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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>
David Howellscf9a2ae2006-08-29 19:05:54 +010035#include <linux/buffer_head.h>
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 Fengguange98be2d2010-08-29 11:22:30 -060045 * Estimate write bandwidth at 200ms intervals.
46 */
47#define BANDWIDTH_INTERVAL max(HZ/5, 1)
48
Wu Fengguang6c14ae12011-03-02 16:04:18 -060049#define RATELIMIT_CALC_SHIFT 10
50
Wu Fengguange98be2d2010-08-29 11:22:30 -060051/*
Linus Torvalds1da177e2005-04-16 15:20:36 -070052 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
53 * will look to see if it needs to force writeback or throttling.
54 */
55static long ratelimit_pages = 32;
56
Linus Torvalds1da177e2005-04-16 15:20:36 -070057/* The following parameters are exported via /proc/sys/vm */
58
59/*
Jens Axboe5b0830c2009-09-23 19:37:09 +020060 * Start background writeback (via writeback threads) at this percentage
Linus Torvalds1da177e2005-04-16 15:20:36 -070061 */
Wu Fengguang1b5e62b2009-03-23 08:57:38 +080062int dirty_background_ratio = 10;
Linus Torvalds1da177e2005-04-16 15:20:36 -070063
64/*
David Rientjes2da02992009-01-06 14:39:31 -080065 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
66 * dirty_background_ratio * the amount of dirtyable memory
67 */
68unsigned long dirty_background_bytes;
69
70/*
Bron Gondwana195cf452008-02-04 22:29:20 -080071 * free highmem will not be subtracted from the total free memory
72 * for calculating free ratios if vm_highmem_is_dirtyable is true
73 */
74int vm_highmem_is_dirtyable;
75
76/*
Linus Torvalds1da177e2005-04-16 15:20:36 -070077 * The generator of dirty data starts writeback at this percentage
78 */
Wu Fengguang1b5e62b2009-03-23 08:57:38 +080079int vm_dirty_ratio = 20;
Linus Torvalds1da177e2005-04-16 15:20:36 -070080
81/*
David Rientjes2da02992009-01-06 14:39:31 -080082 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
83 * vm_dirty_ratio * the amount of dirtyable memory
84 */
85unsigned long vm_dirty_bytes;
86
87/*
Alexey Dobriyan704503d2009-03-31 15:23:18 -070088 * The interval between `kupdate'-style writebacks
Linus Torvalds1da177e2005-04-16 15:20:36 -070089 */
Toshiyuki Okajima22ef37e2009-05-16 22:56:28 -070090unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
Linus Torvalds1da177e2005-04-16 15:20:36 -070091
92/*
Alexey Dobriyan704503d2009-03-31 15:23:18 -070093 * The longest time for which data is allowed to remain dirty
Linus Torvalds1da177e2005-04-16 15:20:36 -070094 */
Toshiyuki Okajima22ef37e2009-05-16 22:56:28 -070095unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
Linus Torvalds1da177e2005-04-16 15:20:36 -070096
97/*
98 * Flag that makes the machine dump writes/reads and block dirtyings.
99 */
100int block_dump;
101
102/*
Bart Samweled5b43f2006-03-24 03:15:49 -0800103 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
104 * a full sync is triggered after this time elapses without any disk activity.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700105 */
106int laptop_mode;
107
108EXPORT_SYMBOL(laptop_mode);
109
110/* End of sysctl-exported parameters */
111
Wu Fengguangc42843f2011-03-02 15:54:09 -0600112unsigned long global_dirty_limit;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700113
Linus Torvalds1da177e2005-04-16 15:20:36 -0700114/*
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700115 * Scale the writeback cache size proportional to the relative writeout speeds.
116 *
117 * We do this by keeping a floating proportion between BDIs, based on page
118 * writeback completions [end_page_writeback()]. Those devices that write out
119 * pages fastest will get the larger share, while the slower will get a smaller
120 * share.
121 *
122 * We use page writeout completions because we are interested in getting rid of
123 * dirty pages. Having them written out is the primary goal.
124 *
125 * We introduce a concept of time, a period over which we measure these events,
126 * because demand can/will vary over time. The length of this period itself is
127 * measured in page writeback completions.
128 *
129 */
130static struct prop_descriptor vm_completions;
Peter Zijlstra3e26c142007-10-16 23:25:50 -0700131static struct prop_descriptor vm_dirties;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700132
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700133/*
134 * couple the period to the dirty_ratio:
135 *
136 * period/2 ~ roundup_pow_of_two(dirty limit)
137 */
138static int calc_period_shift(void)
139{
140 unsigned long dirty_total;
141
David Rientjes2da02992009-01-06 14:39:31 -0800142 if (vm_dirty_bytes)
143 dirty_total = vm_dirty_bytes / PAGE_SIZE;
144 else
145 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
146 100;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700147 return 2 + ilog2(dirty_total - 1);
148}
149
150/*
David Rientjes2da02992009-01-06 14:39:31 -0800151 * update the period when the dirty threshold changes.
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700152 */
David Rientjes2da02992009-01-06 14:39:31 -0800153static void update_completion_period(void)
154{
155 int shift = calc_period_shift();
156 prop_change_shift(&vm_completions, shift);
157 prop_change_shift(&vm_dirties, shift);
Wu Fengguang9d823e82011-06-11 18:10:12 -0600158
159 writeback_set_ratelimit();
David Rientjes2da02992009-01-06 14:39:31 -0800160}
161
162int dirty_background_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700163 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800164 loff_t *ppos)
165{
166 int ret;
167
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700168 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800169 if (ret == 0 && write)
170 dirty_background_bytes = 0;
171 return ret;
172}
173
174int dirty_background_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700175 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800176 loff_t *ppos)
177{
178 int ret;
179
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700180 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800181 if (ret == 0 && write)
182 dirty_background_ratio = 0;
183 return ret;
184}
185
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700186int dirty_ratio_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700187 void __user *buffer, size_t *lenp,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700188 loff_t *ppos)
189{
190 int old_ratio = vm_dirty_ratio;
David Rientjes2da02992009-01-06 14:39:31 -0800191 int ret;
192
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700193 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700194 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
David Rientjes2da02992009-01-06 14:39:31 -0800195 update_completion_period();
196 vm_dirty_bytes = 0;
197 }
198 return ret;
199}
200
201
202int dirty_bytes_handler(struct ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700203 void __user *buffer, size_t *lenp,
David Rientjes2da02992009-01-06 14:39:31 -0800204 loff_t *ppos)
205{
Sven Wegenerfc3501d2009-02-11 13:04:23 -0800206 unsigned long old_bytes = vm_dirty_bytes;
David Rientjes2da02992009-01-06 14:39:31 -0800207 int ret;
208
Alexey Dobriyan8d65af72009-09-23 15:57:19 -0700209 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
David Rientjes2da02992009-01-06 14:39:31 -0800210 if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
211 update_completion_period();
212 vm_dirty_ratio = 0;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700213 }
214 return ret;
215}
216
217/*
218 * Increment the BDI's writeout completion count and the global writeout
219 * completion count. Called from test_clear_page_writeback().
220 */
221static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
222{
Jan Karaf7d2b1e2010-12-08 22:44:24 -0600223 __inc_bdi_stat(bdi, BDI_WRITTEN);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700224 __prop_inc_percpu_max(&vm_completions, &bdi->completions,
225 bdi->max_prop_frac);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700226}
227
Miklos Szeredidd5656e2008-04-30 00:54:37 -0700228void bdi_writeout_inc(struct backing_dev_info *bdi)
229{
230 unsigned long flags;
231
232 local_irq_save(flags);
233 __bdi_writeout_inc(bdi);
234 local_irq_restore(flags);
235}
236EXPORT_SYMBOL_GPL(bdi_writeout_inc);
237
Nick Piggin1cf6e7d2009-02-18 14:48:18 -0800238void task_dirty_inc(struct task_struct *tsk)
Peter Zijlstra3e26c142007-10-16 23:25:50 -0700239{
240 prop_inc_single(&vm_dirties, &tsk->dirties);
241}
242
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700243/*
244 * Obtain an accurate fraction of the BDI's portion.
245 */
246static void bdi_writeout_fraction(struct backing_dev_info *bdi,
247 long *numerator, long *denominator)
248{
Wu Fengguang3efaf0f2010-12-16 22:22:00 -0600249 prop_fraction_percpu(&vm_completions, &bdi->completions,
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700250 numerator, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700251}
252
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700253/*
Johannes Weinerd08c4292011-10-31 17:07:05 -0700254 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
255 * registered backing devices, which, for obvious reasons, can not
256 * exceed 100%.
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700257 */
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700258static unsigned int bdi_min_ratio;
259
260int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
261{
262 int ret = 0;
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700263
Jens Axboecfc4ba52009-09-14 13:12:40 +0200264 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700265 if (min_ratio > bdi->max_ratio) {
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700266 ret = -EINVAL;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700267 } else {
268 min_ratio -= bdi->min_ratio;
269 if (bdi_min_ratio + min_ratio < 100) {
270 bdi_min_ratio += min_ratio;
271 bdi->min_ratio += min_ratio;
272 } else {
273 ret = -EINVAL;
274 }
275 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200276 spin_unlock_bh(&bdi_lock);
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700277
278 return ret;
279}
280
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700281int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
282{
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700283 int ret = 0;
284
285 if (max_ratio > 100)
286 return -EINVAL;
287
Jens Axboecfc4ba52009-09-14 13:12:40 +0200288 spin_lock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700289 if (bdi->min_ratio > max_ratio) {
290 ret = -EINVAL;
291 } else {
292 bdi->max_ratio = max_ratio;
293 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
294 }
Jens Axboecfc4ba52009-09-14 13:12:40 +0200295 spin_unlock_bh(&bdi_lock);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700296
297 return ret;
298}
299EXPORT_SYMBOL(bdi_set_max_ratio);
300
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700301/*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700302 * Work out the current dirty-memory clamping and background writeout
303 * thresholds.
304 *
305 * The main aim here is to lower them aggressively if there is a lot of mapped
306 * memory around. To avoid stressing page reclaim with lots of unreclaimable
307 * pages. It is better to clamp down on writers than to start swapping, and
308 * performing lots of scanning.
309 *
310 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
311 *
312 * We don't permit the clamping level to fall below 5% - that is getting rather
313 * excessive.
314 *
315 * We make sure that the background writeout level is below the adjusted
316 * clamping level.
317 */
Christoph Lameter1b424462007-05-06 14:48:59 -0700318
319static unsigned long highmem_dirtyable_memory(unsigned long total)
320{
321#ifdef CONFIG_HIGHMEM
322 int node;
323 unsigned long x = 0;
324
Lee Schermerhorn37b07e42007-10-16 01:25:39 -0700325 for_each_node_state(node, N_HIGH_MEMORY) {
Christoph Lameter1b424462007-05-06 14:48:59 -0700326 struct zone *z =
327 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
328
Wu Fengguangadea02a2009-09-21 17:01:42 -0700329 x += zone_page_state(z, NR_FREE_PAGES) +
330 zone_reclaimable_pages(z);
Christoph Lameter1b424462007-05-06 14:48:59 -0700331 }
332 /*
333 * Make sure that the number of highmem pages is never larger
334 * than the number of the total dirtyable memory. This can only
335 * occur in very strange VM situations but we want to make sure
336 * that this does not occur.
337 */
338 return min(x, total);
339#else
340 return 0;
341#endif
342}
343
Steven Rostedt3eefae92008-05-12 21:21:04 +0200344/**
345 * determine_dirtyable_memory - amount of memory that may be used
346 *
347 * Returns the numebr of pages that can currently be freed and used
348 * by the kernel for direct mappings.
349 */
350unsigned long determine_dirtyable_memory(void)
Christoph Lameter1b424462007-05-06 14:48:59 -0700351{
352 unsigned long x;
353
Wu Fengguangadea02a2009-09-21 17:01:42 -0700354 x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
Bron Gondwana195cf452008-02-04 22:29:20 -0800355
356 if (!vm_highmem_is_dirtyable)
357 x -= highmem_dirtyable_memory(x);
358
Christoph Lameter1b424462007-05-06 14:48:59 -0700359 return x + 1; /* Ensure that we never return 0 */
360}
361
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600362static unsigned long dirty_freerun_ceiling(unsigned long thresh,
363 unsigned long bg_thresh)
364{
365 return (thresh + bg_thresh) / 2;
366}
367
Wu Fengguangffd1f602011-06-19 22:18:42 -0600368static unsigned long hard_dirty_limit(unsigned long thresh)
369{
370 return max(thresh, global_dirty_limit);
371}
372
Randy Dunlap03ab4502010-08-14 13:05:17 -0700373/*
Wu Fengguang1babe182010-08-11 14:17:40 -0700374 * global_dirty_limits - background-writeback and dirty-throttling thresholds
375 *
376 * Calculate the dirty thresholds based on sysctl parameters
377 * - vm.dirty_background_ratio or vm.dirty_background_bytes
378 * - vm.dirty_ratio or vm.dirty_bytes
379 * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
Minchan Kimebd13732011-01-04 01:36:48 +0900380 * real-time tasks.
Wu Fengguang1babe182010-08-11 14:17:40 -0700381 */
Wu Fengguang16c40422010-08-11 14:17:39 -0700382void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700383{
David Rientjes364aeb22009-01-06 14:39:29 -0800384 unsigned long background;
385 unsigned long dirty;
Minchan Kim240c8792011-01-13 15:46:27 -0800386 unsigned long uninitialized_var(available_memory);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700387 struct task_struct *tsk;
388
Minchan Kim240c8792011-01-13 15:46:27 -0800389 if (!vm_dirty_bytes || !dirty_background_bytes)
390 available_memory = determine_dirtyable_memory();
391
David Rientjes2da02992009-01-06 14:39:31 -0800392 if (vm_dirty_bytes)
393 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
Wu Fengguang4cbec4c2010-10-26 14:21:45 -0700394 else
395 dirty = (vm_dirty_ratio * available_memory) / 100;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700396
David Rientjes2da02992009-01-06 14:39:31 -0800397 if (dirty_background_bytes)
398 background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
399 else
400 background = (dirty_background_ratio * available_memory) / 100;
401
402 if (background >= dirty)
403 background = dirty / 2;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700404 tsk = current;
405 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
406 background += background / 4;
407 dirty += dirty / 4;
408 }
409 *pbackground = background;
410 *pdirty = dirty;
Wu Fengguange1cbe232010-12-06 22:34:29 -0600411 trace_global_dirty_state(background, dirty);
Wu Fengguang16c40422010-08-11 14:17:39 -0700412}
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700413
Wu Fengguang6f718652011-03-02 17:14:34 -0600414/**
Wu Fengguang1babe182010-08-11 14:17:40 -0700415 * bdi_dirty_limit - @bdi's share of dirty throttling threshold
Wu Fengguang6f718652011-03-02 17:14:34 -0600416 * @bdi: the backing_dev_info to query
417 * @dirty: global dirty limit in pages
Wu Fengguang1babe182010-08-11 14:17:40 -0700418 *
Wu Fengguang6f718652011-03-02 17:14:34 -0600419 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
420 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
421 * And the "limit" in the name is not seriously taken as hard limit in
422 * balance_dirty_pages().
423 *
424 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
Wu Fengguang1babe182010-08-11 14:17:40 -0700425 * - starving fast devices
426 * - piling up dirty pages (that will take long time to sync) on slow devices
427 *
428 * The bdi's share of dirty limit will be adapting to its throughput and
429 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
430 */
431unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
Wu Fengguang16c40422010-08-11 14:17:39 -0700432{
433 u64 bdi_dirty;
434 long numerator, denominator;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700435
Wu Fengguang16c40422010-08-11 14:17:39 -0700436 /*
437 * Calculate this BDI's share of the dirty ratio.
438 */
439 bdi_writeout_fraction(bdi, &numerator, &denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700440
Wu Fengguang16c40422010-08-11 14:17:39 -0700441 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
442 bdi_dirty *= numerator;
443 do_div(bdi_dirty, denominator);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700444
Wu Fengguang16c40422010-08-11 14:17:39 -0700445 bdi_dirty += (dirty * bdi->min_ratio) / 100;
446 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
447 bdi_dirty = dirty * bdi->max_ratio / 100;
448
449 return bdi_dirty;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700450}
451
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600452/*
453 * Dirty position control.
454 *
455 * (o) global/bdi setpoints
456 *
457 * We want the dirty pages be balanced around the global/bdi setpoints.
458 * When the number of dirty pages is higher/lower than the setpoint, the
459 * dirty position control ratio (and hence task dirty ratelimit) will be
460 * decreased/increased to bring the dirty pages back to the setpoint.
461 *
462 * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
463 *
464 * if (dirty < setpoint) scale up pos_ratio
465 * if (dirty > setpoint) scale down pos_ratio
466 *
467 * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
468 * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
469 *
470 * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
471 *
472 * (o) global control line
473 *
474 * ^ pos_ratio
475 * |
476 * | |<===== global dirty control scope ======>|
477 * 2.0 .............*
478 * | .*
479 * | . *
480 * | . *
481 * | . *
482 * | . *
483 * | . *
484 * 1.0 ................................*
485 * | . . *
486 * | . . *
487 * | . . *
488 * | . . *
489 * | . . *
490 * 0 +------------.------------------.----------------------*------------->
491 * freerun^ setpoint^ limit^ dirty pages
492 *
493 * (o) bdi control line
494 *
495 * ^ pos_ratio
496 * |
497 * | *
498 * | *
499 * | *
500 * | *
501 * | * |<=========== span ============>|
502 * 1.0 .......................*
503 * | . *
504 * | . *
505 * | . *
506 * | . *
507 * | . *
508 * | . *
509 * | . *
510 * | . *
511 * | . *
512 * | . *
513 * | . *
514 * 1/4 ...............................................* * * * * * * * * * * *
515 * | . .
516 * | . .
517 * | . .
518 * 0 +----------------------.-------------------------------.------------->
519 * bdi_setpoint^ x_intercept^
520 *
521 * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
522 * be smoothly throttled down to normal if it starts high in situations like
523 * - start writing to a slow SD card and a fast disk at the same time. The SD
524 * card's bdi_dirty may rush to many times higher than bdi_setpoint.
525 * - the bdi dirty thresh drops quickly due to change of JBOD workload
526 */
527static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
528 unsigned long thresh,
529 unsigned long bg_thresh,
530 unsigned long dirty,
531 unsigned long bdi_thresh,
532 unsigned long bdi_dirty)
533{
534 unsigned long write_bw = bdi->avg_write_bandwidth;
535 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
536 unsigned long limit = hard_dirty_limit(thresh);
537 unsigned long x_intercept;
538 unsigned long setpoint; /* dirty pages' target balance point */
539 unsigned long bdi_setpoint;
540 unsigned long span;
541 long long pos_ratio; /* for scaling up/down the rate limit */
542 long x;
543
544 if (unlikely(dirty >= limit))
545 return 0;
546
547 /*
548 * global setpoint
549 *
550 * setpoint - dirty 3
551 * f(dirty) := 1.0 + (----------------)
552 * limit - setpoint
553 *
554 * it's a 3rd order polynomial that subjects to
555 *
556 * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
557 * (2) f(setpoint) = 1.0 => the balance point
558 * (3) f(limit) = 0 => the hard limit
559 * (4) df/dx <= 0 => negative feedback control
560 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
561 * => fast response on large errors; small oscillation near setpoint
562 */
563 setpoint = (freerun + limit) / 2;
564 x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
565 limit - setpoint + 1);
566 pos_ratio = x;
567 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
568 pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
569 pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
570
571 /*
572 * We have computed basic pos_ratio above based on global situation. If
573 * the bdi is over/under its share of dirty pages, we want to scale
574 * pos_ratio further down/up. That is done by the following mechanism.
575 */
576
577 /*
578 * bdi setpoint
579 *
580 * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
581 *
582 * x_intercept - bdi_dirty
583 * := --------------------------
584 * x_intercept - bdi_setpoint
585 *
586 * The main bdi control line is a linear function that subjects to
587 *
588 * (1) f(bdi_setpoint) = 1.0
589 * (2) k = - 1 / (8 * write_bw) (in single bdi case)
590 * or equally: x_intercept = bdi_setpoint + 8 * write_bw
591 *
592 * For single bdi case, the dirty pages are observed to fluctuate
593 * regularly within range
594 * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
595 * for various filesystems, where (2) can yield in a reasonable 12.5%
596 * fluctuation range for pos_ratio.
597 *
598 * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
599 * own size, so move the slope over accordingly and choose a slope that
600 * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
601 */
602 if (unlikely(bdi_thresh > thresh))
603 bdi_thresh = thresh;
Wu Fengguang8927f662011-08-04 22:16:46 -0600604 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600605 /*
606 * scale global setpoint to bdi's:
607 * bdi_setpoint = setpoint * bdi_thresh / thresh
608 */
609 x = div_u64((u64)bdi_thresh << 16, thresh + 1);
610 bdi_setpoint = setpoint * (u64)x >> 16;
611 /*
612 * Use span=(8*write_bw) in single bdi case as indicated by
613 * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
614 *
615 * bdi_thresh thresh - bdi_thresh
616 * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
617 * thresh thresh
618 */
619 span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
620 x_intercept = bdi_setpoint + span;
621
622 if (bdi_dirty < x_intercept - span / 4) {
Wu Fengguang50657fc2011-10-11 17:06:33 -0600623 pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
624 x_intercept - bdi_setpoint + 1);
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600625 } else
626 pos_ratio /= 4;
627
Wu Fengguang8927f662011-08-04 22:16:46 -0600628 /*
629 * bdi reserve area, safeguard against dirty pool underrun and disk idle
630 * It may push the desired control point of global dirty pages higher
631 * than setpoint.
632 */
633 x_intercept = bdi_thresh / 2;
634 if (bdi_dirty < x_intercept) {
Wu Fengguang50657fc2011-10-11 17:06:33 -0600635 if (bdi_dirty > x_intercept / 8)
636 pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
637 else
Wu Fengguang8927f662011-08-04 22:16:46 -0600638 pos_ratio *= 8;
639 }
640
Wu Fengguang6c14ae12011-03-02 16:04:18 -0600641 return pos_ratio;
642}
643
Wu Fengguange98be2d2010-08-29 11:22:30 -0600644static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
645 unsigned long elapsed,
646 unsigned long written)
647{
648 const unsigned long period = roundup_pow_of_two(3 * HZ);
649 unsigned long avg = bdi->avg_write_bandwidth;
650 unsigned long old = bdi->write_bandwidth;
651 u64 bw;
652
653 /*
654 * bw = written * HZ / elapsed
655 *
656 * bw * elapsed + write_bandwidth * (period - elapsed)
657 * write_bandwidth = ---------------------------------------------------
658 * period
659 */
660 bw = written - bdi->written_stamp;
661 bw *= HZ;
662 if (unlikely(elapsed > period)) {
663 do_div(bw, elapsed);
664 avg = bw;
665 goto out;
666 }
667 bw += (u64)bdi->write_bandwidth * (period - elapsed);
668 bw >>= ilog2(period);
669
670 /*
671 * one more level of smoothing, for filtering out sudden spikes
672 */
673 if (avg > old && old >= (unsigned long)bw)
674 avg -= (avg - old) >> 3;
675
676 if (avg < old && old <= (unsigned long)bw)
677 avg += (old - avg) >> 3;
678
679out:
680 bdi->write_bandwidth = bw;
681 bdi->avg_write_bandwidth = avg;
682}
683
Wu Fengguangc42843f2011-03-02 15:54:09 -0600684/*
685 * The global dirtyable memory and dirty threshold could be suddenly knocked
686 * down by a large amount (eg. on the startup of KVM in a swapless system).
687 * This may throw the system into deep dirty exceeded state and throttle
688 * heavy/light dirtiers alike. To retain good responsiveness, maintain
689 * global_dirty_limit for tracking slowly down to the knocked down dirty
690 * threshold.
691 */
692static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
693{
694 unsigned long limit = global_dirty_limit;
695
696 /*
697 * Follow up in one step.
698 */
699 if (limit < thresh) {
700 limit = thresh;
701 goto update;
702 }
703
704 /*
705 * Follow down slowly. Use the higher one as the target, because thresh
706 * may drop below dirty. This is exactly the reason to introduce
707 * global_dirty_limit which is guaranteed to lie above the dirty pages.
708 */
709 thresh = max(thresh, dirty);
710 if (limit > thresh) {
711 limit -= (limit - thresh) >> 5;
712 goto update;
713 }
714 return;
715update:
716 global_dirty_limit = limit;
717}
718
719static void global_update_bandwidth(unsigned long thresh,
720 unsigned long dirty,
721 unsigned long now)
722{
723 static DEFINE_SPINLOCK(dirty_lock);
724 static unsigned long update_time;
725
726 /*
727 * check locklessly first to optimize away locking for the most time
728 */
729 if (time_before(now, update_time + BANDWIDTH_INTERVAL))
730 return;
731
732 spin_lock(&dirty_lock);
733 if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
734 update_dirty_limit(thresh, dirty);
735 update_time = now;
736 }
737 spin_unlock(&dirty_lock);
738}
739
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600740/*
741 * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
742 *
743 * Normal bdi tasks will be curbed at or below it in long term.
744 * Obviously it should be around (write_bw / N) when there are N dd tasks.
745 */
746static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
747 unsigned long thresh,
748 unsigned long bg_thresh,
749 unsigned long dirty,
750 unsigned long bdi_thresh,
751 unsigned long bdi_dirty,
752 unsigned long dirtied,
753 unsigned long elapsed)
754{
Wu Fengguang73811312011-08-26 15:53:24 -0600755 unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
756 unsigned long limit = hard_dirty_limit(thresh);
757 unsigned long setpoint = (freerun + limit) / 2;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600758 unsigned long write_bw = bdi->avg_write_bandwidth;
759 unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
760 unsigned long dirty_rate;
761 unsigned long task_ratelimit;
762 unsigned long balanced_dirty_ratelimit;
763 unsigned long pos_ratio;
Wu Fengguang73811312011-08-26 15:53:24 -0600764 unsigned long step;
765 unsigned long x;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600766
767 /*
768 * The dirty rate will match the writeout rate in long term, except
769 * when dirty pages are truncated by userspace or re-dirtied by FS.
770 */
771 dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
772
773 pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
774 bdi_thresh, bdi_dirty);
775 /*
776 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
777 */
778 task_ratelimit = (u64)dirty_ratelimit *
779 pos_ratio >> RATELIMIT_CALC_SHIFT;
780 task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
781
782 /*
783 * A linear estimation of the "balanced" throttle rate. The theory is,
784 * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
785 * dirty_rate will be measured to be (N * task_ratelimit). So the below
786 * formula will yield the balanced rate limit (write_bw / N).
787 *
788 * Note that the expanded form is not a pure rate feedback:
789 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
790 * but also takes pos_ratio into account:
791 * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
792 *
793 * (1) is not realistic because pos_ratio also takes part in balancing
794 * the dirty rate. Consider the state
795 * pos_ratio = 0.5 (3)
796 * rate = 2 * (write_bw / N) (4)
797 * If (1) is used, it will stuck in that state! Because each dd will
798 * be throttled at
799 * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
800 * yielding
801 * dirty_rate = N * task_ratelimit = write_bw (6)
802 * put (6) into (1) we get
803 * rate_(i+1) = rate_(i) (7)
804 *
805 * So we end up using (2) to always keep
806 * rate_(i+1) ~= (write_bw / N) (8)
807 * regardless of the value of pos_ratio. As long as (8) is satisfied,
808 * pos_ratio is able to drive itself to 1.0, which is not only where
809 * the dirty count meet the setpoint, but also where the slope of
810 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
811 */
812 balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
813 dirty_rate | 1);
814
Wu Fengguang73811312011-08-26 15:53:24 -0600815 /*
816 * We could safely do this and return immediately:
817 *
818 * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
819 *
820 * However to get a more stable dirty_ratelimit, the below elaborated
821 * code makes use of task_ratelimit to filter out sigular points and
822 * limit the step size.
823 *
824 * The below code essentially only uses the relative value of
825 *
826 * task_ratelimit - dirty_ratelimit
827 * = (pos_ratio - 1) * dirty_ratelimit
828 *
829 * which reflects the direction and size of dirty position error.
830 */
831
832 /*
833 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
834 * task_ratelimit is on the same side of dirty_ratelimit, too.
835 * For example, when
836 * - dirty_ratelimit > balanced_dirty_ratelimit
837 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
838 * lowering dirty_ratelimit will help meet both the position and rate
839 * control targets. Otherwise, don't update dirty_ratelimit if it will
840 * only help meet the rate target. After all, what the users ultimately
841 * feel and care are stable dirty rate and small position error.
842 *
843 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
844 * and filter out the sigular points of balanced_dirty_ratelimit. Which
845 * keeps jumping around randomly and can even leap far away at times
846 * due to the small 200ms estimation period of dirty_rate (we want to
847 * keep that period small to reduce time lags).
848 */
849 step = 0;
850 if (dirty < setpoint) {
851 x = min(bdi->balanced_dirty_ratelimit,
852 min(balanced_dirty_ratelimit, task_ratelimit));
853 if (dirty_ratelimit < x)
854 step = x - dirty_ratelimit;
855 } else {
856 x = max(bdi->balanced_dirty_ratelimit,
857 max(balanced_dirty_ratelimit, task_ratelimit));
858 if (dirty_ratelimit > x)
859 step = dirty_ratelimit - x;
860 }
861
862 /*
863 * Don't pursue 100% rate matching. It's impossible since the balanced
864 * rate itself is constantly fluctuating. So decrease the track speed
865 * when it gets close to the target. Helps eliminate pointless tremors.
866 */
867 step >>= dirty_ratelimit / (2 * step + 1);
868 /*
869 * Limit the tracking speed to avoid overshooting.
870 */
871 step = (step + 7) / 8;
872
873 if (dirty_ratelimit < balanced_dirty_ratelimit)
874 dirty_ratelimit += step;
875 else
876 dirty_ratelimit -= step;
877
878 bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
879 bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
Wu Fengguangb48c1042011-03-02 17:22:49 -0600880
881 trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600882}
883
Wu Fengguange98be2d2010-08-29 11:22:30 -0600884void __bdi_update_bandwidth(struct backing_dev_info *bdi,
Wu Fengguangc42843f2011-03-02 15:54:09 -0600885 unsigned long thresh,
Wu Fengguangaf6a3112011-10-03 20:46:17 -0600886 unsigned long bg_thresh,
Wu Fengguangc42843f2011-03-02 15:54:09 -0600887 unsigned long dirty,
888 unsigned long bdi_thresh,
889 unsigned long bdi_dirty,
Wu Fengguange98be2d2010-08-29 11:22:30 -0600890 unsigned long start_time)
891{
892 unsigned long now = jiffies;
893 unsigned long elapsed = now - bdi->bw_time_stamp;
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600894 unsigned long dirtied;
Wu Fengguange98be2d2010-08-29 11:22:30 -0600895 unsigned long written;
896
897 /*
898 * rate-limit, only update once every 200ms.
899 */
900 if (elapsed < BANDWIDTH_INTERVAL)
901 return;
902
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600903 dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
Wu Fengguange98be2d2010-08-29 11:22:30 -0600904 written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
905
906 /*
907 * Skip quiet periods when disk bandwidth is under-utilized.
908 * (at least 1s idle time between two flusher runs)
909 */
910 if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
911 goto snapshot;
912
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600913 if (thresh) {
Wu Fengguangc42843f2011-03-02 15:54:09 -0600914 global_update_bandwidth(thresh, dirty, now);
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600915 bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
916 bdi_thresh, bdi_dirty,
917 dirtied, elapsed);
918 }
Wu Fengguange98be2d2010-08-29 11:22:30 -0600919 bdi_update_write_bandwidth(bdi, elapsed, written);
920
921snapshot:
Wu Fengguangbe3ffa22011-06-12 10:51:31 -0600922 bdi->dirtied_stamp = dirtied;
Wu Fengguange98be2d2010-08-29 11:22:30 -0600923 bdi->written_stamp = written;
924 bdi->bw_time_stamp = now;
925}
926
927static void bdi_update_bandwidth(struct backing_dev_info *bdi,
Wu Fengguangc42843f2011-03-02 15:54:09 -0600928 unsigned long thresh,
Wu Fengguangaf6a3112011-10-03 20:46:17 -0600929 unsigned long bg_thresh,
Wu Fengguangc42843f2011-03-02 15:54:09 -0600930 unsigned long dirty,
931 unsigned long bdi_thresh,
932 unsigned long bdi_dirty,
Wu Fengguange98be2d2010-08-29 11:22:30 -0600933 unsigned long start_time)
934{
935 if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
936 return;
937 spin_lock(&bdi->wb.list_lock);
Wu Fengguangaf6a3112011-10-03 20:46:17 -0600938 __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
939 bdi_thresh, bdi_dirty, start_time);
Wu Fengguange98be2d2010-08-29 11:22:30 -0600940 spin_unlock(&bdi->wb.list_lock);
941}
942
Linus Torvalds1da177e2005-04-16 15:20:36 -0700943/*
Wu Fengguang9d823e82011-06-11 18:10:12 -0600944 * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
945 * will look to see if it needs to start dirty throttling.
946 *
947 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
948 * global_page_state() too often. So scale it near-sqrt to the safety margin
949 * (the number of pages we may dirty without exceeding the dirty limits).
950 */
951static unsigned long dirty_poll_interval(unsigned long dirty,
952 unsigned long thresh)
953{
954 if (thresh > dirty)
955 return 1UL << (ilog2(thresh - dirty) >> 1);
956
957 return 1;
958}
959
Wu Fengguangc8462cc2011-06-11 19:21:43 -0600960static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
961 unsigned long bdi_dirty)
962{
963 unsigned long bw = bdi->avg_write_bandwidth;
964 unsigned long hi = ilog2(bw);
965 unsigned long lo = ilog2(bdi->dirty_ratelimit);
966 unsigned long t;
967
968 /* target for 20ms max pause on 1-dd case */
969 t = HZ / 50;
970
971 /*
972 * Scale up pause time for concurrent dirtiers in order to reduce CPU
973 * overheads.
974 *
975 * (N * 20ms) on 2^N concurrent tasks.
976 */
977 if (hi > lo)
978 t += (hi - lo) * (20 * HZ) / 1024;
979
980 /*
981 * Limit pause time for small memory systems. If sleeping for too long
982 * time, a small pool of dirty/writeback pages may go empty and disk go
983 * idle.
984 *
985 * 8 serves as the safety ratio.
986 */
987 if (bdi_dirty)
988 t = min(t, bdi_dirty * HZ / (8 * bw + 1));
989
990 /*
991 * The pause time will be settled within range (max_pause/4, max_pause).
992 * Apply a minimal value of 4 to get a non-zero max_pause/4.
993 */
994 return clamp_val(t, 4, MAX_PAUSE);
995}
996
Wu Fengguang9d823e82011-06-11 18:10:12 -0600997/*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700998 * balance_dirty_pages() must be called by processes which are generating dirty
999 * data. It looks at the number of dirty pages in the machine and will force
Wu Fengguang143dfe82010-08-27 18:45:12 -06001000 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
Jens Axboe5b0830c2009-09-23 19:37:09 +02001001 * If we're over `background_thresh' then the writeback threads are woken to
1002 * perform some writeout.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001003 */
Wu Fengguang3a2e9a52009-09-23 21:56:00 +08001004static void balance_dirty_pages(struct address_space *mapping,
Wu Fengguang143dfe82010-08-27 18:45:12 -06001005 unsigned long pages_dirtied)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001006{
Wu Fengguang143dfe82010-08-27 18:45:12 -06001007 unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
1008 unsigned long bdi_reclaimable;
Wu Fengguang77627412010-09-12 13:34:05 -06001009 unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
1010 unsigned long bdi_dirty;
Wu Fengguang6c14ae12011-03-02 16:04:18 -06001011 unsigned long freerun;
David Rientjes364aeb22009-01-06 14:39:29 -08001012 unsigned long background_thresh;
1013 unsigned long dirty_thresh;
1014 unsigned long bdi_thresh;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001015 long pause = 0;
Wu Fengguang50657fc2011-10-11 17:06:33 -06001016 long uninitialized_var(max_pause);
Wu Fengguange50e3722010-08-11 14:17:37 -07001017 bool dirty_exceeded = false;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001018 unsigned long task_ratelimit;
Wu Fengguang50657fc2011-10-11 17:06:33 -06001019 unsigned long uninitialized_var(dirty_ratelimit);
Wu Fengguang143dfe82010-08-27 18:45:12 -06001020 unsigned long pos_ratio;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001021 struct backing_dev_info *bdi = mapping->backing_dev_info;
Wu Fengguange98be2d2010-08-29 11:22:30 -06001022 unsigned long start_time = jiffies;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001023
1024 for (;;) {
Wu Fengguang143dfe82010-08-27 18:45:12 -06001025 /*
1026 * Unstable writes are a feature of certain networked
1027 * filesystems (i.e. NFS) in which data may have been
1028 * written to the server's write cache, but has not yet
1029 * been flushed to permanent storage.
1030 */
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001031 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
1032 global_page_state(NR_UNSTABLE_NFS);
Wu Fengguang77627412010-09-12 13:34:05 -06001033 nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001034
Wu Fengguang16c40422010-08-11 14:17:39 -07001035 global_dirty_limits(&background_thresh, &dirty_thresh);
1036
1037 /*
1038 * Throttle it only when the background writeback cannot
1039 * catch-up. This avoids (excessively) small writeouts
1040 * when the bdi limits are ramping up.
1041 */
Wu Fengguang6c14ae12011-03-02 16:04:18 -06001042 freerun = dirty_freerun_ceiling(dirty_thresh,
1043 background_thresh);
1044 if (nr_dirty <= freerun)
Wu Fengguang16c40422010-08-11 14:17:39 -07001045 break;
1046
Wu Fengguang143dfe82010-08-27 18:45:12 -06001047 if (unlikely(!writeback_in_progress(bdi)))
1048 bdi_start_background_writeback(bdi);
1049
1050 /*
1051 * bdi_thresh is not treated as some limiting factor as
1052 * dirty_thresh, due to reasons
1053 * - in JBOD setup, bdi_thresh can fluctuate a lot
1054 * - in a system with HDD and USB key, the USB key may somehow
1055 * go into state (bdi_dirty >> bdi_thresh) either because
1056 * bdi_dirty starts high, or because bdi_thresh drops low.
1057 * In this case we don't want to hard throttle the USB key
1058 * dirtiers for 100 seconds until bdi_dirty drops under
1059 * bdi_thresh. Instead the auxiliary bdi control line in
1060 * bdi_position_ratio() will let the dirtier task progress
1061 * at some rate <= (write_bw / 2) for bringing down bdi_dirty.
1062 */
Wu Fengguang16c40422010-08-11 14:17:39 -07001063 bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
Wu Fengguang16c40422010-08-11 14:17:39 -07001064
Wu Fengguange50e3722010-08-11 14:17:37 -07001065 /*
1066 * In order to avoid the stacked BDI deadlock we need
1067 * to ensure we accurately count the 'dirty' pages when
1068 * the threshold is low.
1069 *
1070 * Otherwise it would be possible to get thresh+n pages
1071 * reported dirty, even though there are thresh-m pages
1072 * actually dirty; with m+n sitting in the percpu
1073 * deltas.
1074 */
Wu Fengguang143dfe82010-08-27 18:45:12 -06001075 if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
1076 bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
1077 bdi_dirty = bdi_reclaimable +
Wu Fengguang77627412010-09-12 13:34:05 -06001078 bdi_stat_sum(bdi, BDI_WRITEBACK);
Wu Fengguange50e3722010-08-11 14:17:37 -07001079 } else {
Wu Fengguang143dfe82010-08-27 18:45:12 -06001080 bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
1081 bdi_dirty = bdi_reclaimable +
Wu Fengguang77627412010-09-12 13:34:05 -06001082 bdi_stat(bdi, BDI_WRITEBACK);
Wu Fengguange50e3722010-08-11 14:17:37 -07001083 }
Peter Zijlstra5fce25a2007-11-14 16:59:15 -08001084
Wu Fengguang143dfe82010-08-27 18:45:12 -06001085 dirty_exceeded = (bdi_dirty > bdi_thresh) ||
Wu Fengguang77627412010-09-12 13:34:05 -06001086 (nr_dirty > dirty_thresh);
Wu Fengguang143dfe82010-08-27 18:45:12 -06001087 if (dirty_exceeded && !bdi->dirty_exceeded)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001088 bdi->dirty_exceeded = 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001089
Wu Fengguangaf6a3112011-10-03 20:46:17 -06001090 bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
1091 nr_dirty, bdi_thresh, bdi_dirty,
1092 start_time);
Wu Fengguange98be2d2010-08-29 11:22:30 -06001093
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001094 max_pause = bdi_max_pause(bdi, bdi_dirty);
1095
Wu Fengguang143dfe82010-08-27 18:45:12 -06001096 dirty_ratelimit = bdi->dirty_ratelimit;
1097 pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
1098 background_thresh, nr_dirty,
1099 bdi_thresh, bdi_dirty);
Wu Fengguang3a73dbb2011-11-07 19:19:28 +08001100 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
1101 RATELIMIT_CALC_SHIFT;
1102 if (unlikely(task_ratelimit == 0)) {
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001103 pause = max_pause;
Wu Fengguang143dfe82010-08-27 18:45:12 -06001104 goto pause;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001105 }
Wu Fengguang3a73dbb2011-11-07 19:19:28 +08001106 pause = HZ * pages_dirtied / task_ratelimit;
Wu Fengguang57fc9782011-06-11 19:32:32 -06001107 if (unlikely(pause <= 0)) {
Wu Fengguangece13ac2010-08-29 23:33:20 -06001108 trace_balance_dirty_pages(bdi,
1109 dirty_thresh,
1110 background_thresh,
1111 nr_dirty,
1112 bdi_thresh,
1113 bdi_dirty,
1114 dirty_ratelimit,
1115 task_ratelimit,
1116 pages_dirtied,
1117 pause,
1118 start_time);
Wu Fengguang57fc9782011-06-11 19:32:32 -06001119 pause = 1; /* avoid resetting nr_dirtied_pause below */
1120 break;
1121 }
Wu Fengguangc8462cc2011-06-11 19:21:43 -06001122 pause = min(pause, max_pause);
Wu Fengguang143dfe82010-08-27 18:45:12 -06001123
1124pause:
Wu Fengguangece13ac2010-08-29 23:33:20 -06001125 trace_balance_dirty_pages(bdi,
1126 dirty_thresh,
1127 background_thresh,
1128 nr_dirty,
1129 bdi_thresh,
1130 bdi_dirty,
1131 dirty_ratelimit,
1132 task_ratelimit,
1133 pages_dirtied,
1134 pause,
1135 start_time);
Wu Fengguangd153ba62010-12-21 17:24:21 -08001136 __set_current_state(TASK_UNINTERRUPTIBLE);
Wu Fengguangd25105e2009-10-09 12:40:42 +02001137 io_schedule_timeout(pause);
Jens Axboe87c6a9b2009-09-17 19:59:14 +02001138
Wu Fengguangffd1f602011-06-19 22:18:42 -06001139 dirty_thresh = hard_dirty_limit(dirty_thresh);
1140 /*
1141 * max-pause area. If dirty exceeded but still within this
1142 * area, no need to sleep for more than 200ms: (a) 8 pages per
1143 * 200ms is typically more than enough to curb heavy dirtiers;
1144 * (b) the pause time limit makes the dirtiers more responsive.
1145 */
Wu Fengguang143dfe82010-08-27 18:45:12 -06001146 if (nr_dirty < dirty_thresh)
Wu Fengguangffd1f602011-06-19 22:18:42 -06001147 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001148 }
1149
Wu Fengguang143dfe82010-08-27 18:45:12 -06001150 if (!dirty_exceeded && bdi->dirty_exceeded)
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001151 bdi->dirty_exceeded = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001152
Wu Fengguang9d823e82011-06-11 18:10:12 -06001153 current->nr_dirtied = 0;
Wu Fengguang57fc9782011-06-11 19:32:32 -06001154 if (pause == 0) { /* in freerun area */
1155 current->nr_dirtied_pause =
1156 dirty_poll_interval(nr_dirty, dirty_thresh);
1157 } else if (pause <= max_pause / 4 &&
1158 pages_dirtied >= current->nr_dirtied_pause) {
1159 current->nr_dirtied_pause = clamp_val(
1160 dirty_ratelimit * (max_pause / 2) / HZ,
1161 pages_dirtied + pages_dirtied / 8,
1162 pages_dirtied * 4);
1163 } else if (pause >= max_pause) {
1164 current->nr_dirtied_pause = 1 | clamp_val(
1165 dirty_ratelimit * (max_pause / 2) / HZ,
1166 pages_dirtied / 4,
1167 pages_dirtied - pages_dirtied / 8);
1168 }
Wu Fengguang9d823e82011-06-11 18:10:12 -06001169
Linus Torvalds1da177e2005-04-16 15:20:36 -07001170 if (writeback_in_progress(bdi))
Jens Axboe5b0830c2009-09-23 19:37:09 +02001171 return;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001172
1173 /*
1174 * In laptop mode, we wait until hitting the higher threshold before
1175 * starting background writeout, and then write out all the way down
1176 * to the lower threshold. So slow writers cause minimal disk activity.
1177 *
1178 * In normal mode, we start background writeout at the lower
1179 * background_thresh, to keep the amount of dirty memory low.
1180 */
Wu Fengguang143dfe82010-08-27 18:45:12 -06001181 if (laptop_mode)
1182 return;
1183
1184 if (nr_reclaimable > background_thresh)
Christoph Hellwigc5444192010-06-08 18:15:15 +02001185 bdi_start_background_writeback(bdi);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001186}
1187
Peter Zijlstraa200ee12007-10-08 18:54:37 +02001188void set_page_dirty_balance(struct page *page, int page_mkwrite)
Peter Zijlstraedc79b22006-09-25 23:30:58 -07001189{
Peter Zijlstraa200ee12007-10-08 18:54:37 +02001190 if (set_page_dirty(page) || page_mkwrite) {
Peter Zijlstraedc79b22006-09-25 23:30:58 -07001191 struct address_space *mapping = page_mapping(page);
1192
1193 if (mapping)
1194 balance_dirty_pages_ratelimited(mapping);
1195 }
1196}
1197
Wu Fengguang9d823e82011-06-11 18:10:12 -06001198static DEFINE_PER_CPU(int, bdp_ratelimits);
Tejun Heo245b2e72009-06-24 15:13:48 +09001199
Linus Torvalds1da177e2005-04-16 15:20:36 -07001200/**
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001201 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
Martin Waitz67be2dd2005-05-01 08:59:26 -07001202 * @mapping: address_space which was dirtied
Martin Waitza5802902006-04-02 13:59:55 +02001203 * @nr_pages_dirtied: number of pages which the caller has just dirtied
Linus Torvalds1da177e2005-04-16 15:20:36 -07001204 *
1205 * Processes which are dirtying memory should call in here once for each page
1206 * which was newly dirtied. The function will periodically check the system's
1207 * dirty state and will initiate writeback if needed.
1208 *
1209 * On really big machines, get_writeback_state is expensive, so try to avoid
1210 * calling it too often (ratelimiting). But once we're over the dirty memory
1211 * limit we decrease the ratelimiting by a lot, to prevent individual processes
1212 * from overshooting the limit by (ratelimit_pages) each.
1213 */
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001214void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
1215 unsigned long nr_pages_dirtied)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001216{
Wu Fengguang36715ce2011-06-11 17:53:57 -06001217 struct backing_dev_info *bdi = mapping->backing_dev_info;
Wu Fengguang9d823e82011-06-11 18:10:12 -06001218 int ratelimit;
1219 int *p;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001220
Wu Fengguang36715ce2011-06-11 17:53:57 -06001221 if (!bdi_cap_account_dirty(bdi))
1222 return;
1223
Wu Fengguang9d823e82011-06-11 18:10:12 -06001224 ratelimit = current->nr_dirtied_pause;
1225 if (bdi->dirty_exceeded)
1226 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
Linus Torvalds1da177e2005-04-16 15:20:36 -07001227
Wu Fengguang9d823e82011-06-11 18:10:12 -06001228 current->nr_dirtied += nr_pages_dirtied;
1229
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001230 preempt_disable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001231 /*
1232 * This prevents one CPU to accumulate too many dirtied pages without
1233 * calling into balance_dirty_pages(), which can happen when there are
1234 * 1000+ tasks, all of them start dirtying pages at exactly the same
1235 * time, hence all honoured too large initial task->nr_dirtied_pause.
1236 */
Tejun Heo245b2e72009-06-24 15:13:48 +09001237 p = &__get_cpu_var(bdp_ratelimits);
Wu Fengguang9d823e82011-06-11 18:10:12 -06001238 if (unlikely(current->nr_dirtied >= ratelimit))
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001239 *p = 0;
Wu Fengguang9d823e82011-06-11 18:10:12 -06001240 else {
1241 *p += nr_pages_dirtied;
1242 if (unlikely(*p >= ratelimit_pages)) {
1243 *p = 0;
1244 ratelimit = 0;
1245 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07001246 }
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001247 preempt_enable();
Wu Fengguang9d823e82011-06-11 18:10:12 -06001248
1249 if (unlikely(current->nr_dirtied >= ratelimit))
1250 balance_dirty_pages(mapping, current->nr_dirtied);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001251}
Andrew Mortonfa5a7342006-03-24 03:18:10 -08001252EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001253
Andrew Morton232ea4d2007-02-28 20:13:21 -08001254void throttle_vm_writeout(gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001255{
David Rientjes364aeb22009-01-06 14:39:29 -08001256 unsigned long background_thresh;
1257 unsigned long dirty_thresh;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001258
1259 for ( ; ; ) {
Wu Fengguang16c40422010-08-11 14:17:39 -07001260 global_dirty_limits(&background_thresh, &dirty_thresh);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001261
1262 /*
1263 * Boost the allowable dirty threshold a bit for page
1264 * allocators so they don't get DoS'ed by heavy writers
1265 */
1266 dirty_thresh += dirty_thresh / 10; /* wheeee... */
1267
Christoph Lameterc24f21b2006-06-30 01:55:42 -07001268 if (global_page_state(NR_UNSTABLE_NFS) +
1269 global_page_state(NR_WRITEBACK) <= dirty_thresh)
1270 break;
Jens Axboe8aa7e842009-07-09 14:52:32 +02001271 congestion_wait(BLK_RW_ASYNC, HZ/10);
Fengguang Wu369f2382007-10-16 23:30:45 -07001272
1273 /*
1274 * The caller might hold locks which can prevent IO completion
1275 * or progress in the filesystem. So we cannot just sit here
1276 * waiting for IO to complete.
1277 */
1278 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
1279 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001280 }
1281}
1282
Linus Torvalds1da177e2005-04-16 15:20:36 -07001283/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001284 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1285 */
1286int dirty_writeback_centisecs_handler(ctl_table *table, int write,
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001287 void __user *buffer, size_t *length, loff_t *ppos)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001288{
Alexey Dobriyan8d65af72009-09-23 15:57:19 -07001289 proc_dointvec(table, write, buffer, length, ppos);
Jens Axboe64231042010-05-21 20:00:35 +02001290 bdi_arm_supers_timer();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001291 return 0;
1292}
1293
Jens Axboec2c49862010-05-20 09:18:47 +02001294#ifdef CONFIG_BLOCK
Matthew Garrett31373d02010-04-06 14:25:14 +02001295void laptop_mode_timer_fn(unsigned long data)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001296{
Matthew Garrett31373d02010-04-06 14:25:14 +02001297 struct request_queue *q = (struct request_queue *)data;
1298 int nr_pages = global_page_state(NR_FILE_DIRTY) +
1299 global_page_state(NR_UNSTABLE_NFS);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001300
Matthew Garrett31373d02010-04-06 14:25:14 +02001301 /*
1302 * We want to write everything out, not just down to the dirty
1303 * threshold
1304 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001305 if (bdi_has_dirty_io(&q->backing_dev_info))
Curt Wohlgemuth0e175a12011-10-07 21:54:10 -06001306 bdi_start_writeback(&q->backing_dev_info, nr_pages,
1307 WB_REASON_LAPTOP_TIMER);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001308}
1309
1310/*
1311 * We've spun up the disk and we're in laptop mode: schedule writeback
1312 * of all dirty data a few seconds from now. If the flush is already scheduled
1313 * then push it back - the user is still using the disk.
1314 */
Matthew Garrett31373d02010-04-06 14:25:14 +02001315void laptop_io_completion(struct backing_dev_info *info)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001316{
Matthew Garrett31373d02010-04-06 14:25:14 +02001317 mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001318}
1319
1320/*
1321 * We're in laptop mode and we've just synced. The sync's writes will have
1322 * caused another writeback to be scheduled by laptop_io_completion.
1323 * Nothing needs to be written back anymore, so we unschedule the writeback.
1324 */
1325void laptop_sync_completion(void)
1326{
Matthew Garrett31373d02010-04-06 14:25:14 +02001327 struct backing_dev_info *bdi;
1328
1329 rcu_read_lock();
1330
1331 list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
1332 del_timer(&bdi->laptop_mode_wb_timer);
1333
1334 rcu_read_unlock();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001335}
Jens Axboec2c49862010-05-20 09:18:47 +02001336#endif
Linus Torvalds1da177e2005-04-16 15:20:36 -07001337
1338/*
1339 * If ratelimit_pages is too high then we can get into dirty-data overload
1340 * if a large number of processes all perform writes at the same time.
1341 * If it is too low then SMP machines will call the (expensive)
1342 * get_writeback_state too often.
1343 *
1344 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
1345 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
Wu Fengguang9d823e82011-06-11 18:10:12 -06001346 * thresholds.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001347 */
1348
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001349void writeback_set_ratelimit(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001350{
Wu Fengguang9d823e82011-06-11 18:10:12 -06001351 unsigned long background_thresh;
1352 unsigned long dirty_thresh;
1353 global_dirty_limits(&background_thresh, &dirty_thresh);
1354 ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001355 if (ratelimit_pages < 16)
1356 ratelimit_pages = 16;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001357}
1358
Chandra Seetharaman26c21432006-06-27 02:54:10 -07001359static int __cpuinit
Linus Torvalds1da177e2005-04-16 15:20:36 -07001360ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
1361{
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001362 writeback_set_ratelimit();
Paul E. McKenneyaa0f0302007-02-10 01:46:37 -08001363 return NOTIFY_DONE;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001364}
1365
Chandra Seetharaman74b85f32006-06-27 02:54:09 -07001366static struct notifier_block __cpuinitdata ratelimit_nb = {
Linus Torvalds1da177e2005-04-16 15:20:36 -07001367 .notifier_call = ratelimit_handler,
1368 .next = NULL,
1369};
1370
1371/*
Linus Torvaldsdc6e29d2007-01-29 16:37:38 -08001372 * Called early on to tune the page writeback dirty limits.
1373 *
1374 * We used to scale dirty pages according to how total memory
1375 * related to pages that could be allocated for buffers (by
1376 * comparing nr_free_buffer_pages() to vm_total_pages.
1377 *
1378 * However, that was when we used "dirty_ratio" to scale with
1379 * all memory, and we don't do that any more. "dirty_ratio"
1380 * is now applied to total non-HIGHPAGE memory (by subtracting
1381 * totalhigh_pages from vm_total_pages), and as such we can't
1382 * get into the old insane situation any more where we had
1383 * large amounts of dirty pages compared to a small amount of
1384 * non-HIGHMEM memory.
1385 *
1386 * But we might still want to scale the dirty_ratio by how
1387 * much memory the box has..
Linus Torvalds1da177e2005-04-16 15:20:36 -07001388 */
1389void __init page_writeback_init(void)
1390{
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001391 int shift;
1392
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -07001393 writeback_set_ratelimit();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001394 register_cpu_notifier(&ratelimit_nb);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001395
1396 shift = calc_period_shift();
1397 prop_descriptor_init(&vm_completions, shift);
Peter Zijlstra3e26c142007-10-16 23:25:50 -07001398 prop_descriptor_init(&vm_dirties, shift);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001399}
1400
David Howells811d7362006-08-29 19:06:09 +01001401/**
Jan Karaf446daa2010-08-09 17:19:12 -07001402 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
1403 * @mapping: address space structure to write
1404 * @start: starting page index
1405 * @end: ending page index (inclusive)
1406 *
1407 * This function scans the page range from @start to @end (inclusive) and tags
1408 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
1409 * that write_cache_pages (or whoever calls this function) will then use
1410 * TOWRITE tag to identify pages eligible for writeback. This mechanism is
1411 * used to avoid livelocking of writeback by a process steadily creating new
1412 * dirty pages in the file (thus it is important for this function to be quick
1413 * so that it can tag pages faster than a dirtying process can create them).
1414 */
1415/*
1416 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
1417 */
Jan Karaf446daa2010-08-09 17:19:12 -07001418void tag_pages_for_writeback(struct address_space *mapping,
1419 pgoff_t start, pgoff_t end)
1420{
Randy Dunlap3c111a02010-08-11 14:17:30 -07001421#define WRITEBACK_TAG_BATCH 4096
Jan Karaf446daa2010-08-09 17:19:12 -07001422 unsigned long tagged;
1423
1424 do {
1425 spin_lock_irq(&mapping->tree_lock);
1426 tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
1427 &start, end, WRITEBACK_TAG_BATCH,
1428 PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
1429 spin_unlock_irq(&mapping->tree_lock);
1430 WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
1431 cond_resched();
Jan Karad5ed3a42010-08-19 14:13:33 -07001432 /* We check 'start' to handle wrapping when end == ~0UL */
1433 } while (tagged >= WRITEBACK_TAG_BATCH && start);
Jan Karaf446daa2010-08-09 17:19:12 -07001434}
1435EXPORT_SYMBOL(tag_pages_for_writeback);
1436
1437/**
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001438 * 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 +01001439 * @mapping: address space structure to write
1440 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001441 * @writepage: function called for each page
1442 * @data: data passed to writepage function
David Howells811d7362006-08-29 19:06:09 +01001443 *
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001444 * If a page is already under I/O, write_cache_pages() skips it, even
David Howells811d7362006-08-29 19:06:09 +01001445 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
1446 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
1447 * and msync() need to guarantee that all the data which was dirty at the time
1448 * the call was made get new I/O started against them. If wbc->sync_mode is
1449 * WB_SYNC_ALL then we were called for data integrity and we must wait for
1450 * existing IO to complete.
Jan Karaf446daa2010-08-09 17:19:12 -07001451 *
1452 * To avoid livelocks (when other process dirties new pages), we first tag
1453 * pages which should be written back with TOWRITE tag and only then start
1454 * writing them. For data-integrity sync we have to be careful so that we do
1455 * not miss some pages (e.g., because some other process has cleared TOWRITE
1456 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
1457 * by the process clearing the DIRTY tag (and submitting the page for IO).
David Howells811d7362006-08-29 19:06:09 +01001458 */
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001459int write_cache_pages(struct address_space *mapping,
1460 struct writeback_control *wbc, writepage_t writepage,
1461 void *data)
David Howells811d7362006-08-29 19:06:09 +01001462{
David Howells811d7362006-08-29 19:06:09 +01001463 int ret = 0;
1464 int done = 0;
David Howells811d7362006-08-29 19:06:09 +01001465 struct pagevec pvec;
1466 int nr_pages;
Nick Piggin31a12662009-01-06 14:39:04 -08001467 pgoff_t uninitialized_var(writeback_index);
David Howells811d7362006-08-29 19:06:09 +01001468 pgoff_t index;
1469 pgoff_t end; /* Inclusive */
Nick Pigginbd19e012009-01-06 14:39:06 -08001470 pgoff_t done_index;
Nick Piggin31a12662009-01-06 14:39:04 -08001471 int cycled;
David Howells811d7362006-08-29 19:06:09 +01001472 int range_whole = 0;
Jan Karaf446daa2010-08-09 17:19:12 -07001473 int tag;
David Howells811d7362006-08-29 19:06:09 +01001474
David Howells811d7362006-08-29 19:06:09 +01001475 pagevec_init(&pvec, 0);
1476 if (wbc->range_cyclic) {
Nick Piggin31a12662009-01-06 14:39:04 -08001477 writeback_index = mapping->writeback_index; /* prev offset */
1478 index = writeback_index;
1479 if (index == 0)
1480 cycled = 1;
1481 else
1482 cycled = 0;
David Howells811d7362006-08-29 19:06:09 +01001483 end = -1;
1484 } else {
1485 index = wbc->range_start >> PAGE_CACHE_SHIFT;
1486 end = wbc->range_end >> PAGE_CACHE_SHIFT;
1487 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
1488 range_whole = 1;
Nick Piggin31a12662009-01-06 14:39:04 -08001489 cycled = 1; /* ignore range_cyclic tests */
David Howells811d7362006-08-29 19:06:09 +01001490 }
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001491 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daa2010-08-09 17:19:12 -07001492 tag = PAGECACHE_TAG_TOWRITE;
1493 else
1494 tag = PAGECACHE_TAG_DIRTY;
David Howells811d7362006-08-29 19:06:09 +01001495retry:
Wu Fengguang6e6938b2010-06-06 10:38:15 -06001496 if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
Jan Karaf446daa2010-08-09 17:19:12 -07001497 tag_pages_for_writeback(mapping, index, end);
Nick Pigginbd19e012009-01-06 14:39:06 -08001498 done_index = index;
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001499 while (!done && (index <= end)) {
1500 int i;
1501
Jan Karaf446daa2010-08-09 17:19:12 -07001502 nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001503 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
1504 if (nr_pages == 0)
1505 break;
David Howells811d7362006-08-29 19:06:09 +01001506
David Howells811d7362006-08-29 19:06:09 +01001507 for (i = 0; i < nr_pages; i++) {
1508 struct page *page = pvec.pages[i];
1509
Nick Piggind5482cd2009-01-06 14:39:11 -08001510 /*
1511 * At this point, the page may be truncated or
1512 * invalidated (changing page->mapping to NULL), or
1513 * even swizzled back from swapper_space to tmpfs file
1514 * mapping. However, page->index will not change
1515 * because we have a reference on the page.
1516 */
1517 if (page->index > end) {
1518 /*
1519 * can't be range_cyclic (1st pass) because
1520 * end == -1 in that case.
1521 */
1522 done = 1;
1523 break;
1524 }
1525
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001526 done_index = page->index;
Nick Pigginbd19e012009-01-06 14:39:06 -08001527
David Howells811d7362006-08-29 19:06:09 +01001528 lock_page(page);
1529
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001530 /*
1531 * Page truncated or invalidated. We can freely skip it
1532 * then, even for data integrity operations: the page
1533 * has disappeared concurrently, so there could be no
1534 * real expectation of this data interity operation
1535 * even if there is now a new, dirty page at the same
1536 * pagecache address.
1537 */
David Howells811d7362006-08-29 19:06:09 +01001538 if (unlikely(page->mapping != mapping)) {
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001539continue_unlock:
David Howells811d7362006-08-29 19:06:09 +01001540 unlock_page(page);
1541 continue;
1542 }
1543
Nick Piggin515f4a02009-01-06 14:39:10 -08001544 if (!PageDirty(page)) {
1545 /* someone wrote it for us */
1546 goto continue_unlock;
1547 }
David Howells811d7362006-08-29 19:06:09 +01001548
Nick Piggin515f4a02009-01-06 14:39:10 -08001549 if (PageWriteback(page)) {
1550 if (wbc->sync_mode != WB_SYNC_NONE)
1551 wait_on_page_writeback(page);
1552 else
1553 goto continue_unlock;
1554 }
1555
1556 BUG_ON(PageWriteback(page));
1557 if (!clear_page_dirty_for_io(page))
Nick Piggin5a3d5c92009-01-06 14:39:09 -08001558 goto continue_unlock;
David Howells811d7362006-08-29 19:06:09 +01001559
Dave Chinner9e094382010-07-07 13:24:08 +10001560 trace_wbc_writepage(wbc, mapping->backing_dev_info);
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001561 ret = (*writepage)(page, wbc, data);
Nick Piggin00266772009-01-06 14:39:06 -08001562 if (unlikely(ret)) {
1563 if (ret == AOP_WRITEPAGE_ACTIVATE) {
1564 unlock_page(page);
1565 ret = 0;
1566 } else {
1567 /*
1568 * done_index is set past this page,
1569 * so media errors will not choke
1570 * background writeout for the entire
1571 * file. This has consequences for
1572 * range_cyclic semantics (ie. it may
1573 * not be suitable for data integrity
1574 * writeout).
1575 */
Jun'ichi Nomuracf15b072011-03-22 16:33:40 -07001576 done_index = page->index + 1;
Nick Piggin00266772009-01-06 14:39:06 -08001577 done = 1;
1578 break;
1579 }
Dave Chinner0b564922010-06-09 10:37:18 +10001580 }
David Howells811d7362006-08-29 19:06:09 +01001581
Dave Chinner546a1922010-08-24 11:44:34 +10001582 /*
1583 * We stop writing back only if we are not doing
1584 * integrity sync. In case of integrity sync we have to
1585 * keep going until we have written all the pages
1586 * we tagged for writeback prior to entering this loop.
1587 */
1588 if (--wbc->nr_to_write <= 0 &&
1589 wbc->sync_mode == WB_SYNC_NONE) {
1590 done = 1;
1591 break;
Nick Piggin05fe4782009-01-06 14:39:08 -08001592 }
David Howells811d7362006-08-29 19:06:09 +01001593 }
1594 pagevec_release(&pvec);
1595 cond_resched();
1596 }
Nick Piggin3a4c6802009-02-12 04:34:23 +01001597 if (!cycled && !done) {
David Howells811d7362006-08-29 19:06:09 +01001598 /*
Nick Piggin31a12662009-01-06 14:39:04 -08001599 * range_cyclic:
David Howells811d7362006-08-29 19:06:09 +01001600 * We hit the last page and there is more work to be done: wrap
1601 * back to the start of the file
1602 */
Nick Piggin31a12662009-01-06 14:39:04 -08001603 cycled = 1;
David Howells811d7362006-08-29 19:06:09 +01001604 index = 0;
Nick Piggin31a12662009-01-06 14:39:04 -08001605 end = writeback_index - 1;
David Howells811d7362006-08-29 19:06:09 +01001606 goto retry;
1607 }
Dave Chinner0b564922010-06-09 10:37:18 +10001608 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
1609 mapping->writeback_index = done_index;
Aneesh Kumar K.V06d6cf62008-07-11 19:27:31 -04001610
David Howells811d7362006-08-29 19:06:09 +01001611 return ret;
1612}
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001613EXPORT_SYMBOL(write_cache_pages);
1614
1615/*
1616 * Function used by generic_writepages to call the real writepage
1617 * function and set the mapping flags on error
1618 */
1619static int __writepage(struct page *page, struct writeback_control *wbc,
1620 void *data)
1621{
1622 struct address_space *mapping = data;
1623 int ret = mapping->a_ops->writepage(page, wbc);
1624 mapping_set_error(mapping, ret);
1625 return ret;
1626}
1627
1628/**
1629 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
1630 * @mapping: address space structure to write
1631 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
1632 *
1633 * This is a library function, which implements the writepages()
1634 * address_space_operation.
1635 */
1636int generic_writepages(struct address_space *mapping,
1637 struct writeback_control *wbc)
1638{
Shaohua Li9b6096a2011-03-17 10:47:06 +01001639 struct blk_plug plug;
1640 int ret;
1641
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001642 /* deal with chardevs and other special file */
1643 if (!mapping->a_ops->writepage)
1644 return 0;
1645
Shaohua Li9b6096a2011-03-17 10:47:06 +01001646 blk_start_plug(&plug);
1647 ret = write_cache_pages(mapping, wbc, __writepage, mapping);
1648 blk_finish_plug(&plug);
1649 return ret;
Miklos Szeredi0ea97182007-05-10 22:22:51 -07001650}
David Howells811d7362006-08-29 19:06:09 +01001651
1652EXPORT_SYMBOL(generic_writepages);
1653
Linus Torvalds1da177e2005-04-16 15:20:36 -07001654int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1655{
Andrew Morton22905f72005-11-16 15:07:01 -08001656 int ret;
1657
Linus Torvalds1da177e2005-04-16 15:20:36 -07001658 if (wbc->nr_to_write <= 0)
1659 return 0;
1660 if (mapping->a_ops->writepages)
Peter Zijlstrad08b3852006-09-25 23:30:57 -07001661 ret = mapping->a_ops->writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08001662 else
1663 ret = generic_writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08001664 return ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001665}
1666
1667/**
1668 * write_one_page - write out a single page and optionally wait on I/O
Martin Waitz67be2dd2005-05-01 08:59:26 -07001669 * @page: the page to write
1670 * @wait: if true, wait on writeout
Linus Torvalds1da177e2005-04-16 15:20:36 -07001671 *
1672 * The page must be locked by the caller and will be unlocked upon return.
1673 *
1674 * write_one_page() returns a negative error code if I/O failed.
1675 */
1676int write_one_page(struct page *page, int wait)
1677{
1678 struct address_space *mapping = page->mapping;
1679 int ret = 0;
1680 struct writeback_control wbc = {
1681 .sync_mode = WB_SYNC_ALL,
1682 .nr_to_write = 1,
1683 };
1684
1685 BUG_ON(!PageLocked(page));
1686
1687 if (wait)
1688 wait_on_page_writeback(page);
1689
1690 if (clear_page_dirty_for_io(page)) {
1691 page_cache_get(page);
1692 ret = mapping->a_ops->writepage(page, &wbc);
1693 if (ret == 0 && wait) {
1694 wait_on_page_writeback(page);
1695 if (PageError(page))
1696 ret = -EIO;
1697 }
1698 page_cache_release(page);
1699 } else {
1700 unlock_page(page);
1701 }
1702 return ret;
1703}
1704EXPORT_SYMBOL(write_one_page);
1705
1706/*
Ken Chen76719322007-02-10 01:43:15 -08001707 * For address_spaces which do not use buffers nor write back.
1708 */
1709int __set_page_dirty_no_writeback(struct page *page)
1710{
1711 if (!PageDirty(page))
Bob Liuc3f0da62011-01-13 15:45:49 -08001712 return !TestSetPageDirty(page);
Ken Chen76719322007-02-10 01:43:15 -08001713 return 0;
1714}
1715
1716/*
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001717 * Helper function for set_page_dirty family.
1718 * NOTE: This relies on being atomic wrt interrupts.
1719 */
1720void account_page_dirtied(struct page *page, struct address_space *mapping)
1721{
1722 if (mapping_cap_account_dirty(mapping)) {
1723 __inc_zone_page_state(page, NR_FILE_DIRTY);
Michael Rubinea941f02010-10-26 14:21:35 -07001724 __inc_zone_page_state(page, NR_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001725 __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
Wu Fengguangc8e28ce2011-01-23 10:07:47 -06001726 __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001727 task_dirty_inc(current);
1728 task_io_account_write(PAGE_CACHE_SIZE);
1729 }
1730}
Michael Rubin679ceac2010-08-20 02:31:26 -07001731EXPORT_SYMBOL(account_page_dirtied);
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001732
1733/*
Michael Rubinf629d1c2010-10-26 14:21:33 -07001734 * Helper function for set_page_writeback family.
1735 * NOTE: Unlike account_page_dirtied this does not rely on being atomic
1736 * wrt interrupts.
1737 */
1738void account_page_writeback(struct page *page)
1739{
1740 inc_zone_page_state(page, NR_WRITEBACK);
1741}
1742EXPORT_SYMBOL(account_page_writeback);
1743
1744/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001745 * For address_spaces which do not use buffers. Just tag the page as dirty in
1746 * its radix tree.
1747 *
1748 * This is also used when a single buffer is being dirtied: we want to set the
1749 * page dirty in that case, but not all the buffers. This is a "bottom-up"
1750 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1751 *
1752 * Most callers have locked the page, which pins the address_space in memory.
1753 * But zap_pte_range() does not lock the page, however in that case the
1754 * mapping is pinned by the vma's ->vm_file reference.
1755 *
1756 * We take care to handle the case where the page was truncated from the
Simon Arlott183ff222007-10-20 01:27:18 +02001757 * mapping by re-checking page_mapping() inside tree_lock.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001758 */
1759int __set_page_dirty_nobuffers(struct page *page)
1760{
Linus Torvalds1da177e2005-04-16 15:20:36 -07001761 if (!TestSetPageDirty(page)) {
1762 struct address_space *mapping = page_mapping(page);
1763 struct address_space *mapping2;
1764
Andrew Morton8c085402006-12-10 02:19:24 -08001765 if (!mapping)
1766 return 1;
1767
Nick Piggin19fd6232008-07-25 19:45:32 -07001768 spin_lock_irq(&mapping->tree_lock);
Andrew Morton8c085402006-12-10 02:19:24 -08001769 mapping2 = page_mapping(page);
1770 if (mapping2) { /* Race with truncate? */
1771 BUG_ON(mapping2 != mapping);
Nick Piggin787d2212007-07-17 04:03:34 -07001772 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
Edward Shishkine3a7cca2009-03-31 15:19:39 -07001773 account_page_dirtied(page, mapping);
Andrew Morton8c085402006-12-10 02:19:24 -08001774 radix_tree_tag_set(&mapping->page_tree,
1775 page_index(page), PAGECACHE_TAG_DIRTY);
1776 }
Nick Piggin19fd6232008-07-25 19:45:32 -07001777 spin_unlock_irq(&mapping->tree_lock);
Andrew Morton8c085402006-12-10 02:19:24 -08001778 if (mapping->host) {
1779 /* !PageAnon && !swapper_space */
1780 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001781 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08001782 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001783 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08001784 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001785}
1786EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1787
1788/*
1789 * When a writepage implementation decides that it doesn't want to write this
1790 * page for some reason, it should redirty the locked page via
1791 * redirty_page_for_writepage() and it should then unlock the page and return 0
1792 */
1793int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1794{
1795 wbc->pages_skipped++;
1796 return __set_page_dirty_nobuffers(page);
1797}
1798EXPORT_SYMBOL(redirty_page_for_writepage);
1799
1800/*
Wu Fengguang6746aff2009-09-16 11:50:14 +02001801 * Dirty a page.
1802 *
1803 * For pages with a mapping this should be done under the page lock
1804 * for the benefit of asynchronous memory errors who prefer a consistent
1805 * dirty state. This rule can be broken in some special cases,
1806 * but should be better not to.
1807 *
Linus Torvalds1da177e2005-04-16 15:20:36 -07001808 * If the mapping doesn't provide a set_page_dirty a_op, then
1809 * just fall through and assume that it wants buffer_heads.
1810 */
Nick Piggin1cf6e7d2009-02-18 14:48:18 -08001811int set_page_dirty(struct page *page)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001812{
1813 struct address_space *mapping = page_mapping(page);
1814
1815 if (likely(mapping)) {
1816 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
Minchan Kim278df9f2011-03-22 16:32:54 -07001817 /*
1818 * readahead/lru_deactivate_page could remain
1819 * PG_readahead/PG_reclaim due to race with end_page_writeback
1820 * About readahead, if the page is written, the flags would be
1821 * reset. So no problem.
1822 * About lru_deactivate_page, if the page is redirty, the flag
1823 * will be reset. So no problem. but if the page is used by readahead
1824 * it will confuse readahead and make it restart the size rampup
1825 * process. But it's a trivial problem.
1826 */
1827 ClearPageReclaim(page);
David Howells93614012006-09-30 20:45:40 +02001828#ifdef CONFIG_BLOCK
1829 if (!spd)
1830 spd = __set_page_dirty_buffers;
1831#endif
1832 return (*spd)(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001833 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08001834 if (!PageDirty(page)) {
1835 if (!TestSetPageDirty(page))
1836 return 1;
1837 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07001838 return 0;
1839}
1840EXPORT_SYMBOL(set_page_dirty);
1841
1842/*
1843 * set_page_dirty() is racy if the caller has no reference against
1844 * page->mapping->host, and if the page is unlocked. This is because another
1845 * CPU could truncate the page off the mapping and then free the mapping.
1846 *
1847 * Usually, the page _is_ locked, or the caller is a user-space process which
1848 * holds a reference on the inode by having an open file.
1849 *
1850 * In other cases, the page should be locked before running set_page_dirty().
1851 */
1852int set_page_dirty_lock(struct page *page)
1853{
1854 int ret;
1855
Jens Axboe7eaceac2011-03-10 08:52:07 +01001856 lock_page(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001857 ret = set_page_dirty(page);
1858 unlock_page(page);
1859 return ret;
1860}
1861EXPORT_SYMBOL(set_page_dirty_lock);
1862
1863/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001864 * Clear a page's dirty flag, while caring for dirty memory accounting.
1865 * Returns true if the page was previously dirty.
1866 *
1867 * This is for preparing to put the page under writeout. We leave the page
1868 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1869 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
1870 * implementation will run either set_page_writeback() or set_page_dirty(),
1871 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1872 * back into sync.
1873 *
1874 * This incoherency between the page's dirty flag and radix-tree tag is
1875 * unfortunate, but it only exists while the page is locked.
1876 */
1877int clear_page_dirty_for_io(struct page *page)
1878{
1879 struct address_space *mapping = page_mapping(page);
1880
Nick Piggin79352892007-07-19 01:47:22 -07001881 BUG_ON(!PageLocked(page));
1882
Linus Torvalds7658cc22006-12-29 10:00:58 -08001883 if (mapping && mapping_cap_account_dirty(mapping)) {
1884 /*
1885 * Yes, Virginia, this is indeed insane.
1886 *
1887 * We use this sequence to make sure that
1888 * (a) we account for dirty stats properly
1889 * (b) we tell the low-level filesystem to
1890 * mark the whole page dirty if it was
1891 * dirty in a pagetable. Only to then
1892 * (c) clean the page again and return 1 to
1893 * cause the writeback.
1894 *
1895 * This way we avoid all nasty races with the
1896 * dirty bit in multiple places and clearing
1897 * them concurrently from different threads.
1898 *
1899 * Note! Normally the "set_page_dirty(page)"
1900 * has no effect on the actual dirty bit - since
1901 * that will already usually be set. But we
1902 * need the side effects, and it can help us
1903 * avoid races.
1904 *
1905 * We basically use the page "master dirty bit"
1906 * as a serialization point for all the different
1907 * threads doing their things.
Linus Torvalds7658cc22006-12-29 10:00:58 -08001908 */
1909 if (page_mkclean(page))
1910 set_page_dirty(page);
Nick Piggin79352892007-07-19 01:47:22 -07001911 /*
1912 * We carefully synchronise fault handlers against
1913 * installing a dirty pte and marking the page dirty
1914 * at this point. We do this by having them hold the
1915 * page lock at some point after installing their
1916 * pte, but before marking the page dirty.
1917 * Pages are always locked coming in here, so we get
1918 * the desired exclusion. See mm/memory.c:do_wp_page()
1919 * for more comments.
1920 */
Linus Torvalds7658cc22006-12-29 10:00:58 -08001921 if (TestClearPageDirty(page)) {
Andrew Morton8c085402006-12-10 02:19:24 -08001922 dec_zone_page_state(page, NR_FILE_DIRTY);
Peter Zijlstrac9e51e42007-10-16 23:25:47 -07001923 dec_bdi_stat(mapping->backing_dev_info,
1924 BDI_RECLAIMABLE);
Linus Torvalds7658cc22006-12-29 10:00:58 -08001925 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001926 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08001927 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001928 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08001929 return TestClearPageDirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001930}
Hans Reiser58bb01a2005-11-18 01:10:53 -08001931EXPORT_SYMBOL(clear_page_dirty_for_io);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001932
1933int test_clear_page_writeback(struct page *page)
1934{
1935 struct address_space *mapping = page_mapping(page);
1936 int ret;
1937
1938 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001939 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001940 unsigned long flags;
1941
Nick Piggin19fd6232008-07-25 19:45:32 -07001942 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001943 ret = TestClearPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001944 if (ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07001945 radix_tree_tag_clear(&mapping->page_tree,
1946 page_index(page),
1947 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07001948 if (bdi_cap_account_writeback(bdi)) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001949 __dec_bdi_stat(bdi, BDI_WRITEBACK);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001950 __bdi_writeout_inc(bdi);
1951 }
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001952 }
Nick Piggin19fd6232008-07-25 19:45:32 -07001953 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001954 } else {
1955 ret = TestClearPageWriteback(page);
1956 }
Wu Fengguang99b12e32011-07-25 17:12:37 -07001957 if (ret) {
Andrew Mortond688abf2007-07-19 01:49:17 -07001958 dec_zone_page_state(page, NR_WRITEBACK);
Wu Fengguang99b12e32011-07-25 17:12:37 -07001959 inc_zone_page_state(page, NR_WRITTEN);
1960 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07001961 return ret;
1962}
1963
1964int test_set_page_writeback(struct page *page)
1965{
1966 struct address_space *mapping = page_mapping(page);
1967 int ret;
1968
1969 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001970 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001971 unsigned long flags;
1972
Nick Piggin19fd6232008-07-25 19:45:32 -07001973 spin_lock_irqsave(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001974 ret = TestSetPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001975 if (!ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07001976 radix_tree_tag_set(&mapping->page_tree,
1977 page_index(page),
1978 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07001979 if (bdi_cap_account_writeback(bdi))
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001980 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1981 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07001982 if (!PageDirty(page))
1983 radix_tree_tag_clear(&mapping->page_tree,
1984 page_index(page),
1985 PAGECACHE_TAG_DIRTY);
Jan Karaf446daa2010-08-09 17:19:12 -07001986 radix_tree_tag_clear(&mapping->page_tree,
1987 page_index(page),
1988 PAGECACHE_TAG_TOWRITE);
Nick Piggin19fd6232008-07-25 19:45:32 -07001989 spin_unlock_irqrestore(&mapping->tree_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001990 } else {
1991 ret = TestSetPageWriteback(page);
1992 }
Andrew Mortond688abf2007-07-19 01:49:17 -07001993 if (!ret)
Michael Rubinf629d1c2010-10-26 14:21:33 -07001994 account_page_writeback(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001995 return ret;
1996
1997}
1998EXPORT_SYMBOL(test_set_page_writeback);
1999
2000/*
Nick Piggin00128182007-10-16 01:24:40 -07002001 * Return true if any of the pages in the mapping are marked with the
Linus Torvalds1da177e2005-04-16 15:20:36 -07002002 * passed tag.
2003 */
2004int mapping_tagged(struct address_space *mapping, int tag)
2005{
Konstantin Khlebnikov72c47832011-07-25 17:12:31 -07002006 return radix_tree_tagged(&mapping->page_tree, tag);
Linus Torvalds1da177e2005-04-16 15:20:36 -07002007}
2008EXPORT_SYMBOL(mapping_tagged);