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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 <trace/events/writeback.h> |
38 | |
39 | /* |
40 | * Sleep at most 200ms at a time in balance_dirty_pages(). |
41 | */ |
42 | #define MAX_PAUSE max(HZ/5, 1) |
43 | |
44 | /* |
45 | * Try to keep balance_dirty_pages() call intervals higher than this many pages |
46 | * by raising pause time to max_pause when falls below it. |
47 | */ |
48 | #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10)) |
49 | |
50 | /* |
51 | * Estimate write bandwidth at 200ms intervals. |
52 | */ |
53 | #define BANDWIDTH_INTERVAL max(HZ/5, 1) |
54 | |
55 | #define RATELIMIT_CALC_SHIFT 10 |
56 | |
57 | /* |
58 | * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited |
59 | * will look to see if it needs to force writeback or throttling. |
60 | */ |
61 | static long ratelimit_pages = 32; |
62 | |
63 | /* The following parameters are exported via /proc/sys/vm */ |
64 | |
65 | /* |
66 | * Start background writeback (via writeback threads) at this percentage |
67 | */ |
68 | int dirty_background_ratio = 10; |
69 | |
70 | /* |
71 | * dirty_background_bytes starts at 0 (disabled) so that it is a function of |
72 | * dirty_background_ratio * the amount of dirtyable memory |
73 | */ |
74 | unsigned long dirty_background_bytes; |
75 | |
76 | /* |
77 | * free highmem will not be subtracted from the total free memory |
78 | * for calculating free ratios if vm_highmem_is_dirtyable is true |
79 | */ |
80 | int vm_highmem_is_dirtyable; |
81 | |
82 | /* |
83 | * The generator of dirty data starts writeback at this percentage |
84 | */ |
85 | int vm_dirty_ratio = 20; |
86 | |
87 | /* |
88 | * vm_dirty_bytes starts at 0 (disabled) so that it is a function of |
89 | * vm_dirty_ratio * the amount of dirtyable memory |
90 | */ |
91 | unsigned long vm_dirty_bytes; |
92 | |
93 | /* |
94 | * The interval between `kupdate'-style writebacks |
95 | */ |
96 | unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ |
97 | |
98 | EXPORT_SYMBOL_GPL(dirty_writeback_interval); |
99 | |
100 | /* |
101 | * The longest time for which data is allowed to remain dirty |
102 | */ |
103 | unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ |
104 | |
105 | /* |
106 | * Flag that makes the machine dump writes/reads and block dirtyings. |
107 | */ |
108 | int block_dump; |
109 | |
110 | /* |
111 | * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: |
112 | * a full sync is triggered after this time elapses without any disk activity. |
113 | */ |
114 | int laptop_mode; |
115 | |
116 | EXPORT_SYMBOL(laptop_mode); |
117 | |
118 | /* End of sysctl-exported parameters */ |
119 | |
120 | unsigned long global_dirty_limit; |
121 | |
122 | /* |
123 | * Scale the writeback cache size proportional to the relative writeout speeds. |
124 | * |
125 | * We do this by keeping a floating proportion between BDIs, based on page |
126 | * writeback completions [end_page_writeback()]. Those devices that write out |
127 | * pages fastest will get the larger share, while the slower will get a smaller |
128 | * share. |
129 | * |
130 | * We use page writeout completions because we are interested in getting rid of |
131 | * dirty pages. Having them written out is the primary goal. |
132 | * |
133 | * We introduce a concept of time, a period over which we measure these events, |
134 | * because demand can/will vary over time. The length of this period itself is |
135 | * measured in page writeback completions. |
136 | * |
137 | */ |
138 | static struct prop_descriptor vm_completions; |
139 | |
140 | /* |
141 | * Work out the current dirty-memory clamping and background writeout |
142 | * thresholds. |
143 | * |
144 | * The main aim here is to lower them aggressively if there is a lot of mapped |
145 | * memory around. To avoid stressing page reclaim with lots of unreclaimable |
146 | * pages. It is better to clamp down on writers than to start swapping, and |
147 | * performing lots of scanning. |
148 | * |
149 | * We only allow 1/2 of the currently-unmapped memory to be dirtied. |
150 | * |
151 | * We don't permit the clamping level to fall below 5% - that is getting rather |
152 | * excessive. |
153 | * |
154 | * We make sure that the background writeout level is below the adjusted |
155 | * clamping level. |
156 | */ |
157 | |
158 | /* |
159 | * In a memory zone, there is a certain amount of pages we consider |
160 | * available for the page cache, which is essentially the number of |
161 | * free and reclaimable pages, minus some zone reserves to protect |
162 | * lowmem and the ability to uphold the zone's watermarks without |
163 | * requiring writeback. |
164 | * |
165 | * This number of dirtyable pages is the base value of which the |
166 | * user-configurable dirty ratio is the effictive number of pages that |
167 | * are allowed to be actually dirtied. Per individual zone, or |
168 | * globally by using the sum of dirtyable pages over all zones. |
169 | * |
170 | * Because the user is allowed to specify the dirty limit globally as |
171 | * absolute number of bytes, calculating the per-zone dirty limit can |
172 | * require translating the configured limit into a percentage of |
173 | * global dirtyable memory first. |
174 | */ |
175 | |
176 | static unsigned long highmem_dirtyable_memory(unsigned long total) |
177 | { |
178 | #ifdef CONFIG_HIGHMEM |
179 | int node; |
180 | unsigned long x = 0; |
181 | |
182 | for_each_node_state(node, N_HIGH_MEMORY) { |
183 | struct zone *z = |
184 | &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; |
185 | |
186 | x += zone_page_state(z, NR_FREE_PAGES) + |
187 | zone_reclaimable_pages(z) - z->dirty_balance_reserve; |
188 | } |
189 | /* |
190 | * Make sure that the number of highmem pages is never larger |
191 | * than the number of the total dirtyable memory. This can only |
192 | * occur in very strange VM situations but we want to make sure |
193 | * that this does not occur. |
194 | */ |
195 | return min(x, total); |
196 | #else |
197 | return 0; |
198 | #endif |
199 | } |
200 | |
201 | /** |
202 | * global_dirtyable_memory - number of globally dirtyable pages |
203 | * |
204 | * Returns the global number of pages potentially available for dirty |
205 | * page cache. This is the base value for the global dirty limits. |
206 | */ |
207 | unsigned long global_dirtyable_memory(void) |
208 | { |
209 | unsigned long x; |
210 | |
211 | x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() - |
212 | dirty_balance_reserve; |
213 | |
214 | if (!vm_highmem_is_dirtyable) |
215 | x -= highmem_dirtyable_memory(x); |
216 | |
217 | return x + 1; /* Ensure that we never return 0 */ |
218 | } |
219 | |
220 | /* |
221 | * global_dirty_limits - background-writeback and dirty-throttling thresholds |
222 | * |
223 | * Calculate the dirty thresholds based on sysctl parameters |
224 | * - vm.dirty_background_ratio or vm.dirty_background_bytes |
225 | * - vm.dirty_ratio or vm.dirty_bytes |
226 | * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and |
227 | * real-time tasks. |
228 | */ |
229 | void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) |
230 | { |
231 | unsigned long background; |
232 | unsigned long dirty; |
233 | unsigned long uninitialized_var(available_memory); |
234 | struct task_struct *tsk; |
235 | |
236 | if (!vm_dirty_bytes || !dirty_background_bytes) |
237 | available_memory = global_dirtyable_memory(); |
238 | |
239 | if (vm_dirty_bytes) |
240 | dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); |
241 | else |
242 | dirty = (vm_dirty_ratio * available_memory) / 100; |
243 | |
244 | if (dirty_background_bytes) |
245 | background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE); |
246 | else |
247 | background = (dirty_background_ratio * available_memory) / 100; |
248 | |
249 | if (background >= dirty) |
250 | background = dirty / 2; |
251 | tsk = current; |
252 | if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { |
253 | background += background / 4; |
254 | dirty += dirty / 4; |
255 | } |
256 | *pbackground = background; |
257 | *pdirty = dirty; |
258 | trace_global_dirty_state(background, dirty); |
259 | } |
260 | |
261 | /** |
262 | * zone_dirtyable_memory - number of dirtyable pages in a zone |
263 | * @zone: the zone |
264 | * |
265 | * Returns the zone's number of pages potentially available for dirty |
266 | * page cache. This is the base value for the per-zone dirty limits. |
267 | */ |
268 | static unsigned long zone_dirtyable_memory(struct zone *zone) |
269 | { |
270 | /* |
271 | * The effective global number of dirtyable pages may exclude |
272 | * highmem as a big-picture measure to keep the ratio between |
273 | * dirty memory and lowmem reasonable. |
274 | * |
275 | * But this function is purely about the individual zone and a |
276 | * highmem zone can hold its share of dirty pages, so we don't |
277 | * care about vm_highmem_is_dirtyable here. |
278 | */ |
279 | return zone_page_state(zone, NR_FREE_PAGES) + |
280 | zone_reclaimable_pages(zone) - |
281 | zone->dirty_balance_reserve; |
282 | } |
283 | |
284 | /** |
285 | * zone_dirty_limit - maximum number of dirty pages allowed in a zone |
286 | * @zone: the zone |
287 | * |
288 | * Returns the maximum number of dirty pages allowed in a zone, based |
289 | * on the zone's dirtyable memory. |
290 | */ |
291 | static unsigned long zone_dirty_limit(struct zone *zone) |
292 | { |
293 | unsigned long zone_memory = zone_dirtyable_memory(zone); |
294 | struct task_struct *tsk = current; |
295 | unsigned long dirty; |
296 | |
297 | if (vm_dirty_bytes) |
298 | dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) * |
299 | zone_memory / global_dirtyable_memory(); |
300 | else |
301 | dirty = vm_dirty_ratio * zone_memory / 100; |
302 | |
303 | if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) |
304 | dirty += dirty / 4; |
305 | |
306 | return dirty; |
307 | } |
308 | |
309 | /** |
310 | * zone_dirty_ok - tells whether a zone is within its dirty limits |
311 | * @zone: the zone to check |
312 | * |
313 | * Returns %true when the dirty pages in @zone are within the zone's |
314 | * dirty limit, %false if the limit is exceeded. |
315 | */ |
316 | bool zone_dirty_ok(struct zone *zone) |
317 | { |
318 | unsigned long limit = zone_dirty_limit(zone); |
319 | |
320 | return zone_page_state(zone, NR_FILE_DIRTY) + |
321 | zone_page_state(zone, NR_UNSTABLE_NFS) + |
322 | zone_page_state(zone, NR_WRITEBACK) <= limit; |
323 | } |
324 | |
325 | /* |
326 | * couple the period to the dirty_ratio: |
327 | * |
328 | * period/2 ~ roundup_pow_of_two(dirty limit) |
329 | */ |
330 | static int calc_period_shift(void) |
331 | { |
332 | unsigned long dirty_total; |
333 | |
334 | if (vm_dirty_bytes) |
335 | dirty_total = vm_dirty_bytes / PAGE_SIZE; |
336 | else |
337 | dirty_total = (vm_dirty_ratio * global_dirtyable_memory()) / |
338 | 100; |
339 | return 2 + ilog2(dirty_total - 1); |
340 | } |
341 | |
342 | /* |
343 | * update the period when the dirty threshold changes. |
344 | */ |
345 | static void update_completion_period(void) |
346 | { |
347 | int shift = calc_period_shift(); |
348 | prop_change_shift(&vm_completions, shift); |
349 | |
350 | writeback_set_ratelimit(); |
351 | } |
352 | |
353 | int dirty_background_ratio_handler(struct ctl_table *table, int write, |
354 | void __user *buffer, size_t *lenp, |
355 | loff_t *ppos) |
356 | { |
357 | int ret; |
358 | |
359 | ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
360 | if (ret == 0 && write) |
361 | dirty_background_bytes = 0; |
362 | return ret; |
363 | } |
364 | |
365 | int dirty_background_bytes_handler(struct ctl_table *table, int write, |
366 | void __user *buffer, size_t *lenp, |
367 | loff_t *ppos) |
368 | { |
369 | int ret; |
370 | |
371 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
372 | if (ret == 0 && write) |
373 | dirty_background_ratio = 0; |
374 | return ret; |
375 | } |
376 | |
377 | int dirty_ratio_handler(struct ctl_table *table, int write, |
378 | void __user *buffer, size_t *lenp, |
379 | loff_t *ppos) |
380 | { |
381 | int old_ratio = vm_dirty_ratio; |
382 | int ret; |
383 | |
384 | ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
385 | if (ret == 0 && write && vm_dirty_ratio != old_ratio) { |
386 | update_completion_period(); |
387 | vm_dirty_bytes = 0; |
388 | } |
389 | return ret; |
390 | } |
391 | |
392 | int dirty_bytes_handler(struct ctl_table *table, int write, |
393 | void __user *buffer, size_t *lenp, |
394 | loff_t *ppos) |
395 | { |
396 | unsigned long old_bytes = vm_dirty_bytes; |
397 | int ret; |
398 | |
399 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
400 | if (ret == 0 && write && vm_dirty_bytes != old_bytes) { |
401 | update_completion_period(); |
402 | vm_dirty_ratio = 0; |
403 | } |
404 | return ret; |
405 | } |
406 | |
407 | /* |
408 | * Increment the BDI's writeout completion count and the global writeout |
409 | * completion count. Called from test_clear_page_writeback(). |
410 | */ |
411 | static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) |
412 | { |
413 | __inc_bdi_stat(bdi, BDI_WRITTEN); |
414 | __prop_inc_percpu_max(&vm_completions, &bdi->completions, |
415 | bdi->max_prop_frac); |
416 | } |
417 | |
418 | void bdi_writeout_inc(struct backing_dev_info *bdi) |
419 | { |
420 | unsigned long flags; |
421 | |
422 | local_irq_save(flags); |
423 | __bdi_writeout_inc(bdi); |
424 | local_irq_restore(flags); |
425 | } |
426 | EXPORT_SYMBOL_GPL(bdi_writeout_inc); |
427 | |
428 | /* |
429 | * Obtain an accurate fraction of the BDI's portion. |
430 | */ |
431 | static void bdi_writeout_fraction(struct backing_dev_info *bdi, |
432 | long *numerator, long *denominator) |
433 | { |
434 | prop_fraction_percpu(&vm_completions, &bdi->completions, |
435 | numerator, denominator); |
436 | } |
437 | |
438 | /* |
439 | * bdi_min_ratio keeps the sum of the minimum dirty shares of all |
440 | * registered backing devices, which, for obvious reasons, can not |
441 | * exceed 100%. |
442 | */ |
443 | static unsigned int bdi_min_ratio; |
444 | |
445 | int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) |
446 | { |
447 | int ret = 0; |
448 | |
449 | spin_lock_bh(&bdi_lock); |
450 | if (min_ratio > bdi->max_ratio) { |
451 | ret = -EINVAL; |
452 | } else { |
453 | min_ratio -= bdi->min_ratio; |
454 | if (bdi_min_ratio + min_ratio < 100) { |
455 | bdi_min_ratio += min_ratio; |
456 | bdi->min_ratio += min_ratio; |
457 | } else { |
458 | ret = -EINVAL; |
459 | } |
460 | } |
461 | spin_unlock_bh(&bdi_lock); |
462 | |
463 | return ret; |
464 | } |
465 | |
466 | int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) |
467 | { |
468 | int ret = 0; |
469 | |
470 | if (max_ratio > 100) |
471 | return -EINVAL; |
472 | |
473 | spin_lock_bh(&bdi_lock); |
474 | if (bdi->min_ratio > max_ratio) { |
475 | ret = -EINVAL; |
476 | } else { |
477 | bdi->max_ratio = max_ratio; |
478 | bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100; |
479 | } |
480 | spin_unlock_bh(&bdi_lock); |
481 | |
482 | return ret; |
483 | } |
484 | EXPORT_SYMBOL(bdi_set_max_ratio); |
485 | |
486 | static unsigned long dirty_freerun_ceiling(unsigned long thresh, |
487 | unsigned long bg_thresh) |
488 | { |
489 | return (thresh + bg_thresh) / 2; |
490 | } |
491 | |
492 | static unsigned long hard_dirty_limit(unsigned long thresh) |
493 | { |
494 | return max(thresh, global_dirty_limit); |
495 | } |
496 | |
497 | /** |
498 | * bdi_dirty_limit - @bdi's share of dirty throttling threshold |
499 | * @bdi: the backing_dev_info to query |
500 | * @dirty: global dirty limit in pages |
501 | * |
502 | * Returns @bdi's dirty limit in pages. The term "dirty" in the context of |
503 | * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages. |
504 | * |
505 | * Note that balance_dirty_pages() will only seriously take it as a hard limit |
506 | * when sleeping max_pause per page is not enough to keep the dirty pages under |
507 | * control. For example, when the device is completely stalled due to some error |
508 | * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key. |
509 | * In the other normal situations, it acts more gently by throttling the tasks |
510 | * more (rather than completely block them) when the bdi dirty pages go high. |
511 | * |
512 | * It allocates high/low dirty limits to fast/slow devices, in order to prevent |
513 | * - starving fast devices |
514 | * - piling up dirty pages (that will take long time to sync) on slow devices |
515 | * |
516 | * The bdi's share of dirty limit will be adapting to its throughput and |
517 | * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. |
518 | */ |
519 | unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) |
520 | { |
521 | u64 bdi_dirty; |
522 | long numerator, denominator; |
523 | |
524 | /* |
525 | * Calculate this BDI's share of the dirty ratio. |
526 | */ |
527 | bdi_writeout_fraction(bdi, &numerator, &denominator); |
528 | |
529 | bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; |
530 | bdi_dirty *= numerator; |
531 | do_div(bdi_dirty, denominator); |
532 | |
533 | bdi_dirty += (dirty * bdi->min_ratio) / 100; |
534 | if (bdi_dirty > (dirty * bdi->max_ratio) / 100) |
535 | bdi_dirty = dirty * bdi->max_ratio / 100; |
536 | |
537 | return bdi_dirty; |
538 | } |
539 | |
540 | /* |
541 | * Dirty position control. |
542 | * |
543 | * (o) global/bdi setpoints |
544 | * |
545 | * We want the dirty pages be balanced around the global/bdi setpoints. |
546 | * When the number of dirty pages is higher/lower than the setpoint, the |
547 | * dirty position control ratio (and hence task dirty ratelimit) will be |
548 | * decreased/increased to bring the dirty pages back to the setpoint. |
549 | * |
550 | * pos_ratio = 1 << RATELIMIT_CALC_SHIFT |
551 | * |
552 | * if (dirty < setpoint) scale up pos_ratio |
553 | * if (dirty > setpoint) scale down pos_ratio |
554 | * |
555 | * if (bdi_dirty < bdi_setpoint) scale up pos_ratio |
556 | * if (bdi_dirty > bdi_setpoint) scale down pos_ratio |
557 | * |
558 | * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT |
559 | * |
560 | * (o) global control line |
561 | * |
562 | * ^ pos_ratio |
563 | * | |
564 | * | |<===== global dirty control scope ======>| |
565 | * 2.0 .............* |
566 | * | .* |
567 | * | . * |
568 | * | . * |
569 | * | . * |
570 | * | . * |
571 | * | . * |
572 | * 1.0 ................................* |
573 | * | . . * |
574 | * | . . * |
575 | * | . . * |
576 | * | . . * |
577 | * | . . * |
578 | * 0 +------------.------------------.----------------------*-------------> |
579 | * freerun^ setpoint^ limit^ dirty pages |
580 | * |
581 | * (o) bdi control line |
582 | * |
583 | * ^ pos_ratio |
584 | * | |
585 | * | * |
586 | * | * |
587 | * | * |
588 | * | * |
589 | * | * |<=========== span ============>| |
590 | * 1.0 .......................* |
591 | * | . * |
592 | * | . * |
593 | * | . * |
594 | * | . * |
595 | * | . * |
596 | * | . * |
597 | * | . * |
598 | * | . * |
599 | * | . * |
600 | * | . * |
601 | * | . * |
602 | * 1/4 ...............................................* * * * * * * * * * * * |
603 | * | . . |
604 | * | . . |
605 | * | . . |
606 | * 0 +----------------------.-------------------------------.-------------> |
607 | * bdi_setpoint^ x_intercept^ |
608 | * |
609 | * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can |
610 | * be smoothly throttled down to normal if it starts high in situations like |
611 | * - start writing to a slow SD card and a fast disk at the same time. The SD |
612 | * card's bdi_dirty may rush to many times higher than bdi_setpoint. |
613 | * - the bdi dirty thresh drops quickly due to change of JBOD workload |
614 | */ |
615 | static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, |
616 | unsigned long thresh, |
617 | unsigned long bg_thresh, |
618 | unsigned long dirty, |
619 | unsigned long bdi_thresh, |
620 | unsigned long bdi_dirty) |
621 | { |
622 | unsigned long write_bw = bdi->avg_write_bandwidth; |
623 | unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); |
624 | unsigned long limit = hard_dirty_limit(thresh); |
625 | unsigned long x_intercept; |
626 | unsigned long setpoint; /* dirty pages' target balance point */ |
627 | unsigned long bdi_setpoint; |
628 | unsigned long span; |
629 | long long pos_ratio; /* for scaling up/down the rate limit */ |
630 | long x; |
631 | |
632 | if (unlikely(dirty >= limit)) |
633 | return 0; |
634 | |
635 | /* |
636 | * global setpoint |
637 | * |
638 | * setpoint - dirty 3 |
639 | * f(dirty) := 1.0 + (----------------) |
640 | * limit - setpoint |
641 | * |
642 | * it's a 3rd order polynomial that subjects to |
643 | * |
644 | * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast |
645 | * (2) f(setpoint) = 1.0 => the balance point |
646 | * (3) f(limit) = 0 => the hard limit |
647 | * (4) df/dx <= 0 => negative feedback control |
648 | * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) |
649 | * => fast response on large errors; small oscillation near setpoint |
650 | */ |
651 | setpoint = (freerun + limit) / 2; |
652 | x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT, |
653 | limit - setpoint + 1); |
654 | pos_ratio = x; |
655 | pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
656 | pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
657 | pos_ratio += 1 << RATELIMIT_CALC_SHIFT; |
658 | |
659 | /* |
660 | * We have computed basic pos_ratio above based on global situation. If |
661 | * the bdi is over/under its share of dirty pages, we want to scale |
662 | * pos_ratio further down/up. That is done by the following mechanism. |
663 | */ |
664 | |
665 | /* |
666 | * bdi setpoint |
667 | * |
668 | * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint) |
669 | * |
670 | * x_intercept - bdi_dirty |
671 | * := -------------------------- |
672 | * x_intercept - bdi_setpoint |
673 | * |
674 | * The main bdi control line is a linear function that subjects to |
675 | * |
676 | * (1) f(bdi_setpoint) = 1.0 |
677 | * (2) k = - 1 / (8 * write_bw) (in single bdi case) |
678 | * or equally: x_intercept = bdi_setpoint + 8 * write_bw |
679 | * |
680 | * For single bdi case, the dirty pages are observed to fluctuate |
681 | * regularly within range |
682 | * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2] |
683 | * for various filesystems, where (2) can yield in a reasonable 12.5% |
684 | * fluctuation range for pos_ratio. |
685 | * |
686 | * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its |
687 | * own size, so move the slope over accordingly and choose a slope that |
688 | * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh. |
689 | */ |
690 | if (unlikely(bdi_thresh > thresh)) |
691 | bdi_thresh = thresh; |
692 | /* |
693 | * It's very possible that bdi_thresh is close to 0 not because the |
694 | * device is slow, but that it has remained inactive for long time. |
695 | * Honour such devices a reasonable good (hopefully IO efficient) |
696 | * threshold, so that the occasional writes won't be blocked and active |
697 | * writes can rampup the threshold quickly. |
698 | */ |
699 | bdi_thresh = max(bdi_thresh, (limit - dirty) / 8); |
700 | /* |
701 | * scale global setpoint to bdi's: |
702 | * bdi_setpoint = setpoint * bdi_thresh / thresh |
703 | */ |
704 | x = div_u64((u64)bdi_thresh << 16, thresh + 1); |
705 | bdi_setpoint = setpoint * (u64)x >> 16; |
706 | /* |
707 | * Use span=(8*write_bw) in single bdi case as indicated by |
708 | * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case. |
709 | * |
710 | * bdi_thresh thresh - bdi_thresh |
711 | * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh |
712 | * thresh thresh |
713 | */ |
714 | span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16; |
715 | x_intercept = bdi_setpoint + span; |
716 | |
717 | if (bdi_dirty < x_intercept - span / 4) { |
718 | pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty), |
719 | x_intercept - bdi_setpoint + 1); |
720 | } else |
721 | pos_ratio /= 4; |
722 | |
723 | /* |
724 | * bdi reserve area, safeguard against dirty pool underrun and disk idle |
725 | * It may push the desired control point of global dirty pages higher |
726 | * than setpoint. |
727 | */ |
728 | x_intercept = bdi_thresh / 2; |
729 | if (bdi_dirty < x_intercept) { |
730 | if (bdi_dirty > x_intercept / 8) |
731 | pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty); |
732 | else |
733 | pos_ratio *= 8; |
734 | } |
735 | |
736 | return pos_ratio; |
737 | } |
738 | |
739 | static void bdi_update_write_bandwidth(struct backing_dev_info *bdi, |
740 | unsigned long elapsed, |
741 | unsigned long written) |
742 | { |
743 | const unsigned long period = roundup_pow_of_two(3 * HZ); |
744 | unsigned long avg = bdi->avg_write_bandwidth; |
745 | unsigned long old = bdi->write_bandwidth; |
746 | u64 bw; |
747 | |
748 | /* |
749 | * bw = written * HZ / elapsed |
750 | * |
751 | * bw * elapsed + write_bandwidth * (period - elapsed) |
752 | * write_bandwidth = --------------------------------------------------- |
753 | * period |
754 | */ |
755 | bw = written - bdi->written_stamp; |
756 | bw *= HZ; |
757 | if (unlikely(elapsed > period)) { |
758 | do_div(bw, elapsed); |
759 | avg = bw; |
760 | goto out; |
761 | } |
762 | bw += (u64)bdi->write_bandwidth * (period - elapsed); |
763 | bw >>= ilog2(period); |
764 | |
765 | /* |
766 | * one more level of smoothing, for filtering out sudden spikes |
767 | */ |
768 | if (avg > old && old >= (unsigned long)bw) |
769 | avg -= (avg - old) >> 3; |
770 | |
771 | if (avg < old && old <= (unsigned long)bw) |
772 | avg += (old - avg) >> 3; |
773 | |
774 | out: |
775 | bdi->write_bandwidth = bw; |
776 | bdi->avg_write_bandwidth = avg; |
777 | } |
778 | |
779 | /* |
780 | * The global dirtyable memory and dirty threshold could be suddenly knocked |
781 | * down by a large amount (eg. on the startup of KVM in a swapless system). |
782 | * This may throw the system into deep dirty exceeded state and throttle |
783 | * heavy/light dirtiers alike. To retain good responsiveness, maintain |
784 | * global_dirty_limit for tracking slowly down to the knocked down dirty |
785 | * threshold. |
786 | */ |
787 | static void update_dirty_limit(unsigned long thresh, unsigned long dirty) |
788 | { |
789 | unsigned long limit = global_dirty_limit; |
790 | |
791 | /* |
792 | * Follow up in one step. |
793 | */ |
794 | if (limit < thresh) { |
795 | limit = thresh; |
796 | goto update; |
797 | } |
798 | |
799 | /* |
800 | * Follow down slowly. Use the higher one as the target, because thresh |
801 | * may drop below dirty. This is exactly the reason to introduce |
802 | * global_dirty_limit which is guaranteed to lie above the dirty pages. |
803 | */ |
804 | thresh = max(thresh, dirty); |
805 | if (limit > thresh) { |
806 | limit -= (limit - thresh) >> 5; |
807 | goto update; |
808 | } |
809 | return; |
810 | update: |
811 | global_dirty_limit = limit; |
812 | } |
813 | |
814 | static void global_update_bandwidth(unsigned long thresh, |
815 | unsigned long dirty, |
816 | unsigned long now) |
817 | { |
818 | static DEFINE_SPINLOCK(dirty_lock); |
819 | static unsigned long update_time; |
820 | |
821 | /* |
822 | * check locklessly first to optimize away locking for the most time |
823 | */ |
824 | if (time_before(now, update_time + BANDWIDTH_INTERVAL)) |
825 | return; |
826 | |
827 | spin_lock(&dirty_lock); |
828 | if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) { |
829 | update_dirty_limit(thresh, dirty); |
830 | update_time = now; |
831 | } |
832 | spin_unlock(&dirty_lock); |
833 | } |
834 | |
835 | /* |
836 | * Maintain bdi->dirty_ratelimit, the base dirty throttle rate. |
837 | * |
838 | * Normal bdi tasks will be curbed at or below it in long term. |
839 | * Obviously it should be around (write_bw / N) when there are N dd tasks. |
840 | */ |
841 | static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi, |
842 | unsigned long thresh, |
843 | unsigned long bg_thresh, |
844 | unsigned long dirty, |
845 | unsigned long bdi_thresh, |
846 | unsigned long bdi_dirty, |
847 | unsigned long dirtied, |
848 | unsigned long elapsed) |
849 | { |
850 | unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); |
851 | unsigned long limit = hard_dirty_limit(thresh); |
852 | unsigned long setpoint = (freerun + limit) / 2; |
853 | unsigned long write_bw = bdi->avg_write_bandwidth; |
854 | unsigned long dirty_ratelimit = bdi->dirty_ratelimit; |
855 | unsigned long dirty_rate; |
856 | unsigned long task_ratelimit; |
857 | unsigned long balanced_dirty_ratelimit; |
858 | unsigned long pos_ratio; |
859 | unsigned long step; |
860 | unsigned long x; |
861 | |
862 | /* |
863 | * The dirty rate will match the writeout rate in long term, except |
864 | * when dirty pages are truncated by userspace or re-dirtied by FS. |
865 | */ |
866 | dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed; |
867 | |
868 | pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty, |
869 | bdi_thresh, bdi_dirty); |
870 | /* |
871 | * task_ratelimit reflects each dd's dirty rate for the past 200ms. |
872 | */ |
873 | task_ratelimit = (u64)dirty_ratelimit * |
874 | pos_ratio >> RATELIMIT_CALC_SHIFT; |
875 | task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */ |
876 | |
877 | /* |
878 | * A linear estimation of the "balanced" throttle rate. The theory is, |
879 | * if there are N dd tasks, each throttled at task_ratelimit, the bdi's |
880 | * dirty_rate will be measured to be (N * task_ratelimit). So the below |
881 | * formula will yield the balanced rate limit (write_bw / N). |
882 | * |
883 | * Note that the expanded form is not a pure rate feedback: |
884 | * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1) |
885 | * but also takes pos_ratio into account: |
886 | * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2) |
887 | * |
888 | * (1) is not realistic because pos_ratio also takes part in balancing |
889 | * the dirty rate. Consider the state |
890 | * pos_ratio = 0.5 (3) |
891 | * rate = 2 * (write_bw / N) (4) |
892 | * If (1) is used, it will stuck in that state! Because each dd will |
893 | * be throttled at |
894 | * task_ratelimit = pos_ratio * rate = (write_bw / N) (5) |
895 | * yielding |
896 | * dirty_rate = N * task_ratelimit = write_bw (6) |
897 | * put (6) into (1) we get |
898 | * rate_(i+1) = rate_(i) (7) |
899 | * |
900 | * So we end up using (2) to always keep |
901 | * rate_(i+1) ~= (write_bw / N) (8) |
902 | * regardless of the value of pos_ratio. As long as (8) is satisfied, |
903 | * pos_ratio is able to drive itself to 1.0, which is not only where |
904 | * the dirty count meet the setpoint, but also where the slope of |
905 | * pos_ratio is most flat and hence task_ratelimit is least fluctuated. |
906 | */ |
907 | balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw, |
908 | dirty_rate | 1); |
909 | /* |
910 | * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw |
911 | */ |
912 | if (unlikely(balanced_dirty_ratelimit > write_bw)) |
913 | balanced_dirty_ratelimit = write_bw; |
914 | |
915 | /* |
916 | * We could safely do this and return immediately: |
917 | * |
918 | * bdi->dirty_ratelimit = balanced_dirty_ratelimit; |
919 | * |
920 | * However to get a more stable dirty_ratelimit, the below elaborated |
921 | * code makes use of task_ratelimit to filter out sigular points and |
922 | * limit the step size. |
923 | * |
924 | * The below code essentially only uses the relative value of |
925 | * |
926 | * task_ratelimit - dirty_ratelimit |
927 | * = (pos_ratio - 1) * dirty_ratelimit |
928 | * |
929 | * which reflects the direction and size of dirty position error. |
930 | */ |
931 | |
932 | /* |
933 | * dirty_ratelimit will follow balanced_dirty_ratelimit iff |
934 | * task_ratelimit is on the same side of dirty_ratelimit, too. |
935 | * For example, when |
936 | * - dirty_ratelimit > balanced_dirty_ratelimit |
937 | * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint) |
938 | * lowering dirty_ratelimit will help meet both the position and rate |
939 | * control targets. Otherwise, don't update dirty_ratelimit if it will |
940 | * only help meet the rate target. After all, what the users ultimately |
941 | * feel and care are stable dirty rate and small position error. |
942 | * |
943 | * |task_ratelimit - dirty_ratelimit| is used to limit the step size |
944 | * and filter out the sigular points of balanced_dirty_ratelimit. Which |
945 | * keeps jumping around randomly and can even leap far away at times |
946 | * due to the small 200ms estimation period of dirty_rate (we want to |
947 | * keep that period small to reduce time lags). |
948 | */ |
949 | step = 0; |
950 | if (dirty < setpoint) { |
951 | x = min(bdi->balanced_dirty_ratelimit, |
952 | min(balanced_dirty_ratelimit, task_ratelimit)); |
953 | if (dirty_ratelimit < x) |
954 | step = x - dirty_ratelimit; |
955 | } else { |
956 | x = max(bdi->balanced_dirty_ratelimit, |
957 | max(balanced_dirty_ratelimit, task_ratelimit)); |
958 | if (dirty_ratelimit > x) |
959 | step = dirty_ratelimit - x; |
960 | } |
961 | |
962 | /* |
963 | * Don't pursue 100% rate matching. It's impossible since the balanced |
964 | * rate itself is constantly fluctuating. So decrease the track speed |
965 | * when it gets close to the target. Helps eliminate pointless tremors. |
966 | */ |
967 | step >>= dirty_ratelimit / (2 * step + 1); |
968 | /* |
969 | * Limit the tracking speed to avoid overshooting. |
970 | */ |
971 | step = (step + 7) / 8; |
972 | |
973 | if (dirty_ratelimit < balanced_dirty_ratelimit) |
974 | dirty_ratelimit += step; |
975 | else |
976 | dirty_ratelimit -= step; |
977 | |
978 | bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL); |
979 | bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit; |
980 | |
981 | trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit); |
982 | } |
983 | |
984 | void __bdi_update_bandwidth(struct backing_dev_info *bdi, |
985 | unsigned long thresh, |
986 | unsigned long bg_thresh, |
987 | unsigned long dirty, |
988 | unsigned long bdi_thresh, |
989 | unsigned long bdi_dirty, |
990 | unsigned long start_time) |
991 | { |
992 | unsigned long now = jiffies; |
993 | unsigned long elapsed = now - bdi->bw_time_stamp; |
994 | unsigned long dirtied; |
995 | unsigned long written; |
996 | |
997 | /* |
998 | * rate-limit, only update once every 200ms. |
999 | */ |
1000 | if (elapsed < BANDWIDTH_INTERVAL) |
1001 | return; |
1002 | |
1003 | dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]); |
1004 | written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]); |
1005 | |
1006 | /* |
1007 | * Skip quiet periods when disk bandwidth is under-utilized. |
1008 | * (at least 1s idle time between two flusher runs) |
1009 | */ |
1010 | if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time)) |
1011 | goto snapshot; |
1012 | |
1013 | if (thresh) { |
1014 | global_update_bandwidth(thresh, dirty, now); |
1015 | bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty, |
1016 | bdi_thresh, bdi_dirty, |
1017 | dirtied, elapsed); |
1018 | } |
1019 | bdi_update_write_bandwidth(bdi, elapsed, written); |
1020 | |
1021 | snapshot: |
1022 | bdi->dirtied_stamp = dirtied; |
1023 | bdi->written_stamp = written; |
1024 | bdi->bw_time_stamp = now; |
1025 | } |
1026 | |
1027 | static void bdi_update_bandwidth(struct backing_dev_info *bdi, |
1028 | unsigned long thresh, |
1029 | unsigned long bg_thresh, |
1030 | unsigned long dirty, |
1031 | unsigned long bdi_thresh, |
1032 | unsigned long bdi_dirty, |
1033 | unsigned long start_time) |
1034 | { |
1035 | if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL)) |
1036 | return; |
1037 | spin_lock(&bdi->wb.list_lock); |
1038 | __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty, |
1039 | bdi_thresh, bdi_dirty, start_time); |
1040 | spin_unlock(&bdi->wb.list_lock); |
1041 | } |
1042 | |
1043 | /* |
1044 | * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr() |
1045 | * will look to see if it needs to start dirty throttling. |
1046 | * |
1047 | * If dirty_poll_interval is too low, big NUMA machines will call the expensive |
1048 | * global_page_state() too often. So scale it near-sqrt to the safety margin |
1049 | * (the number of pages we may dirty without exceeding the dirty limits). |
1050 | */ |
1051 | static unsigned long dirty_poll_interval(unsigned long dirty, |
1052 | unsigned long thresh) |
1053 | { |
1054 | if (thresh > dirty) |
1055 | return 1UL << (ilog2(thresh - dirty) >> 1); |
1056 | |
1057 | return 1; |
1058 | } |
1059 | |
1060 | static long bdi_max_pause(struct backing_dev_info *bdi, |
1061 | unsigned long bdi_dirty) |
1062 | { |
1063 | long bw = bdi->avg_write_bandwidth; |
1064 | long t; |
1065 | |
1066 | /* |
1067 | * Limit pause time for small memory systems. If sleeping for too long |
1068 | * time, a small pool of dirty/writeback pages may go empty and disk go |
1069 | * idle. |
1070 | * |
1071 | * 8 serves as the safety ratio. |
1072 | */ |
1073 | t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8)); |
1074 | t++; |
1075 | |
1076 | return min_t(long, t, MAX_PAUSE); |
1077 | } |
1078 | |
1079 | static long bdi_min_pause(struct backing_dev_info *bdi, |
1080 | long max_pause, |
1081 | unsigned long task_ratelimit, |
1082 | unsigned long dirty_ratelimit, |
1083 | int *nr_dirtied_pause) |
1084 | { |
1085 | long hi = ilog2(bdi->avg_write_bandwidth); |
1086 | long lo = ilog2(bdi->dirty_ratelimit); |
1087 | long t; /* target pause */ |
1088 | long pause; /* estimated next pause */ |
1089 | int pages; /* target nr_dirtied_pause */ |
1090 | |
1091 | /* target for 10ms pause on 1-dd case */ |
1092 | t = max(1, HZ / 100); |
1093 | |
1094 | /* |
1095 | * Scale up pause time for concurrent dirtiers in order to reduce CPU |
1096 | * overheads. |
1097 | * |
1098 | * (N * 10ms) on 2^N concurrent tasks. |
1099 | */ |
1100 | if (hi > lo) |
1101 | t += (hi - lo) * (10 * HZ) / 1024; |
1102 | |
1103 | /* |
1104 | * This is a bit convoluted. We try to base the next nr_dirtied_pause |
1105 | * on the much more stable dirty_ratelimit. However the next pause time |
1106 | * will be computed based on task_ratelimit and the two rate limits may |
1107 | * depart considerably at some time. Especially if task_ratelimit goes |
1108 | * below dirty_ratelimit/2 and the target pause is max_pause, the next |
1109 | * pause time will be max_pause*2 _trimmed down_ to max_pause. As a |
1110 | * result task_ratelimit won't be executed faithfully, which could |
1111 | * eventually bring down dirty_ratelimit. |
1112 | * |
1113 | * We apply two rules to fix it up: |
1114 | * 1) try to estimate the next pause time and if necessary, use a lower |
1115 | * nr_dirtied_pause so as not to exceed max_pause. When this happens, |
1116 | * nr_dirtied_pause will be "dancing" with task_ratelimit. |
1117 | * 2) limit the target pause time to max_pause/2, so that the normal |
1118 | * small fluctuations of task_ratelimit won't trigger rule (1) and |
1119 | * nr_dirtied_pause will remain as stable as dirty_ratelimit. |
1120 | */ |
1121 | t = min(t, 1 + max_pause / 2); |
1122 | pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); |
1123 | |
1124 | /* |
1125 | * Tiny nr_dirtied_pause is found to hurt I/O performance in the test |
1126 | * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}. |
1127 | * When the 16 consecutive reads are often interrupted by some dirty |
1128 | * throttling pause during the async writes, cfq will go into idles |
1129 | * (deadline is fine). So push nr_dirtied_pause as high as possible |
1130 | * until reaches DIRTY_POLL_THRESH=32 pages. |
1131 | */ |
1132 | if (pages < DIRTY_POLL_THRESH) { |
1133 | t = max_pause; |
1134 | pages = dirty_ratelimit * t / roundup_pow_of_two(HZ); |
1135 | if (pages > DIRTY_POLL_THRESH) { |
1136 | pages = DIRTY_POLL_THRESH; |
1137 | t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit; |
1138 | } |
1139 | } |
1140 | |
1141 | pause = HZ * pages / (task_ratelimit + 1); |
1142 | if (pause > max_pause) { |
1143 | t = max_pause; |
1144 | pages = task_ratelimit * t / roundup_pow_of_two(HZ); |
1145 | } |
1146 | |
1147 | *nr_dirtied_pause = pages; |
1148 | /* |
1149 | * The minimal pause time will normally be half the target pause time. |
1150 | */ |
1151 | return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t; |
1152 | } |
1153 | |
1154 | /* |
1155 | * balance_dirty_pages() must be called by processes which are generating dirty |
1156 | * data. It looks at the number of dirty pages in the machine and will force |
1157 | * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2. |
1158 | * If we're over `background_thresh' then the writeback threads are woken to |
1159 | * perform some writeout. |
1160 | */ |
1161 | static void balance_dirty_pages(struct address_space *mapping, |
1162 | unsigned long pages_dirtied) |
1163 | { |
1164 | unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */ |
1165 | unsigned long bdi_reclaimable; |
1166 | unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */ |
1167 | unsigned long bdi_dirty; |
1168 | unsigned long freerun; |
1169 | unsigned long background_thresh; |
1170 | unsigned long dirty_thresh; |
1171 | unsigned long bdi_thresh; |
1172 | long period; |
1173 | long pause; |
1174 | long max_pause; |
1175 | long min_pause; |
1176 | int nr_dirtied_pause; |
1177 | bool dirty_exceeded = false; |
1178 | unsigned long task_ratelimit; |
1179 | unsigned long dirty_ratelimit; |
1180 | unsigned long pos_ratio; |
1181 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
1182 | unsigned long start_time = jiffies; |
1183 | |
1184 | for (;;) { |
1185 | unsigned long now = jiffies; |
1186 | |
1187 | /* |
1188 | * Unstable writes are a feature of certain networked |
1189 | * filesystems (i.e. NFS) in which data may have been |
1190 | * written to the server's write cache, but has not yet |
1191 | * been flushed to permanent storage. |
1192 | */ |
1193 | nr_reclaimable = global_page_state(NR_FILE_DIRTY) + |
1194 | global_page_state(NR_UNSTABLE_NFS); |
1195 | nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK); |
1196 | |
1197 | global_dirty_limits(&background_thresh, &dirty_thresh); |
1198 | |
1199 | /* |
1200 | * Throttle it only when the background writeback cannot |
1201 | * catch-up. This avoids (excessively) small writeouts |
1202 | * when the bdi limits are ramping up. |
1203 | */ |
1204 | freerun = dirty_freerun_ceiling(dirty_thresh, |
1205 | background_thresh); |
1206 | if (nr_dirty <= freerun) { |
1207 | current->dirty_paused_when = now; |
1208 | current->nr_dirtied = 0; |
1209 | current->nr_dirtied_pause = |
1210 | dirty_poll_interval(nr_dirty, dirty_thresh); |
1211 | break; |
1212 | } |
1213 | |
1214 | if (unlikely(!writeback_in_progress(bdi))) |
1215 | bdi_start_background_writeback(bdi); |
1216 | |
1217 | /* |
1218 | * bdi_thresh is not treated as some limiting factor as |
1219 | * dirty_thresh, due to reasons |
1220 | * - in JBOD setup, bdi_thresh can fluctuate a lot |
1221 | * - in a system with HDD and USB key, the USB key may somehow |
1222 | * go into state (bdi_dirty >> bdi_thresh) either because |
1223 | * bdi_dirty starts high, or because bdi_thresh drops low. |
1224 | * In this case we don't want to hard throttle the USB key |
1225 | * dirtiers for 100 seconds until bdi_dirty drops under |
1226 | * bdi_thresh. Instead the auxiliary bdi control line in |
1227 | * bdi_position_ratio() will let the dirtier task progress |
1228 | * at some rate <= (write_bw / 2) for bringing down bdi_dirty. |
1229 | */ |
1230 | bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); |
1231 | |
1232 | /* |
1233 | * In order to avoid the stacked BDI deadlock we need |
1234 | * to ensure we accurately count the 'dirty' pages when |
1235 | * the threshold is low. |
1236 | * |
1237 | * Otherwise it would be possible to get thresh+n pages |
1238 | * reported dirty, even though there are thresh-m pages |
1239 | * actually dirty; with m+n sitting in the percpu |
1240 | * deltas. |
1241 | */ |
1242 | if (bdi_thresh < 2 * bdi_stat_error(bdi)) { |
1243 | bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); |
1244 | bdi_dirty = bdi_reclaimable + |
1245 | bdi_stat_sum(bdi, BDI_WRITEBACK); |
1246 | } else { |
1247 | bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); |
1248 | bdi_dirty = bdi_reclaimable + |
1249 | bdi_stat(bdi, BDI_WRITEBACK); |
1250 | } |
1251 | |
1252 | dirty_exceeded = (bdi_dirty > bdi_thresh) && |
1253 | (nr_dirty > dirty_thresh); |
1254 | if (dirty_exceeded && !bdi->dirty_exceeded) |
1255 | bdi->dirty_exceeded = 1; |
1256 | |
1257 | bdi_update_bandwidth(bdi, dirty_thresh, background_thresh, |
1258 | nr_dirty, bdi_thresh, bdi_dirty, |
1259 | start_time); |
1260 | |
1261 | dirty_ratelimit = bdi->dirty_ratelimit; |
1262 | pos_ratio = bdi_position_ratio(bdi, dirty_thresh, |
1263 | background_thresh, nr_dirty, |
1264 | bdi_thresh, bdi_dirty); |
1265 | task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >> |
1266 | RATELIMIT_CALC_SHIFT; |
1267 | max_pause = bdi_max_pause(bdi, bdi_dirty); |
1268 | min_pause = bdi_min_pause(bdi, max_pause, |
1269 | task_ratelimit, dirty_ratelimit, |
1270 | &nr_dirtied_pause); |
1271 | |
1272 | if (unlikely(task_ratelimit == 0)) { |
1273 | period = max_pause; |
1274 | pause = max_pause; |
1275 | goto pause; |
1276 | } |
1277 | period = HZ * pages_dirtied / task_ratelimit; |
1278 | pause = period; |
1279 | if (current->dirty_paused_when) |
1280 | pause -= now - current->dirty_paused_when; |
1281 | /* |
1282 | * For less than 1s think time (ext3/4 may block the dirtier |
1283 | * for up to 800ms from time to time on 1-HDD; so does xfs, |
1284 | * however at much less frequency), try to compensate it in |
1285 | * future periods by updating the virtual time; otherwise just |
1286 | * do a reset, as it may be a light dirtier. |
1287 | */ |
1288 | if (pause < min_pause) { |
1289 | trace_balance_dirty_pages(bdi, |
1290 | dirty_thresh, |
1291 | background_thresh, |
1292 | nr_dirty, |
1293 | bdi_thresh, |
1294 | bdi_dirty, |
1295 | dirty_ratelimit, |
1296 | task_ratelimit, |
1297 | pages_dirtied, |
1298 | period, |
1299 | min(pause, 0L), |
1300 | start_time); |
1301 | if (pause < -HZ) { |
1302 | current->dirty_paused_when = now; |
1303 | current->nr_dirtied = 0; |
1304 | } else if (period) { |
1305 | current->dirty_paused_when += period; |
1306 | current->nr_dirtied = 0; |
1307 | } else if (current->nr_dirtied_pause <= pages_dirtied) |
1308 | current->nr_dirtied_pause += pages_dirtied; |
1309 | break; |
1310 | } |
1311 | if (unlikely(pause > max_pause)) { |
1312 | /* for occasional dropped task_ratelimit */ |
1313 | now += min(pause - max_pause, max_pause); |
1314 | pause = max_pause; |
1315 | } |
1316 | |
1317 | pause: |
1318 | trace_balance_dirty_pages(bdi, |
1319 | dirty_thresh, |
1320 | background_thresh, |
1321 | nr_dirty, |
1322 | bdi_thresh, |
1323 | bdi_dirty, |
1324 | dirty_ratelimit, |
1325 | task_ratelimit, |
1326 | pages_dirtied, |
1327 | period, |
1328 | pause, |
1329 | start_time); |
1330 | __set_current_state(TASK_KILLABLE); |
1331 | io_schedule_timeout(pause); |
1332 | |
1333 | current->dirty_paused_when = now + pause; |
1334 | current->nr_dirtied = 0; |
1335 | current->nr_dirtied_pause = nr_dirtied_pause; |
1336 | |
1337 | /* |
1338 | * This is typically equal to (nr_dirty < dirty_thresh) and can |
1339 | * also keep "1000+ dd on a slow USB stick" under control. |
1340 | */ |
1341 | if (task_ratelimit) |
1342 | break; |
1343 | |
1344 | /* |
1345 | * In the case of an unresponding NFS server and the NFS dirty |
1346 | * pages exceeds dirty_thresh, give the other good bdi's a pipe |
1347 | * to go through, so that tasks on them still remain responsive. |
1348 | * |
1349 | * In theory 1 page is enough to keep the comsumer-producer |
1350 | * pipe going: the flusher cleans 1 page => the task dirties 1 |
1351 | * more page. However bdi_dirty has accounting errors. So use |
1352 | * the larger and more IO friendly bdi_stat_error. |
1353 | */ |
1354 | if (bdi_dirty <= bdi_stat_error(bdi)) |
1355 | break; |
1356 | |
1357 | if (fatal_signal_pending(current)) |
1358 | break; |
1359 | } |
1360 | |
1361 | if (!dirty_exceeded && bdi->dirty_exceeded) |
1362 | bdi->dirty_exceeded = 0; |
1363 | |
1364 | if (writeback_in_progress(bdi)) |
1365 | return; |
1366 | |
1367 | /* |
1368 | * In laptop mode, we wait until hitting the higher threshold before |
1369 | * starting background writeout, and then write out all the way down |
1370 | * to the lower threshold. So slow writers cause minimal disk activity. |
1371 | * |
1372 | * In normal mode, we start background writeout at the lower |
1373 | * background_thresh, to keep the amount of dirty memory low. |
1374 | */ |
1375 | if (laptop_mode) |
1376 | return; |
1377 | |
1378 | if (nr_reclaimable > background_thresh) |
1379 | bdi_start_background_writeback(bdi); |
1380 | } |
1381 | |
1382 | void set_page_dirty_balance(struct page *page, int page_mkwrite) |
1383 | { |
1384 | if (set_page_dirty(page) || page_mkwrite) { |
1385 | struct address_space *mapping = page_mapping(page); |
1386 | |
1387 | if (mapping) |
1388 | balance_dirty_pages_ratelimited(mapping); |
1389 | } |
1390 | } |
1391 | |
1392 | static DEFINE_PER_CPU(int, bdp_ratelimits); |
1393 | |
1394 | /* |
1395 | * Normal tasks are throttled by |
1396 | * loop { |
1397 | * dirty tsk->nr_dirtied_pause pages; |
1398 | * take a snap in balance_dirty_pages(); |
1399 | * } |
1400 | * However there is a worst case. If every task exit immediately when dirtied |
1401 | * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be |
1402 | * called to throttle the page dirties. The solution is to save the not yet |
1403 | * throttled page dirties in dirty_throttle_leaks on task exit and charge them |
1404 | * randomly into the running tasks. This works well for the above worst case, |
1405 | * as the new task will pick up and accumulate the old task's leaked dirty |
1406 | * count and eventually get throttled. |
1407 | */ |
1408 | DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0; |
1409 | |
1410 | /** |
1411 | * balance_dirty_pages_ratelimited_nr - balance dirty memory state |
1412 | * @mapping: address_space which was dirtied |
1413 | * @nr_pages_dirtied: number of pages which the caller has just dirtied |
1414 | * |
1415 | * Processes which are dirtying memory should call in here once for each page |
1416 | * which was newly dirtied. The function will periodically check the system's |
1417 | * dirty state and will initiate writeback if needed. |
1418 | * |
1419 | * On really big machines, get_writeback_state is expensive, so try to avoid |
1420 | * calling it too often (ratelimiting). But once we're over the dirty memory |
1421 | * limit we decrease the ratelimiting by a lot, to prevent individual processes |
1422 | * from overshooting the limit by (ratelimit_pages) each. |
1423 | */ |
1424 | void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, |
1425 | unsigned long nr_pages_dirtied) |
1426 | { |
1427 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
1428 | int ratelimit; |
1429 | int *p; |
1430 | |
1431 | if (!bdi_cap_account_dirty(bdi)) |
1432 | return; |
1433 | |
1434 | ratelimit = current->nr_dirtied_pause; |
1435 | if (bdi->dirty_exceeded) |
1436 | ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10)); |
1437 | |
1438 | preempt_disable(); |
1439 | /* |
1440 | * This prevents one CPU to accumulate too many dirtied pages without |
1441 | * calling into balance_dirty_pages(), which can happen when there are |
1442 | * 1000+ tasks, all of them start dirtying pages at exactly the same |
1443 | * time, hence all honoured too large initial task->nr_dirtied_pause. |
1444 | */ |
1445 | p = &__get_cpu_var(bdp_ratelimits); |
1446 | if (unlikely(current->nr_dirtied >= ratelimit)) |
1447 | *p = 0; |
1448 | else if (unlikely(*p >= ratelimit_pages)) { |
1449 | *p = 0; |
1450 | ratelimit = 0; |
1451 | } |
1452 | /* |
1453 | * Pick up the dirtied pages by the exited tasks. This avoids lots of |
1454 | * short-lived tasks (eg. gcc invocations in a kernel build) escaping |
1455 | * the dirty throttling and livelock other long-run dirtiers. |
1456 | */ |
1457 | p = &__get_cpu_var(dirty_throttle_leaks); |
1458 | if (*p > 0 && current->nr_dirtied < ratelimit) { |
1459 | nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied); |
1460 | *p -= nr_pages_dirtied; |
1461 | current->nr_dirtied += nr_pages_dirtied; |
1462 | } |
1463 | preempt_enable(); |
1464 | |
1465 | if (unlikely(current->nr_dirtied >= ratelimit)) |
1466 | balance_dirty_pages(mapping, current->nr_dirtied); |
1467 | } |
1468 | EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); |
1469 | |
1470 | void throttle_vm_writeout(gfp_t gfp_mask) |
1471 | { |
1472 | unsigned long background_thresh; |
1473 | unsigned long dirty_thresh; |
1474 | |
1475 | for ( ; ; ) { |
1476 | global_dirty_limits(&background_thresh, &dirty_thresh); |
1477 | dirty_thresh = hard_dirty_limit(dirty_thresh); |
1478 | |
1479 | /* |
1480 | * Boost the allowable dirty threshold a bit for page |
1481 | * allocators so they don't get DoS'ed by heavy writers |
1482 | */ |
1483 | dirty_thresh += dirty_thresh / 10; /* wheeee... */ |
1484 | |
1485 | if (global_page_state(NR_UNSTABLE_NFS) + |
1486 | global_page_state(NR_WRITEBACK) <= dirty_thresh) |
1487 | break; |
1488 | congestion_wait(BLK_RW_ASYNC, HZ/10); |
1489 | |
1490 | /* |
1491 | * The caller might hold locks which can prevent IO completion |
1492 | * or progress in the filesystem. So we cannot just sit here |
1493 | * waiting for IO to complete. |
1494 | */ |
1495 | if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) |
1496 | break; |
1497 | } |
1498 | } |
1499 | |
1500 | /* |
1501 | * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs |
1502 | */ |
1503 | int dirty_writeback_centisecs_handler(ctl_table *table, int write, |
1504 | void __user *buffer, size_t *length, loff_t *ppos) |
1505 | { |
1506 | proc_dointvec(table, write, buffer, length, ppos); |
1507 | bdi_arm_supers_timer(); |
1508 | return 0; |
1509 | } |
1510 | |
1511 | #ifdef CONFIG_BLOCK |
1512 | void laptop_mode_timer_fn(unsigned long data) |
1513 | { |
1514 | struct request_queue *q = (struct request_queue *)data; |
1515 | int nr_pages = global_page_state(NR_FILE_DIRTY) + |
1516 | global_page_state(NR_UNSTABLE_NFS); |
1517 | |
1518 | /* |
1519 | * We want to write everything out, not just down to the dirty |
1520 | * threshold |
1521 | */ |
1522 | if (bdi_has_dirty_io(&q->backing_dev_info)) |
1523 | bdi_start_writeback(&q->backing_dev_info, nr_pages, |
1524 | WB_REASON_LAPTOP_TIMER); |
1525 | } |
1526 | |
1527 | /* |
1528 | * We've spun up the disk and we're in laptop mode: schedule writeback |
1529 | * of all dirty data a few seconds from now. If the flush is already scheduled |
1530 | * then push it back - the user is still using the disk. |
1531 | */ |
1532 | void laptop_io_completion(struct backing_dev_info *info) |
1533 | { |
1534 | mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); |
1535 | } |
1536 | |
1537 | /* |
1538 | * We're in laptop mode and we've just synced. The sync's writes will have |
1539 | * caused another writeback to be scheduled by laptop_io_completion. |
1540 | * Nothing needs to be written back anymore, so we unschedule the writeback. |
1541 | */ |
1542 | void laptop_sync_completion(void) |
1543 | { |
1544 | struct backing_dev_info *bdi; |
1545 | |
1546 | rcu_read_lock(); |
1547 | |
1548 | list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) |
1549 | del_timer(&bdi->laptop_mode_wb_timer); |
1550 | |
1551 | rcu_read_unlock(); |
1552 | } |
1553 | #endif |
1554 | |
1555 | /* |
1556 | * If ratelimit_pages is too high then we can get into dirty-data overload |
1557 | * if a large number of processes all perform writes at the same time. |
1558 | * If it is too low then SMP machines will call the (expensive) |
1559 | * get_writeback_state too often. |
1560 | * |
1561 | * Here we set ratelimit_pages to a level which ensures that when all CPUs are |
1562 | * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory |
1563 | * thresholds. |
1564 | */ |
1565 | |
1566 | void writeback_set_ratelimit(void) |
1567 | { |
1568 | unsigned long background_thresh; |
1569 | unsigned long dirty_thresh; |
1570 | global_dirty_limits(&background_thresh, &dirty_thresh); |
1571 | ratelimit_pages = dirty_thresh / (num_online_cpus() * 32); |
1572 | if (ratelimit_pages < 16) |
1573 | ratelimit_pages = 16; |
1574 | } |
1575 | |
1576 | static int __cpuinit |
1577 | ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) |
1578 | { |
1579 | writeback_set_ratelimit(); |
1580 | return NOTIFY_DONE; |
1581 | } |
1582 | |
1583 | static struct notifier_block __cpuinitdata ratelimit_nb = { |
1584 | .notifier_call = ratelimit_handler, |
1585 | .next = NULL, |
1586 | }; |
1587 | |
1588 | /* |
1589 | * Called early on to tune the page writeback dirty limits. |
1590 | * |
1591 | * We used to scale dirty pages according to how total memory |
1592 | * related to pages that could be allocated for buffers (by |
1593 | * comparing nr_free_buffer_pages() to vm_total_pages. |
1594 | * |
1595 | * However, that was when we used "dirty_ratio" to scale with |
1596 | * all memory, and we don't do that any more. "dirty_ratio" |
1597 | * is now applied to total non-HIGHPAGE memory (by subtracting |
1598 | * totalhigh_pages from vm_total_pages), and as such we can't |
1599 | * get into the old insane situation any more where we had |
1600 | * large amounts of dirty pages compared to a small amount of |
1601 | * non-HIGHMEM memory. |
1602 | * |
1603 | * But we might still want to scale the dirty_ratio by how |
1604 | * much memory the box has.. |
1605 | */ |
1606 | void __init page_writeback_init(void) |
1607 | { |
1608 | int shift; |
1609 | |
1610 | writeback_set_ratelimit(); |
1611 | register_cpu_notifier(&ratelimit_nb); |
1612 | |
1613 | shift = calc_period_shift(); |
1614 | prop_descriptor_init(&vm_completions, shift); |
1615 | } |
1616 | |
1617 | /** |
1618 | * tag_pages_for_writeback - tag pages to be written by write_cache_pages |
1619 | * @mapping: address space structure to write |
1620 | * @start: starting page index |
1621 | * @end: ending page index (inclusive) |
1622 | * |
1623 | * This function scans the page range from @start to @end (inclusive) and tags |
1624 | * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is |
1625 | * that write_cache_pages (or whoever calls this function) will then use |
1626 | * TOWRITE tag to identify pages eligible for writeback. This mechanism is |
1627 | * used to avoid livelocking of writeback by a process steadily creating new |
1628 | * dirty pages in the file (thus it is important for this function to be quick |
1629 | * so that it can tag pages faster than a dirtying process can create them). |
1630 | */ |
1631 | /* |
1632 | * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency. |
1633 | */ |
1634 | void tag_pages_for_writeback(struct address_space *mapping, |
1635 | pgoff_t start, pgoff_t end) |
1636 | { |
1637 | #define WRITEBACK_TAG_BATCH 4096 |
1638 | unsigned long tagged; |
1639 | |
1640 | do { |
1641 | spin_lock_irq(&mapping->tree_lock); |
1642 | tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree, |
1643 | &start, end, WRITEBACK_TAG_BATCH, |
1644 | PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE); |
1645 | spin_unlock_irq(&mapping->tree_lock); |
1646 | WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH); |
1647 | cond_resched(); |
1648 | /* We check 'start' to handle wrapping when end == ~0UL */ |
1649 | } while (tagged >= WRITEBACK_TAG_BATCH && start); |
1650 | } |
1651 | EXPORT_SYMBOL(tag_pages_for_writeback); |
1652 | |
1653 | /** |
1654 | * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. |
1655 | * @mapping: address space structure to write |
1656 | * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
1657 | * @writepage: function called for each page |
1658 | * @data: data passed to writepage function |
1659 | * |
1660 | * If a page is already under I/O, write_cache_pages() skips it, even |
1661 | * if it's dirty. This is desirable behaviour for memory-cleaning writeback, |
1662 | * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() |
1663 | * and msync() need to guarantee that all the data which was dirty at the time |
1664 | * the call was made get new I/O started against them. If wbc->sync_mode is |
1665 | * WB_SYNC_ALL then we were called for data integrity and we must wait for |
1666 | * existing IO to complete. |
1667 | * |
1668 | * To avoid livelocks (when other process dirties new pages), we first tag |
1669 | * pages which should be written back with TOWRITE tag and only then start |
1670 | * writing them. For data-integrity sync we have to be careful so that we do |
1671 | * not miss some pages (e.g., because some other process has cleared TOWRITE |
1672 | * tag we set). The rule we follow is that TOWRITE tag can be cleared only |
1673 | * by the process clearing the DIRTY tag (and submitting the page for IO). |
1674 | */ |
1675 | int write_cache_pages(struct address_space *mapping, |
1676 | struct writeback_control *wbc, writepage_t writepage, |
1677 | void *data) |
1678 | { |
1679 | int ret = 0; |
1680 | int done = 0; |
1681 | struct pagevec pvec; |
1682 | int nr_pages; |
1683 | pgoff_t uninitialized_var(writeback_index); |
1684 | pgoff_t index; |
1685 | pgoff_t end; /* Inclusive */ |
1686 | pgoff_t done_index; |
1687 | int cycled; |
1688 | int range_whole = 0; |
1689 | int tag; |
1690 | |
1691 | pagevec_init(&pvec, 0); |
1692 | if (wbc->range_cyclic) { |
1693 | writeback_index = mapping->writeback_index; /* prev offset */ |
1694 | index = writeback_index; |
1695 | if (index == 0) |
1696 | cycled = 1; |
1697 | else |
1698 | cycled = 0; |
1699 | end = -1; |
1700 | } else { |
1701 | index = wbc->range_start >> PAGE_CACHE_SHIFT; |
1702 | end = wbc->range_end >> PAGE_CACHE_SHIFT; |
1703 | if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) |
1704 | range_whole = 1; |
1705 | cycled = 1; /* ignore range_cyclic tests */ |
1706 | } |
1707 | if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) |
1708 | tag = PAGECACHE_TAG_TOWRITE; |
1709 | else |
1710 | tag = PAGECACHE_TAG_DIRTY; |
1711 | retry: |
1712 | if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) |
1713 | tag_pages_for_writeback(mapping, index, end); |
1714 | done_index = index; |
1715 | while (!done && (index <= end)) { |
1716 | int i; |
1717 | |
1718 | nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag, |
1719 | min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); |
1720 | if (nr_pages == 0) |
1721 | break; |
1722 | |
1723 | for (i = 0; i < nr_pages; i++) { |
1724 | struct page *page = pvec.pages[i]; |
1725 | |
1726 | /* |
1727 | * At this point, the page may be truncated or |
1728 | * invalidated (changing page->mapping to NULL), or |
1729 | * even swizzled back from swapper_space to tmpfs file |
1730 | * mapping. However, page->index will not change |
1731 | * because we have a reference on the page. |
1732 | */ |
1733 | if (page->index > end) { |
1734 | /* |
1735 | * can't be range_cyclic (1st pass) because |
1736 | * end == -1 in that case. |
1737 | */ |
1738 | done = 1; |
1739 | break; |
1740 | } |
1741 | |
1742 | done_index = page->index; |
1743 | |
1744 | lock_page(page); |
1745 | |
1746 | /* |
1747 | * Page truncated or invalidated. We can freely skip it |
1748 | * then, even for data integrity operations: the page |
1749 | * has disappeared concurrently, so there could be no |
1750 | * real expectation of this data interity operation |
1751 | * even if there is now a new, dirty page at the same |
1752 | * pagecache address. |
1753 | */ |
1754 | if (unlikely(page->mapping != mapping)) { |
1755 | continue_unlock: |
1756 | unlock_page(page); |
1757 | continue; |
1758 | } |
1759 | |
1760 | if (!PageDirty(page)) { |
1761 | /* someone wrote it for us */ |
1762 | goto continue_unlock; |
1763 | } |
1764 | |
1765 | if (PageWriteback(page)) { |
1766 | if (wbc->sync_mode != WB_SYNC_NONE) |
1767 | wait_on_page_writeback(page); |
1768 | else |
1769 | goto continue_unlock; |
1770 | } |
1771 | |
1772 | BUG_ON(PageWriteback(page)); |
1773 | if (!clear_page_dirty_for_io(page)) |
1774 | goto continue_unlock; |
1775 | |
1776 | trace_wbc_writepage(wbc, mapping->backing_dev_info); |
1777 | ret = (*writepage)(page, wbc, data); |
1778 | if (unlikely(ret)) { |
1779 | if (ret == AOP_WRITEPAGE_ACTIVATE) { |
1780 | unlock_page(page); |
1781 | ret = 0; |
1782 | } else { |
1783 | /* |
1784 | * done_index is set past this page, |
1785 | * so media errors will not choke |
1786 | * background writeout for the entire |
1787 | * file. This has consequences for |
1788 | * range_cyclic semantics (ie. it may |
1789 | * not be suitable for data integrity |
1790 | * writeout). |
1791 | */ |
1792 | done_index = page->index + 1; |
1793 | done = 1; |
1794 | break; |
1795 | } |
1796 | } |
1797 | |
1798 | /* |
1799 | * We stop writing back only if we are not doing |
1800 | * integrity sync. In case of integrity sync we have to |
1801 | * keep going until we have written all the pages |
1802 | * we tagged for writeback prior to entering this loop. |
1803 | */ |
1804 | if (--wbc->nr_to_write <= 0 && |
1805 | wbc->sync_mode == WB_SYNC_NONE) { |
1806 | done = 1; |
1807 | break; |
1808 | } |
1809 | } |
1810 | pagevec_release(&pvec); |
1811 | cond_resched(); |
1812 | } |
1813 | if (!cycled && !done) { |
1814 | /* |
1815 | * range_cyclic: |
1816 | * We hit the last page and there is more work to be done: wrap |
1817 | * back to the start of the file |
1818 | */ |
1819 | cycled = 1; |
1820 | index = 0; |
1821 | end = writeback_index - 1; |
1822 | goto retry; |
1823 | } |
1824 | if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) |
1825 | mapping->writeback_index = done_index; |
1826 | |
1827 | return ret; |
1828 | } |
1829 | EXPORT_SYMBOL(write_cache_pages); |
1830 | |
1831 | /* |
1832 | * Function used by generic_writepages to call the real writepage |
1833 | * function and set the mapping flags on error |
1834 | */ |
1835 | static int __writepage(struct page *page, struct writeback_control *wbc, |
1836 | void *data) |
1837 | { |
1838 | struct address_space *mapping = data; |
1839 | int ret = mapping->a_ops->writepage(page, wbc); |
1840 | mapping_set_error(mapping, ret); |
1841 | return ret; |
1842 | } |
1843 | |
1844 | /** |
1845 | * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. |
1846 | * @mapping: address space structure to write |
1847 | * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
1848 | * |
1849 | * This is a library function, which implements the writepages() |
1850 | * address_space_operation. |
1851 | */ |
1852 | int generic_writepages(struct address_space *mapping, |
1853 | struct writeback_control *wbc) |
1854 | { |
1855 | struct blk_plug plug; |
1856 | int ret; |
1857 | |
1858 | /* deal with chardevs and other special file */ |
1859 | if (!mapping->a_ops->writepage) |
1860 | return 0; |
1861 | |
1862 | blk_start_plug(&plug); |
1863 | ret = write_cache_pages(mapping, wbc, __writepage, mapping); |
1864 | blk_finish_plug(&plug); |
1865 | return ret; |
1866 | } |
1867 | |
1868 | EXPORT_SYMBOL(generic_writepages); |
1869 | |
1870 | int do_writepages(struct address_space *mapping, struct writeback_control *wbc) |
1871 | { |
1872 | int ret; |
1873 | |
1874 | if (wbc->nr_to_write <= 0) |
1875 | return 0; |
1876 | if (mapping->a_ops->writepages) |
1877 | ret = mapping->a_ops->writepages(mapping, wbc); |
1878 | else |
1879 | ret = generic_writepages(mapping, wbc); |
1880 | return ret; |
1881 | } |
1882 | |
1883 | /** |
1884 | * write_one_page - write out a single page and optionally wait on I/O |
1885 | * @page: the page to write |
1886 | * @wait: if true, wait on writeout |
1887 | * |
1888 | * The page must be locked by the caller and will be unlocked upon return. |
1889 | * |
1890 | * write_one_page() returns a negative error code if I/O failed. |
1891 | */ |
1892 | int write_one_page(struct page *page, int wait) |
1893 | { |
1894 | struct address_space *mapping = page->mapping; |
1895 | int ret = 0; |
1896 | struct writeback_control wbc = { |
1897 | .sync_mode = WB_SYNC_ALL, |
1898 | .nr_to_write = 1, |
1899 | }; |
1900 | |
1901 | BUG_ON(!PageLocked(page)); |
1902 | |
1903 | if (wait) |
1904 | wait_on_page_writeback(page); |
1905 | |
1906 | if (clear_page_dirty_for_io(page)) { |
1907 | page_cache_get(page); |
1908 | ret = mapping->a_ops->writepage(page, &wbc); |
1909 | if (ret == 0 && wait) { |
1910 | wait_on_page_writeback(page); |
1911 | if (PageError(page)) |
1912 | ret = -EIO; |
1913 | } |
1914 | page_cache_release(page); |
1915 | } else { |
1916 | unlock_page(page); |
1917 | } |
1918 | return ret; |
1919 | } |
1920 | EXPORT_SYMBOL(write_one_page); |
1921 | |
1922 | /* |
1923 | * For address_spaces which do not use buffers nor write back. |
1924 | */ |
1925 | int __set_page_dirty_no_writeback(struct page *page) |
1926 | { |
1927 | if (!PageDirty(page)) |
1928 | return !TestSetPageDirty(page); |
1929 | return 0; |
1930 | } |
1931 | |
1932 | /* |
1933 | * Helper function for set_page_dirty family. |
1934 | * NOTE: This relies on being atomic wrt interrupts. |
1935 | */ |
1936 | void account_page_dirtied(struct page *page, struct address_space *mapping) |
1937 | { |
1938 | if (mapping_cap_account_dirty(mapping)) { |
1939 | __inc_zone_page_state(page, NR_FILE_DIRTY); |
1940 | __inc_zone_page_state(page, NR_DIRTIED); |
1941 | __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); |
1942 | __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); |
1943 | task_io_account_write(PAGE_CACHE_SIZE); |
1944 | current->nr_dirtied++; |
1945 | this_cpu_inc(bdp_ratelimits); |
1946 | } |
1947 | } |
1948 | EXPORT_SYMBOL(account_page_dirtied); |
1949 | |
1950 | /* |
1951 | * Helper function for set_page_writeback family. |
1952 | * NOTE: Unlike account_page_dirtied this does not rely on being atomic |
1953 | * wrt interrupts. |
1954 | */ |
1955 | void account_page_writeback(struct page *page) |
1956 | { |
1957 | inc_zone_page_state(page, NR_WRITEBACK); |
1958 | } |
1959 | EXPORT_SYMBOL(account_page_writeback); |
1960 | |
1961 | /* |
1962 | * For address_spaces which do not use buffers. Just tag the page as dirty in |
1963 | * its radix tree. |
1964 | * |
1965 | * This is also used when a single buffer is being dirtied: we want to set the |
1966 | * page dirty in that case, but not all the buffers. This is a "bottom-up" |
1967 | * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. |
1968 | * |
1969 | * Most callers have locked the page, which pins the address_space in memory. |
1970 | * But zap_pte_range() does not lock the page, however in that case the |
1971 | * mapping is pinned by the vma's ->vm_file reference. |
1972 | * |
1973 | * We take care to handle the case where the page was truncated from the |
1974 | * mapping by re-checking page_mapping() inside tree_lock. |
1975 | */ |
1976 | int __set_page_dirty_nobuffers(struct page *page) |
1977 | { |
1978 | if (!TestSetPageDirty(page)) { |
1979 | struct address_space *mapping = page_mapping(page); |
1980 | struct address_space *mapping2; |
1981 | |
1982 | if (!mapping) |
1983 | return 1; |
1984 | |
1985 | spin_lock_irq(&mapping->tree_lock); |
1986 | mapping2 = page_mapping(page); |
1987 | if (mapping2) { /* Race with truncate? */ |
1988 | BUG_ON(mapping2 != mapping); |
1989 | WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); |
1990 | account_page_dirtied(page, mapping); |
1991 | radix_tree_tag_set(&mapping->page_tree, |
1992 | page_index(page), PAGECACHE_TAG_DIRTY); |
1993 | } |
1994 | spin_unlock_irq(&mapping->tree_lock); |
1995 | if (mapping->host) { |
1996 | /* !PageAnon && !swapper_space */ |
1997 | __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); |
1998 | } |
1999 | return 1; |
2000 | } |
2001 | return 0; |
2002 | } |
2003 | EXPORT_SYMBOL(__set_page_dirty_nobuffers); |
2004 | |
2005 | /* |
2006 | * Call this whenever redirtying a page, to de-account the dirty counters |
2007 | * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written |
2008 | * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to |
2009 | * systematic errors in balanced_dirty_ratelimit and the dirty pages position |
2010 | * control. |
2011 | */ |
2012 | void account_page_redirty(struct page *page) |
2013 | { |
2014 | struct address_space *mapping = page->mapping; |
2015 | if (mapping && mapping_cap_account_dirty(mapping)) { |
2016 | current->nr_dirtied--; |
2017 | dec_zone_page_state(page, NR_DIRTIED); |
2018 | dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); |
2019 | } |
2020 | } |
2021 | EXPORT_SYMBOL(account_page_redirty); |
2022 | |
2023 | /* |
2024 | * When a writepage implementation decides that it doesn't want to write this |
2025 | * page for some reason, it should redirty the locked page via |
2026 | * redirty_page_for_writepage() and it should then unlock the page and return 0 |
2027 | */ |
2028 | int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) |
2029 | { |
2030 | wbc->pages_skipped++; |
2031 | account_page_redirty(page); |
2032 | return __set_page_dirty_nobuffers(page); |
2033 | } |
2034 | EXPORT_SYMBOL(redirty_page_for_writepage); |
2035 | |
2036 | /* |
2037 | * Dirty a page. |
2038 | * |
2039 | * For pages with a mapping this should be done under the page lock |
2040 | * for the benefit of asynchronous memory errors who prefer a consistent |
2041 | * dirty state. This rule can be broken in some special cases, |
2042 | * but should be better not to. |
2043 | * |
2044 | * If the mapping doesn't provide a set_page_dirty a_op, then |
2045 | * just fall through and assume that it wants buffer_heads. |
2046 | */ |
2047 | int set_page_dirty(struct page *page) |
2048 | { |
2049 | struct address_space *mapping = page_mapping(page); |
2050 | |
2051 | if (likely(mapping)) { |
2052 | int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; |
2053 | /* |
2054 | * readahead/lru_deactivate_page could remain |
2055 | * PG_readahead/PG_reclaim due to race with end_page_writeback |
2056 | * About readahead, if the page is written, the flags would be |
2057 | * reset. So no problem. |
2058 | * About lru_deactivate_page, if the page is redirty, the flag |
2059 | * will be reset. So no problem. but if the page is used by readahead |
2060 | * it will confuse readahead and make it restart the size rampup |
2061 | * process. But it's a trivial problem. |
2062 | */ |
2063 | ClearPageReclaim(page); |
2064 | #ifdef CONFIG_BLOCK |
2065 | if (!spd) |
2066 | spd = __set_page_dirty_buffers; |
2067 | #endif |
2068 | return (*spd)(page); |
2069 | } |
2070 | if (!PageDirty(page)) { |
2071 | if (!TestSetPageDirty(page)) |
2072 | return 1; |
2073 | } |
2074 | return 0; |
2075 | } |
2076 | EXPORT_SYMBOL(set_page_dirty); |
2077 | |
2078 | /* |
2079 | * set_page_dirty() is racy if the caller has no reference against |
2080 | * page->mapping->host, and if the page is unlocked. This is because another |
2081 | * CPU could truncate the page off the mapping and then free the mapping. |
2082 | * |
2083 | * Usually, the page _is_ locked, or the caller is a user-space process which |
2084 | * holds a reference on the inode by having an open file. |
2085 | * |
2086 | * In other cases, the page should be locked before running set_page_dirty(). |
2087 | */ |
2088 | int set_page_dirty_lock(struct page *page) |
2089 | { |
2090 | int ret; |
2091 | |
2092 | lock_page(page); |
2093 | ret = set_page_dirty(page); |
2094 | unlock_page(page); |
2095 | return ret; |
2096 | } |
2097 | EXPORT_SYMBOL(set_page_dirty_lock); |
2098 | |
2099 | /* |
2100 | * Clear a page's dirty flag, while caring for dirty memory accounting. |
2101 | * Returns true if the page was previously dirty. |
2102 | * |
2103 | * This is for preparing to put the page under writeout. We leave the page |
2104 | * tagged as dirty in the radix tree so that a concurrent write-for-sync |
2105 | * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage |
2106 | * implementation will run either set_page_writeback() or set_page_dirty(), |
2107 | * at which stage we bring the page's dirty flag and radix-tree dirty tag |
2108 | * back into sync. |
2109 | * |
2110 | * This incoherency between the page's dirty flag and radix-tree tag is |
2111 | * unfortunate, but it only exists while the page is locked. |
2112 | */ |
2113 | int clear_page_dirty_for_io(struct page *page) |
2114 | { |
2115 | struct address_space *mapping = page_mapping(page); |
2116 | |
2117 | BUG_ON(!PageLocked(page)); |
2118 | |
2119 | if (mapping && mapping_cap_account_dirty(mapping)) { |
2120 | /* |
2121 | * Yes, Virginia, this is indeed insane. |
2122 | * |
2123 | * We use this sequence to make sure that |
2124 | * (a) we account for dirty stats properly |
2125 | * (b) we tell the low-level filesystem to |
2126 | * mark the whole page dirty if it was |
2127 | * dirty in a pagetable. Only to then |
2128 | * (c) clean the page again and return 1 to |
2129 | * cause the writeback. |
2130 | * |
2131 | * This way we avoid all nasty races with the |
2132 | * dirty bit in multiple places and clearing |
2133 | * them concurrently from different threads. |
2134 | * |
2135 | * Note! Normally the "set_page_dirty(page)" |
2136 | * has no effect on the actual dirty bit - since |
2137 | * that will already usually be set. But we |
2138 | * need the side effects, and it can help us |
2139 | * avoid races. |
2140 | * |
2141 | * We basically use the page "master dirty bit" |
2142 | * as a serialization point for all the different |
2143 | * threads doing their things. |
2144 | */ |
2145 | if (page_mkclean(page)) |
2146 | set_page_dirty(page); |
2147 | /* |
2148 | * We carefully synchronise fault handlers against |
2149 | * installing a dirty pte and marking the page dirty |
2150 | * at this point. We do this by having them hold the |
2151 | * page lock at some point after installing their |
2152 | * pte, but before marking the page dirty. |
2153 | * Pages are always locked coming in here, so we get |
2154 | * the desired exclusion. See mm/memory.c:do_wp_page() |
2155 | * for more comments. |
2156 | */ |
2157 | if (TestClearPageDirty(page)) { |
2158 | dec_zone_page_state(page, NR_FILE_DIRTY); |
2159 | dec_bdi_stat(mapping->backing_dev_info, |
2160 | BDI_RECLAIMABLE); |
2161 | return 1; |
2162 | } |
2163 | return 0; |
2164 | } |
2165 | return TestClearPageDirty(page); |
2166 | } |
2167 | EXPORT_SYMBOL(clear_page_dirty_for_io); |
2168 | |
2169 | int test_clear_page_writeback(struct page *page) |
2170 | { |
2171 | struct address_space *mapping = page_mapping(page); |
2172 | int ret; |
2173 | |
2174 | if (mapping) { |
2175 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
2176 | unsigned long flags; |
2177 | |
2178 | spin_lock_irqsave(&mapping->tree_lock, flags); |
2179 | ret = TestClearPageWriteback(page); |
2180 | if (ret) { |
2181 | radix_tree_tag_clear(&mapping->page_tree, |
2182 | page_index(page), |
2183 | PAGECACHE_TAG_WRITEBACK); |
2184 | if (bdi_cap_account_writeback(bdi)) { |
2185 | __dec_bdi_stat(bdi, BDI_WRITEBACK); |
2186 | __bdi_writeout_inc(bdi); |
2187 | } |
2188 | } |
2189 | spin_unlock_irqrestore(&mapping->tree_lock, flags); |
2190 | } else { |
2191 | ret = TestClearPageWriteback(page); |
2192 | } |
2193 | if (ret) { |
2194 | dec_zone_page_state(page, NR_WRITEBACK); |
2195 | inc_zone_page_state(page, NR_WRITTEN); |
2196 | } |
2197 | return ret; |
2198 | } |
2199 | |
2200 | int test_set_page_writeback(struct page *page) |
2201 | { |
2202 | struct address_space *mapping = page_mapping(page); |
2203 | int ret; |
2204 | |
2205 | if (mapping) { |
2206 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
2207 | unsigned long flags; |
2208 | |
2209 | spin_lock_irqsave(&mapping->tree_lock, flags); |
2210 | ret = TestSetPageWriteback(page); |
2211 | if (!ret) { |
2212 | radix_tree_tag_set(&mapping->page_tree, |
2213 | page_index(page), |
2214 | PAGECACHE_TAG_WRITEBACK); |
2215 | if (bdi_cap_account_writeback(bdi)) |
2216 | __inc_bdi_stat(bdi, BDI_WRITEBACK); |
2217 | } |
2218 | if (!PageDirty(page)) |
2219 | radix_tree_tag_clear(&mapping->page_tree, |
2220 | page_index(page), |
2221 | PAGECACHE_TAG_DIRTY); |
2222 | radix_tree_tag_clear(&mapping->page_tree, |
2223 | page_index(page), |
2224 | PAGECACHE_TAG_TOWRITE); |
2225 | spin_unlock_irqrestore(&mapping->tree_lock, flags); |
2226 | } else { |
2227 | ret = TestSetPageWriteback(page); |
2228 | } |
2229 | if (!ret) |
2230 | account_page_writeback(page); |
2231 | return ret; |
2232 | |
2233 | } |
2234 | EXPORT_SYMBOL(test_set_page_writeback); |
2235 | |
2236 | /* |
2237 | * Return true if any of the pages in the mapping are marked with the |
2238 | * passed tag. |
2239 | */ |
2240 | int mapping_tagged(struct address_space *mapping, int tag) |
2241 | { |
2242 | return radix_tree_tagged(&mapping->page_tree, tag); |
2243 | } |
2244 | EXPORT_SYMBOL(mapping_tagged); |
2245 |
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