Branch data Line data Source code
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 <linux/mm_inline.h>
40 : : #include <trace/events/writeback.h>
41 : :
42 : : #include "internal.h"
43 : :
44 : : /*
45 : : * Sleep at most 200ms at a time in balance_dirty_pages().
46 : : */
47 : : #define MAX_PAUSE max(HZ/5, 1)
48 : :
49 : : /*
50 : : * Try to keep balance_dirty_pages() call intervals higher than this many pages
51 : : * by raising pause time to max_pause when falls below it.
52 : : */
53 : : #define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
54 : :
55 : : /*
56 : : * Estimate write bandwidth at 200ms intervals.
57 : : */
58 : : #define BANDWIDTH_INTERVAL max(HZ/5, 1)
59 : :
60 : : #define RATELIMIT_CALC_SHIFT 10
61 : :
62 : : /*
63 : : * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
64 : : * will look to see if it needs to force writeback or throttling.
65 : : */
66 : : static long ratelimit_pages = 32;
67 : :
68 : : /* The following parameters are exported via /proc/sys/vm */
69 : :
70 : : /*
71 : : * Start background writeback (via writeback threads) at this percentage
72 : : */
73 : : int dirty_background_ratio = 10;
74 : :
75 : : /*
76 : : * dirty_background_bytes starts at 0 (disabled) so that it is a function of
77 : : * dirty_background_ratio * the amount of dirtyable memory
78 : : */
79 : : unsigned long dirty_background_bytes;
80 : :
81 : : /*
82 : : * free highmem will not be subtracted from the total free memory
83 : : * for calculating free ratios if vm_highmem_is_dirtyable is true
84 : : */
85 : : int vm_highmem_is_dirtyable;
86 : :
87 : : /*
88 : : * The generator of dirty data starts writeback at this percentage
89 : : */
90 : : int vm_dirty_ratio = 20;
91 : :
92 : : /*
93 : : * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94 : : * vm_dirty_ratio * the amount of dirtyable memory
95 : : */
96 : : unsigned long vm_dirty_bytes;
97 : :
98 : : /*
99 : : * The interval between `kupdate'-style writebacks
100 : : */
101 : : unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
102 : :
103 : : EXPORT_SYMBOL_GPL(dirty_writeback_interval);
104 : :
105 : : /*
106 : : * The longest time for which data is allowed to remain dirty
107 : : */
108 : : unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
109 : :
110 : : /*
111 : : * Flag that makes the machine dump writes/reads and block dirtyings.
112 : : */
113 : : int block_dump;
114 : :
115 : : /*
116 : : * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
117 : : * a full sync is triggered after this time elapses without any disk activity.
118 : : */
119 : : int laptop_mode;
120 : :
121 : : EXPORT_SYMBOL(laptop_mode);
122 : :
123 : : /* End of sysctl-exported parameters */
124 : :
125 : : unsigned long global_dirty_limit;
126 : :
127 : : /*
128 : : * Scale the writeback cache size proportional to the relative writeout speeds.
129 : : *
130 : : * We do this by keeping a floating proportion between BDIs, based on page
131 : : * writeback completions [end_page_writeback()]. Those devices that write out
132 : : * pages fastest will get the larger share, while the slower will get a smaller
133 : : * share.
134 : : *
135 : : * We use page writeout completions because we are interested in getting rid of
136 : : * dirty pages. Having them written out is the primary goal.
137 : : *
138 : : * We introduce a concept of time, a period over which we measure these events,
139 : : * because demand can/will vary over time. The length of this period itself is
140 : : * measured in page writeback completions.
141 : : *
142 : : */
143 : : static struct fprop_global writeout_completions;
144 : :
145 : : static void writeout_period(unsigned long t);
146 : : /* Timer for aging of writeout_completions */
147 : : static struct timer_list writeout_period_timer =
148 : : TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0);
149 : : static unsigned long writeout_period_time = 0;
150 : :
151 : : /*
152 : : * Length of period for aging writeout fractions of bdis. This is an
153 : : * arbitrarily chosen number. The longer the period, the slower fractions will
154 : : * reflect changes in current writeout rate.
155 : : */
156 : : #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
157 : :
158 : : /*
159 : : * Work out the current dirty-memory clamping and background writeout
160 : : * thresholds.
161 : : *
162 : : * The main aim here is to lower them aggressively if there is a lot of mapped
163 : : * memory around. To avoid stressing page reclaim with lots of unreclaimable
164 : : * pages. It is better to clamp down on writers than to start swapping, and
165 : : * performing lots of scanning.
166 : : *
167 : : * We only allow 1/2 of the currently-unmapped memory to be dirtied.
168 : : *
169 : : * We don't permit the clamping level to fall below 5% - that is getting rather
170 : : * excessive.
171 : : *
172 : : * We make sure that the background writeout level is below the adjusted
173 : : * clamping level.
174 : : */
175 : :
176 : : /*
177 : : * In a memory zone, there is a certain amount of pages we consider
178 : : * available for the page cache, which is essentially the number of
179 : : * free and reclaimable pages, minus some zone reserves to protect
180 : : * lowmem and the ability to uphold the zone's watermarks without
181 : : * requiring writeback.
182 : : *
183 : : * This number of dirtyable pages is the base value of which the
184 : : * user-configurable dirty ratio is the effictive number of pages that
185 : : * are allowed to be actually dirtied. Per individual zone, or
186 : : * globally by using the sum of dirtyable pages over all zones.
187 : : *
188 : : * Because the user is allowed to specify the dirty limit globally as
189 : : * absolute number of bytes, calculating the per-zone dirty limit can
190 : : * require translating the configured limit into a percentage of
191 : : * global dirtyable memory first.
192 : : */
193 : :
194 : : /**
195 : : * zone_dirtyable_memory - number of dirtyable pages in a zone
196 : : * @zone: the zone
197 : : *
198 : : * Returns the zone's number of pages potentially available for dirty
199 : : * page cache. This is the base value for the per-zone dirty limits.
200 : : */
201 : : static unsigned long zone_dirtyable_memory(struct zone *zone)
202 : : {
203 : : unsigned long nr_pages;
204 : :
205 : : nr_pages = zone_page_state(zone, NR_FREE_PAGES);
206 : 1821947 : nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
207 : :
208 : 1821947 : nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);
209 : 1821947 : nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);
210 : :
211 : : return nr_pages;
212 : : }
213 : :
214 : 0 : static unsigned long highmem_dirtyable_memory(unsigned long total)
215 : : {
216 : : #ifdef CONFIG_HIGHMEM
217 : : int node;
218 : : unsigned long x = 0;
219 : :
220 [ + + ]: 375428 : for_each_node_state(node, N_HIGH_MEMORY) {
221 : : struct zone *z = &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
222 : :
223 : 187707 : x += zone_dirtyable_memory(z);
224 : : }
225 : : /*
226 : : * Unreclaimable memory (kernel memory or anonymous memory
227 : : * without swap) can bring down the dirtyable pages below
228 : : * the zone's dirty balance reserve and the above calculation
229 : : * will underflow. However we still want to add in nodes
230 : : * which are below threshold (negative values) to get a more
231 : : * accurate calculation but make sure that the total never
232 : : * underflows.
233 : : */
234 [ - + ]: 187721 : if ((long)x < 0)
235 : : x = 0;
236 : :
237 : : /*
238 : : * Make sure that the number of highmem pages is never larger
239 : : * than the number of the total dirtyable memory. This can only
240 : : * occur in very strange VM situations but we want to make sure
241 : : * that this does not occur.
242 : : */
243 : 0 : return min(x, total);
244 : : #else
245 : : return 0;
246 : : #endif
247 : : }
248 : :
249 : : /**
250 : : * global_dirtyable_memory - number of globally dirtyable pages
251 : : *
252 : : * Returns the global number of pages potentially available for dirty
253 : : * page cache. This is the base value for the global dirty limits.
254 : : */
255 : 0 : static unsigned long global_dirtyable_memory(void)
256 : : {
257 : : unsigned long x;
258 : :
259 : : x = global_page_state(NR_FREE_PAGES);
260 : 187710 : x -= min(x, dirty_balance_reserve);
261 : :
262 : 187710 : x += global_page_state(NR_INACTIVE_FILE);
263 : 0 : x += global_page_state(NR_ACTIVE_FILE);
264 : :
265 [ # # ]: 187710 : if (!vm_highmem_is_dirtyable)
266 : 187707 : x -= highmem_dirtyable_memory(x);
267 : :
268 : 27 : return x + 1; /* Ensure that we never return 0 */
269 : : }
270 : :
271 : : /*
272 : : * global_dirty_limits - background-writeback and dirty-throttling thresholds
273 : : *
274 : : * Calculate the dirty thresholds based on sysctl parameters
275 : : * - vm.dirty_background_ratio or vm.dirty_background_bytes
276 : : * - vm.dirty_ratio or vm.dirty_bytes
277 : : * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
278 : : * real-time tasks.
279 : : */
280 : 0 : void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
281 : : {
282 : : unsigned long background;
283 : : unsigned long dirty;
284 : : unsigned long uninitialized_var(available_memory);
285 : : struct task_struct *tsk;
286 : :
287 [ - + ][ # # ]: 187712 : if (!vm_dirty_bytes || !dirty_background_bytes)
288 : 187700 : available_memory = global_dirtyable_memory();
289 : :
290 [ + + ]: 187728 : if (vm_dirty_bytes)
291 : 13 : dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
292 : : else
293 : 187715 : dirty = (vm_dirty_ratio * available_memory) / 100;
294 : :
295 [ - + ]: 187728 : if (dirty_background_bytes)
296 : 0 : background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
297 : : else
298 : 187728 : background = (dirty_background_ratio * available_memory) / 100;
299 : :
300 [ + + ]: 187728 : if (background >= dirty)
301 : 8 : background = dirty / 2;
302 : 187728 : tsk = current;
303 [ + ][ + + ]: 375464 : if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
304 : 0 : background += background / 4;
305 : 0 : dirty += dirty / 4;
306 : : }
307 : 187728 : *pbackground = background;
308 : 187728 : *pdirty = dirty;
309 : : trace_global_dirty_state(background, dirty);
310 : 187728 : }
311 : :
312 : : /**
313 : : * zone_dirty_limit - maximum number of dirty pages allowed in a zone
314 : : * @zone: the zone
315 : : *
316 : : * Returns the maximum number of dirty pages allowed in a zone, based
317 : : * on the zone's dirtyable memory.
318 : : */
319 : 0 : static unsigned long zone_dirty_limit(struct zone *zone)
320 : : {
321 : : unsigned long zone_memory = zone_dirtyable_memory(zone);
322 : 1634240 : struct task_struct *tsk = current;
323 : : unsigned long dirty;
324 : :
325 [ - + ]: 1634240 : if (vm_dirty_bytes)
326 : 0 : dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
327 : 0 : zone_memory / global_dirtyable_memory();
328 : : else
329 : 1634240 : dirty = vm_dirty_ratio * zone_memory / 100;
330 : :
331 [ + ][ + - ]: 3269741 : if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
332 : 0 : dirty += dirty / 4;
333 : :
334 : 0 : return dirty;
335 : : }
336 : :
337 : : /**
338 : : * zone_dirty_ok - tells whether a zone is within its dirty limits
339 : : * @zone: the zone to check
340 : : *
341 : : * Returns %true when the dirty pages in @zone are within the zone's
342 : : * dirty limit, %false if the limit is exceeded.
343 : : */
344 : 0 : bool zone_dirty_ok(struct zone *zone)
345 : : {
346 : 1632874 : unsigned long limit = zone_dirty_limit(zone);
347 : :
348 : 3646 : return zone_page_state(zone, NR_FILE_DIRTY) +
349 : 1823 : zone_page_state(zone, NR_UNSTABLE_NFS) +
350 : : zone_page_state(zone, NR_WRITEBACK) <= limit;
351 : : }
352 : :
353 : 0 : 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 : 2 : ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
360 [ - + ]: 2 : if (ret == 0 && write)
361 : 0 : dirty_background_bytes = 0;
362 : 0 : return ret;
363 : : }
364 : :
365 : 0 : 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 : 2 : ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
372 [ - + ]: 2 : if (ret == 0 && write)
373 : 0 : dirty_background_ratio = 0;
374 : 0 : return ret;
375 : : }
376 : :
377 : 0 : int dirty_ratio_handler(struct ctl_table *table, int write,
378 : : void __user *buffer, size_t *lenp,
379 : : loff_t *ppos)
380 : : {
381 : 2 : int old_ratio = vm_dirty_ratio;
382 : : int ret;
383 : :
384 : 2 : ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
385 [ - + ][ # # ]: 2 : if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
386 : 0 : writeback_set_ratelimit();
387 : 0 : vm_dirty_bytes = 0;
388 : : }
389 : 0 : return ret;
390 : : }
391 : :
392 : 0 : int dirty_bytes_handler(struct ctl_table *table, int write,
393 : : void __user *buffer, size_t *lenp,
394 : : loff_t *ppos)
395 : : {
396 : 2 : unsigned long old_bytes = vm_dirty_bytes;
397 : : int ret;
398 : :
399 : 2 : ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
400 [ - + ][ # # ]: 2 : if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
401 : 0 : writeback_set_ratelimit();
402 : 0 : vm_dirty_ratio = 0;
403 : : }
404 : 0 : return ret;
405 : : }
406 : :
407 : 0 : static unsigned long wp_next_time(unsigned long cur_time)
408 : : {
409 : 2246 : cur_time += VM_COMPLETIONS_PERIOD_LEN;
410 : : /* 0 has a special meaning... */
411 [ + - ][ + - ]: 2246 : if (!cur_time)
412 : : return 1;
413 : 142 : return cur_time;
414 : : }
415 : :
416 : : /*
417 : : * Increment the BDI's writeout completion count and the global writeout
418 : : * completion count. Called from test_clear_page_writeback().
419 : : */
420 : : static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
421 : : {
422 : : __inc_bdi_stat(bdi, BDI_WRITTEN);
423 : 958668 : __fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
424 : 958668 : bdi->max_prop_frac);
425 : : /* First event after period switching was turned off? */
426 [ + + # # ]: 958668 : if (!unlikely(writeout_period_time)) {
427 : : /*
428 : : * We can race with other __bdi_writeout_inc calls here but
429 : : * it does not cause any harm since the resulting time when
430 : : * timer will fire and what is in writeout_period_time will be
431 : : * roughly the same.
432 : : */
433 : 142 : writeout_period_time = wp_next_time(jiffies);
434 : 142 : mod_timer(&writeout_period_timer, writeout_period_time);
435 : : }
436 : : }
437 : :
438 : 0 : void bdi_writeout_inc(struct backing_dev_info *bdi)
439 : : {
440 : : unsigned long flags;
441 : :
442 : : local_irq_save(flags);
443 : : __bdi_writeout_inc(bdi);
444 [ # # ]: 0 : local_irq_restore(flags);
445 : 0 : }
446 : : EXPORT_SYMBOL_GPL(bdi_writeout_inc);
447 : :
448 : : /*
449 : : * Obtain an accurate fraction of the BDI's portion.
450 : : */
451 : : static void bdi_writeout_fraction(struct backing_dev_info *bdi,
452 : : long *numerator, long *denominator)
453 : : {
454 : 8353 : fprop_fraction_percpu(&writeout_completions, &bdi->completions,
455 : : numerator, denominator);
456 : : }
457 : :
458 : : /*
459 : : * On idle system, we can be called long after we scheduled because we use
460 : : * deferred timers so count with missed periods.
461 : : */
462 : 0 : static void writeout_period(unsigned long t)
463 : : {
464 : 2246 : int miss_periods = (jiffies - writeout_period_time) /
465 : : VM_COMPLETIONS_PERIOD_LEN;
466 : :
467 [ + + ]: 2246 : if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
468 : 4208 : writeout_period_time = wp_next_time(writeout_period_time +
469 : 2104 : miss_periods * VM_COMPLETIONS_PERIOD_LEN);
470 : 2104 : mod_timer(&writeout_period_timer, writeout_period_time);
471 : : } else {
472 : : /*
473 : : * Aging has zeroed all fractions. Stop wasting CPU on period
474 : : * updates.
475 : : */
476 : 142 : writeout_period_time = 0;
477 : : }
478 : 2246 : }
479 : :
480 : : /*
481 : : * bdi_min_ratio keeps the sum of the minimum dirty shares of all
482 : : * registered backing devices, which, for obvious reasons, can not
483 : : * exceed 100%.
484 : : */
485 : : static unsigned int bdi_min_ratio;
486 : :
487 : 0 : int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
488 : : {
489 : : int ret = 0;
490 : :
491 : : spin_lock_bh(&bdi_lock);
492 [ # # ]: 0 : if (min_ratio > bdi->max_ratio) {
493 : : ret = -EINVAL;
494 : : } else {
495 : 0 : min_ratio -= bdi->min_ratio;
496 [ # # ]: 0 : if (bdi_min_ratio + min_ratio < 100) {
497 : 0 : bdi_min_ratio += min_ratio;
498 : 0 : bdi->min_ratio += min_ratio;
499 : : } else {
500 : : ret = -EINVAL;
501 : : }
502 : : }
503 : : spin_unlock_bh(&bdi_lock);
504 : :
505 : 0 : return ret;
506 : : }
507 : :
508 : 0 : int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
509 : : {
510 : : int ret = 0;
511 : :
512 [ # # ]: 0 : if (max_ratio > 100)
513 : : return -EINVAL;
514 : :
515 : : spin_lock_bh(&bdi_lock);
516 [ # # ]: 0 : if (bdi->min_ratio > max_ratio) {
517 : : ret = -EINVAL;
518 : : } else {
519 : 0 : bdi->max_ratio = max_ratio;
520 : 0 : bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
521 : : }
522 : : spin_unlock_bh(&bdi_lock);
523 : :
524 : 0 : return ret;
525 : : }
526 : : EXPORT_SYMBOL(bdi_set_max_ratio);
527 : :
528 : : static unsigned long dirty_freerun_ceiling(unsigned long thresh,
529 : : unsigned long bg_thresh)
530 : : {
531 : 27484 : return (thresh + bg_thresh) / 2;
532 : : }
533 : :
534 : : static unsigned long hard_dirty_limit(unsigned long thresh)
535 : : {
536 : 166587 : return max(thresh, global_dirty_limit);
537 : : }
538 : :
539 : : /**
540 : : * bdi_dirty_limit - @bdi's share of dirty throttling threshold
541 : : * @bdi: the backing_dev_info to query
542 : : * @dirty: global dirty limit in pages
543 : : *
544 : : * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
545 : : * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
546 : : *
547 : : * Note that balance_dirty_pages() will only seriously take it as a hard limit
548 : : * when sleeping max_pause per page is not enough to keep the dirty pages under
549 : : * control. For example, when the device is completely stalled due to some error
550 : : * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
551 : : * In the other normal situations, it acts more gently by throttling the tasks
552 : : * more (rather than completely block them) when the bdi dirty pages go high.
553 : : *
554 : : * It allocates high/low dirty limits to fast/slow devices, in order to prevent
555 : : * - starving fast devices
556 : : * - piling up dirty pages (that will take long time to sync) on slow devices
557 : : *
558 : : * The bdi's share of dirty limit will be adapting to its throughput and
559 : : * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
560 : : */
561 : 0 : unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
562 : : {
563 : : u64 bdi_dirty;
564 : : long numerator, denominator;
565 : :
566 : : /*
567 : : * Calculate this BDI's share of the dirty ratio.
568 : : */
569 : : bdi_writeout_fraction(bdi, &numerator, &denominator);
570 : :
571 : 16704 : bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
572 : 16704 : bdi_dirty *= numerator;
573 [ - + ][ # # ]: 16704 : do_div(bdi_dirty, denominator);
[ - + ][ - + ]
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574 : :
575 : 8351 : bdi_dirty += (dirty * bdi->min_ratio) / 100;
576 [ - + ]: 8351 : if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
577 : : bdi_dirty = dirty * bdi->max_ratio / 100;
578 : :
579 : 8351 : return bdi_dirty;
580 : : }
581 : :
582 : : /*
583 : : * setpoint - dirty 3
584 : : * f(dirty) := 1.0 + (----------------)
585 : : * limit - setpoint
586 : : *
587 : : * it's a 3rd order polynomial that subjects to
588 : : *
589 : : * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
590 : : * (2) f(setpoint) = 1.0 => the balance point
591 : : * (3) f(limit) = 0 => the hard limit
592 : : * (4) df/dx <= 0 => negative feedback control
593 : : * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
594 : : * => fast response on large errors; small oscillation near setpoint
595 : : */
596 : : static inline long long pos_ratio_polynom(unsigned long setpoint,
597 : : unsigned long dirty,
598 : : unsigned long limit)
599 : : {
600 : : long long pos_ratio;
601 : : long x;
602 : :
603 : 19367 : x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
604 : 4841 : limit - setpoint + 1);
605 : 9685 : pos_ratio = x;
606 : 9685 : pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
607 : 9685 : pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
608 : 9685 : pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
609 : :
610 : 9685 : return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
611 : : }
612 : :
613 : : /*
614 : : * Dirty position control.
615 : : *
616 : : * (o) global/bdi setpoints
617 : : *
618 : : * We want the dirty pages be balanced around the global/bdi setpoints.
619 : : * When the number of dirty pages is higher/lower than the setpoint, the
620 : : * dirty position control ratio (and hence task dirty ratelimit) will be
621 : : * decreased/increased to bring the dirty pages back to the setpoint.
622 : : *
623 : : * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
624 : : *
625 : : * if (dirty < setpoint) scale up pos_ratio
626 : : * if (dirty > setpoint) scale down pos_ratio
627 : : *
628 : : * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
629 : : * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
630 : : *
631 : : * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
632 : : *
633 : : * (o) global control line
634 : : *
635 : : * ^ pos_ratio
636 : : * |
637 : : * | |<===== global dirty control scope ======>|
638 : : * 2.0 .............*
639 : : * | .*
640 : : * | . *
641 : : * | . *
642 : : * | . *
643 : : * | . *
644 : : * | . *
645 : : * 1.0 ................................*
646 : : * | . . *
647 : : * | . . *
648 : : * | . . *
649 : : * | . . *
650 : : * | . . *
651 : : * 0 +------------.------------------.----------------------*------------->
652 : : * freerun^ setpoint^ limit^ dirty pages
653 : : *
654 : : * (o) bdi control line
655 : : *
656 : : * ^ pos_ratio
657 : : * |
658 : : * | *
659 : : * | *
660 : : * | *
661 : : * | *
662 : : * | * |<=========== span ============>|
663 : : * 1.0 .......................*
664 : : * | . *
665 : : * | . *
666 : : * | . *
667 : : * | . *
668 : : * | . *
669 : : * | . *
670 : : * | . *
671 : : * | . *
672 : : * | . *
673 : : * | . *
674 : : * | . *
675 : : * 1/4 ...............................................* * * * * * * * * * * *
676 : : * | . .
677 : : * | . .
678 : : * | . .
679 : : * 0 +----------------------.-------------------------------.------------->
680 : : * bdi_setpoint^ x_intercept^
681 : : *
682 : : * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
683 : : * be smoothly throttled down to normal if it starts high in situations like
684 : : * - start writing to a slow SD card and a fast disk at the same time. The SD
685 : : * card's bdi_dirty may rush to many times higher than bdi_setpoint.
686 : : * - the bdi dirty thresh drops quickly due to change of JBOD workload
687 : : */
688 : 0 : static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
689 : : unsigned long thresh,
690 : : unsigned long bg_thresh,
691 : : unsigned long dirty,
692 : : unsigned long bdi_thresh,
693 : : unsigned long bdi_dirty)
694 : : {
695 : 4844 : unsigned long write_bw = bdi->avg_write_bandwidth;
696 : : unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
697 : : unsigned long limit = hard_dirty_limit(thresh);
698 : : unsigned long x_intercept;
699 : : unsigned long setpoint; /* dirty pages' target balance point */
700 : : unsigned long bdi_setpoint;
701 : : unsigned long span;
702 : : long long pos_ratio; /* for scaling up/down the rate limit */
703 : : long x;
704 : :
705 [ + + ]: 4844 : if (unlikely(dirty >= limit))
706 : : return 0;
707 : :
708 : : /*
709 : : * global setpoint
710 : : *
711 : : * See comment for pos_ratio_polynom().
712 : : */
713 : 4841 : setpoint = (freerun + limit) / 2;
714 : : pos_ratio = pos_ratio_polynom(setpoint, dirty, limit);
715 : :
716 : : /*
717 : : * The strictlimit feature is a tool preventing mistrusted filesystems
718 : : * from growing a large number of dirty pages before throttling. For
719 : : * such filesystems balance_dirty_pages always checks bdi counters
720 : : * against bdi limits. Even if global "nr_dirty" is under "freerun".
721 : : * This is especially important for fuse which sets bdi->max_ratio to
722 : : * 1% by default. Without strictlimit feature, fuse writeback may
723 : : * consume arbitrary amount of RAM because it is accounted in
724 : : * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
725 : : *
726 : : * Here, in bdi_position_ratio(), we calculate pos_ratio based on
727 : : * two values: bdi_dirty and bdi_thresh. Let's consider an example:
728 : : * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
729 : : * limits are set by default to 10% and 20% (background and throttle).
730 : : * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
731 : : * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
732 : : * about ~6K pages (as the average of background and throttle bdi
733 : : * limits). The 3rd order polynomial will provide positive feedback if
734 : : * bdi_dirty is under bdi_setpoint and vice versa.
735 : : *
736 : : * Note, that we cannot use global counters in these calculations
737 : : * because we want to throttle process writing to a strictlimit BDI
738 : : * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
739 : : * in the example above).
740 : : */
741 [ - + ]: 9685 : if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
742 : : long long bdi_pos_ratio;
743 : : unsigned long bdi_bg_thresh;
744 : :
745 [ # # ]: 0 : if (bdi_dirty < 8)
746 : 0 : return min_t(long long, pos_ratio * 2,
747 : : 2 << RATELIMIT_CALC_SHIFT);
748 : :
749 [ # # ]: 0 : if (bdi_dirty >= bdi_thresh)
750 : : return 0;
751 : :
752 : 0 : bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh);
753 : : bdi_setpoint = dirty_freerun_ceiling(bdi_thresh,
754 : : bdi_bg_thresh);
755 : :
756 [ # # ]: 0 : if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh)
757 : : return 0;
758 : :
759 : : bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
760 : : bdi_thresh);
761 : :
762 : : /*
763 : : * Typically, for strictlimit case, bdi_setpoint << setpoint
764 : : * and pos_ratio >> bdi_pos_ratio. In the other words global
765 : : * state ("dirty") is not limiting factor and we have to
766 : : * make decision based on bdi counters. But there is an
767 : : * important case when global pos_ratio should get precedence:
768 : : * global limits are exceeded (e.g. due to activities on other
769 : : * BDIs) while given strictlimit BDI is below limit.
770 : : *
771 : : * "pos_ratio * bdi_pos_ratio" would work for the case above,
772 : : * but it would look too non-natural for the case of all
773 : : * activity in the system coming from a single strictlimit BDI
774 : : * with bdi->max_ratio == 100%.
775 : : *
776 : : * Note that min() below somewhat changes the dynamics of the
777 : : * control system. Normally, pos_ratio value can be well over 3
778 : : * (when globally we are at freerun and bdi is well below bdi
779 : : * setpoint). Now the maximum pos_ratio in the same situation
780 : : * is 2. We might want to tweak this if we observe the control
781 : : * system is too slow to adapt.
782 : : */
783 : 0 : return min(pos_ratio, bdi_pos_ratio);
784 : : }
785 : :
786 : : /*
787 : : * We have computed basic pos_ratio above based on global situation. If
788 : : * the bdi is over/under its share of dirty pages, we want to scale
789 : : * pos_ratio further down/up. That is done by the following mechanism.
790 : : */
791 : :
792 : : /*
793 : : * bdi setpoint
794 : : *
795 : : * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
796 : : *
797 : : * x_intercept - bdi_dirty
798 : : * := --------------------------
799 : : * x_intercept - bdi_setpoint
800 : : *
801 : : * The main bdi control line is a linear function that subjects to
802 : : *
803 : : * (1) f(bdi_setpoint) = 1.0
804 : : * (2) k = - 1 / (8 * write_bw) (in single bdi case)
805 : : * or equally: x_intercept = bdi_setpoint + 8 * write_bw
806 : : *
807 : : * For single bdi case, the dirty pages are observed to fluctuate
808 : : * regularly within range
809 : : * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
810 : : * for various filesystems, where (2) can yield in a reasonable 12.5%
811 : : * fluctuation range for pos_ratio.
812 : : *
813 : : * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
814 : : * own size, so move the slope over accordingly and choose a slope that
815 : : * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
816 : : */
817 [ - + ]: 9685 : if (unlikely(bdi_thresh > thresh))
818 : : bdi_thresh = thresh;
819 : : /*
820 : : * It's very possible that bdi_thresh is close to 0 not because the
821 : : * device is slow, but that it has remained inactive for long time.
822 : : * Honour such devices a reasonable good (hopefully IO efficient)
823 : : * threshold, so that the occasional writes won't be blocked and active
824 : : * writes can rampup the threshold quickly.
825 : : */
826 : 9685 : bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
827 : : /*
828 : : * scale global setpoint to bdi's:
829 : : * bdi_setpoint = setpoint * bdi_thresh / thresh
830 : : */
831 : 14526 : x = div_u64((u64)bdi_thresh << 16, thresh + 1);
832 : 4841 : bdi_setpoint = setpoint * (u64)x >> 16;
833 : : /*
834 : : * Use span=(8*write_bw) in single bdi case as indicated by
835 : : * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
836 : : *
837 : : * bdi_thresh thresh - bdi_thresh
838 : : * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
839 : : * thresh thresh
840 : : */
841 : 4841 : span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
842 : 4841 : x_intercept = bdi_setpoint + span;
843 : :
844 [ + - ]: 9685 : if (bdi_dirty < x_intercept - span / 4) {
845 : 4841 : pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
846 : 4841 : x_intercept - bdi_setpoint + 1);
847 : : } else
848 : 0 : pos_ratio /= 4;
849 : :
850 : : /*
851 : : * bdi reserve area, safeguard against dirty pool underrun and disk idle
852 : : * It may push the desired control point of global dirty pages higher
853 : : * than setpoint.
854 : : */
855 : 4841 : x_intercept = bdi_thresh / 2;
856 [ - + ]: 4841 : if (bdi_dirty < x_intercept) {
857 [ # # ]: 0 : if (bdi_dirty > x_intercept / 8)
858 : 0 : pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
859 : : else
860 : 0 : pos_ratio *= 8;
861 : : }
862 : :
863 : 4841 : return pos_ratio;
864 : : }
865 : :
866 : 0 : static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
867 : : unsigned long elapsed,
868 : : unsigned long written)
869 : : {
870 : : const unsigned long period = roundup_pow_of_two(3 * HZ);
871 : 1373 : unsigned long avg = bdi->avg_write_bandwidth;
872 : 1373 : unsigned long old = bdi->write_bandwidth;
873 : : u64 bw;
874 : :
875 : : /*
876 : : * bw = written * HZ / elapsed
877 : : *
878 : : * bw * elapsed + write_bandwidth * (period - elapsed)
879 : : * write_bandwidth = ---------------------------------------------------
880 : : * period
881 : : */
882 : 1373 : bw = written - bdi->written_stamp;
883 : 1373 : bw *= HZ;
884 [ + + ]: 1373 : if (unlikely(elapsed > period)) {
885 [ - + ][ # # ]: 8 : do_div(bw, elapsed);
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ]
886 : 8 : avg = bw;
887 : 8 : goto out;
888 : : }
889 : 1365 : bw += (u64)bdi->write_bandwidth * (period - elapsed);
890 : 1365 : bw >>= ilog2(period);
891 : :
892 : : /*
893 : : * one more level of smoothing, for filtering out sudden spikes
894 : : */
895 [ + + ][ + + ]: 1365 : if (avg > old && old >= (unsigned long)bw)
896 : 249 : avg -= (avg - old) >> 3;
897 : :
898 [ + ][ + + ]: 1365 : if (avg < old && old <= (unsigned long)bw)
899 : 376 : avg += (old - avg) >> 3;
900 : :
901 : : out:
902 : 0 : bdi->write_bandwidth = bw;
903 : 0 : bdi->avg_write_bandwidth = avg;
904 : 0 : }
905 : :
906 : : /*
907 : : * The global dirtyable memory and dirty threshold could be suddenly knocked
908 : : * down by a large amount (eg. on the startup of KVM in a swapless system).
909 : : * This may throw the system into deep dirty exceeded state and throttle
910 : : * heavy/light dirtiers alike. To retain good responsiveness, maintain
911 : : * global_dirty_limit for tracking slowly down to the knocked down dirty
912 : : * threshold.
913 : : */
914 : : static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
915 : : {
916 : 464 : unsigned long limit = global_dirty_limit;
917 : :
918 : : /*
919 : : * Follow up in one step.
920 : : */
921 [ + + ]: 928 : if (limit < thresh) {
922 : : limit = thresh;
923 : : goto update;
924 : : }
925 : :
926 : : /*
927 : : * Follow down slowly. Use the higher one as the target, because thresh
928 : : * may drop below dirty. This is exactly the reason to introduce
929 : : * global_dirty_limit which is guaranteed to lie above the dirty pages.
930 : : */
931 : 435 : thresh = max(thresh, dirty);
932 [ + + ]: 435 : if (limit > thresh) {
933 : 418 : limit -= (limit - thresh) >> 5;
934 : : goto update;
935 : : }
936 : : return;
937 : : update:
938 : 447 : global_dirty_limit = limit;
939 : : }
940 : :
941 : 0 : static void global_update_bandwidth(unsigned long thresh,
942 : : unsigned long dirty,
943 : : unsigned long now)
944 : : {
945 : : static DEFINE_SPINLOCK(dirty_lock);
946 : : static unsigned long update_time;
947 : :
948 : : /*
949 : : * check locklessly first to optimize away locking for the most time
950 : : */
951 [ + - ]: 464 : if (time_before(now, update_time + BANDWIDTH_INTERVAL))
952 : 464 : return;
953 : :
954 : : spin_lock(&dirty_lock);
955 [ + ]: 464 : if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
956 : : update_dirty_limit(thresh, dirty);
957 : 464 : update_time = now;
958 : : }
959 : : spin_unlock(&dirty_lock);
960 : : }
961 : :
962 : : /*
963 : : * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
964 : : *
965 : : * Normal bdi tasks will be curbed at or below it in long term.
966 : : * Obviously it should be around (write_bw / N) when there are N dd tasks.
967 : : */
968 : 0 : static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
969 : : unsigned long thresh,
970 : : unsigned long bg_thresh,
971 : : unsigned long dirty,
972 : : unsigned long bdi_thresh,
973 : : unsigned long bdi_dirty,
974 : : unsigned long dirtied,
975 : : unsigned long elapsed)
976 : : {
977 : : unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
978 : : unsigned long limit = hard_dirty_limit(thresh);
979 : 464 : unsigned long setpoint = (freerun + limit) / 2;
980 : 464 : unsigned long write_bw = bdi->avg_write_bandwidth;
981 : 464 : unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
982 : : unsigned long dirty_rate;
983 : : unsigned long task_ratelimit;
984 : : unsigned long balanced_dirty_ratelimit;
985 : : unsigned long pos_ratio;
986 : : unsigned long step;
987 : : unsigned long x;
988 : :
989 : : /*
990 : : * The dirty rate will match the writeout rate in long term, except
991 : : * when dirty pages are truncated by userspace or re-dirtied by FS.
992 : : */
993 : 464 : dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
994 : :
995 : 464 : pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
996 : : bdi_thresh, bdi_dirty);
997 : : /*
998 : : * task_ratelimit reflects each dd's dirty rate for the past 200ms.
999 : : */
1000 : 1856 : task_ratelimit = (u64)dirty_ratelimit *
1001 : 928 : pos_ratio >> RATELIMIT_CALC_SHIFT;
1002 : 928 : task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1003 : :
1004 : : /*
1005 : : * A linear estimation of the "balanced" throttle rate. The theory is,
1006 : : * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
1007 : : * dirty_rate will be measured to be (N * task_ratelimit). So the below
1008 : : * formula will yield the balanced rate limit (write_bw / N).
1009 : : *
1010 : : * Note that the expanded form is not a pure rate feedback:
1011 : : * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1012 : : * but also takes pos_ratio into account:
1013 : : * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1014 : : *
1015 : : * (1) is not realistic because pos_ratio also takes part in balancing
1016 : : * the dirty rate. Consider the state
1017 : : * pos_ratio = 0.5 (3)
1018 : : * rate = 2 * (write_bw / N) (4)
1019 : : * If (1) is used, it will stuck in that state! Because each dd will
1020 : : * be throttled at
1021 : : * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1022 : : * yielding
1023 : : * dirty_rate = N * task_ratelimit = write_bw (6)
1024 : : * put (6) into (1) we get
1025 : : * rate_(i+1) = rate_(i) (7)
1026 : : *
1027 : : * So we end up using (2) to always keep
1028 : : * rate_(i+1) ~= (write_bw / N) (8)
1029 : : * regardless of the value of pos_ratio. As long as (8) is satisfied,
1030 : : * pos_ratio is able to drive itself to 1.0, which is not only where
1031 : : * the dirty count meet the setpoint, but also where the slope of
1032 : : * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1033 : : */
1034 : 1392 : balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1035 : 928 : dirty_rate | 1);
1036 : : /*
1037 : : * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1038 : : */
1039 [ + + ]: 464 : if (unlikely(balanced_dirty_ratelimit > write_bw))
1040 : : balanced_dirty_ratelimit = write_bw;
1041 : :
1042 : : /*
1043 : : * We could safely do this and return immediately:
1044 : : *
1045 : : * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
1046 : : *
1047 : : * However to get a more stable dirty_ratelimit, the below elaborated
1048 : : * code makes use of task_ratelimit to filter out singular points and
1049 : : * limit the step size.
1050 : : *
1051 : : * The below code essentially only uses the relative value of
1052 : : *
1053 : : * task_ratelimit - dirty_ratelimit
1054 : : * = (pos_ratio - 1) * dirty_ratelimit
1055 : : *
1056 : : * which reflects the direction and size of dirty position error.
1057 : : */
1058 : :
1059 : : /*
1060 : : * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1061 : : * task_ratelimit is on the same side of dirty_ratelimit, too.
1062 : : * For example, when
1063 : : * - dirty_ratelimit > balanced_dirty_ratelimit
1064 : : * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1065 : : * lowering dirty_ratelimit will help meet both the position and rate
1066 : : * control targets. Otherwise, don't update dirty_ratelimit if it will
1067 : : * only help meet the rate target. After all, what the users ultimately
1068 : : * feel and care are stable dirty rate and small position error.
1069 : : *
1070 : : * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1071 : : * and filter out the singular points of balanced_dirty_ratelimit. Which
1072 : : * keeps jumping around randomly and can even leap far away at times
1073 : : * due to the small 200ms estimation period of dirty_rate (we want to
1074 : : * keep that period small to reduce time lags).
1075 : : */
1076 : : step = 0;
1077 : :
1078 : : /*
1079 : : * For strictlimit case, calculations above were based on bdi counters
1080 : : * and limits (starting from pos_ratio = bdi_position_ratio() and up to
1081 : : * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1082 : : * Hence, to calculate "step" properly, we have to use bdi_dirty as
1083 : : * "dirty" and bdi_setpoint as "setpoint".
1084 : : *
1085 : : * We rampup dirty_ratelimit forcibly if bdi_dirty is low because
1086 : : * it's possible that bdi_thresh is close to zero due to inactivity
1087 : : * of backing device (see the implementation of bdi_dirty_limit()).
1088 : : */
1089 [ - + ]: 464 : if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1090 : : dirty = bdi_dirty;
1091 [ # # ]: 0 : if (bdi_dirty < 8)
1092 : 0 : setpoint = bdi_dirty + 1;
1093 : : else
1094 : 0 : setpoint = (bdi_thresh +
1095 : 0 : bdi_dirty_limit(bdi, bg_thresh)) / 2;
1096 : : }
1097 : :
1098 [ + + ]: 464 : if (dirty < setpoint) {
1099 : 175 : x = min(bdi->balanced_dirty_ratelimit,
1100 : : min(balanced_dirty_ratelimit, task_ratelimit));
1101 [ + + ]: 175 : if (dirty_ratelimit < x)
1102 : 14 : step = x - dirty_ratelimit;
1103 : : } else {
1104 : 289 : x = max(bdi->balanced_dirty_ratelimit,
1105 : : max(balanced_dirty_ratelimit, task_ratelimit));
1106 [ + + ]: 289 : if (dirty_ratelimit > x)
1107 : 263 : step = dirty_ratelimit - x;
1108 : : }
1109 : :
1110 : : /*
1111 : : * Don't pursue 100% rate matching. It's impossible since the balanced
1112 : : * rate itself is constantly fluctuating. So decrease the track speed
1113 : : * when it gets close to the target. Helps eliminate pointless tremors.
1114 : : */
1115 : 464 : step >>= dirty_ratelimit / (2 * step + 1);
1116 : : /*
1117 : : * Limit the tracking speed to avoid overshooting.
1118 : : */
1119 : 464 : step = (step + 7) / 8;
1120 : :
1121 [ + + ]: 464 : if (dirty_ratelimit < balanced_dirty_ratelimit)
1122 : 52 : dirty_ratelimit += step;
1123 : : else
1124 : 412 : dirty_ratelimit -= step;
1125 : :
1126 : 464 : bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1127 : 464 : bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1128 : :
1129 : : trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
1130 : 464 : }
1131 : :
1132 : 0 : void __bdi_update_bandwidth(struct backing_dev_info *bdi,
1133 : : unsigned long thresh,
1134 : : unsigned long bg_thresh,
1135 : : unsigned long dirty,
1136 : : unsigned long bdi_thresh,
1137 : : unsigned long bdi_dirty,
1138 : : unsigned long start_time)
1139 : : {
1140 : 11601 : unsigned long now = jiffies;
1141 : 11601 : unsigned long elapsed = now - bdi->bw_time_stamp;
1142 : : unsigned long dirtied;
1143 : : unsigned long written;
1144 : :
1145 : : /*
1146 : : * rate-limit, only update once every 200ms.
1147 : : */
1148 [ + + ]: 11601 : if (elapsed < BANDWIDTH_INTERVAL)
1149 : 11601 : return;
1150 : :
1151 : 2987 : dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
1152 : 2987 : written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1153 : :
1154 : : /*
1155 : : * Skip quiet periods when disk bandwidth is under-utilized.
1156 : : * (at least 1s idle time between two flusher runs)
1157 : : */
1158 [ + + ][ + + ]: 2987 : if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1159 : : goto snapshot;
1160 : :
1161 [ + + ]: 1373 : if (thresh) {
1162 : 464 : global_update_bandwidth(thresh, dirty, now);
1163 : 464 : bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1164 : : bdi_thresh, bdi_dirty,
1165 : : dirtied, elapsed);
1166 : : }
1167 : 1373 : bdi_update_write_bandwidth(bdi, elapsed, written);
1168 : :
1169 : : snapshot:
1170 : 2987 : bdi->dirtied_stamp = dirtied;
1171 : 2987 : bdi->written_stamp = written;
1172 : 2987 : bdi->bw_time_stamp = now;
1173 : : }
1174 : :
1175 : 0 : static void bdi_update_bandwidth(struct backing_dev_info *bdi,
1176 : : unsigned long thresh,
1177 : : unsigned long bg_thresh,
1178 : : unsigned long dirty,
1179 : : unsigned long bdi_thresh,
1180 : : unsigned long bdi_dirty,
1181 : : unsigned long start_time)
1182 : : {
1183 [ + + ]: 4379 : if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1184 : 0 : return;
1185 : : spin_lock(&bdi->wb.list_lock);
1186 : 470 : __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1187 : : bdi_thresh, bdi_dirty, start_time);
1188 : : spin_unlock(&bdi->wb.list_lock);
1189 : : }
1190 : :
1191 : : /*
1192 : : * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1193 : : * will look to see if it needs to start dirty throttling.
1194 : : *
1195 : : * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1196 : : * global_page_state() too often. So scale it near-sqrt to the safety margin
1197 : : * (the number of pages we may dirty without exceeding the dirty limits).
1198 : : */
1199 : 0 : static unsigned long dirty_poll_interval(unsigned long dirty,
1200 : : unsigned long thresh)
1201 : : {
1202 [ + ]: 17796 : if (thresh > dirty)
1203 [ + + ][ - + ]: 53388 : return 1UL << (ilog2(thresh - dirty) >> 1);
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1204 : :
1205 : : return 1;
1206 : : }
1207 : :
1208 : : static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
1209 : : unsigned long bdi_dirty)
1210 : : {
1211 : : unsigned long bw = bdi->avg_write_bandwidth;
1212 : : unsigned long t;
1213 : :
1214 : : /*
1215 : : * Limit pause time for small memory systems. If sleeping for too long
1216 : : * time, a small pool of dirty/writeback pages may go empty and disk go
1217 : : * idle.
1218 : : *
1219 : : * 8 serves as the safety ratio.
1220 : : */
1221 : 4380 : t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1222 : 4380 : t++;
1223 : :
1224 : 4380 : return min_t(unsigned long, t, MAX_PAUSE);
1225 : : }
1226 : :
1227 : 0 : static long bdi_min_pause(struct backing_dev_info *bdi,
1228 : : long max_pause,
1229 : : unsigned long task_ratelimit,
1230 : : unsigned long dirty_ratelimit,
1231 : : int *nr_dirtied_pause)
1232 : : {
1233 [ + - ][ - ]: 4379 : long hi = ilog2(bdi->avg_write_bandwidth);
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1234 [ - + ][ # # ]: 4379 : long lo = ilog2(bdi->dirty_ratelimit);
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1235 : : long t; /* target pause */
1236 : : long pause; /* estimated next pause */
1237 : : int pages; /* target nr_dirtied_pause */
1238 : :
1239 : : /* target for 10ms pause on 1-dd case */
1240 : : t = max(1, HZ / 100);
1241 : :
1242 : : /*
1243 : : * Scale up pause time for concurrent dirtiers in order to reduce CPU
1244 : : * overheads.
1245 : : *
1246 : : * (N * 10ms) on 2^N concurrent tasks.
1247 : : */
1248 [ + + ]: 4379 : if (hi > lo)
1249 : 290 : t += (hi - lo) * (10 * HZ) / 1024;
1250 : :
1251 : : /*
1252 : : * This is a bit convoluted. We try to base the next nr_dirtied_pause
1253 : : * on the much more stable dirty_ratelimit. However the next pause time
1254 : : * will be computed based on task_ratelimit and the two rate limits may
1255 : : * depart considerably at some time. Especially if task_ratelimit goes
1256 : : * below dirty_ratelimit/2 and the target pause is max_pause, the next
1257 : : * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1258 : : * result task_ratelimit won't be executed faithfully, which could
1259 : : * eventually bring down dirty_ratelimit.
1260 : : *
1261 : : * We apply two rules to fix it up:
1262 : : * 1) try to estimate the next pause time and if necessary, use a lower
1263 : : * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1264 : : * nr_dirtied_pause will be "dancing" with task_ratelimit.
1265 : : * 2) limit the target pause time to max_pause/2, so that the normal
1266 : : * small fluctuations of task_ratelimit won't trigger rule (1) and
1267 : : * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1268 : : */
1269 : 4379 : t = min(t, 1 + max_pause / 2);
1270 : 4379 : pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1271 : :
1272 : : /*
1273 : : * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1274 : : * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1275 : : * When the 16 consecutive reads are often interrupted by some dirty
1276 : : * throttling pause during the async writes, cfq will go into idles
1277 : : * (deadline is fine). So push nr_dirtied_pause as high as possible
1278 : : * until reaches DIRTY_POLL_THRESH=32 pages.
1279 : : */
1280 [ + + ]: 4379 : if (pages < DIRTY_POLL_THRESH) {
1281 : : t = max_pause;
1282 : 2609 : pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1283 [ + - ]: 2609 : if (pages > DIRTY_POLL_THRESH) {
1284 : : pages = DIRTY_POLL_THRESH;
1285 : 2609 : t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1286 : : }
1287 : : }
1288 : :
1289 : 4379 : pause = HZ * pages / (task_ratelimit + 1);
1290 [ + ]: 4379 : if (pause > max_pause) {
1291 : : t = max_pause;
1292 : 42 : pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1293 : : }
1294 : :
1295 : 0 : *nr_dirtied_pause = pages;
1296 : : /*
1297 : : * The minimal pause time will normally be half the target pause time.
1298 : : */
1299 [ # # ]: 0 : return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1300 : : }
1301 : :
1302 : : static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
1303 : : unsigned long dirty_thresh,
1304 : : unsigned long background_thresh,
1305 : : unsigned long *bdi_dirty,
1306 : : unsigned long *bdi_thresh,
1307 : : unsigned long *bdi_bg_thresh)
1308 : : {
1309 : : unsigned long bdi_reclaimable;
1310 : :
1311 : : /*
1312 : : * bdi_thresh is not treated as some limiting factor as
1313 : : * dirty_thresh, due to reasons
1314 : : * - in JBOD setup, bdi_thresh can fluctuate a lot
1315 : : * - in a system with HDD and USB key, the USB key may somehow
1316 : : * go into state (bdi_dirty >> bdi_thresh) either because
1317 : : * bdi_dirty starts high, or because bdi_thresh drops low.
1318 : : * In this case we don't want to hard throttle the USB key
1319 : : * dirtiers for 100 seconds until bdi_dirty drops under
1320 : : * bdi_thresh. Instead the auxiliary bdi control line in
1321 : : * bdi_position_ratio() will let the dirtier task progress
1322 : : * at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1323 : : */
1324 : 4379 : *bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1325 : :
1326 : : if (bdi_bg_thresh)
1327 : 22174 : *bdi_bg_thresh = div_u64((u64)*bdi_thresh *
1328 : : background_thresh,
1329 : : dirty_thresh);
1330 : :
1331 : : /*
1332 : : * In order to avoid the stacked BDI deadlock we need
1333 : : * to ensure we accurately count the 'dirty' pages when
1334 : : * the threshold is low.
1335 : : *
1336 : : * Otherwise it would be possible to get thresh+n pages
1337 : : * reported dirty, even though there are thresh-m pages
1338 : : * actually dirty; with m+n sitting in the percpu
1339 : : * deltas.
1340 : : */
1341 [ # # ][ - + ]: 4380 : if (*bdi_thresh < 2 * bdi_stat_error(bdi)) {
1342 : 0 : bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1343 : 1 : *bdi_dirty = bdi_reclaimable +
1344 : : bdi_stat_sum(bdi, BDI_WRITEBACK);
1345 : : } else {
1346 : 4380 : bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1347 : 4381 : *bdi_dirty = bdi_reclaimable +
1348 : : bdi_stat(bdi, BDI_WRITEBACK);
1349 : : }
1350 : : }
1351 : :
1352 : : /*
1353 : : * balance_dirty_pages() must be called by processes which are generating dirty
1354 : : * data. It looks at the number of dirty pages in the machine and will force
1355 : : * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1356 : : * If we're over `background_thresh' then the writeback threads are woken to
1357 : : * perform some writeout.
1358 : : */
1359 : 0 : static void balance_dirty_pages(struct address_space *mapping,
1360 : : unsigned long pages_dirtied)
1361 : : {
1362 : : unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1363 : : unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
1364 : : unsigned long background_thresh;
1365 : : unsigned long dirty_thresh;
1366 : : long period;
1367 : : long pause;
1368 : : long max_pause;
1369 : : long min_pause;
1370 : : int nr_dirtied_pause;
1371 : : bool dirty_exceeded = false;
1372 : : unsigned long task_ratelimit;
1373 : : unsigned long dirty_ratelimit;
1374 : : unsigned long pos_ratio;
1375 : 30934 : struct backing_dev_info *bdi = mapping->backing_dev_info;
1376 : 22174 : bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1377 : 22174 : unsigned long start_time = jiffies;
1378 : :
1379 : : for (;;) {
1380 : 22175 : unsigned long now = jiffies;
1381 : : unsigned long uninitialized_var(bdi_thresh);
1382 : : unsigned long thresh;
1383 : : unsigned long uninitialized_var(bdi_dirty);
1384 : : unsigned long dirty;
1385 : : unsigned long bg_thresh;
1386 : :
1387 : : /*
1388 : : * Unstable writes are a feature of certain networked
1389 : : * filesystems (i.e. NFS) in which data may have been
1390 : : * written to the server's write cache, but has not yet
1391 : : * been flushed to permanent storage.
1392 : : */
1393 : 22175 : nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1394 : : global_page_state(NR_UNSTABLE_NFS);
1395 : 22175 : nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1396 : :
1397 : 22175 : global_dirty_limits(&background_thresh, &dirty_thresh);
1398 : :
1399 [ - + ]: 22175 : if (unlikely(strictlimit)) {
1400 : 0 : bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1401 : : &bdi_dirty, &bdi_thresh, &bg_thresh);
1402 : :
1403 : : dirty = bdi_dirty;
1404 : : thresh = bdi_thresh;
1405 : : } else {
1406 : : dirty = nr_dirty;
1407 : 22175 : thresh = dirty_thresh;
1408 : 22175 : bg_thresh = background_thresh;
1409 : : }
1410 : :
1411 : : /*
1412 : : * Throttle it only when the background writeback cannot
1413 : : * catch-up. This avoids (excessively) small writeouts
1414 : : * when the bdi limits are ramping up in case of !strictlimit.
1415 : : *
1416 : : * In strictlimit case make decision based on the bdi counters
1417 : : * and limits. Small writeouts when the bdi limits are ramping
1418 : : * up are the price we consciously pay for strictlimit-ing.
1419 : : */
1420 [ + + ]: 22176 : if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh)) {
1421 : 17796 : current->dirty_paused_when = now;
1422 : 17796 : current->nr_dirtied = 0;
1423 : 17795 : current->nr_dirtied_pause =
1424 : 17796 : dirty_poll_interval(dirty, thresh);
1425 : : break;
1426 : : }
1427 : :
1428 [ - + ]: 4380 : if (unlikely(!writeback_in_progress(bdi)))
1429 : 0 : bdi_start_background_writeback(bdi);
1430 : :
1431 [ + - ]: 4379 : if (!strictlimit)
1432 : 4379 : bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1433 : : &bdi_dirty, &bdi_thresh, NULL);
1434 : :
1435 [ + + ][ - + ]: 4380 : dirty_exceeded = (bdi_dirty > bdi_thresh) &&
1436 [ # # ]: 2652 : ((nr_dirty > dirty_thresh) || strictlimit);
1437 [ + + ][ + + ]: 4380 : if (dirty_exceeded && !bdi->dirty_exceeded)
1438 : 3 : bdi->dirty_exceeded = 1;
1439 : :
1440 : 4380 : bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1441 : : nr_dirty, bdi_thresh, bdi_dirty,
1442 : : start_time);
1443 : :
1444 : 4380 : dirty_ratelimit = bdi->dirty_ratelimit;
1445 : 4380 : pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1446 : : background_thresh, nr_dirty,
1447 : : bdi_thresh, bdi_dirty);
1448 : 4380 : task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1449 : : RATELIMIT_CALC_SHIFT;
1450 : 4380 : max_pause = bdi_max_pause(bdi, bdi_dirty);
1451 : 4380 : min_pause = bdi_min_pause(bdi, max_pause,
1452 : : task_ratelimit, dirty_ratelimit,
1453 : : &nr_dirtied_pause);
1454 : :
1455 [ + + ]: 4380 : if (unlikely(task_ratelimit == 0)) {
1456 : : period = max_pause;
1457 : : pause = max_pause;
1458 : : goto pause;
1459 : : }
1460 : 4377 : period = HZ * pages_dirtied / task_ratelimit;
1461 : : pause = period;
1462 [ + ]: 4377 : if (current->dirty_paused_when)
1463 : 4378 : pause -= now - current->dirty_paused_when;
1464 : : /*
1465 : : * For less than 1s think time (ext3/4 may block the dirtier
1466 : : * for up to 800ms from time to time on 1-HDD; so does xfs,
1467 : : * however at much less frequency), try to compensate it in
1468 : : * future periods by updating the virtual time; otherwise just
1469 : : * do a reset, as it may be a light dirtier.
1470 : : */
1471 [ + + ]: 4377 : if (pause < min_pause) {
1472 : 2067 : trace_balance_dirty_pages(bdi,
1473 : : dirty_thresh,
1474 : : background_thresh,
1475 : : nr_dirty,
1476 : : bdi_thresh,
1477 : : bdi_dirty,
1478 : : dirty_ratelimit,
1479 : : task_ratelimit,
1480 : : pages_dirtied,
1481 : : period,
1482 : 2067 : min(pause, 0L),
1483 : : start_time);
1484 [ + + ]: 2067 : if (pause < -HZ) {
1485 : 10 : current->dirty_paused_when = now;
1486 : 10 : current->nr_dirtied = 0;
1487 [ + + ]: 2057 : } else if (period) {
1488 : 603 : current->dirty_paused_when += period;
1489 : 603 : current->nr_dirtied = 0;
1490 [ + + ]: 1454 : } else if (current->nr_dirtied_pause <= pages_dirtied)
1491 : 26 : current->nr_dirtied_pause += pages_dirtied;
1492 : : break;
1493 : : }
1494 [ + + ]: 2310 : if (unlikely(pause > max_pause)) {
1495 : : /* for occasional dropped task_ratelimit */
1496 : 3 : now += min(pause - max_pause, max_pause);
1497 : : pause = max_pause;
1498 : : }
1499 : :
1500 : : pause:
1501 : 2313 : trace_balance_dirty_pages(bdi,
1502 : : dirty_thresh,
1503 : : background_thresh,
1504 : : nr_dirty,
1505 : : bdi_thresh,
1506 : : bdi_dirty,
1507 : : dirty_ratelimit,
1508 : : task_ratelimit,
1509 : : pages_dirtied,
1510 : : period,
1511 : : pause,
1512 : : start_time);
1513 : 2313 : __set_current_state(TASK_KILLABLE);
1514 : 2313 : io_schedule_timeout(pause);
1515 : :
1516 : 2309 : current->dirty_paused_when = now + pause;
1517 : 2309 : current->nr_dirtied = 0;
1518 : 2309 : current->nr_dirtied_pause = nr_dirtied_pause;
1519 : :
1520 : : /*
1521 : : * This is typically equal to (nr_dirty < dirty_thresh) and can
1522 : : * also keep "1000+ dd on a slow USB stick" under control.
1523 : : */
1524 [ + + ]: 2309 : if (task_ratelimit)
1525 : : break;
1526 : :
1527 : : /*
1528 : : * In the case of an unresponding NFS server and the NFS dirty
1529 : : * pages exceeds dirty_thresh, give the other good bdi's a pipe
1530 : : * to go through, so that tasks on them still remain responsive.
1531 : : *
1532 : : * In theory 1 page is enough to keep the comsumer-producer
1533 : : * pipe going: the flusher cleans 1 page => the task dirties 1
1534 : : * more page. However bdi_dirty has accounting errors. So use
1535 : : * the larger and more IO friendly bdi_stat_error.
1536 : : */
1537 [ + - ]: 2 : if (bdi_dirty <= bdi_stat_error(bdi))
1538 : : break;
1539 : :
1540 [ + + ]: 2 : if (fatal_signal_pending(current))
1541 : : break;
1542 : : }
1543 : :
1544 [ + + ][ + + ]: 22170 : if (!dirty_exceeded && bdi->dirty_exceeded)
1545 : 3 : bdi->dirty_exceeded = 0;
1546 : :
1547 [ + + ]: 22170 : if (writeback_in_progress(bdi))
1548 : 7154 : return;
1549 : :
1550 : : /*
1551 : : * In laptop mode, we wait until hitting the higher threshold before
1552 : : * starting background writeout, and then write out all the way down
1553 : : * to the lower threshold. So slow writers cause minimal disk activity.
1554 : : *
1555 : : * In normal mode, we start background writeout at the lower
1556 : : * background_thresh, to keep the amount of dirty memory low.
1557 : : */
1558 [ + - ]: 15015 : if (laptop_mode)
1559 : : return;
1560 : :
1561 [ + + ]: 15015 : if (nr_reclaimable > background_thresh)
1562 : 15015 : bdi_start_background_writeback(bdi);
1563 : : }
1564 : :
1565 : 0 : void set_page_dirty_balance(struct page *page, int page_mkwrite)
1566 : : {
1567 [ # # ][ # # ]: 0 : if (set_page_dirty(page) || page_mkwrite) {
1568 : 0 : struct address_space *mapping = page_mapping(page);
1569 : :
1570 [ # # ]: 0 : if (mapping)
1571 : 0 : balance_dirty_pages_ratelimited(mapping);
1572 : : }
1573 : 0 : }
1574 : :
1575 : : static DEFINE_PER_CPU(int, bdp_ratelimits);
1576 : :
1577 : : /*
1578 : : * Normal tasks are throttled by
1579 : : * loop {
1580 : : * dirty tsk->nr_dirtied_pause pages;
1581 : : * take a snap in balance_dirty_pages();
1582 : : * }
1583 : : * However there is a worst case. If every task exit immediately when dirtied
1584 : : * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1585 : : * called to throttle the page dirties. The solution is to save the not yet
1586 : : * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1587 : : * randomly into the running tasks. This works well for the above worst case,
1588 : : * as the new task will pick up and accumulate the old task's leaked dirty
1589 : : * count and eventually get throttled.
1590 : : */
1591 : : DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1592 : :
1593 : : /**
1594 : : * balance_dirty_pages_ratelimited - balance dirty memory state
1595 : : * @mapping: address_space which was dirtied
1596 : : *
1597 : : * Processes which are dirtying memory should call in here once for each page
1598 : : * which was newly dirtied. The function will periodically check the system's
1599 : : * dirty state and will initiate writeback if needed.
1600 : : *
1601 : : * On really big machines, get_writeback_state is expensive, so try to avoid
1602 : : * calling it too often (ratelimiting). But once we're over the dirty memory
1603 : : * limit we decrease the ratelimiting by a lot, to prevent individual processes
1604 : : * from overshooting the limit by (ratelimit_pages) each.
1605 : : */
1606 : 0 : void balance_dirty_pages_ratelimited(struct address_space *mapping)
1607 : : {
1608 : 6484057 : struct backing_dev_info *bdi = mapping->backing_dev_info;
1609 : : int ratelimit;
1610 : : int *p;
1611 : :
1612 [ + + ]: 6484057 : if (!bdi_cap_account_dirty(bdi))
1613 : 6487691 : return;
1614 : :
1615 : 6472124 : ratelimit = current->nr_dirtied_pause;
1616 [ + + ]: 6472124 : if (bdi->dirty_exceeded)
1617 : 3966 : ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1618 : :
1619 : 6472124 : preempt_disable();
1620 : : /*
1621 : : * This prevents one CPU to accumulate too many dirtied pages without
1622 : : * calling into balance_dirty_pages(), which can happen when there are
1623 : : * 1000+ tasks, all of them start dirtying pages at exactly the same
1624 : : * time, hence all honoured too large initial task->nr_dirtied_pause.
1625 : : */
1626 : 12950450 : p = &__get_cpu_var(bdp_ratelimits);
1627 [ + + ]: 6475225 : if (unlikely(current->nr_dirtied >= ratelimit))
1628 : 20599 : *p = 0;
1629 [ + + ]: 6454626 : else if (unlikely(*p >= ratelimit_pages)) {
1630 : 633 : *p = 0;
1631 : : ratelimit = 0;
1632 : : }
1633 : : /*
1634 : : * Pick up the dirtied pages by the exited tasks. This avoids lots of
1635 : : * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1636 : : * the dirty throttling and livelock other long-run dirtiers.
1637 : : */
1638 : 12950450 : p = &__get_cpu_var(dirty_throttle_leaks);
1639 [ + + ][ + + ]: 6475225 : if (*p > 0 && current->nr_dirtied < ratelimit) {
1640 : : unsigned long nr_pages_dirtied;
1641 : 8946 : nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1642 : 8946 : *p -= nr_pages_dirtied;
1643 : 8946 : current->nr_dirtied += nr_pages_dirtied;
1644 : : }
1645 : 6475225 : preempt_enable();
1646 : :
1647 [ + + ]: 6475763 : if (unlikely(current->nr_dirtied >= ratelimit))
1648 : 22174 : balance_dirty_pages(mapping, current->nr_dirtied);
1649 : : }
1650 : : EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1651 : :
1652 : 161285 : void throttle_vm_writeout(gfp_t gfp_mask)
1653 : : {
1654 : : unsigned long background_thresh;
1655 : : unsigned long dirty_thresh;
1656 : :
1657 : : for ( ; ; ) {
1658 : 161285 : global_dirty_limits(&background_thresh, &dirty_thresh);
1659 : 322558 : dirty_thresh = hard_dirty_limit(dirty_thresh);
1660 : :
1661 : : /*
1662 : : * Boost the allowable dirty threshold a bit for page
1663 : : * allocators so they don't get DoS'ed by heavy writers
1664 : : */
1665 : 161279 : dirty_thresh += dirty_thresh / 10; /* wheeee... */
1666 : :
1667 [ - ]: 161279 : if (global_page_state(NR_UNSTABLE_NFS) +
1668 : : global_page_state(NR_WRITEBACK) <= dirty_thresh)
1669 : : break;
1670 : 0 : congestion_wait(BLK_RW_ASYNC, HZ/10);
1671 : :
1672 : : /*
1673 : : * The caller might hold locks which can prevent IO completion
1674 : : * or progress in the filesystem. So we cannot just sit here
1675 : : * waiting for IO to complete.
1676 : : */
1677 [ # # ]: 0 : if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1678 : : break;
1679 : : }
1680 : 0 : }
1681 : :
1682 : : /*
1683 : : * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1684 : : */
1685 : 0 : int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1686 : : void __user *buffer, size_t *length, loff_t *ppos)
1687 : : {
1688 : 2 : proc_dointvec(table, write, buffer, length, ppos);
1689 : 2 : return 0;
1690 : : }
1691 : :
1692 : : #ifdef CONFIG_BLOCK
1693 : 0 : void laptop_mode_timer_fn(unsigned long data)
1694 : : {
1695 : 0 : struct request_queue *q = (struct request_queue *)data;
1696 : 0 : int nr_pages = global_page_state(NR_FILE_DIRTY) +
1697 : : global_page_state(NR_UNSTABLE_NFS);
1698 : :
1699 : : /*
1700 : : * We want to write everything out, not just down to the dirty
1701 : : * threshold
1702 : : */
1703 [ # # ]: 0 : if (bdi_has_dirty_io(&q->backing_dev_info))
1704 : 0 : bdi_start_writeback(&q->backing_dev_info, nr_pages,
1705 : : WB_REASON_LAPTOP_TIMER);
1706 : 0 : }
1707 : :
1708 : : /*
1709 : : * We've spun up the disk and we're in laptop mode: schedule writeback
1710 : : * of all dirty data a few seconds from now. If the flush is already scheduled
1711 : : * then push it back - the user is still using the disk.
1712 : : */
1713 : 0 : void laptop_io_completion(struct backing_dev_info *info)
1714 : : {
1715 : 0 : mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1716 : 0 : }
1717 : :
1718 : : /*
1719 : : * We're in laptop mode and we've just synced. The sync's writes will have
1720 : : * caused another writeback to be scheduled by laptop_io_completion.
1721 : : * Nothing needs to be written back anymore, so we unschedule the writeback.
1722 : : */
1723 : 0 : void laptop_sync_completion(void)
1724 : : {
1725 : : struct backing_dev_info *bdi;
1726 : :
1727 : : rcu_read_lock();
1728 : :
1729 [ # # ]: 0 : list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1730 : 0 : del_timer(&bdi->laptop_mode_wb_timer);
1731 : :
1732 : : rcu_read_unlock();
1733 : 0 : }
1734 : : #endif
1735 : :
1736 : : /*
1737 : : * If ratelimit_pages is too high then we can get into dirty-data overload
1738 : : * if a large number of processes all perform writes at the same time.
1739 : : * If it is too low then SMP machines will call the (expensive)
1740 : : * get_writeback_state too often.
1741 : : *
1742 : : * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1743 : : * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1744 : : * thresholds.
1745 : : */
1746 : :
1747 : 0 : void writeback_set_ratelimit(void)
1748 : : {
1749 : : unsigned long background_thresh;
1750 : : unsigned long dirty_thresh;
1751 : 159 : global_dirty_limits(&background_thresh, &dirty_thresh);
1752 : 159 : global_dirty_limit = dirty_thresh;
1753 : 318 : ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1754 [ - + ]: 318 : if (ratelimit_pages < 16)
1755 : 0 : ratelimit_pages = 16;
1756 : 159 : }
1757 : :
1758 : : static int
1759 : 0 : ratelimit_handler(struct notifier_block *self, unsigned long action,
1760 : : void *hcpu)
1761 : : {
1762 : :
1763 [ + + ]: 555 : switch (action & ~CPU_TASKS_FROZEN) {
1764 : : case CPU_ONLINE:
1765 : : case CPU_DEAD:
1766 : 159 : writeback_set_ratelimit();
1767 : 159 : return NOTIFY_OK;
1768 : : default:
1769 : : return NOTIFY_DONE;
1770 : : }
1771 : : }
1772 : :
1773 : : static struct notifier_block ratelimit_nb = {
1774 : : .notifier_call = ratelimit_handler,
1775 : : .next = NULL,
1776 : : };
1777 : :
1778 : : /*
1779 : : * Called early on to tune the page writeback dirty limits.
1780 : : *
1781 : : * We used to scale dirty pages according to how total memory
1782 : : * related to pages that could be allocated for buffers (by
1783 : : * comparing nr_free_buffer_pages() to vm_total_pages.
1784 : : *
1785 : : * However, that was when we used "dirty_ratio" to scale with
1786 : : * all memory, and we don't do that any more. "dirty_ratio"
1787 : : * is now applied to total non-HIGHPAGE memory (by subtracting
1788 : : * totalhigh_pages from vm_total_pages), and as such we can't
1789 : : * get into the old insane situation any more where we had
1790 : : * large amounts of dirty pages compared to a small amount of
1791 : : * non-HIGHMEM memory.
1792 : : *
1793 : : * But we might still want to scale the dirty_ratio by how
1794 : : * much memory the box has..
1795 : : */
1796 : 0 : void __init page_writeback_init(void)
1797 : : {
1798 : 0 : writeback_set_ratelimit();
1799 : 0 : register_cpu_notifier(&ratelimit_nb);
1800 : :
1801 : 0 : fprop_global_init(&writeout_completions);
1802 : 0 : }
1803 : :
1804 : : /**
1805 : : * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1806 : : * @mapping: address space structure to write
1807 : : * @start: starting page index
1808 : : * @end: ending page index (inclusive)
1809 : : *
1810 : : * This function scans the page range from @start to @end (inclusive) and tags
1811 : : * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1812 : : * that write_cache_pages (or whoever calls this function) will then use
1813 : : * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1814 : : * used to avoid livelocking of writeback by a process steadily creating new
1815 : : * dirty pages in the file (thus it is important for this function to be quick
1816 : : * so that it can tag pages faster than a dirtying process can create them).
1817 : : */
1818 : : /*
1819 : : * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1820 : : */
1821 : 37007 : void tag_pages_for_writeback(struct address_space *mapping,
1822 : : pgoff_t start, pgoff_t end)
1823 : : {
1824 : : #define WRITEBACK_TAG_BATCH 4096
1825 : : unsigned long tagged;
1826 : :
1827 : : do {
1828 : : spin_lock_irq(&mapping->tree_lock);
1829 : 37022 : tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1830 : : &start, end, WRITEBACK_TAG_BATCH,
1831 : : PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1832 : : spin_unlock_irq(&mapping->tree_lock);
1833 [ - + ][ # # ]: 37023 : WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
[ # # ]
1834 : 37023 : cond_resched();
1835 : : /* We check 'start' to handle wrapping when end == ~0UL */
1836 [ + + ][ + - ]: 37023 : } while (tagged >= WRITEBACK_TAG_BATCH && start);
1837 : 37010 : }
1838 : : EXPORT_SYMBOL(tag_pages_for_writeback);
1839 : :
1840 : : /**
1841 : : * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1842 : : * @mapping: address space structure to write
1843 : : * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1844 : : * @writepage: function called for each page
1845 : : * @data: data passed to writepage function
1846 : : *
1847 : : * If a page is already under I/O, write_cache_pages() skips it, even
1848 : : * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1849 : : * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1850 : : * and msync() need to guarantee that all the data which was dirty at the time
1851 : : * the call was made get new I/O started against them. If wbc->sync_mode is
1852 : : * WB_SYNC_ALL then we were called for data integrity and we must wait for
1853 : : * existing IO to complete.
1854 : : *
1855 : : * To avoid livelocks (when other process dirties new pages), we first tag
1856 : : * pages which should be written back with TOWRITE tag and only then start
1857 : : * writing them. For data-integrity sync we have to be careful so that we do
1858 : : * not miss some pages (e.g., because some other process has cleared TOWRITE
1859 : : * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1860 : : * by the process clearing the DIRTY tag (and submitting the page for IO).
1861 : : */
1862 : 0 : int write_cache_pages(struct address_space *mapping,
1863 : : struct writeback_control *wbc, writepage_t writepage,
1864 : : void *data)
1865 : : {
1866 : : int ret = 0;
1867 : : int done = 0;
1868 : : struct pagevec pvec;
1869 : : int nr_pages;
1870 : : pgoff_t uninitialized_var(writeback_index);
1871 : : pgoff_t index;
1872 : : pgoff_t end; /* Inclusive */
1873 : : pgoff_t done_index;
1874 : : int cycled;
1875 : : int range_whole = 0;
1876 : : int tag;
1877 : :
1878 : : pagevec_init(&pvec, 0);
1879 [ + + ]: 6902 : if (wbc->range_cyclic) {
1880 : 1668 : writeback_index = mapping->writeback_index; /* prev offset */
1881 : 1668 : index = writeback_index;
1882 [ + + ]: 1668 : if (index == 0)
1883 : : cycled = 1;
1884 : : else
1885 : : cycled = 0;
1886 : : end = -1;
1887 : : } else {
1888 : 5234 : index = wbc->range_start >> PAGE_CACHE_SHIFT;
1889 : 5234 : end = wbc->range_end >> PAGE_CACHE_SHIFT;
1890 [ + - ][ + + ]: 5234 : if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1891 : : range_whole = 1;
1892 : : cycled = 1; /* ignore range_cyclic tests */
1893 : : }
1894 [ + + ][ + + ]: 6902 : if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1895 : : tag = PAGECACHE_TAG_TOWRITE;
1896 : : else
1897 : : tag = PAGECACHE_TAG_DIRTY;
1898 : : retry:
1899 [ + + ][ + + ]: 7168 : if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1900 : 4106 : tag_pages_for_writeback(mapping, index, end);
1901 : 7168 : done_index = index;
1902 [ + + ]: 22230 : while (!done && (index <= end)) {
1903 : : int i;
1904 : :
1905 : 14778 : nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1906 : 14778 : min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1907 [ + + ]: 14780 : if (nr_pages == 0)
1908 : : break;
1909 : :
1910 [ + + ]: 80551 : for (i = 0; i < nr_pages; i++) {
1911 : 72386 : struct page *page = pvec.pages[i];
1912 : :
1913 : : /*
1914 : : * At this point, the page may be truncated or
1915 : : * invalidated (changing page->mapping to NULL), or
1916 : : * even swizzled back from swapper_space to tmpfs file
1917 : : * mapping. However, page->index will not change
1918 : : * because we have a reference on the page.
1919 : : */
1920 [ + + ]: 72386 : if (page->index > end) {
1921 : : /*
1922 : : * can't be range_cyclic (1st pass) because
1923 : : * end == -1 in that case.
1924 : : */
1925 : : done = 1;
1926 : : break;
1927 : : }
1928 : :
1929 : : done_index = page->index;
1930 : :
1931 : : lock_page(page);
1932 : :
1933 : : /*
1934 : : * Page truncated or invalidated. We can freely skip it
1935 : : * then, even for data integrity operations: the page
1936 : : * has disappeared concurrently, so there could be no
1937 : : * real expectation of this data interity operation
1938 : : * even if there is now a new, dirty page at the same
1939 : : * pagecache address.
1940 : : */
1941 [ - + ]: 72386 : if (unlikely(page->mapping != mapping)) {
1942 : : continue_unlock:
1943 : 3797 : unlock_page(page);
1944 : 3806 : continue;
1945 : : }
1946 : :
1947 [ + + ]: 72386 : if (!PageDirty(page)) {
1948 : : /* someone wrote it for us */
1949 : : goto continue_unlock;
1950 : : }
1951 : :
1952 [ + + ]: 68589 : if (PageWriteback(page)) {
1953 [ - + ]: 7 : if (wbc->sync_mode != WB_SYNC_NONE)
1954 : : wait_on_page_writeback(page);
1955 : : else
1956 : : goto continue_unlock;
1957 : : }
1958 : :
1959 [ - + ]: 68589 : BUG_ON(PageWriteback(page));
1960 [ - + ]: 68589 : if (!clear_page_dirty_for_io(page))
1961 : : goto continue_unlock;
1962 : :
1963 : 68589 : trace_wbc_writepage(wbc, mapping->backing_dev_info);
1964 : 68589 : ret = (*writepage)(page, wbc, data);
1965 [ - + ]: 68589 : if (unlikely(ret)) {
1966 [ # # ]: 0 : if (ret == AOP_WRITEPAGE_ACTIVATE) {
1967 : 0 : unlock_page(page);
1968 : : ret = 0;
1969 : : } else {
1970 : : /*
1971 : : * done_index is set past this page,
1972 : : * so media errors will not choke
1973 : : * background writeout for the entire
1974 : : * file. This has consequences for
1975 : : * range_cyclic semantics (ie. it may
1976 : : * not be suitable for data integrity
1977 : : * writeout).
1978 : : */
1979 : 0 : done_index = page->index + 1;
1980 : : done = 1;
1981 : 0 : break;
1982 : : }
1983 : : }
1984 : :
1985 : : /*
1986 : : * We stop writing back only if we are not doing
1987 : : * integrity sync. In case of integrity sync we have to
1988 : : * keep going until we have written all the pages
1989 : : * we tagged for writeback prior to entering this loop.
1990 : : */
1991 [ - + ][ # # ]: 68570 : if (--wbc->nr_to_write <= 0 &&
1992 : 0 : wbc->sync_mode == WB_SYNC_NONE) {
1993 : : done = 1;
1994 : : break;
1995 : : }
1996 : : }
1997 : : pagevec_release(&pvec);
1998 : 8159 : cond_resched();
1999 : : }
2000 [ + + ]: 7168 : if (!cycled && !done) {
2001 : : /*
2002 : : * range_cyclic:
2003 : : * We hit the last page and there is more work to be done: wrap
2004 : : * back to the start of the file
2005 : : */
2006 : : cycled = 1;
2007 : 266 : index = 0;
2008 : 266 : end = writeback_index - 1;
2009 : 266 : goto retry;
2010 : : }
2011 [ + + ][ + + ]: 6902 : if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
[ + - ]
2012 : 5929 : mapping->writeback_index = done_index;
2013 : :
2014 : 6902 : return ret;
2015 : : }
2016 : : EXPORT_SYMBOL(write_cache_pages);
2017 : :
2018 : : /*
2019 : : * Function used by generic_writepages to call the real writepage
2020 : : * function and set the mapping flags on error
2021 : : */
2022 : 0 : static int __writepage(struct page *page, struct writeback_control *wbc,
2023 : : void *data)
2024 : : {
2025 : : struct address_space *mapping = data;
2026 : 67221 : int ret = mapping->a_ops->writepage(page, wbc);
2027 : : mapping_set_error(mapping, ret);
2028 : 0 : return ret;
2029 : : }
2030 : :
2031 : : /**
2032 : : * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2033 : : * @mapping: address space structure to write
2034 : : * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2035 : : *
2036 : : * This is a library function, which implements the writepages()
2037 : : * address_space_operation.
2038 : : */
2039 : 0 : int generic_writepages(struct address_space *mapping,
2040 : : struct writeback_control *wbc)
2041 : : {
2042 : : struct blk_plug plug;
2043 : : int ret;
2044 : :
2045 : : /* deal with chardevs and other special file */
2046 [ + + ]: 6262 : if (!mapping->a_ops->writepage)
2047 : : return 0;
2048 : :
2049 : 5527 : blk_start_plug(&plug);
2050 : 5527 : ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2051 : 5525 : blk_finish_plug(&plug);
2052 : 5524 : return ret;
2053 : : }
2054 : :
2055 : : EXPORT_SYMBOL(generic_writepages);
2056 : :
2057 : 0 : int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2058 : : {
2059 : : int ret;
2060 : :
2061 [ + + ]: 94096 : if (wbc->nr_to_write <= 0)
2062 : : return 0;
2063 [ + + ]: 94093 : if (mapping->a_ops->writepages)
2064 : 93358 : ret = mapping->a_ops->writepages(mapping, wbc);
2065 : : else
2066 : 735 : ret = generic_writepages(mapping, wbc);
2067 : 94092 : return ret;
2068 : : }
2069 : :
2070 : : /**
2071 : : * write_one_page - write out a single page and optionally wait on I/O
2072 : : * @page: the page to write
2073 : : * @wait: if true, wait on writeout
2074 : : *
2075 : : * The page must be locked by the caller and will be unlocked upon return.
2076 : : *
2077 : : * write_one_page() returns a negative error code if I/O failed.
2078 : : */
2079 : 0 : int write_one_page(struct page *page, int wait)
2080 : : {
2081 : 1 : struct address_space *mapping = page->mapping;
2082 : : int ret = 0;
2083 : 1 : struct writeback_control wbc = {
2084 : : .sync_mode = WB_SYNC_ALL,
2085 : : .nr_to_write = 1,
2086 : : };
2087 : :
2088 [ - + ]: 1 : BUG_ON(!PageLocked(page));
2089 : :
2090 [ + - ]: 1 : if (wait)
2091 : : wait_on_page_writeback(page);
2092 : :
2093 [ + - ]: 1 : if (clear_page_dirty_for_io(page)) {
2094 : : page_cache_get(page);
2095 : 1 : ret = mapping->a_ops->writepage(page, &wbc);
2096 [ + - ]: 1 : if (ret == 0 && wait) {
2097 : : wait_on_page_writeback(page);
2098 [ - + ]: 2 : if (PageError(page))
2099 : : ret = -EIO;
2100 : : }
2101 : 1 : page_cache_release(page);
2102 : : } else {
2103 : 0 : unlock_page(page);
2104 : : }
2105 : 1 : return ret;
2106 : : }
2107 : : EXPORT_SYMBOL(write_one_page);
2108 : :
2109 : : /*
2110 : : * For address_spaces which do not use buffers nor write back.
2111 : : */
2112 : 0 : int __set_page_dirty_no_writeback(struct page *page)
2113 : : {
2114 [ + + ]: 177300 : if (!PageDirty(page))
2115 : 11530 : return !TestSetPageDirty(page);
2116 : : return 0;
2117 : : }
2118 : :
2119 : : /*
2120 : : * Helper function for set_page_dirty family.
2121 : : * NOTE: This relies on being atomic wrt interrupts.
2122 : : */
2123 : 0 : void account_page_dirtied(struct page *page, struct address_space *mapping)
2124 : : {
2125 : : trace_writeback_dirty_page(page, mapping);
2126 : :
2127 [ + - ]: 2115818 : if (mapping_cap_account_dirty(mapping)) {
2128 : 2115818 : __inc_zone_page_state(page, NR_FILE_DIRTY);
2129 : 2117656 : __inc_zone_page_state(page, NR_DIRTIED);
2130 : 2117079 : __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
2131 : 2117521 : __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2132 : : task_io_account_write(PAGE_CACHE_SIZE);
2133 : 2118046 : current->nr_dirtied++;
2134 : 4233996 : this_cpu_inc(bdp_ratelimits);
2135 : : }
2136 : 2118131 : }
2137 : : EXPORT_SYMBOL(account_page_dirtied);
2138 : :
2139 : : /*
2140 : : * Helper function for set_page_writeback family.
2141 : : *
2142 : : * The caller must hold mem_cgroup_begin/end_update_page_stat() lock
2143 : : * while calling this function.
2144 : : * See test_set_page_writeback for example.
2145 : : *
2146 : : * NOTE: Unlike account_page_dirtied this does not rely on being atomic
2147 : : * wrt interrupts.
2148 : : */
2149 : 0 : void account_page_writeback(struct page *page)
2150 : : {
2151 : : mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2152 : 958648 : inc_zone_page_state(page, NR_WRITEBACK);
2153 : 0 : }
2154 : : EXPORT_SYMBOL(account_page_writeback);
2155 : :
2156 : : /*
2157 : : * For address_spaces which do not use buffers. Just tag the page as dirty in
2158 : : * its radix tree.
2159 : : *
2160 : : * This is also used when a single buffer is being dirtied: we want to set the
2161 : : * page dirty in that case, but not all the buffers. This is a "bottom-up"
2162 : : * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2163 : : *
2164 : : * Most callers have locked the page, which pins the address_space in memory.
2165 : : * But zap_pte_range() does not lock the page, however in that case the
2166 : : * mapping is pinned by the vma's ->vm_file reference.
2167 : : *
2168 : : * We take care to handle the case where the page was truncated from the
2169 : : * mapping by re-checking page_mapping() inside tree_lock.
2170 : : */
2171 : 0 : int __set_page_dirty_nobuffers(struct page *page)
2172 : : {
2173 [ + - ]: 43092 : if (!TestSetPageDirty(page)) {
2174 : 43092 : struct address_space *mapping = page_mapping(page);
2175 : : struct address_space *mapping2;
2176 : : unsigned long flags;
2177 : :
2178 [ + - ]: 43092 : if (!mapping)
2179 : : return 1;
2180 : :
2181 : 43092 : spin_lock_irqsave(&mapping->tree_lock, flags);
2182 : 43092 : mapping2 = page_mapping(page);
2183 [ + - ]: 43092 : if (mapping2) { /* Race with truncate? */
2184 [ - + ]: 43092 : BUG_ON(mapping2 != mapping);
2185 [ - + ][ # # ]: 43092 : WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
[ - + ][ # # ]
[ # # ]
2186 : 43092 : account_page_dirtied(page, mapping);
2187 : 43092 : radix_tree_tag_set(&mapping->page_tree,
2188 : : page_index(page), PAGECACHE_TAG_DIRTY);
2189 : : }
2190 : : spin_unlock_irqrestore(&mapping->tree_lock, flags);
2191 [ + - ]: 43092 : if (mapping->host) {
2192 : : /* !PageAnon && !swapper_space */
2193 : 43092 : __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2194 : : }
2195 : : return 1;
2196 : : }
2197 : : return 0;
2198 : : }
2199 : : EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2200 : :
2201 : : /*
2202 : : * Call this whenever redirtying a page, to de-account the dirty counters
2203 : : * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2204 : : * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2205 : : * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2206 : : * control.
2207 : : */
2208 : 0 : void account_page_redirty(struct page *page)
2209 : : {
2210 : 86184 : struct address_space *mapping = page->mapping;
2211 [ + - ][ + - ]: 43092 : if (mapping && mapping_cap_account_dirty(mapping)) {
2212 : 43092 : current->nr_dirtied--;
2213 : 43092 : dec_zone_page_state(page, NR_DIRTIED);
2214 : 43092 : dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2215 : : }
2216 : 43092 : }
2217 : : EXPORT_SYMBOL(account_page_redirty);
2218 : :
2219 : : /*
2220 : : * When a writepage implementation decides that it doesn't want to write this
2221 : : * page for some reason, it should redirty the locked page via
2222 : : * redirty_page_for_writepage() and it should then unlock the page and return 0
2223 : : */
2224 : 0 : int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2225 : : {
2226 : 43092 : wbc->pages_skipped++;
2227 : 43092 : account_page_redirty(page);
2228 : 43092 : return __set_page_dirty_nobuffers(page);
2229 : : }
2230 : : EXPORT_SYMBOL(redirty_page_for_writepage);
2231 : :
2232 : : /*
2233 : : * Dirty a page.
2234 : : *
2235 : : * For pages with a mapping this should be done under the page lock
2236 : : * for the benefit of asynchronous memory errors who prefer a consistent
2237 : : * dirty state. This rule can be broken in some special cases,
2238 : : * but should be better not to.
2239 : : *
2240 : : * If the mapping doesn't provide a set_page_dirty a_op, then
2241 : : * just fall through and assume that it wants buffer_heads.
2242 : : */
2243 : 0 : int set_page_dirty(struct page *page)
2244 : : {
2245 : 970676 : struct address_space *mapping = page_mapping(page);
2246 : :
2247 [ + + ]: 970801 : if (likely(mapping)) {
2248 : 793409 : int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2249 : : /*
2250 : : * readahead/lru_deactivate_page could remain
2251 : : * PG_readahead/PG_reclaim due to race with end_page_writeback
2252 : : * About readahead, if the page is written, the flags would be
2253 : : * reset. So no problem.
2254 : : * About lru_deactivate_page, if the page is redirty, the flag
2255 : : * will be reset. So no problem. but if the page is used by readahead
2256 : : * it will confuse readahead and make it restart the size rampup
2257 : : * process. But it's a trivial problem.
2258 : : */
2259 : : ClearPageReclaim(page);
2260 : : #ifdef CONFIG_BLOCK
2261 [ + + ]: 793556 : if (!spd)
2262 : : spd = __set_page_dirty_buffers;
2263 : : #endif
2264 : 793556 : return (*spd)(page);
2265 : : }
2266 [ + + ]: 177392 : if (!PageDirty(page)) {
2267 [ - + ]: 297 : if (!TestSetPageDirty(page))
2268 : : return 1;
2269 : : }
2270 : : return 0;
2271 : : }
2272 : : EXPORT_SYMBOL(set_page_dirty);
2273 : :
2274 : : /*
2275 : : * set_page_dirty() is racy if the caller has no reference against
2276 : : * page->mapping->host, and if the page is unlocked. This is because another
2277 : : * CPU could truncate the page off the mapping and then free the mapping.
2278 : : *
2279 : : * Usually, the page _is_ locked, or the caller is a user-space process which
2280 : : * holds a reference on the inode by having an open file.
2281 : : *
2282 : : * In other cases, the page should be locked before running set_page_dirty().
2283 : : */
2284 : 0 : int set_page_dirty_lock(struct page *page)
2285 : : {
2286 : : int ret;
2287 : :
2288 : : lock_page(page);
2289 : 177392 : ret = set_page_dirty(page);
2290 : 177392 : unlock_page(page);
2291 : 177392 : return ret;
2292 : : }
2293 : : EXPORT_SYMBOL(set_page_dirty_lock);
2294 : :
2295 : : /*
2296 : : * Clear a page's dirty flag, while caring for dirty memory accounting.
2297 : : * Returns true if the page was previously dirty.
2298 : : *
2299 : : * This is for preparing to put the page under writeout. We leave the page
2300 : : * tagged as dirty in the radix tree so that a concurrent write-for-sync
2301 : : * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2302 : : * implementation will run either set_page_writeback() or set_page_dirty(),
2303 : : * at which stage we bring the page's dirty flag and radix-tree dirty tag
2304 : : * back into sync.
2305 : : *
2306 : : * This incoherency between the page's dirty flag and radix-tree tag is
2307 : : * unfortunate, but it only exists while the page is locked.
2308 : : */
2309 : 0 : int clear_page_dirty_for_io(struct page *page)
2310 : : {
2311 : 958634 : struct address_space *mapping = page_mapping(page);
2312 : :
2313 [ - + ]: 958617 : BUG_ON(!PageLocked(page));
2314 : :
2315 [ + + ][ + ]: 958617 : if (mapping && mapping_cap_account_dirty(mapping)) {
2316 : : /*
2317 : : * Yes, Virginia, this is indeed insane.
2318 : : *
2319 : : * We use this sequence to make sure that
2320 : : * (a) we account for dirty stats properly
2321 : : * (b) we tell the low-level filesystem to
2322 : : * mark the whole page dirty if it was
2323 : : * dirty in a pagetable. Only to then
2324 : : * (c) clean the page again and return 1 to
2325 : : * cause the writeback.
2326 : : *
2327 : : * This way we avoid all nasty races with the
2328 : : * dirty bit in multiple places and clearing
2329 : : * them concurrently from different threads.
2330 : : *
2331 : : * Note! Normally the "set_page_dirty(page)"
2332 : : * has no effect on the actual dirty bit - since
2333 : : * that will already usually be set. But we
2334 : : * need the side effects, and it can help us
2335 : : * avoid races.
2336 : : *
2337 : : * We basically use the page "master dirty bit"
2338 : : * as a serialization point for all the different
2339 : : * threads doing their things.
2340 : : */
2341 [ + + ]: 958612 : if (page_mkclean(page))
2342 : 96254 : set_page_dirty(page);
2343 : : /*
2344 : : * We carefully synchronise fault handlers against
2345 : : * installing a dirty pte and marking the page dirty
2346 : : * at this point. We do this by having them hold the
2347 : : * page lock at some point after installing their
2348 : : * pte, but before marking the page dirty.
2349 : : * Pages are always locked coming in here, so we get
2350 : : * the desired exclusion. See mm/memory.c:do_wp_page()
2351 : : * for more comments.
2352 : : */
2353 [ + + ]: 958621 : if (TestClearPageDirty(page)) {
2354 : 958617 : dec_zone_page_state(page, NR_FILE_DIRTY);
2355 : 958621 : dec_bdi_stat(mapping->backing_dev_info,
2356 : : BDI_RECLAIMABLE);
2357 : : return 1;
2358 : : }
2359 : : return 0;
2360 : : }
2361 : 0 : return TestClearPageDirty(page);
2362 : : }
2363 : : EXPORT_SYMBOL(clear_page_dirty_for_io);
2364 : :
2365 : 0 : int test_clear_page_writeback(struct page *page)
2366 : : {
2367 : 958667 : struct address_space *mapping = page_mapping(page);
2368 : : int ret;
2369 : : bool locked;
2370 : : unsigned long memcg_flags;
2371 : :
2372 : : mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
2373 [ + - ]: 958667 : if (mapping) {
2374 : 1917335 : struct backing_dev_info *bdi = mapping->backing_dev_info;
2375 : : unsigned long flags;
2376 : :
2377 : 958667 : spin_lock_irqsave(&mapping->tree_lock, flags);
2378 : : ret = TestClearPageWriteback(page);
2379 [ + - ]: 958668 : if (ret) {
2380 : 958668 : radix_tree_tag_clear(&mapping->page_tree,
2381 : : page_index(page),
2382 : : PAGECACHE_TAG_WRITEBACK);
2383 [ + - ]: 958668 : if (bdi_cap_account_writeback(bdi)) {
2384 : : __dec_bdi_stat(bdi, BDI_WRITEBACK);
2385 : : __bdi_writeout_inc(bdi);
2386 : : }
2387 : : }
2388 : : spin_unlock_irqrestore(&mapping->tree_lock, flags);
2389 : : } else {
2390 : : ret = TestClearPageWriteback(page);
2391 : : }
2392 [ + - ]: 958668 : if (ret) {
2393 : : mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2394 : 958668 : dec_zone_page_state(page, NR_WRITEBACK);
2395 : 958668 : inc_zone_page_state(page, NR_WRITTEN);
2396 : : }
2397 : : mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
2398 : 958668 : return ret;
2399 : : }
2400 : :
2401 : 0 : int test_set_page_writeback(struct page *page)
2402 : : {
2403 : 958612 : struct address_space *mapping = page_mapping(page);
2404 : : int ret;
2405 : : bool locked;
2406 : : unsigned long memcg_flags;
2407 : :
2408 : : mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
2409 [ + - ]: 958611 : if (mapping) {
2410 : 1917221 : struct backing_dev_info *bdi = mapping->backing_dev_info;
2411 : : unsigned long flags;
2412 : :
2413 : 958611 : spin_lock_irqsave(&mapping->tree_lock, flags);
2414 : : ret = TestSetPageWriteback(page);
2415 [ + ]: 958541 : if (!ret) {
2416 : 958544 : radix_tree_tag_set(&mapping->page_tree,
2417 : : page_index(page),
2418 : : PAGECACHE_TAG_WRITEBACK);
2419 [ + ]: 958610 : if (bdi_cap_account_writeback(bdi))
2420 : : __inc_bdi_stat(bdi, BDI_WRITEBACK);
2421 : : }
2422 [ + + ]: 958644 : if (!PageDirty(page))
2423 : 915549 : radix_tree_tag_clear(&mapping->page_tree,
2424 : : page_index(page),
2425 : : PAGECACHE_TAG_DIRTY);
2426 : 958624 : radix_tree_tag_clear(&mapping->page_tree,
2427 : : page_index(page),
2428 : : PAGECACHE_TAG_TOWRITE);
2429 : : spin_unlock_irqrestore(&mapping->tree_lock, flags);
2430 : : } else {
2431 : : ret = TestSetPageWriteback(page);
2432 : : }
2433 [ + - ]: 958648 : if (!ret)
2434 : : account_page_writeback(page);
2435 : : mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
2436 : 958645 : return ret;
2437 : :
2438 : : }
2439 : : EXPORT_SYMBOL(test_set_page_writeback);
2440 : :
2441 : : /*
2442 : : * Return true if any of the pages in the mapping are marked with the
2443 : : * passed tag.
2444 : : */
2445 : 0 : int mapping_tagged(struct address_space *mapping, int tag)
2446 : : {
2447 : 246515 : return radix_tree_tagged(&mapping->page_tree, tag);
2448 : : }
2449 : : EXPORT_SYMBOL(mapping_tagged);
2450 : :
2451 : : /**
2452 : : * wait_for_stable_page() - wait for writeback to finish, if necessary.
2453 : : * @page: The page to wait on.
2454 : : *
2455 : : * This function determines if the given page is related to a backing device
2456 : : * that requires page contents to be held stable during writeback. If so, then
2457 : : * it will wait for any pending writeback to complete.
2458 : : */
2459 : 0 : void wait_for_stable_page(struct page *page)
2460 : : {
2461 : 12742460 : struct address_space *mapping = page_mapping(page);
2462 : 12745161 : struct backing_dev_info *bdi = mapping->backing_dev_info;
2463 : :
2464 [ - + ]: 12745161 : if (!bdi_cap_stable_pages_required(bdi))
2465 : 2701 : return;
2466 : :
2467 : : wait_on_page_writeback(page);
2468 : : }
2469 : : EXPORT_SYMBOL_GPL(wait_for_stable_page);
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