xref: /openbmc/linux/mm/page-writeback.c (revision f6ef943813ac3085ece7252ea101d663581219f6)
1 /*
2  * mm/page-writeback.c.
3  *
4  * Copyright (C) 2002, Linus Torvalds.
5  *
6  * Contains functions related to writing back dirty pages at the
7  * address_space level.
8  *
9  * 10Apr2002	akpm@zip.com.au
10  *		Initial version
11  */
12 
13 #include <linux/kernel.h>
14 #include <linux/module.h>
15 #include <linux/spinlock.h>
16 #include <linux/fs.h>
17 #include <linux/mm.h>
18 #include <linux/swap.h>
19 #include <linux/slab.h>
20 #include <linux/pagemap.h>
21 #include <linux/writeback.h>
22 #include <linux/init.h>
23 #include <linux/backing-dev.h>
24 #include <linux/blkdev.h>
25 #include <linux/mpage.h>
26 #include <linux/percpu.h>
27 #include <linux/notifier.h>
28 #include <linux/smp.h>
29 #include <linux/sysctl.h>
30 #include <linux/cpu.h>
31 #include <linux/syscalls.h>
32 
33 /*
34  * The maximum number of pages to writeout in a single bdflush/kupdate
35  * operation.  We do this so we don't hold I_LOCK against an inode for
36  * enormous amounts of time, which would block a userspace task which has
37  * been forced to throttle against that inode.  Also, the code reevaluates
38  * the dirty each time it has written this many pages.
39  */
40 #define MAX_WRITEBACK_PAGES	1024
41 
42 /*
43  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
44  * will look to see if it needs to force writeback or throttling.
45  */
46 static long ratelimit_pages = 32;
47 
48 static long total_pages;	/* The total number of pages in the machine. */
49 static int dirty_exceeded __cacheline_aligned_in_smp;	/* Dirty mem may be over limit */
50 
51 /*
52  * When balance_dirty_pages decides that the caller needs to perform some
53  * non-background writeback, this is how many pages it will attempt to write.
54  * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
55  * large amounts of I/O are submitted.
56  */
57 static inline long sync_writeback_pages(void)
58 {
59 	return ratelimit_pages + ratelimit_pages / 2;
60 }
61 
62 /* The following parameters are exported via /proc/sys/vm */
63 
64 /*
65  * Start background writeback (via pdflush) at this percentage
66  */
67 int dirty_background_ratio = 10;
68 
69 /*
70  * The generator of dirty data starts writeback at this percentage
71  */
72 int vm_dirty_ratio = 40;
73 
74 /*
75  * The interval between `kupdate'-style writebacks, in centiseconds
76  * (hundredths of a second)
77  */
78 int dirty_writeback_interval = 5 * HZ;
79 
80 /*
81  * The longest number of centiseconds for which data is allowed to remain dirty
82  */
83 int dirty_expire_interval = 30 * HZ;
84 
85 /*
86  * Flag that makes the machine dump writes/reads and block dirtyings.
87  */
88 int block_dump;
89 
90 /*
91  * Flag that puts the machine in "laptop mode".
92  */
93 int laptop_mode;
94 
95 EXPORT_SYMBOL(laptop_mode);
96 
97 /* End of sysctl-exported parameters */
98 
99 
100 static void background_writeout(unsigned long _min_pages);
101 
102 struct writeback_state
103 {
104 	unsigned long nr_dirty;
105 	unsigned long nr_unstable;
106 	unsigned long nr_mapped;
107 	unsigned long nr_writeback;
108 };
109 
110 static void get_writeback_state(struct writeback_state *wbs)
111 {
112 	wbs->nr_dirty = read_page_state(nr_dirty);
113 	wbs->nr_unstable = read_page_state(nr_unstable);
114 	wbs->nr_mapped = read_page_state(nr_mapped);
115 	wbs->nr_writeback = read_page_state(nr_writeback);
116 }
117 
118 /*
119  * Work out the current dirty-memory clamping and background writeout
120  * thresholds.
121  *
122  * The main aim here is to lower them aggressively if there is a lot of mapped
123  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
124  * pages.  It is better to clamp down on writers than to start swapping, and
125  * performing lots of scanning.
126  *
127  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
128  *
129  * We don't permit the clamping level to fall below 5% - that is getting rather
130  * excessive.
131  *
132  * We make sure that the background writeout level is below the adjusted
133  * clamping level.
134  */
135 static void
136 get_dirty_limits(struct writeback_state *wbs, long *pbackground, long *pdirty,
137 		struct address_space *mapping)
138 {
139 	int background_ratio;		/* Percentages */
140 	int dirty_ratio;
141 	int unmapped_ratio;
142 	long background;
143 	long dirty;
144 	unsigned long available_memory = total_pages;
145 	struct task_struct *tsk;
146 
147 	get_writeback_state(wbs);
148 
149 #ifdef CONFIG_HIGHMEM
150 	/*
151 	 * If this mapping can only allocate from low memory,
152 	 * we exclude high memory from our count.
153 	 */
154 	if (mapping && !(mapping_gfp_mask(mapping) & __GFP_HIGHMEM))
155 		available_memory -= totalhigh_pages;
156 #endif
157 
158 
159 	unmapped_ratio = 100 - (wbs->nr_mapped * 100) / total_pages;
160 
161 	dirty_ratio = vm_dirty_ratio;
162 	if (dirty_ratio > unmapped_ratio / 2)
163 		dirty_ratio = unmapped_ratio / 2;
164 
165 	if (dirty_ratio < 5)
166 		dirty_ratio = 5;
167 
168 	background_ratio = dirty_background_ratio;
169 	if (background_ratio >= dirty_ratio)
170 		background_ratio = dirty_ratio / 2;
171 
172 	background = (background_ratio * available_memory) / 100;
173 	dirty = (dirty_ratio * available_memory) / 100;
174 	tsk = current;
175 	if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
176 		background += background / 4;
177 		dirty += dirty / 4;
178 	}
179 	*pbackground = background;
180 	*pdirty = dirty;
181 }
182 
183 /*
184  * balance_dirty_pages() must be called by processes which are generating dirty
185  * data.  It looks at the number of dirty pages in the machine and will force
186  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
187  * If we're over `background_thresh' then pdflush is woken to perform some
188  * writeout.
189  */
190 static void balance_dirty_pages(struct address_space *mapping)
191 {
192 	struct writeback_state wbs;
193 	long nr_reclaimable;
194 	long background_thresh;
195 	long dirty_thresh;
196 	unsigned long pages_written = 0;
197 	unsigned long write_chunk = sync_writeback_pages();
198 
199 	struct backing_dev_info *bdi = mapping->backing_dev_info;
200 
201 	for (;;) {
202 		struct writeback_control wbc = {
203 			.bdi		= bdi,
204 			.sync_mode	= WB_SYNC_NONE,
205 			.older_than_this = NULL,
206 			.nr_to_write	= write_chunk,
207 		};
208 
209 		get_dirty_limits(&wbs, &background_thresh,
210 					&dirty_thresh, mapping);
211 		nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
212 		if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
213 			break;
214 
215 		if (!dirty_exceeded)
216 			dirty_exceeded = 1;
217 
218 		/* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
219 		 * Unstable writes are a feature of certain networked
220 		 * filesystems (i.e. NFS) in which data may have been
221 		 * written to the server's write cache, but has not yet
222 		 * been flushed to permanent storage.
223 		 */
224 		if (nr_reclaimable) {
225 			writeback_inodes(&wbc);
226 			get_dirty_limits(&wbs, &background_thresh,
227 					&dirty_thresh, mapping);
228 			nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
229 			if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
230 				break;
231 			pages_written += write_chunk - wbc.nr_to_write;
232 			if (pages_written >= write_chunk)
233 				break;		/* We've done our duty */
234 		}
235 		blk_congestion_wait(WRITE, HZ/10);
236 	}
237 
238 	if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh && dirty_exceeded)
239 		dirty_exceeded = 0;
240 
241 	if (writeback_in_progress(bdi))
242 		return;		/* pdflush is already working this queue */
243 
244 	/*
245 	 * In laptop mode, we wait until hitting the higher threshold before
246 	 * starting background writeout, and then write out all the way down
247 	 * to the lower threshold.  So slow writers cause minimal disk activity.
248 	 *
249 	 * In normal mode, we start background writeout at the lower
250 	 * background_thresh, to keep the amount of dirty memory low.
251 	 */
252 	if ((laptop_mode && pages_written) ||
253 	     (!laptop_mode && (nr_reclaimable > background_thresh)))
254 		pdflush_operation(background_writeout, 0);
255 }
256 
257 /**
258  * balance_dirty_pages_ratelimited - balance dirty memory state
259  * @mapping: address_space which was dirtied
260  *
261  * Processes which are dirtying memory should call in here once for each page
262  * which was newly dirtied.  The function will periodically check the system's
263  * dirty state and will initiate writeback if needed.
264  *
265  * On really big machines, get_writeback_state is expensive, so try to avoid
266  * calling it too often (ratelimiting).  But once we're over the dirty memory
267  * limit we decrease the ratelimiting by a lot, to prevent individual processes
268  * from overshooting the limit by (ratelimit_pages) each.
269  */
270 void balance_dirty_pages_ratelimited(struct address_space *mapping)
271 {
272 	static DEFINE_PER_CPU(int, ratelimits) = 0;
273 	long ratelimit;
274 
275 	ratelimit = ratelimit_pages;
276 	if (dirty_exceeded)
277 		ratelimit = 8;
278 
279 	/*
280 	 * Check the rate limiting. Also, we do not want to throttle real-time
281 	 * tasks in balance_dirty_pages(). Period.
282 	 */
283 	if (get_cpu_var(ratelimits)++ >= ratelimit) {
284 		__get_cpu_var(ratelimits) = 0;
285 		put_cpu_var(ratelimits);
286 		balance_dirty_pages(mapping);
287 		return;
288 	}
289 	put_cpu_var(ratelimits);
290 }
291 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
292 
293 void throttle_vm_writeout(void)
294 {
295 	struct writeback_state wbs;
296 	long background_thresh;
297 	long dirty_thresh;
298 
299         for ( ; ; ) {
300 		get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
301 
302                 /*
303                  * Boost the allowable dirty threshold a bit for page
304                  * allocators so they don't get DoS'ed by heavy writers
305                  */
306                 dirty_thresh += dirty_thresh / 10;      /* wheeee... */
307 
308                 if (wbs.nr_unstable + wbs.nr_writeback <= dirty_thresh)
309                         break;
310                 blk_congestion_wait(WRITE, HZ/10);
311         }
312 }
313 
314 
315 /*
316  * writeback at least _min_pages, and keep writing until the amount of dirty
317  * memory is less than the background threshold, or until we're all clean.
318  */
319 static void background_writeout(unsigned long _min_pages)
320 {
321 	long min_pages = _min_pages;
322 	struct writeback_control wbc = {
323 		.bdi		= NULL,
324 		.sync_mode	= WB_SYNC_NONE,
325 		.older_than_this = NULL,
326 		.nr_to_write	= 0,
327 		.nonblocking	= 1,
328 	};
329 
330 	for ( ; ; ) {
331 		struct writeback_state wbs;
332 		long background_thresh;
333 		long dirty_thresh;
334 
335 		get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
336 		if (wbs.nr_dirty + wbs.nr_unstable < background_thresh
337 				&& min_pages <= 0)
338 			break;
339 		wbc.encountered_congestion = 0;
340 		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
341 		wbc.pages_skipped = 0;
342 		writeback_inodes(&wbc);
343 		min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
344 		if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
345 			/* Wrote less than expected */
346 			blk_congestion_wait(WRITE, HZ/10);
347 			if (!wbc.encountered_congestion)
348 				break;
349 		}
350 	}
351 }
352 
353 /*
354  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
355  * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
356  * -1 if all pdflush threads were busy.
357  */
358 int wakeup_pdflush(long nr_pages)
359 {
360 	if (nr_pages == 0) {
361 		struct writeback_state wbs;
362 
363 		get_writeback_state(&wbs);
364 		nr_pages = wbs.nr_dirty + wbs.nr_unstable;
365 	}
366 	return pdflush_operation(background_writeout, nr_pages);
367 }
368 
369 static void wb_timer_fn(unsigned long unused);
370 static void laptop_timer_fn(unsigned long unused);
371 
372 static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
373 static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
374 
375 /*
376  * Periodic writeback of "old" data.
377  *
378  * Define "old": the first time one of an inode's pages is dirtied, we mark the
379  * dirtying-time in the inode's address_space.  So this periodic writeback code
380  * just walks the superblock inode list, writing back any inodes which are
381  * older than a specific point in time.
382  *
383  * Try to run once per dirty_writeback_interval.  But if a writeback event
384  * takes longer than a dirty_writeback_interval interval, then leave a
385  * one-second gap.
386  *
387  * older_than_this takes precedence over nr_to_write.  So we'll only write back
388  * all dirty pages if they are all attached to "old" mappings.
389  */
390 static void wb_kupdate(unsigned long arg)
391 {
392 	unsigned long oldest_jif;
393 	unsigned long start_jif;
394 	unsigned long next_jif;
395 	long nr_to_write;
396 	struct writeback_state wbs;
397 	struct writeback_control wbc = {
398 		.bdi		= NULL,
399 		.sync_mode	= WB_SYNC_NONE,
400 		.older_than_this = &oldest_jif,
401 		.nr_to_write	= 0,
402 		.nonblocking	= 1,
403 		.for_kupdate	= 1,
404 	};
405 
406 	sync_supers();
407 
408 	get_writeback_state(&wbs);
409 	oldest_jif = jiffies - dirty_expire_interval;
410 	start_jif = jiffies;
411 	next_jif = start_jif + dirty_writeback_interval;
412 	nr_to_write = wbs.nr_dirty + wbs.nr_unstable +
413 			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
414 	while (nr_to_write > 0) {
415 		wbc.encountered_congestion = 0;
416 		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
417 		writeback_inodes(&wbc);
418 		if (wbc.nr_to_write > 0) {
419 			if (wbc.encountered_congestion)
420 				blk_congestion_wait(WRITE, HZ/10);
421 			else
422 				break;	/* All the old data is written */
423 		}
424 		nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
425 	}
426 	if (time_before(next_jif, jiffies + HZ))
427 		next_jif = jiffies + HZ;
428 	if (dirty_writeback_interval)
429 		mod_timer(&wb_timer, next_jif);
430 }
431 
432 /*
433  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
434  */
435 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
436 		struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
437 {
438 	proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
439 	if (dirty_writeback_interval) {
440 		mod_timer(&wb_timer,
441 			jiffies + dirty_writeback_interval);
442 		} else {
443 		del_timer(&wb_timer);
444 	}
445 	return 0;
446 }
447 
448 static void wb_timer_fn(unsigned long unused)
449 {
450 	if (pdflush_operation(wb_kupdate, 0) < 0)
451 		mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
452 }
453 
454 static void laptop_flush(unsigned long unused)
455 {
456 	sys_sync();
457 }
458 
459 static void laptop_timer_fn(unsigned long unused)
460 {
461 	pdflush_operation(laptop_flush, 0);
462 }
463 
464 /*
465  * We've spun up the disk and we're in laptop mode: schedule writeback
466  * of all dirty data a few seconds from now.  If the flush is already scheduled
467  * then push it back - the user is still using the disk.
468  */
469 void laptop_io_completion(void)
470 {
471 	mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode * HZ);
472 }
473 
474 /*
475  * We're in laptop mode and we've just synced. The sync's writes will have
476  * caused another writeback to be scheduled by laptop_io_completion.
477  * Nothing needs to be written back anymore, so we unschedule the writeback.
478  */
479 void laptop_sync_completion(void)
480 {
481 	del_timer(&laptop_mode_wb_timer);
482 }
483 
484 /*
485  * If ratelimit_pages is too high then we can get into dirty-data overload
486  * if a large number of processes all perform writes at the same time.
487  * If it is too low then SMP machines will call the (expensive)
488  * get_writeback_state too often.
489  *
490  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
491  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
492  * thresholds before writeback cuts in.
493  *
494  * But the limit should not be set too high.  Because it also controls the
495  * amount of memory which the balance_dirty_pages() caller has to write back.
496  * If this is too large then the caller will block on the IO queue all the
497  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
498  * will write six megabyte chunks, max.
499  */
500 
501 static void set_ratelimit(void)
502 {
503 	ratelimit_pages = total_pages / (num_online_cpus() * 32);
504 	if (ratelimit_pages < 16)
505 		ratelimit_pages = 16;
506 	if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
507 		ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
508 }
509 
510 static int
511 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
512 {
513 	set_ratelimit();
514 	return 0;
515 }
516 
517 static struct notifier_block ratelimit_nb = {
518 	.notifier_call	= ratelimit_handler,
519 	.next		= NULL,
520 };
521 
522 /*
523  * If the machine has a large highmem:lowmem ratio then scale back the default
524  * dirty memory thresholds: allowing too much dirty highmem pins an excessive
525  * number of buffer_heads.
526  */
527 void __init page_writeback_init(void)
528 {
529 	long buffer_pages = nr_free_buffer_pages();
530 	long correction;
531 
532 	total_pages = nr_free_pagecache_pages();
533 
534 	correction = (100 * 4 * buffer_pages) / total_pages;
535 
536 	if (correction < 100) {
537 		dirty_background_ratio *= correction;
538 		dirty_background_ratio /= 100;
539 		vm_dirty_ratio *= correction;
540 		vm_dirty_ratio /= 100;
541 
542 		if (dirty_background_ratio <= 0)
543 			dirty_background_ratio = 1;
544 		if (vm_dirty_ratio <= 0)
545 			vm_dirty_ratio = 1;
546 	}
547 	mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
548 	set_ratelimit();
549 	register_cpu_notifier(&ratelimit_nb);
550 }
551 
552 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
553 {
554 	int ret;
555 
556 	if (wbc->nr_to_write <= 0)
557 		return 0;
558 	wbc->for_writepages = 1;
559 	if (mapping->a_ops->writepages)
560 		ret =  mapping->a_ops->writepages(mapping, wbc);
561 	else
562 		ret = generic_writepages(mapping, wbc);
563 	wbc->for_writepages = 0;
564 	return ret;
565 }
566 
567 /**
568  * write_one_page - write out a single page and optionally wait on I/O
569  *
570  * @page: the page to write
571  * @wait: if true, wait on writeout
572  *
573  * The page must be locked by the caller and will be unlocked upon return.
574  *
575  * write_one_page() returns a negative error code if I/O failed.
576  */
577 int write_one_page(struct page *page, int wait)
578 {
579 	struct address_space *mapping = page->mapping;
580 	int ret = 0;
581 	struct writeback_control wbc = {
582 		.sync_mode = WB_SYNC_ALL,
583 		.nr_to_write = 1,
584 	};
585 
586 	BUG_ON(!PageLocked(page));
587 
588 	if (wait)
589 		wait_on_page_writeback(page);
590 
591 	if (clear_page_dirty_for_io(page)) {
592 		page_cache_get(page);
593 		ret = mapping->a_ops->writepage(page, &wbc);
594 		if (ret == 0 && wait) {
595 			wait_on_page_writeback(page);
596 			if (PageError(page))
597 				ret = -EIO;
598 		}
599 		page_cache_release(page);
600 	} else {
601 		unlock_page(page);
602 	}
603 	return ret;
604 }
605 EXPORT_SYMBOL(write_one_page);
606 
607 /*
608  * For address_spaces which do not use buffers.  Just tag the page as dirty in
609  * its radix tree.
610  *
611  * This is also used when a single buffer is being dirtied: we want to set the
612  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
613  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
614  *
615  * Most callers have locked the page, which pins the address_space in memory.
616  * But zap_pte_range() does not lock the page, however in that case the
617  * mapping is pinned by the vma's ->vm_file reference.
618  *
619  * We take care to handle the case where the page was truncated from the
620  * mapping by re-checking page_mapping() insode tree_lock.
621  */
622 int __set_page_dirty_nobuffers(struct page *page)
623 {
624 	int ret = 0;
625 
626 	if (!TestSetPageDirty(page)) {
627 		struct address_space *mapping = page_mapping(page);
628 		struct address_space *mapping2;
629 
630 		if (mapping) {
631 			write_lock_irq(&mapping->tree_lock);
632 			mapping2 = page_mapping(page);
633 			if (mapping2) { /* Race with truncate? */
634 				BUG_ON(mapping2 != mapping);
635 				if (mapping_cap_account_dirty(mapping))
636 					inc_page_state(nr_dirty);
637 				radix_tree_tag_set(&mapping->page_tree,
638 					page_index(page), PAGECACHE_TAG_DIRTY);
639 			}
640 			write_unlock_irq(&mapping->tree_lock);
641 			if (mapping->host) {
642 				/* !PageAnon && !swapper_space */
643 				__mark_inode_dirty(mapping->host,
644 							I_DIRTY_PAGES);
645 			}
646 		}
647 	}
648 	return ret;
649 }
650 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
651 
652 /*
653  * When a writepage implementation decides that it doesn't want to write this
654  * page for some reason, it should redirty the locked page via
655  * redirty_page_for_writepage() and it should then unlock the page and return 0
656  */
657 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
658 {
659 	wbc->pages_skipped++;
660 	return __set_page_dirty_nobuffers(page);
661 }
662 EXPORT_SYMBOL(redirty_page_for_writepage);
663 
664 /*
665  * If the mapping doesn't provide a set_page_dirty a_op, then
666  * just fall through and assume that it wants buffer_heads.
667  */
668 int fastcall set_page_dirty(struct page *page)
669 {
670 	struct address_space *mapping = page_mapping(page);
671 
672 	if (likely(mapping)) {
673 		int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
674 		if (spd)
675 			return (*spd)(page);
676 		return __set_page_dirty_buffers(page);
677 	}
678 	if (!PageDirty(page))
679 		SetPageDirty(page);
680 	return 0;
681 }
682 EXPORT_SYMBOL(set_page_dirty);
683 
684 /*
685  * set_page_dirty() is racy if the caller has no reference against
686  * page->mapping->host, and if the page is unlocked.  This is because another
687  * CPU could truncate the page off the mapping and then free the mapping.
688  *
689  * Usually, the page _is_ locked, or the caller is a user-space process which
690  * holds a reference on the inode by having an open file.
691  *
692  * In other cases, the page should be locked before running set_page_dirty().
693  */
694 int set_page_dirty_lock(struct page *page)
695 {
696 	int ret;
697 
698 	lock_page(page);
699 	ret = set_page_dirty(page);
700 	unlock_page(page);
701 	return ret;
702 }
703 EXPORT_SYMBOL(set_page_dirty_lock);
704 
705 /*
706  * Clear a page's dirty flag, while caring for dirty memory accounting.
707  * Returns true if the page was previously dirty.
708  */
709 int test_clear_page_dirty(struct page *page)
710 {
711 	struct address_space *mapping = page_mapping(page);
712 	unsigned long flags;
713 
714 	if (mapping) {
715 		write_lock_irqsave(&mapping->tree_lock, flags);
716 		if (TestClearPageDirty(page)) {
717 			radix_tree_tag_clear(&mapping->page_tree,
718 						page_index(page),
719 						PAGECACHE_TAG_DIRTY);
720 			write_unlock_irqrestore(&mapping->tree_lock, flags);
721 			if (mapping_cap_account_dirty(mapping))
722 				dec_page_state(nr_dirty);
723 			return 1;
724 		}
725 		write_unlock_irqrestore(&mapping->tree_lock, flags);
726 		return 0;
727 	}
728 	return TestClearPageDirty(page);
729 }
730 EXPORT_SYMBOL(test_clear_page_dirty);
731 
732 /*
733  * Clear a page's dirty flag, while caring for dirty memory accounting.
734  * Returns true if the page was previously dirty.
735  *
736  * This is for preparing to put the page under writeout.  We leave the page
737  * tagged as dirty in the radix tree so that a concurrent write-for-sync
738  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
739  * implementation will run either set_page_writeback() or set_page_dirty(),
740  * at which stage we bring the page's dirty flag and radix-tree dirty tag
741  * back into sync.
742  *
743  * This incoherency between the page's dirty flag and radix-tree tag is
744  * unfortunate, but it only exists while the page is locked.
745  */
746 int clear_page_dirty_for_io(struct page *page)
747 {
748 	struct address_space *mapping = page_mapping(page);
749 
750 	if (mapping) {
751 		if (TestClearPageDirty(page)) {
752 			if (mapping_cap_account_dirty(mapping))
753 				dec_page_state(nr_dirty);
754 			return 1;
755 		}
756 		return 0;
757 	}
758 	return TestClearPageDirty(page);
759 }
760 EXPORT_SYMBOL(clear_page_dirty_for_io);
761 
762 int test_clear_page_writeback(struct page *page)
763 {
764 	struct address_space *mapping = page_mapping(page);
765 	int ret;
766 
767 	if (mapping) {
768 		unsigned long flags;
769 
770 		write_lock_irqsave(&mapping->tree_lock, flags);
771 		ret = TestClearPageWriteback(page);
772 		if (ret)
773 			radix_tree_tag_clear(&mapping->page_tree,
774 						page_index(page),
775 						PAGECACHE_TAG_WRITEBACK);
776 		write_unlock_irqrestore(&mapping->tree_lock, flags);
777 	} else {
778 		ret = TestClearPageWriteback(page);
779 	}
780 	return ret;
781 }
782 
783 int test_set_page_writeback(struct page *page)
784 {
785 	struct address_space *mapping = page_mapping(page);
786 	int ret;
787 
788 	if (mapping) {
789 		unsigned long flags;
790 
791 		write_lock_irqsave(&mapping->tree_lock, flags);
792 		ret = TestSetPageWriteback(page);
793 		if (!ret)
794 			radix_tree_tag_set(&mapping->page_tree,
795 						page_index(page),
796 						PAGECACHE_TAG_WRITEBACK);
797 		if (!PageDirty(page))
798 			radix_tree_tag_clear(&mapping->page_tree,
799 						page_index(page),
800 						PAGECACHE_TAG_DIRTY);
801 		write_unlock_irqrestore(&mapping->tree_lock, flags);
802 	} else {
803 		ret = TestSetPageWriteback(page);
804 	}
805 	return ret;
806 
807 }
808 EXPORT_SYMBOL(test_set_page_writeback);
809 
810 /*
811  * Return true if any of the pages in the mapping are marged with the
812  * passed tag.
813  */
814 int mapping_tagged(struct address_space *mapping, int tag)
815 {
816 	unsigned long flags;
817 	int ret;
818 
819 	read_lock_irqsave(&mapping->tree_lock, flags);
820 	ret = radix_tree_tagged(&mapping->page_tree, tag);
821 	read_unlock_irqrestore(&mapping->tree_lock, flags);
822 	return ret;
823 }
824 EXPORT_SYMBOL(mapping_tagged);
825