 0; |
1872 | end = writeback_index - 1; |
1873 | goto retry; |
1874 | } |
1875 | if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) |
1876 | mapping->writeback_index = done_index; |
1877 | |
1878 | return ret; |
1879 | } |
1880 | EXPORT_SYMBOL(write_cache_pages); |
1881 | |
1882 | /* |
1883 | * Function used by generic_writepages to call the real writepage |
1884 | * function and set the mapping flags on error |
1885 | */ |
1886 | static int __writepage(struct page *page, struct writeback_control *wbc, |
1887 | void *data) |
1888 | { |
1889 | struct address_space *mapping = data; |
1890 | int ret = mapping->a_ops->writepage(page, wbc); |
1891 | mapping_set_error(mapping, ret); |
1892 | return ret; |
1893 | } |
1894 | |
1895 | /** |
1896 | * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. |
1897 | * @mapping: address space structure to write |
1898 | * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
1899 | * |
1900 | * This is a library function, which implements the writepages() |
1901 | * address_space_operation. |
1902 | */ |
1903 | int generic_writepages(struct address_space *mapping, |
1904 | struct writeback_control *wbc) |
1905 | { |
1906 | struct blk_plug plug; |
1907 | int ret; |
1908 | |
1909 | /* deal with chardevs and other special file */ |
1910 | if (!mapping->a_ops->writepage) |
1911 | return 0; |
1912 | |
1913 | blk_start_plug(&plug); |
1914 | ret = write_cache_pages(mapping, wbc, __writepage, mapping); |
1915 | blk_finish_plug(&plug); |
1916 | return ret; |
1917 | } |
1918 | |
1919 | EXPORT_SYMBOL(generic_writepages); |
1920 | |
1921 | int do_writepages(struct address_space *mapping, struct writeback_control *wbc) |
1922 | { |
1923 | int ret; |
1924 | |
1925 | if (wbc->nr_to_write <= 0) |
1926 | return 0; |
1927 | if (mapping->a_ops->writepages) |
1928 | ret = mapping->a_ops->writepages(mapping, wbc); |
1929 | else |
1930 | ret = generic_writepages(mapping, wbc); |
1931 | return ret; |
1932 | } |
1933 | |
1934 | /** |
1935 | * write_one_page - write out a single page and optionally wait on I/O |
1936 | * @page: the page to write |
1937 | * @wait: if true, wait on writeout |
1938 | * |
1939 | * The page must be locked by the caller and will be unlocked upon return. |
1940 | * |
1941 | * write_one_page() returns a negative error code if I/O failed. |
1942 | */ |
1943 | int write_one_page(struct page *page, int wait) |
1944 | { |
1945 | struct address_space *mapping = page->mapping; |
1946 | int ret = 0; |
1947 | struct writeback_control wbc = { |
1948 | .sync_mode = WB_SYNC_ALL, |
1949 | .nr_to_write = 1, |
1950 | }; |
1951 | |
1952 | BUG_ON(!PageLocked(page)); |
1953 | |
1954 | if (wait) |
1955 | wait_on_page_writeback(page); |
1956 | |
1957 | if (clear_page_dirty_for_io(page)) { |
1958 | page_cache_get(page); |
1959 | ret = mapping->a_ops->writepage(page, &wbc); |
1960 | if (ret == 0 && wait) { |
1961 | wait_on_page_writeback(page); |
1962 | if (PageError(page)) |
1963 | ret = -EIO; |
1964 | } |
1965 | page_cache_release(page); |
1966 | } else { |
1967 | unlock_page(page); |
1968 | } |
1969 | return ret; |
1970 | } |
1971 | EXPORT_SYMBOL(write_one_page); |
1972 | |
1973 | /* |
1974 | * For address_spaces which do not use buffers nor write back. |
1975 | */ |
1976 | int __set_page_dirty_no_writeback(struct page *page) |
1977 | { |
1978 | if (!PageDirty(page)) |
1979 | return !TestSetPageDirty(page); |
1980 | return 0; |
1981 | } |
1982 | |
1983 | /* |
1984 | * Helper function for set_page_dirty family. |
1985 | * NOTE: This relies on being atomic wrt interrupts. |
1986 | */ |
1987 | void account_page_dirtied(struct page *page, struct address_space *mapping) |
1988 | { |
1989 | trace_writeback_dirty_page(page, mapping); |
1990 | |
1991 | if (mapping_cap_account_dirty(mapping)) { |
1992 | __inc_zone_page_state(page, NR_FILE_DIRTY); |
1993 | __inc_zone_page_state(page, NR_DIRTIED); |
1994 | __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); |
1995 | __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); |
1996 | task_io_account_write(PAGE_CACHE_SIZE); |
1997 | current->nr_dirtied++; |
1998 | this_cpu_inc(bdp_ratelimits); |
1999 | } |
2000 | } |
2001 | EXPORT_SYMBOL(account_page_dirtied); |
2002 | |
2003 | /* |
2004 | * Helper function for set_page_writeback family. |
2005 | * NOTE: Unlike account_page_dirtied this does not rely on being atomic |
2006 | * wrt interrupts. |
2007 | */ |
2008 | void account_page_writeback(struct page *page) |
2009 | { |
2010 | inc_zone_page_state(page, NR_WRITEBACK); |
2011 | } |
2012 | EXPORT_SYMBOL(account_page_writeback); |
2013 | |
2014 | /* |
2015 | * For address_spaces which do not use buffers. Just tag the page as dirty in |
2016 | * its radix tree. |
2017 | * |
2018 | * This is also used when a single buffer is being dirtied: we want to set the |
2019 | * page dirty in that case, but not all the buffers. This is a "bottom-up" |
2020 | * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. |
2021 | * |
2022 | * Most callers have locked the page, which pins the address_space in memory. |
2023 | * But zap_pte_range() does not lock the page, however in that case the |
2024 | * mapping is pinned by the vma's ->vm_file reference. |
2025 | * |
2026 | * We take care to handle the case where the page was truncated from the |
2027 | * mapping by re-checking page_mapping() inside tree_lock. |
2028 | */ |
2029 | int __set_page_dirty_nobuffers(struct page *page) |
2030 | { |
2031 | if (!TestSetPageDirty(page)) { |
2032 | struct address_space *mapping = page_mapping(page); |
2033 | struct address_space *mapping2; |
2034 | |
2035 | if (!mapping) |
2036 | return 1; |
2037 | |
2038 | spin_lock_irq(&mapping->tree_lock); |
2039 | mapping2 = page_mapping(page); |
2040 | if (mapping2) { /* Race with truncate? */ |
2041 | BUG_ON(mapping2 != mapping); |
2042 | WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); |
2043 | account_page_dirtied(page, mapping); |
2044 | radix_tree_tag_set(&mapping->page_tree, |
2045 | page_index(page), PAGECACHE_TAG_DIRTY); |
2046 | } |
2047 | spin_unlock_irq(&mapping->tree_lock); |
2048 | if (mapping->host) { |
2049 | /* !PageAnon && !swapper_space */ |
2050 | __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); |
2051 | } |
2052 | return 1; |
2053 | } |
2054 | return 0; |
2055 | } |
2056 | EXPORT_SYMBOL(__set_page_dirty_nobuffers); |
2057 | |
2058 | /* |
2059 | * Call this whenever redirtying a page, to de-account the dirty counters |
2060 | * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written |
2061 | * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to |
2062 | * systematic errors in balanced_dirty_ratelimit and the dirty pages position |
2063 | * control. |
2064 | */ |
2065 | void account_page_redirty(struct page *page) |
2066 | { |
2067 | struct address_space *mapping = page->mapping; |
2068 | if (mapping && mapping_cap_account_dirty(mapping)) { |
2069 | current->nr_dirtied--; |
2070 | dec_zone_page_state(page, NR_DIRTIED); |
2071 | dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); |
2072 | } |
2073 | } |
2074 | EXPORT_SYMBOL(account_page_redirty); |
2075 | |
2076 | /* |
2077 | * When a writepage implementation decides that it doesn't want to write this |
2078 | * page for some reason, it should redirty the locked page via |
2079 | * redirty_page_for_writepage() and it should then unlock the page and return 0 |
2080 | */ |
2081 | int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) |
2082 | { |
2083 | wbc->pages_skipped++; |
2084 | account_page_redirty(page); |
2085 | return __set_page_dirty_nobuffers(page); |
2086 | } |
2087 | EXPORT_SYMBOL(redirty_page_for_writepage); |
2088 | |
2089 | /* |
2090 | * Dirty a page. |
2091 | * |
2092 | * For pages with a mapping this should be done under the page lock |
2093 | * for the benefit of asynchronous memory errors who prefer a consistent |
2094 | * dirty state. This rule can be broken in some special cases, |
2095 | * but should be better not to. |
2096 | * |
2097 | * If the mapping doesn't provide a set_page_dirty a_op, then |
2098 | * just fall through and assume that it wants buffer_heads. |
2099 | */ |
2100 | int set_page_dirty(struct page *page) |
2101 | { |
2102 | struct address_space *mapping = page_mapping(page); |
2103 | |
2104 | if (likely(mapping)) { |
2105 | int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; |
2106 | /* |
2107 | * readahead/lru_deactivate_page could remain |
2108 | * PG_readahead/PG_reclaim due to race with end_page_writeback |
2109 | * About readahead, if the page is written, the flags would be |
2110 | * reset. So no problem. |
2111 | * About lru_deactivate_page, if the page is redirty, the flag |
2112 | * will be reset. So no problem. but if the page is used by readahead |
2113 | * it will confuse readahead and make it restart the size rampup |
2114 | * process. But it's a trivial problem. |
2115 | */ |
2116 | ClearPageReclaim(page); |
2117 | #ifdef CONFIG_BLOCK |
2118 | if (!spd) |
2119 | spd = __set_page_dirty_buffers; |
2120 | #endif |
2121 | return (*spd)(page); |
2122 | } |
2123 | if (!PageDirty(page)) { |
2124 | if (!TestSetPageDirty(page)) |
2125 | return 1; |
2126 | } |
2127 | return 0; |
2128 | } |
2129 | EXPORT_SYMBOL(set_page_dirty); |
2130 | |
2131 | /* |
2132 | * set_page_dirty() is racy if the caller has no reference against |
2133 | * page->mapping->host, and if the page is unlocked. This is because another |
2134 | * CPU could truncate the page off the mapping and then free the mapping. |
2135 | * |
2136 | * Usually, the page _is_ locked, or the caller is a user-space process which |
2137 | * holds a reference on the inode by having an open file. |
2138 | * |
2139 | * In other cases, the page should be locked before running set_page_dirty(). |
2140 | */ |
2141 | int set_page_dirty_lock(struct page *page) |
2142 | { |
2143 | int ret; |
2144 | |
2145 | lock_page(page); |
2146 | ret = set_page_dirty(page); |
2147 | unlock_page(page); |
2148 | return ret; |
2149 | } |
2150 | EXPORT_SYMBOL(set_page_dirty_lock); |
2151 | |
2152 | /* |
2153 | * Clear a page's dirty flag, while caring for dirty memory accounting. |
2154 | * Returns true if the page was previously dirty. |
2155 | * |
2156 | * This is for preparing to put the page under writeout. We leave the page |
2157 | * tagged as dirty in the radix tree so that a concurrent write-for-sync |
2158 | * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage |
2159 | * implementation will run either set_page_writeback() or set_page_dirty(), |
2160 | * at which stage we bring the page's dirty flag and radix-tree dirty tag |
2161 | * back into sync. |
2162 | * |
2163 | * This incoherency between the page's dirty flag and radix-tree tag is |
2164 | * unfortunate, but it only exists while the page is locked. |
2165 | */ |
2166 | int clear_page_dirty_for_io(struct page *page) |
2167 | { |
2168 | struct address_space *mapping = page_mapping(page); |
2169 | |
2170 | BUG_ON(!PageLocked(page)); |
2171 | |
2172 | if (mapping && mapping_cap_account_dirty(mapping)) { |
2173 | /* |
2174 | * Yes, Virginia, this is indeed insane. |
2175 | * |
2176 | * We use this sequence to make sure that |
2177 | * (a) we account for dirty stats properly |
2178 | * (b) we tell the low-level filesystem to |
2179 | * mark the whole page dirty if it was |
2180 | * dirty in a pagetable. Only to then |
2181 | * (c) clean the page again and return 1 to |
2182 | * cause the writeback. |
2183 | * |
2184 | * This way we avoid all nasty races with the |
2185 | * dirty bit in multiple places and clearing |
2186 | * them concurrently from different threads. |
2187 | * |
2188 | * Note! Normally the "set_page_dirty(page)" |
2189 | * has no effect on the actual dirty bit - since |
2190 | * that will already usually be set. But we |
2191 | * need the side effects, and it can help us |
2192 | * avoid races. |
2193 | * |
2194 | * We basically use the page "master dirty bit" |
2195 | * as a serialization point for all the different |
2196 | * threads doing their things. |
2197 | */ |
2198 | if (page_mkclean(page)) |
2199 | set_page_dirty(page); |
2200 | /* |
2201 | * We carefully synchronise fault handlers against |
2202 | * installing a dirty pte and marking the page dirty |
2203 | * at this point. We do this by having them hold the |
2204 | * page lock at some point after installing their |
2205 | * pte, but before marking the page dirty. |
2206 | * Pages are always locked coming in here, so we get |
2207 | * the desired exclusion. See mm/memory.c:do_wp_page() |
2208 | * for more comments. |
2209 | */ |
2210 | if (TestClearPageDirty(page)) { |
2211 | dec_zone_page_state(page, NR_FILE_DIRTY); |
2212 | dec_bdi_stat(mapping->backing_dev_info, |
2213 | BDI_RECLAIMABLE); |
2214 | return 1; |
2215 | } |
2216 | return 0; |
2217 | } |
2218 | return TestClearPageDirty(page); |
2219 | } |
2220 | EXPORT_SYMBOL(clear_page_dirty_for_io); |
2221 | |
2222 | int test_clear_page_writeback(struct page *page) |
2223 | { |
2224 | struct address_space *mapping = page_mapping(page); |
2225 | int ret; |
2226 | |
2227 | if (mapping) { |
2228 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
2229 | unsigned long flags; |
2230 | |
2231 | spin_lock_irqsave(&mapping->tree_lock, flags); |
2232 | ret = TestClearPageWriteback(page); |
2233 | if (ret) { |
2234 | radix_tree_tag_clear(&mapping->page_tree, |
2235 | page_index(page), |
2236 | PAGECACHE_TAG_WRITEBACK); |
2237 | if (bdi_cap_account_writeback(bdi)) { |
2238 | __dec_bdi_stat(bdi, BDI_WRITEBACK); |
2239 | __bdi_writeout_inc(bdi); |
2240 | } |
2241 | } |
2242 | spin_unlock_irqrestore(&mapping->tree_lock, flags); |
2243 | } else { |
2244 | ret = TestClearPageWriteback(page); |
2245 | } |
2246 | if (ret) { |
2247 | dec_zone_page_state(page, NR_WRITEBACK); |
2248 | inc_zone_page_state(page, NR_WRITTEN); |
2249 | } |
2250 | return ret; |
2251 | } |
2252 | |
2253 | int test_set_page_writeback(struct page *page) |
2254 | { |
2255 | struct address_space *mapping = page_mapping(page); |
2256 | int ret; |
2257 | |
2258 | if (mapping) { |
2259 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
2260 | unsigned long flags; |
2261 | |
2262 | spin_lock_irqsave(&mapping->tree_lock, flags); |
2263 | ret = TestSetPageWriteback(page); |
2264 | if (!ret) { |
2265 | radix_tree_tag_set(&mapping->page_tree, |
2266 | page_index(page), |
2267 | PAGECACHE_TAG_WRITEBACK); |
2268 | if (bdi_cap_account_writeback(bdi)) |
2269 | __inc_bdi_stat(bdi, BDI_WRITEBACK); |
2270 | } |
2271 | if (!PageDirty(page)) |
2272 | radix_tree_tag_clear(&mapping->page_tree, |
2273 | page_index(page), |
2274 | PAGECACHE_TAG_DIRTY); |
2275 | radix_tree_tag_clear(&mapping->page_tree, |
2276 | page_index(page), |
2277 | PAGECACHE_TAG_TOWRITE); |
2278 | spin_unlock_irqrestore(&mapping->tree_lock, flags); |
2279 | } else { |
2280 | ret = TestSetPageWriteback(page); |
2281 | } |
2282 | if (!ret) |
2283 | account_page_writeback(page); |
2284 | return ret; |
2285 | |
2286 | } |
2287 | EXPORT_SYMBOL(test_set_page_writeback); |
2288 | |
2289 | /* |
2290 | * Return true if any of the pages in the mapping are marked with the |
2291 | * passed tag. |
2292 | */ |
2293 | int mapping_tagged(struct address_space *mapping, int tag) |
2294 | { |
2295 | return radix_tree_tagged(&mapping->page_tree, tag); |
2296 | } |
2297 | EXPORT_SYMBOL(mapping_tagged); |
2298 | |
2299 | /** |
2300 | * wait_for_stable_page() - wait for writeback to finish, if necessary. |
2301 | * @page: The page to wait on. |
2302 | * |
2303 | * This function determines if the given page is related to a backing device |
2304 | * that requires page contents to be held stable during writeback. If so, then |
2305 | * it will wait for any pending writeback to complete. |
2306 | */ |
2307 | void wait_for_stable_page(struct page *page) |
2308 | { |
2309 | struct address_space *mapping = page_mapping(page); |
2310 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
2311 | |
2312 | if (!bdi_cap_stable_pages_required(bdi)) |
2313 | return; |
2314 | #ifdef CONFIG_NEED_BOUNCE_POOL |
2315 | if (mapping->host->i_sb->s_flags & MS_SNAP_STABLE) |
2316 | return; |
2317 | #endif /* CONFIG_NEED_BOUNCE_POOL */ |
2318 | |
2319 | wait_on_page_writeback(page); |
2320 | } |
2321 | EXPORT_SYMBOL_GPL(wait_for_stable_page); |
2322 |
Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master
Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9