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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 *
10 * 10Apr2002 akpm@zip.com.au
11 * Initial version
12 */
13
14#include <linux/kernel.h>
15#include <linux/module.h>
16#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>
Linus Torvalds1da177e2005-04-16 15:20:36 -070037
38/*
39 * The maximum number of pages to writeout in a single bdflush/kupdate
Joern Engel1c0eeaf2007-10-16 23:30:44 -070040 * operation. We do this so we don't hold I_SYNC against an inode for
Linus Torvalds1da177e2005-04-16 15:20:36 -070041 * enormous amounts of time, which would block a userspace task which has
42 * been forced to throttle against that inode. Also, the code reevaluates
43 * the dirty each time it has written this many pages.
44 */
45#define MAX_WRITEBACK_PAGES 1024
46
47/*
48 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
49 * will look to see if it needs to force writeback or throttling.
50 */
51static long ratelimit_pages = 32;
52
Linus Torvalds1da177e2005-04-16 15:20:36 -070053/*
54 * When balance_dirty_pages decides that the caller needs to perform some
55 * non-background writeback, this is how many pages it will attempt to write.
56 * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
57 * large amounts of I/O are submitted.
58 */
59static inline long sync_writeback_pages(void)
60{
61 return ratelimit_pages + ratelimit_pages / 2;
62}
63
64/* The following parameters are exported via /proc/sys/vm */
65
66/*
67 * Start background writeback (via pdflush) at this percentage
68 */
Linus Torvalds07db59b2007-04-27 09:10:47 -070069int dirty_background_ratio = 5;
Linus Torvalds1da177e2005-04-16 15:20:36 -070070
71/*
Bron Gondwana195cf4532008-02-04 22:29:20 -080072 * free highmem will not be subtracted from the total free memory
73 * for calculating free ratios if vm_highmem_is_dirtyable is true
74 */
75int vm_highmem_is_dirtyable;
76
77/*
Linus Torvalds1da177e2005-04-16 15:20:36 -070078 * The generator of dirty data starts writeback at this percentage
79 */
Linus Torvalds07db59b2007-04-27 09:10:47 -070080int vm_dirty_ratio = 10;
Linus Torvalds1da177e2005-04-16 15:20:36 -070081
82/*
Coywolf Qi Huntfd5403c2006-04-10 22:54:35 -070083 * The interval between `kupdate'-style writebacks, in jiffies
Linus Torvalds1da177e2005-04-16 15:20:36 -070084 */
Bart Samwelf6ef9432006-03-24 03:15:48 -080085int dirty_writeback_interval = 5 * HZ;
Linus Torvalds1da177e2005-04-16 15:20:36 -070086
87/*
Coywolf Qi Huntfd5403c2006-04-10 22:54:35 -070088 * The longest number of jiffies for which data is allowed to remain dirty
Linus Torvalds1da177e2005-04-16 15:20:36 -070089 */
Bart Samwelf6ef9432006-03-24 03:15:48 -080090int dirty_expire_interval = 30 * HZ;
Linus Torvalds1da177e2005-04-16 15:20:36 -070091
92/*
93 * Flag that makes the machine dump writes/reads and block dirtyings.
94 */
95int block_dump;
96
97/*
Bart Samweled5b43f2006-03-24 03:15:49 -080098 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
99 * a full sync is triggered after this time elapses without any disk activity.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700100 */
101int laptop_mode;
102
103EXPORT_SYMBOL(laptop_mode);
104
105/* End of sysctl-exported parameters */
106
107
108static void background_writeout(unsigned long _min_pages);
109
Linus Torvalds1da177e2005-04-16 15:20:36 -0700110/*
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700111 * Scale the writeback cache size proportional to the relative writeout speeds.
112 *
113 * We do this by keeping a floating proportion between BDIs, based on page
114 * writeback completions [end_page_writeback()]. Those devices that write out
115 * pages fastest will get the larger share, while the slower will get a smaller
116 * share.
117 *
118 * We use page writeout completions because we are interested in getting rid of
119 * dirty pages. Having them written out is the primary goal.
120 *
121 * We introduce a concept of time, a period over which we measure these events,
122 * because demand can/will vary over time. The length of this period itself is
123 * measured in page writeback completions.
124 *
125 */
126static struct prop_descriptor vm_completions;
Peter Zijlstra3e26c142007-10-16 23:25:50 -0700127static struct prop_descriptor vm_dirties;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700128
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700129/*
130 * couple the period to the dirty_ratio:
131 *
132 * period/2 ~ roundup_pow_of_two(dirty limit)
133 */
134static int calc_period_shift(void)
135{
136 unsigned long dirty_total;
137
138 dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / 100;
139 return 2 + ilog2(dirty_total - 1);
140}
141
142/*
143 * update the period when the dirty ratio changes.
144 */
145int dirty_ratio_handler(struct ctl_table *table, int write,
146 struct file *filp, void __user *buffer, size_t *lenp,
147 loff_t *ppos)
148{
149 int old_ratio = vm_dirty_ratio;
150 int ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
151 if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
152 int shift = calc_period_shift();
153 prop_change_shift(&vm_completions, shift);
Peter Zijlstra3e26c142007-10-16 23:25:50 -0700154 prop_change_shift(&vm_dirties, shift);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700155 }
156 return ret;
157}
158
159/*
160 * Increment the BDI's writeout completion count and the global writeout
161 * completion count. Called from test_clear_page_writeback().
162 */
163static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
164{
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700165 __prop_inc_percpu_max(&vm_completions, &bdi->completions,
166 bdi->max_prop_frac);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700167}
168
Miklos Szeredidd5656e2008-04-30 00:54:37 -0700169void bdi_writeout_inc(struct backing_dev_info *bdi)
170{
171 unsigned long flags;
172
173 local_irq_save(flags);
174 __bdi_writeout_inc(bdi);
175 local_irq_restore(flags);
176}
177EXPORT_SYMBOL_GPL(bdi_writeout_inc);
178
Peter Zijlstra3e26c142007-10-16 23:25:50 -0700179static inline void task_dirty_inc(struct task_struct *tsk)
180{
181 prop_inc_single(&vm_dirties, &tsk->dirties);
182}
183
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700184/*
185 * Obtain an accurate fraction of the BDI's portion.
186 */
187static void bdi_writeout_fraction(struct backing_dev_info *bdi,
188 long *numerator, long *denominator)
189{
190 if (bdi_cap_writeback_dirty(bdi)) {
191 prop_fraction_percpu(&vm_completions, &bdi->completions,
192 numerator, denominator);
193 } else {
194 *numerator = 0;
195 *denominator = 1;
196 }
197}
198
199/*
200 * Clip the earned share of dirty pages to that which is actually available.
201 * This avoids exceeding the total dirty_limit when the floating averages
202 * fluctuate too quickly.
203 */
204static void
205clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long *pbdi_dirty)
206{
207 long avail_dirty;
208
209 avail_dirty = dirty -
210 (global_page_state(NR_FILE_DIRTY) +
211 global_page_state(NR_WRITEBACK) +
Miklos Szeredifc3ba692008-04-30 00:54:38 -0700212 global_page_state(NR_UNSTABLE_NFS) +
213 global_page_state(NR_WRITEBACK_TEMP));
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700214
215 if (avail_dirty < 0)
216 avail_dirty = 0;
217
218 avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) +
219 bdi_stat(bdi, BDI_WRITEBACK);
220
221 *pbdi_dirty = min(*pbdi_dirty, avail_dirty);
222}
223
Peter Zijlstra3e26c142007-10-16 23:25:50 -0700224static inline void task_dirties_fraction(struct task_struct *tsk,
225 long *numerator, long *denominator)
226{
227 prop_fraction_single(&vm_dirties, &tsk->dirties,
228 numerator, denominator);
229}
230
231/*
232 * scale the dirty limit
233 *
234 * task specific dirty limit:
235 *
236 * dirty -= (dirty/8) * p_{t}
237 */
Adrian Bunkf61eaf92008-02-04 22:29:08 -0800238static void task_dirty_limit(struct task_struct *tsk, long *pdirty)
Peter Zijlstra3e26c142007-10-16 23:25:50 -0700239{
240 long numerator, denominator;
241 long dirty = *pdirty;
242 u64 inv = dirty >> 3;
243
244 task_dirties_fraction(tsk, &numerator, &denominator);
245 inv *= numerator;
246 do_div(inv, denominator);
247
248 dirty -= inv;
249 if (dirty < *pdirty/2)
250 dirty = *pdirty/2;
251
252 *pdirty = dirty;
253}
254
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700255/*
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700256 *
257 */
258static DEFINE_SPINLOCK(bdi_lock);
259static unsigned int bdi_min_ratio;
260
261int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
262{
263 int ret = 0;
264 unsigned long flags;
265
266 spin_lock_irqsave(&bdi_lock, flags);
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700267 if (min_ratio > bdi->max_ratio) {
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700268 ret = -EINVAL;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700269 } else {
270 min_ratio -= bdi->min_ratio;
271 if (bdi_min_ratio + min_ratio < 100) {
272 bdi_min_ratio += min_ratio;
273 bdi->min_ratio += min_ratio;
274 } else {
275 ret = -EINVAL;
276 }
277 }
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700278 spin_unlock_irqrestore(&bdi_lock, flags);
279
280 return ret;
281}
282
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700283int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
284{
285 unsigned long flags;
286 int ret = 0;
287
288 if (max_ratio > 100)
289 return -EINVAL;
290
291 spin_lock_irqsave(&bdi_lock, flags);
292 if (bdi->min_ratio > max_ratio) {
293 ret = -EINVAL;
294 } else {
295 bdi->max_ratio = max_ratio;
296 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
297 }
298 spin_unlock_irqrestore(&bdi_lock, flags);
299
300 return ret;
301}
302EXPORT_SYMBOL(bdi_set_max_ratio);
303
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700304/*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700305 * Work out the current dirty-memory clamping and background writeout
306 * thresholds.
307 *
308 * The main aim here is to lower them aggressively if there is a lot of mapped
309 * memory around. To avoid stressing page reclaim with lots of unreclaimable
310 * pages. It is better to clamp down on writers than to start swapping, and
311 * performing lots of scanning.
312 *
313 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
314 *
315 * We don't permit the clamping level to fall below 5% - that is getting rather
316 * excessive.
317 *
318 * We make sure that the background writeout level is below the adjusted
319 * clamping level.
320 */
Christoph Lameter1b424462007-05-06 14:48:59 -0700321
322static unsigned long highmem_dirtyable_memory(unsigned long total)
323{
324#ifdef CONFIG_HIGHMEM
325 int node;
326 unsigned long x = 0;
327
Lee Schermerhorn37b07e42007-10-16 01:25:39 -0700328 for_each_node_state(node, N_HIGH_MEMORY) {
Christoph Lameter1b424462007-05-06 14:48:59 -0700329 struct zone *z =
330 &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
331
332 x += zone_page_state(z, NR_FREE_PAGES)
333 + zone_page_state(z, NR_INACTIVE)
334 + zone_page_state(z, NR_ACTIVE);
335 }
336 /*
337 * Make sure that the number of highmem pages is never larger
338 * than the number of the total dirtyable memory. This can only
339 * occur in very strange VM situations but we want to make sure
340 * that this does not occur.
341 */
342 return min(x, total);
343#else
344 return 0;
345#endif
346}
347
Steven Rostedt3eefae92008-05-12 21:21:04 +0200348/**
349 * determine_dirtyable_memory - amount of memory that may be used
350 *
351 * Returns the numebr of pages that can currently be freed and used
352 * by the kernel for direct mappings.
353 */
354unsigned long determine_dirtyable_memory(void)
Christoph Lameter1b424462007-05-06 14:48:59 -0700355{
356 unsigned long x;
357
358 x = global_page_state(NR_FREE_PAGES)
359 + global_page_state(NR_INACTIVE)
360 + global_page_state(NR_ACTIVE);
Bron Gondwana195cf4532008-02-04 22:29:20 -0800361
362 if (!vm_highmem_is_dirtyable)
363 x -= highmem_dirtyable_memory(x);
364
Christoph Lameter1b424462007-05-06 14:48:59 -0700365 return x + 1; /* Ensure that we never return 0 */
366}
367
Peter Zijlstracf0ca9f2008-04-30 00:54:32 -0700368void
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700369get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty,
370 struct backing_dev_info *bdi)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700371{
372 int background_ratio; /* Percentages */
373 int dirty_ratio;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700374 long background;
375 long dirty;
Christoph Lameter1b424462007-05-06 14:48:59 -0700376 unsigned long available_memory = determine_dirtyable_memory();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700377 struct task_struct *tsk;
378
Linus Torvalds1da177e2005-04-16 15:20:36 -0700379 dirty_ratio = vm_dirty_ratio;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700380 if (dirty_ratio < 5)
381 dirty_ratio = 5;
382
383 background_ratio = dirty_background_ratio;
384 if (background_ratio >= dirty_ratio)
385 background_ratio = dirty_ratio / 2;
386
387 background = (background_ratio * available_memory) / 100;
388 dirty = (dirty_ratio * available_memory) / 100;
389 tsk = current;
390 if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
391 background += background / 4;
392 dirty += dirty / 4;
393 }
394 *pbackground = background;
395 *pdirty = dirty;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700396
397 if (bdi) {
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700398 u64 bdi_dirty;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700399 long numerator, denominator;
400
401 /*
402 * Calculate this BDI's share of the dirty ratio.
403 */
404 bdi_writeout_fraction(bdi, &numerator, &denominator);
405
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700406 bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700407 bdi_dirty *= numerator;
408 do_div(bdi_dirty, denominator);
Peter Zijlstra189d3c42008-04-30 00:54:35 -0700409 bdi_dirty += (dirty * bdi->min_ratio) / 100;
Peter Zijlstraa42dde02008-04-30 00:54:36 -0700410 if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
411 bdi_dirty = dirty * bdi->max_ratio / 100;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700412
413 *pbdi_dirty = bdi_dirty;
414 clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);
Peter Zijlstra3e26c142007-10-16 23:25:50 -0700415 task_dirty_limit(current, pbdi_dirty);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700416 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700417}
418
419/*
420 * balance_dirty_pages() must be called by processes which are generating dirty
421 * data. It looks at the number of dirty pages in the machine and will force
422 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
423 * If we're over `background_thresh' then pdflush is woken to perform some
424 * writeout.
425 */
426static void balance_dirty_pages(struct address_space *mapping)
427{
Peter Zijlstra5fce25a2007-11-14 16:59:15 -0800428 long nr_reclaimable, bdi_nr_reclaimable;
429 long nr_writeback, bdi_nr_writeback;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700430 long background_thresh;
431 long dirty_thresh;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700432 long bdi_thresh;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700433 unsigned long pages_written = 0;
434 unsigned long write_chunk = sync_writeback_pages();
435
436 struct backing_dev_info *bdi = mapping->backing_dev_info;
437
438 for (;;) {
439 struct writeback_control wbc = {
440 .bdi = bdi,
441 .sync_mode = WB_SYNC_NONE,
442 .older_than_this = NULL,
443 .nr_to_write = write_chunk,
OGAWA Hirofumi111ebb62006-06-23 02:03:26 -0700444 .range_cyclic = 1,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700445 };
446
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700447 get_dirty_limits(&background_thresh, &dirty_thresh,
448 &bdi_thresh, bdi);
Peter Zijlstra5fce25a2007-11-14 16:59:15 -0800449
450 nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
451 global_page_state(NR_UNSTABLE_NFS);
452 nr_writeback = global_page_state(NR_WRITEBACK);
453
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700454 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
455 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
Peter Zijlstra5fce25a2007-11-14 16:59:15 -0800456
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700457 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
458 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700459
Peter Zijlstra5fce25a2007-11-14 16:59:15 -0800460 /*
461 * Throttle it only when the background writeback cannot
462 * catch-up. This avoids (excessively) small writeouts
463 * when the bdi limits are ramping up.
464 */
465 if (nr_reclaimable + nr_writeback <
466 (background_thresh + dirty_thresh) / 2)
467 break;
468
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700469 if (!bdi->dirty_exceeded)
470 bdi->dirty_exceeded = 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700471
472 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
473 * Unstable writes are a feature of certain networked
474 * filesystems (i.e. NFS) in which data may have been
475 * written to the server's write cache, but has not yet
476 * been flushed to permanent storage.
477 */
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700478 if (bdi_nr_reclaimable) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700479 writeback_inodes(&wbc);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700480 pages_written += write_chunk - wbc.nr_to_write;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700481 get_dirty_limits(&background_thresh, &dirty_thresh,
482 &bdi_thresh, bdi);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700483 }
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700484
485 /*
486 * In order to avoid the stacked BDI deadlock we need
487 * to ensure we accurately count the 'dirty' pages when
488 * the threshold is low.
489 *
490 * Otherwise it would be possible to get thresh+n pages
491 * reported dirty, even though there are thresh-m pages
492 * actually dirty; with m+n sitting in the percpu
493 * deltas.
494 */
495 if (bdi_thresh < 2*bdi_stat_error(bdi)) {
496 bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
497 bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
498 } else if (bdi_nr_reclaimable) {
499 bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
500 bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
501 }
502
503 if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
504 break;
505 if (pages_written >= write_chunk)
506 break; /* We've done our duty */
507
Andrew Morton3fcfab12006-10-19 23:28:16 -0700508 congestion_wait(WRITE, HZ/10);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700509 }
510
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700511 if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh &&
512 bdi->dirty_exceeded)
513 bdi->dirty_exceeded = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700514
515 if (writeback_in_progress(bdi))
516 return; /* pdflush is already working this queue */
517
518 /*
519 * In laptop mode, we wait until hitting the higher threshold before
520 * starting background writeout, and then write out all the way down
521 * to the lower threshold. So slow writers cause minimal disk activity.
522 *
523 * In normal mode, we start background writeout at the lower
524 * background_thresh, to keep the amount of dirty memory low.
525 */
526 if ((laptop_mode && pages_written) ||
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700527 (!laptop_mode && (global_page_state(NR_FILE_DIRTY)
528 + global_page_state(NR_UNSTABLE_NFS)
529 > background_thresh)))
Linus Torvalds1da177e2005-04-16 15:20:36 -0700530 pdflush_operation(background_writeout, 0);
531}
532
Peter Zijlstraa200ee12007-10-08 18:54:37 +0200533void set_page_dirty_balance(struct page *page, int page_mkwrite)
Peter Zijlstraedc79b22006-09-25 23:30:58 -0700534{
Peter Zijlstraa200ee12007-10-08 18:54:37 +0200535 if (set_page_dirty(page) || page_mkwrite) {
Peter Zijlstraedc79b22006-09-25 23:30:58 -0700536 struct address_space *mapping = page_mapping(page);
537
538 if (mapping)
539 balance_dirty_pages_ratelimited(mapping);
540 }
541}
542
Linus Torvalds1da177e2005-04-16 15:20:36 -0700543/**
Andrew Mortonfa5a7342006-03-24 03:18:10 -0800544 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
Martin Waitz67be2dd2005-05-01 08:59:26 -0700545 * @mapping: address_space which was dirtied
Martin Waitza5802902006-04-02 13:59:55 +0200546 * @nr_pages_dirtied: number of pages which the caller has just dirtied
Linus Torvalds1da177e2005-04-16 15:20:36 -0700547 *
548 * Processes which are dirtying memory should call in here once for each page
549 * which was newly dirtied. The function will periodically check the system's
550 * dirty state and will initiate writeback if needed.
551 *
552 * On really big machines, get_writeback_state is expensive, so try to avoid
553 * calling it too often (ratelimiting). But once we're over the dirty memory
554 * limit we decrease the ratelimiting by a lot, to prevent individual processes
555 * from overshooting the limit by (ratelimit_pages) each.
556 */
Andrew Mortonfa5a7342006-03-24 03:18:10 -0800557void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
558 unsigned long nr_pages_dirtied)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700559{
Andrew Mortonfa5a7342006-03-24 03:18:10 -0800560 static DEFINE_PER_CPU(unsigned long, ratelimits) = 0;
561 unsigned long ratelimit;
562 unsigned long *p;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700563
564 ratelimit = ratelimit_pages;
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700565 if (mapping->backing_dev_info->dirty_exceeded)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700566 ratelimit = 8;
567
568 /*
569 * Check the rate limiting. Also, we do not want to throttle real-time
570 * tasks in balance_dirty_pages(). Period.
571 */
Andrew Mortonfa5a7342006-03-24 03:18:10 -0800572 preempt_disable();
573 p = &__get_cpu_var(ratelimits);
574 *p += nr_pages_dirtied;
575 if (unlikely(*p >= ratelimit)) {
576 *p = 0;
577 preempt_enable();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700578 balance_dirty_pages(mapping);
579 return;
580 }
Andrew Mortonfa5a7342006-03-24 03:18:10 -0800581 preempt_enable();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700582}
Andrew Mortonfa5a7342006-03-24 03:18:10 -0800583EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700584
Andrew Morton232ea4d2007-02-28 20:13:21 -0800585void throttle_vm_writeout(gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700586{
Linus Torvalds1da177e2005-04-16 15:20:36 -0700587 long background_thresh;
588 long dirty_thresh;
589
590 for ( ; ; ) {
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700591 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700592
593 /*
594 * Boost the allowable dirty threshold a bit for page
595 * allocators so they don't get DoS'ed by heavy writers
596 */
597 dirty_thresh += dirty_thresh / 10; /* wheeee... */
598
Christoph Lameterc24f21b2006-06-30 01:55:42 -0700599 if (global_page_state(NR_UNSTABLE_NFS) +
600 global_page_state(NR_WRITEBACK) <= dirty_thresh)
601 break;
Andrew Morton3fcfab12006-10-19 23:28:16 -0700602 congestion_wait(WRITE, HZ/10);
Fengguang Wu369f2382007-10-16 23:30:45 -0700603
604 /*
605 * The caller might hold locks which can prevent IO completion
606 * or progress in the filesystem. So we cannot just sit here
607 * waiting for IO to complete.
608 */
609 if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
610 break;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700611 }
612}
613
Linus Torvalds1da177e2005-04-16 15:20:36 -0700614/*
615 * writeback at least _min_pages, and keep writing until the amount of dirty
616 * memory is less than the background threshold, or until we're all clean.
617 */
618static void background_writeout(unsigned long _min_pages)
619{
620 long min_pages = _min_pages;
621 struct writeback_control wbc = {
622 .bdi = NULL,
623 .sync_mode = WB_SYNC_NONE,
624 .older_than_this = NULL,
625 .nr_to_write = 0,
626 .nonblocking = 1,
OGAWA Hirofumi111ebb62006-06-23 02:03:26 -0700627 .range_cyclic = 1,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700628 };
629
630 for ( ; ; ) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700631 long background_thresh;
632 long dirty_thresh;
633
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700634 get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
Christoph Lameterc24f21b2006-06-30 01:55:42 -0700635 if (global_page_state(NR_FILE_DIRTY) +
636 global_page_state(NR_UNSTABLE_NFS) < background_thresh
Linus Torvalds1da177e2005-04-16 15:20:36 -0700637 && min_pages <= 0)
638 break;
Fengguang Wu8bc3be22008-02-04 22:29:36 -0800639 wbc.more_io = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700640 wbc.encountered_congestion = 0;
641 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
642 wbc.pages_skipped = 0;
643 writeback_inodes(&wbc);
644 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
645 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
646 /* Wrote less than expected */
Fengguang Wu8bc3be22008-02-04 22:29:36 -0800647 if (wbc.encountered_congestion || wbc.more_io)
648 congestion_wait(WRITE, HZ/10);
649 else
Linus Torvalds1da177e2005-04-16 15:20:36 -0700650 break;
651 }
652 }
653}
654
655/*
656 * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
657 * the whole world. Returns 0 if a pdflush thread was dispatched. Returns
658 * -1 if all pdflush threads were busy.
659 */
Pekka J Enberg687a21c2005-06-28 20:44:55 -0700660int wakeup_pdflush(long nr_pages)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700661{
Christoph Lameterc24f21b2006-06-30 01:55:42 -0700662 if (nr_pages == 0)
663 nr_pages = global_page_state(NR_FILE_DIRTY) +
664 global_page_state(NR_UNSTABLE_NFS);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700665 return pdflush_operation(background_writeout, nr_pages);
666}
667
668static void wb_timer_fn(unsigned long unused);
669static void laptop_timer_fn(unsigned long unused);
670
Ingo Molnar8d06afa2005-09-09 13:10:40 -0700671static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
672static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700673
674/*
675 * Periodic writeback of "old" data.
676 *
677 * Define "old": the first time one of an inode's pages is dirtied, we mark the
678 * dirtying-time in the inode's address_space. So this periodic writeback code
679 * just walks the superblock inode list, writing back any inodes which are
680 * older than a specific point in time.
681 *
Bart Samwelf6ef9432006-03-24 03:15:48 -0800682 * Try to run once per dirty_writeback_interval. But if a writeback event
683 * takes longer than a dirty_writeback_interval interval, then leave a
Linus Torvalds1da177e2005-04-16 15:20:36 -0700684 * one-second gap.
685 *
686 * older_than_this takes precedence over nr_to_write. So we'll only write back
687 * all dirty pages if they are all attached to "old" mappings.
688 */
689static void wb_kupdate(unsigned long arg)
690{
691 unsigned long oldest_jif;
692 unsigned long start_jif;
693 unsigned long next_jif;
694 long nr_to_write;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700695 struct writeback_control wbc = {
696 .bdi = NULL,
697 .sync_mode = WB_SYNC_NONE,
698 .older_than_this = &oldest_jif,
699 .nr_to_write = 0,
700 .nonblocking = 1,
701 .for_kupdate = 1,
OGAWA Hirofumi111ebb62006-06-23 02:03:26 -0700702 .range_cyclic = 1,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700703 };
704
705 sync_supers();
706
Bart Samwelf6ef9432006-03-24 03:15:48 -0800707 oldest_jif = jiffies - dirty_expire_interval;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700708 start_jif = jiffies;
Bart Samwelf6ef9432006-03-24 03:15:48 -0800709 next_jif = start_jif + dirty_writeback_interval;
Christoph Lameterc24f21b2006-06-30 01:55:42 -0700710 nr_to_write = global_page_state(NR_FILE_DIRTY) +
711 global_page_state(NR_UNSTABLE_NFS) +
Linus Torvalds1da177e2005-04-16 15:20:36 -0700712 (inodes_stat.nr_inodes - inodes_stat.nr_unused);
713 while (nr_to_write > 0) {
Fengguang Wu8bc3be22008-02-04 22:29:36 -0800714 wbc.more_io = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700715 wbc.encountered_congestion = 0;
716 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
717 writeback_inodes(&wbc);
718 if (wbc.nr_to_write > 0) {
Fengguang Wu8bc3be22008-02-04 22:29:36 -0800719 if (wbc.encountered_congestion || wbc.more_io)
Andrew Morton3fcfab12006-10-19 23:28:16 -0700720 congestion_wait(WRITE, HZ/10);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700721 else
722 break; /* All the old data is written */
723 }
724 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
725 }
726 if (time_before(next_jif, jiffies + HZ))
727 next_jif = jiffies + HZ;
Bart Samwelf6ef9432006-03-24 03:15:48 -0800728 if (dirty_writeback_interval)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700729 mod_timer(&wb_timer, next_jif);
730}
731
732/*
733 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
734 */
735int dirty_writeback_centisecs_handler(ctl_table *table, int write,
Andrew Morton3e733f02007-07-15 23:41:05 -0700736 struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700737{
Bart Samwelf6ef9432006-03-24 03:15:48 -0800738 proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
Andrew Morton3e733f02007-07-15 23:41:05 -0700739 if (dirty_writeback_interval)
740 mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
741 else
Linus Torvalds1da177e2005-04-16 15:20:36 -0700742 del_timer(&wb_timer);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700743 return 0;
744}
745
746static void wb_timer_fn(unsigned long unused)
747{
748 if (pdflush_operation(wb_kupdate, 0) < 0)
749 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
750}
751
752static void laptop_flush(unsigned long unused)
753{
754 sys_sync();
755}
756
757static void laptop_timer_fn(unsigned long unused)
758{
759 pdflush_operation(laptop_flush, 0);
760}
761
762/*
763 * We've spun up the disk and we're in laptop mode: schedule writeback
764 * of all dirty data a few seconds from now. If the flush is already scheduled
765 * then push it back - the user is still using the disk.
766 */
767void laptop_io_completion(void)
768{
Bart Samweled5b43f2006-03-24 03:15:49 -0800769 mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700770}
771
772/*
773 * We're in laptop mode and we've just synced. The sync's writes will have
774 * caused another writeback to be scheduled by laptop_io_completion.
775 * Nothing needs to be written back anymore, so we unschedule the writeback.
776 */
777void laptop_sync_completion(void)
778{
779 del_timer(&laptop_mode_wb_timer);
780}
781
782/*
783 * If ratelimit_pages is too high then we can get into dirty-data overload
784 * if a large number of processes all perform writes at the same time.
785 * If it is too low then SMP machines will call the (expensive)
786 * get_writeback_state too often.
787 *
788 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
789 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
790 * thresholds before writeback cuts in.
791 *
792 * But the limit should not be set too high. Because it also controls the
793 * amount of memory which the balance_dirty_pages() caller has to write back.
794 * If this is too large then the caller will block on the IO queue all the
795 * time. So limit it to four megabytes - the balance_dirty_pages() caller
796 * will write six megabyte chunks, max.
797 */
798
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -0700799void writeback_set_ratelimit(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700800{
Chandra Seetharaman40c99aa2006-09-29 02:01:24 -0700801 ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700802 if (ratelimit_pages < 16)
803 ratelimit_pages = 16;
804 if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
805 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
806}
807
Chandra Seetharaman26c21432006-06-27 02:54:10 -0700808static int __cpuinit
Linus Torvalds1da177e2005-04-16 15:20:36 -0700809ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
810{
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -0700811 writeback_set_ratelimit();
Paul E. McKenneyaa0f0302007-02-10 01:46:37 -0800812 return NOTIFY_DONE;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700813}
814
Chandra Seetharaman74b85f32006-06-27 02:54:09 -0700815static struct notifier_block __cpuinitdata ratelimit_nb = {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700816 .notifier_call = ratelimit_handler,
817 .next = NULL,
818};
819
820/*
Linus Torvaldsdc6e29d2007-01-29 16:37:38 -0800821 * Called early on to tune the page writeback dirty limits.
822 *
823 * We used to scale dirty pages according to how total memory
824 * related to pages that could be allocated for buffers (by
825 * comparing nr_free_buffer_pages() to vm_total_pages.
826 *
827 * However, that was when we used "dirty_ratio" to scale with
828 * all memory, and we don't do that any more. "dirty_ratio"
829 * is now applied to total non-HIGHPAGE memory (by subtracting
830 * totalhigh_pages from vm_total_pages), and as such we can't
831 * get into the old insane situation any more where we had
832 * large amounts of dirty pages compared to a small amount of
833 * non-HIGHMEM memory.
834 *
835 * But we might still want to scale the dirty_ratio by how
836 * much memory the box has..
Linus Torvalds1da177e2005-04-16 15:20:36 -0700837 */
838void __init page_writeback_init(void)
839{
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700840 int shift;
841
Bart Samwelf6ef9432006-03-24 03:15:48 -0800842 mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
Chandra Seetharaman2d1d43f2006-09-29 02:01:25 -0700843 writeback_set_ratelimit();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700844 register_cpu_notifier(&ratelimit_nb);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -0700845
846 shift = calc_period_shift();
847 prop_descriptor_init(&vm_completions, shift);
Peter Zijlstra3e26c142007-10-16 23:25:50 -0700848 prop_descriptor_init(&vm_dirties, shift);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700849}
850
David Howells811d7362006-08-29 19:06:09 +0100851/**
Miklos Szeredi0ea97182007-05-10 22:22:51 -0700852 * 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 +0100853 * @mapping: address space structure to write
854 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
Miklos Szeredi0ea97182007-05-10 22:22:51 -0700855 * @writepage: function called for each page
856 * @data: data passed to writepage function
David Howells811d7362006-08-29 19:06:09 +0100857 *
Miklos Szeredi0ea97182007-05-10 22:22:51 -0700858 * If a page is already under I/O, write_cache_pages() skips it, even
David Howells811d7362006-08-29 19:06:09 +0100859 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
860 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
861 * and msync() need to guarantee that all the data which was dirty at the time
862 * the call was made get new I/O started against them. If wbc->sync_mode is
863 * WB_SYNC_ALL then we were called for data integrity and we must wait for
864 * existing IO to complete.
David Howells811d7362006-08-29 19:06:09 +0100865 */
Miklos Szeredi0ea97182007-05-10 22:22:51 -0700866int write_cache_pages(struct address_space *mapping,
867 struct writeback_control *wbc, writepage_t writepage,
868 void *data)
David Howells811d7362006-08-29 19:06:09 +0100869{
870 struct backing_dev_info *bdi = mapping->backing_dev_info;
871 int ret = 0;
872 int done = 0;
David Howells811d7362006-08-29 19:06:09 +0100873 struct pagevec pvec;
874 int nr_pages;
875 pgoff_t index;
876 pgoff_t end; /* Inclusive */
877 int scanned = 0;
878 int range_whole = 0;
879
880 if (wbc->nonblocking && bdi_write_congested(bdi)) {
881 wbc->encountered_congestion = 1;
882 return 0;
883 }
884
David Howells811d7362006-08-29 19:06:09 +0100885 pagevec_init(&pvec, 0);
886 if (wbc->range_cyclic) {
887 index = mapping->writeback_index; /* Start from prev offset */
888 end = -1;
889 } else {
890 index = wbc->range_start >> PAGE_CACHE_SHIFT;
891 end = wbc->range_end >> PAGE_CACHE_SHIFT;
892 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
893 range_whole = 1;
894 scanned = 1;
895 }
896retry:
897 while (!done && (index <= end) &&
898 (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
899 PAGECACHE_TAG_DIRTY,
900 min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
901 unsigned i;
902
903 scanned = 1;
904 for (i = 0; i < nr_pages; i++) {
905 struct page *page = pvec.pages[i];
906
907 /*
908 * At this point we hold neither mapping->tree_lock nor
909 * lock on the page itself: the page may be truncated or
910 * invalidated (changing page->mapping to NULL), or even
911 * swizzled back from swapper_space to tmpfs file
912 * mapping
913 */
914 lock_page(page);
915
916 if (unlikely(page->mapping != mapping)) {
917 unlock_page(page);
918 continue;
919 }
920
921 if (!wbc->range_cyclic && page->index > end) {
922 done = 1;
923 unlock_page(page);
924 continue;
925 }
926
927 if (wbc->sync_mode != WB_SYNC_NONE)
928 wait_on_page_writeback(page);
929
930 if (PageWriteback(page) ||
931 !clear_page_dirty_for_io(page)) {
932 unlock_page(page);
933 continue;
934 }
935
Miklos Szeredi0ea97182007-05-10 22:22:51 -0700936 ret = (*writepage)(page, wbc, data);
David Howells811d7362006-08-29 19:06:09 +0100937
Andrew Mortone4230032007-10-16 23:26:02 -0700938 if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
David Howells811d7362006-08-29 19:06:09 +0100939 unlock_page(page);
Andrew Mortone4230032007-10-16 23:26:02 -0700940 ret = 0;
941 }
David Howells811d7362006-08-29 19:06:09 +0100942 if (ret || (--(wbc->nr_to_write) <= 0))
943 done = 1;
944 if (wbc->nonblocking && bdi_write_congested(bdi)) {
945 wbc->encountered_congestion = 1;
946 done = 1;
947 }
948 }
949 pagevec_release(&pvec);
950 cond_resched();
951 }
952 if (!scanned && !done) {
953 /*
954 * We hit the last page and there is more work to be done: wrap
955 * back to the start of the file
956 */
957 scanned = 1;
958 index = 0;
959 goto retry;
960 }
961 if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
962 mapping->writeback_index = index;
Aneesh Kumar K.V06d6cf62008-07-11 19:27:31 -0400963
964 if (wbc->range_cont)
965 wbc->range_start = index << PAGE_CACHE_SHIFT;
David Howells811d7362006-08-29 19:06:09 +0100966 return ret;
967}
Miklos Szeredi0ea97182007-05-10 22:22:51 -0700968EXPORT_SYMBOL(write_cache_pages);
969
970/*
971 * Function used by generic_writepages to call the real writepage
972 * function and set the mapping flags on error
973 */
974static int __writepage(struct page *page, struct writeback_control *wbc,
975 void *data)
976{
977 struct address_space *mapping = data;
978 int ret = mapping->a_ops->writepage(page, wbc);
979 mapping_set_error(mapping, ret);
980 return ret;
981}
982
983/**
984 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
985 * @mapping: address space structure to write
986 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
987 *
988 * This is a library function, which implements the writepages()
989 * address_space_operation.
990 */
991int generic_writepages(struct address_space *mapping,
992 struct writeback_control *wbc)
993{
994 /* deal with chardevs and other special file */
995 if (!mapping->a_ops->writepage)
996 return 0;
997
998 return write_cache_pages(mapping, wbc, __writepage, mapping);
999}
David Howells811d7362006-08-29 19:06:09 +01001000
1001EXPORT_SYMBOL(generic_writepages);
1002
Linus Torvalds1da177e2005-04-16 15:20:36 -07001003int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
1004{
Andrew Morton22905f72005-11-16 15:07:01 -08001005 int ret;
1006
Linus Torvalds1da177e2005-04-16 15:20:36 -07001007 if (wbc->nr_to_write <= 0)
1008 return 0;
Andrew Morton22905f72005-11-16 15:07:01 -08001009 wbc->for_writepages = 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001010 if (mapping->a_ops->writepages)
Peter Zijlstrad08b3852006-09-25 23:30:57 -07001011 ret = mapping->a_ops->writepages(mapping, wbc);
Andrew Morton22905f72005-11-16 15:07:01 -08001012 else
1013 ret = generic_writepages(mapping, wbc);
1014 wbc->for_writepages = 0;
1015 return ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001016}
1017
1018/**
1019 * write_one_page - write out a single page and optionally wait on I/O
Martin Waitz67be2dd2005-05-01 08:59:26 -07001020 * @page: the page to write
1021 * @wait: if true, wait on writeout
Linus Torvalds1da177e2005-04-16 15:20:36 -07001022 *
1023 * The page must be locked by the caller and will be unlocked upon return.
1024 *
1025 * write_one_page() returns a negative error code if I/O failed.
1026 */
1027int write_one_page(struct page *page, int wait)
1028{
1029 struct address_space *mapping = page->mapping;
1030 int ret = 0;
1031 struct writeback_control wbc = {
1032 .sync_mode = WB_SYNC_ALL,
1033 .nr_to_write = 1,
1034 };
1035
1036 BUG_ON(!PageLocked(page));
1037
1038 if (wait)
1039 wait_on_page_writeback(page);
1040
1041 if (clear_page_dirty_for_io(page)) {
1042 page_cache_get(page);
1043 ret = mapping->a_ops->writepage(page, &wbc);
1044 if (ret == 0 && wait) {
1045 wait_on_page_writeback(page);
1046 if (PageError(page))
1047 ret = -EIO;
1048 }
1049 page_cache_release(page);
1050 } else {
1051 unlock_page(page);
1052 }
1053 return ret;
1054}
1055EXPORT_SYMBOL(write_one_page);
1056
1057/*
Ken Chen76719322007-02-10 01:43:15 -08001058 * For address_spaces which do not use buffers nor write back.
1059 */
1060int __set_page_dirty_no_writeback(struct page *page)
1061{
1062 if (!PageDirty(page))
1063 SetPageDirty(page);
1064 return 0;
1065}
1066
1067/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001068 * For address_spaces which do not use buffers. Just tag the page as dirty in
1069 * its radix tree.
1070 *
1071 * This is also used when a single buffer is being dirtied: we want to set the
1072 * page dirty in that case, but not all the buffers. This is a "bottom-up"
1073 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
1074 *
1075 * Most callers have locked the page, which pins the address_space in memory.
1076 * But zap_pte_range() does not lock the page, however in that case the
1077 * mapping is pinned by the vma's ->vm_file reference.
1078 *
1079 * We take care to handle the case where the page was truncated from the
Simon Arlott183ff222007-10-20 01:27:18 +02001080 * mapping by re-checking page_mapping() inside tree_lock.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001081 */
1082int __set_page_dirty_nobuffers(struct page *page)
1083{
Linus Torvalds1da177e2005-04-16 15:20:36 -07001084 if (!TestSetPageDirty(page)) {
1085 struct address_space *mapping = page_mapping(page);
1086 struct address_space *mapping2;
1087
Andrew Morton8c085402006-12-10 02:19:24 -08001088 if (!mapping)
1089 return 1;
1090
1091 write_lock_irq(&mapping->tree_lock);
1092 mapping2 = page_mapping(page);
1093 if (mapping2) { /* Race with truncate? */
1094 BUG_ON(mapping2 != mapping);
Nick Piggin787d2212007-07-17 04:03:34 -07001095 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
Andrew Morton55e829a2006-12-10 02:19:27 -08001096 if (mapping_cap_account_dirty(mapping)) {
Andrew Morton8c085402006-12-10 02:19:24 -08001097 __inc_zone_page_state(page, NR_FILE_DIRTY);
Peter Zijlstrac9e51e42007-10-16 23:25:47 -07001098 __inc_bdi_stat(mapping->backing_dev_info,
1099 BDI_RECLAIMABLE);
Andrew Morton55e829a2006-12-10 02:19:27 -08001100 task_io_account_write(PAGE_CACHE_SIZE);
1101 }
Andrew Morton8c085402006-12-10 02:19:24 -08001102 radix_tree_tag_set(&mapping->page_tree,
1103 page_index(page), PAGECACHE_TAG_DIRTY);
1104 }
1105 write_unlock_irq(&mapping->tree_lock);
1106 if (mapping->host) {
1107 /* !PageAnon && !swapper_space */
1108 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001109 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08001110 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001111 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08001112 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001113}
1114EXPORT_SYMBOL(__set_page_dirty_nobuffers);
1115
1116/*
1117 * When a writepage implementation decides that it doesn't want to write this
1118 * page for some reason, it should redirty the locked page via
1119 * redirty_page_for_writepage() and it should then unlock the page and return 0
1120 */
1121int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
1122{
1123 wbc->pages_skipped++;
1124 return __set_page_dirty_nobuffers(page);
1125}
1126EXPORT_SYMBOL(redirty_page_for_writepage);
1127
1128/*
1129 * If the mapping doesn't provide a set_page_dirty a_op, then
1130 * just fall through and assume that it wants buffer_heads.
1131 */
Peter Zijlstra3e26c142007-10-16 23:25:50 -07001132static int __set_page_dirty(struct page *page)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001133{
1134 struct address_space *mapping = page_mapping(page);
1135
1136 if (likely(mapping)) {
1137 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
David Howells93614012006-09-30 20:45:40 +02001138#ifdef CONFIG_BLOCK
1139 if (!spd)
1140 spd = __set_page_dirty_buffers;
1141#endif
1142 return (*spd)(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001143 }
Andrew Morton4741c9f2006-03-24 03:18:11 -08001144 if (!PageDirty(page)) {
1145 if (!TestSetPageDirty(page))
1146 return 1;
1147 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07001148 return 0;
1149}
Peter Zijlstra3e26c142007-10-16 23:25:50 -07001150
Harvey Harrison920c7a52008-02-04 22:29:26 -08001151int set_page_dirty(struct page *page)
Peter Zijlstra3e26c142007-10-16 23:25:50 -07001152{
1153 int ret = __set_page_dirty(page);
1154 if (ret)
1155 task_dirty_inc(current);
1156 return ret;
1157}
Linus Torvalds1da177e2005-04-16 15:20:36 -07001158EXPORT_SYMBOL(set_page_dirty);
1159
1160/*
1161 * set_page_dirty() is racy if the caller has no reference against
1162 * page->mapping->host, and if the page is unlocked. This is because another
1163 * CPU could truncate the page off the mapping and then free the mapping.
1164 *
1165 * Usually, the page _is_ locked, or the caller is a user-space process which
1166 * holds a reference on the inode by having an open file.
1167 *
1168 * In other cases, the page should be locked before running set_page_dirty().
1169 */
1170int set_page_dirty_lock(struct page *page)
1171{
1172 int ret;
1173
Nick Piggindb376482006-09-25 23:31:24 -07001174 lock_page_nosync(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001175 ret = set_page_dirty(page);
1176 unlock_page(page);
1177 return ret;
1178}
1179EXPORT_SYMBOL(set_page_dirty_lock);
1180
1181/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07001182 * Clear a page's dirty flag, while caring for dirty memory accounting.
1183 * Returns true if the page was previously dirty.
1184 *
1185 * This is for preparing to put the page under writeout. We leave the page
1186 * tagged as dirty in the radix tree so that a concurrent write-for-sync
1187 * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
1188 * implementation will run either set_page_writeback() or set_page_dirty(),
1189 * at which stage we bring the page's dirty flag and radix-tree dirty tag
1190 * back into sync.
1191 *
1192 * This incoherency between the page's dirty flag and radix-tree tag is
1193 * unfortunate, but it only exists while the page is locked.
1194 */
1195int clear_page_dirty_for_io(struct page *page)
1196{
1197 struct address_space *mapping = page_mapping(page);
1198
Nick Piggin79352892007-07-19 01:47:22 -07001199 BUG_ON(!PageLocked(page));
1200
Fengguang Wufe3cba12007-07-19 01:48:07 -07001201 ClearPageReclaim(page);
Linus Torvalds7658cc22006-12-29 10:00:58 -08001202 if (mapping && mapping_cap_account_dirty(mapping)) {
1203 /*
1204 * Yes, Virginia, this is indeed insane.
1205 *
1206 * We use this sequence to make sure that
1207 * (a) we account for dirty stats properly
1208 * (b) we tell the low-level filesystem to
1209 * mark the whole page dirty if it was
1210 * dirty in a pagetable. Only to then
1211 * (c) clean the page again and return 1 to
1212 * cause the writeback.
1213 *
1214 * This way we avoid all nasty races with the
1215 * dirty bit in multiple places and clearing
1216 * them concurrently from different threads.
1217 *
1218 * Note! Normally the "set_page_dirty(page)"
1219 * has no effect on the actual dirty bit - since
1220 * that will already usually be set. But we
1221 * need the side effects, and it can help us
1222 * avoid races.
1223 *
1224 * We basically use the page "master dirty bit"
1225 * as a serialization point for all the different
1226 * threads doing their things.
Linus Torvalds7658cc22006-12-29 10:00:58 -08001227 */
1228 if (page_mkclean(page))
1229 set_page_dirty(page);
Nick Piggin79352892007-07-19 01:47:22 -07001230 /*
1231 * We carefully synchronise fault handlers against
1232 * installing a dirty pte and marking the page dirty
1233 * at this point. We do this by having them hold the
1234 * page lock at some point after installing their
1235 * pte, but before marking the page dirty.
1236 * Pages are always locked coming in here, so we get
1237 * the desired exclusion. See mm/memory.c:do_wp_page()
1238 * for more comments.
1239 */
Linus Torvalds7658cc22006-12-29 10:00:58 -08001240 if (TestClearPageDirty(page)) {
Andrew Morton8c085402006-12-10 02:19:24 -08001241 dec_zone_page_state(page, NR_FILE_DIRTY);
Peter Zijlstrac9e51e42007-10-16 23:25:47 -07001242 dec_bdi_stat(mapping->backing_dev_info,
1243 BDI_RECLAIMABLE);
Linus Torvalds7658cc22006-12-29 10:00:58 -08001244 return 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001245 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08001246 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001247 }
Linus Torvalds7658cc22006-12-29 10:00:58 -08001248 return TestClearPageDirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001249}
Hans Reiser58bb01a2005-11-18 01:10:53 -08001250EXPORT_SYMBOL(clear_page_dirty_for_io);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001251
1252int test_clear_page_writeback(struct page *page)
1253{
1254 struct address_space *mapping = page_mapping(page);
1255 int ret;
1256
1257 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001258 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001259 unsigned long flags;
1260
1261 write_lock_irqsave(&mapping->tree_lock, flags);
1262 ret = TestClearPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001263 if (ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07001264 radix_tree_tag_clear(&mapping->page_tree,
1265 page_index(page),
1266 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07001267 if (bdi_cap_account_writeback(bdi)) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001268 __dec_bdi_stat(bdi, BDI_WRITEBACK);
Peter Zijlstra04fbfdc2007-10-16 23:25:50 -07001269 __bdi_writeout_inc(bdi);
1270 }
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001271 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07001272 write_unlock_irqrestore(&mapping->tree_lock, flags);
1273 } else {
1274 ret = TestClearPageWriteback(page);
1275 }
Andrew Mortond688abf2007-07-19 01:49:17 -07001276 if (ret)
1277 dec_zone_page_state(page, NR_WRITEBACK);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001278 return ret;
1279}
1280
1281int test_set_page_writeback(struct page *page)
1282{
1283 struct address_space *mapping = page_mapping(page);
1284 int ret;
1285
1286 if (mapping) {
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001287 struct backing_dev_info *bdi = mapping->backing_dev_info;
Linus Torvalds1da177e2005-04-16 15:20:36 -07001288 unsigned long flags;
1289
1290 write_lock_irqsave(&mapping->tree_lock, flags);
1291 ret = TestSetPageWriteback(page);
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001292 if (!ret) {
Linus Torvalds1da177e2005-04-16 15:20:36 -07001293 radix_tree_tag_set(&mapping->page_tree,
1294 page_index(page),
1295 PAGECACHE_TAG_WRITEBACK);
Miklos Szeredie4ad08f2008-04-30 00:54:37 -07001296 if (bdi_cap_account_writeback(bdi))
Peter Zijlstra69cb51d2007-10-16 23:25:48 -07001297 __inc_bdi_stat(bdi, BDI_WRITEBACK);
1298 }
Linus Torvalds1da177e2005-04-16 15:20:36 -07001299 if (!PageDirty(page))
1300 radix_tree_tag_clear(&mapping->page_tree,
1301 page_index(page),
1302 PAGECACHE_TAG_DIRTY);
1303 write_unlock_irqrestore(&mapping->tree_lock, flags);
1304 } else {
1305 ret = TestSetPageWriteback(page);
1306 }
Andrew Mortond688abf2007-07-19 01:49:17 -07001307 if (!ret)
1308 inc_zone_page_state(page, NR_WRITEBACK);
Linus Torvalds1da177e2005-04-16 15:20:36 -07001309 return ret;
1310
1311}
1312EXPORT_SYMBOL(test_set_page_writeback);
1313
1314/*
Nick Piggin00128182007-10-16 01:24:40 -07001315 * Return true if any of the pages in the mapping are marked with the
Linus Torvalds1da177e2005-04-16 15:20:36 -07001316 * passed tag.
1317 */
1318int mapping_tagged(struct address_space *mapping, int tag)
1319{
Linus Torvalds1da177e2005-04-16 15:20:36 -07001320 int ret;
Nick Piggin00128182007-10-16 01:24:40 -07001321 rcu_read_lock();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001322 ret = radix_tree_tagged(&mapping->page_tree, tag);
Nick Piggin00128182007-10-16 01:24:40 -07001323 rcu_read_unlock();
Linus Torvalds1da177e2005-04-16 15:20:36 -07001324 return ret;
1325}
1326EXPORT_SYMBOL(mapping_tagged);