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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 Viroff01bb482011-09-16 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>
Jan Karaeb608e32012-05-24 18:59:11 +020037#include <linux/timer.h>
Clark Williams8bd75c72013-02-07 09:47:07 -060038#include <linux/sched/rt.h>
Lisa Du6e543d52013-09-11 14:22:36 -070039#include <linux/mm_inline.h>
Dave Chinner028c2dd2010-07-07 13:24:07 +100040#include <trace/events/writeback.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070041
Lisa Du6e543d52013-09-11 14:22:36 -070042#include "internal.h"
43
Linus Torvalds1da177e2005-04-16 15:20:36 -070044/*
Wu Fengguangffd1f602011-06-19 22:18:42 -060045 * Sleep at most 200ms at a time in balance_dirty_pages().
46 */
47#define MAX_PAUSE max(HZ/5, 1)
48
49/*
Wu Fengguang5b9b3572011-12-06 13:17:17 -060050 * Try to keep balance_dirty_pages() call intervals higher than this many pages
51 * by raising pause time to max_pause when falls below it.
52 */
53#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
54
55/*
Wu Fengguange98be2d2010-08-29 11:22:30 -060056 * Estimate write bandwidth at 200ms intervals.
57 */
58#define BANDWIDTH_INTERVAL max(HZ/5, 1)
59
Wu Fengguang6c14ae12011-03-02 16:04:18 -060060#define RATELIMIT_CALC_SHIFT 10
61
Wu Fengguange98be2d2010-08-29 11:22:30 -060062/*
Linus Torvalds1da177e2005-04-16 15:20:36 -070063 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
64 * will look to see if it needs to force writeback or throttling.
65 */
66static long ratelimit_pages = 32;
67
Linus Torvalds1da177e2005-04-16 15:20:36 -070068/* The following parameters are exported via /proc/sys/vm */
69
70/*
Jens Axboe5b0830c2009-09-23 19:37:09 +020071 * Start background writeback (via writeback threads) at this percentage
Linus Torvalds1da177e2005-04-16 15:20:36 -070072 */
Wu Fengguang1b5e62b2009-03-23 08:57:38 +080073int dirty_background_ratio = 10;
Linus Torvalds1da177e2005-04-16 15:20:36 -070074
75/*
David Rientjes2da02992009-01-06 14:39:31 -080076 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
77 * dirty_background_ratio * the amount of dirtyable memory
78 */
79unsigned long dirty_background_bytes;
80
81/*
Bron Gondwana195cf4532008-02-04 22:29:20 -080082 * free highmem will not be subtracted from the total free memory
83 * for calculating free ratios if vm_highmem_is_dirtyable is true
84 */
85int vm_highmem_is_dirtyable;
86
87/*
Linus Torvalds1da177e2005-04-16 15:20:36 -070088 * The generator of dirty data starts writeback at this percentage
89 */
Wu Fengguang1b5e62b2009-03-23 08:57:38 +080090int vm_dirty_ratio = 20;
Linus Torvalds1da177e2005-04-16 15:20:36 -070091
92/*
David Rientjes2da02992009-01-06 14:39:31 -080093 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
94 * vm_dirty_ratio * the amount of dirtyable memory
95 */
96unsigned long vm_dirty_bytes;
97
98/*
Alexey Dobriyan704503d2009-03-31 15:23:18 -070099 * The interval between `kupdate'-style writebacks
Linus Torvalds1da177e2005-04-16 15:20:36 -0700100 */
Toshiyuki Okajima22ef37e2009-05-16 22:56:28 -0700101unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700102
Artem Bityutskiy91913a22012-03-21 22:33:00 -0400103EXPORT_SYMBOL_GPL(dirty_writeback_interval);
104
Linus Torvalds1da177e2005-04-16 15:20:36 -0700105/*
Alexey Dobriyan704503d2009-03-31 15:23:18 -0700106 * The longest time for which data is allowed to remain dirty
Linus Torvalds1da177e2005-04-16 15:20:36 -0700107 */
Toshiyuki Okajima22ef37e2009-05-16 22:56:28 -0700108unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700109
110/*
111 * Flag that makes the machine dump writes/reads and block dirtyings.
112 */
113int block_dump;
114
115/*
Bart Samweled5b43f2006-03-24 03:15:49 -0800116 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
117 * a full sync is triggered after this time elapses without any disk activity.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700118 */
119int laptop_mode;
120
121EXPORT_SYMBOL(laptop_mode);
122
123/* End of sysctl-exported parameters */
124
Wu Fengguangc42843f2011-03-02 15:54:09 -0600125unsigned long global_dirty_limit;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700126
Linus Torvalds1da177e2005-04-16 15:20:36 -0700127/*
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700128 * Scale the writeback cache size proportional to the relative writeout speeds.
129 *
130 * We do this by keeping a floating proportion between BDIs, based on page
131 * writeback completions [end_page_writeback()]. Those devices that write out
132 * pages fastest will get the larger share, while the slower will get a smaller
133 * share.
134 *
135 * We use page writeout completions because we are interested in getting rid of
136 * dirty pages. Having them written out is the primary goal.
137 *
138 * We introduce a concept of time, a period over which we measure these events,
139 * because demand can/will vary over time. The length of this period itself is
140 * measured in page writeback completions.
141 *
142 */
Jan Karaeb608e32012-05-24 18:59:11 +0200143static struct fprop_global writeout_completions;
144
145static void writeout_period(unsigned long t);
146/* Timer for aging of writeout_completions */
147static struct timer_list writeout_period_timer =
148 TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0);
149static unsigned long writeout_period_time = 0;
150
151/*
152 * Length of period for aging writeout fractions of bdis. This is an
153 * arbitrarily chosen number. The longer the period, the slower fractions will
154 * reflect changes in current writeout rate.
155 */
156#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700157
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700158/*
Johannes Weiner1edf2232012-01-10 15:06:57 -0800159 * Work out the current dirty-memory clamping and background writeout
160 * thresholds.
161 *
162 * The main aim here is to lower them aggressively if there is a lot of mapped
163 * memory around. To avoid stressing page reclaim with lots of unreclaimable
164 * pages. It is better to clamp down on writers than to start swapping, and
165 * performing lots of scanning.
166 *
167 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
168 *
169 * We don't permit the clamping level to fall below 5% - that is getting rather
170 * excessive.
171 *
172 * We make sure that the background writeout level is below the adjusted
173 * clamping level.
174 */
Johannes Weinerccafa282012-01-10 15:07:44 -0800175
Johannes Weinera756cf52012-01-10 15:07:49 -0800176/*
177 * In a memory zone, there is a certain amount of pages we consider
178 * available for the page cache, which is essentially the number of
179 * free and reclaimable pages, minus some zone reserves to protect
180 * lowmem and the ability to uphold the zone's watermarks without
181 * requiring writeback.
182 *
183 * This number of dirtyable pages is the base value of which the
184 * user-configurable dirty ratio is the effictive number of pages that
185 * are allowed to be actually dirtied. Per individual zone, or
186 * globally by using the sum of dirtyable pages over all zones.
187 *
188 * Because the user is allowed to specify the dirty limit globally as
189 * absolute number of bytes, calculating the per-zone dirty limit can
190 * require translating the configured limit into a percentage of
191 * global dirtyable memory first.
192 */
193
Johannes Weiner1edf2232012-01-10 15:06:57 -0800194static unsigned long highmem_dirtyable_memory(unsigned long total)
195{
196#ifdef CONFIG_HIGHMEM
197 int node;
198 unsigned long x = 0;
199
200 for_each_node_state(node, N_HIGH_MEMORY) {
201 struct zone *z =
202 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
203
204 x += zone_page_state(z, NR_FREE_PAGES) +
Johannes Weinerab8fabd2012-01-10 15:07:42 -0800205 zone_reclaimable_pages(z) - z->dirty_balance_reserve;
Johannes Weiner1edf2232012-01-10 15:06:57 -0800206 }
207 /*
Sonny Raoc8b74c2f2012-12-20 15:05:07 -0800208 * Unreclaimable memory (kernel memory or anonymous memory
209 * without swap) can bring down the dirtyable pages below
210 * the zone's dirty balance reserve and the above calculation
211 * will underflow. However we still want to add in nodes
212 * which are below threshold (negative values) to get a more
213 * accurate calculation but make sure that the total never
214 * underflows.
215 */
216 if ((long)x < 0)
217 x = 0;
218
219 /*
Johannes Weiner1edf2232012-01-10 15:06:57 -0800220 * Make sure that the number of highmem pages is never larger
221 * than the number of the total dirtyable memory. This can only
222 * occur in very strange VM situations but we want to make sure
223 * that this does not occur.
224 */
225 return min(x, total);
226#else
227 return 0;
228#endif
229}
230
231/**
Johannes Weinerccafa282012-01-10 15:07:44 -0800232 * global_dirtyable_memory - number of globally dirtyable pages
Johannes Weiner1edf2232012-01-10 15:06:57 -0800233 *
Johannes Weinerccafa282012-01-10 15:07:44 -0800234 * Returns the global number of pages potentially available for dirty
235 * page cache. This is the base value for the global dirty limits.
Johannes Weiner1edf2232012-01-10 15:06:57 -0800236 */
H Hartley Sweeten18cf8cf2012-04-12 13:44:20 -0700237static unsigned long global_dirtyable_memory(void)
Johannes Weiner1edf2232012-01-10 15:06:57 -0800238{
239 unsigned long x;
240
Sonny Raoc8b74c2f2012-12-20 15:05:07 -0800241 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
242 x -= min(x, dirty_balance_reserve);
Johannes Weiner1edf2232012-01-10 15:06:57 -0800243
244 if (!vm_highmem_is_dirtyable)
245 x -= highmem_dirtyable_memory(x);
246
247 return x + 1; /* Ensure that we never return 0 */
248}
249
250/*
Johannes Weinerccafa282012-01-10 15:07:44 -0800251 * global_dirty_limits - background-writeback and dirty-throttling thresholds
252 *
253 * Calculate the dirty thresholds based on sysctl parameters
254 * - vm.dirty_background_ratio or vm.dirty_background_bytes
255 * - vm.dirty_ratio or vm.dirty_bytes
256 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
257 * real-time tasks.
258 */
259void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
260{
261 unsigned long background;
262 unsigned long dirty;
263 unsigned long uninitialized_var(available_memory);
264 struct task_struct *tsk;
265
266 if (!vm_dirty_bytes || !dirty_background_bytes)
267 available_memory = global_dirtyable_memory();
268
269 if (vm_dirty_bytes)
270 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
271 else
272 dirty = (vm_dirty_ratio * available_memory) / 100;
273
274 if (dirty_background_bytes)
275 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
276 else
277 background = (dirty_background_ratio * available_memory) / 100;
278
279 if (background >= dirty)
280 background = dirty / 2;
281 tsk = current;
282 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
283 background += background / 4;
284 dirty += dirty / 4;
285 }
286 *pbackground = background;
287 *pdirty = dirty;
288 trace_global_dirty_state(background, dirty);
289}
290
Johannes Weinera756cf52012-01-10 15:07:49 -0800291/**
292 * zone_dirtyable_memory - number of dirtyable pages in a zone
293 * @zone: the zone
294 *
295 * Returns the zone's number of pages potentially available for dirty
296 * page cache. This is the base value for the per-zone dirty limits.
297 */
298static unsigned long zone_dirtyable_memory(struct zone *zone)
299{
300 /*
301 * The effective global number of dirtyable pages may exclude
302 * highmem as a big-picture measure to keep the ratio between
303 * dirty memory and lowmem reasonable.
304 *
305 * But this function is purely about the individual zone and a
306 * highmem zone can hold its share of dirty pages, so we don't
307 * care about vm_highmem_is_dirtyable here.
308 */
Sonny Raoc8b74c2f2012-12-20 15:05:07 -0800309 unsigned long nr_pages = zone_page_state(zone, NR_FREE_PAGES) +
310 zone_reclaimable_pages(zone);
311
312 /* don't allow this to underflow */
313 nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
314 return nr_pages;
Johannes Weinera756cf52012-01-10 15:07:49 -0800315}
316
317/**
318 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
319 * @zone: the zone
320 *
321 * Returns the maximum number of dirty pages allowed in a zone, based
322 * on the zone's dirtyable memory.
323 */
324static unsigned long zone_dirty_limit(struct zone *zone)
325{
326 unsigned long zone_memory = zone_dirtyable_memory(zone);
327 struct task_struct *tsk = current;
328 unsigned long dirty;
329
330 if (vm_dirty_bytes)
331 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
332 zone_memory / global_dirtyable_memory();
333 else
334 dirty = vm_dirty_ratio * zone_memory / 100;
335
336 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
337 dirty += dirty / 4;
338
339 return dirty;
340}
341
342/**
343 * zone_dirty_ok - tells whether a zone is within its dirty limits
344 * @zone: the zone to check
345 *
346 * Returns %true when the dirty pages in @zone are within the zone's
347 * dirty limit, %false if the limit is exceeded.
348 */
349bool zone_dirty_ok(struct zone *zone)
350{
351 unsigned long limit = zone_dirty_limit(zone);
352
353 return zone_page_state(zone, NR_FILE_DIRTY) +
354 zone_page_state(zone, NR_UNSTABLE_NFS) +
355 zone_page_state(zone, NR_WRITEBACK) <= limit;
356}
357
David Rientjes2da02992009-01-06 14:39:31 -0800358int dirty_background_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700359 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800360 loff_t *ppos)
361{
362 int ret;
363
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700364 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800365 if (ret == 0 && write)
366 dirty_background_bytes = 0;
367 return ret;
368}
369
370int dirty_background_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700371 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800372 loff_t *ppos)
373{
374 int ret;
375
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700376 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800377 if (ret == 0 && write)
378 dirty_background_ratio = 0;
379 return ret;
380}
381
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700382int dirty_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700383 void __user *buffer, size_t *lenp,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700384 loff_t *ppos)
385{
386 int old_ratio = vm_dirty_ratio;
David Rientjes2da02992009-01-06 14:39:31 -0800387 int ret;
388
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700389 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700390 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
Jan Karaeb608e32012-05-24 18:59:11 +0200391 writeback_set_ratelimit();
David Rientjes2da02992009-01-06 14:39:31 -0800392 vm_dirty_bytes = 0;
393 }
394 return ret;
395}
396
David Rientjes2da02992009-01-06 14:39:31 -0800397int dirty_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700398 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800399 loff_t *ppos)
400{
Sven Wegenerfc3501d2009-02-11 13:04:23 -0800401 unsigned long old_bytes = vm_dirty_bytes;
David Rientjes2da02992009-01-06 14:39:31 -0800402 int ret;
403
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700404 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800405 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
Jan Karaeb608e32012-05-24 18:59:11 +0200406 writeback_set_ratelimit();
David Rientjes2da02992009-01-06 14:39:31 -0800407 vm_dirty_ratio = 0;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700408 }
409 return ret;
410}
411
Jan Karaeb608e32012-05-24 18:59:11 +0200412static unsigned long wp_next_time(unsigned long cur_time)
413{
414 cur_time += VM_COMPLETIONS_PERIOD_LEN;
415 /* 0 has a special meaning... */
416 if (!cur_time)
417 return 1;
418 return cur_time;
419}
420
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700421/*
422 * Increment the BDI's writeout completion count and the global writeout
423 * completion count. Called from test_clear_page_writeback().
424 */
425static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
426{
Jan Karaf7d2b1e2010-12-08 22:44:24 -0600427 __inc_bdi_stat(bdi, BDI_WRITTEN);
Jan Karaeb608e32012-05-24 18:59:11 +0200428 __fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
429 bdi->max_prop_frac);
430 /* First event after period switching was turned off? */
431 if (!unlikely(writeout_period_time)) {
432 /*
433 * We can race with other __bdi_writeout_inc calls here but
434 * it does not cause any harm since the resulting time when
435 * timer will fire and what is in writeout_period_time will be
436 * roughly the same.
437 */
438 writeout_period_time = wp_next_time(jiffies);
439 mod_timer(&writeout_period_timer, writeout_period_time);
440 }
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700441}
442
Miklos Szeredidd5656e2008-04-30 00:54:37 -0700443void bdi_writeout_inc(struct backing_dev_info *bdi)
444{
445 unsigned long flags;
446
447 local_irq_save(flags);
448 __bdi_writeout_inc(bdi);
449 local_irq_restore(flags);
450}
451EXPORT_SYMBOL_GPL(bdi_writeout_inc);
452
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700453/*
454 * Obtain an accurate fraction of the BDI's portion.
455 */
456static void bdi_writeout_fraction(struct backing_dev_info *bdi,
457 long *numerator, long *denominator)
458{
Jan Karaeb608e32012-05-24 18:59:11 +0200459 fprop_fraction_percpu(&writeout_completions, &bdi->completions,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700460 numerator, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700461}
462
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700463/*
Jan Karaeb608e32012-05-24 18:59:11 +0200464 * On idle system, we can be called long after we scheduled because we use
465 * deferred timers so count with missed periods.
466 */
467static void writeout_period(unsigned long t)
468{
469 int miss_periods = (jiffies - writeout_period_time) /
470 VM_COMPLETIONS_PERIOD_LEN;
471
472 if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
473 writeout_period_time = wp_next_time(writeout_period_time +
474 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
475 mod_timer(&writeout_period_timer, writeout_period_time);
476 } else {
477 /*
478 * Aging has zeroed all fractions. Stop wasting CPU on period
479 * updates.
480 */
481 writeout_period_time = 0;
482 }
483}
484
485/*
Johannes Weinerd08c4292011-10-31 17:07:05 -0700486 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
487 * registered backing devices, which, for obvious reasons, can not
488 * exceed 100%.
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700489 */
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700490static unsigned int bdi_min_ratio;
491
492int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
493{
494 int ret = 0;
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700495
Jens Axboecfc4ba52009-09-14 13:12:40 +0200496 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700497 if (min_ratio > bdi->max_ratio) {
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700498 ret = -EINVAL;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700499 } else {
500 min_ratio -= bdi->min_ratio;
501 if (bdi_min_ratio + min_ratio < 100) {
502 bdi_min_ratio += min_ratio;
503 bdi->min_ratio += min_ratio;
504 } else {
505 ret = -EINVAL;
506 }
507 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200508 spin_unlock_bh(&bdi_lock);
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700509
510 return ret;
511}
512
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700513int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
514{
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700515 int ret = 0;
516
517 if (max_ratio > 100)
518 return -EINVAL;
519
Jens Axboecfc4ba52009-09-14 13:12:40 +0200520 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700521 if (bdi->min_ratio > max_ratio) {
522 ret = -EINVAL;
523 } else {
524 bdi->max_ratio = max_ratio;
Jan Karaeb608e32012-05-24 18:59:11 +0200525 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700526 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200527 spin_unlock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700528
529 return ret;
530}
531EXPORT_SYMBOL(bdi_set_max_ratio);
532
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600533static unsigned long dirty_freerun_ceiling(unsigned long thresh,
534 unsigned long bg_thresh)
535{
536 return (thresh + bg_thresh) / 2;
537}
538
Wu Fengguangffd1f602011-06-19 22:18:42 -0600539static unsigned long hard_dirty_limit(unsigned long thresh)
540{
541 return max(thresh, global_dirty_limit);
542}
543
Wu Fengguang6f718652011-03-02 17:14:34 -0600544/**
Wu Fengguang1babe182010-08-11 14:17:40 -0700545 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
Wu Fengguang6f718652011-03-02 17:14:34 -0600546 * @bdi: the backing_dev_info to query
547 * @dirty: global dirty limit in pages
Wu Fengguang1babe182010-08-11 14:17:40 -0700548 *
Wu Fengguang6f718652011-03-02 17:14:34 -0600549 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
550 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
Wu Fengguangaed21ad2011-11-23 11:44:41 -0600551 *
552 * Note that balance_dirty_pages() will only seriously take it as a hard limit
553 * when sleeping max_pause per page is not enough to keep the dirty pages under
554 * control. For example, when the device is completely stalled due to some error
555 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
556 * In the other normal situations, it acts more gently by throttling the tasks
557 * more (rather than completely block them) when the bdi dirty pages go high.
Wu Fengguang6f718652011-03-02 17:14:34 -0600558 *
559 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
Wu Fengguang1babe182010-08-11 14:17:40 -0700560 * - starving fast devices
561 * - piling up dirty pages (that will take long time to sync) on slow devices
562 *
563 * The bdi's share of dirty limit will be adapting to its throughput and
564 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
565 */
566unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
Wu Fengguang16c40422010-08-11 14:17:39 -0700567{
568 u64 bdi_dirty;
569 long numerator, denominator;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700570
Wu Fengguang16c40422010-08-11 14:17:39 -0700571 /*
572 * Calculate this BDI's share of the dirty ratio.
573 */
574 bdi_writeout_fraction(bdi, &numerator, &denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700575
Wu Fengguang16c40422010-08-11 14:17:39 -0700576 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
577 bdi_dirty *= numerator;
578 do_div(bdi_dirty, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700579
Wu Fengguang16c40422010-08-11 14:17:39 -0700580 bdi_dirty += (dirty * bdi->min_ratio) / 100;
581 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
582 bdi_dirty = dirty * bdi->max_ratio / 100;
583
584 return bdi_dirty;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700585}
586
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600587/*
Maxim Patlasov5a537482013-09-11 14:22:46 -0700588 * setpoint - dirty 3
589 * f(dirty) := 1.0 + (----------------)
590 * limit - setpoint
591 *
592 * it's a 3rd order polynomial that subjects to
593 *
594 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
595 * (2) f(setpoint) = 1.0 => the balance point
596 * (3) f(limit) = 0 => the hard limit
597 * (4) df/dx <= 0 => negative feedback control
598 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
599 * => fast response on large errors; small oscillation near setpoint
600 */
601static inline long long pos_ratio_polynom(unsigned long setpoint,
602 unsigned long dirty,
603 unsigned long limit)
604{
605 long long pos_ratio;
606 long x;
607
608 x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
609 limit - setpoint + 1);
610 pos_ratio = x;
611 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
612 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
613 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
614
615 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
616}
617
618/*
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600619 * Dirty position control.
620 *
621 * (o) global/bdi setpoints
622 *
623 * We want the dirty pages be balanced around the global/bdi setpoints.
624 * When the number of dirty pages is higher/lower than the setpoint, the
625 * dirty position control ratio (and hence task dirty ratelimit) will be
626 * decreased/increased to bring the dirty pages back to the setpoint.
627 *
628 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
629 *
630 * if (dirty < setpoint) scale up pos_ratio
631 * if (dirty > setpoint) scale down pos_ratio
632 *
633 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
634 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
635 *
636 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
637 *
638 * (o) global control line
639 *
640 * ^ pos_ratio
641 * |
642 * | |<===== global dirty control scope ======>|
643 * 2.0 .............*
644 * | .*
645 * | . *
646 * | . *
647 * | . *
648 * | . *
649 * | . *
650 * 1.0 ................................*
651 * | . . *
652 * | . . *
653 * | . . *
654 * | . . *
655 * | . . *
656 * 0 +------------.------------------.----------------------*------------->
657 * freerun^ setpoint^ limit^ dirty pages
658 *
659 * (o) bdi control line
660 *
661 * ^ pos_ratio
662 * |
663 * | *
664 * | *
665 * | *
666 * | *
667 * | * |<=========== span ============>|
668 * 1.0 .......................*
669 * | . *
670 * | . *
671 * | . *
672 * | . *
673 * | . *
674 * | . *
675 * | . *
676 * | . *
677 * | . *
678 * | . *
679 * | . *
680 * 1/4 ...............................................* * * * * * * * * * * *
681 * | . .
682 * | . .
683 * | . .
684 * 0 +----------------------.-------------------------------.------------->
685 * bdi_setpoint^ x_intercept^
686 *
687 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
688 * be smoothly throttled down to normal if it starts high in situations like
689 * - start writing to a slow SD card and a fast disk at the same time. The SD
690 * card's bdi_dirty may rush to many times higher than bdi_setpoint.
691 * - the bdi dirty thresh drops quickly due to change of JBOD workload
692 */
693static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
694 unsigned long thresh,
695 unsigned long bg_thresh,
696 unsigned long dirty,
697 unsigned long bdi_thresh,
698 unsigned long bdi_dirty)
699{
700 unsigned long write_bw = bdi->avg_write_bandwidth;
701 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
702 unsigned long limit = hard_dirty_limit(thresh);
703 unsigned long x_intercept;
704 unsigned long setpoint; /* dirty pages' target balance point */
705 unsigned long bdi_setpoint;
706 unsigned long span;
707 long long pos_ratio; /* for scaling up/down the rate limit */
708 long x;
709
710 if (unlikely(dirty >= limit))
711 return 0;
712
713 /*
714 * global setpoint
715 *
Maxim Patlasov5a537482013-09-11 14:22:46 -0700716 * See comment for pos_ratio_polynom().
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600717 */
718 setpoint = (freerun + limit) / 2;
Maxim Patlasov5a537482013-09-11 14:22:46 -0700719 pos_ratio = pos_ratio_polynom(setpoint, dirty, limit);
720
721 /*
722 * The strictlimit feature is a tool preventing mistrusted filesystems
723 * from growing a large number of dirty pages before throttling. For
724 * such filesystems balance_dirty_pages always checks bdi counters
725 * against bdi limits. Even if global "nr_dirty" is under "freerun".
726 * This is especially important for fuse which sets bdi->max_ratio to
727 * 1% by default. Without strictlimit feature, fuse writeback may
728 * consume arbitrary amount of RAM because it is accounted in
729 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
730 *
731 * Here, in bdi_position_ratio(), we calculate pos_ratio based on
732 * two values: bdi_dirty and bdi_thresh. Let's consider an example:
733 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
734 * limits are set by default to 10% and 20% (background and throttle).
735 * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
736 * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
737 * about ~6K pages (as the average of background and throttle bdi
738 * limits). The 3rd order polynomial will provide positive feedback if
739 * bdi_dirty is under bdi_setpoint and vice versa.
740 *
741 * Note, that we cannot use global counters in these calculations
742 * because we want to throttle process writing to a strictlimit BDI
743 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
744 * in the example above).
745 */
746 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
747 long long bdi_pos_ratio;
748 unsigned long bdi_bg_thresh;
749
750 if (bdi_dirty < 8)
751 return min_t(long long, pos_ratio * 2,
752 2 << RATELIMIT_CALC_SHIFT);
753
754 if (bdi_dirty >= bdi_thresh)
755 return 0;
756
757 bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh);
758 bdi_setpoint = dirty_freerun_ceiling(bdi_thresh,
759 bdi_bg_thresh);
760
761 if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh)
762 return 0;
763
764 bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
765 bdi_thresh);
766
767 /*
768 * Typically, for strictlimit case, bdi_setpoint << setpoint
769 * and pos_ratio >> bdi_pos_ratio. In the other words global
770 * state ("dirty") is not limiting factor and we have to
771 * make decision based on bdi counters. But there is an
772 * important case when global pos_ratio should get precedence:
773 * global limits are exceeded (e.g. due to activities on other
774 * BDIs) while given strictlimit BDI is below limit.
775 *
776 * "pos_ratio * bdi_pos_ratio" would work for the case above,
777 * but it would look too non-natural for the case of all
778 * activity in the system coming from a single strictlimit BDI
779 * with bdi->max_ratio == 100%.
780 *
781 * Note that min() below somewhat changes the dynamics of the
782 * control system. Normally, pos_ratio value can be well over 3
783 * (when globally we are at freerun and bdi is well below bdi
784 * setpoint). Now the maximum pos_ratio in the same situation
785 * is 2. We might want to tweak this if we observe the control
786 * system is too slow to adapt.
787 */
788 return min(pos_ratio, bdi_pos_ratio);
789 }
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600790
791 /*
792 * We have computed basic pos_ratio above based on global situation. If
793 * the bdi is over/under its share of dirty pages, we want to scale
794 * pos_ratio further down/up. That is done by the following mechanism.
795 */
796
797 /*
798 * bdi setpoint
799 *
800 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
801 *
802 * x_intercept - bdi_dirty
803 * := --------------------------
804 * x_intercept - bdi_setpoint
805 *
806 * The main bdi control line is a linear function that subjects to
807 *
808 * (1) f(bdi_setpoint) = 1.0
809 * (2) k = - 1 / (8 * write_bw) (in single bdi case)
810 * or equally: x_intercept = bdi_setpoint + 8 * write_bw
811 *
812 * For single bdi case, the dirty pages are observed to fluctuate
813 * regularly within range
814 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
815 * for various filesystems, where (2) can yield in a reasonable 12.5%
816 * fluctuation range for pos_ratio.
817 *
818 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
819 * own size, so move the slope over accordingly and choose a slope that
820 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
821 */
822 if (unlikely(bdi_thresh > thresh))
823 bdi_thresh = thresh;
Wu Fengguangaed21ad2011-11-23 11:44:41 -0600824 /*
825 * It's very possible that bdi_thresh is close to 0 not because the
826 * device is slow, but that it has remained inactive for long time.
827 * Honour such devices a reasonable good (hopefully IO efficient)
828 * threshold, so that the occasional writes won't be blocked and active
829 * writes can rampup the threshold quickly.
830 */
Wu Fengguang8927f662011-08-04 22:16:46 -0600831 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600832 /*
833 * scale global setpoint to bdi's:
834 * bdi_setpoint = setpoint * bdi_thresh / thresh
835 */
836 x = div_u64((u64)bdi_thresh << 16, thresh + 1);
837 bdi_setpoint = setpoint * (u64)x >> 16;
838 /*
839 * Use span=(8*write_bw) in single bdi case as indicated by
840 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
841 *
842 * bdi_thresh thresh - bdi_thresh
843 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
844 * thresh thresh
845 */
846 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
847 x_intercept = bdi_setpoint + span;
848
849 if (bdi_dirty < x_intercept - span / 4) {
Wu Fengguang50657fc2011-10-11 17:06:33 -0600850 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
851 x_intercept - bdi_setpoint + 1);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600852 } else
853 pos_ratio /= 4;
854
Wu Fengguang8927f662011-08-04 22:16:46 -0600855 /*
856 * bdi reserve area, safeguard against dirty pool underrun and disk idle
857 * It may push the desired control point of global dirty pages higher
858 * than setpoint.
859 */
860 x_intercept = bdi_thresh / 2;
861 if (bdi_dirty < x_intercept) {
Wu Fengguang50657fc2011-10-11 17:06:33 -0600862 if (bdi_dirty > x_intercept / 8)
863 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
864 else
Wu Fengguang8927f662011-08-04 22:16:46 -0600865 pos_ratio *= 8;
866 }
867
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600868 return pos_ratio;
869}
870
Wu Fengguange98be2d2010-08-29 11:22:30 -0600871static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
872 unsigned long elapsed,
873 unsigned long written)
874{
875 const unsigned long period = roundup_pow_of_two(3 * HZ);
876 unsigned long avg = bdi->avg_write_bandwidth;
877 unsigned long old = bdi->write_bandwidth;
878 u64 bw;
879
880 /*
881 * bw = written * HZ / elapsed
882 *
883 * bw * elapsed + write_bandwidth * (period - elapsed)
884 * write_bandwidth = ---------------------------------------------------
885 * period
886 */
887 bw = written - bdi->written_stamp;
888 bw *= HZ;
889 if (unlikely(elapsed > period)) {
890 do_div(bw, elapsed);
891 avg = bw;
892 goto out;
893 }
894 bw += (u64)bdi->write_bandwidth * (period - elapsed);
895 bw >>= ilog2(period);
896
897 /*
898 * one more level of smoothing, for filtering out sudden spikes
899 */
900 if (avg > old && old >= (unsigned long)bw)
901 avg -= (avg - old) >> 3;
902
903 if (avg < old && old <= (unsigned long)bw)
904 avg += (old - avg) >> 3;
905
906out:
907 bdi->write_bandwidth = bw;
908 bdi->avg_write_bandwidth = avg;
909}
910
Wu Fengguangc42843f2011-03-02 15:54:09 -0600911/*
912 * The global dirtyable memory and dirty threshold could be suddenly knocked
913 * down by a large amount (eg. on the startup of KVM in a swapless system).
914 * This may throw the system into deep dirty exceeded state and throttle
915 * heavy/light dirtiers alike. To retain good responsiveness, maintain
916 * global_dirty_limit for tracking slowly down to the knocked down dirty
917 * threshold.
918 */
919static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
920{
921 unsigned long limit = global_dirty_limit;
922
923 /*
924 * Follow up in one step.
925 */
926 if (limit < thresh) {
927 limit = thresh;
928 goto update;
929 }
930
931 /*
932 * Follow down slowly. Use the higher one as the target, because thresh
933 * may drop below dirty. This is exactly the reason to introduce
934 * global_dirty_limit which is guaranteed to lie above the dirty pages.
935 */
936 thresh = max(thresh, dirty);
937 if (limit > thresh) {
938 limit -= (limit - thresh) >> 5;
939 goto update;
940 }
941 return;
942update:
943 global_dirty_limit = limit;
944}
945
946static void global_update_bandwidth(unsigned long thresh,
947 unsigned long dirty,
948 unsigned long now)
949{
950 static DEFINE_SPINLOCK(dirty_lock);
951 static unsigned long update_time;
952
953 /*
954 * check locklessly first to optimize away locking for the most time
955 */
956 if (time_before(now, update_time + BANDWIDTH_INTERVAL))
957 return;
958
959 spin_lock(&dirty_lock);
960 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
961 update_dirty_limit(thresh, dirty);
962 update_time = now;
963 }
964 spin_unlock(&dirty_lock);
965}
966
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600967/*
968 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
969 *
970 * Normal bdi tasks will be curbed at or below it in long term.
971 * Obviously it should be around (write_bw / N) when there are N dd tasks.
972 */
973static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
974 unsigned long thresh,
975 unsigned long bg_thresh,
976 unsigned long dirty,
977 unsigned long bdi_thresh,
978 unsigned long bdi_dirty,
979 unsigned long dirtied,
980 unsigned long elapsed)
981{
Wu Fengguang73811312011-08-26 15:53:24 -0600982 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
983 unsigned long limit = hard_dirty_limit(thresh);
984 unsigned long setpoint = (freerun + limit) / 2;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600985 unsigned long write_bw = bdi->avg_write_bandwidth;
986 unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
987 unsigned long dirty_rate;
988 unsigned long task_ratelimit;
989 unsigned long balanced_dirty_ratelimit;
990 unsigned long pos_ratio;
Wu Fengguang73811312011-08-26 15:53:24 -0600991 unsigned long step;
992 unsigned long x;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600993
994 /*
995 * The dirty rate will match the writeout rate in long term, except
996 * when dirty pages are truncated by userspace or re-dirtied by FS.
997 */
998 dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
999
1000 pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
1001 bdi_thresh, bdi_dirty);
1002 /*
1003 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1004 */
1005 task_ratelimit = (u64)dirty_ratelimit *
1006 pos_ratio >> RATELIMIT_CALC_SHIFT;
1007 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1008
1009 /*
1010 * A linear estimation of the "balanced" throttle rate. The theory is,
1011 * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
1012 * dirty_rate will be measured to be (N * task_ratelimit). So the below
1013 * formula will yield the balanced rate limit (write_bw / N).
1014 *
1015 * Note that the expanded form is not a pure rate feedback:
1016 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
1017 * but also takes pos_ratio into account:
1018 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
1019 *
1020 * (1) is not realistic because pos_ratio also takes part in balancing
1021 * the dirty rate. Consider the state
1022 * pos_ratio = 0.5 (3)
1023 * rate = 2 * (write_bw / N) (4)
1024 * If (1) is used, it will stuck in that state! Because each dd will
1025 * be throttled at
1026 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1027 * yielding
1028 * dirty_rate = N * task_ratelimit = write_bw (6)
1029 * put (6) into (1) we get
1030 * rate_(i+1) = rate_(i) (7)
1031 *
1032 * So we end up using (2) to always keep
1033 * rate_(i+1) ~= (write_bw / N) (8)
1034 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1035 * pos_ratio is able to drive itself to 1.0, which is not only where
1036 * the dirty count meet the setpoint, but also where the slope of
1037 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1038 */
1039 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1040 dirty_rate | 1);
Wu Fengguangbdaac492011-08-03 14:30:36 -06001041 /*
1042 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1043 */
1044 if (unlikely(balanced_dirty_ratelimit > write_bw))
1045 balanced_dirty_ratelimit = write_bw;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001046
Wu Fengguang73811312011-08-26 15:53:24 -06001047 /*
1048 * We could safely do this and return immediately:
1049 *
1050 * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
1051 *
1052 * However to get a more stable dirty_ratelimit, the below elaborated
Wanpeng Li331cbde2012-06-09 11:10:55 +08001053 * code makes use of task_ratelimit to filter out singular points and
Wu Fengguang73811312011-08-26 15:53:24 -06001054 * limit the step size.
1055 *
1056 * The below code essentially only uses the relative value of
1057 *
1058 * task_ratelimit - dirty_ratelimit
1059 * = (pos_ratio - 1) * dirty_ratelimit
1060 *
1061 * which reflects the direction and size of dirty position error.
1062 */
1063
1064 /*
1065 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1066 * task_ratelimit is on the same side of dirty_ratelimit, too.
1067 * For example, when
1068 * - dirty_ratelimit > balanced_dirty_ratelimit
1069 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1070 * lowering dirty_ratelimit will help meet both the position and rate
1071 * control targets. Otherwise, don't update dirty_ratelimit if it will
1072 * only help meet the rate target. After all, what the users ultimately
1073 * feel and care are stable dirty rate and small position error.
1074 *
1075 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
Wanpeng Li331cbde2012-06-09 11:10:55 +08001076 * and filter out the singular points of balanced_dirty_ratelimit. Which
Wu Fengguang73811312011-08-26 15:53:24 -06001077 * keeps jumping around randomly and can even leap far away at times
1078 * due to the small 200ms estimation period of dirty_rate (we want to
1079 * keep that period small to reduce time lags).
1080 */
1081 step = 0;
Maxim Patlasov5a537482013-09-11 14:22:46 -07001082
1083 /*
1084 * For strictlimit case, calculations above were based on bdi counters
1085 * and limits (starting from pos_ratio = bdi_position_ratio() and up to
1086 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1087 * Hence, to calculate "step" properly, we have to use bdi_dirty as
1088 * "dirty" and bdi_setpoint as "setpoint".
1089 *
1090 * We rampup dirty_ratelimit forcibly if bdi_dirty is low because
1091 * it's possible that bdi_thresh is close to zero due to inactivity
1092 * of backing device (see the implementation of bdi_dirty_limit()).
1093 */
1094 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1095 dirty = bdi_dirty;
1096 if (bdi_dirty < 8)
1097 setpoint = bdi_dirty + 1;
1098 else
1099 setpoint = (bdi_thresh +
1100 bdi_dirty_limit(bdi, bg_thresh)) / 2;
1101 }
1102
Wu Fengguang73811312011-08-26 15:53:24 -06001103 if (dirty < setpoint) {
1104 x = min(bdi->balanced_dirty_ratelimit,
1105 min(balanced_dirty_ratelimit, task_ratelimit));
1106 if (dirty_ratelimit < x)
1107 step = x - dirty_ratelimit;
1108 } else {
1109 x = max(bdi->balanced_dirty_ratelimit,
1110 max(balanced_dirty_ratelimit, task_ratelimit));
1111 if (dirty_ratelimit > x)
1112 step = dirty_ratelimit - x;
1113 }
1114
1115 /*
1116 * Don't pursue 100% rate matching. It's impossible since the balanced
1117 * rate itself is constantly fluctuating. So decrease the track speed
1118 * when it gets close to the target. Helps eliminate pointless tremors.
1119 */
1120 step >>= dirty_ratelimit / (2 * step + 1);
1121 /*
1122 * Limit the tracking speed to avoid overshooting.
1123 */
1124 step = (step + 7) / 8;
1125
1126 if (dirty_ratelimit < balanced_dirty_ratelimit)
1127 dirty_ratelimit += step;
1128 else
1129 dirty_ratelimit -= step;
1130
1131 bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1132 bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
Wu Fengguangb48c1042011-03-02 17:22:49 -06001133
1134 trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001135}
1136
Wu Fengguange98be2d2010-08-29 11:22:30 -06001137void __bdi_update_bandwidth(struct backing_dev_info *bdi,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001138 unsigned long thresh,
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001139 unsigned long bg_thresh,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001140 unsigned long dirty,
1141 unsigned long bdi_thresh,
1142 unsigned long bdi_dirty,
Wu Fengguange98be2d2010-08-29 11:22:30 -06001143 unsigned long start_time)
1144{
1145 unsigned long now = jiffies;
1146 unsigned long elapsed = now - bdi->bw_time_stamp;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001147 unsigned long dirtied;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001148 unsigned long written;
1149
1150 /*
1151 * rate-limit, only update once every 200ms.
1152 */
1153 if (elapsed < BANDWIDTH_INTERVAL)
1154 return;
1155
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001156 dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001157 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1158
1159 /*
1160 * Skip quiet periods when disk bandwidth is under-utilized.
1161 * (at least 1s idle time between two flusher runs)
1162 */
1163 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1164 goto snapshot;
1165
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001166 if (thresh) {
Wu Fengguangc42843f2011-03-02 15:54:09 -06001167 global_update_bandwidth(thresh, dirty, now);
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001168 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1169 bdi_thresh, bdi_dirty,
1170 dirtied, elapsed);
1171 }
Wu Fengguange98be2d2010-08-29 11:22:30 -06001172 bdi_update_write_bandwidth(bdi, elapsed, written);
1173
1174snapshot:
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001175 bdi->dirtied_stamp = dirtied;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001176 bdi->written_stamp = written;
1177 bdi->bw_time_stamp = now;
1178}
1179
1180static void bdi_update_bandwidth(struct backing_dev_info *bdi,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001181 unsigned long thresh,
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001182 unsigned long bg_thresh,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001183 unsigned long dirty,
1184 unsigned long bdi_thresh,
1185 unsigned long bdi_dirty,
Wu Fengguange98be2d2010-08-29 11:22:30 -06001186 unsigned long start_time)
1187{
1188 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1189 return;
1190 spin_lock(&bdi->wb.list_lock);
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001191 __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1192 bdi_thresh, bdi_dirty, start_time);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001193 spin_unlock(&bdi->wb.list_lock);
1194}
1195
Linus Torvalds1da177e2005-04-16 15:20:36 -07001196/*
Namjae Jeond0e1d662012-12-11 16:00:21 -08001197 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
Wu Fengguang9d823e82011-06-11 18:10:12 -06001198 * will look to see if it needs to start dirty throttling.
1199 *
1200 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1201 * global_page_state() too often. So scale it near-sqrt to the safety margin
1202 * (the number of pages we may dirty without exceeding the dirty limits).
1203 */
1204static unsigned long dirty_poll_interval(unsigned long dirty,
1205 unsigned long thresh)
1206{
1207 if (thresh > dirty)
1208 return 1UL << (ilog2(thresh - dirty) >> 1);
1209
1210 return 1;
1211}
1212
Fengguang Wue3b6c652013-10-16 13:47:03 -07001213static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
1214 unsigned long bdi_dirty)
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001215{
Fengguang Wue3b6c652013-10-16 13:47:03 -07001216 unsigned long bw = bdi->avg_write_bandwidth;
1217 unsigned long t;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001218
1219 /*
1220 * Limit pause time for small memory systems. If sleeping for too long
1221 * time, a small pool of dirty/writeback pages may go empty and disk go
1222 * idle.
1223 *
1224 * 8 serves as the safety ratio.
1225 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001226 t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1227 t++;
1228
Fengguang Wue3b6c652013-10-16 13:47:03 -07001229 return min_t(unsigned long, t, MAX_PAUSE);
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001230}
1231
1232static long bdi_min_pause(struct backing_dev_info *bdi,
1233 long max_pause,
1234 unsigned long task_ratelimit,
1235 unsigned long dirty_ratelimit,
1236 int *nr_dirtied_pause)
1237{
1238 long hi = ilog2(bdi->avg_write_bandwidth);
1239 long lo = ilog2(bdi->dirty_ratelimit);
1240 long t; /* target pause */
1241 long pause; /* estimated next pause */
1242 int pages; /* target nr_dirtied_pause */
1243
1244 /* target for 10ms pause on 1-dd case */
1245 t = max(1, HZ / 100);
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001246
1247 /*
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001248 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1249 * overheads.
1250 *
1251 * (N * 10ms) on 2^N concurrent tasks.
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001252 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001253 if (hi > lo)
1254 t += (hi - lo) * (10 * HZ) / 1024;
1255
1256 /*
1257 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1258 * on the much more stable dirty_ratelimit. However the next pause time
1259 * will be computed based on task_ratelimit and the two rate limits may
1260 * depart considerably at some time. Especially if task_ratelimit goes
1261 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1262 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1263 * result task_ratelimit won't be executed faithfully, which could
1264 * eventually bring down dirty_ratelimit.
1265 *
1266 * We apply two rules to fix it up:
1267 * 1) try to estimate the next pause time and if necessary, use a lower
1268 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1269 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1270 * 2) limit the target pause time to max_pause/2, so that the normal
1271 * small fluctuations of task_ratelimit won't trigger rule (1) and
1272 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1273 */
1274 t = min(t, 1 + max_pause / 2);
1275 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1276
Wu Fengguang5b9b3572011-12-06 13:17:17 -06001277 /*
1278 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1279 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1280 * When the 16 consecutive reads are often interrupted by some dirty
1281 * throttling pause during the async writes, cfq will go into idles
1282 * (deadline is fine). So push nr_dirtied_pause as high as possible
1283 * until reaches DIRTY_POLL_THRESH=32 pages.
1284 */
1285 if (pages < DIRTY_POLL_THRESH) {
1286 t = max_pause;
1287 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1288 if (pages > DIRTY_POLL_THRESH) {
1289 pages = DIRTY_POLL_THRESH;
1290 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1291 }
1292 }
1293
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001294 pause = HZ * pages / (task_ratelimit + 1);
1295 if (pause > max_pause) {
1296 t = max_pause;
1297 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1298 }
1299
1300 *nr_dirtied_pause = pages;
1301 /*
1302 * The minimal pause time will normally be half the target pause time.
1303 */
Wu Fengguang5b9b3572011-12-06 13:17:17 -06001304 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001305}
1306
Maxim Patlasov5a537482013-09-11 14:22:46 -07001307static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
1308 unsigned long dirty_thresh,
1309 unsigned long background_thresh,
1310 unsigned long *bdi_dirty,
1311 unsigned long *bdi_thresh,
1312 unsigned long *bdi_bg_thresh)
1313{
1314 unsigned long bdi_reclaimable;
1315
1316 /*
1317 * bdi_thresh is not treated as some limiting factor as
1318 * dirty_thresh, due to reasons
1319 * - in JBOD setup, bdi_thresh can fluctuate a lot
1320 * - in a system with HDD and USB key, the USB key may somehow
1321 * go into state (bdi_dirty >> bdi_thresh) either because
1322 * bdi_dirty starts high, or because bdi_thresh drops low.
1323 * In this case we don't want to hard throttle the USB key
1324 * dirtiers for 100 seconds until bdi_dirty drops under
1325 * bdi_thresh. Instead the auxiliary bdi control line in
1326 * bdi_position_ratio() will let the dirtier task progress
1327 * at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1328 */
1329 *bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1330
1331 if (bdi_bg_thresh)
1332 *bdi_bg_thresh = div_u64((u64)*bdi_thresh *
1333 background_thresh,
1334 dirty_thresh);
1335
1336 /*
1337 * In order to avoid the stacked BDI deadlock we need
1338 * to ensure we accurately count the 'dirty' pages when
1339 * the threshold is low.
1340 *
1341 * Otherwise it would be possible to get thresh+n pages
1342 * reported dirty, even though there are thresh-m pages
1343 * actually dirty; with m+n sitting in the percpu
1344 * deltas.
1345 */
1346 if (*bdi_thresh < 2 * bdi_stat_error(bdi)) {
1347 bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1348 *bdi_dirty = bdi_reclaimable +
1349 bdi_stat_sum(bdi, BDI_WRITEBACK);
1350 } else {
1351 bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1352 *bdi_dirty = bdi_reclaimable +
1353 bdi_stat(bdi, BDI_WRITEBACK);
1354 }
1355}
1356
Wu Fengguang9d823e82011-06-11 18:10:12 -06001357/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001358 * balance_dirty_pages() must be called by processes which are generating dirty
1359 * data. It looks at the number of dirty pages in the machine and will force
Wu Fengguang143dfe82010-08-27 18:45:12 -06001360 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
Jens Axboe5b0830c2009-09-23 19:37:09 +02001361 * If we're over `background_thresh' then the writeback threads are woken to
1362 * perform some writeout.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001363 */
Wu Fengguang3a2e9a52009-09-23 21:56:00 +08001364static void balance_dirty_pages(struct address_space *mapping,
Wu Fengguang143dfe82010-08-27 18:45:12 -06001365 unsigned long pages_dirtied)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001366{
Wu Fengguang143dfe82010-08-27 18:45:12 -06001367 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
Wu Fengguang77627412010-09-12 13:34:05 -06001368 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
David Rientjes364aeb22009-01-06 14:39:29 -08001369 unsigned long background_thresh;
1370 unsigned long dirty_thresh;
Wu Fengguang83712352011-06-11 19:25:42 -06001371 long period;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001372 long pause;
1373 long max_pause;
1374 long min_pause;
1375 int nr_dirtied_pause;
Wu Fengguange50e3722010-08-11 14:17:37 -07001376 bool dirty_exceeded = false;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001377 unsigned long task_ratelimit;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001378 unsigned long dirty_ratelimit;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001379 unsigned long pos_ratio;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001380 struct backing_dev_info *bdi = mapping->backing_dev_info;
Maxim Patlasov5a537482013-09-11 14:22:46 -07001381 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001382 unsigned long start_time = jiffies;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001383
1384 for (;;) {
Wu Fengguang83712352011-06-11 19:25:42 -06001385 unsigned long now = jiffies;
Maxim Patlasov5a537482013-09-11 14:22:46 -07001386 unsigned long uninitialized_var(bdi_thresh);
1387 unsigned long thresh;
1388 unsigned long uninitialized_var(bdi_dirty);
1389 unsigned long dirty;
1390 unsigned long bg_thresh;
Wu Fengguang83712352011-06-11 19:25:42 -06001391
Wu Fengguang143dfe82010-08-27 18:45:12 -06001392 /*
1393 * Unstable writes are a feature of certain networked
1394 * filesystems (i.e. NFS) in which data may have been
1395 * written to the server's write cache, but has not yet
1396 * been flushed to permanent storage.
1397 */
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001398 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1399 global_page_state(NR_UNSTABLE_NFS);
Wu Fengguang77627412010-09-12 13:34:05 -06001400 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001401
Wu Fengguang16c40422010-08-11 14:17:39 -07001402 global_dirty_limits(&background_thresh, &dirty_thresh);
1403
Maxim Patlasov5a537482013-09-11 14:22:46 -07001404 if (unlikely(strictlimit)) {
1405 bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1406 &bdi_dirty, &bdi_thresh, &bg_thresh);
1407
1408 dirty = bdi_dirty;
1409 thresh = bdi_thresh;
1410 } else {
1411 dirty = nr_dirty;
1412 thresh = dirty_thresh;
1413 bg_thresh = background_thresh;
1414 }
1415
Wu Fengguang16c40422010-08-11 14:17:39 -07001416 /*
1417 * Throttle it only when the background writeback cannot
1418 * catch-up. This avoids (excessively) small writeouts
Maxim Patlasov5a537482013-09-11 14:22:46 -07001419 * when the bdi limits are ramping up in case of !strictlimit.
1420 *
1421 * In strictlimit case make decision based on the bdi counters
1422 * and limits. Small writeouts when the bdi limits are ramping
1423 * up are the price we consciously pay for strictlimit-ing.
Wu Fengguang16c40422010-08-11 14:17:39 -07001424 */
Maxim Patlasov5a537482013-09-11 14:22:46 -07001425 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh)) {
Wu Fengguang83712352011-06-11 19:25:42 -06001426 current->dirty_paused_when = now;
1427 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001428 current->nr_dirtied_pause =
Maxim Patlasov5a537482013-09-11 14:22:46 -07001429 dirty_poll_interval(dirty, thresh);
Wu Fengguang16c40422010-08-11 14:17:39 -07001430 break;
Wu Fengguang83712352011-06-11 19:25:42 -06001431 }
Wu Fengguang16c40422010-08-11 14:17:39 -07001432
Wu Fengguang143dfe82010-08-27 18:45:12 -06001433 if (unlikely(!writeback_in_progress(bdi)))
1434 bdi_start_background_writeback(bdi);
1435
Maxim Patlasov5a537482013-09-11 14:22:46 -07001436 if (!strictlimit)
1437 bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1438 &bdi_dirty, &bdi_thresh, NULL);
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001439
Wu Fengguang82791942011-12-03 21:26:01 -06001440 dirty_exceeded = (bdi_dirty > bdi_thresh) &&
Maxim Patlasov5a537482013-09-11 14:22:46 -07001441 ((nr_dirty > dirty_thresh) || strictlimit);
Wu Fengguang143dfe82010-08-27 18:45:12 -06001442 if (dirty_exceeded && !bdi->dirty_exceeded)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001443 bdi->dirty_exceeded = 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001444
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001445 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1446 nr_dirty, bdi_thresh, bdi_dirty,
1447 start_time);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001448
Wu Fengguang143dfe82010-08-27 18:45:12 -06001449 dirty_ratelimit = bdi->dirty_ratelimit;
1450 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1451 background_thresh, nr_dirty,
1452 bdi_thresh, bdi_dirty);
Wu Fengguang3a73dbb2011-11-07 19:19:28 +08001453 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1454 RATELIMIT_CALC_SHIFT;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001455 max_pause = bdi_max_pause(bdi, bdi_dirty);
1456 min_pause = bdi_min_pause(bdi, max_pause,
1457 task_ratelimit, dirty_ratelimit,
1458 &nr_dirtied_pause);
1459
Wu Fengguang3a73dbb2011-11-07 19:19:28 +08001460 if (unlikely(task_ratelimit == 0)) {
Wu Fengguang83712352011-06-11 19:25:42 -06001461 period = max_pause;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001462 pause = max_pause;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001463 goto pause;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001464 }
Wu Fengguang83712352011-06-11 19:25:42 -06001465 period = HZ * pages_dirtied / task_ratelimit;
1466 pause = period;
1467 if (current->dirty_paused_when)
1468 pause -= now - current->dirty_paused_when;
1469 /*
1470 * For less than 1s think time (ext3/4 may block the dirtier
1471 * for up to 800ms from time to time on 1-HDD; so does xfs,
1472 * however at much less frequency), try to compensate it in
1473 * future periods by updating the virtual time; otherwise just
1474 * do a reset, as it may be a light dirtier.
1475 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001476 if (pause < min_pause) {
Wu Fengguangece13ac2010-08-29 23:33:20 -06001477 trace_balance_dirty_pages(bdi,
1478 dirty_thresh,
1479 background_thresh,
1480 nr_dirty,
1481 bdi_thresh,
1482 bdi_dirty,
1483 dirty_ratelimit,
1484 task_ratelimit,
1485 pages_dirtied,
Wu Fengguang83712352011-06-11 19:25:42 -06001486 period,
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001487 min(pause, 0L),
Wu Fengguangece13ac2010-08-29 23:33:20 -06001488 start_time);
Wu Fengguang83712352011-06-11 19:25:42 -06001489 if (pause < -HZ) {
1490 current->dirty_paused_when = now;
1491 current->nr_dirtied = 0;
1492 } else if (period) {
1493 current->dirty_paused_when += period;
1494 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001495 } else if (current->nr_dirtied_pause <= pages_dirtied)
1496 current->nr_dirtied_pause += pages_dirtied;
Wu Fengguang57fc9782011-06-11 19:32:32 -06001497 break;
1498 }
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001499 if (unlikely(pause > max_pause)) {
1500 /* for occasional dropped task_ratelimit */
1501 now += min(pause - max_pause, max_pause);
1502 pause = max_pause;
1503 }
Wu Fengguang143dfe82010-08-27 18:45:12 -06001504
1505pause:
Wu Fengguangece13ac2010-08-29 23:33:20 -06001506 trace_balance_dirty_pages(bdi,
1507 dirty_thresh,
1508 background_thresh,
1509 nr_dirty,
1510 bdi_thresh,
1511 bdi_dirty,
1512 dirty_ratelimit,
1513 task_ratelimit,
1514 pages_dirtied,
Wu Fengguang83712352011-06-11 19:25:42 -06001515 period,
Wu Fengguangece13ac2010-08-29 23:33:20 -06001516 pause,
1517 start_time);
Jan Kara499d05e2011-11-16 19:34:48 +08001518 __set_current_state(TASK_KILLABLE);
Wu Fengguangd25105e2009-10-09 12:40:42 +02001519 io_schedule_timeout(pause);
Jens Axboe87c6a9b2009-09-17 19:59:14 +02001520
Wu Fengguang83712352011-06-11 19:25:42 -06001521 current->dirty_paused_when = now + pause;
1522 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001523 current->nr_dirtied_pause = nr_dirtied_pause;
Wu Fengguang83712352011-06-11 19:25:42 -06001524
Wu Fengguangffd1f602011-06-19 22:18:42 -06001525 /*
Wu Fengguang1df64712011-11-13 19:47:32 -06001526 * This is typically equal to (nr_dirty < dirty_thresh) and can
1527 * also keep "1000+ dd on a slow USB stick" under control.
Wu Fengguangffd1f602011-06-19 22:18:42 -06001528 */
Wu Fengguang1df64712011-11-13 19:47:32 -06001529 if (task_ratelimit)
Wu Fengguangffd1f602011-06-19 22:18:42 -06001530 break;
Jan Kara499d05e2011-11-16 19:34:48 +08001531
Wu Fengguangc5c63432011-12-02 10:21:33 -06001532 /*
1533 * In the case of an unresponding NFS server and the NFS dirty
1534 * pages exceeds dirty_thresh, give the other good bdi's a pipe
1535 * to go through, so that tasks on them still remain responsive.
1536 *
1537 * In theory 1 page is enough to keep the comsumer-producer
1538 * pipe going: the flusher cleans 1 page => the task dirties 1
1539 * more page. However bdi_dirty has accounting errors. So use
1540 * the larger and more IO friendly bdi_stat_error.
1541 */
1542 if (bdi_dirty <= bdi_stat_error(bdi))
1543 break;
1544
Jan Kara499d05e2011-11-16 19:34:48 +08001545 if (fatal_signal_pending(current))
1546 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001547 }
1548
Wu Fengguang143dfe82010-08-27 18:45:12 -06001549 if (!dirty_exceeded && bdi->dirty_exceeded)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001550 bdi->dirty_exceeded = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001551
1552 if (writeback_in_progress(bdi))
Jens Axboe5b0830c2009-09-23 19:37:09 +02001553 return;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001554
1555 /*
1556 * In laptop mode, we wait until hitting the higher threshold before
1557 * starting background writeout, and then write out all the way down
1558 * to the lower threshold. So slow writers cause minimal disk activity.
1559 *
1560 * In normal mode, we start background writeout at the lower
1561 * background_thresh, to keep the amount of dirty memory low.
1562 */
Wu Fengguang143dfe82010-08-27 18:45:12 -06001563 if (laptop_mode)
1564 return;
1565
1566 if (nr_reclaimable > background_thresh)
Christoph Hellwigc5444192010-06-08 18:15:15 +02001567 bdi_start_background_writeback(bdi);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001568}
1569
Peter Zijlstraa200ee12007-10-08 18:54:37 +02001570void set_page_dirty_balance(struct page *page, int page_mkwrite)
Peter Zijlstraedc79b22006-09-25 23:30:58 -07001571{
Peter Zijlstraa200ee12007-10-08 18:54:37 +02001572 if (set_page_dirty(page) || page_mkwrite) {
Peter Zijlstraedc79b22006-09-25 23:30:58 -07001573 struct address_space *mapping = page_mapping(page);
1574
1575 if (mapping)
1576 balance_dirty_pages_ratelimited(mapping);
1577 }
1578}
1579
Wu Fengguang9d823e82011-06-11 18:10:12 -06001580static DEFINE_PER_CPU(int, bdp_ratelimits);
Tejun Heo245b2e72009-06-24 15:13:48 +09001581
Wu Fengguang54848d72011-04-05 13:21:19 -06001582/*
1583 * Normal tasks are throttled by
1584 * loop {
1585 * dirty tsk->nr_dirtied_pause pages;
1586 * take a snap in balance_dirty_pages();
1587 * }
1588 * However there is a worst case. If every task exit immediately when dirtied
1589 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1590 * called to throttle the page dirties. The solution is to save the not yet
1591 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1592 * randomly into the running tasks. This works well for the above worst case,
1593 * as the new task will pick up and accumulate the old task's leaked dirty
1594 * count and eventually get throttled.
1595 */
1596DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1597
Linus Torvalds1da177e2005-04-16 15:20:36 -07001598/**
Namjae Jeond0e1d662012-12-11 16:00:21 -08001599 * balance_dirty_pages_ratelimited - balance dirty memory state
Martin Waitz67be2dd2005-05-01 08:59:26 -07001600 * @mapping: address_space which was dirtied
Linus Torvalds1da177e2005-04-16 15:20:36 -07001601 *
1602 * Processes which are dirtying memory should call in here once for each page
1603 * which was newly dirtied. The function will periodically check the system's
1604 * dirty state and will initiate writeback if needed.
1605 *
1606 * On really big machines, get_writeback_state is expensive, so try to avoid
1607 * calling it too often (ratelimiting). But once we're over the dirty memory
1608 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1609 * from overshooting the limit by (ratelimit_pages) each.
1610 */
Namjae Jeond0e1d662012-12-11 16:00:21 -08001611void balance_dirty_pages_ratelimited(struct address_space *mapping)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001612{
Wu Fengguang36715ce2011-06-11 17:53:57 -06001613 struct backing_dev_info *bdi = mapping->backing_dev_info;
Wu Fengguang9d823e82011-06-11 18:10:12 -06001614 int ratelimit;
1615 int *p;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001616
Wu Fengguang36715ce2011-06-11 17:53:57 -06001617 if (!bdi_cap_account_dirty(bdi))
1618 return;
1619
Wu Fengguang9d823e82011-06-11 18:10:12 -06001620 ratelimit = current->nr_dirtied_pause;
1621 if (bdi->dirty_exceeded)
1622 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
Linus Torvalds1da177e2005-04-16 15:20:36 -07001623
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001624 preempt_disable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001625 /*
1626 * This prevents one CPU to accumulate too many dirtied pages without
1627 * calling into balance_dirty_pages(), which can happen when there are
1628 * 1000+ tasks, all of them start dirtying pages at exactly the same
1629 * time, hence all honoured too large initial task->nr_dirtied_pause.
1630 */
Tejun Heo245b2e72009-06-24 15:13:48 +09001631 p = &__get_cpu_var(bdp_ratelimits);
Wu Fengguang9d823e82011-06-11 18:10:12 -06001632 if (unlikely(current->nr_dirtied >= ratelimit))
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001633 *p = 0;
Wu Fengguangd3bc1fe2011-04-14 07:52:37 -06001634 else if (unlikely(*p >= ratelimit_pages)) {
1635 *p = 0;
1636 ratelimit = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001637 }
Wu Fengguang54848d72011-04-05 13:21:19 -06001638 /*
1639 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1640 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1641 * the dirty throttling and livelock other long-run dirtiers.
1642 */
1643 p = &__get_cpu_var(dirty_throttle_leaks);
1644 if (*p > 0 && current->nr_dirtied < ratelimit) {
Namjae Jeond0e1d662012-12-11 16:00:21 -08001645 unsigned long nr_pages_dirtied;
Wu Fengguang54848d72011-04-05 13:21:19 -06001646 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1647 *p -= nr_pages_dirtied;
1648 current->nr_dirtied += nr_pages_dirtied;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001649 }
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001650 preempt_enable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001651
1652 if (unlikely(current->nr_dirtied >= ratelimit))
1653 balance_dirty_pages(mapping, current->nr_dirtied);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001654}
Namjae Jeond0e1d662012-12-11 16:00:21 -08001655EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001656
Andrew Morton232ea4d2007-02-28 20:13:21 -08001657void throttle_vm_writeout(gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001658{
David Rientjes364aeb22009-01-06 14:39:29 -08001659 unsigned long background_thresh;
1660 unsigned long dirty_thresh;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001661
1662 for ( ; ; ) {
Wu Fengguang16c40422010-08-11 14:17:39 -07001663 global_dirty_limits(&background_thresh, &dirty_thresh);
Fengguang Wu47a13332012-03-21 16:34:09 -07001664 dirty_thresh = hard_dirty_limit(dirty_thresh);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001665
1666 /*
1667 * Boost the allowable dirty threshold a bit for page
1668 * allocators so they don't get DoS'ed by heavy writers
1669 */
1670 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1671
Christoph Lameterc24f21b2006-06-30 01:55:42 -07001672 if (global_page_state(NR_UNSTABLE_NFS) +
1673 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1674 break;
Jens Axboe8aa7e842009-07-09 14:52:32 +02001675 congestion_wait(BLK_RW_ASYNC, HZ/10);
Fengguang Wu369f2382007-10-16 23:30:45 -07001676
1677 /*
1678 * The caller might hold locks which can prevent IO completion
1679 * or progress in the filesystem. So we cannot just sit here
1680 * waiting for IO to complete.
1681 */
1682 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1683 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001684 }
1685}
1686
Linus Torvalds1da177e2005-04-16 15:20:36 -07001687/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001688 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1689 */
1690int dirty_writeback_centisecs_handler(ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001691 void __user *buffer, size_t *length, loff_t *ppos)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001692{
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001693 proc_dointvec(table, write, buffer, length, ppos);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001694 return 0;
1695}
1696
Jens Axboec2c49862010-05-20 09:18:47 +02001697#ifdef CONFIG_BLOCK
Matthew Garrett31373d02010-04-06 14:25:14 +02001698void laptop_mode_timer_fn(unsigned long data)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001699{
Matthew Garrett31373d02010-04-06 14:25:14 +02001700 struct request_queue *q = (struct request_queue *)data;
1701 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1702 global_page_state(NR_UNSTABLE_NFS);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001703
Matthew Garrett31373d02010-04-06 14:25:14 +02001704 /*
1705 * We want to write everything out, not just down to the dirty
1706 * threshold
1707 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001708 if (bdi_has_dirty_io(&q->backing_dev_info))
Curt Wohlgemuth0e175a12011-10-07 21:54:10 -06001709 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1710 WB_REASON_LAPTOP_TIMER);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001711}
1712
1713/*
1714 * We've spun up the disk and we're in laptop mode: schedule writeback
1715 * of all dirty data a few seconds from now. If the flush is already scheduled
1716 * then push it back - the user is still using the disk.
1717 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001718void laptop_io_completion(struct backing_dev_info *info)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001719{
Matthew Garrett31373d02010-04-06 14:25:14 +02001720 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001721}
1722
1723/*
1724 * We're in laptop mode and we've just synced. The sync's writes will have
1725 * caused another writeback to be scheduled by laptop_io_completion.
1726 * Nothing needs to be written back anymore, so we unschedule the writeback.
1727 */
1728void laptop_sync_completion(void)
1729{
Matthew Garrett31373d02010-04-06 14:25:14 +02001730 struct backing_dev_info *bdi;
1731
1732 rcu_read_lock();
1733
1734 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1735 del_timer(&bdi->laptop_mode_wb_timer);
1736
1737 rcu_read_unlock();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001738}
Jens Axboec2c49862010-05-20 09:18:47 +02001739#endif
Linus Torvalds1da177e2005-04-16 15:20:36 -07001740
1741/*
1742 * If ratelimit_pages is too high then we can get into dirty-data overload
1743 * if a large number of processes all perform writes at the same time.
1744 * If it is too low then SMP machines will call the (expensive)
1745 * get_writeback_state too often.
1746 *
1747 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1748 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
Wu Fengguang9d823e82011-06-11 18:10:12 -06001749 * thresholds.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001750 */
1751
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001752void writeback_set_ratelimit(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001753{
Wu Fengguang9d823e82011-06-11 18:10:12 -06001754 unsigned long background_thresh;
1755 unsigned long dirty_thresh;
1756 global_dirty_limits(&background_thresh, &dirty_thresh);
Fengguang Wu68809c72012-05-06 13:21:42 +08001757 global_dirty_limit = dirty_thresh;
Wu Fengguang9d823e82011-06-11 18:10:12 -06001758 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001759 if (ratelimit_pages < 16)
1760 ratelimit_pages = 16;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001761}
1762
Paul Gortmaker0db06282013-06-19 14:53:51 -04001763static int
Srivatsa S. Bhat2f60d622012-09-28 20:27:49 +08001764ratelimit_handler(struct notifier_block *self, unsigned long action,
1765 void *hcpu)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001766{
Srivatsa S. Bhat2f60d622012-09-28 20:27:49 +08001767
1768 switch (action & ~CPU_TASKS_FROZEN) {
1769 case CPU_ONLINE:
1770 case CPU_DEAD:
1771 writeback_set_ratelimit();
1772 return NOTIFY_OK;
1773 default:
1774 return NOTIFY_DONE;
1775 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07001776}
1777
Paul Gortmaker0db06282013-06-19 14:53:51 -04001778static struct notifier_block ratelimit_nb = {
Linus Torvalds1da177e2005-04-16 15:20:36 -07001779 .notifier_call = ratelimit_handler,
1780 .next = NULL,
1781};
1782
1783/*
Linus Torvaldsdc6e29d2007-01-29 16:37:38 -08001784 * Called early on to tune the page writeback dirty limits.
1785 *
1786 * We used to scale dirty pages according to how total memory
1787 * related to pages that could be allocated for buffers (by
1788 * comparing nr_free_buffer_pages() to vm_total_pages.
1789 *
1790 * However, that was when we used "dirty_ratio" to scale with
1791 * all memory, and we don't do that any more. "dirty_ratio"
1792 * is now applied to total non-HIGHPAGE memory (by subtracting
1793 * totalhigh_pages from vm_total_pages), and as such we can't
1794 * get into the old insane situation any more where we had
1795 * large amounts of dirty pages compared to a small amount of
1796 * non-HIGHMEM memory.
1797 *
1798 * But we might still want to scale the dirty_ratio by how
1799 * much memory the box has..
Linus Torvalds1da177e2005-04-16 15:20:36 -07001800 */
1801void __init page_writeback_init(void)
1802{
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001803 writeback_set_ratelimit();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001804 register_cpu_notifier(&ratelimit_nb);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001805
Jan Karaeb608e32012-05-24 18:59:11 +02001806 fprop_global_init(&writeout_completions);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001807}
1808
David Howells811d7362006-08-29 19:06:09 +01001809/**
Jan Karaf446daae2010-08-09 17:19:12 -07001810 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1811 * @mapping: address space structure to write
1812 * @start: starting page index
1813 * @end: ending page index (inclusive)
1814 *
1815 * This function scans the page range from @start to @end (inclusive) and tags
1816 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1817 * that write_cache_pages (or whoever calls this function) will then use
1818 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1819 * used to avoid livelocking of writeback by a process steadily creating new
1820 * dirty pages in the file (thus it is important for this function to be quick
1821 * so that it can tag pages faster than a dirtying process can create them).
1822 */
1823/*
1824 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1825 */
Jan Karaf446daae2010-08-09 17:19:12 -07001826void tag_pages_for_writeback(struct address_space *mapping,
1827 pgoff_t start, pgoff_t end)
1828{
Randy Dunlap3c111a02010-08-11 14:17:30 -07001829#define WRITEBACK_TAG_BATCH 4096
Jan Karaf446daae2010-08-09 17:19:12 -07001830 unsigned long tagged;
1831
1832 do {
1833 spin_lock_irq(&mapping->tree_lock);
1834 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1835 &start, end, WRITEBACK_TAG_BATCH,
1836 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1837 spin_unlock_irq(&mapping->tree_lock);
1838 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1839 cond_resched();
Jan Karad5ed3a42010-08-19 14:13:33 -07001840 /* We check 'start' to handle wrapping when end == ~0UL */
1841 } while (tagged >= WRITEBACK_TAG_BATCH && start);
Jan Karaf446daae2010-08-09 17:19:12 -07001842}
1843EXPORT_SYMBOL(tag_pages_for_writeback);
1844
1845/**
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001846 * 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 +01001847 * @mapping: address space structure to write
1848 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001849 * @writepage: function called for each page
1850 * @data: data passed to writepage function
David Howells811d7362006-08-29 19:06:09 +01001851 *
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001852 * If a page is already under I/O, write_cache_pages() skips it, even
David Howells811d7362006-08-29 19:06:09 +01001853 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1854 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1855 * and msync() need to guarantee that all the data which was dirty at the time
1856 * the call was made get new I/O started against them. If wbc->sync_mode is
1857 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1858 * existing IO to complete.
Jan Karaf446daae2010-08-09 17:19:12 -07001859 *
1860 * To avoid livelocks (when other process dirties new pages), we first tag
1861 * pages which should be written back with TOWRITE tag and only then start
1862 * writing them. For data-integrity sync we have to be careful so that we do
1863 * not miss some pages (e.g., because some other process has cleared TOWRITE
1864 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1865 * by the process clearing the DIRTY tag (and submitting the page for IO).
David Howells811d7362006-08-29 19:06:09 +01001866 */
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001867int write_cache_pages(struct address_space *mapping,
1868 struct writeback_control *wbc, writepage_t writepage,
1869 void *data)
David Howells811d7362006-08-29 19:06:09 +01001870{
David Howells811d7362006-08-29 19:06:09 +01001871 int ret = 0;
1872 int done = 0;
David Howells811d7362006-08-29 19:06:09 +01001873 struct pagevec pvec;
1874 int nr_pages;
Nick Piggin31a12662009-01-06 14:39:04 -08001875 pgoff_t uninitialized_var(writeback_index);
David Howells811d7362006-08-29 19:06:09 +01001876 pgoff_t index;
1877 pgoff_t end; /* Inclusive */
Nick Pigginbd19e012009-01-06 14:39:06 -08001878 pgoff_t done_index;
Nick Piggin31a12662009-01-06 14:39:04 -08001879 int cycled;
David Howells811d7362006-08-29 19:06:09 +01001880 int range_whole = 0;
Jan Karaf446daae2010-08-09 17:19:12 -07001881 int tag;
David Howells811d7362006-08-29 19:06:09 +01001882
David Howells811d7362006-08-29 19:06:09 +01001883 pagevec_init(&pvec, 0);
1884 if (wbc->range_cyclic) {
Nick Piggin31a12662009-01-06 14:39:04 -08001885 writeback_index = mapping->writeback_index; /* prev offset */
1886 index = writeback_index;
1887 if (index == 0)
1888 cycled = 1;
1889 else
1890 cycled = 0;
David Howells811d7362006-08-29 19:06:09 +01001891 end = -1;
1892 } else {
1893 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1894 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1895 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1896 range_whole = 1;
Nick Piggin31a12662009-01-06 14:39:04 -08001897 cycled = 1; /* ignore range_cyclic tests */
David Howells811d7362006-08-29 19:06:09 +01001898 }
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001899 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daae2010-08-09 17:19:12 -07001900 tag = PAGECACHE_TAG_TOWRITE;
1901 else
1902 tag = PAGECACHE_TAG_DIRTY;
David Howells811d7362006-08-29 19:06:09 +01001903retry:
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001904 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daae2010-08-09 17:19:12 -07001905 tag_pages_for_writeback(mapping, index, end);
Nick Pigginbd19e012009-01-06 14:39:06 -08001906 done_index = index;
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001907 while (!done && (index <= end)) {
1908 int i;
1909
Jan Karaf446daae2010-08-09 17:19:12 -07001910 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001911 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1912 if (nr_pages == 0)
1913 break;
David Howells811d7362006-08-29 19:06:09 +01001914
David Howells811d7362006-08-29 19:06:09 +01001915 for (i = 0; i < nr_pages; i++) {
1916 struct page *page = pvec.pages[i];
1917
Nick Piggind5482cd2009-01-06 14:39:11 -08001918 /*
1919 * At this point, the page may be truncated or
1920 * invalidated (changing page->mapping to NULL), or
1921 * even swizzled back from swapper_space to tmpfs file
1922 * mapping. However, page->index will not change
1923 * because we have a reference on the page.
1924 */
1925 if (page->index > end) {
1926 /*
1927 * can't be range_cyclic (1st pass) because
1928 * end == -1 in that case.
1929 */
1930 done = 1;
1931 break;
1932 }
1933
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001934 done_index = page->index;
Nick Pigginbd19e012009-01-06 14:39:06 -08001935
David Howells811d7362006-08-29 19:06:09 +01001936 lock_page(page);
1937
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001938 /*
1939 * Page truncated or invalidated. We can freely skip it
1940 * then, even for data integrity operations: the page
1941 * has disappeared concurrently, so there could be no
1942 * real expectation of this data interity operation
1943 * even if there is now a new, dirty page at the same
1944 * pagecache address.
1945 */
David Howells811d7362006-08-29 19:06:09 +01001946 if (unlikely(page->mapping != mapping)) {
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001947continue_unlock:
David Howells811d7362006-08-29 19:06:09 +01001948 unlock_page(page);
1949 continue;
1950 }
1951
Nick Piggin515f4a02009-01-06 14:39:10 -08001952 if (!PageDirty(page)) {
1953 /* someone wrote it for us */
1954 goto continue_unlock;
1955 }
David Howells811d7362006-08-29 19:06:09 +01001956
Nick Piggin515f4a02009-01-06 14:39:10 -08001957 if (PageWriteback(page)) {
1958 if (wbc->sync_mode != WB_SYNC_NONE)
1959 wait_on_page_writeback(page);
1960 else
1961 goto continue_unlock;
1962 }
1963
1964 BUG_ON(PageWriteback(page));
1965 if (!clear_page_dirty_for_io(page))
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001966 goto continue_unlock;
David Howells811d7362006-08-29 19:06:09 +01001967
Dave Chinner9e094382010-07-07 13:24:08 +10001968 trace_wbc_writepage(wbc, mapping->backing_dev_info);
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001969 ret = (*writepage)(page, wbc, data);
Nick Piggin00266772009-01-06 14:39:06 -08001970 if (unlikely(ret)) {
1971 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1972 unlock_page(page);
1973 ret = 0;
1974 } else {
1975 /*
1976 * done_index is set past this page,
1977 * so media errors will not choke
1978 * background writeout for the entire
1979 * file. This has consequences for
1980 * range_cyclic semantics (ie. it may
1981 * not be suitable for data integrity
1982 * writeout).
1983 */
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001984 done_index = page->index + 1;
Nick Piggin00266772009-01-06 14:39:06 -08001985 done = 1;
1986 break;
1987 }
Dave Chinner0b564922010-06-09 10:37:18 +10001988 }
David Howells811d7362006-08-29 19:06:09 +01001989
Dave Chinner546a1922010-08-24 11:44:34 +10001990 /*
1991 * We stop writing back only if we are not doing
1992 * integrity sync. In case of integrity sync we have to
1993 * keep going until we have written all the pages
1994 * we tagged for writeback prior to entering this loop.
1995 */
1996 if (--wbc->nr_to_write <= 0 &&
1997 wbc->sync_mode == WB_SYNC_NONE) {
1998 done = 1;
1999 break;
Nick Piggin05fe4782009-01-06 14:39:08 -08002000 }
David Howells811d7362006-08-29 19:06:09 +01002001 }
2002 pagevec_release(&pvec);
2003 cond_resched();
2004 }
Nick Piggin3a4c6802009-02-12 04:34:23 +01002005 if (!cycled && !done) {
David Howells811d7362006-08-29 19:06:09 +01002006 /*
Nick Piggin31a12662009-01-06 14:39:04 -08002007 * range_cyclic:
David Howells811d7362006-08-29 19:06:09 +01002008 * We hit the last page and there is more work to be done: wrap
2009 * back to the start of the file
2010 */
Nick Piggin31a12662009-01-06 14:39:04 -08002011 cycled = 1;
David Howells811d7362006-08-29 19:06:09 +01002012 index = 0;
Nick Piggin31a12662009-01-06 14:39:04 -08002013 end = writeback_index - 1;
David Howells811d7362006-08-29 19:06:09 +01002014 goto retry;
2015 }
Dave Chinner0b564922010-06-09 10:37:18 +10002016 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2017 mapping->writeback_index = done_index;
Aneesh Kumar K.V06d6cf62008-07-11 19:27:31 -04002018
David Howells811d7362006-08-29 19:06:09 +01002019 return ret;
2020}
Miklos Szeredi0ea97182007-05-10 22:22:51 -07002021EXPORT_SYMBOL(write_cache_pages);
2022
2023/*
2024 * Function used by generic_writepages to call the real writepage
2025 * function and set the mapping flags on error
2026 */
2027static int __writepage(struct page *page, struct writeback_control *wbc,
2028 void *data)
2029{
2030 struct address_space *mapping = data;
2031 int ret = mapping->a_ops->writepage(page, wbc);
2032 mapping_set_error(mapping, ret);
2033 return ret;
2034}
2035
2036/**
2037 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2038 * @mapping: address space structure to write
2039 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2040 *
2041 * This is a library function, which implements the writepages()
2042 * address_space_operation.
2043 */
2044int generic_writepages(struct address_space *mapping,
2045 struct writeback_control *wbc)
2046{
Shaohua Li9b6096a2011-03-17 10:47:06 +01002047 struct blk_plug plug;
2048 int ret;
2049
Miklos Szeredi0ea97182007-05-10 22:22:51 -07002050 /* deal with chardevs and other special file */
2051 if (!mapping->a_ops->writepage)
2052 return 0;
2053
Shaohua Li9b6096a2011-03-17 10:47:06 +01002054 blk_start_plug(&plug);
2055 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2056 blk_finish_plug(&plug);
2057 return ret;
Miklos Szeredi0ea97182007-05-10 22:22:51 -07002058}
David Howells811d7362006-08-29 19:06:09 +01002059
2060EXPORT_SYMBOL(generic_writepages);
2061
Linus Torvalds1da177e2005-04-16 15:20:36 -07002062int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2063{
Andrew Morton22905f72005-11-16 15:07:01 -08002064 int ret;
2065
Linus Torvalds1da177e2005-04-16 15:20:36 -07002066 if (wbc->nr_to_write <= 0)
2067 return 0;
2068 if (mapping->a_ops->writepages)
Peter Zijlstrad08b3852006-09-25 23:30:57 -07002069 ret = mapping->a_ops->writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08002070 else
2071 ret = generic_writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08002072 return ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002073}
2074
2075/**
2076 * write_one_page - write out a single page and optionally wait on I/O
Martin Waitz67be2dd2005-05-01 08:59:26 -07002077 * @page: the page to write
2078 * @wait: if true, wait on writeout
Linus Torvalds1da177e2005-04-16 15:20:36 -07002079 *
2080 * The page must be locked by the caller and will be unlocked upon return.
2081 *
2082 * write_one_page() returns a negative error code if I/O failed.
2083 */
2084int write_one_page(struct page *page, int wait)
2085{
2086 struct address_space *mapping = page->mapping;
2087 int ret = 0;
2088 struct writeback_control wbc = {
2089 .sync_mode = WB_SYNC_ALL,
2090 .nr_to_write = 1,
2091 };
2092
2093 BUG_ON(!PageLocked(page));
2094
2095 if (wait)
2096 wait_on_page_writeback(page);
2097
2098 if (clear_page_dirty_for_io(page)) {
2099 page_cache_get(page);
2100 ret = mapping->a_ops->writepage(page, &wbc);
2101 if (ret == 0 && wait) {
2102 wait_on_page_writeback(page);
2103 if (PageError(page))
2104 ret = -EIO;
2105 }
2106 page_cache_release(page);
2107 } else {
2108 unlock_page(page);
2109 }
2110 return ret;
2111}
2112EXPORT_SYMBOL(write_one_page);
2113
2114/*
Ken Chen76719322007-02-10 01:43:15 -08002115 * For address_spaces which do not use buffers nor write back.
2116 */
2117int __set_page_dirty_no_writeback(struct page *page)
2118{
2119 if (!PageDirty(page))
Bob Liuc3f0da62011-01-13 15:45:49 -08002120 return !TestSetPageDirty(page);
Ken Chen76719322007-02-10 01:43:15 -08002121 return 0;
2122}
2123
2124/*
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002125 * Helper function for set_page_dirty family.
2126 * NOTE: This relies on being atomic wrt interrupts.
2127 */
2128void account_page_dirtied(struct page *page, struct address_space *mapping)
2129{
Tejun Heo9fb0a7d2013-01-11 13:06:37 -08002130 trace_writeback_dirty_page(page, mapping);
2131
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002132 if (mapping_cap_account_dirty(mapping)) {
2133 __inc_zone_page_state(page, NR_FILE_DIRTY);
Michael Rubinea941f02010-10-26 14:21:35 -07002134 __inc_zone_page_state(page, NR_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002135 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
Wu Fengguangc8e28ce2011-01-23 10:07:47 -06002136 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002137 task_io_account_write(PAGE_CACHE_SIZE);
Wu Fengguangd3bc1fe2011-04-14 07:52:37 -06002138 current->nr_dirtied++;
2139 this_cpu_inc(bdp_ratelimits);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002140 }
2141}
Michael Rubin679ceac2010-08-20 02:31:26 -07002142EXPORT_SYMBOL(account_page_dirtied);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002143
2144/*
Michael Rubinf629d1c2010-10-26 14:21:33 -07002145 * Helper function for set_page_writeback family.
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002146 *
2147 * The caller must hold mem_cgroup_begin/end_update_page_stat() lock
2148 * while calling this function.
2149 * See test_set_page_writeback for example.
2150 *
Michael Rubinf629d1c2010-10-26 14:21:33 -07002151 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
2152 * wrt interrupts.
2153 */
2154void account_page_writeback(struct page *page)
2155{
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002156 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
Michael Rubinf629d1c2010-10-26 14:21:33 -07002157 inc_zone_page_state(page, NR_WRITEBACK);
2158}
2159EXPORT_SYMBOL(account_page_writeback);
2160
2161/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002162 * For address_spaces which do not use buffers. Just tag the page as dirty in
2163 * its radix tree.
2164 *
2165 * This is also used when a single buffer is being dirtied: we want to set the
2166 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2167 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2168 *
2169 * Most callers have locked the page, which pins the address_space in memory.
2170 * But zap_pte_range() does not lock the page, however in that case the
2171 * mapping is pinned by the vma's ->vm_file reference.
2172 *
2173 * We take care to handle the case where the page was truncated from the
Simon Arlott183ff222007-10-20 01:27:18 +02002174 * mapping by re-checking page_mapping() inside tree_lock.
Linus Torvalds1da177e2005-04-16 15:20:36 -07002175 */
2176int __set_page_dirty_nobuffers(struct page *page)
2177{
Linus Torvalds1da177e2005-04-16 15:20:36 -07002178 if (!TestSetPageDirty(page)) {
2179 struct address_space *mapping = page_mapping(page);
2180 struct address_space *mapping2;
2181
Andrew Morton8c085402006-12-10 02:19:24 -08002182 if (!mapping)
2183 return 1;
2184
Nick Piggin19fd6232008-07-25 19:45:32 -07002185 spin_lock_irq(&mapping->tree_lock);
Andrew Morton8c085402006-12-10 02:19:24 -08002186 mapping2 = page_mapping(page);
2187 if (mapping2) { /* Race with truncate? */
2188 BUG_ON(mapping2 != mapping);
Nick Piggin787d2212007-07-17 04:03:34 -07002189 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002190 account_page_dirtied(page, mapping);
Andrew Morton8c085402006-12-10 02:19:24 -08002191 radix_tree_tag_set(&mapping->page_tree,
2192 page_index(page), PAGECACHE_TAG_DIRTY);
2193 }
Nick Piggin19fd6232008-07-25 19:45:32 -07002194 spin_unlock_irq(&mapping->tree_lock);
Andrew Morton8c085402006-12-10 02:19:24 -08002195 if (mapping->host) {
2196 /* !PageAnon && !swapper_space */
2197 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002198 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002199 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002200 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002201 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002202}
2203EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2204
2205/*
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002206 * Call this whenever redirtying a page, to de-account the dirty counters
2207 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2208 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2209 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2210 * control.
2211 */
2212void account_page_redirty(struct page *page)
2213{
2214 struct address_space *mapping = page->mapping;
2215 if (mapping && mapping_cap_account_dirty(mapping)) {
2216 current->nr_dirtied--;
2217 dec_zone_page_state(page, NR_DIRTIED);
2218 dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2219 }
2220}
2221EXPORT_SYMBOL(account_page_redirty);
2222
2223/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002224 * When a writepage implementation decides that it doesn't want to write this
2225 * page for some reason, it should redirty the locked page via
2226 * redirty_page_for_writepage() and it should then unlock the page and return 0
2227 */
2228int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2229{
2230 wbc->pages_skipped++;
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002231 account_page_redirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002232 return __set_page_dirty_nobuffers(page);
2233}
2234EXPORT_SYMBOL(redirty_page_for_writepage);
2235
2236/*
Wu Fengguang6746aff2009-09-16 11:50:14 +02002237 * Dirty a page.
2238 *
2239 * For pages with a mapping this should be done under the page lock
2240 * for the benefit of asynchronous memory errors who prefer a consistent
2241 * dirty state. This rule can be broken in some special cases,
2242 * but should be better not to.
2243 *
Linus Torvalds1da177e2005-04-16 15:20:36 -07002244 * If the mapping doesn't provide a set_page_dirty a_op, then
2245 * just fall through and assume that it wants buffer_heads.
2246 */
Nick Piggin1cf6e7d2009-02-18 14:48:18 -08002247int set_page_dirty(struct page *page)
Linus Torvalds1da177e2005-04-16 15:20:36 -07002248{
2249 struct address_space *mapping = page_mapping(page);
2250
2251 if (likely(mapping)) {
2252 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
Minchan Kim278df9f2011-03-22 16:32:54 -07002253 /*
2254 * readahead/lru_deactivate_page could remain
2255 * PG_readahead/PG_reclaim due to race with end_page_writeback
2256 * About readahead, if the page is written, the flags would be
2257 * reset. So no problem.
2258 * About lru_deactivate_page, if the page is redirty, the flag
2259 * will be reset. So no problem. but if the page is used by readahead
2260 * it will confuse readahead and make it restart the size rampup
2261 * process. But it's a trivial problem.
2262 */
2263 ClearPageReclaim(page);
David Howells93614012006-09-30 20:45:40 +02002264#ifdef CONFIG_BLOCK
2265 if (!spd)
2266 spd = __set_page_dirty_buffers;
2267#endif
2268 return (*spd)(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002269 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002270 if (!PageDirty(page)) {
2271 if (!TestSetPageDirty(page))
2272 return 1;
2273 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002274 return 0;
2275}
2276EXPORT_SYMBOL(set_page_dirty);
2277
2278/*
2279 * set_page_dirty() is racy if the caller has no reference against
2280 * page->mapping->host, and if the page is unlocked. This is because another
2281 * CPU could truncate the page off the mapping and then free the mapping.
2282 *
2283 * Usually, the page _is_ locked, or the caller is a user-space process which
2284 * holds a reference on the inode by having an open file.
2285 *
2286 * In other cases, the page should be locked before running set_page_dirty().
2287 */
2288int set_page_dirty_lock(struct page *page)
2289{
2290 int ret;
2291
Jens Axboe7eaceac2011-03-10 08:52:07 +01002292 lock_page(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002293 ret = set_page_dirty(page);
2294 unlock_page(page);
2295 return ret;
2296}
2297EXPORT_SYMBOL(set_page_dirty_lock);
2298
2299/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002300 * Clear a page's dirty flag, while caring for dirty memory accounting.
2301 * Returns true if the page was previously dirty.
2302 *
2303 * This is for preparing to put the page under writeout. We leave the page
2304 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2305 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2306 * implementation will run either set_page_writeback() or set_page_dirty(),
2307 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2308 * back into sync.
2309 *
2310 * This incoherency between the page's dirty flag and radix-tree tag is
2311 * unfortunate, but it only exists while the page is locked.
2312 */
2313int clear_page_dirty_for_io(struct page *page)
2314{
2315 struct address_space *mapping = page_mapping(page);
2316
Nick Piggin79352892007-07-19 01:47:22 -07002317 BUG_ON(!PageLocked(page));
2318
Linus Torvalds7658cc22006-12-29 10:00:58 -08002319 if (mapping && mapping_cap_account_dirty(mapping)) {
2320 /*
2321 * Yes, Virginia, this is indeed insane.
2322 *
2323 * We use this sequence to make sure that
2324 * (a) we account for dirty stats properly
2325 * (b) we tell the low-level filesystem to
2326 * mark the whole page dirty if it was
2327 * dirty in a pagetable. Only to then
2328 * (c) clean the page again and return 1 to
2329 * cause the writeback.
2330 *
2331 * This way we avoid all nasty races with the
2332 * dirty bit in multiple places and clearing
2333 * them concurrently from different threads.
2334 *
2335 * Note! Normally the "set_page_dirty(page)"
2336 * has no effect on the actual dirty bit - since
2337 * that will already usually be set. But we
2338 * need the side effects, and it can help us
2339 * avoid races.
2340 *
2341 * We basically use the page "master dirty bit"
2342 * as a serialization point for all the different
2343 * threads doing their things.
Linus Torvalds7658cc22006-12-29 10:00:58 -08002344 */
2345 if (page_mkclean(page))
2346 set_page_dirty(page);
Nick Piggin79352892007-07-19 01:47:22 -07002347 /*
2348 * We carefully synchronise fault handlers against
2349 * installing a dirty pte and marking the page dirty
2350 * at this point. We do this by having them hold the
2351 * page lock at some point after installing their
2352 * pte, but before marking the page dirty.
2353 * Pages are always locked coming in here, so we get
2354 * the desired exclusion. See mm/memory.c:do_wp_page()
2355 * for more comments.
2356 */
Linus Torvalds7658cc22006-12-29 10:00:58 -08002357 if (TestClearPageDirty(page)) {
Andrew Morton8c085402006-12-10 02:19:24 -08002358 dec_zone_page_state(page, NR_FILE_DIRTY);
Peter Zijlstrac9e51e42007-10-16 23:25:47 -07002359 dec_bdi_stat(mapping->backing_dev_info,
2360 BDI_RECLAIMABLE);
Linus Torvalds7658cc22006-12-29 10:00:58 -08002361 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002362 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08002363 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002364 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08002365 return TestClearPageDirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002366}
Hans Reiser58bb01a2005-11-18 01:10:53 -08002367EXPORT_SYMBOL(clear_page_dirty_for_io);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002368
2369int test_clear_page_writeback(struct page *page)
2370{
2371 struct address_space *mapping = page_mapping(page);
2372 int ret;
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002373 bool locked;
2374 unsigned long memcg_flags;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002375
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002376 mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002377 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002378 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002379 unsigned long flags;
2380
Nick Piggin19fd6232008-07-25 19:45:32 -07002381 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002382 ret = TestClearPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002383 if (ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07002384 radix_tree_tag_clear(&mapping->page_tree,
2385 page_index(page),
2386 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07002387 if (bdi_cap_account_writeback(bdi)) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002388 __dec_bdi_stat(bdi, BDI_WRITEBACK);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07002389 __bdi_writeout_inc(bdi);
2390 }
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002391 }
Nick Piggin19fd6232008-07-25 19:45:32 -07002392 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002393 } else {
2394 ret = TestClearPageWriteback(page);
2395 }
Wu Fengguang99b12e32011-07-25 17:12:37 -07002396 if (ret) {
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002397 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
Andrew Mortond688abf2007-07-19 01:49:17 -07002398 dec_zone_page_state(page, NR_WRITEBACK);
Wu Fengguang99b12e32011-07-25 17:12:37 -07002399 inc_zone_page_state(page, NR_WRITTEN);
2400 }
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002401 mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002402 return ret;
2403}
2404
2405int test_set_page_writeback(struct page *page)
2406{
2407 struct address_space *mapping = page_mapping(page);
2408 int ret;
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002409 bool locked;
2410 unsigned long memcg_flags;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002411
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002412 mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002413 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002414 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002415 unsigned long flags;
2416
Nick Piggin19fd6232008-07-25 19:45:32 -07002417 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002418 ret = TestSetPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002419 if (!ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07002420 radix_tree_tag_set(&mapping->page_tree,
2421 page_index(page),
2422 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07002423 if (bdi_cap_account_writeback(bdi))
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002424 __inc_bdi_stat(bdi, BDI_WRITEBACK);
2425 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002426 if (!PageDirty(page))
2427 radix_tree_tag_clear(&mapping->page_tree,
2428 page_index(page),
2429 PAGECACHE_TAG_DIRTY);
Jan Karaf446daae2010-08-09 17:19:12 -07002430 radix_tree_tag_clear(&mapping->page_tree,
2431 page_index(page),
2432 PAGECACHE_TAG_TOWRITE);
Nick Piggin19fd6232008-07-25 19:45:32 -07002433 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002434 } else {
2435 ret = TestSetPageWriteback(page);
2436 }
Andrew Mortond688abf2007-07-19 01:49:17 -07002437 if (!ret)
Michael Rubinf629d1c2010-10-26 14:21:33 -07002438 account_page_writeback(page);
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002439 mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002440 return ret;
2441
2442}
2443EXPORT_SYMBOL(test_set_page_writeback);
2444
2445/*
Nick Piggin00128182007-10-16 01:24:40 -07002446 * Return true if any of the pages in the mapping are marked with the
Linus Torvalds1da177e2005-04-16 15:20:36 -07002447 * passed tag.
2448 */
2449int mapping_tagged(struct address_space *mapping, int tag)
2450{
Konstantin Khlebnikov72c47832011-07-25 17:12:31 -07002451 return radix_tree_tagged(&mapping->page_tree, tag);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002452}
2453EXPORT_SYMBOL(mapping_tagged);
Darrick J. Wong1d1d1a72013-02-21 16:42:51 -08002454
2455/**
2456 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2457 * @page: The page to wait on.
2458 *
2459 * This function determines if the given page is related to a backing device
2460 * that requires page contents to be held stable during writeback. If so, then
2461 * it will wait for any pending writeback to complete.
2462 */
2463void wait_for_stable_page(struct page *page)
2464{
2465 struct address_space *mapping = page_mapping(page);
2466 struct backing_dev_info *bdi = mapping->backing_dev_info;
2467
2468 if (!bdi_cap_stable_pages_required(bdi))
2469 return;
2470
2471 wait_on_page_writeback(page);
2472}
2473EXPORT_SYMBOL_GPL(wait_for_stable_page);