Root/
1 | /* |
2 | * mm/page-writeback.c |
3 | * |
4 | * Copyright (C) 2002, Linus Torvalds. |
5 | * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> |
6 | * |
7 | * Contains functions related to writing back dirty pages at the |
8 | * address_space level. |
9 | * |
10 | * 10Apr2002 Andrew Morton |
11 | * Initial version |
12 | */ |
13 | |
14 | #include <linux/kernel.h> |
15 | #include <linux/module.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> |
36 | #include <linux/pagevec.h> |
37 | #include <trace/events/writeback.h> |
38 | |
39 | /* |
40 | * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited |
41 | * will look to see if it needs to force writeback or throttling. |
42 | */ |
43 | static long ratelimit_pages = 32; |
44 | |
45 | /* |
46 | * When balance_dirty_pages decides that the caller needs to perform some |
47 | * non-background writeback, this is how many pages it will attempt to write. |
48 | * It should be somewhat larger than dirtied pages to ensure that reasonably |
49 | * large amounts of I/O are submitted. |
50 | */ |
51 | static inline long sync_writeback_pages(unsigned long dirtied) |
52 | { |
53 | if (dirtied < ratelimit_pages) |
54 | dirtied = ratelimit_pages; |
55 | |
56 | return dirtied + dirtied / 2; |
57 | } |
58 | |
59 | /* The following parameters are exported via /proc/sys/vm */ |
60 | |
61 | /* |
62 | * Start background writeback (via writeback threads) at this percentage |
63 | */ |
64 | int dirty_background_ratio = 10; |
65 | |
66 | /* |
67 | * dirty_background_bytes starts at 0 (disabled) so that it is a function of |
68 | * dirty_background_ratio * the amount of dirtyable memory |
69 | */ |
70 | unsigned long dirty_background_bytes; |
71 | |
72 | /* |
73 | * free highmem will not be subtracted from the total free memory |
74 | * for calculating free ratios if vm_highmem_is_dirtyable is true |
75 | */ |
76 | int vm_highmem_is_dirtyable; |
77 | |
78 | /* |
79 | * The generator of dirty data starts writeback at this percentage |
80 | */ |
81 | int vm_dirty_ratio = 20; |
82 | |
83 | /* |
84 | * vm_dirty_bytes starts at 0 (disabled) so that it is a function of |
85 | * vm_dirty_ratio * the amount of dirtyable memory |
86 | */ |
87 | unsigned long vm_dirty_bytes; |
88 | |
89 | /* |
90 | * The interval between `kupdate'-style writebacks |
91 | */ |
92 | unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ |
93 | |
94 | /* |
95 | * The longest time for which data is allowed to remain dirty |
96 | */ |
97 | unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ |
98 | |
99 | /* |
100 | * Flag that makes the machine dump writes/reads and block dirtyings. |
101 | */ |
102 | int block_dump; |
103 | |
104 | /* |
105 | * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: |
106 | * a full sync is triggered after this time elapses without any disk activity. |
107 | */ |
108 | int laptop_mode; |
109 | |
110 | EXPORT_SYMBOL(laptop_mode); |
111 | |
112 | /* End of sysctl-exported parameters */ |
113 | |
114 | |
115 | /* |
116 | * Scale the writeback cache size proportional to the relative writeout speeds. |
117 | * |
118 | * We do this by keeping a floating proportion between BDIs, based on page |
119 | * writeback completions [end_page_writeback()]. Those devices that write out |
120 | * pages fastest will get the larger share, while the slower will get a smaller |
121 | * share. |
122 | * |
123 | * We use page writeout completions because we are interested in getting rid of |
124 | * dirty pages. Having them written out is the primary goal. |
125 | * |
126 | * We introduce a concept of time, a period over which we measure these events, |
127 | * because demand can/will vary over time. The length of this period itself is |
128 | * measured in page writeback completions. |
129 | * |
130 | */ |
131 | static struct prop_descriptor vm_completions; |
132 | static struct prop_descriptor vm_dirties; |
133 | |
134 | /* |
135 | * couple the period to the dirty_ratio: |
136 | * |
137 | * period/2 ~ roundup_pow_of_two(dirty limit) |
138 | */ |
139 | static int calc_period_shift(void) |
140 | { |
141 | unsigned long dirty_total; |
142 | |
143 | if (vm_dirty_bytes) |
144 | dirty_total = vm_dirty_bytes / PAGE_SIZE; |
145 | else |
146 | dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / |
147 | 100; |
148 | return 2 + ilog2(dirty_total - 1); |
149 | } |
150 | |
151 | /* |
152 | * update the period when the dirty threshold changes. |
153 | */ |
154 | static void update_completion_period(void) |
155 | { |
156 | int shift = calc_period_shift(); |
157 | prop_change_shift(&vm_completions, shift); |
158 | prop_change_shift(&vm_dirties, shift); |
159 | } |
160 | |
161 | int dirty_background_ratio_handler(struct ctl_table *table, int write, |
162 | void __user *buffer, size_t *lenp, |
163 | loff_t *ppos) |
164 | { |
165 | int ret; |
166 | |
167 | ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
168 | if (ret == 0 && write) |
169 | dirty_background_bytes = 0; |
170 | return ret; |
171 | } |
172 | |
173 | int dirty_background_bytes_handler(struct ctl_table *table, int write, |
174 | void __user *buffer, size_t *lenp, |
175 | loff_t *ppos) |
176 | { |
177 | int ret; |
178 | |
179 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
180 | if (ret == 0 && write) |
181 | dirty_background_ratio = 0; |
182 | return ret; |
183 | } |
184 | |
185 | int dirty_ratio_handler(struct ctl_table *table, int write, |
186 | void __user *buffer, size_t *lenp, |
187 | loff_t *ppos) |
188 | { |
189 | int old_ratio = vm_dirty_ratio; |
190 | int ret; |
191 | |
192 | ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
193 | if (ret == 0 && write && vm_dirty_ratio != old_ratio) { |
194 | update_completion_period(); |
195 | vm_dirty_bytes = 0; |
196 | } |
197 | return ret; |
198 | } |
199 | |
200 | |
201 | int dirty_bytes_handler(struct ctl_table *table, int write, |
202 | void __user *buffer, size_t *lenp, |
203 | loff_t *ppos) |
204 | { |
205 | unsigned long old_bytes = vm_dirty_bytes; |
206 | int ret; |
207 | |
208 | ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
209 | if (ret == 0 && write && vm_dirty_bytes != old_bytes) { |
210 | update_completion_period(); |
211 | vm_dirty_ratio = 0; |
212 | } |
213 | return ret; |
214 | } |
215 | |
216 | /* |
217 | * Increment the BDI's writeout completion count and the global writeout |
218 | * completion count. Called from test_clear_page_writeback(). |
219 | */ |
220 | static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) |
221 | { |
222 | __prop_inc_percpu_max(&vm_completions, &bdi->completions, |
223 | bdi->max_prop_frac); |
224 | } |
225 | |
226 | void bdi_writeout_inc(struct backing_dev_info *bdi) |
227 | { |
228 | unsigned long flags; |
229 | |
230 | local_irq_save(flags); |
231 | __bdi_writeout_inc(bdi); |
232 | local_irq_restore(flags); |
233 | } |
234 | EXPORT_SYMBOL_GPL(bdi_writeout_inc); |
235 | |
236 | void task_dirty_inc(struct task_struct *tsk) |
237 | { |
238 | prop_inc_single(&vm_dirties, &tsk->dirties); |
239 | } |
240 | |
241 | /* |
242 | * Obtain an accurate fraction of the BDI's portion. |
243 | */ |
244 | static void bdi_writeout_fraction(struct backing_dev_info *bdi, |
245 | long *numerator, long *denominator) |
246 | { |
247 | if (bdi_cap_writeback_dirty(bdi)) { |
248 | prop_fraction_percpu(&vm_completions, &bdi->completions, |
249 | numerator, denominator); |
250 | } else { |
251 | *numerator = 0; |
252 | *denominator = 1; |
253 | } |
254 | } |
255 | |
256 | static inline void task_dirties_fraction(struct task_struct *tsk, |
257 | long *numerator, long *denominator) |
258 | { |
259 | prop_fraction_single(&vm_dirties, &tsk->dirties, |
260 | numerator, denominator); |
261 | } |
262 | |
263 | /* |
264 | * task_dirty_limit - scale down dirty throttling threshold for one task |
265 | * |
266 | * task specific dirty limit: |
267 | * |
268 | * dirty -= (dirty/8) * p_{t} |
269 | * |
270 | * To protect light/slow dirtying tasks from heavier/fast ones, we start |
271 | * throttling individual tasks before reaching the bdi dirty limit. |
272 | * Relatively low thresholds will be allocated to heavy dirtiers. So when |
273 | * dirty pages grow large, heavy dirtiers will be throttled first, which will |
274 | * effectively curb the growth of dirty pages. Light dirtiers with high enough |
275 | * dirty threshold may never get throttled. |
276 | */ |
277 | static unsigned long task_dirty_limit(struct task_struct *tsk, |
278 | unsigned long bdi_dirty) |
279 | { |
280 | long numerator, denominator; |
281 | unsigned long dirty = bdi_dirty; |
282 | u64 inv = dirty >> 3; |
283 | |
284 | task_dirties_fraction(tsk, &numerator, &denominator); |
285 | inv *= numerator; |
286 | do_div(inv, denominator); |
287 | |
288 | dirty -= inv; |
289 | |
290 | return max(dirty, bdi_dirty/2); |
291 | } |
292 | |
293 | /* |
294 | * |
295 | */ |
296 | static unsigned int bdi_min_ratio; |
297 | |
298 | int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) |
299 | { |
300 | int ret = 0; |
301 | |
302 | spin_lock_bh(&bdi_lock); |
303 | if (min_ratio > bdi->max_ratio) { |
304 | ret = -EINVAL; |
305 | } else { |
306 | min_ratio -= bdi->min_ratio; |
307 | if (bdi_min_ratio + min_ratio < 100) { |
308 | bdi_min_ratio += min_ratio; |
309 | bdi->min_ratio += min_ratio; |
310 | } else { |
311 | ret = -EINVAL; |
312 | } |
313 | } |
314 | spin_unlock_bh(&bdi_lock); |
315 | |
316 | return ret; |
317 | } |
318 | |
319 | int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) |
320 | { |
321 | int ret = 0; |
322 | |
323 | if (max_ratio > 100) |
324 | return -EINVAL; |
325 | |
326 | spin_lock_bh(&bdi_lock); |
327 | if (bdi->min_ratio > max_ratio) { |
328 | ret = -EINVAL; |
329 | } else { |
330 | bdi->max_ratio = max_ratio; |
331 | bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100; |
332 | } |
333 | spin_unlock_bh(&bdi_lock); |
334 | |
335 | return ret; |
336 | } |
337 | EXPORT_SYMBOL(bdi_set_max_ratio); |
338 | |
339 | /* |
340 | * Work out the current dirty-memory clamping and background writeout |
341 | * thresholds. |
342 | * |
343 | * The main aim here is to lower them aggressively if there is a lot of mapped |
344 | * memory around. To avoid stressing page reclaim with lots of unreclaimable |
345 | * pages. It is better to clamp down on writers than to start swapping, and |
346 | * performing lots of scanning. |
347 | * |
348 | * We only allow 1/2 of the currently-unmapped memory to be dirtied. |
349 | * |
350 | * We don't permit the clamping level to fall below 5% - that is getting rather |
351 | * excessive. |
352 | * |
353 | * We make sure that the background writeout level is below the adjusted |
354 | * clamping level. |
355 | */ |
356 | |
357 | static unsigned long highmem_dirtyable_memory(unsigned long total) |
358 | { |
359 | #ifdef CONFIG_HIGHMEM |
360 | int node; |
361 | unsigned long x = 0; |
362 | |
363 | for_each_node_state(node, N_HIGH_MEMORY) { |
364 | struct zone *z = |
365 | &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; |
366 | |
367 | x += zone_page_state(z, NR_FREE_PAGES) + |
368 | zone_reclaimable_pages(z); |
369 | } |
370 | /* |
371 | * Make sure that the number of highmem pages is never larger |
372 | * than the number of the total dirtyable memory. This can only |
373 | * occur in very strange VM situations but we want to make sure |
374 | * that this does not occur. |
375 | */ |
376 | return min(x, total); |
377 | #else |
378 | return 0; |
379 | #endif |
380 | } |
381 | |
382 | /** |
383 | * determine_dirtyable_memory - amount of memory that may be used |
384 | * |
385 | * Returns the numebr of pages that can currently be freed and used |
386 | * by the kernel for direct mappings. |
387 | */ |
388 | unsigned long determine_dirtyable_memory(void) |
389 | { |
390 | unsigned long x; |
391 | |
392 | x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages(); |
393 | |
394 | if (!vm_highmem_is_dirtyable) |
395 | x -= highmem_dirtyable_memory(x); |
396 | |
397 | return x + 1; /* Ensure that we never return 0 */ |
398 | } |
399 | |
400 | /* |
401 | * global_dirty_limits - background-writeback and dirty-throttling thresholds |
402 | * |
403 | * Calculate the dirty thresholds based on sysctl parameters |
404 | * - vm.dirty_background_ratio or vm.dirty_background_bytes |
405 | * - vm.dirty_ratio or vm.dirty_bytes |
406 | * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and |
407 | * real-time tasks. |
408 | */ |
409 | void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) |
410 | { |
411 | unsigned long background; |
412 | unsigned long dirty; |
413 | unsigned long uninitialized_var(available_memory); |
414 | struct task_struct *tsk; |
415 | |
416 | if (!vm_dirty_bytes || !dirty_background_bytes) |
417 | available_memory = determine_dirtyable_memory(); |
418 | |
419 | if (vm_dirty_bytes) |
420 | dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); |
421 | else |
422 | dirty = (vm_dirty_ratio * available_memory) / 100; |
423 | |
424 | if (dirty_background_bytes) |
425 | background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE); |
426 | else |
427 | background = (dirty_background_ratio * available_memory) / 100; |
428 | |
429 | if (background >= dirty) |
430 | background = dirty / 2; |
431 | tsk = current; |
432 | if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { |
433 | background += background / 4; |
434 | dirty += dirty / 4; |
435 | } |
436 | *pbackground = background; |
437 | *pdirty = dirty; |
438 | } |
439 | |
440 | /* |
441 | * bdi_dirty_limit - @bdi's share of dirty throttling threshold |
442 | * |
443 | * Allocate high/low dirty limits to fast/slow devices, in order to prevent |
444 | * - starving fast devices |
445 | * - piling up dirty pages (that will take long time to sync) on slow devices |
446 | * |
447 | * The bdi's share of dirty limit will be adapting to its throughput and |
448 | * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. |
449 | */ |
450 | unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) |
451 | { |
452 | u64 bdi_dirty; |
453 | long numerator, denominator; |
454 | |
455 | /* |
456 | * Calculate this BDI's share of the dirty ratio. |
457 | */ |
458 | bdi_writeout_fraction(bdi, &numerator, &denominator); |
459 | |
460 | bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100; |
461 | bdi_dirty *= numerator; |
462 | do_div(bdi_dirty, denominator); |
463 | |
464 | bdi_dirty += (dirty * bdi->min_ratio) / 100; |
465 | if (bdi_dirty > (dirty * bdi->max_ratio) / 100) |
466 | bdi_dirty = dirty * bdi->max_ratio / 100; |
467 | |
468 | return bdi_dirty; |
469 | } |
470 | |
471 | /* |
472 | * balance_dirty_pages() must be called by processes which are generating dirty |
473 | * data. It looks at the number of dirty pages in the machine and will force |
474 | * the caller to perform writeback if the system is over `vm_dirty_ratio'. |
475 | * If we're over `background_thresh' then the writeback threads are woken to |
476 | * perform some writeout. |
477 | */ |
478 | static void balance_dirty_pages(struct address_space *mapping, |
479 | unsigned long write_chunk) |
480 | { |
481 | long nr_reclaimable, bdi_nr_reclaimable; |
482 | long nr_writeback, bdi_nr_writeback; |
483 | unsigned long background_thresh; |
484 | unsigned long dirty_thresh; |
485 | unsigned long bdi_thresh; |
486 | unsigned long pages_written = 0; |
487 | unsigned long pause = 1; |
488 | bool dirty_exceeded = false; |
489 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
490 | |
491 | for (;;) { |
492 | struct writeback_control wbc = { |
493 | .sync_mode = WB_SYNC_NONE, |
494 | .older_than_this = NULL, |
495 | .nr_to_write = write_chunk, |
496 | .range_cyclic = 1, |
497 | }; |
498 | |
499 | nr_reclaimable = global_page_state(NR_FILE_DIRTY) + |
500 | global_page_state(NR_UNSTABLE_NFS); |
501 | nr_writeback = global_page_state(NR_WRITEBACK); |
502 | |
503 | global_dirty_limits(&background_thresh, &dirty_thresh); |
504 | |
505 | /* |
506 | * Throttle it only when the background writeback cannot |
507 | * catch-up. This avoids (excessively) small writeouts |
508 | * when the bdi limits are ramping up. |
509 | */ |
510 | if (nr_reclaimable + nr_writeback <= |
511 | (background_thresh + dirty_thresh) / 2) |
512 | break; |
513 | |
514 | bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); |
515 | bdi_thresh = task_dirty_limit(current, bdi_thresh); |
516 | |
517 | /* |
518 | * In order to avoid the stacked BDI deadlock we need |
519 | * to ensure we accurately count the 'dirty' pages when |
520 | * the threshold is low. |
521 | * |
522 | * Otherwise it would be possible to get thresh+n pages |
523 | * reported dirty, even though there are thresh-m pages |
524 | * actually dirty; with m+n sitting in the percpu |
525 | * deltas. |
526 | */ |
527 | if (bdi_thresh < 2*bdi_stat_error(bdi)) { |
528 | bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); |
529 | bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK); |
530 | } else { |
531 | bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); |
532 | bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK); |
533 | } |
534 | |
535 | /* |
536 | * The bdi thresh is somehow "soft" limit derived from the |
537 | * global "hard" limit. The former helps to prevent heavy IO |
538 | * bdi or process from holding back light ones; The latter is |
539 | * the last resort safeguard. |
540 | */ |
541 | dirty_exceeded = |
542 | (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh) |
543 | || (nr_reclaimable + nr_writeback > dirty_thresh); |
544 | |
545 | if (!dirty_exceeded) |
546 | break; |
547 | |
548 | if (!bdi->dirty_exceeded) |
549 | bdi->dirty_exceeded = 1; |
550 | |
551 | /* Note: nr_reclaimable denotes nr_dirty + nr_unstable. |
552 | * Unstable writes are a feature of certain networked |
553 | * filesystems (i.e. NFS) in which data may have been |
554 | * written to the server's write cache, but has not yet |
555 | * been flushed to permanent storage. |
556 | * Only move pages to writeback if this bdi is over its |
557 | * threshold otherwise wait until the disk writes catch |
558 | * up. |
559 | */ |
560 | trace_wbc_balance_dirty_start(&wbc, bdi); |
561 | if (bdi_nr_reclaimable > bdi_thresh) { |
562 | writeback_inodes_wb(&bdi->wb, &wbc); |
563 | pages_written += write_chunk - wbc.nr_to_write; |
564 | trace_wbc_balance_dirty_written(&wbc, bdi); |
565 | if (pages_written >= write_chunk) |
566 | break; /* We've done our duty */ |
567 | } |
568 | trace_wbc_balance_dirty_wait(&wbc, bdi); |
569 | __set_current_state(TASK_UNINTERRUPTIBLE); |
570 | io_schedule_timeout(pause); |
571 | |
572 | /* |
573 | * Increase the delay for each loop, up to our previous |
574 | * default of taking a 100ms nap. |
575 | */ |
576 | pause <<= 1; |
577 | if (pause > HZ / 10) |
578 | pause = HZ / 10; |
579 | } |
580 | |
581 | if (!dirty_exceeded && bdi->dirty_exceeded) |
582 | bdi->dirty_exceeded = 0; |
583 | |
584 | if (writeback_in_progress(bdi)) |
585 | return; |
586 | |
587 | /* |
588 | * In laptop mode, we wait until hitting the higher threshold before |
589 | * starting background writeout, and then write out all the way down |
590 | * to the lower threshold. So slow writers cause minimal disk activity. |
591 | * |
592 | * In normal mode, we start background writeout at the lower |
593 | * background_thresh, to keep the amount of dirty memory low. |
594 | */ |
595 | if ((laptop_mode && pages_written) || |
596 | (!laptop_mode && (nr_reclaimable > background_thresh))) |
597 | bdi_start_background_writeback(bdi); |
598 | } |
599 | |
600 | void set_page_dirty_balance(struct page *page, int page_mkwrite) |
601 | { |
602 | if (set_page_dirty(page) || page_mkwrite) { |
603 | struct address_space *mapping = page_mapping(page); |
604 | |
605 | if (mapping) |
606 | balance_dirty_pages_ratelimited(mapping); |
607 | } |
608 | } |
609 | |
610 | static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0; |
611 | |
612 | /** |
613 | * balance_dirty_pages_ratelimited_nr - balance dirty memory state |
614 | * @mapping: address_space which was dirtied |
615 | * @nr_pages_dirtied: number of pages which the caller has just dirtied |
616 | * |
617 | * Processes which are dirtying memory should call in here once for each page |
618 | * which was newly dirtied. The function will periodically check the system's |
619 | * dirty state and will initiate writeback if needed. |
620 | * |
621 | * On really big machines, get_writeback_state is expensive, so try to avoid |
622 | * calling it too often (ratelimiting). But once we're over the dirty memory |
623 | * limit we decrease the ratelimiting by a lot, to prevent individual processes |
624 | * from overshooting the limit by (ratelimit_pages) each. |
625 | */ |
626 | void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, |
627 | unsigned long nr_pages_dirtied) |
628 | { |
629 | unsigned long ratelimit; |
630 | unsigned long *p; |
631 | |
632 | ratelimit = ratelimit_pages; |
633 | if (mapping->backing_dev_info->dirty_exceeded) |
634 | ratelimit = 8; |
635 | |
636 | /* |
637 | * Check the rate limiting. Also, we do not want to throttle real-time |
638 | * tasks in balance_dirty_pages(). Period. |
639 | */ |
640 | preempt_disable(); |
641 | p = &__get_cpu_var(bdp_ratelimits); |
642 | *p += nr_pages_dirtied; |
643 | if (unlikely(*p >= ratelimit)) { |
644 | ratelimit = sync_writeback_pages(*p); |
645 | *p = 0; |
646 | preempt_enable(); |
647 | balance_dirty_pages(mapping, ratelimit); |
648 | return; |
649 | } |
650 | preempt_enable(); |
651 | } |
652 | EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); |
653 | |
654 | void throttle_vm_writeout(gfp_t gfp_mask) |
655 | { |
656 | unsigned long background_thresh; |
657 | unsigned long dirty_thresh; |
658 | |
659 | for ( ; ; ) { |
660 | global_dirty_limits(&background_thresh, &dirty_thresh); |
661 | |
662 | /* |
663 | * Boost the allowable dirty threshold a bit for page |
664 | * allocators so they don't get DoS'ed by heavy writers |
665 | */ |
666 | dirty_thresh += dirty_thresh / 10; /* wheeee... */ |
667 | |
668 | if (global_page_state(NR_UNSTABLE_NFS) + |
669 | global_page_state(NR_WRITEBACK) <= dirty_thresh) |
670 | break; |
671 | congestion_wait(BLK_RW_ASYNC, HZ/10); |
672 | |
673 | /* |
674 | * The caller might hold locks which can prevent IO completion |
675 | * or progress in the filesystem. So we cannot just sit here |
676 | * waiting for IO to complete. |
677 | */ |
678 | if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) |
679 | break; |
680 | } |
681 | } |
682 | |
683 | /* |
684 | * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs |
685 | */ |
686 | int dirty_writeback_centisecs_handler(ctl_table *table, int write, |
687 | void __user *buffer, size_t *length, loff_t *ppos) |
688 | { |
689 | proc_dointvec(table, write, buffer, length, ppos); |
690 | bdi_arm_supers_timer(); |
691 | return 0; |
692 | } |
693 | |
694 | #ifdef CONFIG_BLOCK |
695 | void laptop_mode_timer_fn(unsigned long data) |
696 | { |
697 | struct request_queue *q = (struct request_queue *)data; |
698 | int nr_pages = global_page_state(NR_FILE_DIRTY) + |
699 | global_page_state(NR_UNSTABLE_NFS); |
700 | |
701 | /* |
702 | * We want to write everything out, not just down to the dirty |
703 | * threshold |
704 | */ |
705 | if (bdi_has_dirty_io(&q->backing_dev_info)) |
706 | bdi_start_writeback(&q->backing_dev_info, nr_pages); |
707 | } |
708 | |
709 | /* |
710 | * We've spun up the disk and we're in laptop mode: schedule writeback |
711 | * of all dirty data a few seconds from now. If the flush is already scheduled |
712 | * then push it back - the user is still using the disk. |
713 | */ |
714 | void laptop_io_completion(struct backing_dev_info *info) |
715 | { |
716 | mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); |
717 | } |
718 | |
719 | /* |
720 | * We're in laptop mode and we've just synced. The sync's writes will have |
721 | * caused another writeback to be scheduled by laptop_io_completion. |
722 | * Nothing needs to be written back anymore, so we unschedule the writeback. |
723 | */ |
724 | void laptop_sync_completion(void) |
725 | { |
726 | struct backing_dev_info *bdi; |
727 | |
728 | rcu_read_lock(); |
729 | |
730 | list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) |
731 | del_timer(&bdi->laptop_mode_wb_timer); |
732 | |
733 | rcu_read_unlock(); |
734 | } |
735 | #endif |
736 | |
737 | /* |
738 | * If ratelimit_pages is too high then we can get into dirty-data overload |
739 | * if a large number of processes all perform writes at the same time. |
740 | * If it is too low then SMP machines will call the (expensive) |
741 | * get_writeback_state too often. |
742 | * |
743 | * Here we set ratelimit_pages to a level which ensures that when all CPUs are |
744 | * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory |
745 | * thresholds before writeback cuts in. |
746 | * |
747 | * But the limit should not be set too high. Because it also controls the |
748 | * amount of memory which the balance_dirty_pages() caller has to write back. |
749 | * If this is too large then the caller will block on the IO queue all the |
750 | * time. So limit it to four megabytes - the balance_dirty_pages() caller |
751 | * will write six megabyte chunks, max. |
752 | */ |
753 | |
754 | void writeback_set_ratelimit(void) |
755 | { |
756 | ratelimit_pages = vm_total_pages / (num_online_cpus() * 32); |
757 | if (ratelimit_pages < 16) |
758 | ratelimit_pages = 16; |
759 | if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024) |
760 | ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE; |
761 | } |
762 | |
763 | static int __cpuinit |
764 | ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) |
765 | { |
766 | writeback_set_ratelimit(); |
767 | return NOTIFY_DONE; |
768 | } |
769 | |
770 | static struct notifier_block __cpuinitdata ratelimit_nb = { |
771 | .notifier_call = ratelimit_handler, |
772 | .next = NULL, |
773 | }; |
774 | |
775 | /* |
776 | * Called early on to tune the page writeback dirty limits. |
777 | * |
778 | * We used to scale dirty pages according to how total memory |
779 | * related to pages that could be allocated for buffers (by |
780 | * comparing nr_free_buffer_pages() to vm_total_pages. |
781 | * |
782 | * However, that was when we used "dirty_ratio" to scale with |
783 | * all memory, and we don't do that any more. "dirty_ratio" |
784 | * is now applied to total non-HIGHPAGE memory (by subtracting |
785 | * totalhigh_pages from vm_total_pages), and as such we can't |
786 | * get into the old insane situation any more where we had |
787 | * large amounts of dirty pages compared to a small amount of |
788 | * non-HIGHMEM memory. |
789 | * |
790 | * But we might still want to scale the dirty_ratio by how |
791 | * much memory the box has.. |
792 | */ |
793 | void __init page_writeback_init(void) |
794 | { |
795 | int shift; |
796 | |
797 | writeback_set_ratelimit(); |
798 | register_cpu_notifier(&ratelimit_nb); |
799 | |
800 | shift = calc_period_shift(); |
801 | prop_descriptor_init(&vm_completions, shift); |
802 | prop_descriptor_init(&vm_dirties, shift); |
803 | } |
804 | |
805 | /** |
806 | * tag_pages_for_writeback - tag pages to be written by write_cache_pages |
807 | * @mapping: address space structure to write |
808 | * @start: starting page index |
809 | * @end: ending page index (inclusive) |
810 | * |
811 | * This function scans the page range from @start to @end (inclusive) and tags |
812 | * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is |
813 | * that write_cache_pages (or whoever calls this function) will then use |
814 | * TOWRITE tag to identify pages eligible for writeback. This mechanism is |
815 | * used to avoid livelocking of writeback by a process steadily creating new |
816 | * dirty pages in the file (thus it is important for this function to be quick |
817 | * so that it can tag pages faster than a dirtying process can create them). |
818 | */ |
819 | /* |
820 | * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency. |
821 | */ |
822 | void tag_pages_for_writeback(struct address_space *mapping, |
823 | pgoff_t start, pgoff_t end) |
824 | { |
825 | #define WRITEBACK_TAG_BATCH 4096 |
826 | unsigned long tagged; |
827 | |
828 | do { |
829 | spin_lock_irq(&mapping->tree_lock); |
830 | tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree, |
831 | &start, end, WRITEBACK_TAG_BATCH, |
832 | PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE); |
833 | spin_unlock_irq(&mapping->tree_lock); |
834 | WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH); |
835 | cond_resched(); |
836 | /* We check 'start' to handle wrapping when end == ~0UL */ |
837 | } while (tagged >= WRITEBACK_TAG_BATCH && start); |
838 | } |
839 | EXPORT_SYMBOL(tag_pages_for_writeback); |
840 | |
841 | /** |
842 | * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. |
843 | * @mapping: address space structure to write |
844 | * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
845 | * @writepage: function called for each page |
846 | * @data: data passed to writepage function |
847 | * |
848 | * If a page is already under I/O, write_cache_pages() skips it, even |
849 | * if it's dirty. This is desirable behaviour for memory-cleaning writeback, |
850 | * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() |
851 | * and msync() need to guarantee that all the data which was dirty at the time |
852 | * the call was made get new I/O started against them. If wbc->sync_mode is |
853 | * WB_SYNC_ALL then we were called for data integrity and we must wait for |
854 | * existing IO to complete. |
855 | * |
856 | * To avoid livelocks (when other process dirties new pages), we first tag |
857 | * pages which should be written back with TOWRITE tag and only then start |
858 | * writing them. For data-integrity sync we have to be careful so that we do |
859 | * not miss some pages (e.g., because some other process has cleared TOWRITE |
860 | * tag we set). The rule we follow is that TOWRITE tag can be cleared only |
861 | * by the process clearing the DIRTY tag (and submitting the page for IO). |
862 | */ |
863 | int write_cache_pages(struct address_space *mapping, |
864 | struct writeback_control *wbc, writepage_t writepage, |
865 | void *data) |
866 | { |
867 | int ret = 0; |
868 | int done = 0; |
869 | struct pagevec pvec; |
870 | int nr_pages; |
871 | pgoff_t uninitialized_var(writeback_index); |
872 | pgoff_t index; |
873 | pgoff_t end; /* Inclusive */ |
874 | pgoff_t done_index; |
875 | int cycled; |
876 | int range_whole = 0; |
877 | int tag; |
878 | |
879 | pagevec_init(&pvec, 0); |
880 | if (wbc->range_cyclic) { |
881 | writeback_index = mapping->writeback_index; /* prev offset */ |
882 | index = writeback_index; |
883 | if (index == 0) |
884 | cycled = 1; |
885 | else |
886 | cycled = 0; |
887 | end = -1; |
888 | } else { |
889 | index = wbc->range_start >> PAGE_CACHE_SHIFT; |
890 | end = wbc->range_end >> PAGE_CACHE_SHIFT; |
891 | if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) |
892 | range_whole = 1; |
893 | cycled = 1; /* ignore range_cyclic tests */ |
894 | } |
895 | if (wbc->sync_mode == WB_SYNC_ALL) |
896 | tag = PAGECACHE_TAG_TOWRITE; |
897 | else |
898 | tag = PAGECACHE_TAG_DIRTY; |
899 | retry: |
900 | if (wbc->sync_mode == WB_SYNC_ALL) |
901 | tag_pages_for_writeback(mapping, index, end); |
902 | done_index = index; |
903 | while (!done && (index <= end)) { |
904 | int i; |
905 | |
906 | nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag, |
907 | min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); |
908 | if (nr_pages == 0) |
909 | break; |
910 | |
911 | for (i = 0; i < nr_pages; i++) { |
912 | struct page *page = pvec.pages[i]; |
913 | |
914 | /* |
915 | * At this point, the page may be truncated or |
916 | * invalidated (changing page->mapping to NULL), or |
917 | * even swizzled back from swapper_space to tmpfs file |
918 | * mapping. However, page->index will not change |
919 | * because we have a reference on the page. |
920 | */ |
921 | if (page->index > end) { |
922 | /* |
923 | * can't be range_cyclic (1st pass) because |
924 | * end == -1 in that case. |
925 | */ |
926 | done = 1; |
927 | break; |
928 | } |
929 | |
930 | done_index = page->index; |
931 | |
932 | lock_page(page); |
933 | |
934 | /* |
935 | * Page truncated or invalidated. We can freely skip it |
936 | * then, even for data integrity operations: the page |
937 | * has disappeared concurrently, so there could be no |
938 | * real expectation of this data interity operation |
939 | * even if there is now a new, dirty page at the same |
940 | * pagecache address. |
941 | */ |
942 | if (unlikely(page->mapping != mapping)) { |
943 | continue_unlock: |
944 | unlock_page(page); |
945 | continue; |
946 | } |
947 | |
948 | if (!PageDirty(page)) { |
949 | /* someone wrote it for us */ |
950 | goto continue_unlock; |
951 | } |
952 | |
953 | if (PageWriteback(page)) { |
954 | if (wbc->sync_mode != WB_SYNC_NONE) |
955 | wait_on_page_writeback(page); |
956 | else |
957 | goto continue_unlock; |
958 | } |
959 | |
960 | BUG_ON(PageWriteback(page)); |
961 | if (!clear_page_dirty_for_io(page)) |
962 | goto continue_unlock; |
963 | |
964 | trace_wbc_writepage(wbc, mapping->backing_dev_info); |
965 | ret = (*writepage)(page, wbc, data); |
966 | if (unlikely(ret)) { |
967 | if (ret == AOP_WRITEPAGE_ACTIVATE) { |
968 | unlock_page(page); |
969 | ret = 0; |
970 | } else { |
971 | /* |
972 | * done_index is set past this page, |
973 | * so media errors will not choke |
974 | * background writeout for the entire |
975 | * file. This has consequences for |
976 | * range_cyclic semantics (ie. it may |
977 | * not be suitable for data integrity |
978 | * writeout). |
979 | */ |
980 | done_index = page->index + 1; |
981 | done = 1; |
982 | break; |
983 | } |
984 | } |
985 | |
986 | /* |
987 | * We stop writing back only if we are not doing |
988 | * integrity sync. In case of integrity sync we have to |
989 | * keep going until we have written all the pages |
990 | * we tagged for writeback prior to entering this loop. |
991 | */ |
992 | if (--wbc->nr_to_write <= 0 && |
993 | wbc->sync_mode == WB_SYNC_NONE) { |
994 | done = 1; |
995 | break; |
996 | } |
997 | } |
998 | pagevec_release(&pvec); |
999 | cond_resched(); |
1000 | } |
1001 | if (!cycled && !done) { |
1002 | /* |
1003 | * range_cyclic: |
1004 | * We hit the last page and there is more work to be done: wrap |
1005 | * back to the start of the file |
1006 | */ |
1007 | cycled = 1; |
1008 | index = 0; |
1009 | end = writeback_index - 1; |
1010 | goto retry; |
1011 | } |
1012 | if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) |
1013 | mapping->writeback_index = done_index; |
1014 | |
1015 | return ret; |
1016 | } |
1017 | EXPORT_SYMBOL(write_cache_pages); |
1018 | |
1019 | /* |
1020 | * Function used by generic_writepages to call the real writepage |
1021 | * function and set the mapping flags on error |
1022 | */ |
1023 | static int __writepage(struct page *page, struct writeback_control *wbc, |
1024 | void *data) |
1025 | { |
1026 | struct address_space *mapping = data; |
1027 | int ret = mapping->a_ops->writepage(page, wbc); |
1028 | mapping_set_error(mapping, ret); |
1029 | return ret; |
1030 | } |
1031 | |
1032 | /** |
1033 | * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. |
1034 | * @mapping: address space structure to write |
1035 | * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
1036 | * |
1037 | * This is a library function, which implements the writepages() |
1038 | * address_space_operation. |
1039 | */ |
1040 | int generic_writepages(struct address_space *mapping, |
1041 | struct writeback_control *wbc) |
1042 | { |
1043 | struct blk_plug plug; |
1044 | int ret; |
1045 | |
1046 | /* deal with chardevs and other special file */ |
1047 | if (!mapping->a_ops->writepage) |
1048 | return 0; |
1049 | |
1050 | blk_start_plug(&plug); |
1051 | ret = write_cache_pages(mapping, wbc, __writepage, mapping); |
1052 | blk_finish_plug(&plug); |
1053 | return ret; |
1054 | } |
1055 | |
1056 | EXPORT_SYMBOL(generic_writepages); |
1057 | |
1058 | int do_writepages(struct address_space *mapping, struct writeback_control *wbc) |
1059 | { |
1060 | int ret; |
1061 | |
1062 | if (wbc->nr_to_write <= 0) |
1063 | return 0; |
1064 | if (mapping->a_ops->writepages) |
1065 | ret = mapping->a_ops->writepages(mapping, wbc); |
1066 | else |
1067 | ret = generic_writepages(mapping, wbc); |
1068 | return ret; |
1069 | } |
1070 | |
1071 | /** |
1072 | * write_one_page - write out a single page and optionally wait on I/O |
1073 | * @page: the page to write |
1074 | * @wait: if true, wait on writeout |
1075 | * |
1076 | * The page must be locked by the caller and will be unlocked upon return. |
1077 | * |
1078 | * write_one_page() returns a negative error code if I/O failed. |
1079 | */ |
1080 | int write_one_page(struct page *page, int wait) |
1081 | { |
1082 | struct address_space *mapping = page->mapping; |
1083 | int ret = 0; |
1084 | struct writeback_control wbc = { |
1085 | .sync_mode = WB_SYNC_ALL, |
1086 | .nr_to_write = 1, |
1087 | }; |
1088 | |
1089 | BUG_ON(!PageLocked(page)); |
1090 | |
1091 | if (wait) |
1092 | wait_on_page_writeback(page); |
1093 | |
1094 | if (clear_page_dirty_for_io(page)) { |
1095 | page_cache_get(page); |
1096 | ret = mapping->a_ops->writepage(page, &wbc); |
1097 | if (ret == 0 && wait) { |
1098 | wait_on_page_writeback(page); |
1099 | if (PageError(page)) |
1100 | ret = -EIO; |
1101 | } |
1102 | page_cache_release(page); |
1103 | } else { |
1104 | unlock_page(page); |
1105 | } |
1106 | return ret; |
1107 | } |
1108 | EXPORT_SYMBOL(write_one_page); |
1109 | |
1110 | /* |
1111 | * For address_spaces which do not use buffers nor write back. |
1112 | */ |
1113 | int __set_page_dirty_no_writeback(struct page *page) |
1114 | { |
1115 | if (!PageDirty(page)) |
1116 | return !TestSetPageDirty(page); |
1117 | return 0; |
1118 | } |
1119 | |
1120 | /* |
1121 | * Helper function for set_page_dirty family. |
1122 | * NOTE: This relies on being atomic wrt interrupts. |
1123 | */ |
1124 | void account_page_dirtied(struct page *page, struct address_space *mapping) |
1125 | { |
1126 | if (mapping_cap_account_dirty(mapping)) { |
1127 | __inc_zone_page_state(page, NR_FILE_DIRTY); |
1128 | __inc_zone_page_state(page, NR_DIRTIED); |
1129 | __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); |
1130 | task_dirty_inc(current); |
1131 | task_io_account_write(PAGE_CACHE_SIZE); |
1132 | } |
1133 | } |
1134 | EXPORT_SYMBOL(account_page_dirtied); |
1135 | |
1136 | /* |
1137 | * Helper function for set_page_writeback family. |
1138 | * NOTE: Unlike account_page_dirtied this does not rely on being atomic |
1139 | * wrt interrupts. |
1140 | */ |
1141 | void account_page_writeback(struct page *page) |
1142 | { |
1143 | inc_zone_page_state(page, NR_WRITEBACK); |
1144 | inc_zone_page_state(page, NR_WRITTEN); |
1145 | } |
1146 | EXPORT_SYMBOL(account_page_writeback); |
1147 | |
1148 | /* |
1149 | * For address_spaces which do not use buffers. Just tag the page as dirty in |
1150 | * its radix tree. |
1151 | * |
1152 | * This is also used when a single buffer is being dirtied: we want to set the |
1153 | * page dirty in that case, but not all the buffers. This is a "bottom-up" |
1154 | * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. |
1155 | * |
1156 | * Most callers have locked the page, which pins the address_space in memory. |
1157 | * But zap_pte_range() does not lock the page, however in that case the |
1158 | * mapping is pinned by the vma's ->vm_file reference. |
1159 | * |
1160 | * We take care to handle the case where the page was truncated from the |
1161 | * mapping by re-checking page_mapping() inside tree_lock. |
1162 | */ |
1163 | int __set_page_dirty_nobuffers(struct page *page) |
1164 | { |
1165 | if (!TestSetPageDirty(page)) { |
1166 | struct address_space *mapping = page_mapping(page); |
1167 | struct address_space *mapping2; |
1168 | |
1169 | if (!mapping) |
1170 | return 1; |
1171 | |
1172 | spin_lock_irq(&mapping->tree_lock); |
1173 | mapping2 = page_mapping(page); |
1174 | if (mapping2) { /* Race with truncate? */ |
1175 | BUG_ON(mapping2 != mapping); |
1176 | WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); |
1177 | account_page_dirtied(page, mapping); |
1178 | radix_tree_tag_set(&mapping->page_tree, |
1179 | page_index(page), PAGECACHE_TAG_DIRTY); |
1180 | } |
1181 | spin_unlock_irq(&mapping->tree_lock); |
1182 | if (mapping->host) { |
1183 | /* !PageAnon && !swapper_space */ |
1184 | __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); |
1185 | } |
1186 | return 1; |
1187 | } |
1188 | return 0; |
1189 | } |
1190 | EXPORT_SYMBOL(__set_page_dirty_nobuffers); |
1191 | |
1192 | /* |
1193 | * When a writepage implementation decides that it doesn't want to write this |
1194 | * page for some reason, it should redirty the locked page via |
1195 | * redirty_page_for_writepage() and it should then unlock the page and return 0 |
1196 | */ |
1197 | int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) |
1198 | { |
1199 | wbc->pages_skipped++; |
1200 | return __set_page_dirty_nobuffers(page); |
1201 | } |
1202 | EXPORT_SYMBOL(redirty_page_for_writepage); |
1203 | |
1204 | /* |
1205 | * Dirty a page. |
1206 | * |
1207 | * For pages with a mapping this should be done under the page lock |
1208 | * for the benefit of asynchronous memory errors who prefer a consistent |
1209 | * dirty state. This rule can be broken in some special cases, |
1210 | * but should be better not to. |
1211 | * |
1212 | * If the mapping doesn't provide a set_page_dirty a_op, then |
1213 | * just fall through and assume that it wants buffer_heads. |
1214 | */ |
1215 | int set_page_dirty(struct page *page) |
1216 | { |
1217 | struct address_space *mapping = page_mapping(page); |
1218 | |
1219 | if (likely(mapping)) { |
1220 | int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; |
1221 | /* |
1222 | * readahead/lru_deactivate_page could remain |
1223 | * PG_readahead/PG_reclaim due to race with end_page_writeback |
1224 | * About readahead, if the page is written, the flags would be |
1225 | * reset. So no problem. |
1226 | * About lru_deactivate_page, if the page is redirty, the flag |
1227 | * will be reset. So no problem. but if the page is used by readahead |
1228 | * it will confuse readahead and make it restart the size rampup |
1229 | * process. But it's a trivial problem. |
1230 | */ |
1231 | ClearPageReclaim(page); |
1232 | #ifdef CONFIG_BLOCK |
1233 | if (!spd) |
1234 | spd = __set_page_dirty_buffers; |
1235 | #endif |
1236 | return (*spd)(page); |
1237 | } |
1238 | if (!PageDirty(page)) { |
1239 | if (!TestSetPageDirty(page)) |
1240 | return 1; |
1241 | } |
1242 | return 0; |
1243 | } |
1244 | EXPORT_SYMBOL(set_page_dirty); |
1245 | |
1246 | /* |
1247 | * set_page_dirty() is racy if the caller has no reference against |
1248 | * page->mapping->host, and if the page is unlocked. This is because another |
1249 | * CPU could truncate the page off the mapping and then free the mapping. |
1250 | * |
1251 | * Usually, the page _is_ locked, or the caller is a user-space process which |
1252 | * holds a reference on the inode by having an open file. |
1253 | * |
1254 | * In other cases, the page should be locked before running set_page_dirty(). |
1255 | */ |
1256 | int set_page_dirty_lock(struct page *page) |
1257 | { |
1258 | int ret; |
1259 | |
1260 | lock_page(page); |
1261 | ret = set_page_dirty(page); |
1262 | unlock_page(page); |
1263 | return ret; |
1264 | } |
1265 | EXPORT_SYMBOL(set_page_dirty_lock); |
1266 | |
1267 | /* |
1268 | * Clear a page's dirty flag, while caring for dirty memory accounting. |
1269 | * Returns true if the page was previously dirty. |
1270 | * |
1271 | * This is for preparing to put the page under writeout. We leave the page |
1272 | * tagged as dirty in the radix tree so that a concurrent write-for-sync |
1273 | * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage |
1274 | * implementation will run either set_page_writeback() or set_page_dirty(), |
1275 | * at which stage we bring the page's dirty flag and radix-tree dirty tag |
1276 | * back into sync. |
1277 | * |
1278 | * This incoherency between the page's dirty flag and radix-tree tag is |
1279 | * unfortunate, but it only exists while the page is locked. |
1280 | */ |
1281 | int clear_page_dirty_for_io(struct page *page) |
1282 | { |
1283 | struct address_space *mapping = page_mapping(page); |
1284 | |
1285 | BUG_ON(!PageLocked(page)); |
1286 | |
1287 | if (mapping && mapping_cap_account_dirty(mapping)) { |
1288 | /* |
1289 | * Yes, Virginia, this is indeed insane. |
1290 | * |
1291 | * We use this sequence to make sure that |
1292 | * (a) we account for dirty stats properly |
1293 | * (b) we tell the low-level filesystem to |
1294 | * mark the whole page dirty if it was |
1295 | * dirty in a pagetable. Only to then |
1296 | * (c) clean the page again and return 1 to |
1297 | * cause the writeback. |
1298 | * |
1299 | * This way we avoid all nasty races with the |
1300 | * dirty bit in multiple places and clearing |
1301 | * them concurrently from different threads. |
1302 | * |
1303 | * Note! Normally the "set_page_dirty(page)" |
1304 | * has no effect on the actual dirty bit - since |
1305 | * that will already usually be set. But we |
1306 | * need the side effects, and it can help us |
1307 | * avoid races. |
1308 | * |
1309 | * We basically use the page "master dirty bit" |
1310 | * as a serialization point for all the different |
1311 | * threads doing their things. |
1312 | */ |
1313 | if (page_mkclean(page)) |
1314 | set_page_dirty(page); |
1315 | /* |
1316 | * We carefully synchronise fault handlers against |
1317 | * installing a dirty pte and marking the page dirty |
1318 | * at this point. We do this by having them hold the |
1319 | * page lock at some point after installing their |
1320 | * pte, but before marking the page dirty. |
1321 | * Pages are always locked coming in here, so we get |
1322 | * the desired exclusion. See mm/memory.c:do_wp_page() |
1323 | * for more comments. |
1324 | */ |
1325 | if (TestClearPageDirty(page)) { |
1326 | dec_zone_page_state(page, NR_FILE_DIRTY); |
1327 | dec_bdi_stat(mapping->backing_dev_info, |
1328 | BDI_RECLAIMABLE); |
1329 | return 1; |
1330 | } |
1331 | return 0; |
1332 | } |
1333 | return TestClearPageDirty(page); |
1334 | } |
1335 | EXPORT_SYMBOL(clear_page_dirty_for_io); |
1336 | |
1337 | int test_clear_page_writeback(struct page *page) |
1338 | { |
1339 | struct address_space *mapping = page_mapping(page); |
1340 | int ret; |
1341 | |
1342 | if (mapping) { |
1343 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
1344 | unsigned long flags; |
1345 | |
1346 | spin_lock_irqsave(&mapping->tree_lock, flags); |
1347 | ret = TestClearPageWriteback(page); |
1348 | if (ret) { |
1349 | radix_tree_tag_clear(&mapping->page_tree, |
1350 | page_index(page), |
1351 | PAGECACHE_TAG_WRITEBACK); |
1352 | if (bdi_cap_account_writeback(bdi)) { |
1353 | __dec_bdi_stat(bdi, BDI_WRITEBACK); |
1354 | __bdi_writeout_inc(bdi); |
1355 | } |
1356 | } |
1357 | spin_unlock_irqrestore(&mapping->tree_lock, flags); |
1358 | } else { |
1359 | ret = TestClearPageWriteback(page); |
1360 | } |
1361 | if (ret) |
1362 | dec_zone_page_state(page, NR_WRITEBACK); |
1363 | return ret; |
1364 | } |
1365 | |
1366 | int test_set_page_writeback(struct page *page) |
1367 | { |
1368 | struct address_space *mapping = page_mapping(page); |
1369 | int ret; |
1370 | |
1371 | if (mapping) { |
1372 | struct backing_dev_info *bdi = mapping->backing_dev_info; |
1373 | unsigned long flags; |
1374 | |
1375 | spin_lock_irqsave(&mapping->tree_lock, flags); |
1376 | ret = TestSetPageWriteback(page); |
1377 | if (!ret) { |
1378 | radix_tree_tag_set(&mapping->page_tree, |
1379 | page_index(page), |
1380 | PAGECACHE_TAG_WRITEBACK); |
1381 | if (bdi_cap_account_writeback(bdi)) |
1382 | __inc_bdi_stat(bdi, BDI_WRITEBACK); |
1383 | } |
1384 | if (!PageDirty(page)) |
1385 | radix_tree_tag_clear(&mapping->page_tree, |
1386 | page_index(page), |
1387 | PAGECACHE_TAG_DIRTY); |
1388 | radix_tree_tag_clear(&mapping->page_tree, |
1389 | page_index(page), |
1390 | PAGECACHE_TAG_TOWRITE); |
1391 | spin_unlock_irqrestore(&mapping->tree_lock, flags); |
1392 | } else { |
1393 | ret = TestSetPageWriteback(page); |
1394 | } |
1395 | if (!ret) |
1396 | account_page_writeback(page); |
1397 | return ret; |
1398 | |
1399 | } |
1400 | EXPORT_SYMBOL(test_set_page_writeback); |
1401 | |
1402 | /* |
1403 | * Return true if any of the pages in the mapping are marked with the |
1404 | * passed tag. |
1405 | */ |
1406 | int mapping_tagged(struct address_space *mapping, int tag) |
1407 | { |
1408 | int ret; |
1409 | rcu_read_lock(); |
1410 | ret = radix_tree_tagged(&mapping->page_tree, tag); |
1411 | rcu_read_unlock(); |
1412 | return ret; |
1413 | } |
1414 | EXPORT_SYMBOL(mapping_tagged); |
1415 |
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