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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{
David Rientjes9ef0a0f2014-08-06 16:07:31 -0700264 const unsigned long available_memory = global_dirtyable_memory();
Johannes Weinerccafa282012-01-10 15:07:44 -0800265 unsigned long background;
266 unsigned long dirty;
Johannes Weinerccafa282012-01-10 15:07:44 -0800267 struct task_struct *tsk;
268
Johannes Weinerccafa282012-01-10 15:07:44 -0800269 if (vm_dirty_bytes)
270 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
271 else
272 dirty = (vm_dirty_ratio * available_memory) / 100;
273
274 if (dirty_background_bytes)
275 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
276 else
277 background = (dirty_background_ratio * available_memory) / 100;
278
279 if (background >= dirty)
280 background = dirty / 2;
281 tsk = current;
282 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
283 background += background / 4;
284 dirty += dirty / 4;
285 }
286 *pbackground = background;
287 *pdirty = dirty;
288 trace_global_dirty_state(background, dirty);
289}
290
Johannes Weinera756cf52012-01-10 15:07:49 -0800291/**
Johannes Weinera756cf52012-01-10 15:07:49 -0800292 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
293 * @zone: the zone
294 *
295 * Returns the maximum number of dirty pages allowed in a zone, based
296 * on the zone's dirtyable memory.
297 */
298static unsigned long zone_dirty_limit(struct zone *zone)
299{
300 unsigned long zone_memory = zone_dirtyable_memory(zone);
301 struct task_struct *tsk = current;
302 unsigned long dirty;
303
304 if (vm_dirty_bytes)
305 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
306 zone_memory / global_dirtyable_memory();
307 else
308 dirty = vm_dirty_ratio * zone_memory / 100;
309
310 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
311 dirty += dirty / 4;
312
313 return dirty;
314}
315
316/**
317 * zone_dirty_ok - tells whether a zone is within its dirty limits
318 * @zone: the zone to check
319 *
320 * Returns %true when the dirty pages in @zone are within the zone's
321 * dirty limit, %false if the limit is exceeded.
322 */
323bool zone_dirty_ok(struct zone *zone)
324{
325 unsigned long limit = zone_dirty_limit(zone);
326
327 return zone_page_state(zone, NR_FILE_DIRTY) +
328 zone_page_state(zone, NR_UNSTABLE_NFS) +
329 zone_page_state(zone, NR_WRITEBACK) <= limit;
330}
331
David Rientjes2da02992009-01-06 14:39:31 -0800332int dirty_background_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700333 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800334 loff_t *ppos)
335{
336 int ret;
337
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700338 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800339 if (ret == 0 && write)
340 dirty_background_bytes = 0;
341 return ret;
342}
343
344int dirty_background_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700345 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800346 loff_t *ppos)
347{
348 int ret;
349
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700350 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800351 if (ret == 0 && write)
352 dirty_background_ratio = 0;
353 return ret;
354}
355
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700356int dirty_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700357 void __user *buffer, size_t *lenp,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700358 loff_t *ppos)
359{
360 int old_ratio = vm_dirty_ratio;
David Rientjes2da02992009-01-06 14:39:31 -0800361 int ret;
362
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700363 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700364 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
Jan Karaeb608e32012-05-24 18:59:11 +0200365 writeback_set_ratelimit();
David Rientjes2da02992009-01-06 14:39:31 -0800366 vm_dirty_bytes = 0;
367 }
368 return ret;
369}
370
David Rientjes2da02992009-01-06 14:39:31 -0800371int dirty_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700372 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800373 loff_t *ppos)
374{
Sven Wegenerfc3501d2009-02-11 13:04:23 -0800375 unsigned long old_bytes = vm_dirty_bytes;
David Rientjes2da02992009-01-06 14:39:31 -0800376 int ret;
377
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700378 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800379 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
Jan Karaeb608e32012-05-24 18:59:11 +0200380 writeback_set_ratelimit();
David Rientjes2da02992009-01-06 14:39:31 -0800381 vm_dirty_ratio = 0;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700382 }
383 return ret;
384}
385
Jan Karaeb608e32012-05-24 18:59:11 +0200386static unsigned long wp_next_time(unsigned long cur_time)
387{
388 cur_time += VM_COMPLETIONS_PERIOD_LEN;
389 /* 0 has a special meaning... */
390 if (!cur_time)
391 return 1;
392 return cur_time;
393}
394
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700395/*
396 * Increment the BDI's writeout completion count and the global writeout
397 * completion count. Called from test_clear_page_writeback().
398 */
399static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
400{
Jan Karaf7d2b1e2010-12-08 22:44:24 -0600401 __inc_bdi_stat(bdi, BDI_WRITTEN);
Jan Karaeb608e32012-05-24 18:59:11 +0200402 __fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
403 bdi->max_prop_frac);
404 /* First event after period switching was turned off? */
405 if (!unlikely(writeout_period_time)) {
406 /*
407 * We can race with other __bdi_writeout_inc calls here but
408 * it does not cause any harm since the resulting time when
409 * timer will fire and what is in writeout_period_time will be
410 * roughly the same.
411 */
412 writeout_period_time = wp_next_time(jiffies);
413 mod_timer(&writeout_period_timer, writeout_period_time);
414 }
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700415}
416
Miklos Szeredidd5656e2008-04-30 00:54:37 -0700417void bdi_writeout_inc(struct backing_dev_info *bdi)
418{
419 unsigned long flags;
420
421 local_irq_save(flags);
422 __bdi_writeout_inc(bdi);
423 local_irq_restore(flags);
424}
425EXPORT_SYMBOL_GPL(bdi_writeout_inc);
426
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700427/*
428 * Obtain an accurate fraction of the BDI's portion.
429 */
430static void bdi_writeout_fraction(struct backing_dev_info *bdi,
431 long *numerator, long *denominator)
432{
Jan Karaeb608e32012-05-24 18:59:11 +0200433 fprop_fraction_percpu(&writeout_completions, &bdi->completions,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700434 numerator, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700435}
436
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700437/*
Jan Karaeb608e32012-05-24 18:59:11 +0200438 * On idle system, we can be called long after we scheduled because we use
439 * deferred timers so count with missed periods.
440 */
441static void writeout_period(unsigned long t)
442{
443 int miss_periods = (jiffies - writeout_period_time) /
444 VM_COMPLETIONS_PERIOD_LEN;
445
446 if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
447 writeout_period_time = wp_next_time(writeout_period_time +
448 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
449 mod_timer(&writeout_period_timer, writeout_period_time);
450 } else {
451 /*
452 * Aging has zeroed all fractions. Stop wasting CPU on period
453 * updates.
454 */
455 writeout_period_time = 0;
456 }
457}
458
459/*
Johannes Weinerd08c4292011-10-31 17:07:05 -0700460 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
461 * registered backing devices, which, for obvious reasons, can not
462 * exceed 100%.
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700463 */
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700464static unsigned int bdi_min_ratio;
465
466int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
467{
468 int ret = 0;
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700469
Jens Axboecfc4ba52009-09-14 13:12:40 +0200470 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700471 if (min_ratio > bdi->max_ratio) {
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700472 ret = -EINVAL;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700473 } else {
474 min_ratio -= bdi->min_ratio;
475 if (bdi_min_ratio + min_ratio < 100) {
476 bdi_min_ratio += min_ratio;
477 bdi->min_ratio += min_ratio;
478 } else {
479 ret = -EINVAL;
480 }
481 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200482 spin_unlock_bh(&bdi_lock);
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700483
484 return ret;
485}
486
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700487int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
488{
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700489 int ret = 0;
490
491 if (max_ratio > 100)
492 return -EINVAL;
493
Jens Axboecfc4ba52009-09-14 13:12:40 +0200494 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700495 if (bdi->min_ratio > max_ratio) {
496 ret = -EINVAL;
497 } else {
498 bdi->max_ratio = max_ratio;
Jan Karaeb608e32012-05-24 18:59:11 +0200499 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700500 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200501 spin_unlock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700502
503 return ret;
504}
505EXPORT_SYMBOL(bdi_set_max_ratio);
506
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600507static unsigned long dirty_freerun_ceiling(unsigned long thresh,
508 unsigned long bg_thresh)
509{
510 return (thresh + bg_thresh) / 2;
511}
512
Wu Fengguangffd1f602011-06-19 22:18:42 -0600513static unsigned long hard_dirty_limit(unsigned long thresh)
514{
515 return max(thresh, global_dirty_limit);
516}
517
Wu Fengguang6f718652011-03-02 17:14:34 -0600518/**
Wu Fengguang1babe182010-08-11 14:17:40 -0700519 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
Wu Fengguang6f718652011-03-02 17:14:34 -0600520 * @bdi: the backing_dev_info to query
521 * @dirty: global dirty limit in pages
Wu Fengguang1babe182010-08-11 14:17:40 -0700522 *
Wu Fengguang6f718652011-03-02 17:14:34 -0600523 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
524 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
Wu Fengguangaed21ad2011-11-23 11:44:41 -0600525 *
526 * Note that balance_dirty_pages() will only seriously take it as a hard limit
527 * when sleeping max_pause per page is not enough to keep the dirty pages under
528 * control. For example, when the device is completely stalled due to some error
529 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
530 * In the other normal situations, it acts more gently by throttling the tasks
531 * more (rather than completely block them) when the bdi dirty pages go high.
Wu Fengguang6f718652011-03-02 17:14:34 -0600532 *
533 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
Wu Fengguang1babe182010-08-11 14:17:40 -0700534 * - starving fast devices
535 * - piling up dirty pages (that will take long time to sync) on slow devices
536 *
537 * The bdi's share of dirty limit will be adapting to its throughput and
538 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
539 */
540unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
Wu Fengguang16c40422010-08-11 14:17:39 -0700541{
542 u64 bdi_dirty;
543 long numerator, denominator;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700544
Wu Fengguang16c40422010-08-11 14:17:39 -0700545 /*
546 * Calculate this BDI's share of the dirty ratio.
547 */
548 bdi_writeout_fraction(bdi, &numerator, &denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700549
Wu Fengguang16c40422010-08-11 14:17:39 -0700550 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
551 bdi_dirty *= numerator;
552 do_div(bdi_dirty, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700553
Wu Fengguang16c40422010-08-11 14:17:39 -0700554 bdi_dirty += (dirty * bdi->min_ratio) / 100;
555 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
556 bdi_dirty = dirty * bdi->max_ratio / 100;
557
558 return bdi_dirty;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700559}
560
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600561/*
Maxim Patlasov5a537482013-09-11 14:22:46 -0700562 * setpoint - dirty 3
563 * f(dirty) := 1.0 + (----------------)
564 * limit - setpoint
565 *
566 * it's a 3rd order polynomial that subjects to
567 *
568 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
569 * (2) f(setpoint) = 1.0 => the balance point
570 * (3) f(limit) = 0 => the hard limit
571 * (4) df/dx <= 0 => negative feedback control
572 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
573 * => fast response on large errors; small oscillation near setpoint
574 */
Rik van Rield5c9fde2014-05-06 12:50:01 -0700575static long long pos_ratio_polynom(unsigned long setpoint,
Maxim Patlasov5a537482013-09-11 14:22:46 -0700576 unsigned long dirty,
577 unsigned long limit)
578{
579 long long pos_ratio;
580 long x;
581
Rik van Rield5c9fde2014-05-06 12:50:01 -0700582 x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
Tejun Heo464d1382015-04-21 16:49:13 -0400583 (limit - setpoint) | 1);
Maxim Patlasov5a537482013-09-11 14:22:46 -0700584 pos_ratio = x;
585 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
586 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
587 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
588
589 return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
590}
591
592/*
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600593 * Dirty position control.
594 *
595 * (o) global/bdi setpoints
596 *
597 * We want the dirty pages be balanced around the global/bdi setpoints.
598 * When the number of dirty pages is higher/lower than the setpoint, the
599 * dirty position control ratio (and hence task dirty ratelimit) will be
600 * decreased/increased to bring the dirty pages back to the setpoint.
601 *
602 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
603 *
604 * if (dirty < setpoint) scale up pos_ratio
605 * if (dirty > setpoint) scale down pos_ratio
606 *
607 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
608 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
609 *
610 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
611 *
612 * (o) global control line
613 *
614 * ^ pos_ratio
615 * |
616 * | |<===== global dirty control scope ======>|
617 * 2.0 .............*
618 * | .*
619 * | . *
620 * | . *
621 * | . *
622 * | . *
623 * | . *
624 * 1.0 ................................*
625 * | . . *
626 * | . . *
627 * | . . *
628 * | . . *
629 * | . . *
630 * 0 +------------.------------------.----------------------*------------->
631 * freerun^ setpoint^ limit^ dirty pages
632 *
633 * (o) bdi control line
634 *
635 * ^ pos_ratio
636 * |
637 * | *
638 * | *
639 * | *
640 * | *
641 * | * |<=========== span ============>|
642 * 1.0 .......................*
643 * | . *
644 * | . *
645 * | . *
646 * | . *
647 * | . *
648 * | . *
649 * | . *
650 * | . *
651 * | . *
652 * | . *
653 * | . *
654 * 1/4 ...............................................* * * * * * * * * * * *
655 * | . .
656 * | . .
657 * | . .
658 * 0 +----------------------.-------------------------------.------------->
659 * bdi_setpoint^ x_intercept^
660 *
661 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
662 * be smoothly throttled down to normal if it starts high in situations like
663 * - start writing to a slow SD card and a fast disk at the same time. The SD
664 * card's bdi_dirty may rush to many times higher than bdi_setpoint.
665 * - the bdi dirty thresh drops quickly due to change of JBOD workload
666 */
667static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
668 unsigned long thresh,
669 unsigned long bg_thresh,
670 unsigned long dirty,
671 unsigned long bdi_thresh,
672 unsigned long bdi_dirty)
673{
674 unsigned long write_bw = bdi->avg_write_bandwidth;
675 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
676 unsigned long limit = hard_dirty_limit(thresh);
677 unsigned long x_intercept;
678 unsigned long setpoint; /* dirty pages' target balance point */
679 unsigned long bdi_setpoint;
680 unsigned long span;
681 long long pos_ratio; /* for scaling up/down the rate limit */
682 long x;
683
684 if (unlikely(dirty >= limit))
685 return 0;
686
687 /*
688 * global setpoint
689 *
Maxim Patlasov5a537482013-09-11 14:22:46 -0700690 * See comment for pos_ratio_polynom().
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600691 */
692 setpoint = (freerun + limit) / 2;
Maxim Patlasov5a537482013-09-11 14:22:46 -0700693 pos_ratio = pos_ratio_polynom(setpoint, dirty, limit);
694
695 /*
696 * The strictlimit feature is a tool preventing mistrusted filesystems
697 * from growing a large number of dirty pages before throttling. For
698 * such filesystems balance_dirty_pages always checks bdi counters
699 * against bdi limits. Even if global "nr_dirty" is under "freerun".
700 * This is especially important for fuse which sets bdi->max_ratio to
701 * 1% by default. Without strictlimit feature, fuse writeback may
702 * consume arbitrary amount of RAM because it is accounted in
703 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
704 *
705 * Here, in bdi_position_ratio(), we calculate pos_ratio based on
706 * two values: bdi_dirty and bdi_thresh. Let's consider an example:
707 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
708 * limits are set by default to 10% and 20% (background and throttle).
709 * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
710 * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
711 * about ~6K pages (as the average of background and throttle bdi
712 * limits). The 3rd order polynomial will provide positive feedback if
713 * bdi_dirty is under bdi_setpoint and vice versa.
714 *
715 * Note, that we cannot use global counters in these calculations
716 * because we want to throttle process writing to a strictlimit BDI
717 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
718 * in the example above).
719 */
720 if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
721 long long bdi_pos_ratio;
722 unsigned long bdi_bg_thresh;
723
724 if (bdi_dirty < 8)
725 return min_t(long long, pos_ratio * 2,
726 2 << RATELIMIT_CALC_SHIFT);
727
728 if (bdi_dirty >= bdi_thresh)
729 return 0;
730
731 bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh);
732 bdi_setpoint = dirty_freerun_ceiling(bdi_thresh,
733 bdi_bg_thresh);
734
735 if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh)
736 return 0;
737
738 bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
739 bdi_thresh);
740
741 /*
742 * Typically, for strictlimit case, bdi_setpoint << setpoint
743 * and pos_ratio >> bdi_pos_ratio. In the other words global
744 * state ("dirty") is not limiting factor and we have to
745 * make decision based on bdi counters. But there is an
746 * important case when global pos_ratio should get precedence:
747 * global limits are exceeded (e.g. due to activities on other
748 * BDIs) while given strictlimit BDI is below limit.
749 *
750 * "pos_ratio * bdi_pos_ratio" would work for the case above,
751 * but it would look too non-natural for the case of all
752 * activity in the system coming from a single strictlimit BDI
753 * with bdi->max_ratio == 100%.
754 *
755 * Note that min() below somewhat changes the dynamics of the
756 * control system. Normally, pos_ratio value can be well over 3
757 * (when globally we are at freerun and bdi is well below bdi
758 * setpoint). Now the maximum pos_ratio in the same situation
759 * is 2. We might want to tweak this if we observe the control
760 * system is too slow to adapt.
761 */
762 return min(pos_ratio, bdi_pos_ratio);
763 }
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600764
765 /*
766 * We have computed basic pos_ratio above based on global situation. If
767 * the bdi is over/under its share of dirty pages, we want to scale
768 * pos_ratio further down/up. That is done by the following mechanism.
769 */
770
771 /*
772 * bdi setpoint
773 *
774 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
775 *
776 * x_intercept - bdi_dirty
777 * := --------------------------
778 * x_intercept - bdi_setpoint
779 *
780 * The main bdi control line is a linear function that subjects to
781 *
782 * (1) f(bdi_setpoint) = 1.0
783 * (2) k = - 1 / (8 * write_bw) (in single bdi case)
784 * or equally: x_intercept = bdi_setpoint + 8 * write_bw
785 *
786 * For single bdi case, the dirty pages are observed to fluctuate
787 * regularly within range
788 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
789 * for various filesystems, where (2) can yield in a reasonable 12.5%
790 * fluctuation range for pos_ratio.
791 *
792 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
793 * own size, so move the slope over accordingly and choose a slope that
794 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
795 */
796 if (unlikely(bdi_thresh > thresh))
797 bdi_thresh = thresh;
Wu Fengguangaed21ad2011-11-23 11:44:41 -0600798 /*
799 * It's very possible that bdi_thresh is close to 0 not because the
800 * device is slow, but that it has remained inactive for long time.
801 * Honour such devices a reasonable good (hopefully IO efficient)
802 * threshold, so that the occasional writes won't be blocked and active
803 * writes can rampup the threshold quickly.
804 */
Wu Fengguang8927f662011-08-04 22:16:46 -0600805 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600806 /*
807 * scale global setpoint to bdi's:
808 * bdi_setpoint = setpoint * bdi_thresh / thresh
809 */
Tejun Heo464d1382015-04-21 16:49:13 -0400810 x = div_u64((u64)bdi_thresh << 16, thresh | 1);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600811 bdi_setpoint = setpoint * (u64)x >> 16;
812 /*
813 * Use span=(8*write_bw) in single bdi case as indicated by
814 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
815 *
816 * bdi_thresh thresh - bdi_thresh
817 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
818 * thresh thresh
819 */
820 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
821 x_intercept = bdi_setpoint + span;
822
823 if (bdi_dirty < x_intercept - span / 4) {
Rik van Rield5c9fde2014-05-06 12:50:01 -0700824 pos_ratio = div64_u64(pos_ratio * (x_intercept - bdi_dirty),
Tejun Heo464d1382015-04-21 16:49:13 -0400825 (x_intercept - bdi_setpoint) | 1);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600826 } else
827 pos_ratio /= 4;
828
Wu Fengguang8927f662011-08-04 22:16:46 -0600829 /*
830 * bdi reserve area, safeguard against dirty pool underrun and disk idle
831 * It may push the desired control point of global dirty pages higher
832 * than setpoint.
833 */
834 x_intercept = bdi_thresh / 2;
835 if (bdi_dirty < x_intercept) {
Wu Fengguang50657fc2011-10-11 17:06:33 -0600836 if (bdi_dirty > x_intercept / 8)
837 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
838 else
Wu Fengguang8927f662011-08-04 22:16:46 -0600839 pos_ratio *= 8;
840 }
841
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600842 return pos_ratio;
843}
844
Wu Fengguange98be2d2010-08-29 11:22:30 -0600845static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
846 unsigned long elapsed,
847 unsigned long written)
848{
849 const unsigned long period = roundup_pow_of_two(3 * HZ);
850 unsigned long avg = bdi->avg_write_bandwidth;
851 unsigned long old = bdi->write_bandwidth;
852 u64 bw;
853
854 /*
855 * bw = written * HZ / elapsed
856 *
857 * bw * elapsed + write_bandwidth * (period - elapsed)
858 * write_bandwidth = ---------------------------------------------------
859 * period
Tejun Heoc72efb62015-03-23 00:18:48 -0400860 *
861 * @written may have decreased due to account_page_redirty().
862 * Avoid underflowing @bw calculation.
Wu Fengguange98be2d2010-08-29 11:22:30 -0600863 */
Tejun Heoc72efb62015-03-23 00:18:48 -0400864 bw = written - min(written, bdi->written_stamp);
Wu Fengguange98be2d2010-08-29 11:22:30 -0600865 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);
Tejun Heo7d70e152015-03-04 10:37:43 -0500928 static unsigned long update_time = INITIAL_JIFFIES;
Wu Fengguangc42843f2011-03-02 15:54:09 -0600929
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) {
Mark Rustad7c809962014-10-09 15:28:15 -07001081 x = min3(bdi->balanced_dirty_ratelimit,
1082 balanced_dirty_ratelimit, task_ratelimit);
Wu Fengguang73811312011-08-26 15:53:24 -06001083 if (dirty_ratelimit < x)
1084 step = x - dirty_ratelimit;
1085 } else {
Mark Rustad7c809962014-10-09 15:28:15 -07001086 x = max3(bdi->balanced_dirty_ratelimit,
1087 balanced_dirty_ratelimit, task_ratelimit);
Wu Fengguang73811312011-08-26 15:53:24 -06001088 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)
Maxim Patlasovf6789592014-07-30 16:08:21 -07001309 *bdi_bg_thresh = dirty_thresh ? div_u64((u64)*bdi_thresh *
1310 background_thresh,
1311 dirty_thresh) : 0;
Maxim Patlasov5a537482013-09-11 14:22:46 -07001312
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;
Christoph Hellwigde1414a2015-01-14 10:42:36 +01001357 struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
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
Wu Fengguang9d823e82011-06-11 18:10:12 -06001547static DEFINE_PER_CPU(int, bdp_ratelimits);
Tejun Heo245b2e72009-06-24 15:13:48 +09001548
Wu Fengguang54848d72011-04-05 13:21:19 -06001549/*
1550 * Normal tasks are throttled by
1551 * loop {
1552 * dirty tsk->nr_dirtied_pause pages;
1553 * take a snap in balance_dirty_pages();
1554 * }
1555 * However there is a worst case. If every task exit immediately when dirtied
1556 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1557 * called to throttle the page dirties. The solution is to save the not yet
1558 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1559 * randomly into the running tasks. This works well for the above worst case,
1560 * as the new task will pick up and accumulate the old task's leaked dirty
1561 * count and eventually get throttled.
1562 */
1563DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1564
Linus Torvalds1da177e2005-04-16 15:20:36 -07001565/**
Namjae Jeond0e1d662012-12-11 16:00:21 -08001566 * balance_dirty_pages_ratelimited - balance dirty memory state
Martin Waitz67be2dd2005-05-01 08:59:26 -07001567 * @mapping: address_space which was dirtied
Linus Torvalds1da177e2005-04-16 15:20:36 -07001568 *
1569 * Processes which are dirtying memory should call in here once for each page
1570 * which was newly dirtied. The function will periodically check the system's
1571 * dirty state and will initiate writeback if needed.
1572 *
1573 * On really big machines, get_writeback_state is expensive, so try to avoid
1574 * calling it too often (ratelimiting). But once we're over the dirty memory
1575 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1576 * from overshooting the limit by (ratelimit_pages) each.
1577 */
Namjae Jeond0e1d662012-12-11 16:00:21 -08001578void balance_dirty_pages_ratelimited(struct address_space *mapping)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001579{
Christoph Hellwigde1414a2015-01-14 10:42:36 +01001580 struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
Wu Fengguang9d823e82011-06-11 18:10:12 -06001581 int ratelimit;
1582 int *p;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001583
Wu Fengguang36715ce2011-06-11 17:53:57 -06001584 if (!bdi_cap_account_dirty(bdi))
1585 return;
1586
Wu Fengguang9d823e82011-06-11 18:10:12 -06001587 ratelimit = current->nr_dirtied_pause;
1588 if (bdi->dirty_exceeded)
1589 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
Linus Torvalds1da177e2005-04-16 15:20:36 -07001590
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001591 preempt_disable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001592 /*
1593 * This prevents one CPU to accumulate too many dirtied pages without
1594 * calling into balance_dirty_pages(), which can happen when there are
1595 * 1000+ tasks, all of them start dirtying pages at exactly the same
1596 * time, hence all honoured too large initial task->nr_dirtied_pause.
1597 */
Christoph Lameter7c8e0182014-06-04 16:07:56 -07001598 p = this_cpu_ptr(&bdp_ratelimits);
Wu Fengguang9d823e82011-06-11 18:10:12 -06001599 if (unlikely(current->nr_dirtied >= ratelimit))
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001600 *p = 0;
Wu Fengguangd3bc1fe2011-04-14 07:52:37 -06001601 else if (unlikely(*p >= ratelimit_pages)) {
1602 *p = 0;
1603 ratelimit = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001604 }
Wu Fengguang54848d72011-04-05 13:21:19 -06001605 /*
1606 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1607 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1608 * the dirty throttling and livelock other long-run dirtiers.
1609 */
Christoph Lameter7c8e0182014-06-04 16:07:56 -07001610 p = this_cpu_ptr(&dirty_throttle_leaks);
Wu Fengguang54848d72011-04-05 13:21:19 -06001611 if (*p > 0 && current->nr_dirtied < ratelimit) {
Namjae Jeond0e1d662012-12-11 16:00:21 -08001612 unsigned long nr_pages_dirtied;
Wu Fengguang54848d72011-04-05 13:21:19 -06001613 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1614 *p -= nr_pages_dirtied;
1615 current->nr_dirtied += nr_pages_dirtied;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001616 }
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001617 preempt_enable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001618
1619 if (unlikely(current->nr_dirtied >= ratelimit))
1620 balance_dirty_pages(mapping, current->nr_dirtied);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001621}
Namjae Jeond0e1d662012-12-11 16:00:21 -08001622EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001623
Andrew Morton232ea4d2007-02-28 20:13:21 -08001624void throttle_vm_writeout(gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001625{
David Rientjes364aeb22009-01-06 14:39:29 -08001626 unsigned long background_thresh;
1627 unsigned long dirty_thresh;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001628
1629 for ( ; ; ) {
Wu Fengguang16c40422010-08-11 14:17:39 -07001630 global_dirty_limits(&background_thresh, &dirty_thresh);
Fengguang Wu47a13332012-03-21 16:34:09 -07001631 dirty_thresh = hard_dirty_limit(dirty_thresh);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001632
1633 /*
1634 * Boost the allowable dirty threshold a bit for page
1635 * allocators so they don't get DoS'ed by heavy writers
1636 */
1637 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1638
Christoph Lameterc24f21b2006-06-30 01:55:42 -07001639 if (global_page_state(NR_UNSTABLE_NFS) +
1640 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1641 break;
Jens Axboe8aa7e842009-07-09 14:52:32 +02001642 congestion_wait(BLK_RW_ASYNC, HZ/10);
Fengguang Wu369f2382007-10-16 23:30:45 -07001643
1644 /*
1645 * The caller might hold locks which can prevent IO completion
1646 * or progress in the filesystem. So we cannot just sit here
1647 * waiting for IO to complete.
1648 */
1649 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1650 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001651 }
1652}
1653
Linus Torvalds1da177e2005-04-16 15:20:36 -07001654/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001655 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1656 */
Joe Perchescccad5b2014-06-06 14:38:09 -07001657int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001658 void __user *buffer, size_t *length, loff_t *ppos)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001659{
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001660 proc_dointvec(table, write, buffer, length, ppos);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001661 return 0;
1662}
1663
Jens Axboec2c49862010-05-20 09:18:47 +02001664#ifdef CONFIG_BLOCK
Matthew Garrett31373d02010-04-06 14:25:14 +02001665void laptop_mode_timer_fn(unsigned long data)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001666{
Matthew Garrett31373d02010-04-06 14:25:14 +02001667 struct request_queue *q = (struct request_queue *)data;
1668 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1669 global_page_state(NR_UNSTABLE_NFS);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001670
Matthew Garrett31373d02010-04-06 14:25:14 +02001671 /*
1672 * We want to write everything out, not just down to the dirty
1673 * threshold
1674 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001675 if (bdi_has_dirty_io(&q->backing_dev_info))
Curt Wohlgemuth0e175a12011-10-07 21:54:10 -06001676 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1677 WB_REASON_LAPTOP_TIMER);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001678}
1679
1680/*
1681 * We've spun up the disk and we're in laptop mode: schedule writeback
1682 * of all dirty data a few seconds from now. If the flush is already scheduled
1683 * then push it back - the user is still using the disk.
1684 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001685void laptop_io_completion(struct backing_dev_info *info)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001686{
Matthew Garrett31373d02010-04-06 14:25:14 +02001687 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001688}
1689
1690/*
1691 * We're in laptop mode and we've just synced. The sync's writes will have
1692 * caused another writeback to be scheduled by laptop_io_completion.
1693 * Nothing needs to be written back anymore, so we unschedule the writeback.
1694 */
1695void laptop_sync_completion(void)
1696{
Matthew Garrett31373d02010-04-06 14:25:14 +02001697 struct backing_dev_info *bdi;
1698
1699 rcu_read_lock();
1700
1701 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1702 del_timer(&bdi->laptop_mode_wb_timer);
1703
1704 rcu_read_unlock();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001705}
Jens Axboec2c49862010-05-20 09:18:47 +02001706#endif
Linus Torvalds1da177e2005-04-16 15:20:36 -07001707
1708/*
1709 * If ratelimit_pages is too high then we can get into dirty-data overload
1710 * if a large number of processes all perform writes at the same time.
1711 * If it is too low then SMP machines will call the (expensive)
1712 * get_writeback_state too often.
1713 *
1714 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1715 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
Wu Fengguang9d823e82011-06-11 18:10:12 -06001716 * thresholds.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001717 */
1718
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001719void writeback_set_ratelimit(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001720{
Wu Fengguang9d823e82011-06-11 18:10:12 -06001721 unsigned long background_thresh;
1722 unsigned long dirty_thresh;
1723 global_dirty_limits(&background_thresh, &dirty_thresh);
Fengguang Wu68809c72012-05-06 13:21:42 +08001724 global_dirty_limit = dirty_thresh;
Wu Fengguang9d823e82011-06-11 18:10:12 -06001725 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001726 if (ratelimit_pages < 16)
1727 ratelimit_pages = 16;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001728}
1729
Paul Gortmaker0db06282013-06-19 14:53:51 -04001730static int
Srivatsa S. Bhat2f60d622012-09-28 20:27:49 +08001731ratelimit_handler(struct notifier_block *self, unsigned long action,
1732 void *hcpu)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001733{
Srivatsa S. Bhat2f60d622012-09-28 20:27:49 +08001734
1735 switch (action & ~CPU_TASKS_FROZEN) {
1736 case CPU_ONLINE:
1737 case CPU_DEAD:
1738 writeback_set_ratelimit();
1739 return NOTIFY_OK;
1740 default:
1741 return NOTIFY_DONE;
1742 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07001743}
1744
Paul Gortmaker0db06282013-06-19 14:53:51 -04001745static struct notifier_block ratelimit_nb = {
Linus Torvalds1da177e2005-04-16 15:20:36 -07001746 .notifier_call = ratelimit_handler,
1747 .next = NULL,
1748};
1749
1750/*
Linus Torvaldsdc6e29d2007-01-29 16:37:38 -08001751 * Called early on to tune the page writeback dirty limits.
1752 *
1753 * We used to scale dirty pages according to how total memory
1754 * related to pages that could be allocated for buffers (by
1755 * comparing nr_free_buffer_pages() to vm_total_pages.
1756 *
1757 * However, that was when we used "dirty_ratio" to scale with
1758 * all memory, and we don't do that any more. "dirty_ratio"
1759 * is now applied to total non-HIGHPAGE memory (by subtracting
1760 * totalhigh_pages from vm_total_pages), and as such we can't
1761 * get into the old insane situation any more where we had
1762 * large amounts of dirty pages compared to a small amount of
1763 * non-HIGHMEM memory.
1764 *
1765 * But we might still want to scale the dirty_ratio by how
1766 * much memory the box has..
Linus Torvalds1da177e2005-04-16 15:20:36 -07001767 */
1768void __init page_writeback_init(void)
1769{
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001770 writeback_set_ratelimit();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001771 register_cpu_notifier(&ratelimit_nb);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001772
Tejun Heo20ae0072014-09-08 09:51:30 +09001773 fprop_global_init(&writeout_completions, GFP_KERNEL);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001774}
1775
David Howells811d7362006-08-29 19:06:09 +01001776/**
Jan Karaf446daae2010-08-09 17:19:12 -07001777 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1778 * @mapping: address space structure to write
1779 * @start: starting page index
1780 * @end: ending page index (inclusive)
1781 *
1782 * This function scans the page range from @start to @end (inclusive) and tags
1783 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1784 * that write_cache_pages (or whoever calls this function) will then use
1785 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1786 * used to avoid livelocking of writeback by a process steadily creating new
1787 * dirty pages in the file (thus it is important for this function to be quick
1788 * so that it can tag pages faster than a dirtying process can create them).
1789 */
1790/*
1791 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1792 */
Jan Karaf446daae2010-08-09 17:19:12 -07001793void tag_pages_for_writeback(struct address_space *mapping,
1794 pgoff_t start, pgoff_t end)
1795{
Randy Dunlap3c111a02010-08-11 14:17:30 -07001796#define WRITEBACK_TAG_BATCH 4096
Jan Karaf446daae2010-08-09 17:19:12 -07001797 unsigned long tagged;
1798
1799 do {
1800 spin_lock_irq(&mapping->tree_lock);
1801 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1802 &start, end, WRITEBACK_TAG_BATCH,
1803 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1804 spin_unlock_irq(&mapping->tree_lock);
1805 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1806 cond_resched();
Jan Karad5ed3a42010-08-19 14:13:33 -07001807 /* We check 'start' to handle wrapping when end == ~0UL */
1808 } while (tagged >= WRITEBACK_TAG_BATCH && start);
Jan Karaf446daae2010-08-09 17:19:12 -07001809}
1810EXPORT_SYMBOL(tag_pages_for_writeback);
1811
1812/**
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001813 * 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 +01001814 * @mapping: address space structure to write
1815 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001816 * @writepage: function called for each page
1817 * @data: data passed to writepage function
David Howells811d7362006-08-29 19:06:09 +01001818 *
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001819 * If a page is already under I/O, write_cache_pages() skips it, even
David Howells811d7362006-08-29 19:06:09 +01001820 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1821 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1822 * and msync() need to guarantee that all the data which was dirty at the time
1823 * the call was made get new I/O started against them. If wbc->sync_mode is
1824 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1825 * existing IO to complete.
Jan Karaf446daae2010-08-09 17:19:12 -07001826 *
1827 * To avoid livelocks (when other process dirties new pages), we first tag
1828 * pages which should be written back with TOWRITE tag and only then start
1829 * writing them. For data-integrity sync we have to be careful so that we do
1830 * not miss some pages (e.g., because some other process has cleared TOWRITE
1831 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1832 * by the process clearing the DIRTY tag (and submitting the page for IO).
David Howells811d7362006-08-29 19:06:09 +01001833 */
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001834int write_cache_pages(struct address_space *mapping,
1835 struct writeback_control *wbc, writepage_t writepage,
1836 void *data)
David Howells811d7362006-08-29 19:06:09 +01001837{
David Howells811d7362006-08-29 19:06:09 +01001838 int ret = 0;
1839 int done = 0;
David Howells811d7362006-08-29 19:06:09 +01001840 struct pagevec pvec;
1841 int nr_pages;
Nick Piggin31a12662009-01-06 14:39:04 -08001842 pgoff_t uninitialized_var(writeback_index);
David Howells811d7362006-08-29 19:06:09 +01001843 pgoff_t index;
1844 pgoff_t end; /* Inclusive */
Nick Pigginbd19e012009-01-06 14:39:06 -08001845 pgoff_t done_index;
Nick Piggin31a12662009-01-06 14:39:04 -08001846 int cycled;
David Howells811d7362006-08-29 19:06:09 +01001847 int range_whole = 0;
Jan Karaf446daae2010-08-09 17:19:12 -07001848 int tag;
David Howells811d7362006-08-29 19:06:09 +01001849
David Howells811d7362006-08-29 19:06:09 +01001850 pagevec_init(&pvec, 0);
1851 if (wbc->range_cyclic) {
Nick Piggin31a12662009-01-06 14:39:04 -08001852 writeback_index = mapping->writeback_index; /* prev offset */
1853 index = writeback_index;
1854 if (index == 0)
1855 cycled = 1;
1856 else
1857 cycled = 0;
David Howells811d7362006-08-29 19:06:09 +01001858 end = -1;
1859 } else {
1860 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1861 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1862 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1863 range_whole = 1;
Nick Piggin31a12662009-01-06 14:39:04 -08001864 cycled = 1; /* ignore range_cyclic tests */
David Howells811d7362006-08-29 19:06:09 +01001865 }
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001866 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daae2010-08-09 17:19:12 -07001867 tag = PAGECACHE_TAG_TOWRITE;
1868 else
1869 tag = PAGECACHE_TAG_DIRTY;
David Howells811d7362006-08-29 19:06:09 +01001870retry:
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001871 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daae2010-08-09 17:19:12 -07001872 tag_pages_for_writeback(mapping, index, end);
Nick Pigginbd19e012009-01-06 14:39:06 -08001873 done_index = index;
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001874 while (!done && (index <= end)) {
1875 int i;
1876
Jan Karaf446daae2010-08-09 17:19:12 -07001877 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001878 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1879 if (nr_pages == 0)
1880 break;
David Howells811d7362006-08-29 19:06:09 +01001881
David Howells811d7362006-08-29 19:06:09 +01001882 for (i = 0; i < nr_pages; i++) {
1883 struct page *page = pvec.pages[i];
1884
Nick Piggind5482cd2009-01-06 14:39:11 -08001885 /*
1886 * At this point, the page may be truncated or
1887 * invalidated (changing page->mapping to NULL), or
1888 * even swizzled back from swapper_space to tmpfs file
1889 * mapping. However, page->index will not change
1890 * because we have a reference on the page.
1891 */
1892 if (page->index > end) {
1893 /*
1894 * can't be range_cyclic (1st pass) because
1895 * end == -1 in that case.
1896 */
1897 done = 1;
1898 break;
1899 }
1900
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001901 done_index = page->index;
Nick Pigginbd19e012009-01-06 14:39:06 -08001902
David Howells811d7362006-08-29 19:06:09 +01001903 lock_page(page);
1904
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001905 /*
1906 * Page truncated or invalidated. We can freely skip it
1907 * then, even for data integrity operations: the page
1908 * has disappeared concurrently, so there could be no
1909 * real expectation of this data interity operation
1910 * even if there is now a new, dirty page at the same
1911 * pagecache address.
1912 */
David Howells811d7362006-08-29 19:06:09 +01001913 if (unlikely(page->mapping != mapping)) {
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001914continue_unlock:
David Howells811d7362006-08-29 19:06:09 +01001915 unlock_page(page);
1916 continue;
1917 }
1918
Nick Piggin515f4a02009-01-06 14:39:10 -08001919 if (!PageDirty(page)) {
1920 /* someone wrote it for us */
1921 goto continue_unlock;
1922 }
David Howells811d7362006-08-29 19:06:09 +01001923
Nick Piggin515f4a02009-01-06 14:39:10 -08001924 if (PageWriteback(page)) {
1925 if (wbc->sync_mode != WB_SYNC_NONE)
1926 wait_on_page_writeback(page);
1927 else
1928 goto continue_unlock;
1929 }
1930
1931 BUG_ON(PageWriteback(page));
1932 if (!clear_page_dirty_for_io(page))
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001933 goto continue_unlock;
David Howells811d7362006-08-29 19:06:09 +01001934
Christoph Hellwigde1414a2015-01-14 10:42:36 +01001935 trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001936 ret = (*writepage)(page, wbc, data);
Nick Piggin00266772009-01-06 14:39:06 -08001937 if (unlikely(ret)) {
1938 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1939 unlock_page(page);
1940 ret = 0;
1941 } else {
1942 /*
1943 * done_index is set past this page,
1944 * so media errors will not choke
1945 * background writeout for the entire
1946 * file. This has consequences for
1947 * range_cyclic semantics (ie. it may
1948 * not be suitable for data integrity
1949 * writeout).
1950 */
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001951 done_index = page->index + 1;
Nick Piggin00266772009-01-06 14:39:06 -08001952 done = 1;
1953 break;
1954 }
Dave Chinner0b564922010-06-09 10:37:18 +10001955 }
David Howells811d7362006-08-29 19:06:09 +01001956
Dave Chinner546a1922010-08-24 11:44:34 +10001957 /*
1958 * We stop writing back only if we are not doing
1959 * integrity sync. In case of integrity sync we have to
1960 * keep going until we have written all the pages
1961 * we tagged for writeback prior to entering this loop.
1962 */
1963 if (--wbc->nr_to_write <= 0 &&
1964 wbc->sync_mode == WB_SYNC_NONE) {
1965 done = 1;
1966 break;
Nick Piggin05fe4782009-01-06 14:39:08 -08001967 }
David Howells811d7362006-08-29 19:06:09 +01001968 }
1969 pagevec_release(&pvec);
1970 cond_resched();
1971 }
Nick Piggin3a4c6802009-02-12 04:34:23 +01001972 if (!cycled && !done) {
David Howells811d7362006-08-29 19:06:09 +01001973 /*
Nick Piggin31a12662009-01-06 14:39:04 -08001974 * range_cyclic:
David Howells811d7362006-08-29 19:06:09 +01001975 * We hit the last page and there is more work to be done: wrap
1976 * back to the start of the file
1977 */
Nick Piggin31a12662009-01-06 14:39:04 -08001978 cycled = 1;
David Howells811d7362006-08-29 19:06:09 +01001979 index = 0;
Nick Piggin31a12662009-01-06 14:39:04 -08001980 end = writeback_index - 1;
David Howells811d7362006-08-29 19:06:09 +01001981 goto retry;
1982 }
Dave Chinner0b564922010-06-09 10:37:18 +10001983 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1984 mapping->writeback_index = done_index;
Aneesh Kumar K.V06d6cf62008-07-11 19:27:31 -04001985
David Howells811d7362006-08-29 19:06:09 +01001986 return ret;
1987}
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001988EXPORT_SYMBOL(write_cache_pages);
1989
1990/*
1991 * Function used by generic_writepages to call the real writepage
1992 * function and set the mapping flags on error
1993 */
1994static int __writepage(struct page *page, struct writeback_control *wbc,
1995 void *data)
1996{
1997 struct address_space *mapping = data;
1998 int ret = mapping->a_ops->writepage(page, wbc);
1999 mapping_set_error(mapping, ret);
2000 return ret;
2001}
2002
2003/**
2004 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2005 * @mapping: address space structure to write
2006 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2007 *
2008 * This is a library function, which implements the writepages()
2009 * address_space_operation.
2010 */
2011int generic_writepages(struct address_space *mapping,
2012 struct writeback_control *wbc)
2013{
Shaohua Li9b6096a2011-03-17 10:47:06 +01002014 struct blk_plug plug;
2015 int ret;
2016
Miklos Szeredi0ea97182007-05-10 22:22:51 -07002017 /* deal with chardevs and other special file */
2018 if (!mapping->a_ops->writepage)
2019 return 0;
2020
Shaohua Li9b6096a2011-03-17 10:47:06 +01002021 blk_start_plug(&plug);
2022 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2023 blk_finish_plug(&plug);
2024 return ret;
Miklos Szeredi0ea97182007-05-10 22:22:51 -07002025}
David Howells811d7362006-08-29 19:06:09 +01002026
2027EXPORT_SYMBOL(generic_writepages);
2028
Linus Torvalds1da177e2005-04-16 15:20:36 -07002029int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2030{
Andrew Morton22905f72005-11-16 15:07:01 -08002031 int ret;
2032
Linus Torvalds1da177e2005-04-16 15:20:36 -07002033 if (wbc->nr_to_write <= 0)
2034 return 0;
2035 if (mapping->a_ops->writepages)
Peter Zijlstrad08b3852006-09-25 23:30:57 -07002036 ret = mapping->a_ops->writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08002037 else
2038 ret = generic_writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08002039 return ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002040}
2041
2042/**
2043 * write_one_page - write out a single page and optionally wait on I/O
Martin Waitz67be2dd2005-05-01 08:59:26 -07002044 * @page: the page to write
2045 * @wait: if true, wait on writeout
Linus Torvalds1da177e2005-04-16 15:20:36 -07002046 *
2047 * The page must be locked by the caller and will be unlocked upon return.
2048 *
2049 * write_one_page() returns a negative error code if I/O failed.
2050 */
2051int write_one_page(struct page *page, int wait)
2052{
2053 struct address_space *mapping = page->mapping;
2054 int ret = 0;
2055 struct writeback_control wbc = {
2056 .sync_mode = WB_SYNC_ALL,
2057 .nr_to_write = 1,
2058 };
2059
2060 BUG_ON(!PageLocked(page));
2061
2062 if (wait)
2063 wait_on_page_writeback(page);
2064
2065 if (clear_page_dirty_for_io(page)) {
2066 page_cache_get(page);
2067 ret = mapping->a_ops->writepage(page, &wbc);
2068 if (ret == 0 && wait) {
2069 wait_on_page_writeback(page);
2070 if (PageError(page))
2071 ret = -EIO;
2072 }
2073 page_cache_release(page);
2074 } else {
2075 unlock_page(page);
2076 }
2077 return ret;
2078}
2079EXPORT_SYMBOL(write_one_page);
2080
2081/*
Ken Chen76719322007-02-10 01:43:15 -08002082 * For address_spaces which do not use buffers nor write back.
2083 */
2084int __set_page_dirty_no_writeback(struct page *page)
2085{
2086 if (!PageDirty(page))
Bob Liuc3f0da62011-01-13 15:45:49 -08002087 return !TestSetPageDirty(page);
Ken Chen76719322007-02-10 01:43:15 -08002088 return 0;
2089}
2090
2091/*
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002092 * Helper function for set_page_dirty family.
2093 * NOTE: This relies on being atomic wrt interrupts.
2094 */
2095void account_page_dirtied(struct page *page, struct address_space *mapping)
2096{
Tejun Heo9fb0a7d2013-01-11 13:06:37 -08002097 trace_writeback_dirty_page(page, mapping);
2098
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002099 if (mapping_cap_account_dirty(mapping)) {
Christoph Hellwigde1414a2015-01-14 10:42:36 +01002100 struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
2101
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002102 __inc_zone_page_state(page, NR_FILE_DIRTY);
Michael Rubinea941f02010-10-26 14:21:35 -07002103 __inc_zone_page_state(page, NR_DIRTIED);
Christoph Hellwigde1414a2015-01-14 10:42:36 +01002104 __inc_bdi_stat(bdi, BDI_RECLAIMABLE);
2105 __inc_bdi_stat(bdi, BDI_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002106 task_io_account_write(PAGE_CACHE_SIZE);
Wu Fengguangd3bc1fe2011-04-14 07:52:37 -06002107 current->nr_dirtied++;
2108 this_cpu_inc(bdp_ratelimits);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002109 }
2110}
Michael Rubin679ceac2010-08-20 02:31:26 -07002111EXPORT_SYMBOL(account_page_dirtied);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07002112
2113/*
Konstantin Khlebnikovb9ea2512015-04-14 15:45:27 -07002114 * Helper function for deaccounting dirty page without writeback.
2115 *
2116 * Doing this should *normally* only ever be done when a page
2117 * is truncated, and is not actually mapped anywhere at all. However,
2118 * fs/buffer.c does this when it notices that somebody has cleaned
2119 * out all the buffers on a page without actually doing it through
2120 * the VM. Can you say "ext3 is horribly ugly"? Thought you could.
2121 */
2122void account_page_cleaned(struct page *page, struct address_space *mapping)
2123{
2124 if (mapping_cap_account_dirty(mapping)) {
2125 dec_zone_page_state(page, NR_FILE_DIRTY);
2126 dec_bdi_stat(inode_to_bdi(mapping->host), BDI_RECLAIMABLE);
2127 task_io_account_cancelled_write(PAGE_CACHE_SIZE);
2128 }
2129}
2130EXPORT_SYMBOL(account_page_cleaned);
2131
2132/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002133 * For address_spaces which do not use buffers. Just tag the page as dirty in
2134 * its radix tree.
2135 *
2136 * This is also used when a single buffer is being dirtied: we want to set the
2137 * page dirty in that case, but not all the buffers. This is a "bottom-up"
2138 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2139 *
Johannes Weiner2d6d7f92015-01-08 14:32:18 -08002140 * The caller must ensure this doesn't race with truncation. Most will simply
2141 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2142 * the pte lock held, which also locks out truncation.
Linus Torvalds1da177e2005-04-16 15:20:36 -07002143 */
2144int __set_page_dirty_nobuffers(struct page *page)
2145{
Linus Torvalds1da177e2005-04-16 15:20:36 -07002146 if (!TestSetPageDirty(page)) {
2147 struct address_space *mapping = page_mapping(page);
KOSAKI Motohiroa85d9df2014-02-06 12:04:24 -08002148 unsigned long flags;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002149
Andrew Morton8c085402006-12-10 02:19:24 -08002150 if (!mapping)
2151 return 1;
2152
KOSAKI Motohiroa85d9df2014-02-06 12:04:24 -08002153 spin_lock_irqsave(&mapping->tree_lock, flags);
Johannes Weiner2d6d7f92015-01-08 14:32:18 -08002154 BUG_ON(page_mapping(page) != mapping);
2155 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2156 account_page_dirtied(page, mapping);
2157 radix_tree_tag_set(&mapping->page_tree, page_index(page),
2158 PAGECACHE_TAG_DIRTY);
KOSAKI Motohiroa85d9df2014-02-06 12:04:24 -08002159 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Andrew Morton8c085402006-12-10 02:19:24 -08002160 if (mapping->host) {
2161 /* !PageAnon && !swapper_space */
2162 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002163 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002164 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002165 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002166 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002167}
2168EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2169
2170/*
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002171 * Call this whenever redirtying a page, to de-account the dirty counters
2172 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2173 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2174 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2175 * control.
2176 */
2177void account_page_redirty(struct page *page)
2178{
2179 struct address_space *mapping = page->mapping;
2180 if (mapping && mapping_cap_account_dirty(mapping)) {
2181 current->nr_dirtied--;
2182 dec_zone_page_state(page, NR_DIRTIED);
Christoph Hellwigde1414a2015-01-14 10:42:36 +01002183 dec_bdi_stat(inode_to_bdi(mapping->host), BDI_DIRTIED);
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002184 }
2185}
2186EXPORT_SYMBOL(account_page_redirty);
2187
2188/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002189 * When a writepage implementation decides that it doesn't want to write this
2190 * page for some reason, it should redirty the locked page via
2191 * redirty_page_for_writepage() and it should then unlock the page and return 0
2192 */
2193int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2194{
Konstantin Khebnikov8d386332015-02-11 15:26:55 -08002195 int ret;
2196
Linus Torvalds1da177e2005-04-16 15:20:36 -07002197 wbc->pages_skipped++;
Konstantin Khebnikov8d386332015-02-11 15:26:55 -08002198 ret = __set_page_dirty_nobuffers(page);
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002199 account_page_redirty(page);
Konstantin Khebnikov8d386332015-02-11 15:26:55 -08002200 return ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002201}
2202EXPORT_SYMBOL(redirty_page_for_writepage);
2203
2204/*
Wu Fengguang6746aff2009-09-16 11:50:14 +02002205 * Dirty a page.
2206 *
2207 * For pages with a mapping this should be done under the page lock
2208 * for the benefit of asynchronous memory errors who prefer a consistent
2209 * dirty state. This rule can be broken in some special cases,
2210 * but should be better not to.
2211 *
Linus Torvalds1da177e2005-04-16 15:20:36 -07002212 * If the mapping doesn't provide a set_page_dirty a_op, then
2213 * just fall through and assume that it wants buffer_heads.
2214 */
Nick Piggin1cf6e7d2009-02-18 14:48:18 -08002215int set_page_dirty(struct page *page)
Linus Torvalds1da177e2005-04-16 15:20:36 -07002216{
2217 struct address_space *mapping = page_mapping(page);
2218
2219 if (likely(mapping)) {
2220 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
Minchan Kim278df9f2011-03-22 16:32:54 -07002221 /*
2222 * readahead/lru_deactivate_page could remain
2223 * PG_readahead/PG_reclaim due to race with end_page_writeback
2224 * About readahead, if the page is written, the flags would be
2225 * reset. So no problem.
2226 * About lru_deactivate_page, if the page is redirty, the flag
2227 * will be reset. So no problem. but if the page is used by readahead
2228 * it will confuse readahead and make it restart the size rampup
2229 * process. But it's a trivial problem.
2230 */
Naoya Horiguchia4bb3ec2015-04-15 16:13:17 -07002231 if (PageReclaim(page))
2232 ClearPageReclaim(page);
David Howells93614012006-09-30 20:45:40 +02002233#ifdef CONFIG_BLOCK
2234 if (!spd)
2235 spd = __set_page_dirty_buffers;
2236#endif
2237 return (*spd)(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002238 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002239 if (!PageDirty(page)) {
2240 if (!TestSetPageDirty(page))
2241 return 1;
2242 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002243 return 0;
2244}
2245EXPORT_SYMBOL(set_page_dirty);
2246
2247/*
2248 * set_page_dirty() is racy if the caller has no reference against
2249 * page->mapping->host, and if the page is unlocked. This is because another
2250 * CPU could truncate the page off the mapping and then free the mapping.
2251 *
2252 * Usually, the page _is_ locked, or the caller is a user-space process which
2253 * holds a reference on the inode by having an open file.
2254 *
2255 * In other cases, the page should be locked before running set_page_dirty().
2256 */
2257int set_page_dirty_lock(struct page *page)
2258{
2259 int ret;
2260
Jens Axboe7eaceac2011-03-10 08:52:07 +01002261 lock_page(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002262 ret = set_page_dirty(page);
2263 unlock_page(page);
2264 return ret;
2265}
2266EXPORT_SYMBOL(set_page_dirty_lock);
2267
2268/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002269 * Clear a page's dirty flag, while caring for dirty memory accounting.
2270 * Returns true if the page was previously dirty.
2271 *
2272 * This is for preparing to put the page under writeout. We leave the page
2273 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2274 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2275 * implementation will run either set_page_writeback() or set_page_dirty(),
2276 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2277 * back into sync.
2278 *
2279 * This incoherency between the page's dirty flag and radix-tree tag is
2280 * unfortunate, but it only exists while the page is locked.
2281 */
2282int clear_page_dirty_for_io(struct page *page)
2283{
2284 struct address_space *mapping = page_mapping(page);
2285
Nick Piggin79352892007-07-19 01:47:22 -07002286 BUG_ON(!PageLocked(page));
2287
Linus Torvalds7658cc22006-12-29 10:00:58 -08002288 if (mapping && mapping_cap_account_dirty(mapping)) {
2289 /*
2290 * Yes, Virginia, this is indeed insane.
2291 *
2292 * We use this sequence to make sure that
2293 * (a) we account for dirty stats properly
2294 * (b) we tell the low-level filesystem to
2295 * mark the whole page dirty if it was
2296 * dirty in a pagetable. Only to then
2297 * (c) clean the page again and return 1 to
2298 * cause the writeback.
2299 *
2300 * This way we avoid all nasty races with the
2301 * dirty bit in multiple places and clearing
2302 * them concurrently from different threads.
2303 *
2304 * Note! Normally the "set_page_dirty(page)"
2305 * has no effect on the actual dirty bit - since
2306 * that will already usually be set. But we
2307 * need the side effects, and it can help us
2308 * avoid races.
2309 *
2310 * We basically use the page "master dirty bit"
2311 * as a serialization point for all the different
2312 * threads doing their things.
Linus Torvalds7658cc22006-12-29 10:00:58 -08002313 */
2314 if (page_mkclean(page))
2315 set_page_dirty(page);
Nick Piggin79352892007-07-19 01:47:22 -07002316 /*
2317 * We carefully synchronise fault handlers against
2318 * installing a dirty pte and marking the page dirty
Johannes Weiner2d6d7f92015-01-08 14:32:18 -08002319 * at this point. We do this by having them hold the
2320 * page lock while dirtying the page, and pages are
2321 * always locked coming in here, so we get the desired
2322 * exclusion.
Nick Piggin79352892007-07-19 01:47:22 -07002323 */
Linus Torvalds7658cc22006-12-29 10:00:58 -08002324 if (TestClearPageDirty(page)) {
Andrew Morton8c085402006-12-10 02:19:24 -08002325 dec_zone_page_state(page, NR_FILE_DIRTY);
Christoph Hellwigde1414a2015-01-14 10:42:36 +01002326 dec_bdi_stat(inode_to_bdi(mapping->host),
Peter Zijlstrac9e51e42007-10-16 23:25:47 -07002327 BDI_RECLAIMABLE);
Linus Torvalds7658cc22006-12-29 10:00:58 -08002328 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002329 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08002330 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002331 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08002332 return TestClearPageDirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002333}
Hans Reiser58bb01a2005-11-18 01:10:53 -08002334EXPORT_SYMBOL(clear_page_dirty_for_io);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002335
2336int test_clear_page_writeback(struct page *page)
2337{
2338 struct address_space *mapping = page_mapping(page);
Johannes Weinerd7365e72014-10-29 14:50:48 -07002339 struct mem_cgroup *memcg;
Johannes Weinerd7365e72014-10-29 14:50:48 -07002340 int ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002341
Johannes Weiner6de22612015-02-11 15:25:01 -08002342 memcg = mem_cgroup_begin_page_stat(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002343 if (mapping) {
Christoph Hellwigde1414a2015-01-14 10:42:36 +01002344 struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002345 unsigned long flags;
2346
Nick Piggin19fd6232008-07-25 19:45:32 -07002347 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002348 ret = TestClearPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002349 if (ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07002350 radix_tree_tag_clear(&mapping->page_tree,
2351 page_index(page),
2352 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07002353 if (bdi_cap_account_writeback(bdi)) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002354 __dec_bdi_stat(bdi, BDI_WRITEBACK);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07002355 __bdi_writeout_inc(bdi);
2356 }
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002357 }
Nick Piggin19fd6232008-07-25 19:45:32 -07002358 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002359 } else {
2360 ret = TestClearPageWriteback(page);
2361 }
Wu Fengguang99b12e32011-07-25 17:12:37 -07002362 if (ret) {
Johannes Weinerd7365e72014-10-29 14:50:48 -07002363 mem_cgroup_dec_page_stat(memcg, MEM_CGROUP_STAT_WRITEBACK);
Andrew Mortond688abf2007-07-19 01:49:17 -07002364 dec_zone_page_state(page, NR_WRITEBACK);
Wu Fengguang99b12e32011-07-25 17:12:37 -07002365 inc_zone_page_state(page, NR_WRITTEN);
2366 }
Johannes Weiner6de22612015-02-11 15:25:01 -08002367 mem_cgroup_end_page_stat(memcg);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002368 return ret;
2369}
2370
Namjae Jeon1c8349a2014-05-12 08:12:25 -04002371int __test_set_page_writeback(struct page *page, bool keep_write)
Linus Torvalds1da177e2005-04-16 15:20:36 -07002372{
2373 struct address_space *mapping = page_mapping(page);
Johannes Weinerd7365e72014-10-29 14:50:48 -07002374 struct mem_cgroup *memcg;
Johannes Weinerd7365e72014-10-29 14:50:48 -07002375 int ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002376
Johannes Weiner6de22612015-02-11 15:25:01 -08002377 memcg = mem_cgroup_begin_page_stat(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002378 if (mapping) {
Christoph Hellwigde1414a2015-01-14 10:42:36 +01002379 struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002380 unsigned long flags;
2381
Nick Piggin19fd6232008-07-25 19:45:32 -07002382 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002383 ret = TestSetPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002384 if (!ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07002385 radix_tree_tag_set(&mapping->page_tree,
2386 page_index(page),
2387 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07002388 if (bdi_cap_account_writeback(bdi))
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002389 __inc_bdi_stat(bdi, BDI_WRITEBACK);
2390 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002391 if (!PageDirty(page))
2392 radix_tree_tag_clear(&mapping->page_tree,
2393 page_index(page),
2394 PAGECACHE_TAG_DIRTY);
Namjae Jeon1c8349a2014-05-12 08:12:25 -04002395 if (!keep_write)
2396 radix_tree_tag_clear(&mapping->page_tree,
2397 page_index(page),
2398 PAGECACHE_TAG_TOWRITE);
Nick Piggin19fd6232008-07-25 19:45:32 -07002399 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002400 } else {
2401 ret = TestSetPageWriteback(page);
2402 }
Johannes Weiner3a3c02e2014-10-29 14:50:46 -07002403 if (!ret) {
Johannes Weinerd7365e72014-10-29 14:50:48 -07002404 mem_cgroup_inc_page_stat(memcg, MEM_CGROUP_STAT_WRITEBACK);
Johannes Weiner3a3c02e2014-10-29 14:50:46 -07002405 inc_zone_page_state(page, NR_WRITEBACK);
2406 }
Johannes Weiner6de22612015-02-11 15:25:01 -08002407 mem_cgroup_end_page_stat(memcg);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002408 return ret;
2409
2410}
Namjae Jeon1c8349a2014-05-12 08:12:25 -04002411EXPORT_SYMBOL(__test_set_page_writeback);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002412
2413/*
Nick Piggin00128182007-10-16 01:24:40 -07002414 * Return true if any of the pages in the mapping are marked with the
Linus Torvalds1da177e2005-04-16 15:20:36 -07002415 * passed tag.
2416 */
2417int mapping_tagged(struct address_space *mapping, int tag)
2418{
Konstantin Khlebnikov72c47832011-07-25 17:12:31 -07002419 return radix_tree_tagged(&mapping->page_tree, tag);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002420}
2421EXPORT_SYMBOL(mapping_tagged);
Darrick J. Wong1d1d1a72013-02-21 16:42:51 -08002422
2423/**
2424 * wait_for_stable_page() - wait for writeback to finish, if necessary.
2425 * @page: The page to wait on.
2426 *
2427 * This function determines if the given page is related to a backing device
2428 * that requires page contents to be held stable during writeback. If so, then
2429 * it will wait for any pending writeback to complete.
2430 */
2431void wait_for_stable_page(struct page *page)
2432{
Christoph Hellwigde1414a2015-01-14 10:42:36 +01002433 if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host)))
2434 wait_on_page_writeback(page);
Darrick J. Wong1d1d1a72013-02-21 16:42:51 -08002435}
2436EXPORT_SYMBOL_GPL(wait_for_stable_page);