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 : 0 : static unsigned long highmem_dirtyable_memory(unsigned long total)
195 : : {
196 : : #ifdef CONFIG_HIGHMEM
197 : : int node;
198 : : unsigned long x = 0;
199 : :
200 [ + + ]: 2033760 : for_each_node_state(node, N_HIGH_MEMORY) {
201 : : struct zone *z =
202 : : &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
203 : :
204 : 1016884 : x += zone_page_state(z, NR_FREE_PAGES) +
205 : 1016873 : zone_reclaimable_pages(z) - z->dirty_balance_reserve;
206 : : }
207 : : /*
208 : : * Unreclaimable memory (kernel memory or anonymous memory
209 : : * without swap) can bring down the dirtyable pages below
210 : : * the zone's dirty balance reserve and the above calculation
211 : : * will underflow. However we still want to add in nodes
212 : : * which are below threshold (negative values) to get a more
213 : : * accurate calculation but make sure that the total never
214 : : * underflows.
215 : : */
216 [ + + ]: 1016887 : if ((long)x < 0)
217 : : x = 0;
218 : :
219 : : /*
220 : : * Make sure that the number of highmem pages is never larger
221 : : * than the number of the total dirtyable memory. This can only
222 : : * occur in very strange VM situations but we want to make sure
223 : : * that this does not occur.
224 : : */
225 : 1016887 : return min(x, total);
226 : : #else
227 : : return 0;
228 : : #endif
229 : : }
230 : :
231 : : /**
232 : : * global_dirtyable_memory - number of globally dirtyable pages
233 : : *
234 : : * Returns the global number of pages potentially available for dirty
235 : : * page cache. This is the base value for the global dirty limits.
236 : : */
237 : 0 : static unsigned long global_dirtyable_memory(void)
238 : : {
239 : : unsigned long x;
240 : :
241 : 1016886 : x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
242 : 1016886 : x -= min(x, dirty_balance_reserve);
243 : :
244 [ + ]: 1016886 : if (!vm_highmem_is_dirtyable)
245 : 1016898 : x -= highmem_dirtyable_memory(x);
246 : :
247 : 1016878 : return x + 1; /* Ensure that we never return 0 */
248 : : }
249 : :
250 : : /*
251 : : * global_dirty_limits - background-writeback and dirty-throttling thresholds
252 : : *
253 : : * Calculate the dirty thresholds based on sysctl parameters
254 : : * - vm.dirty_background_ratio or vm.dirty_background_bytes
255 : : * - vm.dirty_ratio or vm.dirty_bytes
256 : : * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
257 : : * real-time tasks.
258 : : */
259 : 0 : void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
260 : : {
261 : : unsigned long background;
262 : : unsigned long dirty;
263 : : unsigned long uninitialized_var(available_memory);
264 : : struct task_struct *tsk;
265 : :
266 [ - + ][ # # ]: 1016926 : if (!vm_dirty_bytes || !dirty_background_bytes)
267 : 1016921 : available_memory = global_dirtyable_memory();
268 : :
269 [ + + ]: 1016912 : if (vm_dirty_bytes)
270 : 11 : dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
271 : : else
272 : 1016901 : dirty = (vm_dirty_ratio * available_memory) / 100;
273 : :
274 [ - + ]: 1016912 : if (dirty_background_bytes)
275 : 0 : background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
276 : : else
277 : 1016912 : background = (dirty_background_ratio * available_memory) / 100;
278 : :
279 [ + + ]: 1016912 : if (background >= dirty)
280 : 987056 : background = dirty / 2;
281 : 1016912 : tsk = current;
282 [ + ][ + + ]: 2033833 : if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
283 : 0 : background += background / 4;
284 : 0 : dirty += dirty / 4;
285 : : }
286 : 1016912 : *pbackground = background;
287 : 1016912 : *pdirty = dirty;
288 : : trace_global_dirty_state(background, dirty);
289 : 1016912 : }
290 : :
291 : : /**
292 : : * zone_dirtyable_memory - number of dirtyable pages in a zone
293 : : * @zone: the zone
294 : : *
295 : : * Returns the zone's number of pages potentially available for dirty
296 : : * page cache. This is the base value for the per-zone dirty limits.
297 : : */
298 : 0 : static unsigned long zone_dirtyable_memory(struct zone *zone)
299 : : {
300 : : /*
301 : : * The effective global number of dirtyable pages may exclude
302 : : * highmem as a big-picture measure to keep the ratio between
303 : : * dirty memory and lowmem reasonable.
304 : : *
305 : : * But this function is purely about the individual zone and a
306 : : * highmem zone can hold its share of dirty pages, so we don't
307 : : * care about vm_highmem_is_dirtyable here.
308 : : */
309 : 1675602 : unsigned long nr_pages = zone_page_state(zone, NR_FREE_PAGES) +
310 : 1675600 : zone_reclaimable_pages(zone);
311 : :
312 : : /* don't allow this to underflow */
313 : 1675602 : nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
314 : 1675602 : return nr_pages;
315 : : }
316 : :
317 : : /**
318 : : * zone_dirty_limit - maximum number of dirty pages allowed in a zone
319 : : * @zone: the zone
320 : : *
321 : : * Returns the maximum number of dirty pages allowed in a zone, based
322 : : * on the zone's dirtyable memory.
323 : : */
324 : 0 : static unsigned long zone_dirty_limit(struct zone *zone)
325 : : {
326 : 1675600 : unsigned long zone_memory = zone_dirtyable_memory(zone);
327 : 1675609 : struct task_struct *tsk = current;
328 : : unsigned long dirty;
329 : :
330 [ - + ]: 1675609 : if (vm_dirty_bytes)
331 : 0 : dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
332 : 0 : zone_memory / global_dirtyable_memory();
333 : : else
334 : 1675609 : dirty = vm_dirty_ratio * zone_memory / 100;
335 : :
336 [ + ][ + + ]: 3351222 : if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
337 : 0 : dirty += dirty / 4;
338 : :
339 : 9 : return dirty;
340 : : }
341 : :
342 : : /**
343 : : * zone_dirty_ok - tells whether a zone is within its dirty limits
344 : : * @zone: the zone to check
345 : : *
346 : : * Returns %true when the dirty pages in @zone are within the zone's
347 : : * dirty limit, %false if the limit is exceeded.
348 : : */
349 : 0 : bool zone_dirty_ok(struct zone *zone)
350 : : {
351 : 1675593 : unsigned long limit = zone_dirty_limit(zone);
352 : :
353 : 36 : return zone_page_state(zone, NR_FILE_DIRTY) +
354 : 18 : zone_page_state(zone, NR_UNSTABLE_NFS) +
355 : : zone_page_state(zone, NR_WRITEBACK) <= limit;
356 : : }
357 : :
358 : 0 : int dirty_background_ratio_handler(struct ctl_table *table, int write,
359 : : void __user *buffer, size_t *lenp,
360 : : loff_t *ppos)
361 : : {
362 : : int ret;
363 : :
364 : 2 : ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
365 [ - + ]: 2 : if (ret == 0 && write)
366 : 0 : dirty_background_bytes = 0;
367 : 0 : return ret;
368 : : }
369 : :
370 : 0 : int dirty_background_bytes_handler(struct ctl_table *table, int write,
371 : : void __user *buffer, size_t *lenp,
372 : : loff_t *ppos)
373 : : {
374 : : int ret;
375 : :
376 : 2 : ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
377 [ - + ]: 2 : if (ret == 0 && write)
378 : 0 : dirty_background_ratio = 0;
379 : 0 : return ret;
380 : : }
381 : :
382 : 0 : int dirty_ratio_handler(struct ctl_table *table, int write,
383 : : void __user *buffer, size_t *lenp,
384 : : loff_t *ppos)
385 : : {
386 : 2 : int old_ratio = vm_dirty_ratio;
387 : : int ret;
388 : :
389 : 2 : ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
390 [ - + ][ # # ]: 2 : if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
391 : 0 : writeback_set_ratelimit();
392 : 0 : vm_dirty_bytes = 0;
393 : : }
394 : 0 : return ret;
395 : : }
396 : :
397 : 0 : int dirty_bytes_handler(struct ctl_table *table, int write,
398 : : void __user *buffer, size_t *lenp,
399 : : loff_t *ppos)
400 : : {
401 : 2 : unsigned long old_bytes = vm_dirty_bytes;
402 : : int ret;
403 : :
404 : 2 : ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
405 [ - + ][ # # ]: 2 : if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
406 : 0 : writeback_set_ratelimit();
407 : 0 : vm_dirty_ratio = 0;
408 : : }
409 : 0 : return ret;
410 : : }
411 : :
412 : 0 : static unsigned long wp_next_time(unsigned long cur_time)
413 : : {
414 : 3261 : cur_time += VM_COMPLETIONS_PERIOD_LEN;
415 : : /* 0 has a special meaning... */
416 [ + - ][ + - ]: 3261 : if (!cur_time)
417 : : return 1;
418 : 201 : return cur_time;
419 : : }
420 : :
421 : : /*
422 : : * Increment the BDI's writeout completion count and the global writeout
423 : : * completion count. Called from test_clear_page_writeback().
424 : : */
425 : : static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
426 : : {
427 : : __inc_bdi_stat(bdi, BDI_WRITTEN);
428 : 988652 : __fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
429 : 988652 : bdi->max_prop_frac);
430 : : /* First event after period switching was turned off? */
431 [ + + # # ]: 988652 : if (!unlikely(writeout_period_time)) {
432 : : /*
433 : : * We can race with other __bdi_writeout_inc calls here but
434 : : * it does not cause any harm since the resulting time when
435 : : * timer will fire and what is in writeout_period_time will be
436 : : * roughly the same.
437 : : */
438 : 201 : writeout_period_time = wp_next_time(jiffies);
439 : 201 : mod_timer(&writeout_period_timer, writeout_period_time);
440 : : }
441 : : }
442 : :
443 : 0 : void bdi_writeout_inc(struct backing_dev_info *bdi)
444 : : {
445 : : unsigned long flags;
446 : :
447 : : local_irq_save(flags);
448 : : __bdi_writeout_inc(bdi);
449 [ # # ]: 0 : local_irq_restore(flags);
450 : 0 : }
451 : : EXPORT_SYMBOL_GPL(bdi_writeout_inc);
452 : :
453 : : /*
454 : : * Obtain an accurate fraction of the BDI's portion.
455 : : */
456 : : static void bdi_writeout_fraction(struct backing_dev_info *bdi,
457 : : long *numerator, long *denominator)
458 : : {
459 : 8991 : fprop_fraction_percpu(&writeout_completions, &bdi->completions,
460 : : numerator, denominator);
461 : : }
462 : :
463 : : /*
464 : : * On idle system, we can be called long after we scheduled because we use
465 : : * deferred timers so count with missed periods.
466 : : */
467 : 0 : static void writeout_period(unsigned long t)
468 : : {
469 : 3260 : int miss_periods = (jiffies - writeout_period_time) /
470 : : VM_COMPLETIONS_PERIOD_LEN;
471 : :
472 [ + + ]: 3260 : if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
473 : 6120 : writeout_period_time = wp_next_time(writeout_period_time +
474 : 3060 : miss_periods * VM_COMPLETIONS_PERIOD_LEN);
475 : 3060 : mod_timer(&writeout_period_timer, writeout_period_time);
476 : : } else {
477 : : /*
478 : : * Aging has zeroed all fractions. Stop wasting CPU on period
479 : : * updates.
480 : : */
481 : 200 : writeout_period_time = 0;
482 : : }
483 : 3260 : }
484 : :
485 : : /*
486 : : * bdi_min_ratio keeps the sum of the minimum dirty shares of all
487 : : * registered backing devices, which, for obvious reasons, can not
488 : : * exceed 100%.
489 : : */
490 : : static unsigned int bdi_min_ratio;
491 : :
492 : 0 : int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
493 : : {
494 : : int ret = 0;
495 : :
496 : : spin_lock_bh(&bdi_lock);
497 [ # # ]: 0 : if (min_ratio > bdi->max_ratio) {
498 : : ret = -EINVAL;
499 : : } else {
500 : 0 : min_ratio -= bdi->min_ratio;
501 [ # # ]: 0 : if (bdi_min_ratio + min_ratio < 100) {
502 : 0 : bdi_min_ratio += min_ratio;
503 : 0 : bdi->min_ratio += min_ratio;
504 : : } else {
505 : : ret = -EINVAL;
506 : : }
507 : : }
508 : : spin_unlock_bh(&bdi_lock);
509 : :
510 : 0 : return ret;
511 : : }
512 : :
513 : 0 : int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
514 : : {
515 : : int ret = 0;
516 : :
517 [ # # ]: 0 : if (max_ratio > 100)
518 : : return -EINVAL;
519 : :
520 : : spin_lock_bh(&bdi_lock);
521 [ # # ]: 0 : if (bdi->min_ratio > max_ratio) {
522 : : ret = -EINVAL;
523 : : } else {
524 : 0 : bdi->max_ratio = max_ratio;
525 : 0 : bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
526 : : }
527 : : spin_unlock_bh(&bdi_lock);
528 : :
529 : 0 : return ret;
530 : : }
531 : : EXPORT_SYMBOL(bdi_set_max_ratio);
532 : :
533 : : static unsigned long dirty_freerun_ceiling(unsigned long thresh,
534 : : unsigned long bg_thresh)
535 : : {
536 : 29582 : return (thresh + bg_thresh) / 2;
537 : : }
538 : :
539 : : static unsigned long hard_dirty_limit(unsigned long thresh)
540 : : {
541 : 993845 : return max(thresh, global_dirty_limit);
542 : : }
543 : :
544 : : /**
545 : : * bdi_dirty_limit - @bdi's share of dirty throttling threshold
546 : : * @bdi: the backing_dev_info to query
547 : : * @dirty: global dirty limit in pages
548 : : *
549 : : * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
550 : : * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
551 : : *
552 : : * Note that balance_dirty_pages() will only seriously take it as a hard limit
553 : : * when sleeping max_pause per page is not enough to keep the dirty pages under
554 : : * control. For example, when the device is completely stalled due to some error
555 : : * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
556 : : * In the other normal situations, it acts more gently by throttling the tasks
557 : : * more (rather than completely block them) when the bdi dirty pages go high.
558 : : *
559 : : * It allocates high/low dirty limits to fast/slow devices, in order to prevent
560 : : * - starving fast devices
561 : : * - piling up dirty pages (that will take long time to sync) on slow devices
562 : : *
563 : : * The bdi's share of dirty limit will be adapting to its throughput and
564 : : * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
565 : : */
566 : 0 : unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
567 : : {
568 : : u64 bdi_dirty;
569 : : long numerator, denominator;
570 : :
571 : : /*
572 : : * Calculate this BDI's share of the dirty ratio.
573 : : */
574 : : bdi_writeout_fraction(bdi, &numerator, &denominator);
575 : :
576 : 17982 : bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
577 : 17982 : bdi_dirty *= numerator;
578 [ - + ][ # # ]: 17982 : do_div(bdi_dirty, denominator);
[ - + ][ - + ]
[ - + ][ - + ]
[ - + ][ - + ]
[ - + ][ - + ]
[ - - ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ]
579 : :
580 : 8991 : bdi_dirty += (dirty * bdi->min_ratio) / 100;
581 [ - + ]: 8991 : if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
582 : : bdi_dirty = dirty * bdi->max_ratio / 100;
583 : :
584 : 8991 : return bdi_dirty;
585 : : }
586 : :
587 : : /*
588 : : * setpoint - dirty 3
589 : : * f(dirty) := 1.0 + (----------------)
590 : : * limit - setpoint
591 : : *
592 : : * it's a 3rd order polynomial that subjects to
593 : : *
594 : : * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
595 : : * (2) f(setpoint) = 1.0 => the balance point
596 : : * (3) f(limit) = 0 => the hard limit
597 : : * (4) df/dx <= 0 => negative feedback control
598 : : * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
599 : : * => fast response on large errors; small oscillation near setpoint
600 : : */
601 : : static inline long long pos_ratio_polynom(unsigned long setpoint,
602 : : unsigned long dirty,
603 : : unsigned long limit)
604 : : {
605 : : long long pos_ratio;
606 : : long x;
607 : :
608 : 20224 : x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
609 : 5056 : limit - setpoint + 1);
610 : 10112 : pos_ratio = x;
611 : 10112 : pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
612 : 10112 : pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
613 : 10112 : pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
614 : :
615 : 10112 : return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
616 : : }
617 : :
618 : : /*
619 : : * Dirty position control.
620 : : *
621 : : * (o) global/bdi setpoints
622 : : *
623 : : * We want the dirty pages be balanced around the global/bdi setpoints.
624 : : * When the number of dirty pages is higher/lower than the setpoint, the
625 : : * dirty position control ratio (and hence task dirty ratelimit) will be
626 : : * decreased/increased to bring the dirty pages back to the setpoint.
627 : : *
628 : : * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
629 : : *
630 : : * if (dirty < setpoint) scale up pos_ratio
631 : : * if (dirty > setpoint) scale down pos_ratio
632 : : *
633 : : * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
634 : : * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
635 : : *
636 : : * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
637 : : *
638 : : * (o) global control line
639 : : *
640 : : * ^ pos_ratio
641 : : * |
642 : : * | |<===== global dirty control scope ======>|
643 : : * 2.0 .............*
644 : : * | .*
645 : : * | . *
646 : : * | . *
647 : : * | . *
648 : : * | . *
649 : : * | . *
650 : : * 1.0 ................................*
651 : : * | . . *
652 : : * | . . *
653 : : * | . . *
654 : : * | . . *
655 : : * | . . *
656 : : * 0 +------------.------------------.----------------------*------------->
657 : : * freerun^ setpoint^ limit^ dirty pages
658 : : *
659 : : * (o) bdi control line
660 : : *
661 : : * ^ pos_ratio
662 : : * |
663 : : * | *
664 : : * | *
665 : : * | *
666 : : * | *
667 : : * | * |<=========== span ============>|
668 : : * 1.0 .......................*
669 : : * | . *
670 : : * | . *
671 : : * | . *
672 : : * | . *
673 : : * | . *
674 : : * | . *
675 : : * | . *
676 : : * | . *
677 : : * | . *
678 : : * | . *
679 : : * | . *
680 : : * 1/4 ...............................................* * * * * * * * * * * *
681 : : * | . .
682 : : * | . .
683 : : * | . .
684 : : * 0 +----------------------.-------------------------------.------------->
685 : : * bdi_setpoint^ x_intercept^
686 : : *
687 : : * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
688 : : * be smoothly throttled down to normal if it starts high in situations like
689 : : * - start writing to a slow SD card and a fast disk at the same time. The SD
690 : : * card's bdi_dirty may rush to many times higher than bdi_setpoint.
691 : : * - the bdi dirty thresh drops quickly due to change of JBOD workload
692 : : */
693 : 0 : static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
694 : : unsigned long thresh,
695 : : unsigned long bg_thresh,
696 : : unsigned long dirty,
697 : : unsigned long bdi_thresh,
698 : : unsigned long bdi_dirty)
699 : : {
700 : 5056 : unsigned long write_bw = bdi->avg_write_bandwidth;
701 : : unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
702 : : unsigned long limit = hard_dirty_limit(thresh);
703 : : unsigned long x_intercept;
704 : : unsigned long setpoint; /* dirty pages' target balance point */
705 : : unsigned long bdi_setpoint;
706 : : unsigned long span;
707 : : long long pos_ratio; /* for scaling up/down the rate limit */
708 : : long x;
709 : :
710 [ + - ]: 5056 : if (unlikely(dirty >= limit))
711 : : return 0;
712 : :
713 : : /*
714 : : * global setpoint
715 : : *
716 : : * See comment for pos_ratio_polynom().
717 : : */
718 : 5056 : setpoint = (freerun + limit) / 2;
719 : : pos_ratio = pos_ratio_polynom(setpoint, dirty, limit);
720 : :
721 : : /*
722 : : * The strictlimit feature is a tool preventing mistrusted filesystems
723 : : * from growing a large number of dirty pages before throttling. For
724 : : * such filesystems balance_dirty_pages always checks bdi counters
725 : : * against bdi limits. Even if global "nr_dirty" is under "freerun".
726 : : * This is especially important for fuse which sets bdi->max_ratio to
727 : : * 1% by default. Without strictlimit feature, fuse writeback may
728 : : * consume arbitrary amount of RAM because it is accounted in
729 : : * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
730 : : *
731 : : * Here, in bdi_position_ratio(), we calculate pos_ratio based on
732 : : * two values: bdi_dirty and bdi_thresh. Let's consider an example:
733 : : * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
734 : : * limits are set by default to 10% and 20% (background and throttle).
735 : : * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
736 : : * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
737 : : * about ~6K pages (as the average of background and throttle bdi
738 : : * limits). The 3rd order polynomial will provide positive feedback if
739 : : * bdi_dirty is under bdi_setpoint and vice versa.
740 : : *
741 : : * Note, that we cannot use global counters in these calculations
742 : : * because we want to throttle process writing to a strictlimit BDI
743 : : * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
744 : : * in the example above).
745 : : */
746 [ - + ]: 10112 : if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
747 : : long long bdi_pos_ratio;
748 : : unsigned long bdi_bg_thresh;
749 : :
750 [ # # ]: 0 : if (bdi_dirty < 8)
751 : 0 : return min_t(long long, pos_ratio * 2,
752 : : 2 << RATELIMIT_CALC_SHIFT);
753 : :
754 [ # # ]: 0 : if (bdi_dirty >= bdi_thresh)
755 : : return 0;
756 : :
757 : 0 : bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh);
758 : : bdi_setpoint = dirty_freerun_ceiling(bdi_thresh,
759 : : bdi_bg_thresh);
760 : :
761 [ # # ]: 0 : if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh)
762 : : return 0;
763 : :
764 : : bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
765 : : bdi_thresh);
766 : :
767 : : /*
768 : : * Typically, for strictlimit case, bdi_setpoint << setpoint
769 : : * and pos_ratio >> bdi_pos_ratio. In the other words global
770 : : * state ("dirty") is not limiting factor and we have to
771 : : * make decision based on bdi counters. But there is an
772 : : * important case when global pos_ratio should get precedence:
773 : : * global limits are exceeded (e.g. due to activities on other
774 : : * BDIs) while given strictlimit BDI is below limit.
775 : : *
776 : : * "pos_ratio * bdi_pos_ratio" would work for the case above,
777 : : * but it would look too non-natural for the case of all
778 : : * activity in the system coming from a single strictlimit BDI
779 : : * with bdi->max_ratio == 100%.
780 : : *
781 : : * Note that min() below somewhat changes the dynamics of the
782 : : * control system. Normally, pos_ratio value can be well over 3
783 : : * (when globally we are at freerun and bdi is well below bdi
784 : : * setpoint). Now the maximum pos_ratio in the same situation
785 : : * is 2. We might want to tweak this if we observe the control
786 : : * system is too slow to adapt.
787 : : */
788 : 0 : return min(pos_ratio, bdi_pos_ratio);
789 : : }
790 : :
791 : : /*
792 : : * We have computed basic pos_ratio above based on global situation. If
793 : : * the bdi is over/under its share of dirty pages, we want to scale
794 : : * pos_ratio further down/up. That is done by the following mechanism.
795 : : */
796 : :
797 : : /*
798 : : * bdi setpoint
799 : : *
800 : : * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
801 : : *
802 : : * x_intercept - bdi_dirty
803 : : * := --------------------------
804 : : * x_intercept - bdi_setpoint
805 : : *
806 : : * The main bdi control line is a linear function that subjects to
807 : : *
808 : : * (1) f(bdi_setpoint) = 1.0
809 : : * (2) k = - 1 / (8 * write_bw) (in single bdi case)
810 : : * or equally: x_intercept = bdi_setpoint + 8 * write_bw
811 : : *
812 : : * For single bdi case, the dirty pages are observed to fluctuate
813 : : * regularly within range
814 : : * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
815 : : * for various filesystems, where (2) can yield in a reasonable 12.5%
816 : : * fluctuation range for pos_ratio.
817 : : *
818 : : * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
819 : : * own size, so move the slope over accordingly and choose a slope that
820 : : * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
821 : : */
822 [ - + ]: 10112 : if (unlikely(bdi_thresh > thresh))
823 : : bdi_thresh = thresh;
824 : : /*
825 : : * It's very possible that bdi_thresh is close to 0 not because the
826 : : * device is slow, but that it has remained inactive for long time.
827 : : * Honour such devices a reasonable good (hopefully IO efficient)
828 : : * threshold, so that the occasional writes won't be blocked and active
829 : : * writes can rampup the threshold quickly.
830 : : */
831 : 10112 : bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
832 : : /*
833 : : * scale global setpoint to bdi's:
834 : : * bdi_setpoint = setpoint * bdi_thresh / thresh
835 : : */
836 : 15168 : x = div_u64((u64)bdi_thresh << 16, thresh + 1);
837 : 5056 : bdi_setpoint = setpoint * (u64)x >> 16;
838 : : /*
839 : : * Use span=(8*write_bw) in single bdi case as indicated by
840 : : * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
841 : : *
842 : : * bdi_thresh thresh - bdi_thresh
843 : : * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
844 : : * thresh thresh
845 : : */
846 : 5056 : span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
847 : 5056 : x_intercept = bdi_setpoint + span;
848 : :
849 [ + + ]: 10112 : if (bdi_dirty < x_intercept - span / 4) {
850 : 3515 : pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
851 : 3515 : x_intercept - bdi_setpoint + 1);
852 : : } else
853 : 1541 : pos_ratio /= 4;
854 : :
855 : : /*
856 : : * bdi reserve area, safeguard against dirty pool underrun and disk idle
857 : : * It may push the desired control point of global dirty pages higher
858 : : * than setpoint.
859 : : */
860 : 5056 : x_intercept = bdi_thresh / 2;
861 [ - + ]: 5056 : if (bdi_dirty < x_intercept) {
862 [ # # ]: 0 : if (bdi_dirty > x_intercept / 8)
863 : 0 : pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
864 : : else
865 : 0 : pos_ratio *= 8;
866 : : }
867 : :
868 : 5056 : return pos_ratio;
869 : : }
870 : :
871 : 0 : static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
872 : : unsigned long elapsed,
873 : : unsigned long written)
874 : : {
875 : : const unsigned long period = roundup_pow_of_two(3 * HZ);
876 : 1218 : unsigned long avg = bdi->avg_write_bandwidth;
877 : 1218 : unsigned long old = bdi->write_bandwidth;
878 : : u64 bw;
879 : :
880 : : /*
881 : : * bw = written * HZ / elapsed
882 : : *
883 : : * bw * elapsed + write_bandwidth * (period - elapsed)
884 : : * write_bandwidth = ---------------------------------------------------
885 : : * period
886 : : */
887 : 1218 : bw = written - bdi->written_stamp;
888 : 1218 : bw *= HZ;
889 [ + + ]: 1218 : if (unlikely(elapsed > period)) {
890 [ - + ][ # # ]: 6 : do_div(bw, elapsed);
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ]
891 : 6 : avg = bw;
892 : 6 : goto out;
893 : : }
894 : 1212 : bw += (u64)bdi->write_bandwidth * (period - elapsed);
895 : 1212 : bw >>= ilog2(period);
896 : :
897 : : /*
898 : : * one more level of smoothing, for filtering out sudden spikes
899 : : */
900 [ + + ][ + + ]: 1212 : if (avg > old && old >= (unsigned long)bw)
901 : 304 : avg -= (avg - old) >> 3;
902 : :
903 [ + ][ + + ]: 1212 : if (avg < old && old <= (unsigned long)bw)
904 : 236 : avg += (old - avg) >> 3;
905 : :
906 : : out:
907 : 0 : bdi->write_bandwidth = bw;
908 : 0 : bdi->avg_write_bandwidth = avg;
909 : 0 : }
910 : :
911 : : /*
912 : : * The global dirtyable memory and dirty threshold could be suddenly knocked
913 : : * down by a large amount (eg. on the startup of KVM in a swapless system).
914 : : * This may throw the system into deep dirty exceeded state and throttle
915 : : * heavy/light dirtiers alike. To retain good responsiveness, maintain
916 : : * global_dirty_limit for tracking slowly down to the knocked down dirty
917 : : * threshold.
918 : : */
919 : : static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
920 : : {
921 : 523 : unsigned long limit = global_dirty_limit;
922 : :
923 : : /*
924 : : * Follow up in one step.
925 : : */
926 [ + + ]: 1046 : if (limit < thresh) {
927 : : limit = thresh;
928 : : goto update;
929 : : }
930 : :
931 : : /*
932 : : * Follow down slowly. Use the higher one as the target, because thresh
933 : : * may drop below dirty. This is exactly the reason to introduce
934 : : * global_dirty_limit which is guaranteed to lie above the dirty pages.
935 : : */
936 : 497 : thresh = max(thresh, dirty);
937 [ + + ]: 497 : if (limit > thresh) {
938 : 476 : limit -= (limit - thresh) >> 5;
939 : : goto update;
940 : : }
941 : : return;
942 : : update:
943 : 502 : global_dirty_limit = limit;
944 : : }
945 : :
946 : 0 : static void global_update_bandwidth(unsigned long thresh,
947 : : unsigned long dirty,
948 : : unsigned long now)
949 : : {
950 : : static DEFINE_SPINLOCK(dirty_lock);
951 : : static unsigned long update_time;
952 : :
953 : : /*
954 : : * check locklessly first to optimize away locking for the most time
955 : : */
956 [ + - ]: 523 : if (time_before(now, update_time + BANDWIDTH_INTERVAL))
957 : 523 : return;
958 : :
959 : : spin_lock(&dirty_lock);
960 [ + ]: 523 : if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
961 : : update_dirty_limit(thresh, dirty);
962 : 523 : update_time = now;
963 : : }
964 : : spin_unlock(&dirty_lock);
965 : : }
966 : :
967 : : /*
968 : : * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
969 : : *
970 : : * Normal bdi tasks will be curbed at or below it in long term.
971 : : * Obviously it should be around (write_bw / N) when there are N dd tasks.
972 : : */
973 : 0 : static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
974 : : unsigned long thresh,
975 : : unsigned long bg_thresh,
976 : : unsigned long dirty,
977 : : unsigned long bdi_thresh,
978 : : unsigned long bdi_dirty,
979 : : unsigned long dirtied,
980 : : unsigned long elapsed)
981 : : {
982 : : unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
983 : : unsigned long limit = hard_dirty_limit(thresh);
984 : 523 : unsigned long setpoint = (freerun + limit) / 2;
985 : 523 : unsigned long write_bw = bdi->avg_write_bandwidth;
986 : 523 : unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
987 : : unsigned long dirty_rate;
988 : : unsigned long task_ratelimit;
989 : : unsigned long balanced_dirty_ratelimit;
990 : : unsigned long pos_ratio;
991 : : unsigned long step;
992 : : unsigned long x;
993 : :
994 : : /*
995 : : * The dirty rate will match the writeout rate in long term, except
996 : : * when dirty pages are truncated by userspace or re-dirtied by FS.
997 : : */
998 : 523 : dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
999 : :
1000 : 523 : pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
1001 : : bdi_thresh, bdi_dirty);
1002 : : /*
1003 : : * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1004 : : */
1005 : 2092 : task_ratelimit = (u64)dirty_ratelimit *
1006 : 1046 : pos_ratio >> RATELIMIT_CALC_SHIFT;
1007 : 1046 : task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1008 : :
1009 : : /*
1010 : : * A linear estimation of the "balanced" throttle rate. The theory is,
1011 : : * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
1012 : : * dirty_rate will be measured to be (N * task_ratelimit). So the below
1013 : : * formula will yield the balanced rate limit (write_bw / N).
1014 : : *
1015 : : * Note that the expanded form is not a pure rate feedback:
1016 : : * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1017 : : * but also takes pos_ratio into account:
1018 : : * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1019 : : *
1020 : : * (1) is not realistic because pos_ratio also takes part in balancing
1021 : : * the dirty rate. Consider the state
1022 : : * pos_ratio = 0.5 (3)
1023 : : * rate = 2 * (write_bw / N) (4)
1024 : : * If (1) is used, it will stuck in that state! Because each dd will
1025 : : * be throttled at
1026 : : * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1027 : : * yielding
1028 : : * dirty_rate = N * task_ratelimit = write_bw (6)
1029 : : * put (6) into (1) we get
1030 : : * rate_(i+1) = rate_(i) (7)
1031 : : *
1032 : : * So we end up using (2) to always keep
1033 : : * rate_(i+1) ~= (write_bw / N) (8)
1034 : : * regardless of the value of pos_ratio. As long as (8) is satisfied,
1035 : : * pos_ratio is able to drive itself to 1.0, which is not only where
1036 : : * the dirty count meet the setpoint, but also where the slope of
1037 : : * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1038 : : */
1039 : 1569 : balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1040 : 1046 : dirty_rate | 1);
1041 : : /*
1042 : : * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1043 : : */
1044 [ + + ]: 523 : if (unlikely(balanced_dirty_ratelimit > write_bw))
1045 : : balanced_dirty_ratelimit = write_bw;
1046 : :
1047 : : /*
1048 : : * We could safely do this and return immediately:
1049 : : *
1050 : : * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
1051 : : *
1052 : : * However to get a more stable dirty_ratelimit, the below elaborated
1053 : : * code makes use of task_ratelimit to filter out singular points and
1054 : : * limit the step size.
1055 : : *
1056 : : * The below code essentially only uses the relative value of
1057 : : *
1058 : : * task_ratelimit - dirty_ratelimit
1059 : : * = (pos_ratio - 1) * dirty_ratelimit
1060 : : *
1061 : : * which reflects the direction and size of dirty position error.
1062 : : */
1063 : :
1064 : : /*
1065 : : * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1066 : : * task_ratelimit is on the same side of dirty_ratelimit, too.
1067 : : * For example, when
1068 : : * - dirty_ratelimit > balanced_dirty_ratelimit
1069 : : * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1070 : : * lowering dirty_ratelimit will help meet both the position and rate
1071 : : * control targets. Otherwise, don't update dirty_ratelimit if it will
1072 : : * only help meet the rate target. After all, what the users ultimately
1073 : : * feel and care are stable dirty rate and small position error.
1074 : : *
1075 : : * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1076 : : * and filter out the singular points of balanced_dirty_ratelimit. Which
1077 : : * keeps jumping around randomly and can even leap far away at times
1078 : : * due to the small 200ms estimation period of dirty_rate (we want to
1079 : : * keep that period small to reduce time lags).
1080 : : */
1081 : : step = 0;
1082 : :
1083 : : /*
1084 : : * For strictlimit case, calculations above were based on bdi counters
1085 : : * and limits (starting from pos_ratio = bdi_position_ratio() and up to
1086 : : * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1087 : : * Hence, to calculate "step" properly, we have to use bdi_dirty as
1088 : : * "dirty" and bdi_setpoint as "setpoint".
1089 : : *
1090 : : * We rampup dirty_ratelimit forcibly if bdi_dirty is low because
1091 : : * it's possible that bdi_thresh is close to zero due to inactivity
1092 : : * of backing device (see the implementation of bdi_dirty_limit()).
1093 : : */
1094 [ - + ]: 523 : if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1095 : : dirty = bdi_dirty;
1096 [ # # ]: 0 : if (bdi_dirty < 8)
1097 : 0 : setpoint = bdi_dirty + 1;
1098 : : else
1099 : 0 : setpoint = (bdi_thresh +
1100 : 0 : bdi_dirty_limit(bdi, bg_thresh)) / 2;
1101 : : }
1102 : :
1103 [ + + ]: 523 : if (dirty < setpoint) {
1104 : 234 : x = min(bdi->balanced_dirty_ratelimit,
1105 : : min(balanced_dirty_ratelimit, task_ratelimit));
1106 [ + + ]: 234 : if (dirty_ratelimit < x)
1107 : 31 : step = x - dirty_ratelimit;
1108 : : } else {
1109 : 289 : x = max(bdi->balanced_dirty_ratelimit,
1110 : : max(balanced_dirty_ratelimit, task_ratelimit));
1111 [ + + ]: 289 : if (dirty_ratelimit > x)
1112 : 245 : step = dirty_ratelimit - x;
1113 : : }
1114 : :
1115 : : /*
1116 : : * Don't pursue 100% rate matching. It's impossible since the balanced
1117 : : * rate itself is constantly fluctuating. So decrease the track speed
1118 : : * when it gets close to the target. Helps eliminate pointless tremors.
1119 : : */
1120 : 523 : step >>= dirty_ratelimit / (2 * step + 1);
1121 : : /*
1122 : : * Limit the tracking speed to avoid overshooting.
1123 : : */
1124 : 523 : step = (step + 7) / 8;
1125 : :
1126 [ + + ]: 523 : if (dirty_ratelimit < balanced_dirty_ratelimit)
1127 : 89 : dirty_ratelimit += step;
1128 : : else
1129 : 434 : dirty_ratelimit -= step;
1130 : :
1131 : 523 : bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1132 : 523 : bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1133 : :
1134 : : trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
1135 : 523 : }
1136 : :
1137 : 0 : void __bdi_update_bandwidth(struct backing_dev_info *bdi,
1138 : : unsigned long thresh,
1139 : : unsigned long bg_thresh,
1140 : : unsigned long dirty,
1141 : : unsigned long bdi_thresh,
1142 : : unsigned long bdi_dirty,
1143 : : unsigned long start_time)
1144 : : {
1145 : 12792 : unsigned long now = jiffies;
1146 : 12792 : unsigned long elapsed = now - bdi->bw_time_stamp;
1147 : : unsigned long dirtied;
1148 : : unsigned long written;
1149 : :
1150 : : /*
1151 : : * rate-limit, only update once every 200ms.
1152 : : */
1153 [ + + ]: 12792 : if (elapsed < BANDWIDTH_INTERVAL)
1154 : 12792 : return;
1155 : :
1156 : 3584 : dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
1157 : 3584 : written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1158 : :
1159 : : /*
1160 : : * Skip quiet periods when disk bandwidth is under-utilized.
1161 : : * (at least 1s idle time between two flusher runs)
1162 : : */
1163 [ + + ][ + + ]: 3584 : if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1164 : : goto snapshot;
1165 : :
1166 [ + + ]: 1218 : if (thresh) {
1167 : 523 : global_update_bandwidth(thresh, dirty, now);
1168 : 523 : bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1169 : : bdi_thresh, bdi_dirty,
1170 : : dirtied, elapsed);
1171 : : }
1172 : 1218 : bdi_update_write_bandwidth(bdi, elapsed, written);
1173 : :
1174 : : snapshot:
1175 : 3584 : bdi->dirtied_stamp = dirtied;
1176 : 3584 : bdi->written_stamp = written;
1177 : 3584 : bdi->bw_time_stamp = now;
1178 : : }
1179 : :
1180 : 0 : static void bdi_update_bandwidth(struct backing_dev_info *bdi,
1181 : : unsigned long thresh,
1182 : : unsigned long bg_thresh,
1183 : : unsigned long dirty,
1184 : : unsigned long bdi_thresh,
1185 : : unsigned long bdi_dirty,
1186 : : unsigned long start_time)
1187 : : {
1188 [ + + ]: 4533 : if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1189 : 0 : return;
1190 : : spin_lock(&bdi->wb.list_lock);
1191 : 528 : __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1192 : : bdi_thresh, bdi_dirty, start_time);
1193 : : spin_unlock(&bdi->wb.list_lock);
1194 : : }
1195 : :
1196 : : /*
1197 : : * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1198 : : * will look to see if it needs to start dirty throttling.
1199 : : *
1200 : : * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1201 : : * global_page_state() too often. So scale it near-sqrt to the safety margin
1202 : : * (the number of pages we may dirty without exceeding the dirty limits).
1203 : : */
1204 : 0 : static unsigned long dirty_poll_interval(unsigned long dirty,
1205 : : unsigned long thresh)
1206 : : {
1207 [ + ]: 19471 : if (thresh > dirty)
1208 [ + + ][ - + ]: 58412 : return 1UL << (ilog2(thresh - dirty) >> 1);
[ + + ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ + - ][ + - ]
[ - - ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ]
1209 : :
1210 : : return 1;
1211 : : }
1212 : :
1213 : : static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
1214 : : unsigned long bdi_dirty)
1215 : : {
1216 : : unsigned long bw = bdi->avg_write_bandwidth;
1217 : : unsigned long t;
1218 : :
1219 : : /*
1220 : : * Limit pause time for small memory systems. If sleeping for too long
1221 : : * time, a small pool of dirty/writeback pages may go empty and disk go
1222 : : * idle.
1223 : : *
1224 : : * 8 serves as the safety ratio.
1225 : : */
1226 : 4533 : t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1227 : 4533 : t++;
1228 : :
1229 : 4533 : return min_t(unsigned long, t, MAX_PAUSE);
1230 : : }
1231 : :
1232 : 0 : static long bdi_min_pause(struct backing_dev_info *bdi,
1233 : : long max_pause,
1234 : : unsigned long task_ratelimit,
1235 : : unsigned long dirty_ratelimit,
1236 : : int *nr_dirtied_pause)
1237 : : {
1238 [ - + ][ # # ]: 4533 : long hi = ilog2(bdi->avg_write_bandwidth);
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ]
1239 [ - + ][ # # ]: 4533 : long lo = ilog2(bdi->dirty_ratelimit);
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ]
1240 : : long t; /* target pause */
1241 : : long pause; /* estimated next pause */
1242 : : int pages; /* target nr_dirtied_pause */
1243 : :
1244 : : /* target for 10ms pause on 1-dd case */
1245 : : t = max(1, HZ / 100);
1246 : :
1247 : : /*
1248 : : * Scale up pause time for concurrent dirtiers in order to reduce CPU
1249 : : * overheads.
1250 : : *
1251 : : * (N * 10ms) on 2^N concurrent tasks.
1252 : : */
1253 [ + + ]: 4533 : if (hi > lo)
1254 : 489 : t += (hi - lo) * (10 * HZ) / 1024;
1255 : :
1256 : : /*
1257 : : * This is a bit convoluted. We try to base the next nr_dirtied_pause
1258 : : * on the much more stable dirty_ratelimit. However the next pause time
1259 : : * will be computed based on task_ratelimit and the two rate limits may
1260 : : * depart considerably at some time. Especially if task_ratelimit goes
1261 : : * below dirty_ratelimit/2 and the target pause is max_pause, the next
1262 : : * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1263 : : * result task_ratelimit won't be executed faithfully, which could
1264 : : * eventually bring down dirty_ratelimit.
1265 : : *
1266 : : * We apply two rules to fix it up:
1267 : : * 1) try to estimate the next pause time and if necessary, use a lower
1268 : : * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1269 : : * nr_dirtied_pause will be "dancing" with task_ratelimit.
1270 : : * 2) limit the target pause time to max_pause/2, so that the normal
1271 : : * small fluctuations of task_ratelimit won't trigger rule (1) and
1272 : : * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1273 : : */
1274 : 4533 : t = min(t, 1 + max_pause / 2);
1275 : 4533 : pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1276 : :
1277 : : /*
1278 : : * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1279 : : * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1280 : : * When the 16 consecutive reads are often interrupted by some dirty
1281 : : * throttling pause during the async writes, cfq will go into idles
1282 : : * (deadline is fine). So push nr_dirtied_pause as high as possible
1283 : : * until reaches DIRTY_POLL_THRESH=32 pages.
1284 : : */
1285 [ + + ]: 4533 : if (pages < DIRTY_POLL_THRESH) {
1286 : : t = max_pause;
1287 : 2513 : pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1288 [ + - ]: 2513 : if (pages > DIRTY_POLL_THRESH) {
1289 : : pages = DIRTY_POLL_THRESH;
1290 : 2513 : t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1291 : : }
1292 : : }
1293 : :
1294 : 4533 : pause = HZ * pages / (task_ratelimit + 1);
1295 [ + ]: 4533 : if (pause > max_pause) {
1296 : : t = max_pause;
1297 : 28 : pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1298 : : }
1299 : :
1300 : 0 : *nr_dirtied_pause = pages;
1301 : : /*
1302 : : * The minimal pause time will normally be half the target pause time.
1303 : : */
1304 [ # # ]: 0 : return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1305 : : }
1306 : :
1307 : : static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
1308 : : unsigned long dirty_thresh,
1309 : : unsigned long background_thresh,
1310 : : unsigned long *bdi_dirty,
1311 : : unsigned long *bdi_thresh,
1312 : : unsigned long *bdi_bg_thresh)
1313 : : {
1314 : : unsigned long bdi_reclaimable;
1315 : :
1316 : : /*
1317 : : * bdi_thresh is not treated as some limiting factor as
1318 : : * dirty_thresh, due to reasons
1319 : : * - in JBOD setup, bdi_thresh can fluctuate a lot
1320 : : * - in a system with HDD and USB key, the USB key may somehow
1321 : : * go into state (bdi_dirty >> bdi_thresh) either because
1322 : : * bdi_dirty starts high, or because bdi_thresh drops low.
1323 : : * In this case we don't want to hard throttle the USB key
1324 : : * dirtiers for 100 seconds until bdi_dirty drops under
1325 : : * bdi_thresh. Instead the auxiliary bdi control line in
1326 : : * bdi_position_ratio() will let the dirtier task progress
1327 : : * at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1328 : : */
1329 : 4533 : *bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1330 : :
1331 : : if (bdi_bg_thresh)
1332 : 24003 : *bdi_bg_thresh = div_u64((u64)*bdi_thresh *
1333 : : background_thresh,
1334 : : dirty_thresh);
1335 : :
1336 : : /*
1337 : : * In order to avoid the stacked BDI deadlock we need
1338 : : * to ensure we accurately count the 'dirty' pages when
1339 : : * the threshold is low.
1340 : : *
1341 : : * Otherwise it would be possible to get thresh+n pages
1342 : : * reported dirty, even though there are thresh-m pages
1343 : : * actually dirty; with m+n sitting in the percpu
1344 : : * deltas.
1345 : : */
1346 [ # # ][ - + ]: 4533 : if (*bdi_thresh < 2 * bdi_stat_error(bdi)) {
1347 : 0 : bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1348 : 0 : *bdi_dirty = bdi_reclaimable +
1349 : : bdi_stat_sum(bdi, BDI_WRITEBACK);
1350 : : } else {
1351 : 4533 : bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1352 : 4532 : *bdi_dirty = bdi_reclaimable +
1353 : : bdi_stat(bdi, BDI_WRITEBACK);
1354 : : }
1355 : : }
1356 : :
1357 : : /*
1358 : : * balance_dirty_pages() must be called by processes which are generating dirty
1359 : : * data. It looks at the number of dirty pages in the machine and will force
1360 : : * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1361 : : * If we're over `background_thresh' then the writeback threads are woken to
1362 : : * perform some writeout.
1363 : : */
1364 : 0 : static void balance_dirty_pages(struct address_space *mapping,
1365 : : unsigned long pages_dirtied)
1366 : : {
1367 : : unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1368 : : unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
1369 : : unsigned long background_thresh;
1370 : : unsigned long dirty_thresh;
1371 : : long period;
1372 : : long pause;
1373 : : long max_pause;
1374 : : long min_pause;
1375 : : int nr_dirtied_pause;
1376 : : bool dirty_exceeded = false;
1377 : : unsigned long task_ratelimit;
1378 : : unsigned long dirty_ratelimit;
1379 : : unsigned long pos_ratio;
1380 : 33069 : struct backing_dev_info *bdi = mapping->backing_dev_info;
1381 : 24003 : bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1382 : 24003 : unsigned long start_time = jiffies;
1383 : :
1384 : : for (;;) {
1385 : 24003 : unsigned long now = jiffies;
1386 : : unsigned long uninitialized_var(bdi_thresh);
1387 : : unsigned long thresh;
1388 : : unsigned long uninitialized_var(bdi_dirty);
1389 : : unsigned long dirty;
1390 : : unsigned long bg_thresh;
1391 : :
1392 : : /*
1393 : : * Unstable writes are a feature of certain networked
1394 : : * filesystems (i.e. NFS) in which data may have been
1395 : : * written to the server's write cache, but has not yet
1396 : : * been flushed to permanent storage.
1397 : : */
1398 : 24003 : nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1399 : : global_page_state(NR_UNSTABLE_NFS);
1400 : 24003 : nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
1401 : :
1402 : 24003 : global_dirty_limits(&background_thresh, &dirty_thresh);
1403 : :
1404 [ - + ]: 24004 : if (unlikely(strictlimit)) {
1405 : 0 : bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1406 : : &bdi_dirty, &bdi_thresh, &bg_thresh);
1407 : :
1408 : : dirty = bdi_dirty;
1409 : : thresh = bdi_thresh;
1410 : : } else {
1411 : : dirty = nr_dirty;
1412 : 24004 : thresh = dirty_thresh;
1413 : 24004 : bg_thresh = background_thresh;
1414 : : }
1415 : :
1416 : : /*
1417 : : * Throttle it only when the background writeback cannot
1418 : : * catch-up. This avoids (excessively) small writeouts
1419 : : * when the bdi limits are ramping up in case of !strictlimit.
1420 : : *
1421 : : * In strictlimit case make decision based on the bdi counters
1422 : : * and limits. Small writeouts when the bdi limits are ramping
1423 : : * up are the price we consciously pay for strictlimit-ing.
1424 : : */
1425 [ + + ]: 24003 : if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh)) {
1426 : 19470 : current->dirty_paused_when = now;
1427 : 19470 : current->nr_dirtied = 0;
1428 : 19471 : current->nr_dirtied_pause =
1429 : 19470 : dirty_poll_interval(dirty, thresh);
1430 : : break;
1431 : : }
1432 : :
1433 [ - + ]: 4533 : if (unlikely(!writeback_in_progress(bdi)))
1434 : 0 : bdi_start_background_writeback(bdi);
1435 : :
1436 [ + - ]: 4533 : if (!strictlimit)
1437 : 4533 : bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1438 : : &bdi_dirty, &bdi_thresh, NULL);
1439 : :
1440 [ + + ][ + + ]: 4533 : dirty_exceeded = (bdi_dirty > bdi_thresh) &&
1441 [ + - ]: 2456 : ((nr_dirty > dirty_thresh) || strictlimit);
1442 [ + + ][ + + ]: 4533 : if (dirty_exceeded && !bdi->dirty_exceeded)
1443 : 2 : bdi->dirty_exceeded = 1;
1444 : :
1445 : 4533 : bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1446 : : nr_dirty, bdi_thresh, bdi_dirty,
1447 : : start_time);
1448 : :
1449 : 4533 : dirty_ratelimit = bdi->dirty_ratelimit;
1450 : 4533 : pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1451 : : background_thresh, nr_dirty,
1452 : : bdi_thresh, bdi_dirty);
1453 : 4533 : task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1454 : : RATELIMIT_CALC_SHIFT;
1455 : 4533 : max_pause = bdi_max_pause(bdi, bdi_dirty);
1456 : 4533 : min_pause = bdi_min_pause(bdi, max_pause,
1457 : : task_ratelimit, dirty_ratelimit,
1458 : : &nr_dirtied_pause);
1459 : :
1460 [ + - ]: 4533 : if (unlikely(task_ratelimit == 0)) {
1461 : : period = max_pause;
1462 : : pause = max_pause;
1463 : : goto pause;
1464 : : }
1465 : 4533 : period = HZ * pages_dirtied / task_ratelimit;
1466 : : pause = period;
1467 [ + - ]: 4533 : if (current->dirty_paused_when)
1468 : 4533 : pause -= now - current->dirty_paused_when;
1469 : : /*
1470 : : * For less than 1s think time (ext3/4 may block the dirtier
1471 : : * for up to 800ms from time to time on 1-HDD; so does xfs,
1472 : : * however at much less frequency), try to compensate it in
1473 : : * future periods by updating the virtual time; otherwise just
1474 : : * do a reset, as it may be a light dirtier.
1475 : : */
1476 [ + + ]: 4533 : if (pause < min_pause) {
1477 : 2563 : trace_balance_dirty_pages(bdi,
1478 : : dirty_thresh,
1479 : : background_thresh,
1480 : : nr_dirty,
1481 : : bdi_thresh,
1482 : : bdi_dirty,
1483 : : dirty_ratelimit,
1484 : : task_ratelimit,
1485 : : pages_dirtied,
1486 : : period,
1487 : 2563 : min(pause, 0L),
1488 : : start_time);
1489 [ + + ]: 2563 : if (pause < -HZ) {
1490 : 7 : current->dirty_paused_when = now;
1491 : 7 : current->nr_dirtied = 0;
1492 [ + + ]: 2556 : } else if (period) {
1493 : 887 : current->dirty_paused_when += period;
1494 : 887 : current->nr_dirtied = 0;
1495 [ + + ]: 1669 : } else if (current->nr_dirtied_pause <= pages_dirtied)
1496 : 4 : current->nr_dirtied_pause += pages_dirtied;
1497 : : break;
1498 : : }
1499 [ + + ]: 1970 : if (unlikely(pause > max_pause)) {
1500 : : /* for occasional dropped task_ratelimit */
1501 : 4 : now += min(pause - max_pause, max_pause);
1502 : : pause = max_pause;
1503 : : }
1504 : :
1505 : : pause:
1506 : 1970 : trace_balance_dirty_pages(bdi,
1507 : : dirty_thresh,
1508 : : background_thresh,
1509 : : nr_dirty,
1510 : : bdi_thresh,
1511 : : bdi_dirty,
1512 : : dirty_ratelimit,
1513 : : task_ratelimit,
1514 : : pages_dirtied,
1515 : : period,
1516 : : pause,
1517 : : start_time);
1518 : 1970 : __set_current_state(TASK_KILLABLE);
1519 : 1970 : io_schedule_timeout(pause);
1520 : :
1521 : 1970 : current->dirty_paused_when = now + pause;
1522 : 1970 : current->nr_dirtied = 0;
1523 : 1970 : current->nr_dirtied_pause = nr_dirtied_pause;
1524 : :
1525 : : /*
1526 : : * This is typically equal to (nr_dirty < dirty_thresh) and can
1527 : : * also keep "1000+ dd on a slow USB stick" under control.
1528 : : */
1529 [ - + ]: 1970 : if (task_ratelimit)
1530 : : break;
1531 : :
1532 : : /*
1533 : : * In the case of an unresponding NFS server and the NFS dirty
1534 : : * pages exceeds dirty_thresh, give the other good bdi's a pipe
1535 : : * to go through, so that tasks on them still remain responsive.
1536 : : *
1537 : : * In theory 1 page is enough to keep the comsumer-producer
1538 : : * pipe going: the flusher cleans 1 page => the task dirties 1
1539 : : * more page. However bdi_dirty has accounting errors. So use
1540 : : * the larger and more IO friendly bdi_stat_error.
1541 : : */
1542 [ # # ]: 0 : if (bdi_dirty <= bdi_stat_error(bdi))
1543 : : break;
1544 : :
1545 [ # # ]: 0 : if (fatal_signal_pending(current))
1546 : : break;
1547 : : }
1548 : :
1549 [ + + ][ + + ]: 24004 : if (!dirty_exceeded && bdi->dirty_exceeded)
1550 : 2 : bdi->dirty_exceeded = 0;
1551 : :
1552 [ + + ]: 24004 : if (writeback_in_progress(bdi))
1553 : 6352 : return;
1554 : :
1555 : : /*
1556 : : * In laptop mode, we wait until hitting the higher threshold before
1557 : : * starting background writeout, and then write out all the way down
1558 : : * to the lower threshold. So slow writers cause minimal disk activity.
1559 : : *
1560 : : * In normal mode, we start background writeout at the lower
1561 : : * background_thresh, to keep the amount of dirty memory low.
1562 : : */
1563 [ + - ]: 17652 : if (laptop_mode)
1564 : : return;
1565 : :
1566 [ + + ]: 17652 : if (nr_reclaimable > background_thresh)
1567 : 17652 : bdi_start_background_writeback(bdi);
1568 : : }
1569 : :
1570 : 0 : void set_page_dirty_balance(struct page *page, int page_mkwrite)
1571 : : {
1572 [ # # ][ # # ]: 0 : if (set_page_dirty(page) || page_mkwrite) {
1573 : 0 : struct address_space *mapping = page_mapping(page);
1574 : :
1575 [ # # ]: 0 : if (mapping)
1576 : 0 : balance_dirty_pages_ratelimited(mapping);
1577 : : }
1578 : 0 : }
1579 : :
1580 : : static DEFINE_PER_CPU(int, bdp_ratelimits);
1581 : :
1582 : : /*
1583 : : * Normal tasks are throttled by
1584 : : * loop {
1585 : : * dirty tsk->nr_dirtied_pause pages;
1586 : : * take a snap in balance_dirty_pages();
1587 : : * }
1588 : : * However there is a worst case. If every task exit immediately when dirtied
1589 : : * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1590 : : * called to throttle the page dirties. The solution is to save the not yet
1591 : : * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1592 : : * randomly into the running tasks. This works well for the above worst case,
1593 : : * as the new task will pick up and accumulate the old task's leaked dirty
1594 : : * count and eventually get throttled.
1595 : : */
1596 : : DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1597 : :
1598 : : /**
1599 : : * balance_dirty_pages_ratelimited - balance dirty memory state
1600 : : * @mapping: address_space which was dirtied
1601 : : *
1602 : : * Processes which are dirtying memory should call in here once for each page
1603 : : * which was newly dirtied. The function will periodically check the system's
1604 : : * dirty state and will initiate writeback if needed.
1605 : : *
1606 : : * On really big machines, get_writeback_state is expensive, so try to avoid
1607 : : * calling it too often (ratelimiting). But once we're over the dirty memory
1608 : : * limit we decrease the ratelimiting by a lot, to prevent individual processes
1609 : : * from overshooting the limit by (ratelimit_pages) each.
1610 : : */
1611 : 0 : void balance_dirty_pages_ratelimited(struct address_space *mapping)
1612 : : {
1613 : 7187395 : struct backing_dev_info *bdi = mapping->backing_dev_info;
1614 : : int ratelimit;
1615 : : int *p;
1616 : :
1617 [ + + ]: 7187395 : if (!bdi_cap_account_dirty(bdi))
1618 : 7187557 : return;
1619 : :
1620 : 7175767 : ratelimit = current->nr_dirtied_pause;
1621 [ + + ]: 7175767 : if (bdi->dirty_exceeded)
1622 : 4975 : ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1623 : :
1624 : 7175767 : preempt_disable();
1625 : : /*
1626 : : * This prevents one CPU to accumulate too many dirtied pages without
1627 : : * calling into balance_dirty_pages(), which can happen when there are
1628 : : * 1000+ tasks, all of them start dirtying pages at exactly the same
1629 : : * time, hence all honoured too large initial task->nr_dirtied_pause.
1630 : : */
1631 : 14351362 : p = &__get_cpu_var(bdp_ratelimits);
1632 [ + + ]: 7175681 : if (unlikely(current->nr_dirtied >= ratelimit))
1633 : 22347 : *p = 0;
1634 [ + + ]: 7153334 : else if (unlikely(*p >= ratelimit_pages)) {
1635 : 56 : *p = 0;
1636 : : ratelimit = 0;
1637 : : }
1638 : : /*
1639 : : * Pick up the dirtied pages by the exited tasks. This avoids lots of
1640 : : * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1641 : : * the dirty throttling and livelock other long-run dirtiers.
1642 : : */
1643 : 14351362 : p = &__get_cpu_var(dirty_throttle_leaks);
1644 [ + + ][ + + ]: 7175681 : if (*p > 0 && current->nr_dirtied < ratelimit) {
1645 : : unsigned long nr_pages_dirtied;
1646 : 14016 : nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1647 : 14016 : *p -= nr_pages_dirtied;
1648 : 14016 : current->nr_dirtied += nr_pages_dirtied;
1649 : : }
1650 : 7175681 : preempt_enable();
1651 : :
1652 [ + + ]: 7175929 : if (unlikely(current->nr_dirtied >= ratelimit))
1653 : 24004 : balance_dirty_pages(mapping, current->nr_dirtied);
1654 : : }
1655 : : EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1656 : :
1657 : 988274 : void throttle_vm_writeout(gfp_t gfp_mask)
1658 : : {
1659 : : unsigned long background_thresh;
1660 : : unsigned long dirty_thresh;
1661 : :
1662 : : for ( ; ; ) {
1663 : 988274 : global_dirty_limits(&background_thresh, &dirty_thresh);
1664 : 1976532 : dirty_thresh = hard_dirty_limit(dirty_thresh);
1665 : :
1666 : : /*
1667 : : * Boost the allowable dirty threshold a bit for page
1668 : : * allocators so they don't get DoS'ed by heavy writers
1669 : : */
1670 : 988266 : dirty_thresh += dirty_thresh / 10; /* wheeee... */
1671 : :
1672 [ - ]: 988266 : if (global_page_state(NR_UNSTABLE_NFS) +
1673 : : global_page_state(NR_WRITEBACK) <= dirty_thresh)
1674 : : break;
1675 : 0 : congestion_wait(BLK_RW_ASYNC, HZ/10);
1676 : :
1677 : : /*
1678 : : * The caller might hold locks which can prevent IO completion
1679 : : * or progress in the filesystem. So we cannot just sit here
1680 : : * waiting for IO to complete.
1681 : : */
1682 [ # # ]: 0 : if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1683 : : break;
1684 : : }
1685 : 0 : }
1686 : :
1687 : : /*
1688 : : * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1689 : : */
1690 : 0 : int dirty_writeback_centisecs_handler(ctl_table *table, int write,
1691 : : void __user *buffer, size_t *length, loff_t *ppos)
1692 : : {
1693 : 2 : proc_dointvec(table, write, buffer, length, ppos);
1694 : 2 : return 0;
1695 : : }
1696 : :
1697 : : #ifdef CONFIG_BLOCK
1698 : 0 : void laptop_mode_timer_fn(unsigned long data)
1699 : : {
1700 : 0 : struct request_queue *q = (struct request_queue *)data;
1701 : 0 : int nr_pages = global_page_state(NR_FILE_DIRTY) +
1702 : : global_page_state(NR_UNSTABLE_NFS);
1703 : :
1704 : : /*
1705 : : * We want to write everything out, not just down to the dirty
1706 : : * threshold
1707 : : */
1708 [ # # ]: 0 : if (bdi_has_dirty_io(&q->backing_dev_info))
1709 : 0 : bdi_start_writeback(&q->backing_dev_info, nr_pages,
1710 : : WB_REASON_LAPTOP_TIMER);
1711 : 0 : }
1712 : :
1713 : : /*
1714 : : * We've spun up the disk and we're in laptop mode: schedule writeback
1715 : : * of all dirty data a few seconds from now. If the flush is already scheduled
1716 : : * then push it back - the user is still using the disk.
1717 : : */
1718 : 0 : void laptop_io_completion(struct backing_dev_info *info)
1719 : : {
1720 : 0 : mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
1721 : 0 : }
1722 : :
1723 : : /*
1724 : : * We're in laptop mode and we've just synced. The sync's writes will have
1725 : : * caused another writeback to be scheduled by laptop_io_completion.
1726 : : * Nothing needs to be written back anymore, so we unschedule the writeback.
1727 : : */
1728 : 0 : void laptop_sync_completion(void)
1729 : : {
1730 : : struct backing_dev_info *bdi;
1731 : :
1732 : : rcu_read_lock();
1733 : :
1734 [ # # ]: 0 : list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1735 : 0 : del_timer(&bdi->laptop_mode_wb_timer);
1736 : :
1737 : : rcu_read_unlock();
1738 : 0 : }
1739 : : #endif
1740 : :
1741 : : /*
1742 : : * If ratelimit_pages is too high then we can get into dirty-data overload
1743 : : * if a large number of processes all perform writes at the same time.
1744 : : * If it is too low then SMP machines will call the (expensive)
1745 : : * get_writeback_state too often.
1746 : : *
1747 : : * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1748 : : * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
1749 : : * thresholds.
1750 : : */
1751 : :
1752 : 0 : void writeback_set_ratelimit(void)
1753 : : {
1754 : : unsigned long background_thresh;
1755 : : unsigned long dirty_thresh;
1756 : 0 : global_dirty_limits(&background_thresh, &dirty_thresh);
1757 : 0 : global_dirty_limit = dirty_thresh;
1758 : 0 : ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
1759 [ # # ]: 0 : if (ratelimit_pages < 16)
1760 : 0 : ratelimit_pages = 16;
1761 : 0 : }
1762 : :
1763 : : static int
1764 : 0 : ratelimit_handler(struct notifier_block *self, unsigned long action,
1765 : : void *hcpu)
1766 : : {
1767 : :
1768 [ # # ]: 0 : switch (action & ~CPU_TASKS_FROZEN) {
1769 : : case CPU_ONLINE:
1770 : : case CPU_DEAD:
1771 : 0 : writeback_set_ratelimit();
1772 : 0 : return NOTIFY_OK;
1773 : : default:
1774 : : return NOTIFY_DONE;
1775 : : }
1776 : : }
1777 : :
1778 : : static struct notifier_block ratelimit_nb = {
1779 : : .notifier_call = ratelimit_handler,
1780 : : .next = NULL,
1781 : : };
1782 : :
1783 : : /*
1784 : : * Called early on to tune the page writeback dirty limits.
1785 : : *
1786 : : * We used to scale dirty pages according to how total memory
1787 : : * related to pages that could be allocated for buffers (by
1788 : : * comparing nr_free_buffer_pages() to vm_total_pages.
1789 : : *
1790 : : * However, that was when we used "dirty_ratio" to scale with
1791 : : * all memory, and we don't do that any more. "dirty_ratio"
1792 : : * is now applied to total non-HIGHPAGE memory (by subtracting
1793 : : * totalhigh_pages from vm_total_pages), and as such we can't
1794 : : * get into the old insane situation any more where we had
1795 : : * large amounts of dirty pages compared to a small amount of
1796 : : * non-HIGHMEM memory.
1797 : : *
1798 : : * But we might still want to scale the dirty_ratio by how
1799 : : * much memory the box has..
1800 : : */
1801 : 0 : void __init page_writeback_init(void)
1802 : : {
1803 : 0 : writeback_set_ratelimit();
1804 : 0 : register_cpu_notifier(&ratelimit_nb);
1805 : :
1806 : 0 : fprop_global_init(&writeout_completions);
1807 : 0 : }
1808 : :
1809 : : /**
1810 : : * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1811 : : * @mapping: address space structure to write
1812 : : * @start: starting page index
1813 : : * @end: ending page index (inclusive)
1814 : : *
1815 : : * This function scans the page range from @start to @end (inclusive) and tags
1816 : : * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1817 : : * that write_cache_pages (or whoever calls this function) will then use
1818 : : * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1819 : : * used to avoid livelocking of writeback by a process steadily creating new
1820 : : * dirty pages in the file (thus it is important for this function to be quick
1821 : : * so that it can tag pages faster than a dirtying process can create them).
1822 : : */
1823 : : /*
1824 : : * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1825 : : */
1826 : 39076 : void tag_pages_for_writeback(struct address_space *mapping,
1827 : : pgoff_t start, pgoff_t end)
1828 : : {
1829 : : #define WRITEBACK_TAG_BATCH 4096
1830 : : unsigned long tagged;
1831 : :
1832 : : do {
1833 : : spin_lock_irq(&mapping->tree_lock);
1834 : 39131 : tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1835 : : &start, end, WRITEBACK_TAG_BATCH,
1836 : : PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1837 : : spin_unlock_irq(&mapping->tree_lock);
1838 [ - + ][ # # ]: 39131 : WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
[ # # ]
1839 : 39131 : cond_resched();
1840 : : /* We check 'start' to handle wrapping when end == ~0UL */
1841 [ + + ][ + - ]: 39128 : } while (tagged >= WRITEBACK_TAG_BATCH && start);
1842 : 39114 : }
1843 : : EXPORT_SYMBOL(tag_pages_for_writeback);
1844 : :
1845 : : /**
1846 : : * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
1847 : : * @mapping: address space structure to write
1848 : : * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1849 : : * @writepage: function called for each page
1850 : : * @data: data passed to writepage function
1851 : : *
1852 : : * If a page is already under I/O, write_cache_pages() skips it, even
1853 : : * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1854 : : * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1855 : : * and msync() need to guarantee that all the data which was dirty at the time
1856 : : * the call was made get new I/O started against them. If wbc->sync_mode is
1857 : : * WB_SYNC_ALL then we were called for data integrity and we must wait for
1858 : : * existing IO to complete.
1859 : : *
1860 : : * To avoid livelocks (when other process dirties new pages), we first tag
1861 : : * pages which should be written back with TOWRITE tag and only then start
1862 : : * writing them. For data-integrity sync we have to be careful so that we do
1863 : : * not miss some pages (e.g., because some other process has cleared TOWRITE
1864 : : * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1865 : : * by the process clearing the DIRTY tag (and submitting the page for IO).
1866 : : */
1867 : 0 : int write_cache_pages(struct address_space *mapping,
1868 : : struct writeback_control *wbc, writepage_t writepage,
1869 : : void *data)
1870 : : {
1871 : : int ret = 0;
1872 : : int done = 0;
1873 : : struct pagevec pvec;
1874 : : int nr_pages;
1875 : : pgoff_t uninitialized_var(writeback_index);
1876 : : pgoff_t index;
1877 : : pgoff_t end; /* Inclusive */
1878 : : pgoff_t done_index;
1879 : : int cycled;
1880 : : int range_whole = 0;
1881 : : int tag;
1882 : :
1883 : : pagevec_init(&pvec, 0);
1884 [ + + ]: 10676 : if (wbc->range_cyclic) {
1885 : 5726 : writeback_index = mapping->writeback_index; /* prev offset */
1886 : 5726 : index = writeback_index;
1887 [ + + ]: 5726 : if (index == 0)
1888 : : cycled = 1;
1889 : : else
1890 : : cycled = 0;
1891 : : end = -1;
1892 : : } else {
1893 : 4950 : index = wbc->range_start >> PAGE_CACHE_SHIFT;
1894 : 4950 : end = wbc->range_end >> PAGE_CACHE_SHIFT;
1895 [ + - ][ + + ]: 4950 : if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1896 : : range_whole = 1;
1897 : : cycled = 1; /* ignore range_cyclic tests */
1898 : : }
1899 [ + + ][ + - ]: 10676 : if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1900 : : tag = PAGECACHE_TAG_TOWRITE;
1901 : : else
1902 : : tag = PAGECACHE_TAG_DIRTY;
1903 : : retry:
1904 [ + + ][ - + ]: 10961 : if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
1905 : 3990 : tag_pages_for_writeback(mapping, index, end);
1906 : 10961 : done_index = index;
1907 [ + + ]: 33955 : while (!done && (index <= end)) {
1908 : : int i;
1909 : :
1910 : 22729 : nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
1911 : 22729 : min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1912 [ + + ]: 22728 : if (nr_pages == 0)
1913 : : break;
1914 : :
1915 [ + + ]: 90827 : for (i = 0; i < nr_pages; i++) {
1916 : 78511 : struct page *page = pvec.pages[i];
1917 : :
1918 : : /*
1919 : : * At this point, the page may be truncated or
1920 : : * invalidated (changing page->mapping to NULL), or
1921 : : * even swizzled back from swapper_space to tmpfs file
1922 : : * mapping. However, page->index will not change
1923 : : * because we have a reference on the page.
1924 : : */
1925 [ + ]: 78511 : if (page->index > end) {
1926 : : /*
1927 : : * can't be range_cyclic (1st pass) because
1928 : : * end == -1 in that case.
1929 : : */
1930 : : done = 1;
1931 : : break;
1932 : : }
1933 : :
1934 : : done_index = page->index;
1935 : :
1936 : : lock_page(page);
1937 : :
1938 : : /*
1939 : : * Page truncated or invalidated. We can freely skip it
1940 : : * then, even for data integrity operations: the page
1941 : : * has disappeared concurrently, so there could be no
1942 : : * real expectation of this data interity operation
1943 : : * even if there is now a new, dirty page at the same
1944 : : * pagecache address.
1945 : : */
1946 [ - + ]: 78529 : if (unlikely(page->mapping != mapping)) {
1947 : : continue_unlock:
1948 : 4652 : unlock_page(page);
1949 : 4653 : continue;
1950 : : }
1951 : :
1952 [ + + ]: 78529 : if (!PageDirty(page)) {
1953 : : /* someone wrote it for us */
1954 : : goto continue_unlock;
1955 : : }
1956 : :
1957 [ + + ]: 73877 : if (PageWriteback(page)) {
1958 [ - + ]: 1 : if (wbc->sync_mode != WB_SYNC_NONE)
1959 : : wait_on_page_writeback(page);
1960 : : else
1961 : : goto continue_unlock;
1962 : : }
1963 : :
1964 [ - + ]: 73877 : BUG_ON(PageWriteback(page));
1965 [ - + ]: 73877 : if (!clear_page_dirty_for_io(page))
1966 : : goto continue_unlock;
1967 : :
1968 : 73877 : trace_wbc_writepage(wbc, mapping->backing_dev_info);
1969 : 73877 : ret = (*writepage)(page, wbc, data);
1970 [ - + ]: 73877 : if (unlikely(ret)) {
1971 [ # # ]: 0 : if (ret == AOP_WRITEPAGE_ACTIVATE) {
1972 : 0 : unlock_page(page);
1973 : : ret = 0;
1974 : : } else {
1975 : : /*
1976 : : * done_index is set past this page,
1977 : : * so media errors will not choke
1978 : : * background writeout for the entire
1979 : : * file. This has consequences for
1980 : : * range_cyclic semantics (ie. it may
1981 : : * not be suitable for data integrity
1982 : : * writeout).
1983 : : */
1984 : 0 : done_index = page->index + 1;
1985 : : done = 1;
1986 : 0 : break;
1987 : : }
1988 : : }
1989 : :
1990 : : /*
1991 : : * We stop writing back only if we are not doing
1992 : : * integrity sync. In case of integrity sync we have to
1993 : : * keep going until we have written all the pages
1994 : : * we tagged for writeback prior to entering this loop.
1995 : : */
1996 [ + + ][ + ]: 73855 : if (--wbc->nr_to_write <= 0 &&
1997 : 2 : wbc->sync_mode == WB_SYNC_NONE) {
1998 : : done = 1;
1999 : : break;
2000 : : }
2001 : : }
2002 : : pagevec_release(&pvec);
2003 : 12318 : cond_resched();
2004 : : }
2005 [ + + ]: 10960 : if (!cycled && !done) {
2006 : : /*
2007 : : * range_cyclic:
2008 : : * We hit the last page and there is more work to be done: wrap
2009 : : * back to the start of the file
2010 : : */
2011 : : cycled = 1;
2012 : 285 : index = 0;
2013 : 285 : end = writeback_index - 1;
2014 : 285 : goto retry;
2015 : : }
2016 [ + + ][ + + ]: 10675 : if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
[ + + ]
2017 : 9643 : mapping->writeback_index = done_index;
2018 : :
2019 : 10675 : return ret;
2020 : : }
2021 : : EXPORT_SYMBOL(write_cache_pages);
2022 : :
2023 : : /*
2024 : : * Function used by generic_writepages to call the real writepage
2025 : : * function and set the mapping flags on error
2026 : : */
2027 : 0 : static int __writepage(struct page *page, struct writeback_control *wbc,
2028 : : void *data)
2029 : : {
2030 : : struct address_space *mapping = data;
2031 : 68469 : int ret = mapping->a_ops->writepage(page, wbc);
2032 : : mapping_set_error(mapping, ret);
2033 : 0 : return ret;
2034 : : }
2035 : :
2036 : : /**
2037 : : * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2038 : : * @mapping: address space structure to write
2039 : : * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2040 : : *
2041 : : * This is a library function, which implements the writepages()
2042 : : * address_space_operation.
2043 : : */
2044 : 0 : int generic_writepages(struct address_space *mapping,
2045 : : struct writeback_control *wbc)
2046 : : {
2047 : : struct blk_plug plug;
2048 : : int ret;
2049 : :
2050 : : /* deal with chardevs and other special file */
2051 [ + + ]: 7785 : if (!mapping->a_ops->writepage)
2052 : : return 0;
2053 : :
2054 : 5268 : blk_start_plug(&plug);
2055 : 5268 : ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2056 : 5267 : blk_finish_plug(&plug);
2057 : 5268 : return ret;
2058 : : }
2059 : :
2060 : : EXPORT_SYMBOL(generic_writepages);
2061 : :
2062 : 0 : int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2063 : : {
2064 : : int ret;
2065 : :
2066 [ + - ]: 122275 : if (wbc->nr_to_write <= 0)
2067 : : return 0;
2068 [ + + ]: 122275 : if (mapping->a_ops->writepages)
2069 : 119758 : ret = mapping->a_ops->writepages(mapping, wbc);
2070 : : else
2071 : 2517 : ret = generic_writepages(mapping, wbc);
2072 : 122257 : return ret;
2073 : : }
2074 : :
2075 : : /**
2076 : : * write_one_page - write out a single page and optionally wait on I/O
2077 : : * @page: the page to write
2078 : : * @wait: if true, wait on writeout
2079 : : *
2080 : : * The page must be locked by the caller and will be unlocked upon return.
2081 : : *
2082 : : * write_one_page() returns a negative error code if I/O failed.
2083 : : */
2084 : 0 : int write_one_page(struct page *page, int wait)
2085 : : {
2086 : 0 : struct address_space *mapping = page->mapping;
2087 : : int ret = 0;
2088 : 0 : struct writeback_control wbc = {
2089 : : .sync_mode = WB_SYNC_ALL,
2090 : : .nr_to_write = 1,
2091 : : };
2092 : :
2093 [ # # ]: 0 : BUG_ON(!PageLocked(page));
2094 : :
2095 [ # # ]: 0 : if (wait)
2096 : : wait_on_page_writeback(page);
2097 : :
2098 [ # # ]: 0 : if (clear_page_dirty_for_io(page)) {
2099 : : page_cache_get(page);
2100 : 0 : ret = mapping->a_ops->writepage(page, &wbc);
2101 [ # # ]: 0 : if (ret == 0 && wait) {
2102 : : wait_on_page_writeback(page);
2103 [ # # ]: 0 : if (PageError(page))
2104 : : ret = -EIO;
2105 : : }
2106 : 0 : page_cache_release(page);
2107 : : } else {
2108 : 0 : unlock_page(page);
2109 : : }
2110 : 0 : return ret;
2111 : : }
2112 : : EXPORT_SYMBOL(write_one_page);
2113 : :
2114 : : /*
2115 : : * For address_spaces which do not use buffers nor write back.
2116 : : */
2117 : 0 : int __set_page_dirty_no_writeback(struct page *page)
2118 : : {
2119 [ + + ]: 249517 : if (!PageDirty(page))
2120 : 11315 : return !TestSetPageDirty(page);
2121 : : return 0;
2122 : : }
2123 : :
2124 : : /*
2125 : : * Helper function for set_page_dirty family.
2126 : : * NOTE: This relies on being atomic wrt interrupts.
2127 : : */
2128 : 0 : void account_page_dirtied(struct page *page, struct address_space *mapping)
2129 : : {
2130 : : trace_writeback_dirty_page(page, mapping);
2131 : :
2132 [ + - ]: 2181138 : if (mapping_cap_account_dirty(mapping)) {
2133 : 2181138 : __inc_zone_page_state(page, NR_FILE_DIRTY);
2134 : 2181083 : __inc_zone_page_state(page, NR_DIRTIED);
2135 : 2180900 : __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
2136 : 2181066 : __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2137 : : task_io_account_write(PAGE_CACHE_SIZE);
2138 : 2181104 : current->nr_dirtied++;
2139 : 4362176 : this_cpu_inc(bdp_ratelimits);
2140 : : }
2141 : 2181133 : }
2142 : : EXPORT_SYMBOL(account_page_dirtied);
2143 : :
2144 : : /*
2145 : : * Helper function for set_page_writeback family.
2146 : : *
2147 : : * The caller must hold mem_cgroup_begin/end_update_page_stat() lock
2148 : : * while calling this function.
2149 : : * See test_set_page_writeback for example.
2150 : : *
2151 : : * NOTE: Unlike account_page_dirtied this does not rely on being atomic
2152 : : * wrt interrupts.
2153 : : */
2154 : 0 : void account_page_writeback(struct page *page)
2155 : : {
2156 : : mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2157 : 988644 : inc_zone_page_state(page, NR_WRITEBACK);
2158 : 0 : }
2159 : : EXPORT_SYMBOL(account_page_writeback);
2160 : :
2161 : : /*
2162 : : * For address_spaces which do not use buffers. Just tag the page as dirty in
2163 : : * its radix tree.
2164 : : *
2165 : : * This is also used when a single buffer is being dirtied: we want to set the
2166 : : * page dirty in that case, but not all the buffers. This is a "bottom-up"
2167 : : * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2168 : : *
2169 : : * Most callers have locked the page, which pins the address_space in memory.
2170 : : * But zap_pte_range() does not lock the page, however in that case the
2171 : : * mapping is pinned by the vma's ->vm_file reference.
2172 : : *
2173 : : * We take care to handle the case where the page was truncated from the
2174 : : * mapping by re-checking page_mapping() inside tree_lock.
2175 : : */
2176 : 0 : int __set_page_dirty_nobuffers(struct page *page)
2177 : : {
2178 [ + - ]: 42320 : if (!TestSetPageDirty(page)) {
2179 : 42320 : struct address_space *mapping = page_mapping(page);
2180 : : struct address_space *mapping2;
2181 : :
2182 [ + - ]: 42320 : if (!mapping)
2183 : : return 1;
2184 : :
2185 : : spin_lock_irq(&mapping->tree_lock);
2186 : 42320 : mapping2 = page_mapping(page);
2187 [ + - ]: 42320 : if (mapping2) { /* Race with truncate? */
2188 [ - + ]: 42320 : BUG_ON(mapping2 != mapping);
2189 [ - + ][ # # ]: 42320 : WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
[ - + ][ # # ]
[ # # ]
2190 : 42320 : account_page_dirtied(page, mapping);
2191 : 42320 : radix_tree_tag_set(&mapping->page_tree,
2192 : : page_index(page), PAGECACHE_TAG_DIRTY);
2193 : : }
2194 : : spin_unlock_irq(&mapping->tree_lock);
2195 [ + - ]: 42320 : if (mapping->host) {
2196 : : /* !PageAnon && !swapper_space */
2197 : 42320 : __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2198 : : }
2199 : : return 1;
2200 : : }
2201 : : return 0;
2202 : : }
2203 : : EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2204 : :
2205 : : /*
2206 : : * Call this whenever redirtying a page, to de-account the dirty counters
2207 : : * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2208 : : * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2209 : : * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2210 : : * control.
2211 : : */
2212 : 0 : void account_page_redirty(struct page *page)
2213 : : {
2214 : 84640 : struct address_space *mapping = page->mapping;
2215 [ + - ][ + - ]: 42320 : if (mapping && mapping_cap_account_dirty(mapping)) {
2216 : 42320 : current->nr_dirtied--;
2217 : 42320 : dec_zone_page_state(page, NR_DIRTIED);
2218 : 42320 : dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2219 : : }
2220 : 42320 : }
2221 : : EXPORT_SYMBOL(account_page_redirty);
2222 : :
2223 : : /*
2224 : : * When a writepage implementation decides that it doesn't want to write this
2225 : : * page for some reason, it should redirty the locked page via
2226 : : * redirty_page_for_writepage() and it should then unlock the page and return 0
2227 : : */
2228 : 0 : int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2229 : : {
2230 : 42320 : wbc->pages_skipped++;
2231 : 42320 : account_page_redirty(page);
2232 : 42320 : return __set_page_dirty_nobuffers(page);
2233 : : }
2234 : : EXPORT_SYMBOL(redirty_page_for_writepage);
2235 : :
2236 : : /*
2237 : : * Dirty a page.
2238 : : *
2239 : : * For pages with a mapping this should be done under the page lock
2240 : : * for the benefit of asynchronous memory errors who prefer a consistent
2241 : : * dirty state. This rule can be broken in some special cases,
2242 : : * but should be better not to.
2243 : : *
2244 : : * If the mapping doesn't provide a set_page_dirty a_op, then
2245 : : * just fall through and assume that it wants buffer_heads.
2246 : : */
2247 : 0 : int set_page_dirty(struct page *page)
2248 : : {
2249 : 1219886 : struct address_space *mapping = page_mapping(page);
2250 : :
2251 [ + + ]: 1219890 : if (likely(mapping)) {
2252 : 1042498 : int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2253 : : /*
2254 : : * readahead/lru_deactivate_page could remain
2255 : : * PG_readahead/PG_reclaim due to race with end_page_writeback
2256 : : * About readahead, if the page is written, the flags would be
2257 : : * reset. So no problem.
2258 : : * About lru_deactivate_page, if the page is redirty, the flag
2259 : : * will be reset. So no problem. but if the page is used by readahead
2260 : : * it will confuse readahead and make it restart the size rampup
2261 : : * process. But it's a trivial problem.
2262 : : */
2263 : : ClearPageReclaim(page);
2264 : : #ifdef CONFIG_BLOCK
2265 [ + + ]: 1042501 : if (!spd)
2266 : : spd = __set_page_dirty_buffers;
2267 : : #endif
2268 : 1042501 : return (*spd)(page);
2269 : : }
2270 [ + + ]: 177392 : if (!PageDirty(page)) {
2271 [ - + ]: 297 : if (!TestSetPageDirty(page))
2272 : : return 1;
2273 : : }
2274 : : return 0;
2275 : : }
2276 : : EXPORT_SYMBOL(set_page_dirty);
2277 : :
2278 : : /*
2279 : : * set_page_dirty() is racy if the caller has no reference against
2280 : : * page->mapping->host, and if the page is unlocked. This is because another
2281 : : * CPU could truncate the page off the mapping and then free the mapping.
2282 : : *
2283 : : * Usually, the page _is_ locked, or the caller is a user-space process which
2284 : : * holds a reference on the inode by having an open file.
2285 : : *
2286 : : * In other cases, the page should be locked before running set_page_dirty().
2287 : : */
2288 : 0 : int set_page_dirty_lock(struct page *page)
2289 : : {
2290 : : int ret;
2291 : :
2292 : : lock_page(page);
2293 : 177392 : ret = set_page_dirty(page);
2294 : 177392 : unlock_page(page);
2295 : 177392 : return ret;
2296 : : }
2297 : : EXPORT_SYMBOL(set_page_dirty_lock);
2298 : :
2299 : : /*
2300 : : * Clear a page's dirty flag, while caring for dirty memory accounting.
2301 : : * Returns true if the page was previously dirty.
2302 : : *
2303 : : * This is for preparing to put the page under writeout. We leave the page
2304 : : * tagged as dirty in the radix tree so that a concurrent write-for-sync
2305 : : * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2306 : : * implementation will run either set_page_writeback() or set_page_dirty(),
2307 : : * at which stage we bring the page's dirty flag and radix-tree dirty tag
2308 : : * back into sync.
2309 : : *
2310 : : * This incoherency between the page's dirty flag and radix-tree tag is
2311 : : * unfortunate, but it only exists while the page is locked.
2312 : : */
2313 : 0 : int clear_page_dirty_for_io(struct page *page)
2314 : : {
2315 : 988645 : struct address_space *mapping = page_mapping(page);
2316 : :
2317 [ - + ]: 988645 : BUG_ON(!PageLocked(page));
2318 : :
2319 [ + ][ + + ]: 988645 : if (mapping && mapping_cap_account_dirty(mapping)) {
2320 : : /*
2321 : : * Yes, Virginia, this is indeed insane.
2322 : : *
2323 : : * We use this sequence to make sure that
2324 : : * (a) we account for dirty stats properly
2325 : : * (b) we tell the low-level filesystem to
2326 : : * mark the whole page dirty if it was
2327 : : * dirty in a pagetable. Only to then
2328 : : * (c) clean the page again and return 1 to
2329 : : * cause the writeback.
2330 : : *
2331 : : * This way we avoid all nasty races with the
2332 : : * dirty bit in multiple places and clearing
2333 : : * them concurrently from different threads.
2334 : : *
2335 : : * Note! Normally the "set_page_dirty(page)"
2336 : : * has no effect on the actual dirty bit - since
2337 : : * that will already usually be set. But we
2338 : : * need the side effects, and it can help us
2339 : : * avoid races.
2340 : : *
2341 : : * We basically use the page "master dirty bit"
2342 : : * as a serialization point for all the different
2343 : : * threads doing their things.
2344 : : */
2345 [ + + ]: 988637 : if (page_mkclean(page))
2346 : 109218 : set_page_dirty(page);
2347 : : /*
2348 : : * We carefully synchronise fault handlers against
2349 : : * installing a dirty pte and marking the page dirty
2350 : : * at this point. We do this by having them hold the
2351 : : * page lock at some point after installing their
2352 : : * pte, but before marking the page dirty.
2353 : : * Pages are always locked coming in here, so we get
2354 : : * the desired exclusion. See mm/memory.c:do_wp_page()
2355 : : * for more comments.
2356 : : */
2357 [ + ]: 988608 : if (TestClearPageDirty(page)) {
2358 : 988635 : dec_zone_page_state(page, NR_FILE_DIRTY);
2359 : 988657 : dec_bdi_stat(mapping->backing_dev_info,
2360 : : BDI_RECLAIMABLE);
2361 : : return 1;
2362 : : }
2363 : : return 0;
2364 : : }
2365 : 0 : return TestClearPageDirty(page);
2366 : : }
2367 : : EXPORT_SYMBOL(clear_page_dirty_for_io);
2368 : :
2369 : 0 : int test_clear_page_writeback(struct page *page)
2370 : : {
2371 : 988652 : struct address_space *mapping = page_mapping(page);
2372 : : int ret;
2373 : : bool locked;
2374 : : unsigned long memcg_flags;
2375 : :
2376 : : mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
2377 [ + - ]: 988652 : if (mapping) {
2378 : 1977304 : struct backing_dev_info *bdi = mapping->backing_dev_info;
2379 : : unsigned long flags;
2380 : :
2381 : 988652 : spin_lock_irqsave(&mapping->tree_lock, flags);
2382 : : ret = TestClearPageWriteback(page);
2383 [ + - ]: 988652 : if (ret) {
2384 : 988652 : radix_tree_tag_clear(&mapping->page_tree,
2385 : : page_index(page),
2386 : : PAGECACHE_TAG_WRITEBACK);
2387 [ + - ]: 988652 : if (bdi_cap_account_writeback(bdi)) {
2388 : : __dec_bdi_stat(bdi, BDI_WRITEBACK);
2389 : : __bdi_writeout_inc(bdi);
2390 : : }
2391 : : }
2392 : : spin_unlock_irqrestore(&mapping->tree_lock, flags);
2393 : : } else {
2394 : : ret = TestClearPageWriteback(page);
2395 : : }
2396 [ + - ]: 988652 : if (ret) {
2397 : : mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
2398 : 988652 : dec_zone_page_state(page, NR_WRITEBACK);
2399 : 988652 : inc_zone_page_state(page, NR_WRITTEN);
2400 : : }
2401 : : mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
2402 : 988652 : return ret;
2403 : : }
2404 : :
2405 : 0 : int test_set_page_writeback(struct page *page)
2406 : : {
2407 : 988630 : struct address_space *mapping = page_mapping(page);
2408 : : int ret;
2409 : : bool locked;
2410 : : unsigned long memcg_flags;
2411 : :
2412 : : mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
2413 [ + - ]: 988629 : if (mapping) {
2414 : 1977270 : struct backing_dev_info *bdi = mapping->backing_dev_info;
2415 : : unsigned long flags;
2416 : :
2417 : 988629 : spin_lock_irqsave(&mapping->tree_lock, flags);
2418 : : ret = TestSetPageWriteback(page);
2419 [ + ]: 988646 : if (!ret) {
2420 : 988647 : radix_tree_tag_set(&mapping->page_tree,
2421 : : page_index(page),
2422 : : PAGECACHE_TAG_WRITEBACK);
2423 [ + ]: 988641 : if (bdi_cap_account_writeback(bdi))
2424 : : __inc_bdi_stat(bdi, BDI_WRITEBACK);
2425 : : }
2426 [ + + ]: 988659 : if (!PageDirty(page))
2427 : 946342 : radix_tree_tag_clear(&mapping->page_tree,
2428 : : page_index(page),
2429 : : PAGECACHE_TAG_DIRTY);
2430 : 988628 : radix_tree_tag_clear(&mapping->page_tree,
2431 : : page_index(page),
2432 : : PAGECACHE_TAG_TOWRITE);
2433 : : spin_unlock_irqrestore(&mapping->tree_lock, flags);
2434 : : } else {
2435 : : ret = TestSetPageWriteback(page);
2436 : : }
2437 [ + - ]: 988644 : if (!ret)
2438 : : account_page_writeback(page);
2439 : : mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
2440 : 988625 : return ret;
2441 : :
2442 : : }
2443 : : EXPORT_SYMBOL(test_set_page_writeback);
2444 : :
2445 : : /*
2446 : : * Return true if any of the pages in the mapping are marked with the
2447 : : * passed tag.
2448 : : */
2449 : 0 : int mapping_tagged(struct address_space *mapping, int tag)
2450 : : {
2451 : 342033 : return radix_tree_tagged(&mapping->page_tree, tag);
2452 : : }
2453 : : EXPORT_SYMBOL(mapping_tagged);
2454 : :
2455 : : /**
2456 : : * wait_for_stable_page() - wait for writeback to finish, if necessary.
2457 : : * @page: The page to wait on.
2458 : : *
2459 : : * This function determines if the given page is related to a backing device
2460 : : * that requires page contents to be held stable during writeback. If so, then
2461 : : * it will wait for any pending writeback to complete.
2462 : : */
2463 : 0 : void wait_for_stable_page(struct page *page)
2464 : : {
2465 : 14103329 : struct address_space *mapping = page_mapping(page);
2466 : 14103373 : struct backing_dev_info *bdi = mapping->backing_dev_info;
2467 : :
2468 [ - + ]: 14103373 : if (!bdi_cap_stable_pages_required(bdi))
2469 : 44 : return;
2470 : :
2471 : : wait_on_page_writeback(page);
2472 : : }
2473 : : EXPORT_SYMBOL_GPL(wait_for_stable_page);
|
