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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 Weinera756cf52012-01-10 15:07:49 -0800159 * In a memory zone, there is a certain amount of pages we consider
160 * available for the page cache, which is essentially the number of
161 * free and reclaimable pages, minus some zone reserves to protect
162 * lowmem and the ability to uphold the zone's watermarks without
163 * requiring writeback.
164 *
165 * This number of dirtyable pages is the base value of which the
166 * user-configurable dirty ratio is the effictive number of pages that
167 * are allowed to be actually dirtied. Per individual zone, or
168 * globally by using the sum of dirtyable pages over all zones.
169 *
170 * Because the user is allowed to specify the dirty limit globally as
171 * absolute number of bytes, calculating the per-zone dirty limit can
172 * require translating the configured limit into a percentage of
173 * global dirtyable memory first.
174 */
175
Johannes Weinera8045522014-01-29 14:05:39 -0800176/**
177 * zone_dirtyable_memory - number of dirtyable pages in a zone
178 * @zone: the zone
179 *
180 * Returns the zone's number of pages potentially available for dirty
181 * page cache. This is the base value for the per-zone dirty limits.
182 */
183static unsigned long zone_dirtyable_memory(struct zone *zone)
184{
185 unsigned long nr_pages;
186
187 nr_pages = zone_page_state(zone, NR_FREE_PAGES);
188 nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
189
Johannes Weinera1c3bfb2014-01-29 14:05:41 -0800190 nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);
191 nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);
Johannes Weinera8045522014-01-29 14:05:39 -0800192
193 return nr_pages;
194}
195
Johannes Weiner1edf2232012-01-10 15:06:57 -0800196static unsigned long highmem_dirtyable_memory(unsigned long total)
197{
198#ifdef CONFIG_HIGHMEM
199 int node;
200 unsigned long x = 0;
201
202 for_each_node_state(node, N_HIGH_MEMORY) {
Johannes Weinera8045522014-01-29 14:05:39 -0800203 struct zone *z = &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
Johannes Weiner1edf2232012-01-10 15:06:57 -0800204
Johannes Weinera8045522014-01-29 14:05:39 -0800205 x += zone_dirtyable_memory(z);
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
Johannes Weinera8045522014-01-29 14:05:39 -0800241 x = global_page_state(NR_FREE_PAGES);
Sonny Raoc8b74c2f2012-12-20 15:05:07 -0800242 x -= min(x, dirty_balance_reserve);
Johannes Weiner1edf2232012-01-10 15:06:57 -0800243
Johannes Weinera1c3bfb2014-01-29 14:05:41 -0800244 x += global_page_state(NR_INACTIVE_FILE);
245 x += global_page_state(NR_ACTIVE_FILE);
Johannes Weinera8045522014-01-29 14:05:39 -0800246
Johannes Weiner1edf2232012-01-10 15:06:57 -0800247 if (!vm_highmem_is_dirtyable)
248 x -= highmem_dirtyable_memory(x);
249
250 return x + 1; /* Ensure that we never return 0 */
251}
252
253/*
Johannes Weinerccafa282012-01-10 15:07:44 -0800254 * global_dirty_limits - background-writeback and dirty-throttling thresholds
255 *
256 * Calculate the dirty thresholds based on sysctl parameters
257 * - vm.dirty_background_ratio or vm.dirty_background_bytes
258 * - vm.dirty_ratio or vm.dirty_bytes
259 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
260 * real-time tasks.
261 */
262void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
263{
264 unsigned long background;
265 unsigned long dirty;
266 unsigned long uninitialized_var(available_memory);
267 struct task_struct *tsk;
268
269 if (!vm_dirty_bytes || !dirty_background_bytes)
270 available_memory = global_dirtyable_memory();
271
272 if (vm_dirty_bytes)
273 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
274 else
275 dirty = (vm_dirty_ratio * available_memory) / 100;
276
277 if (dirty_background_bytes)
278 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
279 else
280 background = (dirty_background_ratio * available_memory) / 100;
281
282 if (background >= dirty)
283 background = dirty / 2;
284 tsk = current;
285 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
286 background += background / 4;
287 dirty += dirty / 4;
288 }
289 *pbackground = background;
290 *pdirty = dirty;
291 trace_global_dirty_state(background, dirty);
292}
293
Johannes Weinera756cf52012-01-10 15:07:49 -0800294/**
Johannes Weinera756cf52012-01-10 15:07:49 -0800295 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
296 * @zone: the zone
297 *
298 * Returns the maximum number of dirty pages allowed in a zone, based
299 * on the zone's dirtyable memory.
300 */
301static unsigned long zone_dirty_limit(struct zone *zone)
302{
303 unsigned long zone_memory = zone_dirtyable_memory(zone);
304 struct task_struct *tsk = current;
305 unsigned long dirty;
306
307 if (vm_dirty_bytes)
308 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
309 zone_memory / global_dirtyable_memory();
310 else
311 dirty = vm_dirty_ratio * zone_memory / 100;
312
313 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
314 dirty += dirty / 4;
315
316 return dirty;
317}
318
319/**
320 * zone_dirty_ok - tells whether a zone is within its dirty limits
321 * @zone: the zone to check
322 *
323 * Returns %true when the dirty pages in @zone are within the zone's
324 * dirty limit, %false if the limit is exceeded.
325 */
326bool zone_dirty_ok(struct zone *zone)
327{
328 unsigned long limit = zone_dirty_limit(zone);
329
330 return zone_page_state(zone, NR_FILE_DIRTY) +
331 zone_page_state(zone, NR_UNSTABLE_NFS) +
332 zone_page_state(zone, NR_WRITEBACK) <= limit;
333}
334
David Rientjes2da02992009-01-06 14:39:31 -0800335int dirty_background_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700336 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800337 loff_t *ppos)
338{
339 int ret;
340
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700341 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800342 if (ret == 0 && write)
343 dirty_background_bytes = 0;
344 return ret;
345}
346
347int dirty_background_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700348 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800349 loff_t *ppos)
350{
351 int ret;
352
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700353 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800354 if (ret == 0 && write)
355 dirty_background_ratio = 0;
356 return ret;
357}
358
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700359int dirty_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700360 void __user *buffer, size_t *lenp,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700361 loff_t *ppos)
362{
363 int old_ratio = vm_dirty_ratio;
David Rientjes2da02992009-01-06 14:39:31 -0800364 int ret;
365
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700366 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700367 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
Jan Karaeb608e32012-05-24 18:59:11 +0200368 writeback_set_ratelimit();
David Rientjes2da02992009-01-06 14:39:31 -0800369 vm_dirty_bytes = 0;
370 }
371 return ret;
372}
373
David Rientjes2da02992009-01-06 14:39:31 -0800374int dirty_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700375 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800376 loff_t *ppos)
377{
Sven Wegenerfc3501d2009-02-11 13:04:23 -0800378 unsigned long old_bytes = vm_dirty_bytes;
David Rientjes2da02992009-01-06 14:39:31 -0800379 int ret;
380
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700381 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800382 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
Jan Karaeb608e32012-05-24 18:59:11 +0200383 writeback_set_ratelimit();
David Rientjes2da02992009-01-06 14:39:31 -0800384 vm_dirty_ratio = 0;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700385 }
386 return ret;
387}
388
Jan Karaeb608e32012-05-24 18:59:11 +0200389static unsigned long wp_next_time(unsigned long cur_time)
390{
391 cur_time += VM_COMPLETIONS_PERIOD_LEN;
392 /* 0 has a special meaning... */
393 if (!cur_time)
394 return 1;
395 return cur_time;
396}
397
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700398/*
399 * Increment the BDI's writeout completion count and the global writeout
400 * completion count. Called from test_clear_page_writeback().
401 */
402static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
403{
Jan Karaf7d2b1e2010-12-08 22:44:24 -0600404 __inc_bdi_stat(bdi, BDI_WRITTEN);
Jan Karaeb608e32012-05-24 18:59:11 +0200405 __fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
406 bdi->max_prop_frac);
407 /* First event after period switching was turned off? */
408 if (!unlikely(writeout_period_time)) {
409 /*
410 * We can race with other __bdi_writeout_inc calls here but
411 * it does not cause any harm since the resulting time when
412 * timer will fire and what is in writeout_period_time will be
413 * roughly the same.
414 */
415 writeout_period_time = wp_next_time(jiffies);
416 mod_timer(&writeout_period_timer, writeout_period_time);
417 }
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700418}
419
Miklos Szeredidd5656e2008-04-30 00:54:37 -0700420void bdi_writeout_inc(struct backing_dev_info *bdi)
421{
422 unsigned long flags;
423
424 local_irq_save(flags);
425 __bdi_writeout_inc(bdi);
426 local_irq_restore(flags);
427}
428EXPORT_SYMBOL_GPL(bdi_writeout_inc);
429
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700430/*
431 * Obtain an accurate fraction of the BDI's portion.
432 */
433static void bdi_writeout_fraction(struct backing_dev_info *bdi,
434 long *numerator, long *denominator)
435{
Jan Karaeb608e32012-05-24 18:59:11 +0200436 fprop_fraction_percpu(&writeout_completions, &bdi->completions,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700437 numerator, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700438}
439
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700440/*
Jan Karaeb608e32012-05-24 18:59:11 +0200441 * On idle system, we can be called long after we scheduled because we use
442 * deferred timers so count with missed periods.
443 */
444static void writeout_period(unsigned long t)
445{
446 int miss_periods = (jiffies - writeout_period_time) /
447 VM_COMPLETIONS_PERIOD_LEN;
448
449 if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
450 writeout_period_time = wp_next_time(writeout_period_time +
451 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
452 mod_timer(&writeout_period_timer, writeout_period_time);
453 } else {
454 /*
455 * Aging has zeroed all fractions. Stop wasting CPU on period
456 * updates.
457 */
458 writeout_period_time = 0;
459 }
460}
461
462/*
Johannes Weinerd08c4292011-10-31 17:07:05 -0700463 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
464 * registered backing devices, which, for obvious reasons, can not
465 * exceed 100%.
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700466 */
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700467static unsigned int bdi_min_ratio;
468
469int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
470{
471 int ret = 0;
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700472
Jens Axboecfc4ba52009-09-14 13:12:40 +0200473 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700474 if (min_ratio > bdi->max_ratio) {
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700475 ret = -EINVAL;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700476 } else {
477 min_ratio -= bdi->min_ratio;
478 if (bdi_min_ratio + min_ratio < 100) {
479 bdi_min_ratio += min_ratio;
480 bdi->min_ratio += min_ratio;
481 } else {
482 ret = -EINVAL;
483 }
484 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200485 spin_unlock_bh(&bdi_lock);
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700486
487 return ret;
488}
489
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700490int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
491{
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700492 int ret = 0;
493
494 if (max_ratio > 100)
495 return -EINVAL;
496
Jens Axboecfc4ba52009-09-14 13:12:40 +0200497 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700498 if (bdi->min_ratio > max_ratio) {
499 ret = -EINVAL;
500 } else {
501 bdi->max_ratio = max_ratio;
Jan Karaeb608e32012-05-24 18:59:11 +0200502 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700503 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200504 spin_unlock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700505
506 return ret;
507}
508EXPORT_SYMBOL(bdi_set_max_ratio);
509
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600510static unsigned long dirty_freerun_ceiling(unsigned long thresh,
511 unsigned long bg_thresh)
512{
513 return (thresh + bg_thresh) / 2;
514}
515
Wu Fengguangffd1f602011-06-19 22:18:42 -0600516static unsigned long hard_dirty_limit(unsigned long thresh)
517{
518 return max(thresh, global_dirty_limit);
519}
520
Wu Fengguang6f718652011-03-02 17:14:34 -0600521/**
Wu Fengguang1babe182010-08-11 14:17:40 -0700522 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
Wu Fengguang6f718652011-03-02 17:14:34 -0600523 * @bdi: the backing_dev_info to query
524 * @dirty: global dirty limit in pages
Wu Fengguang1babe182010-08-11 14:17:40 -0700525 *
Wu Fengguang6f718652011-03-02 17:14:34 -0600526 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
527 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
Wu Fengguangaed21ad2011-11-23 11:44:41 -0600528 *
529 * Note that balance_dirty_pages() will only seriously take it as a hard limit
530 * when sleeping max_pause per page is not enough to keep the dirty pages under
531 * control. For example, when the device is completely stalled due to some error
532 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
533 * In the other normal situations, it acts more gently by throttling the tasks
534 * more (rather than completely block them) when the bdi dirty pages go high.
Wu Fengguang6f718652011-03-02 17:14:34 -0600535 *
536 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
Wu Fengguang1babe182010-08-11 14:17:40 -0700537 * - starving fast devices
538 * - piling up dirty pages (that will take long time to sync) on slow devices
539 *
540 * The bdi's share of dirty limit will be adapting to its throughput and
541 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
542 */
543unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
Wu Fengguang16c40422010-08-11 14:17:39 -0700544{
545 u64 bdi_dirty;
546 long numerator, denominator;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700547
Wu Fengguang16c40422010-08-11 14:17:39 -0700548 /*
549 * Calculate this BDI's share of the dirty ratio.
550 */
551 bdi_writeout_fraction(bdi, &numerator, &denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700552
Wu Fengguang16c40422010-08-11 14:17:39 -0700553 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
554 bdi_dirty *= numerator;
555 do_div(bdi_dirty, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700556
Wu Fengguang16c40422010-08-11 14:17:39 -0700557 bdi_dirty += (dirty * bdi->min_ratio) / 100;
558 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
559 bdi_dirty = dirty * bdi->max_ratio / 100;
560
561 return bdi_dirty;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700562}
563
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600564/*
Maxim Patlasov5a537482013-09-11 14:22:46 -0700565 * setpoint - dirty 3
566 * f(dirty) := 1.0 + (----------------)
567 * limit - setpoint
568 *
569 * it's a 3rd order polynomial that subjects to
570 *
571 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
572 * (2) f(setpoint) = 1.0 => the balance point
573 * (3) f(limit) = 0 => the hard limit
574 * (4) df/dx <= 0 => negative feedback control
575 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
576 * => fast response on large errors; small oscillation near setpoint
577 */
Rik van Rield5c9fde2014-05-06 12:50:01 -0700578static long long pos_ratio_polynom(unsigned long setpoint,
Maxim Patlasov5a537482013-09-11 14:22:46 -0700579 unsigned long dirty,
580 unsigned long limit)
581{
582 long long pos_ratio;
583 long x;
584
Rik van Rield5c9fde2014-05-06 12:50:01 -0700585 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
Maxim Patlasov5a537482013-09-11 14:22:46 -0700586 limit - setpoint + 1);
587 pos_ratio = x;
588 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
589 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
590 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
591
592 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
593}
594
595/*
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600596 * Dirty position control.
597 *
598 * (o) global/bdi setpoints
599 *
600 * We want the dirty pages be balanced around the global/bdi setpoints.
601 * When the number of dirty pages is higher/lower than the setpoint, the
602 * dirty position control ratio (and hence task dirty ratelimit) will be
603 * decreased/increased to bring the dirty pages back to the setpoint.
604 *
605 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
606 *
607 * if (dirty < setpoint) scale up pos_ratio
608 * if (dirty > setpoint) scale down pos_ratio
609 *
610 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
611 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
612 *
613 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
614 *
615 * (o) global control line
616 *
617 * ^ pos_ratio
618 * |
619 * | |<===== global dirty control scope ======>|
620 * 2.0 .............*
621 * | .*
622 * | . *
623 * | . *
624 * | . *
625 * | . *
626 * | . *
627 * 1.0 ................................*
628 * | . . *
629 * | . . *
630 * | . . *
631 * | . . *
632 * | . . *
633 * 0 +------------.------------------.----------------------*------------->
634 * freerun^ setpoint^ limit^ dirty pages
635 *
636 * (o) bdi control line
637 *
638 * ^ pos_ratio
639 * |
640 * | *
641 * | *
642 * | *
643 * | *
644 * | * |<=========== span ============>|
645 * 1.0 .......................*
646 * | . *
647 * | . *
648 * | . *
649 * | . *
650 * | . *
651 * | . *
652 * | . *
653 * | . *
654 * | . *
655 * | . *
656 * | . *
657 * 1/4 ...............................................* * * * * * * * * * * *
658 * | . .
659 * | . .
660 * | . .
661 * 0 +----------------------.-------------------------------.------------->
662 * bdi_setpoint^ x_intercept^
663 *
664 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
665 * be smoothly throttled down to normal if it starts high in situations like
666 * - start writing to a slow SD card and a fast disk at the same time. The SD
667 * card's bdi_dirty may rush to many times higher than bdi_setpoint.
668 * - the bdi dirty thresh drops quickly due to change of JBOD workload
669 */
670static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
671 unsigned long thresh,
672 unsigned long bg_thresh,
673 unsigned long dirty,
674 unsigned long bdi_thresh,
675 unsigned long bdi_dirty)
676{
677 unsigned long write_bw = bdi->avg_write_bandwidth;
678 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
679 unsigned long limit = hard_dirty_limit(thresh);
680 unsigned long x_intercept;
681 unsigned long setpoint; /* dirty pages' target balance point */
682 unsigned long bdi_setpoint;
683 unsigned long span;
684 long long pos_ratio; /* for scaling up/down the rate limit */
685 long x;
686
687 if (unlikely(dirty >= limit))
688 return 0;
689
690 /*
691 * global setpoint
692 *
Maxim Patlasov5a537482013-09-11 14:22:46 -0700693 * See comment for pos_ratio_polynom().
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600694 */
695 setpoint = (freerun + limit) / 2;
Maxim Patlasov5a537482013-09-11 14:22:46 -0700696 pos_ratio = pos_ratio_polynom(setpoint, dirty, limit);
697
698 /*
699 * The strictlimit feature is a tool preventing mistrusted filesystems
700 * from growing a large number of dirty pages before throttling. For
701 * such filesystems balance_dirty_pages always checks bdi counters
702 * against bdi limits. Even if global "nr_dirty" is under "freerun".
703 * This is especially important for fuse which sets bdi->max_ratio to
704 * 1% by default. Without strictlimit feature, fuse writeback may
705 * consume arbitrary amount of RAM because it is accounted in
706 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
707 *
708 * Here, in bdi_position_ratio(), we calculate pos_ratio based on
709 * two values: bdi_dirty and bdi_thresh. Let's consider an example:
710 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
711 * limits are set by default to 10% and 20% (background and throttle).
712 * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
713 * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
714 * about ~6K pages (as the average of background and throttle bdi
715 * limits). The 3rd order polynomial will provide positive feedback if
716 * bdi_dirty is under bdi_setpoint and vice versa.
717 *
718 * Note, that we cannot use global counters in these calculations
719 * because we want to throttle process writing to a strictlimit BDI
720 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
721 * in the example above).
722 */
723 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
724 long long bdi_pos_ratio;
725 unsigned long bdi_bg_thresh;
726
727 if (bdi_dirty < 8)
728 return min_t(long long, pos_ratio * 2,
729 2 << RATELIMIT_CALC_SHIFT);
730
731 if (bdi_dirty >= bdi_thresh)
732 return 0;
733
734 bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh);
735 bdi_setpoint = dirty_freerun_ceiling(bdi_thresh,
736 bdi_bg_thresh);
737
738 if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh)
739 return 0;
740
741 bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
742 bdi_thresh);
743
744 /*
745 * Typically, for strictlimit case, bdi_setpoint << setpoint
746 * and pos_ratio >> bdi_pos_ratio. In the other words global
747 * state ("dirty") is not limiting factor and we have to
748 * make decision based on bdi counters. But there is an
749 * important case when global pos_ratio should get precedence:
750 * global limits are exceeded (e.g. due to activities on other
751 * BDIs) while given strictlimit BDI is below limit.
752 *
753 * "pos_ratio * bdi_pos_ratio" would work for the case above,
754 * but it would look too non-natural for the case of all
755 * activity in the system coming from a single strictlimit BDI
756 * with bdi->max_ratio == 100%.
757 *
758 * Note that min() below somewhat changes the dynamics of the
759 * control system. Normally, pos_ratio value can be well over 3
760 * (when globally we are at freerun and bdi is well below bdi
761 * setpoint). Now the maximum pos_ratio in the same situation
762 * is 2. We might want to tweak this if we observe the control
763 * system is too slow to adapt.
764 */
765 return min(pos_ratio, bdi_pos_ratio);
766 }
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600767
768 /*
769 * We have computed basic pos_ratio above based on global situation. If
770 * the bdi is over/under its share of dirty pages, we want to scale
771 * pos_ratio further down/up. That is done by the following mechanism.
772 */
773
774 /*
775 * bdi setpoint
776 *
777 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
778 *
779 * x_intercept - bdi_dirty
780 * := --------------------------
781 * x_intercept - bdi_setpoint
782 *
783 * The main bdi control line is a linear function that subjects to
784 *
785 * (1) f(bdi_setpoint) = 1.0
786 * (2) k = - 1 / (8 * write_bw) (in single bdi case)
787 * or equally: x_intercept = bdi_setpoint + 8 * write_bw
788 *
789 * For single bdi case, the dirty pages are observed to fluctuate
790 * regularly within range
791 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
792 * for various filesystems, where (2) can yield in a reasonable 12.5%
793 * fluctuation range for pos_ratio.
794 *
795 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
796 * own size, so move the slope over accordingly and choose a slope that
797 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
798 */
799 if (unlikely(bdi_thresh > thresh))
800 bdi_thresh = thresh;
Wu Fengguangaed21ad2011-11-23 11:44:41 -0600801 /*
802 * It's very possible that bdi_thresh is close to 0 not because the
803 * device is slow, but that it has remained inactive for long time.
804 * Honour such devices a reasonable good (hopefully IO efficient)
805 * threshold, so that the occasional writes won't be blocked and active
806 * writes can rampup the threshold quickly.
807 */
Wu Fengguang8927f662011-08-04 22:16:46 -0600808 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600809 /*
810 * scale global setpoint to bdi's:
811 * bdi_setpoint = setpoint * bdi_thresh / thresh
812 */
813 x = div_u64((u64)bdi_thresh << 16, thresh + 1);
814 bdi_setpoint = setpoint * (u64)x >> 16;
815 /*
816 * Use span=(8*write_bw) in single bdi case as indicated by
817 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
818 *
819 * bdi_thresh thresh - bdi_thresh
820 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
821 * thresh thresh
822 */
823 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
824 x_intercept = bdi_setpoint + span;
825
826 if (bdi_dirty < x_intercept - span / 4) {
Rik van Rield5c9fde2014-05-06 12:50:01 -0700827 pos_ratio = div64_u64(pos_ratio * (x_intercept - bdi_dirty),
Wu Fengguang50657fc2011-10-11 17:06:33 -0600828 x_intercept - bdi_setpoint + 1);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600829 } else
830 pos_ratio /= 4;
831
Wu Fengguang8927f662011-08-04 22:16:46 -0600832 /*
833 * bdi reserve area, safeguard against dirty pool underrun and disk idle
834 * It may push the desired control point of global dirty pages higher
835 * than setpoint.
836 */
837 x_intercept = bdi_thresh / 2;
838 if (bdi_dirty < x_intercept) {
Wu Fengguang50657fc2011-10-11 17:06:33 -0600839 if (bdi_dirty > x_intercept / 8)
840 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
841 else
Wu Fengguang8927f662011-08-04 22:16:46 -0600842 pos_ratio *= 8;
843 }
844
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600845 return pos_ratio;
846}
847
Wu Fengguange98be2d2010-08-29 11:22:30 -0600848static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
849 unsigned long elapsed,
850 unsigned long written)
851{
852 const unsigned long period = roundup_pow_of_two(3 * HZ);
853 unsigned long avg = bdi->avg_write_bandwidth;
854 unsigned long old = bdi->write_bandwidth;
855 u64 bw;
856
857 /*
858 * bw = written * HZ / elapsed
859 *
860 * bw * elapsed + write_bandwidth * (period - elapsed)
861 * write_bandwidth = ---------------------------------------------------
862 * period
863 */
864 bw = written - bdi->written_stamp;
865 bw *= HZ;
866 if (unlikely(elapsed > period)) {
867 do_div(bw, elapsed);
868 avg = bw;
869 goto out;
870 }
871 bw += (u64)bdi->write_bandwidth * (period - elapsed);
872 bw >>= ilog2(period);
873
874 /*
875 * one more level of smoothing, for filtering out sudden spikes
876 */
877 if (avg > old && old >= (unsigned long)bw)
878 avg -= (avg - old) >> 3;
879
880 if (avg < old && old <= (unsigned long)bw)
881 avg += (old - avg) >> 3;
882
883out:
884 bdi->write_bandwidth = bw;
885 bdi->avg_write_bandwidth = avg;
886}
887
Wu Fengguangc42843f2011-03-02 15:54:09 -0600888/*
889 * The global dirtyable memory and dirty threshold could be suddenly knocked
890 * down by a large amount (eg. on the startup of KVM in a swapless system).
891 * This may throw the system into deep dirty exceeded state and throttle
892 * heavy/light dirtiers alike. To retain good responsiveness, maintain
893 * global_dirty_limit for tracking slowly down to the knocked down dirty
894 * threshold.
895 */
896static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
897{
898 unsigned long limit = global_dirty_limit;
899
900 /*
901 * Follow up in one step.
902 */
903 if (limit < thresh) {
904 limit = thresh;
905 goto update;
906 }
907
908 /*
909 * Follow down slowly. Use the higher one as the target, because thresh
910 * may drop below dirty. This is exactly the reason to introduce
911 * global_dirty_limit which is guaranteed to lie above the dirty pages.
912 */
913 thresh = max(thresh, dirty);
914 if (limit > thresh) {
915 limit -= (limit - thresh) >> 5;
916 goto update;
917 }
918 return;
919update:
920 global_dirty_limit = limit;
921}
922
923static void global_update_bandwidth(unsigned long thresh,
924 unsigned long dirty,
925 unsigned long now)
926{
927 static DEFINE_SPINLOCK(dirty_lock);
928 static unsigned long update_time;
929
930 /*
931 * check locklessly first to optimize away locking for the most time
932 */
933 if (time_before(now, update_time + BANDWIDTH_INTERVAL))
934 return;
935
936 spin_lock(&dirty_lock);
937 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
938 update_dirty_limit(thresh, dirty);
939 update_time = now;
940 }
941 spin_unlock(&dirty_lock);
942}
943
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600944/*
945 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
946 *
947 * Normal bdi tasks will be curbed at or below it in long term.
948 * Obviously it should be around (write_bw / N) when there are N dd tasks.
949 */
950static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
951 unsigned long thresh,
952 unsigned long bg_thresh,
953 unsigned long dirty,
954 unsigned long bdi_thresh,
955 unsigned long bdi_dirty,
956 unsigned long dirtied,
957 unsigned long elapsed)
958{
Wu Fengguang73811312011-08-26 15:53:24 -0600959 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
960 unsigned long limit = hard_dirty_limit(thresh);
961 unsigned long setpoint = (freerun + limit) / 2;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600962 unsigned long write_bw = bdi->avg_write_bandwidth;
963 unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
964 unsigned long dirty_rate;
965 unsigned long task_ratelimit;
966 unsigned long balanced_dirty_ratelimit;
967 unsigned long pos_ratio;
Wu Fengguang73811312011-08-26 15:53:24 -0600968 unsigned long step;
969 unsigned long x;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600970
971 /*
972 * The dirty rate will match the writeout rate in long term, except
973 * when dirty pages are truncated by userspace or re-dirtied by FS.
974 */
975 dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
976
977 pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
978 bdi_thresh, bdi_dirty);
979 /*
980 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
981 */
982 task_ratelimit = (u64)dirty_ratelimit *
983 pos_ratio >> RATELIMIT_CALC_SHIFT;
984 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
985
986 /*
987 * A linear estimation of the "balanced" throttle rate. The theory is,
988 * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
989 * dirty_rate will be measured to be (N * task_ratelimit). So the below
990 * formula will yield the balanced rate limit (write_bw / N).
991 *
992 * Note that the expanded form is not a pure rate feedback:
993 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
994 * but also takes pos_ratio into account:
995 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
996 *
997 * (1) is not realistic because pos_ratio also takes part in balancing
998 * the dirty rate. Consider the state
999 * pos_ratio = 0.5 (3)
1000 * rate = 2 * (write_bw / N) (4)
1001 * If (1) is used, it will stuck in that state! Because each dd will
1002 * be throttled at
1003 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
1004 * yielding
1005 * dirty_rate = N * task_ratelimit = write_bw (6)
1006 * put (6) into (1) we get
1007 * rate_(i+1) = rate_(i) (7)
1008 *
1009 * So we end up using (2) to always keep
1010 * rate_(i+1) ~= (write_bw / N) (8)
1011 * regardless of the value of pos_ratio. As long as (8) is satisfied,
1012 * pos_ratio is able to drive itself to 1.0, which is not only where
1013 * the dirty count meet the setpoint, but also where the slope of
1014 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1015 */
1016 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1017 dirty_rate | 1);
Wu Fengguangbdaac492011-08-03 14:30:36 -06001018 /*
1019 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1020 */
1021 if (unlikely(balanced_dirty_ratelimit > write_bw))
1022 balanced_dirty_ratelimit = write_bw;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001023
Wu Fengguang73811312011-08-26 15:53:24 -06001024 /*
1025 * We could safely do this and return immediately:
1026 *
1027 * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
1028 *
1029 * However to get a more stable dirty_ratelimit, the below elaborated
Wanpeng Li331cbde2012-06-09 11:10:55 +08001030 * code makes use of task_ratelimit to filter out singular points and
Wu Fengguang73811312011-08-26 15:53:24 -06001031 * limit the step size.
1032 *
1033 * The below code essentially only uses the relative value of
1034 *
1035 * task_ratelimit - dirty_ratelimit
1036 * = (pos_ratio - 1) * dirty_ratelimit
1037 *
1038 * which reflects the direction and size of dirty position error.
1039 */
1040
1041 /*
1042 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1043 * task_ratelimit is on the same side of dirty_ratelimit, too.
1044 * For example, when
1045 * - dirty_ratelimit > balanced_dirty_ratelimit
1046 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1047 * lowering dirty_ratelimit will help meet both the position and rate
1048 * control targets. Otherwise, don't update dirty_ratelimit if it will
1049 * only help meet the rate target. After all, what the users ultimately
1050 * feel and care are stable dirty rate and small position error.
1051 *
1052 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
Wanpeng Li331cbde2012-06-09 11:10:55 +08001053 * and filter out the singular points of balanced_dirty_ratelimit. Which
Wu Fengguang73811312011-08-26 15:53:24 -06001054 * keeps jumping around randomly and can even leap far away at times
1055 * due to the small 200ms estimation period of dirty_rate (we want to
1056 * keep that period small to reduce time lags).
1057 */
1058 step = 0;
Maxim Patlasov5a537482013-09-11 14:22:46 -07001059
1060 /*
1061 * For strictlimit case, calculations above were based on bdi counters
1062 * and limits (starting from pos_ratio = bdi_position_ratio() and up to
1063 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1064 * Hence, to calculate "step" properly, we have to use bdi_dirty as
1065 * "dirty" and bdi_setpoint as "setpoint".
1066 *
1067 * We rampup dirty_ratelimit forcibly if bdi_dirty is low because
1068 * it's possible that bdi_thresh is close to zero due to inactivity
1069 * of backing device (see the implementation of bdi_dirty_limit()).
1070 */
1071 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1072 dirty = bdi_dirty;
1073 if (bdi_dirty < 8)
1074 setpoint = bdi_dirty + 1;
1075 else
1076 setpoint = (bdi_thresh +
1077 bdi_dirty_limit(bdi, bg_thresh)) / 2;
1078 }
1079
Wu Fengguang73811312011-08-26 15:53:24 -06001080 if (dirty < setpoint) {
1081 x = min(bdi->balanced_dirty_ratelimit,
1082 min(balanced_dirty_ratelimit, task_ratelimit));
1083 if (dirty_ratelimit < x)
1084 step = x - dirty_ratelimit;
1085 } else {
1086 x = max(bdi->balanced_dirty_ratelimit,
1087 max(balanced_dirty_ratelimit, task_ratelimit));
1088 if (dirty_ratelimit > x)
1089 step = dirty_ratelimit - x;
1090 }
1091
1092 /*
1093 * Don't pursue 100% rate matching. It's impossible since the balanced
1094 * rate itself is constantly fluctuating. So decrease the track speed
1095 * when it gets close to the target. Helps eliminate pointless tremors.
1096 */
1097 step >>= dirty_ratelimit / (2 * step + 1);
1098 /*
1099 * Limit the tracking speed to avoid overshooting.
1100 */
1101 step = (step + 7) / 8;
1102
1103 if (dirty_ratelimit < balanced_dirty_ratelimit)
1104 dirty_ratelimit += step;
1105 else
1106 dirty_ratelimit -= step;
1107
1108 bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1109 bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
Wu Fengguangb48c1042011-03-02 17:22:49 -06001110
1111 trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001112}
1113
Wu Fengguange98be2d2010-08-29 11:22:30 -06001114void __bdi_update_bandwidth(struct backing_dev_info *bdi,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001115 unsigned long thresh,
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001116 unsigned long bg_thresh,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001117 unsigned long dirty,
1118 unsigned long bdi_thresh,
1119 unsigned long bdi_dirty,
Wu Fengguange98be2d2010-08-29 11:22:30 -06001120 unsigned long start_time)
1121{
1122 unsigned long now = jiffies;
1123 unsigned long elapsed = now - bdi->bw_time_stamp;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001124 unsigned long dirtied;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001125 unsigned long written;
1126
1127 /*
1128 * rate-limit, only update once every 200ms.
1129 */
1130 if (elapsed < BANDWIDTH_INTERVAL)
1131 return;
1132
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001133 dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001134 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1135
1136 /*
1137 * Skip quiet periods when disk bandwidth is under-utilized.
1138 * (at least 1s idle time between two flusher runs)
1139 */
1140 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1141 goto snapshot;
1142
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001143 if (thresh) {
Wu Fengguangc42843f2011-03-02 15:54:09 -06001144 global_update_bandwidth(thresh, dirty, now);
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001145 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1146 bdi_thresh, bdi_dirty,
1147 dirtied, elapsed);
1148 }
Wu Fengguange98be2d2010-08-29 11:22:30 -06001149 bdi_update_write_bandwidth(bdi, elapsed, written);
1150
1151snapshot:
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001152 bdi->dirtied_stamp = dirtied;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001153 bdi->written_stamp = written;
1154 bdi->bw_time_stamp = now;
1155}
1156
1157static void bdi_update_bandwidth(struct backing_dev_info *bdi,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001158 unsigned long thresh,
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001159 unsigned long bg_thresh,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001160 unsigned long dirty,
1161 unsigned long bdi_thresh,
1162 unsigned long bdi_dirty,
Wu Fengguange98be2d2010-08-29 11:22:30 -06001163 unsigned long start_time)
1164{
1165 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1166 return;
1167 spin_lock(&bdi->wb.list_lock);
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001168 __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1169 bdi_thresh, bdi_dirty, start_time);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001170 spin_unlock(&bdi->wb.list_lock);
1171}
1172
Linus Torvalds1da177e2005-04-16 15:20:36 -07001173/*
Namjae Jeond0e1d662012-12-11 16:00:21 -08001174 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
Wu Fengguang9d823e82011-06-11 18:10:12 -06001175 * will look to see if it needs to start dirty throttling.
1176 *
1177 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1178 * global_page_state() too often. So scale it near-sqrt to the safety margin
1179 * (the number of pages we may dirty without exceeding the dirty limits).
1180 */
1181static unsigned long dirty_poll_interval(unsigned long dirty,
1182 unsigned long thresh)
1183{
1184 if (thresh > dirty)
1185 return 1UL << (ilog2(thresh - dirty) >> 1);
1186
1187 return 1;
1188}
1189
Fengguang Wue3b6c652013-10-16 13:47:03 -07001190static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
1191 unsigned long bdi_dirty)
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001192{
Fengguang Wue3b6c652013-10-16 13:47:03 -07001193 unsigned long bw = bdi->avg_write_bandwidth;
1194 unsigned long t;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001195
1196 /*
1197 * Limit pause time for small memory systems. If sleeping for too long
1198 * time, a small pool of dirty/writeback pages may go empty and disk go
1199 * idle.
1200 *
1201 * 8 serves as the safety ratio.
1202 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001203 t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1204 t++;
1205
Fengguang Wue3b6c652013-10-16 13:47:03 -07001206 return min_t(unsigned long, t, MAX_PAUSE);
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001207}
1208
1209static long bdi_min_pause(struct backing_dev_info *bdi,
1210 long max_pause,
1211 unsigned long task_ratelimit,
1212 unsigned long dirty_ratelimit,
1213 int *nr_dirtied_pause)
1214{
1215 long hi = ilog2(bdi->avg_write_bandwidth);
1216 long lo = ilog2(bdi->dirty_ratelimit);
1217 long t; /* target pause */
1218 long pause; /* estimated next pause */
1219 int pages; /* target nr_dirtied_pause */
1220
1221 /* target for 10ms pause on 1-dd case */
1222 t = max(1, HZ / 100);
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001223
1224 /*
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001225 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1226 * overheads.
1227 *
1228 * (N * 10ms) on 2^N concurrent tasks.
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001229 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001230 if (hi > lo)
1231 t += (hi - lo) * (10 * HZ) / 1024;
1232
1233 /*
1234 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1235 * on the much more stable dirty_ratelimit. However the next pause time
1236 * will be computed based on task_ratelimit and the two rate limits may
1237 * depart considerably at some time. Especially if task_ratelimit goes
1238 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1239 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1240 * result task_ratelimit won't be executed faithfully, which could
1241 * eventually bring down dirty_ratelimit.
1242 *
1243 * We apply two rules to fix it up:
1244 * 1) try to estimate the next pause time and if necessary, use a lower
1245 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1246 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1247 * 2) limit the target pause time to max_pause/2, so that the normal
1248 * small fluctuations of task_ratelimit won't trigger rule (1) and
1249 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1250 */
1251 t = min(t, 1 + max_pause / 2);
1252 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1253
Wu Fengguang5b9b3572011-12-06 13:17:17 -06001254 /*
1255 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1256 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1257 * When the 16 consecutive reads are often interrupted by some dirty
1258 * throttling pause during the async writes, cfq will go into idles
1259 * (deadline is fine). So push nr_dirtied_pause as high as possible
1260 * until reaches DIRTY_POLL_THRESH=32 pages.
1261 */
1262 if (pages < DIRTY_POLL_THRESH) {
1263 t = max_pause;
1264 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1265 if (pages > DIRTY_POLL_THRESH) {
1266 pages = DIRTY_POLL_THRESH;
1267 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1268 }
1269 }
1270
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001271 pause = HZ * pages / (task_ratelimit + 1);
1272 if (pause > max_pause) {
1273 t = max_pause;
1274 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1275 }
1276
1277 *nr_dirtied_pause = pages;
1278 /*
1279 * The minimal pause time will normally be half the target pause time.
1280 */
Wu Fengguang5b9b3572011-12-06 13:17:17 -06001281 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001282}
1283
Maxim Patlasov5a537482013-09-11 14:22:46 -07001284static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
1285 unsigned long dirty_thresh,
1286 unsigned long background_thresh,
1287 unsigned long *bdi_dirty,
1288 unsigned long *bdi_thresh,
1289 unsigned long *bdi_bg_thresh)
1290{
1291 unsigned long bdi_reclaimable;
1292
1293 /*
1294 * bdi_thresh is not treated as some limiting factor as
1295 * dirty_thresh, due to reasons
1296 * - in JBOD setup, bdi_thresh can fluctuate a lot
1297 * - in a system with HDD and USB key, the USB key may somehow
1298 * go into state (bdi_dirty >> bdi_thresh) either because
1299 * bdi_dirty starts high, or because bdi_thresh drops low.
1300 * In this case we don't want to hard throttle the USB key
1301 * dirtiers for 100 seconds until bdi_dirty drops under
1302 * bdi_thresh. Instead the auxiliary bdi control line in
1303 * bdi_position_ratio() will let the dirtier task progress
1304 * at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1305 */
1306 *bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
1307
1308 if (bdi_bg_thresh)
1309 *bdi_bg_thresh = div_u64((u64)*bdi_thresh *
1310 background_thresh,
1311 dirty_thresh);
1312
1313 /*
1314 * In order to avoid the stacked BDI deadlock we need
1315 * to ensure we accurately count the 'dirty' pages when
1316 * the threshold is low.
1317 *
1318 * Otherwise it would be possible to get thresh+n pages
1319 * reported dirty, even though there are thresh-m pages
1320 * actually dirty; with m+n sitting in the percpu
1321 * deltas.
1322 */
1323 if (*bdi_thresh < 2 * bdi_stat_error(bdi)) {
1324 bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1325 *bdi_dirty = bdi_reclaimable +
1326 bdi_stat_sum(bdi, BDI_WRITEBACK);
1327 } else {
1328 bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1329 *bdi_dirty = bdi_reclaimable +
1330 bdi_stat(bdi, BDI_WRITEBACK);
1331 }
1332}
1333
Wu Fengguang9d823e82011-06-11 18:10:12 -06001334/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001335 * balance_dirty_pages() must be called by processes which are generating dirty
1336 * data. It looks at the number of dirty pages in the machine and will force
Wu Fengguang143dfe82010-08-27 18:45:12 -06001337 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
Jens Axboe5b0830c2009-09-23 19:37:09 +02001338 * If we're over `background_thresh' then the writeback threads are woken to
1339 * perform some writeout.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001340 */
Wu Fengguang3a2e9a52009-09-23 21:56:00 +08001341static void balance_dirty_pages(struct address_space *mapping,
Wu Fengguang143dfe82010-08-27 18:45:12 -06001342 unsigned long pages_dirtied)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001343{
Wu Fengguang143dfe82010-08-27 18:45:12 -06001344 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
Wu Fengguang77627412010-09-12 13:34:05 -06001345 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
David Rientjes364aeb22009-01-06 14:39:29 -08001346 unsigned long background_thresh;
1347 unsigned long dirty_thresh;
Wu Fengguang83712352011-06-11 19:25:42 -06001348 long period;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001349 long pause;
1350 long max_pause;
1351 long min_pause;
1352 int nr_dirtied_pause;
Wu Fengguange50e3722010-08-11 14:17:37 -07001353 bool dirty_exceeded = false;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001354 unsigned long task_ratelimit;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001355 unsigned long dirty_ratelimit;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001356 unsigned long pos_ratio;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001357 struct backing_dev_info *bdi = mapping->backing_dev_info;
Maxim Patlasov5a537482013-09-11 14:22:46 -07001358 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001359 unsigned long start_time = jiffies;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001360
1361 for (;;) {
Wu Fengguang83712352011-06-11 19:25:42 -06001362 unsigned long now = jiffies;
Maxim Patlasov5a537482013-09-11 14:22:46 -07001363 unsigned long uninitialized_var(bdi_thresh);
1364 unsigned long thresh;
1365 unsigned long uninitialized_var(bdi_dirty);
1366 unsigned long dirty;
1367 unsigned long bg_thresh;
Wu Fengguang83712352011-06-11 19:25:42 -06001368
Wu Fengguang143dfe82010-08-27 18:45:12 -06001369 /*
1370 * Unstable writes are a feature of certain networked
1371 * filesystems (i.e. NFS) in which data may have been
1372 * written to the server's write cache, but has not yet
1373 * been flushed to permanent storage.
1374 */
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001375 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1376 global_page_state(NR_UNSTABLE_NFS);
Wu Fengguang77627412010-09-12 13:34:05 -06001377 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001378
Wu Fengguang16c40422010-08-11 14:17:39 -07001379 global_dirty_limits(&background_thresh, &dirty_thresh);
1380
Maxim Patlasov5a537482013-09-11 14:22:46 -07001381 if (unlikely(strictlimit)) {
1382 bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1383 &bdi_dirty, &bdi_thresh, &bg_thresh);
1384
1385 dirty = bdi_dirty;
1386 thresh = bdi_thresh;
1387 } else {
1388 dirty = nr_dirty;
1389 thresh = dirty_thresh;
1390 bg_thresh = background_thresh;
1391 }
1392
Wu Fengguang16c40422010-08-11 14:17:39 -07001393 /*
1394 * Throttle it only when the background writeback cannot
1395 * catch-up. This avoids (excessively) small writeouts
Maxim Patlasov5a537482013-09-11 14:22:46 -07001396 * when the bdi limits are ramping up in case of !strictlimit.
1397 *
1398 * In strictlimit case make decision based on the bdi counters
1399 * and limits. Small writeouts when the bdi limits are ramping
1400 * up are the price we consciously pay for strictlimit-ing.
Wu Fengguang16c40422010-08-11 14:17:39 -07001401 */
Maxim Patlasov5a537482013-09-11 14:22:46 -07001402 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh)) {
Wu Fengguang83712352011-06-11 19:25:42 -06001403 current->dirty_paused_when = now;
1404 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001405 current->nr_dirtied_pause =
Maxim Patlasov5a537482013-09-11 14:22:46 -07001406 dirty_poll_interval(dirty, thresh);
Wu Fengguang16c40422010-08-11 14:17:39 -07001407 break;
Wu Fengguang83712352011-06-11 19:25:42 -06001408 }
Wu Fengguang16c40422010-08-11 14:17:39 -07001409
Wu Fengguang143dfe82010-08-27 18:45:12 -06001410 if (unlikely(!writeback_in_progress(bdi)))
1411 bdi_start_background_writeback(bdi);
1412
Maxim Patlasov5a537482013-09-11 14:22:46 -07001413 if (!strictlimit)
1414 bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
1415 &bdi_dirty, &bdi_thresh, NULL);
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001416
Wu Fengguang82791942011-12-03 21:26:01 -06001417 dirty_exceeded = (bdi_dirty > bdi_thresh) &&
Maxim Patlasov5a537482013-09-11 14:22:46 -07001418 ((nr_dirty > dirty_thresh) || strictlimit);
Wu Fengguang143dfe82010-08-27 18:45:12 -06001419 if (dirty_exceeded && !bdi->dirty_exceeded)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001420 bdi->dirty_exceeded = 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001421
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001422 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1423 nr_dirty, bdi_thresh, bdi_dirty,
1424 start_time);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001425
Wu Fengguang143dfe82010-08-27 18:45:12 -06001426 dirty_ratelimit = bdi->dirty_ratelimit;
1427 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1428 background_thresh, nr_dirty,
1429 bdi_thresh, bdi_dirty);
Wu Fengguang3a73dbb2011-11-07 19:19:28 +08001430 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1431 RATELIMIT_CALC_SHIFT;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001432 max_pause = bdi_max_pause(bdi, bdi_dirty);
1433 min_pause = bdi_min_pause(bdi, max_pause,
1434 task_ratelimit, dirty_ratelimit,
1435 &nr_dirtied_pause);
1436
Wu Fengguang3a73dbb2011-11-07 19:19:28 +08001437 if (unlikely(task_ratelimit == 0)) {
Wu Fengguang83712352011-06-11 19:25:42 -06001438 period = max_pause;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001439 pause = max_pause;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001440 goto pause;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001441 }
Wu Fengguang83712352011-06-11 19:25:42 -06001442 period = HZ * pages_dirtied / task_ratelimit;
1443 pause = period;
1444 if (current->dirty_paused_when)
1445 pause -= now - current->dirty_paused_when;
1446 /*
1447 * For less than 1s think time (ext3/4 may block the dirtier
1448 * for up to 800ms from time to time on 1-HDD; so does xfs,
1449 * however at much less frequency), try to compensate it in
1450 * future periods by updating the virtual time; otherwise just
1451 * do a reset, as it may be a light dirtier.
1452 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001453 if (pause < min_pause) {
Wu Fengguangece13ac2010-08-29 23:33:20 -06001454 trace_balance_dirty_pages(bdi,
1455 dirty_thresh,
1456 background_thresh,
1457 nr_dirty,
1458 bdi_thresh,
1459 bdi_dirty,
1460 dirty_ratelimit,
1461 task_ratelimit,
1462 pages_dirtied,
Wu Fengguang83712352011-06-11 19:25:42 -06001463 period,
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001464 min(pause, 0L),
Wu Fengguangece13ac2010-08-29 23:33:20 -06001465 start_time);
Wu Fengguang83712352011-06-11 19:25:42 -06001466 if (pause < -HZ) {
1467 current->dirty_paused_when = now;
1468 current->nr_dirtied = 0;
1469 } else if (period) {
1470 current->dirty_paused_when += period;
1471 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001472 } else if (current->nr_dirtied_pause <= pages_dirtied)
1473 current->nr_dirtied_pause += pages_dirtied;
Wu Fengguang57fc9782011-06-11 19:32:32 -06001474 break;
1475 }
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001476 if (unlikely(pause > max_pause)) {
1477 /* for occasional dropped task_ratelimit */
1478 now += min(pause - max_pause, max_pause);
1479 pause = max_pause;
1480 }
Wu Fengguang143dfe82010-08-27 18:45:12 -06001481
1482pause:
Wu Fengguangece13ac2010-08-29 23:33:20 -06001483 trace_balance_dirty_pages(bdi,
1484 dirty_thresh,
1485 background_thresh,
1486 nr_dirty,
1487 bdi_thresh,
1488 bdi_dirty,
1489 dirty_ratelimit,
1490 task_ratelimit,
1491 pages_dirtied,
Wu Fengguang83712352011-06-11 19:25:42 -06001492 period,
Wu Fengguangece13ac2010-08-29 23:33:20 -06001493 pause,
1494 start_time);
Jan Kara499d05e2011-11-16 19:34:48 +08001495 __set_current_state(TASK_KILLABLE);
Wu Fengguangd25105e2009-10-09 12:40:42 +02001496 io_schedule_timeout(pause);
Jens Axboe87c6a9b2009-09-17 19:59:14 +02001497
Wu Fengguang83712352011-06-11 19:25:42 -06001498 current->dirty_paused_when = now + pause;
1499 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001500 current->nr_dirtied_pause = nr_dirtied_pause;
Wu Fengguang83712352011-06-11 19:25:42 -06001501
Wu Fengguangffd1f602011-06-19 22:18:42 -06001502 /*
Wu Fengguang1df64712011-11-13 19:47:32 -06001503 * This is typically equal to (nr_dirty < dirty_thresh) and can
1504 * also keep "1000+ dd on a slow USB stick" under control.
Wu Fengguangffd1f602011-06-19 22:18:42 -06001505 */
Wu Fengguang1df64712011-11-13 19:47:32 -06001506 if (task_ratelimit)
Wu Fengguangffd1f602011-06-19 22:18:42 -06001507 break;
Jan Kara499d05e2011-11-16 19:34:48 +08001508
Wu Fengguangc5c63432011-12-02 10:21:33 -06001509 /*
1510 * In the case of an unresponding NFS server and the NFS dirty
1511 * pages exceeds dirty_thresh, give the other good bdi's a pipe
1512 * to go through, so that tasks on them still remain responsive.
1513 *
1514 * In theory 1 page is enough to keep the comsumer-producer
1515 * pipe going: the flusher cleans 1 page => the task dirties 1
1516 * more page. However bdi_dirty has accounting errors. So use
1517 * the larger and more IO friendly bdi_stat_error.
1518 */
1519 if (bdi_dirty <= bdi_stat_error(bdi))
1520 break;
1521
Jan Kara499d05e2011-11-16 19:34:48 +08001522 if (fatal_signal_pending(current))
1523 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001524 }
1525
Wu Fengguang143dfe82010-08-27 18:45:12 -06001526 if (!dirty_exceeded && bdi->dirty_exceeded)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001527 bdi->dirty_exceeded = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001528
1529 if (writeback_in_progress(bdi))
Jens Axboe5b0830c2009-09-23 19:37:09 +02001530 return;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001531
1532 /*
1533 * In laptop mode, we wait until hitting the higher threshold before
1534 * starting background writeout, and then write out all the way down
1535 * to the lower threshold. So slow writers cause minimal disk activity.
1536 *
1537 * In normal mode, we start background writeout at the lower
1538 * background_thresh, to keep the amount of dirty memory low.
1539 */
Wu Fengguang143dfe82010-08-27 18:45:12 -06001540 if (laptop_mode)
1541 return;
1542
1543 if (nr_reclaimable > background_thresh)
Christoph Hellwigc5444192010-06-08 18:15:15 +02001544 bdi_start_background_writeback(bdi);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001545}
1546
Miklos Szeredied6d7c82014-04-07 15:37:51 -07001547void set_page_dirty_balance(struct page *page)
Peter Zijlstraedc79b22006-09-25 23:30:58 -07001548{
Miklos Szeredied6d7c82014-04-07 15:37:51 -07001549 if (set_page_dirty(page)) {
Peter Zijlstraedc79b22006-09-25 23:30:58 -07001550 struct address_space *mapping = page_mapping(page);
1551
1552 if (mapping)
1553 balance_dirty_pages_ratelimited(mapping);
1554 }
1555}
1556
Wu Fengguang9d823e82011-06-11 18:10:12 -06001557static DEFINE_PER_CPU(int, bdp_ratelimits);
Tejun Heo245b2e72009-06-24 15:13:48 +09001558
Wu Fengguang54848d72011-04-05 13:21:19 -06001559/*
1560 * Normal tasks are throttled by
1561 * loop {
1562 * dirty tsk->nr_dirtied_pause pages;
1563 * take a snap in balance_dirty_pages();
1564 * }
1565 * However there is a worst case. If every task exit immediately when dirtied
1566 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1567 * called to throttle the page dirties. The solution is to save the not yet
1568 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1569 * randomly into the running tasks. This works well for the above worst case,
1570 * as the new task will pick up and accumulate the old task's leaked dirty
1571 * count and eventually get throttled.
1572 */
1573DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1574
Linus Torvalds1da177e2005-04-16 15:20:36 -07001575/**
Namjae Jeond0e1d662012-12-11 16:00:21 -08001576 * balance_dirty_pages_ratelimited - balance dirty memory state
Martin Waitz67be2dd2005-05-01 08:59:26 -07001577 * @mapping: address_space which was dirtied
Linus Torvalds1da177e2005-04-16 15:20:36 -07001578 *
1579 * Processes which are dirtying memory should call in here once for each page
1580 * which was newly dirtied. The function will periodically check the system's
1581 * dirty state and will initiate writeback if needed.
1582 *
1583 * On really big machines, get_writeback_state is expensive, so try to avoid
1584 * calling it too often (ratelimiting). But once we're over the dirty memory
1585 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1586 * from overshooting the limit by (ratelimit_pages) each.
1587 */
Namjae Jeond0e1d662012-12-11 16:00:21 -08001588void balance_dirty_pages_ratelimited(struct address_space *mapping)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001589{
Wu Fengguang36715ce2011-06-11 17:53:57 -06001590 struct backing_dev_info *bdi = mapping->backing_dev_info;
Wu Fengguang9d823e82011-06-11 18:10:12 -06001591 int ratelimit;
1592 int *p;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001593
Wu Fengguang36715ce2011-06-11 17:53:57 -06001594 if (!bdi_cap_account_dirty(bdi))
1595 return;
1596
Wu Fengguang9d823e82011-06-11 18:10:12 -06001597 ratelimit = current->nr_dirtied_pause;
1598 if (bdi->dirty_exceeded)
1599 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
Linus Torvalds1da177e2005-04-16 15:20:36 -07001600
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001601 preempt_disable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001602 /*
1603 * This prevents one CPU to accumulate too many dirtied pages without
1604 * calling into balance_dirty_pages(), which can happen when there are
1605 * 1000+ tasks, all of them start dirtying pages at exactly the same
1606 * time, hence all honoured too large initial task->nr_dirtied_pause.
1607 */
Christoph Lameter7c8e0182014-06-04 16:07:56 -07001608 p = this_cpu_ptr(&bdp_ratelimits);
Wu Fengguang9d823e82011-06-11 18:10:12 -06001609 if (unlikely(current->nr_dirtied >= ratelimit))
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001610 *p = 0;
Wu Fengguangd3bc1fe2011-04-14 07:52:37 -06001611 else if (unlikely(*p >= ratelimit_pages)) {
1612 *p = 0;
1613 ratelimit = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001614 }
Wu Fengguang54848d72011-04-05 13:21:19 -06001615 /*
1616 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1617 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1618 * the dirty throttling and livelock other long-run dirtiers.
1619 */
Christoph Lameter7c8e0182014-06-04 16:07:56 -07001620 p = this_cpu_ptr(&dirty_throttle_leaks);
Wu Fengguang54848d72011-04-05 13:21:19 -06001621 if (*p > 0 && current->nr_dirtied < ratelimit) {
Namjae Jeond0e1d662012-12-11 16:00:21 -08001622 unsigned long nr_pages_dirtied;
Wu Fengguang54848d72011-04-05 13:21:19 -06001623 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1624 *p -= nr_pages_dirtied;
1625 current->nr_dirtied += nr_pages_dirtied;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001626 }
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001627 preempt_enable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001628
1629 if (unlikely(current->nr_dirtied >= ratelimit))
1630 balance_dirty_pages(mapping, current->nr_dirtied);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001631}
Namjae Jeond0e1d662012-12-11 16:00:21 -08001632EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001633
Andrew Morton232ea4d2007-02-28 20:13:21 -08001634void throttle_vm_writeout(gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001635{
David Rientjes364aeb22009-01-06 14:39:29 -08001636 unsigned long background_thresh;
1637 unsigned long dirty_thresh;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001638
1639 for ( ; ; ) {
Wu Fengguang16c40422010-08-11 14:17:39 -07001640 global_dirty_limits(&background_thresh, &dirty_thresh);
Fengguang Wu47a13332012-03-21 16:34:09 -07001641 dirty_thresh = hard_dirty_limit(dirty_thresh);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001642
1643 /*
1644 * Boost the allowable dirty threshold a bit for page
1645 * allocators so they don't get DoS'ed by heavy writers
1646 */
1647 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1648
Christoph Lameterc24f21b2006-06-30 01:55:42 -07001649 if (global_page_state(NR_UNSTABLE_NFS) +
1650 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1651 break;
Jens Axboe8aa7e842009-07-09 14:52:32 +02001652 congestion_wait(BLK_RW_ASYNC, HZ/10);
Fengguang Wu369f2382007-10-16 23:30:45 -07001653
1654 /*
1655 * The caller might hold locks which can prevent IO completion
1656 * or progress in the filesystem. So we cannot just sit here
1657 * waiting for IO to complete.
1658 */
1659 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1660 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001661 }
1662}
1663
Linus Torvalds1da177e2005-04-16 15:20:36 -07001664/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001665 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1666 */
Joe Perchescccad5b2014-06-06 14:38:09 -07001667int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001668 void __user *buffer, size_t *length, loff_t *ppos)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001669{
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001670 proc_dointvec(table, write, buffer, length, ppos);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001671 return 0;
1672}
1673
Jens Axboec2c49862010-05-20 09:18:47 +02001674#ifdef CONFIG_BLOCK
Matthew Garrett31373d02010-04-06 14:25:14 +02001675void laptop_mode_timer_fn(unsigned long data)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001676{
Matthew Garrett31373d02010-04-06 14:25:14 +02001677 struct request_queue *q = (struct request_queue *)data;
1678 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1679 global_page_state(NR_UNSTABLE_NFS);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001680
Matthew Garrett31373d02010-04-06 14:25:14 +02001681 /*
1682 * We want to write everything out, not just down to the dirty
1683 * threshold
1684 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001685 if (bdi_has_dirty_io(&q->backing_dev_info))
Curt Wohlgemuth0e175a12011-10-07 21:54:10 -06001686 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1687 WB_REASON_LAPTOP_TIMER);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001688}
1689
1690/*
1691 * We've spun up the disk and we're in laptop mode: schedule writeback
1692 * of all dirty data a few seconds from now. If the flush is already scheduled
1693 * then push it back - the user is still using the disk.
1694 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001695void laptop_io_completion(struct backing_dev_info *info)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001696{
Matthew Garrett31373d02010-04-06 14:25:14 +02001697 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001698}
1699
1700/*
1701 * We're in laptop mode and we've just synced. The sync's writes will have
1702 * caused another writeback to be scheduled by laptop_io_completion.
1703 * Nothing needs to be written back anymore, so we unschedule the writeback.
1704 */
1705void laptop_sync_completion(void)
1706{
Matthew Garrett31373d02010-04-06 14:25:14 +02001707 struct backing_dev_info *bdi;
1708
1709 rcu_read_lock();
1710
1711 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1712 del_timer(&bdi->laptop_mode_wb_timer);
1713
1714 rcu_read_unlock();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001715}
Jens Axboec2c49862010-05-20 09:18:47 +02001716#endif
Linus Torvalds1da177e2005-04-16 15:20:36 -07001717
1718/*
1719 * If ratelimit_pages is too high then we can get into dirty-data overload
1720 * if a large number of processes all perform writes at the same time.
1721 * If it is too low then SMP machines will call the (expensive)
1722 * get_writeback_state too often.
1723 *
1724 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1725 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
Wu Fengguang9d823e82011-06-11 18:10:12 -06001726 * thresholds.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001727 */
1728
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001729void writeback_set_ratelimit(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001730{
Wu Fengguang9d823e82011-06-11 18:10:12 -06001731 unsigned long background_thresh;
1732 unsigned long dirty_thresh;
1733 global_dirty_limits(&background_thresh, &dirty_thresh);
Fengguang Wu68809c72012-05-06 13:21:42 +08001734 global_dirty_limit = dirty_thresh;
Wu Fengguang9d823e82011-06-11 18:10:12 -06001735 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001736 if (ratelimit_pages < 16)
1737 ratelimit_pages = 16;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001738}
1739
Paul Gortmaker0db06282013-06-19 14:53:51 -04001740static int
Srivatsa S. Bhat2f60d622012-09-28 20:27:49 +08001741ratelimit_handler(struct notifier_block *self, unsigned long action,
1742 void *hcpu)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001743{
Srivatsa S. Bhat2f60d622012-09-28 20:27:49 +08001744
1745 switch (action & ~CPU_TASKS_FROZEN) {
1746 case CPU_ONLINE:
1747 case CPU_DEAD:
1748 writeback_set_ratelimit();
1749 return NOTIFY_OK;
1750 default:
1751 return NOTIFY_DONE;
1752 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07001753}
1754
Paul Gortmaker0db06282013-06-19 14:53:51 -04001755static struct notifier_block ratelimit_nb = {
Linus Torvalds1da177e2005-04-16 15:20:36 -07001756 .notifier_call = ratelimit_handler,
1757 .next = NULL,
1758};
1759
1760/*
Linus Torvaldsdc6e29d2007-01-29 16:37:38 -08001761 * Called early on to tune the page writeback dirty limits.
1762 *
1763 * We used to scale dirty pages according to how total memory
1764 * related to pages that could be allocated for buffers (by
1765 * comparing nr_free_buffer_pages() to vm_total_pages.
1766 *
1767 * However, that was when we used "dirty_ratio" to scale with
1768 * all memory, and we don't do that any more. "dirty_ratio"
1769 * is now applied to total non-HIGHPAGE memory (by subtracting
1770 * totalhigh_pages from vm_total_pages), and as such we can't
1771 * get into the old insane situation any more where we had
1772 * large amounts of dirty pages compared to a small amount of
1773 * non-HIGHMEM memory.
1774 *
1775 * But we might still want to scale the dirty_ratio by how
1776 * much memory the box has..
Linus Torvalds1da177e2005-04-16 15:20:36 -07001777 */
1778void __init page_writeback_init(void)
1779{
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001780 writeback_set_ratelimit();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001781 register_cpu_notifier(&ratelimit_nb);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001782
Jan Karaeb608e32012-05-24 18:59:11 +02001783 fprop_global_init(&writeout_completions);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001784}
1785
David Howells811d7362006-08-29 19:06:09 +01001786/**
Jan Karaf446daae2010-08-09 17:19:12 -07001787 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1788 * @mapping: address space structure to write
1789 * @start: starting page index
1790 * @end: ending page index (inclusive)
1791 *
1792 * This function scans the page range from @start to @end (inclusive) and tags
1793 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1794 * that write_cache_pages (or whoever calls this function) will then use
1795 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1796 * used to avoid livelocking of writeback by a process steadily creating new
1797 * dirty pages in the file (thus it is important for this function to be quick
1798 * so that it can tag pages faster than a dirtying process can create them).
1799 */
1800/*
1801 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1802 */
Jan Karaf446daae2010-08-09 17:19:12 -07001803void tag_pages_for_writeback(struct address_space *mapping,
1804 pgoff_t start, pgoff_t end)
1805{
Randy Dunlap3c111a02010-08-11 14:17:30 -07001806#define WRITEBACK_TAG_BATCH 4096
Jan Karaf446daae2010-08-09 17:19:12 -07001807 unsigned long tagged;
1808
1809 do {
1810 spin_lock_irq(&mapping->tree_lock);
1811 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1812 &start, end, WRITEBACK_TAG_BATCH,
1813 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1814 spin_unlock_irq(&mapping->tree_lock);
1815 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1816 cond_resched();
Jan Karad5ed3a42010-08-19 14:13:33 -07001817 /* We check 'start' to handle wrapping when end == ~0UL */
1818 } while (tagged >= WRITEBACK_TAG_BATCH && start);
Jan Karaf446daae2010-08-09 17:19:12 -07001819}
1820EXPORT_SYMBOL(tag_pages_for_writeback);
1821
1822/**
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001823 * 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 +01001824 * @mapping: address space structure to write
1825 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001826 * @writepage: function called for each page
1827 * @data: data passed to writepage function
David Howells811d7362006-08-29 19:06:09 +01001828 *
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001829 * If a page is already under I/O, write_cache_pages() skips it, even
David Howells811d7362006-08-29 19:06:09 +01001830 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1831 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1832 * and msync() need to guarantee that all the data which was dirty at the time
1833 * the call was made get new I/O started against them. If wbc->sync_mode is
1834 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1835 * existing IO to complete.
Jan Karaf446daae2010-08-09 17:19:12 -07001836 *
1837 * To avoid livelocks (when other process dirties new pages), we first tag
1838 * pages which should be written back with TOWRITE tag and only then start
1839 * writing them. For data-integrity sync we have to be careful so that we do
1840 * not miss some pages (e.g., because some other process has cleared TOWRITE
1841 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1842 * by the process clearing the DIRTY tag (and submitting the page for IO).
David Howells811d7362006-08-29 19:06:09 +01001843 */
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001844int write_cache_pages(struct address_space *mapping,
1845 struct writeback_control *wbc, writepage_t writepage,
1846 void *data)
David Howells811d7362006-08-29 19:06:09 +01001847{
David Howells811d7362006-08-29 19:06:09 +01001848 int ret = 0;
1849 int done = 0;
David Howells811d7362006-08-29 19:06:09 +01001850 struct pagevec pvec;
1851 int nr_pages;
Nick Piggin31a12662009-01-06 14:39:04 -08001852 pgoff_t uninitialized_var(writeback_index);
David Howells811d7362006-08-29 19:06:09 +01001853 pgoff_t index;
1854 pgoff_t end; /* Inclusive */
Nick Pigginbd19e012009-01-06 14:39:06 -08001855 pgoff_t done_index;
Nick Piggin31a12662009-01-06 14:39:04 -08001856 int cycled;
David Howells811d7362006-08-29 19:06:09 +01001857 int range_whole = 0;
Jan Karaf446daae2010-08-09 17:19:12 -07001858 int tag;
David Howells811d7362006-08-29 19:06:09 +01001859
David Howells811d7362006-08-29 19:06:09 +01001860 pagevec_init(&pvec, 0);
1861 if (wbc->range_cyclic) {
Nick Piggin31a12662009-01-06 14:39:04 -08001862 writeback_index = mapping->writeback_index; /* prev offset */
1863 index = writeback_index;
1864 if (index == 0)
1865 cycled = 1;
1866 else
1867 cycled = 0;
David Howells811d7362006-08-29 19:06:09 +01001868 end = -1;
1869 } else {
1870 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1871 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1872 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1873 range_whole = 1;
Nick Piggin31a12662009-01-06 14:39:04 -08001874 cycled = 1; /* ignore range_cyclic tests */
David Howells811d7362006-08-29 19:06:09 +01001875 }
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001876 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daae2010-08-09 17:19:12 -07001877 tag = PAGECACHE_TAG_TOWRITE;
1878 else
1879 tag = PAGECACHE_TAG_DIRTY;
David Howells811d7362006-08-29 19:06:09 +01001880retry:
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001881 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daae2010-08-09 17:19:12 -07001882 tag_pages_for_writeback(mapping, index, end);
Nick Pigginbd19e012009-01-06 14:39:06 -08001883 done_index = index;
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001884 while (!done && (index <= end)) {
1885 int i;
1886
Jan Karaf446daae2010-08-09 17:19:12 -07001887 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001888 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1889 if (nr_pages == 0)
1890 break;
David Howells811d7362006-08-29 19:06:09 +01001891
David Howells811d7362006-08-29 19:06:09 +01001892 for (i = 0; i < nr_pages; i++) {
1893 struct page *page = pvec.pages[i];
1894
Nick Piggind5482cd2009-01-06 14:39:11 -08001895 /*
1896 * At this point, the page may be truncated or
1897 * invalidated (changing page->mapping to NULL), or
1898 * even swizzled back from swapper_space to tmpfs file
1899 * mapping. However, page->index will not change
1900 * because we have a reference on the page.
1901 */
1902 if (page->index > end) {
1903 /*
1904 * can't be range_cyclic (1st pass) because
1905 * end == -1 in that case.
1906 */
1907 done = 1;
1908 break;
1909 }
1910
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001911 done_index = page->index;
Nick Pigginbd19e012009-01-06 14:39:06 -08001912
David Howells811d7362006-08-29 19:06:09 +01001913 lock_page(page);
1914
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001915 /*
1916 * Page truncated or invalidated. We can freely skip it
1917 * then, even for data integrity operations: the page
1918 * has disappeared concurrently, so there could be no
1919 * real expectation of this data interity operation
1920 * even if there is now a new, dirty page at the same
1921 * pagecache address.
1922 */
David Howells811d7362006-08-29 19:06:09 +01001923 if (unlikely(page->mapping != mapping)) {
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001924continue_unlock:
David Howells811d7362006-08-29 19:06:09 +01001925 unlock_page(page);
1926 continue;
1927 }
1928
Nick Piggin515f4a02009-01-06 14:39:10 -08001929 if (!PageDirty(page)) {
1930 /* someone wrote it for us */
1931 goto continue_unlock;
1932 }
David Howells811d7362006-08-29 19:06:09 +01001933
Nick Piggin515f4a02009-01-06 14:39:10 -08001934 if (PageWriteback(page)) {
1935 if (wbc->sync_mode != WB_SYNC_NONE)
1936 wait_on_page_writeback(page);
1937 else
1938 goto continue_unlock;
1939 }
1940
1941 BUG_ON(PageWriteback(page));
1942 if (!clear_page_dirty_for_io(page))
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001943 goto continue_unlock;
David Howells811d7362006-08-29 19:06:09 +01001944
Dave Chinner9e094382010-07-07 13:24:08 +10001945 trace_wbc_writepage(wbc, mapping->backing_dev_info);
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001946 ret = (*writepage)(page, wbc, data);
Nick Piggin00266772009-01-06 14:39:06 -08001947 if (unlikely(ret)) {
1948 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1949 unlock_page(page);
1950 ret = 0;
1951 } else {
1952 /*
1953 * done_index is set past this page,
1954 * so media errors will not choke
1955 * background writeout for the entire
1956 * file. This has consequences for
1957 * range_cyclic semantics (ie. it may
1958 * not be suitable for data integrity
1959 * writeout).
1960 */
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001961 done_index = page->index + 1;
Nick Piggin00266772009-01-06 14:39:06 -08001962 done = 1;
1963 break;
1964 }
Dave Chinner0b564922010-06-09 10:37:18 +10001965 }
David Howells811d7362006-08-29 19:06:09 +01001966
Dave Chinner546a1922010-08-24 11:44:34 +10001967 /*
1968 * We stop writing back only if we are not doing
1969 * integrity sync. In case of integrity sync we have to
1970 * keep going until we have written all the pages
1971 * we tagged for writeback prior to entering this loop.
1972 */
1973 if (--wbc->nr_to_write <= 0 &&
1974 wbc->sync_mode == WB_SYNC_NONE) {
1975 done = 1;
1976 break;
Nick Piggin05fe4782009-01-06 14:39:08 -08001977 }
David Howells811d7362006-08-29 19:06:09 +01001978 }
1979 pagevec_release(&pvec);
1980 cond_resched();
1981 }
Nick Piggin3a4c6802009-02-12 04:34:23 +01001982 if (!cycled && !done) {
David Howells811d7362006-08-29 19:06:09 +01001983 /*
Nick Piggin31a12662009-01-06 14:39:04 -08001984 * range_cyclic:
David Howells811d7362006-08-29 19:06:09 +01001985 * We hit the last page and there is more work to be done: wrap
1986 * back to the start of the file
1987 */
Nick Piggin31a12662009-01-06 14:39:04 -08001988 cycled = 1;
David Howells811d7362006-08-29 19:06:09 +01001989 index = 0;
Nick Piggin31a12662009-01-06 14:39:04 -08001990 end = writeback_index - 1;
David Howells811d7362006-08-29 19:06:09 +01001991 goto retry;
1992 }
Dave Chinner0b564922010-06-09 10:37:18 +10001993 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1994 mapping->writeback_index = done_index;
Aneesh Kumar K.V06d6cf62008-07-11 19:27:31 -04001995
David Howells811d7362006-08-29 19:06:09 +01001996 return ret;
1997}
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001998EXPORT_SYMBOL(write_cache_pages);
1999
2000/*
2001 * Function used by generic_writepages to call the real writepage
2002 * function and set the mapping flags on error
2003 */
2004static int __writepage(struct page *page, struct writeback_control *wbc,
2005 void *data)
2006{
2007 struct address_space *mapping = data;
2008 int ret = mapping->a_ops->writepage(page, wbc);
2009 mapping_set_error(mapping, ret);
2010 return ret;
2011}
2012
2013/**
2014 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2015 * @mapping: address space structure to write
2016 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2017 *
2018 * This is a library function, which implements the writepages()
2019 * address_space_operation.
2020 */
2021int generic_writepages(struct address_space *mapping,
2022 struct writeback_control *wbc)
2023{
Shaohua Li9b6096a2011-03-17 10:47:06 +01002024 struct blk_plug plug;
2025 int ret;
2026
Miklos Szeredi0ea97182007-05-10 22:22:51 -07002027 /* deal with chardevs and other special file */
2028 if (!mapping->a_ops->writepage)
2029 return 0;
2030
Shaohua Li9b6096a2011-03-17 10:47:06 +01002031 blk_start_plug(&plug);
2032 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2033 blk_finish_plug(&plug);
2034 return ret;
Miklos Szeredi0ea97182007-05-10 22:22:51 -07002035}
David Howells811d7362006-08-29 19:06:09 +01002036
2037EXPORT_SYMBOL(generic_writepages);
2038
Linus Torvalds1da177e2005-04-16 15:20:36 -07002039int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2040{
Andrew Morton22905f72005-11-16 15:07:01 -08002041 int ret;
2042
Linus Torvalds1da177e2005-04-16 15:20:36 -07002043 if (wbc->nr_to_write <= 0)
2044 return 0;
2045 if (mapping->a_ops->writepages)
Peter Zijlstrad08b3852006-09-25 23:30:57 -07002046 ret = mapping->a_ops->writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08002047 else
2048 ret = generic_writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08002049 return ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002050}
2051
2052/**
2053 * write_one_page - write out a single page and optionally wait on I/O
Martin Waitz67be2dd2005-05-01 08:59:26 -07002054 * @page: the page to write
2055 * @wait: if true, wait on writeout
Linus Torvalds1da177e2005-04-16 15:20:36 -07002056 *
2057 * The page must be locked by the caller and will be unlocked upon return.
2058 *
2059 * write_one_page() returns a negative error code if I/O failed.
2060 */
2061int write_one_page(struct page *page, int wait)
2062{
2063 struct address_space *mapping = page->mapping;
2064 int ret = 0;
2065 struct writeback_control wbc = {
2066 .sync_mode = WB_SYNC_ALL,
2067 .nr_to_write = 1,
2068 };
2069
2070 BUG_ON(!PageLocked(page));
2071
2072 if (wait)
2073 wait_on_page_writeback(page);
2074
2075 if (clear_page_dirty_for_io(page)) {
2076 page_cache_get(page);
2077 ret = mapping->a_ops->writepage(page, &wbc);
2078 if (ret == 0 && wait) {
2079 wait_on_page_writeback(page);
2080 if (PageError(page))
2081 ret = -EIO;
2082 }
2083 page_cache_release(page);
2084 } else {
2085 unlock_page(page);
2086 }
2087 return ret;
2088}
2089EXPORT_SYMBOL(write_one_page);
2090
2091/*
Ken Chen76719322007-02-10 01:43:15 -08002092 * For address_spaces which do not use buffers nor write back.
2093 */
2094int __set_page_dirty_no_writeback(struct page *page)
2095{
2096 if (!PageDirty(page))
Bob Liuc3f0da62011-01-13 15:45:49 -08002097 return !TestSetPageDirty(page);
Ken Chen76719322007-02-10 01:43:15 -08002098 return 0;
2099}
2100
2101/*
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002102 * Helper function for set_page_dirty family.
2103 * NOTE: This relies on being atomic wrt interrupts.
2104 */
2105void account_page_dirtied(struct page *page, struct address_space *mapping)
2106{
Tejun Heo9fb0a7d2013-01-11 13:06:37 -08002107 trace_writeback_dirty_page(page, mapping);
2108
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002109 if (mapping_cap_account_dirty(mapping)) {
2110 __inc_zone_page_state(page, NR_FILE_DIRTY);
Michael Rubinea941f02010-10-26 14:21:35 -07002111 __inc_zone_page_state(page, NR_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002112 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
Wu Fengguangc8e28ce2011-01-23 10:07:47 -06002113 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002114 task_io_account_write(PAGE_CACHE_SIZE);
Wu Fengguangd3bc1fe2011-04-14 07:52:37 -06002115 current->nr_dirtied++;
2116 this_cpu_inc(bdp_ratelimits);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002117 }
2118}
Michael Rubin679ceac2010-08-20 02:31:26 -07002119EXPORT_SYMBOL(account_page_dirtied);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002120
2121/*
Michael Rubinf629d1c2010-10-26 14:21:33 -07002122 * Helper function for set_page_writeback family.
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002123 *
2124 * The caller must hold mem_cgroup_begin/end_update_page_stat() lock
2125 * while calling this function.
2126 * See test_set_page_writeback for example.
2127 *
Michael Rubinf629d1c2010-10-26 14:21:33 -07002128 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
2129 * wrt interrupts.
2130 */
2131void account_page_writeback(struct page *page)
2132{
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002133 mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
Michael Rubinf629d1c2010-10-26 14:21:33 -07002134 inc_zone_page_state(page, NR_WRITEBACK);
2135}
2136EXPORT_SYMBOL(account_page_writeback);
2137
2138/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002139 * For address_spaces which do not use buffers. Just tag the page as dirty in
2140 * its radix tree.
2141 *
2142 * This is also used when a single buffer is being dirtied: we want to set the
2143 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2144 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2145 *
2146 * Most callers have locked the page, which pins the address_space in memory.
2147 * But zap_pte_range() does not lock the page, however in that case the
2148 * mapping is pinned by the vma's ->vm_file reference.
2149 *
2150 * We take care to handle the case where the page was truncated from the
Simon Arlott183ff222007-10-20 01:27:18 +02002151 * mapping by re-checking page_mapping() inside tree_lock.
Linus Torvalds1da177e2005-04-16 15:20:36 -07002152 */
2153int __set_page_dirty_nobuffers(struct page *page)
2154{
Linus Torvalds1da177e2005-04-16 15:20:36 -07002155 if (!TestSetPageDirty(page)) {
2156 struct address_space *mapping = page_mapping(page);
2157 struct address_space *mapping2;
KOSAKI Motohiroa85d9df2014-02-06 12:04:24 -08002158 unsigned long flags;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002159
Andrew Morton8c085402006-12-10 02:19:24 -08002160 if (!mapping)
2161 return 1;
2162
KOSAKI Motohiroa85d9df2014-02-06 12:04:24 -08002163 spin_lock_irqsave(&mapping->tree_lock, flags);
Andrew Morton8c085402006-12-10 02:19:24 -08002164 mapping2 = page_mapping(page);
2165 if (mapping2) { /* Race with truncate? */
2166 BUG_ON(mapping2 != mapping);
Nick Piggin787d2212007-07-17 04:03:34 -07002167 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002168 account_page_dirtied(page, mapping);
Andrew Morton8c085402006-12-10 02:19:24 -08002169 radix_tree_tag_set(&mapping->page_tree,
2170 page_index(page), PAGECACHE_TAG_DIRTY);
2171 }
KOSAKI Motohiroa85d9df2014-02-06 12:04:24 -08002172 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Andrew Morton8c085402006-12-10 02:19:24 -08002173 if (mapping->host) {
2174 /* !PageAnon && !swapper_space */
2175 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002176 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002177 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002178 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002179 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002180}
2181EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2182
2183/*
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002184 * Call this whenever redirtying a page, to de-account the dirty counters
2185 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2186 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2187 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2188 * control.
2189 */
2190void account_page_redirty(struct page *page)
2191{
2192 struct address_space *mapping = page->mapping;
2193 if (mapping && mapping_cap_account_dirty(mapping)) {
2194 current->nr_dirtied--;
2195 dec_zone_page_state(page, NR_DIRTIED);
2196 dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2197 }
2198}
2199EXPORT_SYMBOL(account_page_redirty);
2200
2201/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002202 * When a writepage implementation decides that it doesn't want to write this
2203 * page for some reason, it should redirty the locked page via
2204 * redirty_page_for_writepage() and it should then unlock the page and return 0
2205 */
2206int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2207{
2208 wbc->pages_skipped++;
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002209 account_page_redirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002210 return __set_page_dirty_nobuffers(page);
2211}
2212EXPORT_SYMBOL(redirty_page_for_writepage);
2213
2214/*
Wu Fengguang6746aff2009-09-16 11:50:14 +02002215 * Dirty a page.
2216 *
2217 * For pages with a mapping this should be done under the page lock
2218 * for the benefit of asynchronous memory errors who prefer a consistent
2219 * dirty state. This rule can be broken in some special cases,
2220 * but should be better not to.
2221 *
Linus Torvalds1da177e2005-04-16 15:20:36 -07002222 * If the mapping doesn't provide a set_page_dirty a_op, then
2223 * just fall through and assume that it wants buffer_heads.
2224 */
Nick Piggin1cf6e7d2009-02-18 14:48:18 -08002225int set_page_dirty(struct page *page)
Linus Torvalds1da177e2005-04-16 15:20:36 -07002226{
2227 struct address_space *mapping = page_mapping(page);
2228
2229 if (likely(mapping)) {
2230 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
Minchan Kim278df9f2011-03-22 16:32:54 -07002231 /*
2232 * readahead/lru_deactivate_page could remain
2233 * PG_readahead/PG_reclaim due to race with end_page_writeback
2234 * About readahead, if the page is written, the flags would be
2235 * reset. So no problem.
2236 * About lru_deactivate_page, if the page is redirty, the flag
2237 * will be reset. So no problem. but if the page is used by readahead
2238 * it will confuse readahead and make it restart the size rampup
2239 * process. But it's a trivial problem.
2240 */
2241 ClearPageReclaim(page);
David Howells93614012006-09-30 20:45:40 +02002242#ifdef CONFIG_BLOCK
2243 if (!spd)
2244 spd = __set_page_dirty_buffers;
2245#endif
2246 return (*spd)(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002247 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002248 if (!PageDirty(page)) {
2249 if (!TestSetPageDirty(page))
2250 return 1;
2251 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002252 return 0;
2253}
2254EXPORT_SYMBOL(set_page_dirty);
2255
2256/*
2257 * set_page_dirty() is racy if the caller has no reference against
2258 * page->mapping->host, and if the page is unlocked. This is because another
2259 * CPU could truncate the page off the mapping and then free the mapping.
2260 *
2261 * Usually, the page _is_ locked, or the caller is a user-space process which
2262 * holds a reference on the inode by having an open file.
2263 *
2264 * In other cases, the page should be locked before running set_page_dirty().
2265 */
2266int set_page_dirty_lock(struct page *page)
2267{
2268 int ret;
2269
Jens Axboe7eaceac2011-03-10 08:52:07 +01002270 lock_page(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002271 ret = set_page_dirty(page);
2272 unlock_page(page);
2273 return ret;
2274}
2275EXPORT_SYMBOL(set_page_dirty_lock);
2276
2277/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002278 * Clear a page's dirty flag, while caring for dirty memory accounting.
2279 * Returns true if the page was previously dirty.
2280 *
2281 * This is for preparing to put the page under writeout. We leave the page
2282 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2283 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2284 * implementation will run either set_page_writeback() or set_page_dirty(),
2285 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2286 * back into sync.
2287 *
2288 * This incoherency between the page's dirty flag and radix-tree tag is
2289 * unfortunate, but it only exists while the page is locked.
2290 */
2291int clear_page_dirty_for_io(struct page *page)
2292{
2293 struct address_space *mapping = page_mapping(page);
2294
Nick Piggin79352892007-07-19 01:47:22 -07002295 BUG_ON(!PageLocked(page));
2296
Linus Torvalds7658cc22006-12-29 10:00:58 -08002297 if (mapping && mapping_cap_account_dirty(mapping)) {
2298 /*
2299 * Yes, Virginia, this is indeed insane.
2300 *
2301 * We use this sequence to make sure that
2302 * (a) we account for dirty stats properly
2303 * (b) we tell the low-level filesystem to
2304 * mark the whole page dirty if it was
2305 * dirty in a pagetable. Only to then
2306 * (c) clean the page again and return 1 to
2307 * cause the writeback.
2308 *
2309 * This way we avoid all nasty races with the
2310 * dirty bit in multiple places and clearing
2311 * them concurrently from different threads.
2312 *
2313 * Note! Normally the "set_page_dirty(page)"
2314 * has no effect on the actual dirty bit - since
2315 * that will already usually be set. But we
2316 * need the side effects, and it can help us
2317 * avoid races.
2318 *
2319 * We basically use the page "master dirty bit"
2320 * as a serialization point for all the different
2321 * threads doing their things.
Linus Torvalds7658cc22006-12-29 10:00:58 -08002322 */
2323 if (page_mkclean(page))
2324 set_page_dirty(page);
Nick Piggin79352892007-07-19 01:47:22 -07002325 /*
2326 * We carefully synchronise fault handlers against
2327 * installing a dirty pte and marking the page dirty
2328 * at this point. We do this by having them hold the
2329 * page lock at some point after installing their
2330 * pte, but before marking the page dirty.
2331 * Pages are always locked coming in here, so we get
2332 * the desired exclusion. See mm/memory.c:do_wp_page()
2333 * for more comments.
2334 */
Linus Torvalds7658cc22006-12-29 10:00:58 -08002335 if (TestClearPageDirty(page)) {
Andrew Morton8c085402006-12-10 02:19:24 -08002336 dec_zone_page_state(page, NR_FILE_DIRTY);
Peter Zijlstrac9e51e42007-10-16 23:25:47 -07002337 dec_bdi_stat(mapping->backing_dev_info,
2338 BDI_RECLAIMABLE);
Linus Torvalds7658cc22006-12-29 10:00:58 -08002339 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002340 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08002341 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002342 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08002343 return TestClearPageDirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002344}
Hans Reiser58bb01a2005-11-18 01:10:53 -08002345EXPORT_SYMBOL(clear_page_dirty_for_io);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002346
2347int test_clear_page_writeback(struct page *page)
2348{
2349 struct address_space *mapping = page_mapping(page);
2350 int ret;
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002351 bool locked;
2352 unsigned long memcg_flags;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002353
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002354 mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002355 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002356 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002357 unsigned long flags;
2358
Nick Piggin19fd6232008-07-25 19:45:32 -07002359 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002360 ret = TestClearPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002361 if (ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07002362 radix_tree_tag_clear(&mapping->page_tree,
2363 page_index(page),
2364 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07002365 if (bdi_cap_account_writeback(bdi)) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002366 __dec_bdi_stat(bdi, BDI_WRITEBACK);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07002367 __bdi_writeout_inc(bdi);
2368 }
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002369 }
Nick Piggin19fd6232008-07-25 19:45:32 -07002370 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002371 } else {
2372 ret = TestClearPageWriteback(page);
2373 }
Wu Fengguang99b12e32011-07-25 17:12:37 -07002374 if (ret) {
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002375 mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
Andrew Mortond688abf2007-07-19 01:49:17 -07002376 dec_zone_page_state(page, NR_WRITEBACK);
Wu Fengguang99b12e32011-07-25 17:12:37 -07002377 inc_zone_page_state(page, NR_WRITTEN);
2378 }
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002379 mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002380 return ret;
2381}
2382
Namjae Jeon1c8349a2014-05-12 08:12:25 -04002383int __test_set_page_writeback(struct page *page, bool keep_write)
Linus Torvalds1da177e2005-04-16 15:20:36 -07002384{
2385 struct address_space *mapping = page_mapping(page);
2386 int ret;
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002387 bool locked;
2388 unsigned long memcg_flags;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002389
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002390 mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002391 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002392 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002393 unsigned long flags;
2394
Nick Piggin19fd6232008-07-25 19:45:32 -07002395 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002396 ret = TestSetPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002397 if (!ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07002398 radix_tree_tag_set(&mapping->page_tree,
2399 page_index(page),
2400 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07002401 if (bdi_cap_account_writeback(bdi))
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002402 __inc_bdi_stat(bdi, BDI_WRITEBACK);
2403 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002404 if (!PageDirty(page))
2405 radix_tree_tag_clear(&mapping->page_tree,
2406 page_index(page),
2407 PAGECACHE_TAG_DIRTY);
Namjae Jeon1c8349a2014-05-12 08:12:25 -04002408 if (!keep_write)
2409 radix_tree_tag_clear(&mapping->page_tree,
2410 page_index(page),
2411 PAGECACHE_TAG_TOWRITE);
Nick Piggin19fd6232008-07-25 19:45:32 -07002412 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002413 } else {
2414 ret = TestSetPageWriteback(page);
2415 }
Andrew Mortond688abf2007-07-19 01:49:17 -07002416 if (!ret)
Michael Rubinf629d1c2010-10-26 14:21:33 -07002417 account_page_writeback(page);
Sha Zhengju3ea67d02013-09-12 15:13:53 -07002418 mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002419 return ret;
2420
2421}
Namjae Jeon1c8349a2014-05-12 08:12:25 -04002422EXPORT_SYMBOL(__test_set_page_writeback);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002423
2424/*
Nick Piggin00128182007-10-16 01:24:40 -07002425 * Return true if any of the pages in the mapping are marked with the
Linus Torvalds1da177e2005-04-16 15:20:36 -07002426 * passed tag.
2427 */
2428int mapping_tagged(struct address_space *mapping, int tag)
2429{
Konstantin Khlebnikov72c47832011-07-25 17:12:31 -07002430 return radix_tree_tagged(&mapping->page_tree, tag);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002431}
2432EXPORT_SYMBOL(mapping_tagged);
Darrick J. Wong1d1d1a72013-02-21 16:42:51 -08002433
2434/**
2435 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2436 * @page: The page to wait on.
2437 *
2438 * This function determines if the given page is related to a backing device
2439 * that requires page contents to be held stable during writeback. If so, then
2440 * it will wait for any pending writeback to complete.
2441 */
2442void wait_for_stable_page(struct page *page)
2443{
2444 struct address_space *mapping = page_mapping(page);
2445 struct backing_dev_info *bdi = mapping->backing_dev_info;
2446
2447 if (!bdi_cap_stable_pages_required(bdi))
2448 return;
2449
2450 wait_on_page_writeback(page);
2451}
2452EXPORT_SYMBOL_GPL(wait_for_stable_page);