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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
Uwe Zeisbergerf30c2262006-10-03 23:01:26 +02002 * mm/page-writeback.c
Linus Torvalds1da177e2005-04-16 15:20:36 -07003 *
4 * Copyright (C) 2002, Linus Torvalds.
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07005 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
Linus Torvalds1da177e2005-04-16 15:20:36 -07006 *
7 * Contains functions related to writing back dirty pages at the
8 * address_space level.
9 *
Francois Camie1f8e872008-10-15 22:01:59 -070010 * 10Apr2002 Andrew Morton
Linus Torvalds1da177e2005-04-16 15:20:36 -070011 * Initial version
12 */
13
14#include <linux/kernel.h>
Paul Gortmakerb95f1b312011-10-16 02:01:52 -040015#include <linux/export.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070016#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>
Andrew Morton55e829a2006-12-10 02:19:27 -080025#include <linux/task_io_accounting_ops.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070026#include <linux/blkdev.h>
27#include <linux/mpage.h>
Peter Zijlstrad08b3852006-09-25 23:30:57 -070028#include <linux/rmap.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070029#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>
Al Viroff01bb42011-09-16 02:31:11 -040035#include <linux/buffer_head.h> /* __set_page_dirty_buffers */
David Howells811d7362006-08-29 19:06:09 +010036#include <linux/pagevec.h>
Dave Chinner028c2dd2010-07-07 13:24:07 +100037#include <trace/events/writeback.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070038
39/*
Wu Fengguangffd1f602011-06-19 22:18:42 -060040 * Sleep at most 200ms at a time in balance_dirty_pages().
41 */
42#define MAX_PAUSE max(HZ/5, 1)
43
44/*
Wu Fengguang5b9b3572011-12-06 13:17:17 -060045 * Try to keep balance_dirty_pages() call intervals higher than this many pages
46 * by raising pause time to max_pause when falls below it.
47 */
48#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
49
50/*
Wu Fengguange98be2d2010-08-29 11:22:30 -060051 * Estimate write bandwidth at 200ms intervals.
52 */
53#define BANDWIDTH_INTERVAL max(HZ/5, 1)
54
Wu Fengguang6c14ae12011-03-02 16:04:18 -060055#define RATELIMIT_CALC_SHIFT 10
56
Wu Fengguange98be2d2010-08-29 11:22:30 -060057/*
Linus Torvalds1da177e2005-04-16 15:20:36 -070058 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
59 * will look to see if it needs to force writeback or throttling.
60 */
61static long ratelimit_pages = 32;
62
Linus Torvalds1da177e2005-04-16 15:20:36 -070063/* The following parameters are exported via /proc/sys/vm */
64
65/*
Jens Axboe5b0830c2009-09-23 19:37:09 +020066 * Start background writeback (via writeback threads) at this percentage
Linus Torvalds1da177e2005-04-16 15:20:36 -070067 */
Wu Fengguang1b5e62b2009-03-23 08:57:38 +080068int dirty_background_ratio = 10;
Linus Torvalds1da177e2005-04-16 15:20:36 -070069
70/*
David Rientjes2da02992009-01-06 14:39:31 -080071 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
72 * dirty_background_ratio * the amount of dirtyable memory
73 */
74unsigned long dirty_background_bytes;
75
76/*
Bron Gondwana195cf452008-02-04 22:29:20 -080077 * free highmem will not be subtracted from the total free memory
78 * for calculating free ratios if vm_highmem_is_dirtyable is true
79 */
80int vm_highmem_is_dirtyable;
81
82/*
Linus Torvalds1da177e2005-04-16 15:20:36 -070083 * The generator of dirty data starts writeback at this percentage
84 */
Wu Fengguang1b5e62b2009-03-23 08:57:38 +080085int vm_dirty_ratio = 20;
Linus Torvalds1da177e2005-04-16 15:20:36 -070086
87/*
David Rientjes2da02992009-01-06 14:39:31 -080088 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
89 * vm_dirty_ratio * the amount of dirtyable memory
90 */
91unsigned long vm_dirty_bytes;
92
93/*
Alexey Dobriyan704503d2009-03-31 15:23:18 -070094 * The interval between `kupdate'-style writebacks
Linus Torvalds1da177e2005-04-16 15:20:36 -070095 */
Toshiyuki Okajima22ef37e2009-05-16 22:56:28 -070096unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
Linus Torvalds1da177e2005-04-16 15:20:36 -070097
Artem Bityutskiy91913a22012-03-21 22:33:00 -040098EXPORT_SYMBOL_GPL(dirty_writeback_interval);
99
Linus Torvalds1da177e2005-04-16 15:20:36 -0700100/*
Alexey Dobriyan704503d2009-03-31 15:23:18 -0700101 * The longest time for which data is allowed to remain dirty
Linus Torvalds1da177e2005-04-16 15:20:36 -0700102 */
Toshiyuki Okajima22ef37e2009-05-16 22:56:28 -0700103unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700104
105/*
106 * Flag that makes the machine dump writes/reads and block dirtyings.
107 */
108int block_dump;
109
110/*
Bart Samweled5b43f2006-03-24 03:15:49 -0800111 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
112 * a full sync is triggered after this time elapses without any disk activity.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700113 */
114int laptop_mode;
115
116EXPORT_SYMBOL(laptop_mode);
117
118/* End of sysctl-exported parameters */
119
Wu Fengguangc42843f2011-03-02 15:54:09 -0600120unsigned long global_dirty_limit;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700121
Linus Torvalds1da177e2005-04-16 15:20:36 -0700122/*
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700123 * Scale the writeback cache size proportional to the relative writeout speeds.
124 *
125 * We do this by keeping a floating proportion between BDIs, based on page
126 * writeback completions [end_page_writeback()]. Those devices that write out
127 * pages fastest will get the larger share, while the slower will get a smaller
128 * share.
129 *
130 * We use page writeout completions because we are interested in getting rid of
131 * dirty pages. Having them written out is the primary goal.
132 *
133 * We introduce a concept of time, a period over which we measure these events,
134 * because demand can/will vary over time. The length of this period itself is
135 * measured in page writeback completions.
136 *
137 */
138static struct prop_descriptor vm_completions;
139
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700140/*
Johannes Weiner1edf2232012-01-10 15:06:57 -0800141 * Work out the current dirty-memory clamping and background writeout
142 * thresholds.
143 *
144 * The main aim here is to lower them aggressively if there is a lot of mapped
145 * memory around. To avoid stressing page reclaim with lots of unreclaimable
146 * pages. It is better to clamp down on writers than to start swapping, and
147 * performing lots of scanning.
148 *
149 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
150 *
151 * We don't permit the clamping level to fall below 5% - that is getting rather
152 * excessive.
153 *
154 * We make sure that the background writeout level is below the adjusted
155 * clamping level.
156 */
Johannes Weinerccafa282012-01-10 15:07:44 -0800157
Johannes Weinera756cf52012-01-10 15:07:49 -0800158/*
159 * In a memory zone, there is a certain amount of pages we consider
160 * available for the page cache, which is essentially the number of
161 * free and reclaimable pages, minus some zone reserves to protect
162 * lowmem and the ability to uphold the zone's watermarks without
163 * requiring writeback.
164 *
165 * This number of dirtyable pages is the base value of which the
166 * user-configurable dirty ratio is the effictive number of pages that
167 * are allowed to be actually dirtied. Per individual zone, or
168 * globally by using the sum of dirtyable pages over all zones.
169 *
170 * Because the user is allowed to specify the dirty limit globally as
171 * absolute number of bytes, calculating the per-zone dirty limit can
172 * require translating the configured limit into a percentage of
173 * global dirtyable memory first.
174 */
175
Johannes Weiner1edf2232012-01-10 15:06:57 -0800176static unsigned long highmem_dirtyable_memory(unsigned long total)
177{
178#ifdef CONFIG_HIGHMEM
179 int node;
180 unsigned long x = 0;
181
182 for_each_node_state(node, N_HIGH_MEMORY) {
183 struct zone *z =
184 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
185
186 x += zone_page_state(z, NR_FREE_PAGES) +
Johannes Weinerab8fabd2012-01-10 15:07:42 -0800187 zone_reclaimable_pages(z) - z->dirty_balance_reserve;
Johannes Weiner1edf2232012-01-10 15:06:57 -0800188 }
189 /*
190 * Make sure that the number of highmem pages is never larger
191 * than the number of the total dirtyable memory. This can only
192 * occur in very strange VM situations but we want to make sure
193 * that this does not occur.
194 */
195 return min(x, total);
196#else
197 return 0;
198#endif
199}
200
201/**
Johannes Weinerccafa282012-01-10 15:07:44 -0800202 * global_dirtyable_memory - number of globally dirtyable pages
Johannes Weiner1edf2232012-01-10 15:06:57 -0800203 *
Johannes Weinerccafa282012-01-10 15:07:44 -0800204 * Returns the global number of pages potentially available for dirty
205 * page cache. This is the base value for the global dirty limits.
Johannes Weiner1edf2232012-01-10 15:06:57 -0800206 */
Johannes Weinerccafa282012-01-10 15:07:44 -0800207unsigned long global_dirtyable_memory(void)
Johannes Weiner1edf2232012-01-10 15:06:57 -0800208{
209 unsigned long x;
210
Johannes Weinerab8fabd2012-01-10 15:07:42 -0800211 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() -
212 dirty_balance_reserve;
Johannes Weiner1edf2232012-01-10 15:06:57 -0800213
214 if (!vm_highmem_is_dirtyable)
215 x -= highmem_dirtyable_memory(x);
216
217 return x + 1; /* Ensure that we never return 0 */
218}
219
220/*
Johannes Weinerccafa282012-01-10 15:07:44 -0800221 * global_dirty_limits - background-writeback and dirty-throttling thresholds
222 *
223 * Calculate the dirty thresholds based on sysctl parameters
224 * - vm.dirty_background_ratio or vm.dirty_background_bytes
225 * - vm.dirty_ratio or vm.dirty_bytes
226 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
227 * real-time tasks.
228 */
229void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
230{
231 unsigned long background;
232 unsigned long dirty;
233 unsigned long uninitialized_var(available_memory);
234 struct task_struct *tsk;
235
236 if (!vm_dirty_bytes || !dirty_background_bytes)
237 available_memory = global_dirtyable_memory();
238
239 if (vm_dirty_bytes)
240 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
241 else
242 dirty = (vm_dirty_ratio * available_memory) / 100;
243
244 if (dirty_background_bytes)
245 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
246 else
247 background = (dirty_background_ratio * available_memory) / 100;
248
249 if (background >= dirty)
250 background = dirty / 2;
251 tsk = current;
252 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
253 background += background / 4;
254 dirty += dirty / 4;
255 }
256 *pbackground = background;
257 *pdirty = dirty;
258 trace_global_dirty_state(background, dirty);
259}
260
Johannes Weinera756cf52012-01-10 15:07:49 -0800261/**
262 * zone_dirtyable_memory - number of dirtyable pages in a zone
263 * @zone: the zone
264 *
265 * Returns the zone's number of pages potentially available for dirty
266 * page cache. This is the base value for the per-zone dirty limits.
267 */
268static unsigned long zone_dirtyable_memory(struct zone *zone)
269{
270 /*
271 * The effective global number of dirtyable pages may exclude
272 * highmem as a big-picture measure to keep the ratio between
273 * dirty memory and lowmem reasonable.
274 *
275 * But this function is purely about the individual zone and a
276 * highmem zone can hold its share of dirty pages, so we don't
277 * care about vm_highmem_is_dirtyable here.
278 */
279 return zone_page_state(zone, NR_FREE_PAGES) +
280 zone_reclaimable_pages(zone) -
281 zone->dirty_balance_reserve;
282}
283
284/**
285 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
286 * @zone: the zone
287 *
288 * Returns the maximum number of dirty pages allowed in a zone, based
289 * on the zone's dirtyable memory.
290 */
291static unsigned long zone_dirty_limit(struct zone *zone)
292{
293 unsigned long zone_memory = zone_dirtyable_memory(zone);
294 struct task_struct *tsk = current;
295 unsigned long dirty;
296
297 if (vm_dirty_bytes)
298 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
299 zone_memory / global_dirtyable_memory();
300 else
301 dirty = vm_dirty_ratio * zone_memory / 100;
302
303 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
304 dirty += dirty / 4;
305
306 return dirty;
307}
308
309/**
310 * zone_dirty_ok - tells whether a zone is within its dirty limits
311 * @zone: the zone to check
312 *
313 * Returns %true when the dirty pages in @zone are within the zone's
314 * dirty limit, %false if the limit is exceeded.
315 */
316bool zone_dirty_ok(struct zone *zone)
317{
318 unsigned long limit = zone_dirty_limit(zone);
319
320 return zone_page_state(zone, NR_FILE_DIRTY) +
321 zone_page_state(zone, NR_UNSTABLE_NFS) +
322 zone_page_state(zone, NR_WRITEBACK) <= limit;
323}
324
Johannes Weinerccafa282012-01-10 15:07:44 -0800325/*
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700326 * couple the period to the dirty_ratio:
327 *
328 * period/2 ~ roundup_pow_of_two(dirty limit)
329 */
330static int calc_period_shift(void)
331{
332 unsigned long dirty_total;
333
David Rientjes2da02992009-01-06 14:39:31 -0800334 if (vm_dirty_bytes)
335 dirty_total = vm_dirty_bytes / PAGE_SIZE;
336 else
Johannes Weinerccafa282012-01-10 15:07:44 -0800337 dirty_total = (vm_dirty_ratio * global_dirtyable_memory()) /
David Rientjes2da02992009-01-06 14:39:31 -0800338 100;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700339 return 2 + ilog2(dirty_total - 1);
340}
341
342/*
David Rientjes2da02992009-01-06 14:39:31 -0800343 * update the period when the dirty threshold changes.
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700344 */
David Rientjes2da02992009-01-06 14:39:31 -0800345static void update_completion_period(void)
346{
347 int shift = calc_period_shift();
348 prop_change_shift(&vm_completions, shift);
Wu Fengguang9d823e82011-06-11 18:10:12 -0600349
350 writeback_set_ratelimit();
David Rientjes2da02992009-01-06 14:39:31 -0800351}
352
353int dirty_background_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700354 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800355 loff_t *ppos)
356{
357 int ret;
358
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700359 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800360 if (ret == 0 && write)
361 dirty_background_bytes = 0;
362 return ret;
363}
364
365int dirty_background_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700366 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800367 loff_t *ppos)
368{
369 int ret;
370
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700371 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800372 if (ret == 0 && write)
373 dirty_background_ratio = 0;
374 return ret;
375}
376
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700377int dirty_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700378 void __user *buffer, size_t *lenp,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700379 loff_t *ppos)
380{
381 int old_ratio = vm_dirty_ratio;
David Rientjes2da02992009-01-06 14:39:31 -0800382 int ret;
383
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700384 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700385 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
David Rientjes2da02992009-01-06 14:39:31 -0800386 update_completion_period();
387 vm_dirty_bytes = 0;
388 }
389 return ret;
390}
391
David Rientjes2da02992009-01-06 14:39:31 -0800392int dirty_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700393 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800394 loff_t *ppos)
395{
Sven Wegenerfc3501d2009-02-11 13:04:23 -0800396 unsigned long old_bytes = vm_dirty_bytes;
David Rientjes2da02992009-01-06 14:39:31 -0800397 int ret;
398
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700399 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800400 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
401 update_completion_period();
402 vm_dirty_ratio = 0;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700403 }
404 return ret;
405}
406
407/*
408 * Increment the BDI's writeout completion count and the global writeout
409 * completion count. Called from test_clear_page_writeback().
410 */
411static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
412{
Jan Karaf7d2b1e2010-12-08 22:44:24 -0600413 __inc_bdi_stat(bdi, BDI_WRITTEN);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700414 __prop_inc_percpu_max(&vm_completions, &bdi->completions,
415 bdi->max_prop_frac);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700416}
417
Miklos Szeredidd5656e2008-04-30 00:54:37 -0700418void bdi_writeout_inc(struct backing_dev_info *bdi)
419{
420 unsigned long flags;
421
422 local_irq_save(flags);
423 __bdi_writeout_inc(bdi);
424 local_irq_restore(flags);
425}
426EXPORT_SYMBOL_GPL(bdi_writeout_inc);
427
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700428/*
429 * Obtain an accurate fraction of the BDI's portion.
430 */
431static void bdi_writeout_fraction(struct backing_dev_info *bdi,
432 long *numerator, long *denominator)
433{
Wu Fengguang3efaf0f2010-12-16 22:22:00 -0600434 prop_fraction_percpu(&vm_completions, &bdi->completions,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700435 numerator, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700436}
437
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700438/*
Johannes Weinerd08c4292011-10-31 17:07:05 -0700439 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
440 * registered backing devices, which, for obvious reasons, can not
441 * exceed 100%.
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700442 */
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700443static unsigned int bdi_min_ratio;
444
445int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
446{
447 int ret = 0;
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700448
Jens Axboecfc4ba52009-09-14 13:12:40 +0200449 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700450 if (min_ratio > bdi->max_ratio) {
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700451 ret = -EINVAL;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700452 } else {
453 min_ratio -= bdi->min_ratio;
454 if (bdi_min_ratio + min_ratio < 100) {
455 bdi_min_ratio += min_ratio;
456 bdi->min_ratio += min_ratio;
457 } else {
458 ret = -EINVAL;
459 }
460 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200461 spin_unlock_bh(&bdi_lock);
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700462
463 return ret;
464}
465
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700466int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
467{
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700468 int ret = 0;
469
470 if (max_ratio > 100)
471 return -EINVAL;
472
Jens Axboecfc4ba52009-09-14 13:12:40 +0200473 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700474 if (bdi->min_ratio > max_ratio) {
475 ret = -EINVAL;
476 } else {
477 bdi->max_ratio = max_ratio;
478 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
479 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200480 spin_unlock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700481
482 return ret;
483}
484EXPORT_SYMBOL(bdi_set_max_ratio);
485
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600486static unsigned long dirty_freerun_ceiling(unsigned long thresh,
487 unsigned long bg_thresh)
488{
489 return (thresh + bg_thresh) / 2;
490}
491
Wu Fengguangffd1f602011-06-19 22:18:42 -0600492static unsigned long hard_dirty_limit(unsigned long thresh)
493{
494 return max(thresh, global_dirty_limit);
495}
496
Wu Fengguang6f718652011-03-02 17:14:34 -0600497/**
Wu Fengguang1babe182010-08-11 14:17:40 -0700498 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
Wu Fengguang6f718652011-03-02 17:14:34 -0600499 * @bdi: the backing_dev_info to query
500 * @dirty: global dirty limit in pages
Wu Fengguang1babe182010-08-11 14:17:40 -0700501 *
Wu Fengguang6f718652011-03-02 17:14:34 -0600502 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
503 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
Wu Fengguangaed21ad2011-11-23 11:44:41 -0600504 *
505 * Note that balance_dirty_pages() will only seriously take it as a hard limit
506 * when sleeping max_pause per page is not enough to keep the dirty pages under
507 * control. For example, when the device is completely stalled due to some error
508 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
509 * In the other normal situations, it acts more gently by throttling the tasks
510 * more (rather than completely block them) when the bdi dirty pages go high.
Wu Fengguang6f718652011-03-02 17:14:34 -0600511 *
512 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
Wu Fengguang1babe182010-08-11 14:17:40 -0700513 * - starving fast devices
514 * - piling up dirty pages (that will take long time to sync) on slow devices
515 *
516 * The bdi's share of dirty limit will be adapting to its throughput and
517 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
518 */
519unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
Wu Fengguang16c40422010-08-11 14:17:39 -0700520{
521 u64 bdi_dirty;
522 long numerator, denominator;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700523
Wu Fengguang16c40422010-08-11 14:17:39 -0700524 /*
525 * Calculate this BDI's share of the dirty ratio.
526 */
527 bdi_writeout_fraction(bdi, &numerator, &denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700528
Wu Fengguang16c40422010-08-11 14:17:39 -0700529 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
530 bdi_dirty *= numerator;
531 do_div(bdi_dirty, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700532
Wu Fengguang16c40422010-08-11 14:17:39 -0700533 bdi_dirty += (dirty * bdi->min_ratio) / 100;
534 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
535 bdi_dirty = dirty * bdi->max_ratio / 100;
536
537 return bdi_dirty;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700538}
539
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600540/*
541 * Dirty position control.
542 *
543 * (o) global/bdi setpoints
544 *
545 * We want the dirty pages be balanced around the global/bdi setpoints.
546 * When the number of dirty pages is higher/lower than the setpoint, the
547 * dirty position control ratio (and hence task dirty ratelimit) will be
548 * decreased/increased to bring the dirty pages back to the setpoint.
549 *
550 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
551 *
552 * if (dirty < setpoint) scale up pos_ratio
553 * if (dirty > setpoint) scale down pos_ratio
554 *
555 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
556 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
557 *
558 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
559 *
560 * (o) global control line
561 *
562 * ^ pos_ratio
563 * |
564 * | |<===== global dirty control scope ======>|
565 * 2.0 .............*
566 * | .*
567 * | . *
568 * | . *
569 * | . *
570 * | . *
571 * | . *
572 * 1.0 ................................*
573 * | . . *
574 * | . . *
575 * | . . *
576 * | . . *
577 * | . . *
578 * 0 +------------.------------------.----------------------*------------->
579 * freerun^ setpoint^ limit^ dirty pages
580 *
581 * (o) bdi control line
582 *
583 * ^ pos_ratio
584 * |
585 * | *
586 * | *
587 * | *
588 * | *
589 * | * |<=========== span ============>|
590 * 1.0 .......................*
591 * | . *
592 * | . *
593 * | . *
594 * | . *
595 * | . *
596 * | . *
597 * | . *
598 * | . *
599 * | . *
600 * | . *
601 * | . *
602 * 1/4 ...............................................* * * * * * * * * * * *
603 * | . .
604 * | . .
605 * | . .
606 * 0 +----------------------.-------------------------------.------------->
607 * bdi_setpoint^ x_intercept^
608 *
609 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
610 * be smoothly throttled down to normal if it starts high in situations like
611 * - start writing to a slow SD card and a fast disk at the same time. The SD
612 * card's bdi_dirty may rush to many times higher than bdi_setpoint.
613 * - the bdi dirty thresh drops quickly due to change of JBOD workload
614 */
615static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
616 unsigned long thresh,
617 unsigned long bg_thresh,
618 unsigned long dirty,
619 unsigned long bdi_thresh,
620 unsigned long bdi_dirty)
621{
622 unsigned long write_bw = bdi->avg_write_bandwidth;
623 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
624 unsigned long limit = hard_dirty_limit(thresh);
625 unsigned long x_intercept;
626 unsigned long setpoint; /* dirty pages' target balance point */
627 unsigned long bdi_setpoint;
628 unsigned long span;
629 long long pos_ratio; /* for scaling up/down the rate limit */
630 long x;
631
632 if (unlikely(dirty >= limit))
633 return 0;
634
635 /*
636 * global setpoint
637 *
638 * setpoint - dirty 3
639 * f(dirty) := 1.0 + (----------------)
640 * limit - setpoint
641 *
642 * it's a 3rd order polynomial that subjects to
643 *
644 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
645 * (2) f(setpoint) = 1.0 => the balance point
646 * (3) f(limit) = 0 => the hard limit
647 * (4) df/dx <= 0 => negative feedback control
648 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
649 * => fast response on large errors; small oscillation near setpoint
650 */
651 setpoint = (freerun + limit) / 2;
652 x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
653 limit - setpoint + 1);
654 pos_ratio = x;
655 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
656 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
657 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
658
659 /*
660 * We have computed basic pos_ratio above based on global situation. If
661 * the bdi is over/under its share of dirty pages, we want to scale
662 * pos_ratio further down/up. That is done by the following mechanism.
663 */
664
665 /*
666 * bdi setpoint
667 *
668 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
669 *
670 * x_intercept - bdi_dirty
671 * := --------------------------
672 * x_intercept - bdi_setpoint
673 *
674 * The main bdi control line is a linear function that subjects to
675 *
676 * (1) f(bdi_setpoint) = 1.0
677 * (2) k = - 1 / (8 * write_bw) (in single bdi case)
678 * or equally: x_intercept = bdi_setpoint + 8 * write_bw
679 *
680 * For single bdi case, the dirty pages are observed to fluctuate
681 * regularly within range
682 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
683 * for various filesystems, where (2) can yield in a reasonable 12.5%
684 * fluctuation range for pos_ratio.
685 *
686 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
687 * own size, so move the slope over accordingly and choose a slope that
688 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
689 */
690 if (unlikely(bdi_thresh > thresh))
691 bdi_thresh = thresh;
Wu Fengguangaed21ad2011-11-23 11:44:41 -0600692 /*
693 * It's very possible that bdi_thresh is close to 0 not because the
694 * device is slow, but that it has remained inactive for long time.
695 * Honour such devices a reasonable good (hopefully IO efficient)
696 * threshold, so that the occasional writes won't be blocked and active
697 * writes can rampup the threshold quickly.
698 */
Wu Fengguang8927f662011-08-04 22:16:46 -0600699 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600700 /*
701 * scale global setpoint to bdi's:
702 * bdi_setpoint = setpoint * bdi_thresh / thresh
703 */
704 x = div_u64((u64)bdi_thresh << 16, thresh + 1);
705 bdi_setpoint = setpoint * (u64)x >> 16;
706 /*
707 * Use span=(8*write_bw) in single bdi case as indicated by
708 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
709 *
710 * bdi_thresh thresh - bdi_thresh
711 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
712 * thresh thresh
713 */
714 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
715 x_intercept = bdi_setpoint + span;
716
717 if (bdi_dirty < x_intercept - span / 4) {
Wu Fengguang50657fc2011-10-11 17:06:33 -0600718 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
719 x_intercept - bdi_setpoint + 1);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600720 } else
721 pos_ratio /= 4;
722
Wu Fengguang8927f662011-08-04 22:16:46 -0600723 /*
724 * bdi reserve area, safeguard against dirty pool underrun and disk idle
725 * It may push the desired control point of global dirty pages higher
726 * than setpoint.
727 */
728 x_intercept = bdi_thresh / 2;
729 if (bdi_dirty < x_intercept) {
Wu Fengguang50657fc2011-10-11 17:06:33 -0600730 if (bdi_dirty > x_intercept / 8)
731 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
732 else
Wu Fengguang8927f662011-08-04 22:16:46 -0600733 pos_ratio *= 8;
734 }
735
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600736 return pos_ratio;
737}
738
Wu Fengguange98be2d2010-08-29 11:22:30 -0600739static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
740 unsigned long elapsed,
741 unsigned long written)
742{
743 const unsigned long period = roundup_pow_of_two(3 * HZ);
744 unsigned long avg = bdi->avg_write_bandwidth;
745 unsigned long old = bdi->write_bandwidth;
746 u64 bw;
747
748 /*
749 * bw = written * HZ / elapsed
750 *
751 * bw * elapsed + write_bandwidth * (period - elapsed)
752 * write_bandwidth = ---------------------------------------------------
753 * period
754 */
755 bw = written - bdi->written_stamp;
756 bw *= HZ;
757 if (unlikely(elapsed > period)) {
758 do_div(bw, elapsed);
759 avg = bw;
760 goto out;
761 }
762 bw += (u64)bdi->write_bandwidth * (period - elapsed);
763 bw >>= ilog2(period);
764
765 /*
766 * one more level of smoothing, for filtering out sudden spikes
767 */
768 if (avg > old && old >= (unsigned long)bw)
769 avg -= (avg - old) >> 3;
770
771 if (avg < old && old <= (unsigned long)bw)
772 avg += (old - avg) >> 3;
773
774out:
775 bdi->write_bandwidth = bw;
776 bdi->avg_write_bandwidth = avg;
777}
778
Wu Fengguangc42843f2011-03-02 15:54:09 -0600779/*
780 * The global dirtyable memory and dirty threshold could be suddenly knocked
781 * down by a large amount (eg. on the startup of KVM in a swapless system).
782 * This may throw the system into deep dirty exceeded state and throttle
783 * heavy/light dirtiers alike. To retain good responsiveness, maintain
784 * global_dirty_limit for tracking slowly down to the knocked down dirty
785 * threshold.
786 */
787static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
788{
789 unsigned long limit = global_dirty_limit;
790
791 /*
792 * Follow up in one step.
793 */
794 if (limit < thresh) {
795 limit = thresh;
796 goto update;
797 }
798
799 /*
800 * Follow down slowly. Use the higher one as the target, because thresh
801 * may drop below dirty. This is exactly the reason to introduce
802 * global_dirty_limit which is guaranteed to lie above the dirty pages.
803 */
804 thresh = max(thresh, dirty);
805 if (limit > thresh) {
806 limit -= (limit - thresh) >> 5;
807 goto update;
808 }
809 return;
810update:
811 global_dirty_limit = limit;
812}
813
814static void global_update_bandwidth(unsigned long thresh,
815 unsigned long dirty,
816 unsigned long now)
817{
818 static DEFINE_SPINLOCK(dirty_lock);
819 static unsigned long update_time;
820
821 /*
822 * check locklessly first to optimize away locking for the most time
823 */
824 if (time_before(now, update_time + BANDWIDTH_INTERVAL))
825 return;
826
827 spin_lock(&dirty_lock);
828 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
829 update_dirty_limit(thresh, dirty);
830 update_time = now;
831 }
832 spin_unlock(&dirty_lock);
833}
834
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600835/*
836 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
837 *
838 * Normal bdi tasks will be curbed at or below it in long term.
839 * Obviously it should be around (write_bw / N) when there are N dd tasks.
840 */
841static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
842 unsigned long thresh,
843 unsigned long bg_thresh,
844 unsigned long dirty,
845 unsigned long bdi_thresh,
846 unsigned long bdi_dirty,
847 unsigned long dirtied,
848 unsigned long elapsed)
849{
Wu Fengguang73811312011-08-26 15:53:24 -0600850 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
851 unsigned long limit = hard_dirty_limit(thresh);
852 unsigned long setpoint = (freerun + limit) / 2;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600853 unsigned long write_bw = bdi->avg_write_bandwidth;
854 unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
855 unsigned long dirty_rate;
856 unsigned long task_ratelimit;
857 unsigned long balanced_dirty_ratelimit;
858 unsigned long pos_ratio;
Wu Fengguang73811312011-08-26 15:53:24 -0600859 unsigned long step;
860 unsigned long x;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600861
862 /*
863 * The dirty rate will match the writeout rate in long term, except
864 * when dirty pages are truncated by userspace or re-dirtied by FS.
865 */
866 dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
867
868 pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
869 bdi_thresh, bdi_dirty);
870 /*
871 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
872 */
873 task_ratelimit = (u64)dirty_ratelimit *
874 pos_ratio >> RATELIMIT_CALC_SHIFT;
875 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
876
877 /*
878 * A linear estimation of the "balanced" throttle rate. The theory is,
879 * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
880 * dirty_rate will be measured to be (N * task_ratelimit). So the below
881 * formula will yield the balanced rate limit (write_bw / N).
882 *
883 * Note that the expanded form is not a pure rate feedback:
884 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
885 * but also takes pos_ratio into account:
886 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
887 *
888 * (1) is not realistic because pos_ratio also takes part in balancing
889 * the dirty rate. Consider the state
890 * pos_ratio = 0.5 (3)
891 * rate = 2 * (write_bw / N) (4)
892 * If (1) is used, it will stuck in that state! Because each dd will
893 * be throttled at
894 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
895 * yielding
896 * dirty_rate = N * task_ratelimit = write_bw (6)
897 * put (6) into (1) we get
898 * rate_(i+1) = rate_(i) (7)
899 *
900 * So we end up using (2) to always keep
901 * rate_(i+1) ~= (write_bw / N) (8)
902 * regardless of the value of pos_ratio. As long as (8) is satisfied,
903 * pos_ratio is able to drive itself to 1.0, which is not only where
904 * the dirty count meet the setpoint, but also where the slope of
905 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
906 */
907 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
908 dirty_rate | 1);
Wu Fengguangbdaac492011-08-03 14:30:36 -0600909 /*
910 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
911 */
912 if (unlikely(balanced_dirty_ratelimit > write_bw))
913 balanced_dirty_ratelimit = write_bw;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600914
Wu Fengguang73811312011-08-26 15:53:24 -0600915 /*
916 * We could safely do this and return immediately:
917 *
918 * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
919 *
920 * However to get a more stable dirty_ratelimit, the below elaborated
921 * code makes use of task_ratelimit to filter out sigular points and
922 * limit the step size.
923 *
924 * The below code essentially only uses the relative value of
925 *
926 * task_ratelimit - dirty_ratelimit
927 * = (pos_ratio - 1) * dirty_ratelimit
928 *
929 * which reflects the direction and size of dirty position error.
930 */
931
932 /*
933 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
934 * task_ratelimit is on the same side of dirty_ratelimit, too.
935 * For example, when
936 * - dirty_ratelimit > balanced_dirty_ratelimit
937 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
938 * lowering dirty_ratelimit will help meet both the position and rate
939 * control targets. Otherwise, don't update dirty_ratelimit if it will
940 * only help meet the rate target. After all, what the users ultimately
941 * feel and care are stable dirty rate and small position error.
942 *
943 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
944 * and filter out the sigular points of balanced_dirty_ratelimit. Which
945 * keeps jumping around randomly and can even leap far away at times
946 * due to the small 200ms estimation period of dirty_rate (we want to
947 * keep that period small to reduce time lags).
948 */
949 step = 0;
950 if (dirty < setpoint) {
951 x = min(bdi->balanced_dirty_ratelimit,
952 min(balanced_dirty_ratelimit, task_ratelimit));
953 if (dirty_ratelimit < x)
954 step = x - dirty_ratelimit;
955 } else {
956 x = max(bdi->balanced_dirty_ratelimit,
957 max(balanced_dirty_ratelimit, task_ratelimit));
958 if (dirty_ratelimit > x)
959 step = dirty_ratelimit - x;
960 }
961
962 /*
963 * Don't pursue 100% rate matching. It's impossible since the balanced
964 * rate itself is constantly fluctuating. So decrease the track speed
965 * when it gets close to the target. Helps eliminate pointless tremors.
966 */
967 step >>= dirty_ratelimit / (2 * step + 1);
968 /*
969 * Limit the tracking speed to avoid overshooting.
970 */
971 step = (step + 7) / 8;
972
973 if (dirty_ratelimit < balanced_dirty_ratelimit)
974 dirty_ratelimit += step;
975 else
976 dirty_ratelimit -= step;
977
978 bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
979 bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
Wu Fengguangb48c1042011-03-02 17:22:49 -0600980
981 trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600982}
983
Wu Fengguange98be2d2010-08-29 11:22:30 -0600984void __bdi_update_bandwidth(struct backing_dev_info *bdi,
Wu Fengguangc42843f2011-03-02 15:54:09 -0600985 unsigned long thresh,
Wu Fengguangaf6a3112011-10-03 20:46:17 -0600986 unsigned long bg_thresh,
Wu Fengguangc42843f2011-03-02 15:54:09 -0600987 unsigned long dirty,
988 unsigned long bdi_thresh,
989 unsigned long bdi_dirty,
Wu Fengguange98be2d2010-08-29 11:22:30 -0600990 unsigned long start_time)
991{
992 unsigned long now = jiffies;
993 unsigned long elapsed = now - bdi->bw_time_stamp;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600994 unsigned long dirtied;
Wu Fengguange98be2d2010-08-29 11:22:30 -0600995 unsigned long written;
996
997 /*
998 * rate-limit, only update once every 200ms.
999 */
1000 if (elapsed < BANDWIDTH_INTERVAL)
1001 return;
1002
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001003 dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001004 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1005
1006 /*
1007 * Skip quiet periods when disk bandwidth is under-utilized.
1008 * (at least 1s idle time between two flusher runs)
1009 */
1010 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1011 goto snapshot;
1012
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001013 if (thresh) {
Wu Fengguangc42843f2011-03-02 15:54:09 -06001014 global_update_bandwidth(thresh, dirty, now);
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001015 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1016 bdi_thresh, bdi_dirty,
1017 dirtied, elapsed);
1018 }
Wu Fengguange98be2d2010-08-29 11:22:30 -06001019 bdi_update_write_bandwidth(bdi, elapsed, written);
1020
1021snapshot:
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001022 bdi->dirtied_stamp = dirtied;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001023 bdi->written_stamp = written;
1024 bdi->bw_time_stamp = now;
1025}
1026
1027static void bdi_update_bandwidth(struct backing_dev_info *bdi,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001028 unsigned long thresh,
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001029 unsigned long bg_thresh,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001030 unsigned long dirty,
1031 unsigned long bdi_thresh,
1032 unsigned long bdi_dirty,
Wu Fengguange98be2d2010-08-29 11:22:30 -06001033 unsigned long start_time)
1034{
1035 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1036 return;
1037 spin_lock(&bdi->wb.list_lock);
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001038 __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1039 bdi_thresh, bdi_dirty, start_time);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001040 spin_unlock(&bdi->wb.list_lock);
1041}
1042
Linus Torvalds1da177e2005-04-16 15:20:36 -07001043/*
Wu Fengguang9d823e82011-06-11 18:10:12 -06001044 * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
1045 * will look to see if it needs to start dirty throttling.
1046 *
1047 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1048 * global_page_state() too often. So scale it near-sqrt to the safety margin
1049 * (the number of pages we may dirty without exceeding the dirty limits).
1050 */
1051static unsigned long dirty_poll_interval(unsigned long dirty,
1052 unsigned long thresh)
1053{
1054 if (thresh > dirty)
1055 return 1UL << (ilog2(thresh - dirty) >> 1);
1056
1057 return 1;
1058}
1059
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001060static long bdi_max_pause(struct backing_dev_info *bdi,
1061 unsigned long bdi_dirty)
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001062{
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001063 long bw = bdi->avg_write_bandwidth;
1064 long t;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001065
1066 /*
1067 * Limit pause time for small memory systems. If sleeping for too long
1068 * time, a small pool of dirty/writeback pages may go empty and disk go
1069 * idle.
1070 *
1071 * 8 serves as the safety ratio.
1072 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001073 t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1074 t++;
1075
1076 return min_t(long, t, MAX_PAUSE);
1077}
1078
1079static long bdi_min_pause(struct backing_dev_info *bdi,
1080 long max_pause,
1081 unsigned long task_ratelimit,
1082 unsigned long dirty_ratelimit,
1083 int *nr_dirtied_pause)
1084{
1085 long hi = ilog2(bdi->avg_write_bandwidth);
1086 long lo = ilog2(bdi->dirty_ratelimit);
1087 long t; /* target pause */
1088 long pause; /* estimated next pause */
1089 int pages; /* target nr_dirtied_pause */
1090
1091 /* target for 10ms pause on 1-dd case */
1092 t = max(1, HZ / 100);
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001093
1094 /*
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001095 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1096 * overheads.
1097 *
1098 * (N * 10ms) on 2^N concurrent tasks.
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001099 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001100 if (hi > lo)
1101 t += (hi - lo) * (10 * HZ) / 1024;
1102
1103 /*
1104 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1105 * on the much more stable dirty_ratelimit. However the next pause time
1106 * will be computed based on task_ratelimit and the two rate limits may
1107 * depart considerably at some time. Especially if task_ratelimit goes
1108 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1109 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1110 * result task_ratelimit won't be executed faithfully, which could
1111 * eventually bring down dirty_ratelimit.
1112 *
1113 * We apply two rules to fix it up:
1114 * 1) try to estimate the next pause time and if necessary, use a lower
1115 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1116 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1117 * 2) limit the target pause time to max_pause/2, so that the normal
1118 * small fluctuations of task_ratelimit won't trigger rule (1) and
1119 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1120 */
1121 t = min(t, 1 + max_pause / 2);
1122 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1123
Wu Fengguang5b9b3572011-12-06 13:17:17 -06001124 /*
1125 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1126 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1127 * When the 16 consecutive reads are often interrupted by some dirty
1128 * throttling pause during the async writes, cfq will go into idles
1129 * (deadline is fine). So push nr_dirtied_pause as high as possible
1130 * until reaches DIRTY_POLL_THRESH=32 pages.
1131 */
1132 if (pages < DIRTY_POLL_THRESH) {
1133 t = max_pause;
1134 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1135 if (pages > DIRTY_POLL_THRESH) {
1136 pages = DIRTY_POLL_THRESH;
1137 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1138 }
1139 }
1140
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001141 pause = HZ * pages / (task_ratelimit + 1);
1142 if (pause > max_pause) {
1143 t = max_pause;
1144 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1145 }
1146
1147 *nr_dirtied_pause = pages;
1148 /*
1149 * The minimal pause time will normally be half the target pause time.
1150 */
Wu Fengguang5b9b3572011-12-06 13:17:17 -06001151 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001152}
1153
Wu Fengguang9d823e82011-06-11 18:10:12 -06001154/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001155 * balance_dirty_pages() must be called by processes which are generating dirty
1156 * data. It looks at the number of dirty pages in the machine and will force
Wu Fengguang143dfe82010-08-27 18:45:12 -06001157 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
Jens Axboe5b0830c2009-09-23 19:37:09 +02001158 * If we're over `background_thresh' then the writeback threads are woken to
1159 * perform some writeout.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001160 */
Wu Fengguang3a2e9a52009-09-23 21:56:00 +08001161static void balance_dirty_pages(struct address_space *mapping,
Wu Fengguang143dfe82010-08-27 18:45:12 -06001162 unsigned long pages_dirtied)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001163{
Wu Fengguang143dfe82010-08-27 18:45:12 -06001164 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1165 unsigned long bdi_reclaimable;
Wu Fengguang77627412010-09-12 13:34:05 -06001166 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
1167 unsigned long bdi_dirty;
Wu Fengguang6c14ae12011-03-02 16:04:18 -06001168 unsigned long freerun;
David Rientjes364aeb22009-01-06 14:39:29 -08001169 unsigned long background_thresh;
1170 unsigned long dirty_thresh;
1171 unsigned long bdi_thresh;
Wu Fengguang83712352011-06-11 19:25:42 -06001172 long period;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001173 long pause;
1174 long max_pause;
1175 long min_pause;
1176 int nr_dirtied_pause;
Wu Fengguange50e3722010-08-11 14:17:37 -07001177 bool dirty_exceeded = false;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001178 unsigned long task_ratelimit;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001179 unsigned long dirty_ratelimit;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001180 unsigned long pos_ratio;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001181 struct backing_dev_info *bdi = mapping->backing_dev_info;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001182 unsigned long start_time = jiffies;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001183
1184 for (;;) {
Wu Fengguang83712352011-06-11 19:25:42 -06001185 unsigned long now = jiffies;
1186
Wu Fengguang143dfe82010-08-27 18:45:12 -06001187 /*
1188 * Unstable writes are a feature of certain networked
1189 * filesystems (i.e. NFS) in which data may have been
1190 * written to the server's write cache, but has not yet
1191 * been flushed to permanent storage.
1192 */
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001193 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1194 global_page_state(NR_UNSTABLE_NFS);
Wu Fengguang77627412010-09-12 13:34:05 -06001195 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001196
Wu Fengguang16c40422010-08-11 14:17:39 -07001197 global_dirty_limits(&background_thresh, &dirty_thresh);
1198
1199 /*
1200 * Throttle it only when the background writeback cannot
1201 * catch-up. This avoids (excessively) small writeouts
1202 * when the bdi limits are ramping up.
1203 */
Wu Fengguang6c14ae12011-03-02 16:04:18 -06001204 freerun = dirty_freerun_ceiling(dirty_thresh,
1205 background_thresh);
Wu Fengguang83712352011-06-11 19:25:42 -06001206 if (nr_dirty <= freerun) {
1207 current->dirty_paused_when = now;
1208 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001209 current->nr_dirtied_pause =
1210 dirty_poll_interval(nr_dirty, dirty_thresh);
Wu Fengguang16c40422010-08-11 14:17:39 -07001211 break;
Wu Fengguang83712352011-06-11 19:25:42 -06001212 }
Wu Fengguang16c40422010-08-11 14:17:39 -07001213
Wu Fengguang143dfe82010-08-27 18:45:12 -06001214 if (unlikely(!writeback_in_progress(bdi)))
1215 bdi_start_background_writeback(bdi);
1216
1217 /*
1218 * bdi_thresh is not treated as some limiting factor as
1219 * dirty_thresh, due to reasons
1220 * - in JBOD setup, bdi_thresh can fluctuate a lot
1221 * - in a system with HDD and USB key, the USB key may somehow
1222 * go into state (bdi_dirty >> bdi_thresh) either because
1223 * bdi_dirty starts high, or because bdi_thresh drops low.
1224 * In this case we don't want to hard throttle the USB key
1225 * dirtiers for 100 seconds until bdi_dirty drops under
1226 * bdi_thresh. Instead the auxiliary bdi control line in
1227 * bdi_position_ratio() will let the dirtier task progress
1228 * at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1229 */
Wu Fengguang16c40422010-08-11 14:17:39 -07001230 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
Wu Fengguang16c40422010-08-11 14:17:39 -07001231
Wu Fengguange50e3722010-08-11 14:17:37 -07001232 /*
1233 * In order to avoid the stacked BDI deadlock we need
1234 * to ensure we accurately count the 'dirty' pages when
1235 * the threshold is low.
1236 *
1237 * Otherwise it would be possible to get thresh+n pages
1238 * reported dirty, even though there are thresh-m pages
1239 * actually dirty; with m+n sitting in the percpu
1240 * deltas.
1241 */
Wu Fengguang143dfe82010-08-27 18:45:12 -06001242 if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1243 bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1244 bdi_dirty = bdi_reclaimable +
Wu Fengguang77627412010-09-12 13:34:05 -06001245 bdi_stat_sum(bdi, BDI_WRITEBACK);
Wu Fengguange50e3722010-08-11 14:17:37 -07001246 } else {
Wu Fengguang143dfe82010-08-27 18:45:12 -06001247 bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1248 bdi_dirty = bdi_reclaimable +
Wu Fengguang77627412010-09-12 13:34:05 -06001249 bdi_stat(bdi, BDI_WRITEBACK);
Wu Fengguange50e3722010-08-11 14:17:37 -07001250 }
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001251
Wu Fengguang82791942011-12-03 21:26:01 -06001252 dirty_exceeded = (bdi_dirty > bdi_thresh) &&
Wu Fengguang77627412010-09-12 13:34:05 -06001253 (nr_dirty > dirty_thresh);
Wu Fengguang143dfe82010-08-27 18:45:12 -06001254 if (dirty_exceeded && !bdi->dirty_exceeded)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001255 bdi->dirty_exceeded = 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001256
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001257 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1258 nr_dirty, bdi_thresh, bdi_dirty,
1259 start_time);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001260
Wu Fengguang143dfe82010-08-27 18:45:12 -06001261 dirty_ratelimit = bdi->dirty_ratelimit;
1262 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1263 background_thresh, nr_dirty,
1264 bdi_thresh, bdi_dirty);
Wu Fengguang3a73dbb2011-11-07 19:19:28 +08001265 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1266 RATELIMIT_CALC_SHIFT;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001267 max_pause = bdi_max_pause(bdi, bdi_dirty);
1268 min_pause = bdi_min_pause(bdi, max_pause,
1269 task_ratelimit, dirty_ratelimit,
1270 &nr_dirtied_pause);
1271
Wu Fengguang3a73dbb2011-11-07 19:19:28 +08001272 if (unlikely(task_ratelimit == 0)) {
Wu Fengguang83712352011-06-11 19:25:42 -06001273 period = max_pause;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001274 pause = max_pause;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001275 goto pause;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001276 }
Wu Fengguang83712352011-06-11 19:25:42 -06001277 period = HZ * pages_dirtied / task_ratelimit;
1278 pause = period;
1279 if (current->dirty_paused_when)
1280 pause -= now - current->dirty_paused_when;
1281 /*
1282 * For less than 1s think time (ext3/4 may block the dirtier
1283 * for up to 800ms from time to time on 1-HDD; so does xfs,
1284 * however at much less frequency), try to compensate it in
1285 * future periods by updating the virtual time; otherwise just
1286 * do a reset, as it may be a light dirtier.
1287 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001288 if (pause < min_pause) {
Wu Fengguangece13ac2010-08-29 23:33:20 -06001289 trace_balance_dirty_pages(bdi,
1290 dirty_thresh,
1291 background_thresh,
1292 nr_dirty,
1293 bdi_thresh,
1294 bdi_dirty,
1295 dirty_ratelimit,
1296 task_ratelimit,
1297 pages_dirtied,
Wu Fengguang83712352011-06-11 19:25:42 -06001298 period,
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001299 min(pause, 0L),
Wu Fengguangece13ac2010-08-29 23:33:20 -06001300 start_time);
Wu Fengguang83712352011-06-11 19:25:42 -06001301 if (pause < -HZ) {
1302 current->dirty_paused_when = now;
1303 current->nr_dirtied = 0;
1304 } else if (period) {
1305 current->dirty_paused_when += period;
1306 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001307 } else if (current->nr_dirtied_pause <= pages_dirtied)
1308 current->nr_dirtied_pause += pages_dirtied;
Wu Fengguang57fc9782011-06-11 19:32:32 -06001309 break;
1310 }
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001311 if (unlikely(pause > max_pause)) {
1312 /* for occasional dropped task_ratelimit */
1313 now += min(pause - max_pause, max_pause);
1314 pause = max_pause;
1315 }
Wu Fengguang143dfe82010-08-27 18:45:12 -06001316
1317pause:
Wu Fengguangece13ac2010-08-29 23:33:20 -06001318 trace_balance_dirty_pages(bdi,
1319 dirty_thresh,
1320 background_thresh,
1321 nr_dirty,
1322 bdi_thresh,
1323 bdi_dirty,
1324 dirty_ratelimit,
1325 task_ratelimit,
1326 pages_dirtied,
Wu Fengguang83712352011-06-11 19:25:42 -06001327 period,
Wu Fengguangece13ac2010-08-29 23:33:20 -06001328 pause,
1329 start_time);
Jan Kara499d05e2011-11-16 19:34:48 +08001330 __set_current_state(TASK_KILLABLE);
Wu Fengguangd25105e2009-10-09 12:40:42 +02001331 io_schedule_timeout(pause);
Jens Axboe87c6a9b2009-09-17 19:59:14 +02001332
Wu Fengguang83712352011-06-11 19:25:42 -06001333 current->dirty_paused_when = now + pause;
1334 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001335 current->nr_dirtied_pause = nr_dirtied_pause;
Wu Fengguang83712352011-06-11 19:25:42 -06001336
Wu Fengguangffd1f602011-06-19 22:18:42 -06001337 /*
Wu Fengguang1df64712011-11-13 19:47:32 -06001338 * This is typically equal to (nr_dirty < dirty_thresh) and can
1339 * also keep "1000+ dd on a slow USB stick" under control.
Wu Fengguangffd1f602011-06-19 22:18:42 -06001340 */
Wu Fengguang1df64712011-11-13 19:47:32 -06001341 if (task_ratelimit)
Wu Fengguangffd1f602011-06-19 22:18:42 -06001342 break;
Jan Kara499d05e2011-11-16 19:34:48 +08001343
Wu Fengguangc5c63432011-12-02 10:21:33 -06001344 /*
1345 * In the case of an unresponding NFS server and the NFS dirty
1346 * pages exceeds dirty_thresh, give the other good bdi's a pipe
1347 * to go through, so that tasks on them still remain responsive.
1348 *
1349 * In theory 1 page is enough to keep the comsumer-producer
1350 * pipe going: the flusher cleans 1 page => the task dirties 1
1351 * more page. However bdi_dirty has accounting errors. So use
1352 * the larger and more IO friendly bdi_stat_error.
1353 */
1354 if (bdi_dirty <= bdi_stat_error(bdi))
1355 break;
1356
Jan Kara499d05e2011-11-16 19:34:48 +08001357 if (fatal_signal_pending(current))
1358 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001359 }
1360
Wu Fengguang143dfe82010-08-27 18:45:12 -06001361 if (!dirty_exceeded && bdi->dirty_exceeded)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001362 bdi->dirty_exceeded = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001363
1364 if (writeback_in_progress(bdi))
Jens Axboe5b0830c2009-09-23 19:37:09 +02001365 return;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001366
1367 /*
1368 * In laptop mode, we wait until hitting the higher threshold before
1369 * starting background writeout, and then write out all the way down
1370 * to the lower threshold. So slow writers cause minimal disk activity.
1371 *
1372 * In normal mode, we start background writeout at the lower
1373 * background_thresh, to keep the amount of dirty memory low.
1374 */
Wu Fengguang143dfe82010-08-27 18:45:12 -06001375 if (laptop_mode)
1376 return;
1377
1378 if (nr_reclaimable > background_thresh)
Christoph Hellwigc5444192010-06-08 18:15:15 +02001379 bdi_start_background_writeback(bdi);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001380}
1381
Peter Zijlstraa200ee12007-10-08 18:54:37 +02001382void set_page_dirty_balance(struct page *page, int page_mkwrite)
Peter Zijlstraedc79b22006-09-25 23:30:58 -07001383{
Peter Zijlstraa200ee12007-10-08 18:54:37 +02001384 if (set_page_dirty(page) || page_mkwrite) {
Peter Zijlstraedc79b22006-09-25 23:30:58 -07001385 struct address_space *mapping = page_mapping(page);
1386
1387 if (mapping)
1388 balance_dirty_pages_ratelimited(mapping);
1389 }
1390}
1391
Wu Fengguang9d823e82011-06-11 18:10:12 -06001392static DEFINE_PER_CPU(int, bdp_ratelimits);
Tejun Heo245b2e72009-06-24 15:13:48 +09001393
Wu Fengguang54848d72011-04-05 13:21:19 -06001394/*
1395 * Normal tasks are throttled by
1396 * loop {
1397 * dirty tsk->nr_dirtied_pause pages;
1398 * take a snap in balance_dirty_pages();
1399 * }
1400 * However there is a worst case. If every task exit immediately when dirtied
1401 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1402 * called to throttle the page dirties. The solution is to save the not yet
1403 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1404 * randomly into the running tasks. This works well for the above worst case,
1405 * as the new task will pick up and accumulate the old task's leaked dirty
1406 * count and eventually get throttled.
1407 */
1408DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1409
Linus Torvalds1da177e2005-04-16 15:20:36 -07001410/**
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001411 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
Martin Waitz67be2dd2005-05-01 08:59:26 -07001412 * @mapping: address_space which was dirtied
Martin Waitza5802902006-04-02 13:59:55 +02001413 * @nr_pages_dirtied: number of pages which the caller has just dirtied
Linus Torvalds1da177e2005-04-16 15:20:36 -07001414 *
1415 * Processes which are dirtying memory should call in here once for each page
1416 * which was newly dirtied. The function will periodically check the system's
1417 * dirty state and will initiate writeback if needed.
1418 *
1419 * On really big machines, get_writeback_state is expensive, so try to avoid
1420 * calling it too often (ratelimiting). But once we're over the dirty memory
1421 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1422 * from overshooting the limit by (ratelimit_pages) each.
1423 */
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001424void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
1425 unsigned long nr_pages_dirtied)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001426{
Wu Fengguang36715ce2011-06-11 17:53:57 -06001427 struct backing_dev_info *bdi = mapping->backing_dev_info;
Wu Fengguang9d823e82011-06-11 18:10:12 -06001428 int ratelimit;
1429 int *p;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001430
Wu Fengguang36715ce2011-06-11 17:53:57 -06001431 if (!bdi_cap_account_dirty(bdi))
1432 return;
1433
Wu Fengguang9d823e82011-06-11 18:10:12 -06001434 ratelimit = current->nr_dirtied_pause;
1435 if (bdi->dirty_exceeded)
1436 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
Linus Torvalds1da177e2005-04-16 15:20:36 -07001437
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001438 preempt_disable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001439 /*
1440 * This prevents one CPU to accumulate too many dirtied pages without
1441 * calling into balance_dirty_pages(), which can happen when there are
1442 * 1000+ tasks, all of them start dirtying pages at exactly the same
1443 * time, hence all honoured too large initial task->nr_dirtied_pause.
1444 */
Tejun Heo245b2e72009-06-24 15:13:48 +09001445 p = &__get_cpu_var(bdp_ratelimits);
Wu Fengguang9d823e82011-06-11 18:10:12 -06001446 if (unlikely(current->nr_dirtied >= ratelimit))
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001447 *p = 0;
Wu Fengguangd3bc1fe2011-04-14 07:52:37 -06001448 else if (unlikely(*p >= ratelimit_pages)) {
1449 *p = 0;
1450 ratelimit = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001451 }
Wu Fengguang54848d72011-04-05 13:21:19 -06001452 /*
1453 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1454 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1455 * the dirty throttling and livelock other long-run dirtiers.
1456 */
1457 p = &__get_cpu_var(dirty_throttle_leaks);
1458 if (*p > 0 && current->nr_dirtied < ratelimit) {
1459 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1460 *p -= nr_pages_dirtied;
1461 current->nr_dirtied += nr_pages_dirtied;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001462 }
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001463 preempt_enable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001464
1465 if (unlikely(current->nr_dirtied >= ratelimit))
1466 balance_dirty_pages(mapping, current->nr_dirtied);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001467}
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001468EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001469
Andrew Morton232ea4d2007-02-28 20:13:21 -08001470void throttle_vm_writeout(gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001471{
David Rientjes364aeb22009-01-06 14:39:29 -08001472 unsigned long background_thresh;
1473 unsigned long dirty_thresh;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001474
1475 for ( ; ; ) {
Wu Fengguang16c40422010-08-11 14:17:39 -07001476 global_dirty_limits(&background_thresh, &dirty_thresh);
Fengguang Wu47a13332012-03-21 16:34:09 -07001477 dirty_thresh = hard_dirty_limit(dirty_thresh);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001478
1479 /*
1480 * Boost the allowable dirty threshold a bit for page
1481 * allocators so they don't get DoS'ed by heavy writers
1482 */
1483 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1484
Christoph Lameterc24f21b2006-06-30 01:55:42 -07001485 if (global_page_state(NR_UNSTABLE_NFS) +
1486 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1487 break;
Jens Axboe8aa7e842009-07-09 14:52:32 +02001488 congestion_wait(BLK_RW_ASYNC, HZ/10);
Fengguang Wu369f2382007-10-16 23:30:45 -07001489
1490 /*
1491 * The caller might hold locks which can prevent IO completion
1492 * or progress in the filesystem. So we cannot just sit here
1493 * waiting for IO to complete.
1494 */
1495 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1496 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001497 }
1498}
1499
Linus Torvalds1da177e2005-04-16 15:20:36 -07001500/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001501 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1502 */
1503int dirty_writeback_centisecs_handler(ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001504 void __user *buffer, size_t *length, loff_t *ppos)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001505{
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001506 proc_dointvec(table, write, buffer, length, ppos);
Jens Axboe64231042010-05-21 20:00:35 +02001507 bdi_arm_supers_timer();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001508 return 0;
1509}
1510
Jens Axboec2c49862010-05-20 09:18:47 +02001511#ifdef CONFIG_BLOCK
Matthew Garrett31373d02010-04-06 14:25:14 +02001512void laptop_mode_timer_fn(unsigned long data)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001513{
Matthew Garrett31373d02010-04-06 14:25:14 +02001514 struct request_queue *q = (struct request_queue *)data;
1515 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1516 global_page_state(NR_UNSTABLE_NFS);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001517
Matthew Garrett31373d02010-04-06 14:25:14 +02001518 /*
1519 * We want to write everything out, not just down to the dirty
1520 * threshold
1521 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001522 if (bdi_has_dirty_io(&q->backing_dev_info))
Curt Wohlgemuth0e175a12011-10-07 21:54:10 -06001523 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1524 WB_REASON_LAPTOP_TIMER);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001525}
1526
1527/*
1528 * We've spun up the disk and we're in laptop mode: schedule writeback
1529 * of all dirty data a few seconds from now. If the flush is already scheduled
1530 * then push it back - the user is still using the disk.
1531 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001532void laptop_io_completion(struct backing_dev_info *info)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001533{
Matthew Garrett31373d02010-04-06 14:25:14 +02001534 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001535}
1536
1537/*
1538 * We're in laptop mode and we've just synced. The sync's writes will have
1539 * caused another writeback to be scheduled by laptop_io_completion.
1540 * Nothing needs to be written back anymore, so we unschedule the writeback.
1541 */
1542void laptop_sync_completion(void)
1543{
Matthew Garrett31373d02010-04-06 14:25:14 +02001544 struct backing_dev_info *bdi;
1545
1546 rcu_read_lock();
1547
1548 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1549 del_timer(&bdi->laptop_mode_wb_timer);
1550
1551 rcu_read_unlock();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001552}
Jens Axboec2c49862010-05-20 09:18:47 +02001553#endif
Linus Torvalds1da177e2005-04-16 15:20:36 -07001554
1555/*
1556 * If ratelimit_pages is too high then we can get into dirty-data overload
1557 * if a large number of processes all perform writes at the same time.
1558 * If it is too low then SMP machines will call the (expensive)
1559 * get_writeback_state too often.
1560 *
1561 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1562 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
Wu Fengguang9d823e82011-06-11 18:10:12 -06001563 * thresholds.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001564 */
1565
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001566void writeback_set_ratelimit(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001567{
Wu Fengguang9d823e82011-06-11 18:10:12 -06001568 unsigned long background_thresh;
1569 unsigned long dirty_thresh;
1570 global_dirty_limits(&background_thresh, &dirty_thresh);
1571 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001572 if (ratelimit_pages < 16)
1573 ratelimit_pages = 16;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001574}
1575
Chandra Seetharaman26c21432006-06-27 02:54:10 -07001576static int __cpuinit
Linus Torvalds1da177e2005-04-16 15:20:36 -07001577ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
1578{
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001579 writeback_set_ratelimit();
Paul E. McKenneyaa0f0302007-02-10 01:46:37 -08001580 return NOTIFY_DONE;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001581}
1582
Chandra Seetharaman74b85f32006-06-27 02:54:09 -07001583static struct notifier_block __cpuinitdata ratelimit_nb = {
Linus Torvalds1da177e2005-04-16 15:20:36 -07001584 .notifier_call = ratelimit_handler,
1585 .next = NULL,
1586};
1587
1588/*
Linus Torvaldsdc6e29d2007-01-29 16:37:38 -08001589 * Called early on to tune the page writeback dirty limits.
1590 *
1591 * We used to scale dirty pages according to how total memory
1592 * related to pages that could be allocated for buffers (by
1593 * comparing nr_free_buffer_pages() to vm_total_pages.
1594 *
1595 * However, that was when we used "dirty_ratio" to scale with
1596 * all memory, and we don't do that any more. "dirty_ratio"
1597 * is now applied to total non-HIGHPAGE memory (by subtracting
1598 * totalhigh_pages from vm_total_pages), and as such we can't
1599 * get into the old insane situation any more where we had
1600 * large amounts of dirty pages compared to a small amount of
1601 * non-HIGHMEM memory.
1602 *
1603 * But we might still want to scale the dirty_ratio by how
1604 * much memory the box has..
Linus Torvalds1da177e2005-04-16 15:20:36 -07001605 */
1606void __init page_writeback_init(void)
1607{
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001608 int shift;
1609
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001610 writeback_set_ratelimit();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001611 register_cpu_notifier(&ratelimit_nb);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001612
1613 shift = calc_period_shift();
1614 prop_descriptor_init(&vm_completions, shift);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001615}
1616
David Howells811d7362006-08-29 19:06:09 +01001617/**
Jan Karaf446daa2010-08-09 17:19:12 -07001618 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1619 * @mapping: address space structure to write
1620 * @start: starting page index
1621 * @end: ending page index (inclusive)
1622 *
1623 * This function scans the page range from @start to @end (inclusive) and tags
1624 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1625 * that write_cache_pages (or whoever calls this function) will then use
1626 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1627 * used to avoid livelocking of writeback by a process steadily creating new
1628 * dirty pages in the file (thus it is important for this function to be quick
1629 * so that it can tag pages faster than a dirtying process can create them).
1630 */
1631/*
1632 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1633 */
Jan Karaf446daa2010-08-09 17:19:12 -07001634void tag_pages_for_writeback(struct address_space *mapping,
1635 pgoff_t start, pgoff_t end)
1636{
Randy Dunlap3c111a02010-08-11 14:17:30 -07001637#define WRITEBACK_TAG_BATCH 4096
Jan Karaf446daa2010-08-09 17:19:12 -07001638 unsigned long tagged;
1639
1640 do {
1641 spin_lock_irq(&mapping->tree_lock);
1642 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1643 &start, end, WRITEBACK_TAG_BATCH,
1644 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1645 spin_unlock_irq(&mapping->tree_lock);
1646 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1647 cond_resched();
Jan Karad5ed3a42010-08-19 14:13:33 -07001648 /* We check 'start' to handle wrapping when end == ~0UL */
1649 } while (tagged >= WRITEBACK_TAG_BATCH && start);
Jan Karaf446daa2010-08-09 17:19:12 -07001650}
1651EXPORT_SYMBOL(tag_pages_for_writeback);
1652
1653/**
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001654 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
David Howells811d7362006-08-29 19:06:09 +01001655 * @mapping: address space structure to write
1656 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001657 * @writepage: function called for each page
1658 * @data: data passed to writepage function
David Howells811d7362006-08-29 19:06:09 +01001659 *
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001660 * If a page is already under I/O, write_cache_pages() skips it, even
David Howells811d7362006-08-29 19:06:09 +01001661 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1662 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1663 * and msync() need to guarantee that all the data which was dirty at the time
1664 * the call was made get new I/O started against them. If wbc->sync_mode is
1665 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1666 * existing IO to complete.
Jan Karaf446daa2010-08-09 17:19:12 -07001667 *
1668 * To avoid livelocks (when other process dirties new pages), we first tag
1669 * pages which should be written back with TOWRITE tag and only then start
1670 * writing them. For data-integrity sync we have to be careful so that we do
1671 * not miss some pages (e.g., because some other process has cleared TOWRITE
1672 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1673 * by the process clearing the DIRTY tag (and submitting the page for IO).
David Howells811d7362006-08-29 19:06:09 +01001674 */
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001675int write_cache_pages(struct address_space *mapping,
1676 struct writeback_control *wbc, writepage_t writepage,
1677 void *data)
David Howells811d7362006-08-29 19:06:09 +01001678{
David Howells811d7362006-08-29 19:06:09 +01001679 int ret = 0;
1680 int done = 0;
David Howells811d7362006-08-29 19:06:09 +01001681 struct pagevec pvec;
1682 int nr_pages;
Nick Piggin31a12662009-01-06 14:39:04 -08001683 pgoff_t uninitialized_var(writeback_index);
David Howells811d7362006-08-29 19:06:09 +01001684 pgoff_t index;
1685 pgoff_t end; /* Inclusive */
Nick Pigginbd19e012009-01-06 14:39:06 -08001686 pgoff_t done_index;
Nick Piggin31a12662009-01-06 14:39:04 -08001687 int cycled;
David Howells811d7362006-08-29 19:06:09 +01001688 int range_whole = 0;
Jan Karaf446daa2010-08-09 17:19:12 -07001689 int tag;
David Howells811d7362006-08-29 19:06:09 +01001690
David Howells811d7362006-08-29 19:06:09 +01001691 pagevec_init(&pvec, 0);
1692 if (wbc->range_cyclic) {
Nick Piggin31a12662009-01-06 14:39:04 -08001693 writeback_index = mapping->writeback_index; /* prev offset */
1694 index = writeback_index;
1695 if (index == 0)
1696 cycled = 1;
1697 else
1698 cycled = 0;
David Howells811d7362006-08-29 19:06:09 +01001699 end = -1;
1700 } else {
1701 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1702 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1703 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1704 range_whole = 1;
Nick Piggin31a12662009-01-06 14:39:04 -08001705 cycled = 1; /* ignore range_cyclic tests */
David Howells811d7362006-08-29 19:06:09 +01001706 }
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001707 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daa2010-08-09 17:19:12 -07001708 tag = PAGECACHE_TAG_TOWRITE;
1709 else
1710 tag = PAGECACHE_TAG_DIRTY;
David Howells811d7362006-08-29 19:06:09 +01001711retry:
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001712 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daa2010-08-09 17:19:12 -07001713 tag_pages_for_writeback(mapping, index, end);
Nick Pigginbd19e012009-01-06 14:39:06 -08001714 done_index = index;
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001715 while (!done && (index <= end)) {
1716 int i;
1717
Jan Karaf446daa2010-08-09 17:19:12 -07001718 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001719 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1720 if (nr_pages == 0)
1721 break;
David Howells811d7362006-08-29 19:06:09 +01001722
David Howells811d7362006-08-29 19:06:09 +01001723 for (i = 0; i < nr_pages; i++) {
1724 struct page *page = pvec.pages[i];
1725
Nick Piggind5482cd2009-01-06 14:39:11 -08001726 /*
1727 * At this point, the page may be truncated or
1728 * invalidated (changing page->mapping to NULL), or
1729 * even swizzled back from swapper_space to tmpfs file
1730 * mapping. However, page->index will not change
1731 * because we have a reference on the page.
1732 */
1733 if (page->index > end) {
1734 /*
1735 * can't be range_cyclic (1st pass) because
1736 * end == -1 in that case.
1737 */
1738 done = 1;
1739 break;
1740 }
1741
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001742 done_index = page->index;
Nick Pigginbd19e012009-01-06 14:39:06 -08001743
David Howells811d7362006-08-29 19:06:09 +01001744 lock_page(page);
1745
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001746 /*
1747 * Page truncated or invalidated. We can freely skip it
1748 * then, even for data integrity operations: the page
1749 * has disappeared concurrently, so there could be no
1750 * real expectation of this data interity operation
1751 * even if there is now a new, dirty page at the same
1752 * pagecache address.
1753 */
David Howells811d7362006-08-29 19:06:09 +01001754 if (unlikely(page->mapping != mapping)) {
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001755continue_unlock:
David Howells811d7362006-08-29 19:06:09 +01001756 unlock_page(page);
1757 continue;
1758 }
1759
Nick Piggin515f4a02009-01-06 14:39:10 -08001760 if (!PageDirty(page)) {
1761 /* someone wrote it for us */
1762 goto continue_unlock;
1763 }
David Howells811d7362006-08-29 19:06:09 +01001764
Nick Piggin515f4a02009-01-06 14:39:10 -08001765 if (PageWriteback(page)) {
1766 if (wbc->sync_mode != WB_SYNC_NONE)
1767 wait_on_page_writeback(page);
1768 else
1769 goto continue_unlock;
1770 }
1771
1772 BUG_ON(PageWriteback(page));
1773 if (!clear_page_dirty_for_io(page))
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001774 goto continue_unlock;
David Howells811d7362006-08-29 19:06:09 +01001775
Dave Chinner9e094382010-07-07 13:24:08 +10001776 trace_wbc_writepage(wbc, mapping->backing_dev_info);
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001777 ret = (*writepage)(page, wbc, data);
Nick Piggin00266772009-01-06 14:39:06 -08001778 if (unlikely(ret)) {
1779 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1780 unlock_page(page);
1781 ret = 0;
1782 } else {
1783 /*
1784 * done_index is set past this page,
1785 * so media errors will not choke
1786 * background writeout for the entire
1787 * file. This has consequences for
1788 * range_cyclic semantics (ie. it may
1789 * not be suitable for data integrity
1790 * writeout).
1791 */
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001792 done_index = page->index + 1;
Nick Piggin00266772009-01-06 14:39:06 -08001793 done = 1;
1794 break;
1795 }
Dave Chinner0b564922010-06-09 10:37:18 +10001796 }
David Howells811d7362006-08-29 19:06:09 +01001797
Dave Chinner546a1922010-08-24 11:44:34 +10001798 /*
1799 * We stop writing back only if we are not doing
1800 * integrity sync. In case of integrity sync we have to
1801 * keep going until we have written all the pages
1802 * we tagged for writeback prior to entering this loop.
1803 */
1804 if (--wbc->nr_to_write <= 0 &&
1805 wbc->sync_mode == WB_SYNC_NONE) {
1806 done = 1;
1807 break;
Nick Piggin05fe4782009-01-06 14:39:08 -08001808 }
David Howells811d7362006-08-29 19:06:09 +01001809 }
1810 pagevec_release(&pvec);
1811 cond_resched();
1812 }
Nick Piggin3a4c6802009-02-12 04:34:23 +01001813 if (!cycled && !done) {
David Howells811d7362006-08-29 19:06:09 +01001814 /*
Nick Piggin31a12662009-01-06 14:39:04 -08001815 * range_cyclic:
David Howells811d7362006-08-29 19:06:09 +01001816 * We hit the last page and there is more work to be done: wrap
1817 * back to the start of the file
1818 */
Nick Piggin31a12662009-01-06 14:39:04 -08001819 cycled = 1;
David Howells811d7362006-08-29 19:06:09 +01001820 index = 0;
Nick Piggin31a12662009-01-06 14:39:04 -08001821 end = writeback_index - 1;
David Howells811d7362006-08-29 19:06:09 +01001822 goto retry;
1823 }
Dave Chinner0b564922010-06-09 10:37:18 +10001824 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1825 mapping->writeback_index = done_index;
Aneesh Kumar K.V06d6cf62008-07-11 19:27:31 -04001826
David Howells811d7362006-08-29 19:06:09 +01001827 return ret;
1828}
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001829EXPORT_SYMBOL(write_cache_pages);
1830
1831/*
1832 * Function used by generic_writepages to call the real writepage
1833 * function and set the mapping flags on error
1834 */
1835static int __writepage(struct page *page, struct writeback_control *wbc,
1836 void *data)
1837{
1838 struct address_space *mapping = data;
1839 int ret = mapping->a_ops->writepage(page, wbc);
1840 mapping_set_error(mapping, ret);
1841 return ret;
1842}
1843
1844/**
1845 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1846 * @mapping: address space structure to write
1847 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1848 *
1849 * This is a library function, which implements the writepages()
1850 * address_space_operation.
1851 */
1852int generic_writepages(struct address_space *mapping,
1853 struct writeback_control *wbc)
1854{
Shaohua Li9b6096a2011-03-17 10:47:06 +01001855 struct blk_plug plug;
1856 int ret;
1857
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001858 /* deal with chardevs and other special file */
1859 if (!mapping->a_ops->writepage)
1860 return 0;
1861
Shaohua Li9b6096a2011-03-17 10:47:06 +01001862 blk_start_plug(&plug);
1863 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1864 blk_finish_plug(&plug);
1865 return ret;
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001866}
David Howells811d7362006-08-29 19:06:09 +01001867
1868EXPORT_SYMBOL(generic_writepages);
1869
Linus Torvalds1da177e2005-04-16 15:20:36 -07001870int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1871{
Andrew Morton22905f72005-11-16 15:07:01 -08001872 int ret;
1873
Linus Torvalds1da177e2005-04-16 15:20:36 -07001874 if (wbc->nr_to_write <= 0)
1875 return 0;
1876 if (mapping->a_ops->writepages)
Peter Zijlstrad08b3852006-09-25 23:30:57 -07001877 ret = mapping->a_ops->writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08001878 else
1879 ret = generic_writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08001880 return ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001881}
1882
1883/**
1884 * write_one_page - write out a single page and optionally wait on I/O
Martin Waitz67be2dd2005-05-01 08:59:26 -07001885 * @page: the page to write
1886 * @wait: if true, wait on writeout
Linus Torvalds1da177e2005-04-16 15:20:36 -07001887 *
1888 * The page must be locked by the caller and will be unlocked upon return.
1889 *
1890 * write_one_page() returns a negative error code if I/O failed.
1891 */
1892int write_one_page(struct page *page, int wait)
1893{
1894 struct address_space *mapping = page->mapping;
1895 int ret = 0;
1896 struct writeback_control wbc = {
1897 .sync_mode = WB_SYNC_ALL,
1898 .nr_to_write = 1,
1899 };
1900
1901 BUG_ON(!PageLocked(page));
1902
1903 if (wait)
1904 wait_on_page_writeback(page);
1905
1906 if (clear_page_dirty_for_io(page)) {
1907 page_cache_get(page);
1908 ret = mapping->a_ops->writepage(page, &wbc);
1909 if (ret == 0 && wait) {
1910 wait_on_page_writeback(page);
1911 if (PageError(page))
1912 ret = -EIO;
1913 }
1914 page_cache_release(page);
1915 } else {
1916 unlock_page(page);
1917 }
1918 return ret;
1919}
1920EXPORT_SYMBOL(write_one_page);
1921
1922/*
Ken Chen76719322007-02-10 01:43:15 -08001923 * For address_spaces which do not use buffers nor write back.
1924 */
1925int __set_page_dirty_no_writeback(struct page *page)
1926{
1927 if (!PageDirty(page))
Bob Liuc3f0da62011-01-13 15:45:49 -08001928 return !TestSetPageDirty(page);
Ken Chen76719322007-02-10 01:43:15 -08001929 return 0;
1930}
1931
1932/*
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001933 * Helper function for set_page_dirty family.
1934 * NOTE: This relies on being atomic wrt interrupts.
1935 */
1936void account_page_dirtied(struct page *page, struct address_space *mapping)
1937{
1938 if (mapping_cap_account_dirty(mapping)) {
1939 __inc_zone_page_state(page, NR_FILE_DIRTY);
Michael Rubinea941f02010-10-26 14:21:35 -07001940 __inc_zone_page_state(page, NR_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001941 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
Wu Fengguangc8e28ce2011-01-23 10:07:47 -06001942 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001943 task_io_account_write(PAGE_CACHE_SIZE);
Wu Fengguangd3bc1fe2011-04-14 07:52:37 -06001944 current->nr_dirtied++;
1945 this_cpu_inc(bdp_ratelimits);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001946 }
1947}
Michael Rubin679ceac2010-08-20 02:31:26 -07001948EXPORT_SYMBOL(account_page_dirtied);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001949
1950/*
Michael Rubinf629d1c2010-10-26 14:21:33 -07001951 * Helper function for set_page_writeback family.
1952 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1953 * wrt interrupts.
1954 */
1955void account_page_writeback(struct page *page)
1956{
1957 inc_zone_page_state(page, NR_WRITEBACK);
1958}
1959EXPORT_SYMBOL(account_page_writeback);
1960
1961/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001962 * For address_spaces which do not use buffers. Just tag the page as dirty in
1963 * its radix tree.
1964 *
1965 * This is also used when a single buffer is being dirtied: we want to set the
1966 * page dirty in that case, but not all the buffers. This is a "bottom-up"
1967 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1968 *
1969 * Most callers have locked the page, which pins the address_space in memory.
1970 * But zap_pte_range() does not lock the page, however in that case the
1971 * mapping is pinned by the vma's ->vm_file reference.
1972 *
1973 * We take care to handle the case where the page was truncated from the
Simon Arlott183ff222007-10-20 01:27:18 +02001974 * mapping by re-checking page_mapping() inside tree_lock.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001975 */
1976int __set_page_dirty_nobuffers(struct page *page)
1977{
Linus Torvalds1da177e2005-04-16 15:20:36 -07001978 if (!TestSetPageDirty(page)) {
1979 struct address_space *mapping = page_mapping(page);
1980 struct address_space *mapping2;
1981
Andrew Morton8c085402006-12-10 02:19:24 -08001982 if (!mapping)
1983 return 1;
1984
Nick Piggin19fd6232008-07-25 19:45:32 -07001985 spin_lock_irq(&mapping->tree_lock);
Andrew Morton8c085402006-12-10 02:19:24 -08001986 mapping2 = page_mapping(page);
1987 if (mapping2) { /* Race with truncate? */
1988 BUG_ON(mapping2 != mapping);
Nick Piggin787d2212007-07-17 04:03:34 -07001989 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001990 account_page_dirtied(page, mapping);
Andrew Morton8c085402006-12-10 02:19:24 -08001991 radix_tree_tag_set(&mapping->page_tree,
1992 page_index(page), PAGECACHE_TAG_DIRTY);
1993 }
Nick Piggin19fd6232008-07-25 19:45:32 -07001994 spin_unlock_irq(&mapping->tree_lock);
Andrew Morton8c085402006-12-10 02:19:24 -08001995 if (mapping->host) {
1996 /* !PageAnon && !swapper_space */
1997 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001998 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08001999 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002000 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002001 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002002}
2003EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2004
2005/*
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002006 * Call this whenever redirtying a page, to de-account the dirty counters
2007 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2008 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2009 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2010 * control.
2011 */
2012void account_page_redirty(struct page *page)
2013{
2014 struct address_space *mapping = page->mapping;
2015 if (mapping && mapping_cap_account_dirty(mapping)) {
2016 current->nr_dirtied--;
2017 dec_zone_page_state(page, NR_DIRTIED);
2018 dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2019 }
2020}
2021EXPORT_SYMBOL(account_page_redirty);
2022
2023/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002024 * When a writepage implementation decides that it doesn't want to write this
2025 * page for some reason, it should redirty the locked page via
2026 * redirty_page_for_writepage() and it should then unlock the page and return 0
2027 */
2028int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2029{
2030 wbc->pages_skipped++;
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002031 account_page_redirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002032 return __set_page_dirty_nobuffers(page);
2033}
2034EXPORT_SYMBOL(redirty_page_for_writepage);
2035
2036/*
Wu Fengguang6746aff2009-09-16 11:50:14 +02002037 * Dirty a page.
2038 *
2039 * For pages with a mapping this should be done under the page lock
2040 * for the benefit of asynchronous memory errors who prefer a consistent
2041 * dirty state. This rule can be broken in some special cases,
2042 * but should be better not to.
2043 *
Linus Torvalds1da177e2005-04-16 15:20:36 -07002044 * If the mapping doesn't provide a set_page_dirty a_op, then
2045 * just fall through and assume that it wants buffer_heads.
2046 */
Nick Piggin1cf6e7d2009-02-18 14:48:18 -08002047int set_page_dirty(struct page *page)
Linus Torvalds1da177e2005-04-16 15:20:36 -07002048{
2049 struct address_space *mapping = page_mapping(page);
2050
2051 if (likely(mapping)) {
2052 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
Minchan Kim278df9f2011-03-22 16:32:54 -07002053 /*
2054 * readahead/lru_deactivate_page could remain
2055 * PG_readahead/PG_reclaim due to race with end_page_writeback
2056 * About readahead, if the page is written, the flags would be
2057 * reset. So no problem.
2058 * About lru_deactivate_page, if the page is redirty, the flag
2059 * will be reset. So no problem. but if the page is used by readahead
2060 * it will confuse readahead and make it restart the size rampup
2061 * process. But it's a trivial problem.
2062 */
2063 ClearPageReclaim(page);
David Howells93614012006-09-30 20:45:40 +02002064#ifdef CONFIG_BLOCK
2065 if (!spd)
2066 spd = __set_page_dirty_buffers;
2067#endif
2068 return (*spd)(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002069 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002070 if (!PageDirty(page)) {
2071 if (!TestSetPageDirty(page))
2072 return 1;
2073 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002074 return 0;
2075}
2076EXPORT_SYMBOL(set_page_dirty);
2077
2078/*
2079 * set_page_dirty() is racy if the caller has no reference against
2080 * page->mapping->host, and if the page is unlocked. This is because another
2081 * CPU could truncate the page off the mapping and then free the mapping.
2082 *
2083 * Usually, the page _is_ locked, or the caller is a user-space process which
2084 * holds a reference on the inode by having an open file.
2085 *
2086 * In other cases, the page should be locked before running set_page_dirty().
2087 */
2088int set_page_dirty_lock(struct page *page)
2089{
2090 int ret;
2091
Jens Axboe7eaceac2011-03-10 08:52:07 +01002092 lock_page(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002093 ret = set_page_dirty(page);
2094 unlock_page(page);
2095 return ret;
2096}
2097EXPORT_SYMBOL(set_page_dirty_lock);
2098
2099/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002100 * Clear a page's dirty flag, while caring for dirty memory accounting.
2101 * Returns true if the page was previously dirty.
2102 *
2103 * This is for preparing to put the page under writeout. We leave the page
2104 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2105 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2106 * implementation will run either set_page_writeback() or set_page_dirty(),
2107 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2108 * back into sync.
2109 *
2110 * This incoherency between the page's dirty flag and radix-tree tag is
2111 * unfortunate, but it only exists while the page is locked.
2112 */
2113int clear_page_dirty_for_io(struct page *page)
2114{
2115 struct address_space *mapping = page_mapping(page);
2116
Nick Piggin79352892007-07-19 01:47:22 -07002117 BUG_ON(!PageLocked(page));
2118
Linus Torvalds7658cc22006-12-29 10:00:58 -08002119 if (mapping && mapping_cap_account_dirty(mapping)) {
2120 /*
2121 * Yes, Virginia, this is indeed insane.
2122 *
2123 * We use this sequence to make sure that
2124 * (a) we account for dirty stats properly
2125 * (b) we tell the low-level filesystem to
2126 * mark the whole page dirty if it was
2127 * dirty in a pagetable. Only to then
2128 * (c) clean the page again and return 1 to
2129 * cause the writeback.
2130 *
2131 * This way we avoid all nasty races with the
2132 * dirty bit in multiple places and clearing
2133 * them concurrently from different threads.
2134 *
2135 * Note! Normally the "set_page_dirty(page)"
2136 * has no effect on the actual dirty bit - since
2137 * that will already usually be set. But we
2138 * need the side effects, and it can help us
2139 * avoid races.
2140 *
2141 * We basically use the page "master dirty bit"
2142 * as a serialization point for all the different
2143 * threads doing their things.
Linus Torvalds7658cc22006-12-29 10:00:58 -08002144 */
2145 if (page_mkclean(page))
2146 set_page_dirty(page);
Nick Piggin79352892007-07-19 01:47:22 -07002147 /*
2148 * We carefully synchronise fault handlers against
2149 * installing a dirty pte and marking the page dirty
2150 * at this point. We do this by having them hold the
2151 * page lock at some point after installing their
2152 * pte, but before marking the page dirty.
2153 * Pages are always locked coming in here, so we get
2154 * the desired exclusion. See mm/memory.c:do_wp_page()
2155 * for more comments.
2156 */
Linus Torvalds7658cc22006-12-29 10:00:58 -08002157 if (TestClearPageDirty(page)) {
Andrew Morton8c085402006-12-10 02:19:24 -08002158 dec_zone_page_state(page, NR_FILE_DIRTY);
Peter Zijlstrac9e51e42007-10-16 23:25:47 -07002159 dec_bdi_stat(mapping->backing_dev_info,
2160 BDI_RECLAIMABLE);
Linus Torvalds7658cc22006-12-29 10:00:58 -08002161 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002162 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08002163 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002164 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08002165 return TestClearPageDirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002166}
Hans Reiser58bb01a2005-11-18 01:10:53 -08002167EXPORT_SYMBOL(clear_page_dirty_for_io);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002168
2169int test_clear_page_writeback(struct page *page)
2170{
2171 struct address_space *mapping = page_mapping(page);
2172 int ret;
2173
2174 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002175 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002176 unsigned long flags;
2177
Nick Piggin19fd6232008-07-25 19:45:32 -07002178 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002179 ret = TestClearPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002180 if (ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07002181 radix_tree_tag_clear(&mapping->page_tree,
2182 page_index(page),
2183 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07002184 if (bdi_cap_account_writeback(bdi)) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002185 __dec_bdi_stat(bdi, BDI_WRITEBACK);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07002186 __bdi_writeout_inc(bdi);
2187 }
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002188 }
Nick Piggin19fd6232008-07-25 19:45:32 -07002189 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002190 } else {
2191 ret = TestClearPageWriteback(page);
2192 }
Wu Fengguang99b12e32011-07-25 17:12:37 -07002193 if (ret) {
Andrew Mortond688abf2007-07-19 01:49:17 -07002194 dec_zone_page_state(page, NR_WRITEBACK);
Wu Fengguang99b12e32011-07-25 17:12:37 -07002195 inc_zone_page_state(page, NR_WRITTEN);
2196 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002197 return ret;
2198}
2199
2200int test_set_page_writeback(struct page *page)
2201{
2202 struct address_space *mapping = page_mapping(page);
2203 int ret;
2204
2205 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002206 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002207 unsigned long flags;
2208
Nick Piggin19fd6232008-07-25 19:45:32 -07002209 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002210 ret = TestSetPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002211 if (!ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07002212 radix_tree_tag_set(&mapping->page_tree,
2213 page_index(page),
2214 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07002215 if (bdi_cap_account_writeback(bdi))
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002216 __inc_bdi_stat(bdi, BDI_WRITEBACK);
2217 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002218 if (!PageDirty(page))
2219 radix_tree_tag_clear(&mapping->page_tree,
2220 page_index(page),
2221 PAGECACHE_TAG_DIRTY);
Jan Karaf446daa2010-08-09 17:19:12 -07002222 radix_tree_tag_clear(&mapping->page_tree,
2223 page_index(page),
2224 PAGECACHE_TAG_TOWRITE);
Nick Piggin19fd6232008-07-25 19:45:32 -07002225 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002226 } else {
2227 ret = TestSetPageWriteback(page);
2228 }
Andrew Mortond688abf2007-07-19 01:49:17 -07002229 if (!ret)
Michael Rubinf629d1c2010-10-26 14:21:33 -07002230 account_page_writeback(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002231 return ret;
2232
2233}
2234EXPORT_SYMBOL(test_set_page_writeback);
2235
2236/*
Nick Piggin00128182007-10-16 01:24:40 -07002237 * Return true if any of the pages in the mapping are marked with the
Linus Torvalds1da177e2005-04-16 15:20:36 -07002238 * passed tag.
2239 */
2240int mapping_tagged(struct address_space *mapping, int tag)
2241{
Konstantin Khlebnikov72c47832011-07-25 17:12:31 -07002242 return radix_tree_tagged(&mapping->page_tree, tag);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002243}
2244EXPORT_SYMBOL(mapping_tagged);