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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
Uwe Zeisbergerf30c2262006-10-03 23:01:26 +02002 * mm/page-writeback.c
Linus Torvalds1da177e2005-04-16 15:20:36 -07003 *
4 * Copyright (C) 2002, Linus Torvalds.
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07005 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
Linus Torvalds1da177e2005-04-16 15:20:36 -07006 *
7 * Contains functions related to writing back dirty pages at the
8 * address_space level.
9 *
Francois Camie1f8e872008-10-15 22:01:59 -070010 * 10Apr2002 Andrew Morton
Linus Torvalds1da177e2005-04-16 15:20:36 -070011 * Initial version
12 */
13
14#include <linux/kernel.h>
Paul Gortmakerb95f1b312011-10-16 02:01:52 -040015#include <linux/export.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070016#include <linux/spinlock.h>
17#include <linux/fs.h>
18#include <linux/mm.h>
19#include <linux/swap.h>
20#include <linux/slab.h>
21#include <linux/pagemap.h>
22#include <linux/writeback.h>
23#include <linux/init.h>
24#include <linux/backing-dev.h>
Andrew Morton55e829a2006-12-10 02:19:27 -080025#include <linux/task_io_accounting_ops.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070026#include <linux/blkdev.h>
27#include <linux/mpage.h>
Peter Zijlstrad08b3852006-09-25 23:30:57 -070028#include <linux/rmap.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070029#include <linux/percpu.h>
30#include <linux/notifier.h>
31#include <linux/smp.h>
32#include <linux/sysctl.h>
33#include <linux/cpu.h>
34#include <linux/syscalls.h>
Al Viroff01bb42011-09-16 02:31:11 -040035#include <linux/buffer_head.h> /* __set_page_dirty_buffers */
David Howells811d7362006-08-29 19:06:09 +010036#include <linux/pagevec.h>
Dave Chinner028c2dd2010-07-07 13:24:07 +100037#include <trace/events/writeback.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070038
39/*
Wu Fengguangffd1f602011-06-19 22:18:42 -060040 * Sleep at most 200ms at a time in balance_dirty_pages().
41 */
42#define MAX_PAUSE max(HZ/5, 1)
43
44/*
Wu Fengguang5b9b3572011-12-06 13:17:17 -060045 * Try to keep balance_dirty_pages() call intervals higher than this many pages
46 * by raising pause time to max_pause when falls below it.
47 */
48#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
49
50/*
Wu Fengguange98be2d2010-08-29 11:22:30 -060051 * Estimate write bandwidth at 200ms intervals.
52 */
53#define BANDWIDTH_INTERVAL max(HZ/5, 1)
54
Wu Fengguang6c14ae12011-03-02 16:04:18 -060055#define RATELIMIT_CALC_SHIFT 10
56
Wu Fengguange98be2d2010-08-29 11:22:30 -060057/*
Linus Torvalds1da177e2005-04-16 15:20:36 -070058 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
59 * will look to see if it needs to force writeback or throttling.
60 */
61static long ratelimit_pages = 32;
62
Linus Torvalds1da177e2005-04-16 15:20:36 -070063/* The following parameters are exported via /proc/sys/vm */
64
65/*
Jens Axboe5b0830c2009-09-23 19:37:09 +020066 * Start background writeback (via writeback threads) at this percentage
Linus Torvalds1da177e2005-04-16 15:20:36 -070067 */
Wu Fengguang1b5e62b2009-03-23 08:57:38 +080068int dirty_background_ratio = 10;
Linus Torvalds1da177e2005-04-16 15:20:36 -070069
70/*
David Rientjes2da02992009-01-06 14:39:31 -080071 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
72 * dirty_background_ratio * the amount of dirtyable memory
73 */
74unsigned long dirty_background_bytes;
75
76/*
Bron Gondwana195cf452008-02-04 22:29:20 -080077 * free highmem will not be subtracted from the total free memory
78 * for calculating free ratios if vm_highmem_is_dirtyable is true
79 */
80int vm_highmem_is_dirtyable;
81
82/*
Linus Torvalds1da177e2005-04-16 15:20:36 -070083 * The generator of dirty data starts writeback at this percentage
84 */
Wu Fengguang1b5e62b2009-03-23 08:57:38 +080085int vm_dirty_ratio = 20;
Linus Torvalds1da177e2005-04-16 15:20:36 -070086
87/*
David Rientjes2da02992009-01-06 14:39:31 -080088 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
89 * vm_dirty_ratio * the amount of dirtyable memory
90 */
91unsigned long vm_dirty_bytes;
92
93/*
Alexey Dobriyan704503d2009-03-31 15:23:18 -070094 * The interval between `kupdate'-style writebacks
Linus Torvalds1da177e2005-04-16 15:20:36 -070095 */
Toshiyuki Okajima22ef37e2009-05-16 22:56:28 -070096unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
Linus Torvalds1da177e2005-04-16 15:20:36 -070097
98/*
Alexey Dobriyan704503d2009-03-31 15:23:18 -070099 * The longest time for which data is allowed to remain dirty
Linus Torvalds1da177e2005-04-16 15:20:36 -0700100 */
Toshiyuki Okajima22ef37e2009-05-16 22:56:28 -0700101unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700102
103/*
104 * Flag that makes the machine dump writes/reads and block dirtyings.
105 */
106int block_dump;
107
108/*
Bart Samweled5b43f2006-03-24 03:15:49 -0800109 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
110 * a full sync is triggered after this time elapses without any disk activity.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111 */
112int laptop_mode;
113
114EXPORT_SYMBOL(laptop_mode);
115
116/* End of sysctl-exported parameters */
117
Wu Fengguangc42843f2011-03-02 15:54:09 -0600118unsigned long global_dirty_limit;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119
Linus Torvalds1da177e2005-04-16 15:20:36 -0700120/*
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700121 * Scale the writeback cache size proportional to the relative writeout speeds.
122 *
123 * We do this by keeping a floating proportion between BDIs, based on page
124 * writeback completions [end_page_writeback()]. Those devices that write out
125 * pages fastest will get the larger share, while the slower will get a smaller
126 * share.
127 *
128 * We use page writeout completions because we are interested in getting rid of
129 * dirty pages. Having them written out is the primary goal.
130 *
131 * We introduce a concept of time, a period over which we measure these events,
132 * because demand can/will vary over time. The length of this period itself is
133 * measured in page writeback completions.
134 *
135 */
136static struct prop_descriptor vm_completions;
137
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700138/*
Johannes Weiner1edf2232012-01-10 15:06:57 -0800139 * Work out the current dirty-memory clamping and background writeout
140 * thresholds.
141 *
142 * The main aim here is to lower them aggressively if there is a lot of mapped
143 * memory around. To avoid stressing page reclaim with lots of unreclaimable
144 * pages. It is better to clamp down on writers than to start swapping, and
145 * performing lots of scanning.
146 *
147 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
148 *
149 * We don't permit the clamping level to fall below 5% - that is getting rather
150 * excessive.
151 *
152 * We make sure that the background writeout level is below the adjusted
153 * clamping level.
154 */
Johannes Weinerccafa282012-01-10 15:07:44 -0800155
Johannes Weinera756cf52012-01-10 15:07:49 -0800156/*
157 * In a memory zone, there is a certain amount of pages we consider
158 * available for the page cache, which is essentially the number of
159 * free and reclaimable pages, minus some zone reserves to protect
160 * lowmem and the ability to uphold the zone's watermarks without
161 * requiring writeback.
162 *
163 * This number of dirtyable pages is the base value of which the
164 * user-configurable dirty ratio is the effictive number of pages that
165 * are allowed to be actually dirtied. Per individual zone, or
166 * globally by using the sum of dirtyable pages over all zones.
167 *
168 * Because the user is allowed to specify the dirty limit globally as
169 * absolute number of bytes, calculating the per-zone dirty limit can
170 * require translating the configured limit into a percentage of
171 * global dirtyable memory first.
172 */
173
Johannes Weiner1edf2232012-01-10 15:06:57 -0800174static unsigned long highmem_dirtyable_memory(unsigned long total)
175{
176#ifdef CONFIG_HIGHMEM
177 int node;
178 unsigned long x = 0;
179
180 for_each_node_state(node, N_HIGH_MEMORY) {
181 struct zone *z =
182 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
183
184 x += zone_page_state(z, NR_FREE_PAGES) +
Johannes Weinerab8fabd2012-01-10 15:07:42 -0800185 zone_reclaimable_pages(z) - z->dirty_balance_reserve;
Johannes Weiner1edf2232012-01-10 15:06:57 -0800186 }
187 /*
188 * Make sure that the number of highmem pages is never larger
189 * than the number of the total dirtyable memory. This can only
190 * occur in very strange VM situations but we want to make sure
191 * that this does not occur.
192 */
193 return min(x, total);
194#else
195 return 0;
196#endif
197}
198
199/**
Johannes Weinerccafa282012-01-10 15:07:44 -0800200 * global_dirtyable_memory - number of globally dirtyable pages
Johannes Weiner1edf2232012-01-10 15:06:57 -0800201 *
Johannes Weinerccafa282012-01-10 15:07:44 -0800202 * Returns the global number of pages potentially available for dirty
203 * page cache. This is the base value for the global dirty limits.
Johannes Weiner1edf2232012-01-10 15:06:57 -0800204 */
Johannes Weinerccafa282012-01-10 15:07:44 -0800205unsigned long global_dirtyable_memory(void)
Johannes Weiner1edf2232012-01-10 15:06:57 -0800206{
207 unsigned long x;
208
Johannes Weinerab8fabd2012-01-10 15:07:42 -0800209 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() -
210 dirty_balance_reserve;
Johannes Weiner1edf2232012-01-10 15:06:57 -0800211
212 if (!vm_highmem_is_dirtyable)
213 x -= highmem_dirtyable_memory(x);
214
215 return x + 1; /* Ensure that we never return 0 */
216}
217
218/*
Johannes Weinerccafa282012-01-10 15:07:44 -0800219 * global_dirty_limits - background-writeback and dirty-throttling thresholds
220 *
221 * Calculate the dirty thresholds based on sysctl parameters
222 * - vm.dirty_background_ratio or vm.dirty_background_bytes
223 * - vm.dirty_ratio or vm.dirty_bytes
224 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
225 * real-time tasks.
226 */
227void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
228{
229 unsigned long background;
230 unsigned long dirty;
231 unsigned long uninitialized_var(available_memory);
232 struct task_struct *tsk;
233
234 if (!vm_dirty_bytes || !dirty_background_bytes)
235 available_memory = global_dirtyable_memory();
236
237 if (vm_dirty_bytes)
238 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
239 else
240 dirty = (vm_dirty_ratio * available_memory) / 100;
241
242 if (dirty_background_bytes)
243 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
244 else
245 background = (dirty_background_ratio * available_memory) / 100;
246
247 if (background >= dirty)
248 background = dirty / 2;
249 tsk = current;
250 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
251 background += background / 4;
252 dirty += dirty / 4;
253 }
254 *pbackground = background;
255 *pdirty = dirty;
256 trace_global_dirty_state(background, dirty);
257}
258
Johannes Weinera756cf52012-01-10 15:07:49 -0800259/**
260 * zone_dirtyable_memory - number of dirtyable pages in a zone
261 * @zone: the zone
262 *
263 * Returns the zone's number of pages potentially available for dirty
264 * page cache. This is the base value for the per-zone dirty limits.
265 */
266static unsigned long zone_dirtyable_memory(struct zone *zone)
267{
268 /*
269 * The effective global number of dirtyable pages may exclude
270 * highmem as a big-picture measure to keep the ratio between
271 * dirty memory and lowmem reasonable.
272 *
273 * But this function is purely about the individual zone and a
274 * highmem zone can hold its share of dirty pages, so we don't
275 * care about vm_highmem_is_dirtyable here.
276 */
277 return zone_page_state(zone, NR_FREE_PAGES) +
278 zone_reclaimable_pages(zone) -
279 zone->dirty_balance_reserve;
280}
281
282/**
283 * zone_dirty_limit - maximum number of dirty pages allowed in a zone
284 * @zone: the zone
285 *
286 * Returns the maximum number of dirty pages allowed in a zone, based
287 * on the zone's dirtyable memory.
288 */
289static unsigned long zone_dirty_limit(struct zone *zone)
290{
291 unsigned long zone_memory = zone_dirtyable_memory(zone);
292 struct task_struct *tsk = current;
293 unsigned long dirty;
294
295 if (vm_dirty_bytes)
296 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
297 zone_memory / global_dirtyable_memory();
298 else
299 dirty = vm_dirty_ratio * zone_memory / 100;
300
301 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
302 dirty += dirty / 4;
303
304 return dirty;
305}
306
307/**
308 * zone_dirty_ok - tells whether a zone is within its dirty limits
309 * @zone: the zone to check
310 *
311 * Returns %true when the dirty pages in @zone are within the zone's
312 * dirty limit, %false if the limit is exceeded.
313 */
314bool zone_dirty_ok(struct zone *zone)
315{
316 unsigned long limit = zone_dirty_limit(zone);
317
318 return zone_page_state(zone, NR_FILE_DIRTY) +
319 zone_page_state(zone, NR_UNSTABLE_NFS) +
320 zone_page_state(zone, NR_WRITEBACK) <= limit;
321}
322
Johannes Weinerccafa282012-01-10 15:07:44 -0800323/*
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700324 * couple the period to the dirty_ratio:
325 *
326 * period/2 ~ roundup_pow_of_two(dirty limit)
327 */
328static int calc_period_shift(void)
329{
330 unsigned long dirty_total;
331
David Rientjes2da02992009-01-06 14:39:31 -0800332 if (vm_dirty_bytes)
333 dirty_total = vm_dirty_bytes / PAGE_SIZE;
334 else
Johannes Weinerccafa282012-01-10 15:07:44 -0800335 dirty_total = (vm_dirty_ratio * global_dirtyable_memory()) /
David Rientjes2da02992009-01-06 14:39:31 -0800336 100;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700337 return 2 + ilog2(dirty_total - 1);
338}
339
340/*
David Rientjes2da02992009-01-06 14:39:31 -0800341 * update the period when the dirty threshold changes.
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700342 */
David Rientjes2da02992009-01-06 14:39:31 -0800343static void update_completion_period(void)
344{
345 int shift = calc_period_shift();
346 prop_change_shift(&vm_completions, shift);
Wu Fengguang9d823e82011-06-11 18:10:12 -0600347
348 writeback_set_ratelimit();
David Rientjes2da02992009-01-06 14:39:31 -0800349}
350
351int dirty_background_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700352 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800353 loff_t *ppos)
354{
355 int ret;
356
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700357 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800358 if (ret == 0 && write)
359 dirty_background_bytes = 0;
360 return ret;
361}
362
363int dirty_background_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700364 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800365 loff_t *ppos)
366{
367 int ret;
368
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700369 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800370 if (ret == 0 && write)
371 dirty_background_ratio = 0;
372 return ret;
373}
374
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700375int dirty_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700376 void __user *buffer, size_t *lenp,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700377 loff_t *ppos)
378{
379 int old_ratio = vm_dirty_ratio;
David Rientjes2da02992009-01-06 14:39:31 -0800380 int ret;
381
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700382 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700383 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
David Rientjes2da02992009-01-06 14:39:31 -0800384 update_completion_period();
385 vm_dirty_bytes = 0;
386 }
387 return ret;
388}
389
David Rientjes2da02992009-01-06 14:39:31 -0800390int dirty_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700391 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800392 loff_t *ppos)
393{
Sven Wegenerfc3501d2009-02-11 13:04:23 -0800394 unsigned long old_bytes = vm_dirty_bytes;
David Rientjes2da02992009-01-06 14:39:31 -0800395 int ret;
396
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700397 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800398 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
399 update_completion_period();
400 vm_dirty_ratio = 0;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700401 }
402 return ret;
403}
404
405/*
406 * Increment the BDI's writeout completion count and the global writeout
407 * completion count. Called from test_clear_page_writeback().
408 */
409static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
410{
Jan Karaf7d2b1e2010-12-08 22:44:24 -0600411 __inc_bdi_stat(bdi, BDI_WRITTEN);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700412 __prop_inc_percpu_max(&vm_completions, &bdi->completions,
413 bdi->max_prop_frac);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700414}
415
Miklos Szeredidd5656e2008-04-30 00:54:37 -0700416void bdi_writeout_inc(struct backing_dev_info *bdi)
417{
418 unsigned long flags;
419
420 local_irq_save(flags);
421 __bdi_writeout_inc(bdi);
422 local_irq_restore(flags);
423}
424EXPORT_SYMBOL_GPL(bdi_writeout_inc);
425
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700426/*
427 * Obtain an accurate fraction of the BDI's portion.
428 */
429static void bdi_writeout_fraction(struct backing_dev_info *bdi,
430 long *numerator, long *denominator)
431{
Wu Fengguang3efaf0f2010-12-16 22:22:00 -0600432 prop_fraction_percpu(&vm_completions, &bdi->completions,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700433 numerator, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700434}
435
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700436/*
Johannes Weinerd08c4292011-10-31 17:07:05 -0700437 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
438 * registered backing devices, which, for obvious reasons, can not
439 * exceed 100%.
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700440 */
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700441static unsigned int bdi_min_ratio;
442
443int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
444{
445 int ret = 0;
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700446
Jens Axboecfc4ba52009-09-14 13:12:40 +0200447 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700448 if (min_ratio > bdi->max_ratio) {
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700449 ret = -EINVAL;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700450 } else {
451 min_ratio -= bdi->min_ratio;
452 if (bdi_min_ratio + min_ratio < 100) {
453 bdi_min_ratio += min_ratio;
454 bdi->min_ratio += min_ratio;
455 } else {
456 ret = -EINVAL;
457 }
458 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200459 spin_unlock_bh(&bdi_lock);
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700460
461 return ret;
462}
463
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700464int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
465{
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700466 int ret = 0;
467
468 if (max_ratio > 100)
469 return -EINVAL;
470
Jens Axboecfc4ba52009-09-14 13:12:40 +0200471 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700472 if (bdi->min_ratio > max_ratio) {
473 ret = -EINVAL;
474 } else {
475 bdi->max_ratio = max_ratio;
476 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
477 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200478 spin_unlock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700479
480 return ret;
481}
482EXPORT_SYMBOL(bdi_set_max_ratio);
483
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600484static unsigned long dirty_freerun_ceiling(unsigned long thresh,
485 unsigned long bg_thresh)
486{
487 return (thresh + bg_thresh) / 2;
488}
489
Wu Fengguangffd1f602011-06-19 22:18:42 -0600490static unsigned long hard_dirty_limit(unsigned long thresh)
491{
492 return max(thresh, global_dirty_limit);
493}
494
Wu Fengguang6f718652011-03-02 17:14:34 -0600495/**
Wu Fengguang1babe182010-08-11 14:17:40 -0700496 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
Wu Fengguang6f718652011-03-02 17:14:34 -0600497 * @bdi: the backing_dev_info to query
498 * @dirty: global dirty limit in pages
Wu Fengguang1babe182010-08-11 14:17:40 -0700499 *
Wu Fengguang6f718652011-03-02 17:14:34 -0600500 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
501 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
Wu Fengguangaed21ad2011-11-23 11:44:41 -0600502 *
503 * Note that balance_dirty_pages() will only seriously take it as a hard limit
504 * when sleeping max_pause per page is not enough to keep the dirty pages under
505 * control. For example, when the device is completely stalled due to some error
506 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
507 * In the other normal situations, it acts more gently by throttling the tasks
508 * more (rather than completely block them) when the bdi dirty pages go high.
Wu Fengguang6f718652011-03-02 17:14:34 -0600509 *
510 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
Wu Fengguang1babe182010-08-11 14:17:40 -0700511 * - starving fast devices
512 * - piling up dirty pages (that will take long time to sync) on slow devices
513 *
514 * The bdi's share of dirty limit will be adapting to its throughput and
515 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
516 */
517unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
Wu Fengguang16c40422010-08-11 14:17:39 -0700518{
519 u64 bdi_dirty;
520 long numerator, denominator;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700521
Wu Fengguang16c40422010-08-11 14:17:39 -0700522 /*
523 * Calculate this BDI's share of the dirty ratio.
524 */
525 bdi_writeout_fraction(bdi, &numerator, &denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700526
Wu Fengguang16c40422010-08-11 14:17:39 -0700527 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
528 bdi_dirty *= numerator;
529 do_div(bdi_dirty, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700530
Wu Fengguang16c40422010-08-11 14:17:39 -0700531 bdi_dirty += (dirty * bdi->min_ratio) / 100;
532 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
533 bdi_dirty = dirty * bdi->max_ratio / 100;
534
535 return bdi_dirty;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700536}
537
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600538/*
539 * Dirty position control.
540 *
541 * (o) global/bdi setpoints
542 *
543 * We want the dirty pages be balanced around the global/bdi setpoints.
544 * When the number of dirty pages is higher/lower than the setpoint, the
545 * dirty position control ratio (and hence task dirty ratelimit) will be
546 * decreased/increased to bring the dirty pages back to the setpoint.
547 *
548 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
549 *
550 * if (dirty < setpoint) scale up pos_ratio
551 * if (dirty > setpoint) scale down pos_ratio
552 *
553 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
554 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
555 *
556 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
557 *
558 * (o) global control line
559 *
560 * ^ pos_ratio
561 * |
562 * | |<===== global dirty control scope ======>|
563 * 2.0 .............*
564 * | .*
565 * | . *
566 * | . *
567 * | . *
568 * | . *
569 * | . *
570 * 1.0 ................................*
571 * | . . *
572 * | . . *
573 * | . . *
574 * | . . *
575 * | . . *
576 * 0 +------------.------------------.----------------------*------------->
577 * freerun^ setpoint^ limit^ dirty pages
578 *
579 * (o) bdi control line
580 *
581 * ^ pos_ratio
582 * |
583 * | *
584 * | *
585 * | *
586 * | *
587 * | * |<=========== span ============>|
588 * 1.0 .......................*
589 * | . *
590 * | . *
591 * | . *
592 * | . *
593 * | . *
594 * | . *
595 * | . *
596 * | . *
597 * | . *
598 * | . *
599 * | . *
600 * 1/4 ...............................................* * * * * * * * * * * *
601 * | . .
602 * | . .
603 * | . .
604 * 0 +----------------------.-------------------------------.------------->
605 * bdi_setpoint^ x_intercept^
606 *
607 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
608 * be smoothly throttled down to normal if it starts high in situations like
609 * - start writing to a slow SD card and a fast disk at the same time. The SD
610 * card's bdi_dirty may rush to many times higher than bdi_setpoint.
611 * - the bdi dirty thresh drops quickly due to change of JBOD workload
612 */
613static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
614 unsigned long thresh,
615 unsigned long bg_thresh,
616 unsigned long dirty,
617 unsigned long bdi_thresh,
618 unsigned long bdi_dirty)
619{
620 unsigned long write_bw = bdi->avg_write_bandwidth;
621 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
622 unsigned long limit = hard_dirty_limit(thresh);
623 unsigned long x_intercept;
624 unsigned long setpoint; /* dirty pages' target balance point */
625 unsigned long bdi_setpoint;
626 unsigned long span;
627 long long pos_ratio; /* for scaling up/down the rate limit */
628 long x;
629
630 if (unlikely(dirty >= limit))
631 return 0;
632
633 /*
634 * global setpoint
635 *
636 * setpoint - dirty 3
637 * f(dirty) := 1.0 + (----------------)
638 * limit - setpoint
639 *
640 * it's a 3rd order polynomial that subjects to
641 *
642 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
643 * (2) f(setpoint) = 1.0 => the balance point
644 * (3) f(limit) = 0 => the hard limit
645 * (4) df/dx <= 0 => negative feedback control
646 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
647 * => fast response on large errors; small oscillation near setpoint
648 */
649 setpoint = (freerun + limit) / 2;
650 x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
651 limit - setpoint + 1);
652 pos_ratio = x;
653 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
654 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
655 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
656
657 /*
658 * We have computed basic pos_ratio above based on global situation. If
659 * the bdi is over/under its share of dirty pages, we want to scale
660 * pos_ratio further down/up. That is done by the following mechanism.
661 */
662
663 /*
664 * bdi setpoint
665 *
666 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
667 *
668 * x_intercept - bdi_dirty
669 * := --------------------------
670 * x_intercept - bdi_setpoint
671 *
672 * The main bdi control line is a linear function that subjects to
673 *
674 * (1) f(bdi_setpoint) = 1.0
675 * (2) k = - 1 / (8 * write_bw) (in single bdi case)
676 * or equally: x_intercept = bdi_setpoint + 8 * write_bw
677 *
678 * For single bdi case, the dirty pages are observed to fluctuate
679 * regularly within range
680 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
681 * for various filesystems, where (2) can yield in a reasonable 12.5%
682 * fluctuation range for pos_ratio.
683 *
684 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
685 * own size, so move the slope over accordingly and choose a slope that
686 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
687 */
688 if (unlikely(bdi_thresh > thresh))
689 bdi_thresh = thresh;
Wu Fengguangaed21ad2011-11-23 11:44:41 -0600690 /*
691 * It's very possible that bdi_thresh is close to 0 not because the
692 * device is slow, but that it has remained inactive for long time.
693 * Honour such devices a reasonable good (hopefully IO efficient)
694 * threshold, so that the occasional writes won't be blocked and active
695 * writes can rampup the threshold quickly.
696 */
Wu Fengguang8927f662011-08-04 22:16:46 -0600697 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600698 /*
699 * scale global setpoint to bdi's:
700 * bdi_setpoint = setpoint * bdi_thresh / thresh
701 */
702 x = div_u64((u64)bdi_thresh << 16, thresh + 1);
703 bdi_setpoint = setpoint * (u64)x >> 16;
704 /*
705 * Use span=(8*write_bw) in single bdi case as indicated by
706 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
707 *
708 * bdi_thresh thresh - bdi_thresh
709 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
710 * thresh thresh
711 */
712 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
713 x_intercept = bdi_setpoint + span;
714
715 if (bdi_dirty < x_intercept - span / 4) {
Wu Fengguang50657fc2011-10-11 17:06:33 -0600716 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
717 x_intercept - bdi_setpoint + 1);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600718 } else
719 pos_ratio /= 4;
720
Wu Fengguang8927f662011-08-04 22:16:46 -0600721 /*
722 * bdi reserve area, safeguard against dirty pool underrun and disk idle
723 * It may push the desired control point of global dirty pages higher
724 * than setpoint.
725 */
726 x_intercept = bdi_thresh / 2;
727 if (bdi_dirty < x_intercept) {
Wu Fengguang50657fc2011-10-11 17:06:33 -0600728 if (bdi_dirty > x_intercept / 8)
729 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
730 else
Wu Fengguang8927f662011-08-04 22:16:46 -0600731 pos_ratio *= 8;
732 }
733
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600734 return pos_ratio;
735}
736
Wu Fengguange98be2d2010-08-29 11:22:30 -0600737static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
738 unsigned long elapsed,
739 unsigned long written)
740{
741 const unsigned long period = roundup_pow_of_two(3 * HZ);
742 unsigned long avg = bdi->avg_write_bandwidth;
743 unsigned long old = bdi->write_bandwidth;
744 u64 bw;
745
746 /*
747 * bw = written * HZ / elapsed
748 *
749 * bw * elapsed + write_bandwidth * (period - elapsed)
750 * write_bandwidth = ---------------------------------------------------
751 * period
752 */
753 bw = written - bdi->written_stamp;
754 bw *= HZ;
755 if (unlikely(elapsed > period)) {
756 do_div(bw, elapsed);
757 avg = bw;
758 goto out;
759 }
760 bw += (u64)bdi->write_bandwidth * (period - elapsed);
761 bw >>= ilog2(period);
762
763 /*
764 * one more level of smoothing, for filtering out sudden spikes
765 */
766 if (avg > old && old >= (unsigned long)bw)
767 avg -= (avg - old) >> 3;
768
769 if (avg < old && old <= (unsigned long)bw)
770 avg += (old - avg) >> 3;
771
772out:
773 bdi->write_bandwidth = bw;
774 bdi->avg_write_bandwidth = avg;
775}
776
Wu Fengguangc42843f2011-03-02 15:54:09 -0600777/*
778 * The global dirtyable memory and dirty threshold could be suddenly knocked
779 * down by a large amount (eg. on the startup of KVM in a swapless system).
780 * This may throw the system into deep dirty exceeded state and throttle
781 * heavy/light dirtiers alike. To retain good responsiveness, maintain
782 * global_dirty_limit for tracking slowly down to the knocked down dirty
783 * threshold.
784 */
785static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
786{
787 unsigned long limit = global_dirty_limit;
788
789 /*
790 * Follow up in one step.
791 */
792 if (limit < thresh) {
793 limit = thresh;
794 goto update;
795 }
796
797 /*
798 * Follow down slowly. Use the higher one as the target, because thresh
799 * may drop below dirty. This is exactly the reason to introduce
800 * global_dirty_limit which is guaranteed to lie above the dirty pages.
801 */
802 thresh = max(thresh, dirty);
803 if (limit > thresh) {
804 limit -= (limit - thresh) >> 5;
805 goto update;
806 }
807 return;
808update:
809 global_dirty_limit = limit;
810}
811
812static void global_update_bandwidth(unsigned long thresh,
813 unsigned long dirty,
814 unsigned long now)
815{
816 static DEFINE_SPINLOCK(dirty_lock);
817 static unsigned long update_time;
818
819 /*
820 * check locklessly first to optimize away locking for the most time
821 */
822 if (time_before(now, update_time + BANDWIDTH_INTERVAL))
823 return;
824
825 spin_lock(&dirty_lock);
826 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
827 update_dirty_limit(thresh, dirty);
828 update_time = now;
829 }
830 spin_unlock(&dirty_lock);
831}
832
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600833/*
834 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
835 *
836 * Normal bdi tasks will be curbed at or below it in long term.
837 * Obviously it should be around (write_bw / N) when there are N dd tasks.
838 */
839static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
840 unsigned long thresh,
841 unsigned long bg_thresh,
842 unsigned long dirty,
843 unsigned long bdi_thresh,
844 unsigned long bdi_dirty,
845 unsigned long dirtied,
846 unsigned long elapsed)
847{
Wu Fengguang73811312011-08-26 15:53:24 -0600848 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
849 unsigned long limit = hard_dirty_limit(thresh);
850 unsigned long setpoint = (freerun + limit) / 2;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600851 unsigned long write_bw = bdi->avg_write_bandwidth;
852 unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
853 unsigned long dirty_rate;
854 unsigned long task_ratelimit;
855 unsigned long balanced_dirty_ratelimit;
856 unsigned long pos_ratio;
Wu Fengguang73811312011-08-26 15:53:24 -0600857 unsigned long step;
858 unsigned long x;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600859
860 /*
861 * The dirty rate will match the writeout rate in long term, except
862 * when dirty pages are truncated by userspace or re-dirtied by FS.
863 */
864 dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
865
866 pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
867 bdi_thresh, bdi_dirty);
868 /*
869 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
870 */
871 task_ratelimit = (u64)dirty_ratelimit *
872 pos_ratio >> RATELIMIT_CALC_SHIFT;
873 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
874
875 /*
876 * A linear estimation of the "balanced" throttle rate. The theory is,
877 * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
878 * dirty_rate will be measured to be (N * task_ratelimit). So the below
879 * formula will yield the balanced rate limit (write_bw / N).
880 *
881 * Note that the expanded form is not a pure rate feedback:
882 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
883 * but also takes pos_ratio into account:
884 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
885 *
886 * (1) is not realistic because pos_ratio also takes part in balancing
887 * the dirty rate. Consider the state
888 * pos_ratio = 0.5 (3)
889 * rate = 2 * (write_bw / N) (4)
890 * If (1) is used, it will stuck in that state! Because each dd will
891 * be throttled at
892 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
893 * yielding
894 * dirty_rate = N * task_ratelimit = write_bw (6)
895 * put (6) into (1) we get
896 * rate_(i+1) = rate_(i) (7)
897 *
898 * So we end up using (2) to always keep
899 * rate_(i+1) ~= (write_bw / N) (8)
900 * regardless of the value of pos_ratio. As long as (8) is satisfied,
901 * pos_ratio is able to drive itself to 1.0, which is not only where
902 * the dirty count meet the setpoint, but also where the slope of
903 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
904 */
905 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
906 dirty_rate | 1);
Wu Fengguangbdaac492011-08-03 14:30:36 -0600907 /*
908 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
909 */
910 if (unlikely(balanced_dirty_ratelimit > write_bw))
911 balanced_dirty_ratelimit = write_bw;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600912
Wu Fengguang73811312011-08-26 15:53:24 -0600913 /*
914 * We could safely do this and return immediately:
915 *
916 * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
917 *
918 * However to get a more stable dirty_ratelimit, the below elaborated
919 * code makes use of task_ratelimit to filter out sigular points and
920 * limit the step size.
921 *
922 * The below code essentially only uses the relative value of
923 *
924 * task_ratelimit - dirty_ratelimit
925 * = (pos_ratio - 1) * dirty_ratelimit
926 *
927 * which reflects the direction and size of dirty position error.
928 */
929
930 /*
931 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
932 * task_ratelimit is on the same side of dirty_ratelimit, too.
933 * For example, when
934 * - dirty_ratelimit > balanced_dirty_ratelimit
935 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
936 * lowering dirty_ratelimit will help meet both the position and rate
937 * control targets. Otherwise, don't update dirty_ratelimit if it will
938 * only help meet the rate target. After all, what the users ultimately
939 * feel and care are stable dirty rate and small position error.
940 *
941 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
942 * and filter out the sigular points of balanced_dirty_ratelimit. Which
943 * keeps jumping around randomly and can even leap far away at times
944 * due to the small 200ms estimation period of dirty_rate (we want to
945 * keep that period small to reduce time lags).
946 */
947 step = 0;
948 if (dirty < setpoint) {
949 x = min(bdi->balanced_dirty_ratelimit,
950 min(balanced_dirty_ratelimit, task_ratelimit));
951 if (dirty_ratelimit < x)
952 step = x - dirty_ratelimit;
953 } else {
954 x = max(bdi->balanced_dirty_ratelimit,
955 max(balanced_dirty_ratelimit, task_ratelimit));
956 if (dirty_ratelimit > x)
957 step = dirty_ratelimit - x;
958 }
959
960 /*
961 * Don't pursue 100% rate matching. It's impossible since the balanced
962 * rate itself is constantly fluctuating. So decrease the track speed
963 * when it gets close to the target. Helps eliminate pointless tremors.
964 */
965 step >>= dirty_ratelimit / (2 * step + 1);
966 /*
967 * Limit the tracking speed to avoid overshooting.
968 */
969 step = (step + 7) / 8;
970
971 if (dirty_ratelimit < balanced_dirty_ratelimit)
972 dirty_ratelimit += step;
973 else
974 dirty_ratelimit -= step;
975
976 bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
977 bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
Wu Fengguangb48c1042011-03-02 17:22:49 -0600978
979 trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600980}
981
Wu Fengguange98be2d2010-08-29 11:22:30 -0600982void __bdi_update_bandwidth(struct backing_dev_info *bdi,
Wu Fengguangc42843f2011-03-02 15:54:09 -0600983 unsigned long thresh,
Wu Fengguangaf6a3112011-10-03 20:46:17 -0600984 unsigned long bg_thresh,
Wu Fengguangc42843f2011-03-02 15:54:09 -0600985 unsigned long dirty,
986 unsigned long bdi_thresh,
987 unsigned long bdi_dirty,
Wu Fengguange98be2d2010-08-29 11:22:30 -0600988 unsigned long start_time)
989{
990 unsigned long now = jiffies;
991 unsigned long elapsed = now - bdi->bw_time_stamp;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600992 unsigned long dirtied;
Wu Fengguange98be2d2010-08-29 11:22:30 -0600993 unsigned long written;
994
995 /*
996 * rate-limit, only update once every 200ms.
997 */
998 if (elapsed < BANDWIDTH_INTERVAL)
999 return;
1000
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001001 dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001002 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
1003
1004 /*
1005 * Skip quiet periods when disk bandwidth is under-utilized.
1006 * (at least 1s idle time between two flusher runs)
1007 */
1008 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
1009 goto snapshot;
1010
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001011 if (thresh) {
Wu Fengguangc42843f2011-03-02 15:54:09 -06001012 global_update_bandwidth(thresh, dirty, now);
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001013 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
1014 bdi_thresh, bdi_dirty,
1015 dirtied, elapsed);
1016 }
Wu Fengguange98be2d2010-08-29 11:22:30 -06001017 bdi_update_write_bandwidth(bdi, elapsed, written);
1018
1019snapshot:
Wu Fengguangbe3ffa22011-06-12 10:51:31 -06001020 bdi->dirtied_stamp = dirtied;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001021 bdi->written_stamp = written;
1022 bdi->bw_time_stamp = now;
1023}
1024
1025static void bdi_update_bandwidth(struct backing_dev_info *bdi,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001026 unsigned long thresh,
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001027 unsigned long bg_thresh,
Wu Fengguangc42843f2011-03-02 15:54:09 -06001028 unsigned long dirty,
1029 unsigned long bdi_thresh,
1030 unsigned long bdi_dirty,
Wu Fengguange98be2d2010-08-29 11:22:30 -06001031 unsigned long start_time)
1032{
1033 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
1034 return;
1035 spin_lock(&bdi->wb.list_lock);
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001036 __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
1037 bdi_thresh, bdi_dirty, start_time);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001038 spin_unlock(&bdi->wb.list_lock);
1039}
1040
Linus Torvalds1da177e2005-04-16 15:20:36 -07001041/*
Wu Fengguang9d823e82011-06-11 18:10:12 -06001042 * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
1043 * will look to see if it needs to start dirty throttling.
1044 *
1045 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1046 * global_page_state() too often. So scale it near-sqrt to the safety margin
1047 * (the number of pages we may dirty without exceeding the dirty limits).
1048 */
1049static unsigned long dirty_poll_interval(unsigned long dirty,
1050 unsigned long thresh)
1051{
1052 if (thresh > dirty)
1053 return 1UL << (ilog2(thresh - dirty) >> 1);
1054
1055 return 1;
1056}
1057
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001058static long bdi_max_pause(struct backing_dev_info *bdi,
1059 unsigned long bdi_dirty)
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001060{
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001061 long bw = bdi->avg_write_bandwidth;
1062 long t;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001063
1064 /*
1065 * Limit pause time for small memory systems. If sleeping for too long
1066 * time, a small pool of dirty/writeback pages may go empty and disk go
1067 * idle.
1068 *
1069 * 8 serves as the safety ratio.
1070 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001071 t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1072 t++;
1073
1074 return min_t(long, t, MAX_PAUSE);
1075}
1076
1077static long bdi_min_pause(struct backing_dev_info *bdi,
1078 long max_pause,
1079 unsigned long task_ratelimit,
1080 unsigned long dirty_ratelimit,
1081 int *nr_dirtied_pause)
1082{
1083 long hi = ilog2(bdi->avg_write_bandwidth);
1084 long lo = ilog2(bdi->dirty_ratelimit);
1085 long t; /* target pause */
1086 long pause; /* estimated next pause */
1087 int pages; /* target nr_dirtied_pause */
1088
1089 /* target for 10ms pause on 1-dd case */
1090 t = max(1, HZ / 100);
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001091
1092 /*
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001093 * Scale up pause time for concurrent dirtiers in order to reduce CPU
1094 * overheads.
1095 *
1096 * (N * 10ms) on 2^N concurrent tasks.
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001097 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001098 if (hi > lo)
1099 t += (hi - lo) * (10 * HZ) / 1024;
1100
1101 /*
1102 * This is a bit convoluted. We try to base the next nr_dirtied_pause
1103 * on the much more stable dirty_ratelimit. However the next pause time
1104 * will be computed based on task_ratelimit and the two rate limits may
1105 * depart considerably at some time. Especially if task_ratelimit goes
1106 * below dirty_ratelimit/2 and the target pause is max_pause, the next
1107 * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
1108 * result task_ratelimit won't be executed faithfully, which could
1109 * eventually bring down dirty_ratelimit.
1110 *
1111 * We apply two rules to fix it up:
1112 * 1) try to estimate the next pause time and if necessary, use a lower
1113 * nr_dirtied_pause so as not to exceed max_pause. When this happens,
1114 * nr_dirtied_pause will be "dancing" with task_ratelimit.
1115 * 2) limit the target pause time to max_pause/2, so that the normal
1116 * small fluctuations of task_ratelimit won't trigger rule (1) and
1117 * nr_dirtied_pause will remain as stable as dirty_ratelimit.
1118 */
1119 t = min(t, 1 + max_pause / 2);
1120 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1121
Wu Fengguang5b9b3572011-12-06 13:17:17 -06001122 /*
1123 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1124 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1125 * When the 16 consecutive reads are often interrupted by some dirty
1126 * throttling pause during the async writes, cfq will go into idles
1127 * (deadline is fine). So push nr_dirtied_pause as high as possible
1128 * until reaches DIRTY_POLL_THRESH=32 pages.
1129 */
1130 if (pages < DIRTY_POLL_THRESH) {
1131 t = max_pause;
1132 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1133 if (pages > DIRTY_POLL_THRESH) {
1134 pages = DIRTY_POLL_THRESH;
1135 t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1136 }
1137 }
1138
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001139 pause = HZ * pages / (task_ratelimit + 1);
1140 if (pause > max_pause) {
1141 t = max_pause;
1142 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1143 }
1144
1145 *nr_dirtied_pause = pages;
1146 /*
1147 * The minimal pause time will normally be half the target pause time.
1148 */
Wu Fengguang5b9b3572011-12-06 13:17:17 -06001149 return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001150}
1151
Wu Fengguang9d823e82011-06-11 18:10:12 -06001152/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001153 * balance_dirty_pages() must be called by processes which are generating dirty
1154 * data. It looks at the number of dirty pages in the machine and will force
Wu Fengguang143dfe82010-08-27 18:45:12 -06001155 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
Jens Axboe5b0830c2009-09-23 19:37:09 +02001156 * If we're over `background_thresh' then the writeback threads are woken to
1157 * perform some writeout.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001158 */
Wu Fengguang3a2e9a52009-09-23 21:56:00 +08001159static void balance_dirty_pages(struct address_space *mapping,
Wu Fengguang143dfe82010-08-27 18:45:12 -06001160 unsigned long pages_dirtied)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001161{
Wu Fengguang143dfe82010-08-27 18:45:12 -06001162 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1163 unsigned long bdi_reclaimable;
Wu Fengguang77627412010-09-12 13:34:05 -06001164 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
1165 unsigned long bdi_dirty;
Wu Fengguang6c14ae12011-03-02 16:04:18 -06001166 unsigned long freerun;
David Rientjes364aeb22009-01-06 14:39:29 -08001167 unsigned long background_thresh;
1168 unsigned long dirty_thresh;
1169 unsigned long bdi_thresh;
Wu Fengguang83712352011-06-11 19:25:42 -06001170 long period;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001171 long pause;
1172 long max_pause;
1173 long min_pause;
1174 int nr_dirtied_pause;
Wu Fengguange50e3722010-08-11 14:17:37 -07001175 bool dirty_exceeded = false;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001176 unsigned long task_ratelimit;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001177 unsigned long dirty_ratelimit;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001178 unsigned long pos_ratio;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001179 struct backing_dev_info *bdi = mapping->backing_dev_info;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001180 unsigned long start_time = jiffies;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001181
1182 for (;;) {
Wu Fengguang83712352011-06-11 19:25:42 -06001183 unsigned long now = jiffies;
1184
Wu Fengguang143dfe82010-08-27 18:45:12 -06001185 /*
1186 * Unstable writes are a feature of certain networked
1187 * filesystems (i.e. NFS) in which data may have been
1188 * written to the server's write cache, but has not yet
1189 * been flushed to permanent storage.
1190 */
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001191 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1192 global_page_state(NR_UNSTABLE_NFS);
Wu Fengguang77627412010-09-12 13:34:05 -06001193 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001194
Wu Fengguang16c40422010-08-11 14:17:39 -07001195 global_dirty_limits(&background_thresh, &dirty_thresh);
1196
1197 /*
1198 * Throttle it only when the background writeback cannot
1199 * catch-up. This avoids (excessively) small writeouts
1200 * when the bdi limits are ramping up.
1201 */
Wu Fengguang6c14ae12011-03-02 16:04:18 -06001202 freerun = dirty_freerun_ceiling(dirty_thresh,
1203 background_thresh);
Wu Fengguang83712352011-06-11 19:25:42 -06001204 if (nr_dirty <= freerun) {
1205 current->dirty_paused_when = now;
1206 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001207 current->nr_dirtied_pause =
1208 dirty_poll_interval(nr_dirty, dirty_thresh);
Wu Fengguang16c40422010-08-11 14:17:39 -07001209 break;
Wu Fengguang83712352011-06-11 19:25:42 -06001210 }
Wu Fengguang16c40422010-08-11 14:17:39 -07001211
Wu Fengguang143dfe82010-08-27 18:45:12 -06001212 if (unlikely(!writeback_in_progress(bdi)))
1213 bdi_start_background_writeback(bdi);
1214
1215 /*
1216 * bdi_thresh is not treated as some limiting factor as
1217 * dirty_thresh, due to reasons
1218 * - in JBOD setup, bdi_thresh can fluctuate a lot
1219 * - in a system with HDD and USB key, the USB key may somehow
1220 * go into state (bdi_dirty >> bdi_thresh) either because
1221 * bdi_dirty starts high, or because bdi_thresh drops low.
1222 * In this case we don't want to hard throttle the USB key
1223 * dirtiers for 100 seconds until bdi_dirty drops under
1224 * bdi_thresh. Instead the auxiliary bdi control line in
1225 * bdi_position_ratio() will let the dirtier task progress
1226 * at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1227 */
Wu Fengguang16c40422010-08-11 14:17:39 -07001228 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
Wu Fengguang16c40422010-08-11 14:17:39 -07001229
Wu Fengguange50e3722010-08-11 14:17:37 -07001230 /*
1231 * In order to avoid the stacked BDI deadlock we need
1232 * to ensure we accurately count the 'dirty' pages when
1233 * the threshold is low.
1234 *
1235 * Otherwise it would be possible to get thresh+n pages
1236 * reported dirty, even though there are thresh-m pages
1237 * actually dirty; with m+n sitting in the percpu
1238 * deltas.
1239 */
Wu Fengguang143dfe82010-08-27 18:45:12 -06001240 if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1241 bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1242 bdi_dirty = bdi_reclaimable +
Wu Fengguang77627412010-09-12 13:34:05 -06001243 bdi_stat_sum(bdi, BDI_WRITEBACK);
Wu Fengguange50e3722010-08-11 14:17:37 -07001244 } else {
Wu Fengguang143dfe82010-08-27 18:45:12 -06001245 bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1246 bdi_dirty = bdi_reclaimable +
Wu Fengguang77627412010-09-12 13:34:05 -06001247 bdi_stat(bdi, BDI_WRITEBACK);
Wu Fengguange50e3722010-08-11 14:17:37 -07001248 }
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001249
Wu Fengguang82791942011-12-03 21:26:01 -06001250 dirty_exceeded = (bdi_dirty > bdi_thresh) &&
Wu Fengguang77627412010-09-12 13:34:05 -06001251 (nr_dirty > dirty_thresh);
Wu Fengguang143dfe82010-08-27 18:45:12 -06001252 if (dirty_exceeded && !bdi->dirty_exceeded)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001253 bdi->dirty_exceeded = 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001254
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001255 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1256 nr_dirty, bdi_thresh, bdi_dirty,
1257 start_time);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001258
Wu Fengguang143dfe82010-08-27 18:45:12 -06001259 dirty_ratelimit = bdi->dirty_ratelimit;
1260 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1261 background_thresh, nr_dirty,
1262 bdi_thresh, bdi_dirty);
Wu Fengguang3a73dbb2011-11-07 19:19:28 +08001263 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1264 RATELIMIT_CALC_SHIFT;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001265 max_pause = bdi_max_pause(bdi, bdi_dirty);
1266 min_pause = bdi_min_pause(bdi, max_pause,
1267 task_ratelimit, dirty_ratelimit,
1268 &nr_dirtied_pause);
1269
Wu Fengguang3a73dbb2011-11-07 19:19:28 +08001270 if (unlikely(task_ratelimit == 0)) {
Wu Fengguang83712352011-06-11 19:25:42 -06001271 period = max_pause;
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001272 pause = max_pause;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001273 goto pause;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001274 }
Wu Fengguang83712352011-06-11 19:25:42 -06001275 period = HZ * pages_dirtied / task_ratelimit;
1276 pause = period;
1277 if (current->dirty_paused_when)
1278 pause -= now - current->dirty_paused_when;
1279 /*
1280 * For less than 1s think time (ext3/4 may block the dirtier
1281 * for up to 800ms from time to time on 1-HDD; so does xfs,
1282 * however at much less frequency), try to compensate it in
1283 * future periods by updating the virtual time; otherwise just
1284 * do a reset, as it may be a light dirtier.
1285 */
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001286 if (pause < min_pause) {
Wu Fengguangece13ac2010-08-29 23:33:20 -06001287 trace_balance_dirty_pages(bdi,
1288 dirty_thresh,
1289 background_thresh,
1290 nr_dirty,
1291 bdi_thresh,
1292 bdi_dirty,
1293 dirty_ratelimit,
1294 task_ratelimit,
1295 pages_dirtied,
Wu Fengguang83712352011-06-11 19:25:42 -06001296 period,
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001297 min(pause, 0L),
Wu Fengguangece13ac2010-08-29 23:33:20 -06001298 start_time);
Wu Fengguang83712352011-06-11 19:25:42 -06001299 if (pause < -HZ) {
1300 current->dirty_paused_when = now;
1301 current->nr_dirtied = 0;
1302 } else if (period) {
1303 current->dirty_paused_when += period;
1304 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001305 } else if (current->nr_dirtied_pause <= pages_dirtied)
1306 current->nr_dirtied_pause += pages_dirtied;
Wu Fengguang57fc9782011-06-11 19:32:32 -06001307 break;
1308 }
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001309 if (unlikely(pause > max_pause)) {
1310 /* for occasional dropped task_ratelimit */
1311 now += min(pause - max_pause, max_pause);
1312 pause = max_pause;
1313 }
Wu Fengguang143dfe82010-08-27 18:45:12 -06001314
1315pause:
Wu Fengguangece13ac2010-08-29 23:33:20 -06001316 trace_balance_dirty_pages(bdi,
1317 dirty_thresh,
1318 background_thresh,
1319 nr_dirty,
1320 bdi_thresh,
1321 bdi_dirty,
1322 dirty_ratelimit,
1323 task_ratelimit,
1324 pages_dirtied,
Wu Fengguang83712352011-06-11 19:25:42 -06001325 period,
Wu Fengguangece13ac2010-08-29 23:33:20 -06001326 pause,
1327 start_time);
Jan Kara499d05e2011-11-16 19:34:48 +08001328 __set_current_state(TASK_KILLABLE);
Wu Fengguangd25105e2009-10-09 12:40:42 +02001329 io_schedule_timeout(pause);
Jens Axboe87c6a9b2009-09-17 19:59:14 +02001330
Wu Fengguang83712352011-06-11 19:25:42 -06001331 current->dirty_paused_when = now + pause;
1332 current->nr_dirtied = 0;
Wu Fengguang7ccb9ad2011-11-30 11:08:55 -06001333 current->nr_dirtied_pause = nr_dirtied_pause;
Wu Fengguang83712352011-06-11 19:25:42 -06001334
Wu Fengguangffd1f602011-06-19 22:18:42 -06001335 /*
Wu Fengguang1df64712011-11-13 19:47:32 -06001336 * This is typically equal to (nr_dirty < dirty_thresh) and can
1337 * also keep "1000+ dd on a slow USB stick" under control.
Wu Fengguangffd1f602011-06-19 22:18:42 -06001338 */
Wu Fengguang1df64712011-11-13 19:47:32 -06001339 if (task_ratelimit)
Wu Fengguangffd1f602011-06-19 22:18:42 -06001340 break;
Jan Kara499d05e2011-11-16 19:34:48 +08001341
Wu Fengguangc5c63432011-12-02 10:21:33 -06001342 /*
1343 * In the case of an unresponding NFS server and the NFS dirty
1344 * pages exceeds dirty_thresh, give the other good bdi's a pipe
1345 * to go through, so that tasks on them still remain responsive.
1346 *
1347 * In theory 1 page is enough to keep the comsumer-producer
1348 * pipe going: the flusher cleans 1 page => the task dirties 1
1349 * more page. However bdi_dirty has accounting errors. So use
1350 * the larger and more IO friendly bdi_stat_error.
1351 */
1352 if (bdi_dirty <= bdi_stat_error(bdi))
1353 break;
1354
Jan Kara499d05e2011-11-16 19:34:48 +08001355 if (fatal_signal_pending(current))
1356 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001357 }
1358
Wu Fengguang143dfe82010-08-27 18:45:12 -06001359 if (!dirty_exceeded && bdi->dirty_exceeded)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001360 bdi->dirty_exceeded = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001361
1362 if (writeback_in_progress(bdi))
Jens Axboe5b0830c2009-09-23 19:37:09 +02001363 return;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001364
1365 /*
1366 * In laptop mode, we wait until hitting the higher threshold before
1367 * starting background writeout, and then write out all the way down
1368 * to the lower threshold. So slow writers cause minimal disk activity.
1369 *
1370 * In normal mode, we start background writeout at the lower
1371 * background_thresh, to keep the amount of dirty memory low.
1372 */
Wu Fengguang143dfe82010-08-27 18:45:12 -06001373 if (laptop_mode)
1374 return;
1375
1376 if (nr_reclaimable > background_thresh)
Christoph Hellwigc5444192010-06-08 18:15:15 +02001377 bdi_start_background_writeback(bdi);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001378}
1379
Peter Zijlstraa200ee12007-10-08 18:54:37 +02001380void set_page_dirty_balance(struct page *page, int page_mkwrite)
Peter Zijlstraedc79b22006-09-25 23:30:58 -07001381{
Peter Zijlstraa200ee12007-10-08 18:54:37 +02001382 if (set_page_dirty(page) || page_mkwrite) {
Peter Zijlstraedc79b22006-09-25 23:30:58 -07001383 struct address_space *mapping = page_mapping(page);
1384
1385 if (mapping)
1386 balance_dirty_pages_ratelimited(mapping);
1387 }
1388}
1389
Wu Fengguang9d823e82011-06-11 18:10:12 -06001390static DEFINE_PER_CPU(int, bdp_ratelimits);
Tejun Heo245b2e72009-06-24 15:13:48 +09001391
Wu Fengguang54848d72011-04-05 13:21:19 -06001392/*
1393 * Normal tasks are throttled by
1394 * loop {
1395 * dirty tsk->nr_dirtied_pause pages;
1396 * take a snap in balance_dirty_pages();
1397 * }
1398 * However there is a worst case. If every task exit immediately when dirtied
1399 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1400 * called to throttle the page dirties. The solution is to save the not yet
1401 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1402 * randomly into the running tasks. This works well for the above worst case,
1403 * as the new task will pick up and accumulate the old task's leaked dirty
1404 * count and eventually get throttled.
1405 */
1406DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1407
Linus Torvalds1da177e2005-04-16 15:20:36 -07001408/**
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001409 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
Martin Waitz67be2dd2005-05-01 08:59:26 -07001410 * @mapping: address_space which was dirtied
Martin Waitza5802902006-04-02 13:59:55 +02001411 * @nr_pages_dirtied: number of pages which the caller has just dirtied
Linus Torvalds1da177e2005-04-16 15:20:36 -07001412 *
1413 * Processes which are dirtying memory should call in here once for each page
1414 * which was newly dirtied. The function will periodically check the system's
1415 * dirty state and will initiate writeback if needed.
1416 *
1417 * On really big machines, get_writeback_state is expensive, so try to avoid
1418 * calling it too often (ratelimiting). But once we're over the dirty memory
1419 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1420 * from overshooting the limit by (ratelimit_pages) each.
1421 */
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001422void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
1423 unsigned long nr_pages_dirtied)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001424{
Wu Fengguang36715ce2011-06-11 17:53:57 -06001425 struct backing_dev_info *bdi = mapping->backing_dev_info;
Wu Fengguang9d823e82011-06-11 18:10:12 -06001426 int ratelimit;
1427 int *p;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001428
Wu Fengguang36715ce2011-06-11 17:53:57 -06001429 if (!bdi_cap_account_dirty(bdi))
1430 return;
1431
Wu Fengguang9d823e82011-06-11 18:10:12 -06001432 ratelimit = current->nr_dirtied_pause;
1433 if (bdi->dirty_exceeded)
1434 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
Linus Torvalds1da177e2005-04-16 15:20:36 -07001435
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001436 preempt_disable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001437 /*
1438 * This prevents one CPU to accumulate too many dirtied pages without
1439 * calling into balance_dirty_pages(), which can happen when there are
1440 * 1000+ tasks, all of them start dirtying pages at exactly the same
1441 * time, hence all honoured too large initial task->nr_dirtied_pause.
1442 */
Tejun Heo245b2e72009-06-24 15:13:48 +09001443 p = &__get_cpu_var(bdp_ratelimits);
Wu Fengguang9d823e82011-06-11 18:10:12 -06001444 if (unlikely(current->nr_dirtied >= ratelimit))
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001445 *p = 0;
Wu Fengguangd3bc1fe2011-04-14 07:52:37 -06001446 else if (unlikely(*p >= ratelimit_pages)) {
1447 *p = 0;
1448 ratelimit = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001449 }
Wu Fengguang54848d72011-04-05 13:21:19 -06001450 /*
1451 * Pick up the dirtied pages by the exited tasks. This avoids lots of
1452 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1453 * the dirty throttling and livelock other long-run dirtiers.
1454 */
1455 p = &__get_cpu_var(dirty_throttle_leaks);
1456 if (*p > 0 && current->nr_dirtied < ratelimit) {
1457 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1458 *p -= nr_pages_dirtied;
1459 current->nr_dirtied += nr_pages_dirtied;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001460 }
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001461 preempt_enable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001462
1463 if (unlikely(current->nr_dirtied >= ratelimit))
1464 balance_dirty_pages(mapping, current->nr_dirtied);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001465}
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001466EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001467
Andrew Morton232ea4d2007-02-28 20:13:21 -08001468void throttle_vm_writeout(gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001469{
David Rientjes364aeb22009-01-06 14:39:29 -08001470 unsigned long background_thresh;
1471 unsigned long dirty_thresh;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001472
1473 for ( ; ; ) {
Wu Fengguang16c40422010-08-11 14:17:39 -07001474 global_dirty_limits(&background_thresh, &dirty_thresh);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001475
1476 /*
1477 * Boost the allowable dirty threshold a bit for page
1478 * allocators so they don't get DoS'ed by heavy writers
1479 */
1480 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1481
Christoph Lameterc24f21b2006-06-30 01:55:42 -07001482 if (global_page_state(NR_UNSTABLE_NFS) +
1483 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1484 break;
Jens Axboe8aa7e842009-07-09 14:52:32 +02001485 congestion_wait(BLK_RW_ASYNC, HZ/10);
Fengguang Wu369f2382007-10-16 23:30:45 -07001486
1487 /*
1488 * The caller might hold locks which can prevent IO completion
1489 * or progress in the filesystem. So we cannot just sit here
1490 * waiting for IO to complete.
1491 */
1492 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1493 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001494 }
1495}
1496
Linus Torvalds1da177e2005-04-16 15:20:36 -07001497/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001498 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1499 */
1500int dirty_writeback_centisecs_handler(ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001501 void __user *buffer, size_t *length, loff_t *ppos)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001502{
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001503 proc_dointvec(table, write, buffer, length, ppos);
Jens Axboe64231042010-05-21 20:00:35 +02001504 bdi_arm_supers_timer();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001505 return 0;
1506}
1507
Jens Axboec2c49862010-05-20 09:18:47 +02001508#ifdef CONFIG_BLOCK
Matthew Garrett31373d02010-04-06 14:25:14 +02001509void laptop_mode_timer_fn(unsigned long data)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001510{
Matthew Garrett31373d02010-04-06 14:25:14 +02001511 struct request_queue *q = (struct request_queue *)data;
1512 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1513 global_page_state(NR_UNSTABLE_NFS);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001514
Matthew Garrett31373d02010-04-06 14:25:14 +02001515 /*
1516 * We want to write everything out, not just down to the dirty
1517 * threshold
1518 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001519 if (bdi_has_dirty_io(&q->backing_dev_info))
Curt Wohlgemuth0e175a12011-10-07 21:54:10 -06001520 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1521 WB_REASON_LAPTOP_TIMER);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001522}
1523
1524/*
1525 * We've spun up the disk and we're in laptop mode: schedule writeback
1526 * of all dirty data a few seconds from now. If the flush is already scheduled
1527 * then push it back - the user is still using the disk.
1528 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001529void laptop_io_completion(struct backing_dev_info *info)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001530{
Matthew Garrett31373d02010-04-06 14:25:14 +02001531 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001532}
1533
1534/*
1535 * We're in laptop mode and we've just synced. The sync's writes will have
1536 * caused another writeback to be scheduled by laptop_io_completion.
1537 * Nothing needs to be written back anymore, so we unschedule the writeback.
1538 */
1539void laptop_sync_completion(void)
1540{
Matthew Garrett31373d02010-04-06 14:25:14 +02001541 struct backing_dev_info *bdi;
1542
1543 rcu_read_lock();
1544
1545 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1546 del_timer(&bdi->laptop_mode_wb_timer);
1547
1548 rcu_read_unlock();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001549}
Jens Axboec2c49862010-05-20 09:18:47 +02001550#endif
Linus Torvalds1da177e2005-04-16 15:20:36 -07001551
1552/*
1553 * If ratelimit_pages is too high then we can get into dirty-data overload
1554 * if a large number of processes all perform writes at the same time.
1555 * If it is too low then SMP machines will call the (expensive)
1556 * get_writeback_state too often.
1557 *
1558 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1559 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
Wu Fengguang9d823e82011-06-11 18:10:12 -06001560 * thresholds.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001561 */
1562
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001563void writeback_set_ratelimit(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001564{
Wu Fengguang9d823e82011-06-11 18:10:12 -06001565 unsigned long background_thresh;
1566 unsigned long dirty_thresh;
1567 global_dirty_limits(&background_thresh, &dirty_thresh);
1568 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001569 if (ratelimit_pages < 16)
1570 ratelimit_pages = 16;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001571}
1572
Chandra Seetharaman26c21432006-06-27 02:54:10 -07001573static int __cpuinit
Linus Torvalds1da177e2005-04-16 15:20:36 -07001574ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
1575{
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001576 writeback_set_ratelimit();
Paul E. McKenneyaa0f0302007-02-10 01:46:37 -08001577 return NOTIFY_DONE;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001578}
1579
Chandra Seetharaman74b85f32006-06-27 02:54:09 -07001580static struct notifier_block __cpuinitdata ratelimit_nb = {
Linus Torvalds1da177e2005-04-16 15:20:36 -07001581 .notifier_call = ratelimit_handler,
1582 .next = NULL,
1583};
1584
1585/*
Linus Torvaldsdc6e29d2007-01-29 16:37:38 -08001586 * Called early on to tune the page writeback dirty limits.
1587 *
1588 * We used to scale dirty pages according to how total memory
1589 * related to pages that could be allocated for buffers (by
1590 * comparing nr_free_buffer_pages() to vm_total_pages.
1591 *
1592 * However, that was when we used "dirty_ratio" to scale with
1593 * all memory, and we don't do that any more. "dirty_ratio"
1594 * is now applied to total non-HIGHPAGE memory (by subtracting
1595 * totalhigh_pages from vm_total_pages), and as such we can't
1596 * get into the old insane situation any more where we had
1597 * large amounts of dirty pages compared to a small amount of
1598 * non-HIGHMEM memory.
1599 *
1600 * But we might still want to scale the dirty_ratio by how
1601 * much memory the box has..
Linus Torvalds1da177e2005-04-16 15:20:36 -07001602 */
1603void __init page_writeback_init(void)
1604{
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001605 int shift;
1606
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001607 writeback_set_ratelimit();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001608 register_cpu_notifier(&ratelimit_nb);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001609
1610 shift = calc_period_shift();
1611 prop_descriptor_init(&vm_completions, shift);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001612}
1613
David Howells811d7362006-08-29 19:06:09 +01001614/**
Jan Karaf446daa2010-08-09 17:19:12 -07001615 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1616 * @mapping: address space structure to write
1617 * @start: starting page index
1618 * @end: ending page index (inclusive)
1619 *
1620 * This function scans the page range from @start to @end (inclusive) and tags
1621 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1622 * that write_cache_pages (or whoever calls this function) will then use
1623 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1624 * used to avoid livelocking of writeback by a process steadily creating new
1625 * dirty pages in the file (thus it is important for this function to be quick
1626 * so that it can tag pages faster than a dirtying process can create them).
1627 */
1628/*
1629 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1630 */
Jan Karaf446daa2010-08-09 17:19:12 -07001631void tag_pages_for_writeback(struct address_space *mapping,
1632 pgoff_t start, pgoff_t end)
1633{
Randy Dunlap3c111a02010-08-11 14:17:30 -07001634#define WRITEBACK_TAG_BATCH 4096
Jan Karaf446daa2010-08-09 17:19:12 -07001635 unsigned long tagged;
1636
1637 do {
1638 spin_lock_irq(&mapping->tree_lock);
1639 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1640 &start, end, WRITEBACK_TAG_BATCH,
1641 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1642 spin_unlock_irq(&mapping->tree_lock);
1643 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1644 cond_resched();
Jan Karad5ed3a42010-08-19 14:13:33 -07001645 /* We check 'start' to handle wrapping when end == ~0UL */
1646 } while (tagged >= WRITEBACK_TAG_BATCH && start);
Jan Karaf446daa2010-08-09 17:19:12 -07001647}
1648EXPORT_SYMBOL(tag_pages_for_writeback);
1649
1650/**
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001651 * 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 +01001652 * @mapping: address space structure to write
1653 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001654 * @writepage: function called for each page
1655 * @data: data passed to writepage function
David Howells811d7362006-08-29 19:06:09 +01001656 *
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001657 * If a page is already under I/O, write_cache_pages() skips it, even
David Howells811d7362006-08-29 19:06:09 +01001658 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1659 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1660 * and msync() need to guarantee that all the data which was dirty at the time
1661 * the call was made get new I/O started against them. If wbc->sync_mode is
1662 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1663 * existing IO to complete.
Jan Karaf446daa2010-08-09 17:19:12 -07001664 *
1665 * To avoid livelocks (when other process dirties new pages), we first tag
1666 * pages which should be written back with TOWRITE tag and only then start
1667 * writing them. For data-integrity sync we have to be careful so that we do
1668 * not miss some pages (e.g., because some other process has cleared TOWRITE
1669 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1670 * by the process clearing the DIRTY tag (and submitting the page for IO).
David Howells811d7362006-08-29 19:06:09 +01001671 */
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001672int write_cache_pages(struct address_space *mapping,
1673 struct writeback_control *wbc, writepage_t writepage,
1674 void *data)
David Howells811d7362006-08-29 19:06:09 +01001675{
David Howells811d7362006-08-29 19:06:09 +01001676 int ret = 0;
1677 int done = 0;
David Howells811d7362006-08-29 19:06:09 +01001678 struct pagevec pvec;
1679 int nr_pages;
Nick Piggin31a12662009-01-06 14:39:04 -08001680 pgoff_t uninitialized_var(writeback_index);
David Howells811d7362006-08-29 19:06:09 +01001681 pgoff_t index;
1682 pgoff_t end; /* Inclusive */
Nick Pigginbd19e012009-01-06 14:39:06 -08001683 pgoff_t done_index;
Nick Piggin31a12662009-01-06 14:39:04 -08001684 int cycled;
David Howells811d7362006-08-29 19:06:09 +01001685 int range_whole = 0;
Jan Karaf446daa2010-08-09 17:19:12 -07001686 int tag;
David Howells811d7362006-08-29 19:06:09 +01001687
David Howells811d7362006-08-29 19:06:09 +01001688 pagevec_init(&pvec, 0);
1689 if (wbc->range_cyclic) {
Nick Piggin31a12662009-01-06 14:39:04 -08001690 writeback_index = mapping->writeback_index; /* prev offset */
1691 index = writeback_index;
1692 if (index == 0)
1693 cycled = 1;
1694 else
1695 cycled = 0;
David Howells811d7362006-08-29 19:06:09 +01001696 end = -1;
1697 } else {
1698 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1699 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1700 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1701 range_whole = 1;
Nick Piggin31a12662009-01-06 14:39:04 -08001702 cycled = 1; /* ignore range_cyclic tests */
David Howells811d7362006-08-29 19:06:09 +01001703 }
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001704 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daa2010-08-09 17:19:12 -07001705 tag = PAGECACHE_TAG_TOWRITE;
1706 else
1707 tag = PAGECACHE_TAG_DIRTY;
David Howells811d7362006-08-29 19:06:09 +01001708retry:
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001709 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daa2010-08-09 17:19:12 -07001710 tag_pages_for_writeback(mapping, index, end);
Nick Pigginbd19e012009-01-06 14:39:06 -08001711 done_index = index;
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001712 while (!done && (index <= end)) {
1713 int i;
1714
Jan Karaf446daa2010-08-09 17:19:12 -07001715 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001716 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1717 if (nr_pages == 0)
1718 break;
David Howells811d7362006-08-29 19:06:09 +01001719
David Howells811d7362006-08-29 19:06:09 +01001720 for (i = 0; i < nr_pages; i++) {
1721 struct page *page = pvec.pages[i];
1722
Nick Piggind5482cd2009-01-06 14:39:11 -08001723 /*
1724 * At this point, the page may be truncated or
1725 * invalidated (changing page->mapping to NULL), or
1726 * even swizzled back from swapper_space to tmpfs file
1727 * mapping. However, page->index will not change
1728 * because we have a reference on the page.
1729 */
1730 if (page->index > end) {
1731 /*
1732 * can't be range_cyclic (1st pass) because
1733 * end == -1 in that case.
1734 */
1735 done = 1;
1736 break;
1737 }
1738
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001739 done_index = page->index;
Nick Pigginbd19e012009-01-06 14:39:06 -08001740
David Howells811d7362006-08-29 19:06:09 +01001741 lock_page(page);
1742
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001743 /*
1744 * Page truncated or invalidated. We can freely skip it
1745 * then, even for data integrity operations: the page
1746 * has disappeared concurrently, so there could be no
1747 * real expectation of this data interity operation
1748 * even if there is now a new, dirty page at the same
1749 * pagecache address.
1750 */
David Howells811d7362006-08-29 19:06:09 +01001751 if (unlikely(page->mapping != mapping)) {
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001752continue_unlock:
David Howells811d7362006-08-29 19:06:09 +01001753 unlock_page(page);
1754 continue;
1755 }
1756
Nick Piggin515f4a02009-01-06 14:39:10 -08001757 if (!PageDirty(page)) {
1758 /* someone wrote it for us */
1759 goto continue_unlock;
1760 }
David Howells811d7362006-08-29 19:06:09 +01001761
Nick Piggin515f4a02009-01-06 14:39:10 -08001762 if (PageWriteback(page)) {
1763 if (wbc->sync_mode != WB_SYNC_NONE)
1764 wait_on_page_writeback(page);
1765 else
1766 goto continue_unlock;
1767 }
1768
1769 BUG_ON(PageWriteback(page));
1770 if (!clear_page_dirty_for_io(page))
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001771 goto continue_unlock;
David Howells811d7362006-08-29 19:06:09 +01001772
Dave Chinner9e094382010-07-07 13:24:08 +10001773 trace_wbc_writepage(wbc, mapping->backing_dev_info);
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001774 ret = (*writepage)(page, wbc, data);
Nick Piggin00266772009-01-06 14:39:06 -08001775 if (unlikely(ret)) {
1776 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1777 unlock_page(page);
1778 ret = 0;
1779 } else {
1780 /*
1781 * done_index is set past this page,
1782 * so media errors will not choke
1783 * background writeout for the entire
1784 * file. This has consequences for
1785 * range_cyclic semantics (ie. it may
1786 * not be suitable for data integrity
1787 * writeout).
1788 */
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001789 done_index = page->index + 1;
Nick Piggin00266772009-01-06 14:39:06 -08001790 done = 1;
1791 break;
1792 }
Dave Chinner0b564922010-06-09 10:37:18 +10001793 }
David Howells811d7362006-08-29 19:06:09 +01001794
Dave Chinner546a1922010-08-24 11:44:34 +10001795 /*
1796 * We stop writing back only if we are not doing
1797 * integrity sync. In case of integrity sync we have to
1798 * keep going until we have written all the pages
1799 * we tagged for writeback prior to entering this loop.
1800 */
1801 if (--wbc->nr_to_write <= 0 &&
1802 wbc->sync_mode == WB_SYNC_NONE) {
1803 done = 1;
1804 break;
Nick Piggin05fe4782009-01-06 14:39:08 -08001805 }
David Howells811d7362006-08-29 19:06:09 +01001806 }
1807 pagevec_release(&pvec);
1808 cond_resched();
1809 }
Nick Piggin3a4c6802009-02-12 04:34:23 +01001810 if (!cycled && !done) {
David Howells811d7362006-08-29 19:06:09 +01001811 /*
Nick Piggin31a12662009-01-06 14:39:04 -08001812 * range_cyclic:
David Howells811d7362006-08-29 19:06:09 +01001813 * We hit the last page and there is more work to be done: wrap
1814 * back to the start of the file
1815 */
Nick Piggin31a12662009-01-06 14:39:04 -08001816 cycled = 1;
David Howells811d7362006-08-29 19:06:09 +01001817 index = 0;
Nick Piggin31a12662009-01-06 14:39:04 -08001818 end = writeback_index - 1;
David Howells811d7362006-08-29 19:06:09 +01001819 goto retry;
1820 }
Dave Chinner0b564922010-06-09 10:37:18 +10001821 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1822 mapping->writeback_index = done_index;
Aneesh Kumar K.V06d6cf62008-07-11 19:27:31 -04001823
David Howells811d7362006-08-29 19:06:09 +01001824 return ret;
1825}
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001826EXPORT_SYMBOL(write_cache_pages);
1827
1828/*
1829 * Function used by generic_writepages to call the real writepage
1830 * function and set the mapping flags on error
1831 */
1832static int __writepage(struct page *page, struct writeback_control *wbc,
1833 void *data)
1834{
1835 struct address_space *mapping = data;
1836 int ret = mapping->a_ops->writepage(page, wbc);
1837 mapping_set_error(mapping, ret);
1838 return ret;
1839}
1840
1841/**
1842 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1843 * @mapping: address space structure to write
1844 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1845 *
1846 * This is a library function, which implements the writepages()
1847 * address_space_operation.
1848 */
1849int generic_writepages(struct address_space *mapping,
1850 struct writeback_control *wbc)
1851{
Shaohua Li9b6096a2011-03-17 10:47:06 +01001852 struct blk_plug plug;
1853 int ret;
1854
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001855 /* deal with chardevs and other special file */
1856 if (!mapping->a_ops->writepage)
1857 return 0;
1858
Shaohua Li9b6096a2011-03-17 10:47:06 +01001859 blk_start_plug(&plug);
1860 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1861 blk_finish_plug(&plug);
1862 return ret;
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001863}
David Howells811d7362006-08-29 19:06:09 +01001864
1865EXPORT_SYMBOL(generic_writepages);
1866
Linus Torvalds1da177e2005-04-16 15:20:36 -07001867int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1868{
Andrew Morton22905f72005-11-16 15:07:01 -08001869 int ret;
1870
Linus Torvalds1da177e2005-04-16 15:20:36 -07001871 if (wbc->nr_to_write <= 0)
1872 return 0;
1873 if (mapping->a_ops->writepages)
Peter Zijlstrad08b3852006-09-25 23:30:57 -07001874 ret = mapping->a_ops->writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08001875 else
1876 ret = generic_writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08001877 return ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001878}
1879
1880/**
1881 * write_one_page - write out a single page and optionally wait on I/O
Martin Waitz67be2dd2005-05-01 08:59:26 -07001882 * @page: the page to write
1883 * @wait: if true, wait on writeout
Linus Torvalds1da177e2005-04-16 15:20:36 -07001884 *
1885 * The page must be locked by the caller and will be unlocked upon return.
1886 *
1887 * write_one_page() returns a negative error code if I/O failed.
1888 */
1889int write_one_page(struct page *page, int wait)
1890{
1891 struct address_space *mapping = page->mapping;
1892 int ret = 0;
1893 struct writeback_control wbc = {
1894 .sync_mode = WB_SYNC_ALL,
1895 .nr_to_write = 1,
1896 };
1897
1898 BUG_ON(!PageLocked(page));
1899
1900 if (wait)
1901 wait_on_page_writeback(page);
1902
1903 if (clear_page_dirty_for_io(page)) {
1904 page_cache_get(page);
1905 ret = mapping->a_ops->writepage(page, &wbc);
1906 if (ret == 0 && wait) {
1907 wait_on_page_writeback(page);
1908 if (PageError(page))
1909 ret = -EIO;
1910 }
1911 page_cache_release(page);
1912 } else {
1913 unlock_page(page);
1914 }
1915 return ret;
1916}
1917EXPORT_SYMBOL(write_one_page);
1918
1919/*
Ken Chen76719322007-02-10 01:43:15 -08001920 * For address_spaces which do not use buffers nor write back.
1921 */
1922int __set_page_dirty_no_writeback(struct page *page)
1923{
1924 if (!PageDirty(page))
Bob Liuc3f0da62011-01-13 15:45:49 -08001925 return !TestSetPageDirty(page);
Ken Chen76719322007-02-10 01:43:15 -08001926 return 0;
1927}
1928
1929/*
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001930 * Helper function for set_page_dirty family.
1931 * NOTE: This relies on being atomic wrt interrupts.
1932 */
1933void account_page_dirtied(struct page *page, struct address_space *mapping)
1934{
1935 if (mapping_cap_account_dirty(mapping)) {
1936 __inc_zone_page_state(page, NR_FILE_DIRTY);
Michael Rubinea941f02010-10-26 14:21:35 -07001937 __inc_zone_page_state(page, NR_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001938 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
Wu Fengguangc8e28ce2011-01-23 10:07:47 -06001939 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001940 task_io_account_write(PAGE_CACHE_SIZE);
Wu Fengguangd3bc1fe2011-04-14 07:52:37 -06001941 current->nr_dirtied++;
1942 this_cpu_inc(bdp_ratelimits);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001943 }
1944}
Michael Rubin679ceac2010-08-20 02:31:26 -07001945EXPORT_SYMBOL(account_page_dirtied);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001946
1947/*
Michael Rubinf629d1c2010-10-26 14:21:33 -07001948 * Helper function for set_page_writeback family.
1949 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1950 * wrt interrupts.
1951 */
1952void account_page_writeback(struct page *page)
1953{
1954 inc_zone_page_state(page, NR_WRITEBACK);
1955}
1956EXPORT_SYMBOL(account_page_writeback);
1957
1958/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001959 * For address_spaces which do not use buffers. Just tag the page as dirty in
1960 * its radix tree.
1961 *
1962 * This is also used when a single buffer is being dirtied: we want to set the
1963 * page dirty in that case, but not all the buffers. This is a "bottom-up"
1964 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1965 *
1966 * Most callers have locked the page, which pins the address_space in memory.
1967 * But zap_pte_range() does not lock the page, however in that case the
1968 * mapping is pinned by the vma's ->vm_file reference.
1969 *
1970 * We take care to handle the case where the page was truncated from the
Simon Arlott183ff222007-10-20 01:27:18 +02001971 * mapping by re-checking page_mapping() inside tree_lock.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001972 */
1973int __set_page_dirty_nobuffers(struct page *page)
1974{
Linus Torvalds1da177e2005-04-16 15:20:36 -07001975 if (!TestSetPageDirty(page)) {
1976 struct address_space *mapping = page_mapping(page);
1977 struct address_space *mapping2;
1978
Andrew Morton8c085402006-12-10 02:19:24 -08001979 if (!mapping)
1980 return 1;
1981
Nick Piggin19fd6232008-07-25 19:45:32 -07001982 spin_lock_irq(&mapping->tree_lock);
Andrew Morton8c085402006-12-10 02:19:24 -08001983 mapping2 = page_mapping(page);
1984 if (mapping2) { /* Race with truncate? */
1985 BUG_ON(mapping2 != mapping);
Nick Piggin787d2212007-07-17 04:03:34 -07001986 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001987 account_page_dirtied(page, mapping);
Andrew Morton8c085402006-12-10 02:19:24 -08001988 radix_tree_tag_set(&mapping->page_tree,
1989 page_index(page), PAGECACHE_TAG_DIRTY);
1990 }
Nick Piggin19fd6232008-07-25 19:45:32 -07001991 spin_unlock_irq(&mapping->tree_lock);
Andrew Morton8c085402006-12-10 02:19:24 -08001992 if (mapping->host) {
1993 /* !PageAnon && !swapper_space */
1994 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001995 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08001996 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001997 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08001998 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001999}
2000EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2001
2002/*
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002003 * Call this whenever redirtying a page, to de-account the dirty counters
2004 * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2005 * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2006 * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2007 * control.
2008 */
2009void account_page_redirty(struct page *page)
2010{
2011 struct address_space *mapping = page->mapping;
2012 if (mapping && mapping_cap_account_dirty(mapping)) {
2013 current->nr_dirtied--;
2014 dec_zone_page_state(page, NR_DIRTIED);
2015 dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
2016 }
2017}
2018EXPORT_SYMBOL(account_page_redirty);
2019
2020/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002021 * When a writepage implementation decides that it doesn't want to write this
2022 * page for some reason, it should redirty the locked page via
2023 * redirty_page_for_writepage() and it should then unlock the page and return 0
2024 */
2025int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2026{
2027 wbc->pages_skipped++;
Wu Fengguang2f800fb2011-08-08 15:22:00 -06002028 account_page_redirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002029 return __set_page_dirty_nobuffers(page);
2030}
2031EXPORT_SYMBOL(redirty_page_for_writepage);
2032
2033/*
Wu Fengguang6746aff2009-09-16 11:50:14 +02002034 * Dirty a page.
2035 *
2036 * For pages with a mapping this should be done under the page lock
2037 * for the benefit of asynchronous memory errors who prefer a consistent
2038 * dirty state. This rule can be broken in some special cases,
2039 * but should be better not to.
2040 *
Linus Torvalds1da177e2005-04-16 15:20:36 -07002041 * If the mapping doesn't provide a set_page_dirty a_op, then
2042 * just fall through and assume that it wants buffer_heads.
2043 */
Nick Piggin1cf6e7d2009-02-18 14:48:18 -08002044int set_page_dirty(struct page *page)
Linus Torvalds1da177e2005-04-16 15:20:36 -07002045{
2046 struct address_space *mapping = page_mapping(page);
2047
2048 if (likely(mapping)) {
2049 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
Minchan Kim278df9f2011-03-22 16:32:54 -07002050 /*
2051 * readahead/lru_deactivate_page could remain
2052 * PG_readahead/PG_reclaim due to race with end_page_writeback
2053 * About readahead, if the page is written, the flags would be
2054 * reset. So no problem.
2055 * About lru_deactivate_page, if the page is redirty, the flag
2056 * will be reset. So no problem. but if the page is used by readahead
2057 * it will confuse readahead and make it restart the size rampup
2058 * process. But it's a trivial problem.
2059 */
2060 ClearPageReclaim(page);
David Howells93614012006-09-30 20:45:40 +02002061#ifdef CONFIG_BLOCK
2062 if (!spd)
2063 spd = __set_page_dirty_buffers;
2064#endif
2065 return (*spd)(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002066 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08002067 if (!PageDirty(page)) {
2068 if (!TestSetPageDirty(page))
2069 return 1;
2070 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002071 return 0;
2072}
2073EXPORT_SYMBOL(set_page_dirty);
2074
2075/*
2076 * set_page_dirty() is racy if the caller has no reference against
2077 * page->mapping->host, and if the page is unlocked. This is because another
2078 * CPU could truncate the page off the mapping and then free the mapping.
2079 *
2080 * Usually, the page _is_ locked, or the caller is a user-space process which
2081 * holds a reference on the inode by having an open file.
2082 *
2083 * In other cases, the page should be locked before running set_page_dirty().
2084 */
2085int set_page_dirty_lock(struct page *page)
2086{
2087 int ret;
2088
Jens Axboe7eaceac2011-03-10 08:52:07 +01002089 lock_page(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002090 ret = set_page_dirty(page);
2091 unlock_page(page);
2092 return ret;
2093}
2094EXPORT_SYMBOL(set_page_dirty_lock);
2095
2096/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002097 * Clear a page's dirty flag, while caring for dirty memory accounting.
2098 * Returns true if the page was previously dirty.
2099 *
2100 * This is for preparing to put the page under writeout. We leave the page
2101 * tagged as dirty in the radix tree so that a concurrent write-for-sync
2102 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
2103 * implementation will run either set_page_writeback() or set_page_dirty(),
2104 * at which stage we bring the page's dirty flag and radix-tree dirty tag
2105 * back into sync.
2106 *
2107 * This incoherency between the page's dirty flag and radix-tree tag is
2108 * unfortunate, but it only exists while the page is locked.
2109 */
2110int clear_page_dirty_for_io(struct page *page)
2111{
2112 struct address_space *mapping = page_mapping(page);
2113
Nick Piggin79352892007-07-19 01:47:22 -07002114 BUG_ON(!PageLocked(page));
2115
Linus Torvalds7658cc22006-12-29 10:00:58 -08002116 if (mapping && mapping_cap_account_dirty(mapping)) {
2117 /*
2118 * Yes, Virginia, this is indeed insane.
2119 *
2120 * We use this sequence to make sure that
2121 * (a) we account for dirty stats properly
2122 * (b) we tell the low-level filesystem to
2123 * mark the whole page dirty if it was
2124 * dirty in a pagetable. Only to then
2125 * (c) clean the page again and return 1 to
2126 * cause the writeback.
2127 *
2128 * This way we avoid all nasty races with the
2129 * dirty bit in multiple places and clearing
2130 * them concurrently from different threads.
2131 *
2132 * Note! Normally the "set_page_dirty(page)"
2133 * has no effect on the actual dirty bit - since
2134 * that will already usually be set. But we
2135 * need the side effects, and it can help us
2136 * avoid races.
2137 *
2138 * We basically use the page "master dirty bit"
2139 * as a serialization point for all the different
2140 * threads doing their things.
Linus Torvalds7658cc22006-12-29 10:00:58 -08002141 */
2142 if (page_mkclean(page))
2143 set_page_dirty(page);
Nick Piggin79352892007-07-19 01:47:22 -07002144 /*
2145 * We carefully synchronise fault handlers against
2146 * installing a dirty pte and marking the page dirty
2147 * at this point. We do this by having them hold the
2148 * page lock at some point after installing their
2149 * pte, but before marking the page dirty.
2150 * Pages are always locked coming in here, so we get
2151 * the desired exclusion. See mm/memory.c:do_wp_page()
2152 * for more comments.
2153 */
Linus Torvalds7658cc22006-12-29 10:00:58 -08002154 if (TestClearPageDirty(page)) {
Andrew Morton8c085402006-12-10 02:19:24 -08002155 dec_zone_page_state(page, NR_FILE_DIRTY);
Peter Zijlstrac9e51e42007-10-16 23:25:47 -07002156 dec_bdi_stat(mapping->backing_dev_info,
2157 BDI_RECLAIMABLE);
Linus Torvalds7658cc22006-12-29 10:00:58 -08002158 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002159 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08002160 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002161 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08002162 return TestClearPageDirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002163}
Hans Reiser58bb01a2005-11-18 01:10:53 -08002164EXPORT_SYMBOL(clear_page_dirty_for_io);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002165
2166int test_clear_page_writeback(struct page *page)
2167{
2168 struct address_space *mapping = page_mapping(page);
2169 int ret;
2170
2171 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002172 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002173 unsigned long flags;
2174
Nick Piggin19fd6232008-07-25 19:45:32 -07002175 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002176 ret = TestClearPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002177 if (ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07002178 radix_tree_tag_clear(&mapping->page_tree,
2179 page_index(page),
2180 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07002181 if (bdi_cap_account_writeback(bdi)) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002182 __dec_bdi_stat(bdi, BDI_WRITEBACK);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07002183 __bdi_writeout_inc(bdi);
2184 }
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002185 }
Nick Piggin19fd6232008-07-25 19:45:32 -07002186 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002187 } else {
2188 ret = TestClearPageWriteback(page);
2189 }
Wu Fengguang99b12e32011-07-25 17:12:37 -07002190 if (ret) {
Andrew Mortond688abf2007-07-19 01:49:17 -07002191 dec_zone_page_state(page, NR_WRITEBACK);
Wu Fengguang99b12e32011-07-25 17:12:37 -07002192 inc_zone_page_state(page, NR_WRITTEN);
2193 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002194 return ret;
2195}
2196
2197int test_set_page_writeback(struct page *page)
2198{
2199 struct address_space *mapping = page_mapping(page);
2200 int ret;
2201
2202 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002203 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07002204 unsigned long flags;
2205
Nick Piggin19fd6232008-07-25 19:45:32 -07002206 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002207 ret = TestSetPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002208 if (!ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07002209 radix_tree_tag_set(&mapping->page_tree,
2210 page_index(page),
2211 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07002212 if (bdi_cap_account_writeback(bdi))
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07002213 __inc_bdi_stat(bdi, BDI_WRITEBACK);
2214 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07002215 if (!PageDirty(page))
2216 radix_tree_tag_clear(&mapping->page_tree,
2217 page_index(page),
2218 PAGECACHE_TAG_DIRTY);
Jan Karaf446daa2010-08-09 17:19:12 -07002219 radix_tree_tag_clear(&mapping->page_tree,
2220 page_index(page),
2221 PAGECACHE_TAG_TOWRITE);
Nick Piggin19fd6232008-07-25 19:45:32 -07002222 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002223 } else {
2224 ret = TestSetPageWriteback(page);
2225 }
Andrew Mortond688abf2007-07-19 01:49:17 -07002226 if (!ret)
Michael Rubinf629d1c2010-10-26 14:21:33 -07002227 account_page_writeback(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002228 return ret;
2229
2230}
2231EXPORT_SYMBOL(test_set_page_writeback);
2232
2233/*
Nick Piggin00128182007-10-16 01:24:40 -07002234 * Return true if any of the pages in the mapping are marked with the
Linus Torvalds1da177e2005-04-16 15:20:36 -07002235 * passed tag.
2236 */
2237int mapping_tagged(struct address_space *mapping, int tag)
2238{
Konstantin Khlebnikov72c47832011-07-25 17:12:31 -07002239 return radix_tree_tagged(&mapping->page_tree, tag);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002240}
2241EXPORT_SYMBOL(mapping_tagged);