Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 819 insertions, 0 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
new file mode 100644
index 000000000000..6ddd6a29c73b
--- /dev/null
+++ b/mm/page-writeback.c
@@ -0,0 +1,819 @@
+/*
+ * mm/page-writeback.c.
+ *
+ * Copyright (C) 2002, Linus Torvalds.
+ *
+ * Contains functions related to writing back dirty pages at the
+ * address_space level.
+ *
+ * 10Apr2002	akpm@zip.com.au
+ *		Initial version
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/slab.h>
+#include <linux/pagemap.h>
+#include <linux/writeback.h>
+#include <linux/init.h>
+#include <linux/backing-dev.h>
+#include <linux/blkdev.h>
+#include <linux/mpage.h>
+#include <linux/percpu.h>
+#include <linux/notifier.h>
+#include <linux/smp.h>
+#include <linux/sysctl.h>
+#include <linux/cpu.h>
+#include <linux/syscalls.h>
+
+/*
+ * The maximum number of pages to writeout in a single bdflush/kupdate
+ * operation.  We do this so we don't hold I_LOCK against an inode for
+ * enormous amounts of time, which would block a userspace task which has
+ * been forced to throttle against that inode.  Also, the code reevaluates
+ * the dirty each time it has written this many pages.
+ */
+#define MAX_WRITEBACK_PAGES	1024
+
+/*
+ * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
+ * will look to see if it needs to force writeback or throttling.
+ */
+static long ratelimit_pages = 32;
+
+static long total_pages;	/* The total number of pages in the machine. */
+static int dirty_exceeded;	/* Dirty mem may be over limit */
+
+/*
+ * When balance_dirty_pages decides that the caller needs to perform some
+ * non-background writeback, this is how many pages it will attempt to write.
+ * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
+ * large amounts of I/O are submitted.
+ */
+static inline long sync_writeback_pages(void)
+{
+	return ratelimit_pages + ratelimit_pages / 2;
+}
+
+/* The following parameters are exported via /proc/sys/vm */
+
+/*
+ * Start background writeback (via pdflush) at this percentage
+ */
+int dirty_background_ratio = 10;
+
+/*
+ * The generator of dirty data starts writeback at this percentage
+ */
+int vm_dirty_ratio = 40;
+
+/*
+ * The interval between `kupdate'-style writebacks, in centiseconds
+ * (hundredths of a second)
+ */
+int dirty_writeback_centisecs = 5 * 100;
+
+/*
+ * The longest number of centiseconds for which data is allowed to remain dirty
+ */
+int dirty_expire_centisecs = 30 * 100;
+
+/*
+ * Flag that makes the machine dump writes/reads and block dirtyings.
+ */
+int block_dump;
+
+/*
+ * Flag that puts the machine in "laptop mode".
+ */
+int laptop_mode;
+
+EXPORT_SYMBOL(laptop_mode);
+
+/* End of sysctl-exported parameters */
+
+
+static void background_writeout(unsigned long _min_pages);
+
+struct writeback_state
+{
+	unsigned long nr_dirty;
+	unsigned long nr_unstable;
+	unsigned long nr_mapped;
+	unsigned long nr_writeback;
+};
+
+static void get_writeback_state(struct writeback_state *wbs)
+{
+	wbs->nr_dirty = read_page_state(nr_dirty);
+	wbs->nr_unstable = read_page_state(nr_unstable);
+	wbs->nr_mapped = read_page_state(nr_mapped);
+	wbs->nr_writeback = read_page_state(nr_writeback);
+}
+
+/*
+ * Work out the current dirty-memory clamping and background writeout
+ * thresholds.
+ *
+ * The main aim here is to lower them aggressively if there is a lot of mapped
+ * memory around.  To avoid stressing page reclaim with lots of unreclaimable
+ * pages.  It is better to clamp down on writers than to start swapping, and
+ * performing lots of scanning.
+ *
+ * We only allow 1/2 of the currently-unmapped memory to be dirtied.
+ *
+ * We don't permit the clamping level to fall below 5% - that is getting rather
+ * excessive.
+ *
+ * We make sure that the background writeout level is below the adjusted
+ * clamping level.
+ */
+static void
+get_dirty_limits(struct writeback_state *wbs, long *pbackground, long *pdirty,
+		struct address_space *mapping)
+{
+	int background_ratio;		/* Percentages */
+	int dirty_ratio;
+	int unmapped_ratio;
+	long background;
+	long dirty;
+	unsigned long available_memory = total_pages;
+	struct task_struct *tsk;
+
+	get_writeback_state(wbs);
+
+#ifdef CONFIG_HIGHMEM
+	/*
+	 * If this mapping can only allocate from low memory,
+	 * we exclude high memory from our count.
+	 */
+	if (mapping && !(mapping_gfp_mask(mapping) & __GFP_HIGHMEM))
+		available_memory -= totalhigh_pages;
+#endif
+
+
+	unmapped_ratio = 100 - (wbs->nr_mapped * 100) / total_pages;
+
+	dirty_ratio = vm_dirty_ratio;
+	if (dirty_ratio > unmapped_ratio / 2)
+		dirty_ratio = unmapped_ratio / 2;
+
+	if (dirty_ratio < 5)
+		dirty_ratio = 5;
+
+	background_ratio = dirty_background_ratio;
+	if (background_ratio >= dirty_ratio)
+		background_ratio = dirty_ratio / 2;
+
+	background = (background_ratio * available_memory) / 100;
+	dirty = (dirty_ratio * available_memory) / 100;
+	tsk = current;
+	if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
+		background += background / 4;
+		dirty += dirty / 4;
+	}
+	*pbackground = background;
+	*pdirty = dirty;
+}
+
+/*
+ * balance_dirty_pages() must be called by processes which are generating dirty
+ * data.  It looks at the number of dirty pages in the machine and will force
+ * the caller to perform writeback if the system is over `vm_dirty_ratio'.
+ * If we're over `background_thresh' then pdflush is woken to perform some
+ * writeout.
+ */
+static void balance_dirty_pages(struct address_space *mapping)
+{
+	struct writeback_state wbs;
+	long nr_reclaimable;
+	long background_thresh;
+	long dirty_thresh;
+	unsigned long pages_written = 0;
+	unsigned long write_chunk = sync_writeback_pages();
+
+	struct backing_dev_info *bdi = mapping->backing_dev_info;
+
+	for (;;) {
+		struct writeback_control wbc = {
+			.bdi		= bdi,
+			.sync_mode	= WB_SYNC_NONE,
+			.older_than_this = NULL,
+			.nr_to_write	= write_chunk,
+		};
+
+		get_dirty_limits(&wbs, &background_thresh,
+					&dirty_thresh, mapping);
+		nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
+		if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
+			break;
+
+		dirty_exceeded = 1;
+
+		/* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
+		 * Unstable writes are a feature of certain networked
+		 * filesystems (i.e. NFS) in which data may have been
+		 * written to the server's write cache, but has not yet
+		 * been flushed to permanent storage.
+		 */
+		if (nr_reclaimable) {
+			writeback_inodes(&wbc);
+			get_dirty_limits(&wbs, &background_thresh,
+					&dirty_thresh, mapping);
+			nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
+			if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
+				break;
+			pages_written += write_chunk - wbc.nr_to_write;
+			if (pages_written >= write_chunk)
+				break;		/* We've done our duty */
+		}
+		blk_congestion_wait(WRITE, HZ/10);
+	}
+
+	if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
+		dirty_exceeded = 0;
+
+	if (writeback_in_progress(bdi))
+		return;		/* pdflush is already working this queue */
+
+	/*
+	 * In laptop mode, we wait until hitting the higher threshold before
+	 * starting background writeout, and then write out all the way down
+	 * to the lower threshold.  So slow writers cause minimal disk activity.
+	 *
+	 * In normal mode, we start background writeout at the lower
+	 * background_thresh, to keep the amount of dirty memory low.
+	 */
+	if ((laptop_mode && pages_written) ||
+	     (!laptop_mode && (nr_reclaimable > background_thresh)))
+		pdflush_operation(background_writeout, 0);
+}
+
+/**
+ * balance_dirty_pages_ratelimited - balance dirty memory state
+ * @mapping - address_space which was dirtied
+ *
+ * Processes which are dirtying memory should call in here once for each page
+ * which was newly dirtied.  The function will periodically check the system's
+ * dirty state and will initiate writeback if needed.
+ *
+ * On really big machines, get_writeback_state is expensive, so try to avoid
+ * calling it too often (ratelimiting).  But once we're over the dirty memory
+ * limit we decrease the ratelimiting by a lot, to prevent individual processes
+ * from overshooting the limit by (ratelimit_pages) each.
+ */
+void balance_dirty_pages_ratelimited(struct address_space *mapping)
+{
+	static DEFINE_PER_CPU(int, ratelimits) = 0;
+	long ratelimit;
+
+	ratelimit = ratelimit_pages;
+	if (dirty_exceeded)
+		ratelimit = 8;
+
+	/*
+	 * Check the rate limiting. Also, we do not want to throttle real-time
+	 * tasks in balance_dirty_pages(). Period.
+	 */
+	if (get_cpu_var(ratelimits)++ >= ratelimit) {
+		__get_cpu_var(ratelimits) = 0;
+		put_cpu_var(ratelimits);
+		balance_dirty_pages(mapping);
+		return;
+	}
+	put_cpu_var(ratelimits);
+}
+EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
+
+void throttle_vm_writeout(void)
+{
+	struct writeback_state wbs;
+	long background_thresh;
+	long dirty_thresh;
+
+        for ( ; ; ) {
+		get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
+
+                /*
+                 * Boost the allowable dirty threshold a bit for page
+                 * allocators so they don't get DoS'ed by heavy writers
+                 */
+                dirty_thresh += dirty_thresh / 10;      /* wheeee... */
+
+                if (wbs.nr_unstable + wbs.nr_writeback <= dirty_thresh)
+                        break;
+                blk_congestion_wait(WRITE, HZ/10);
+        }
+}
+
+
+/*
+ * writeback at least _min_pages, and keep writing until the amount of dirty
+ * memory is less than the background threshold, or until we're all clean.
+ */
+static void background_writeout(unsigned long _min_pages)
+{
+	long min_pages = _min_pages;
+	struct writeback_control wbc = {
+		.bdi		= NULL,
+		.sync_mode	= WB_SYNC_NONE,
+		.older_than_this = NULL,
+		.nr_to_write	= 0,
+		.nonblocking	= 1,
+	};
+
+	for ( ; ; ) {
+		struct writeback_state wbs;
+		long background_thresh;
+		long dirty_thresh;
+
+		get_dirty_limits(&wbs, &background_thresh, &dirty_thresh, NULL);
+		if (wbs.nr_dirty + wbs.nr_unstable < background_thresh
+				&& min_pages <= 0)
+			break;
+		wbc.encountered_congestion = 0;
+		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
+		wbc.pages_skipped = 0;
+		writeback_inodes(&wbc);
+		min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+		if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
+			/* Wrote less than expected */
+			blk_congestion_wait(WRITE, HZ/10);
+			if (!wbc.encountered_congestion)
+				break;
+		}
+	}
+}
+
+/*
+ * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
+ * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
+ * -1 if all pdflush threads were busy.
+ */
+int wakeup_bdflush(long nr_pages)
+{
+	if (nr_pages == 0) {
+		struct writeback_state wbs;
+
+		get_writeback_state(&wbs);
+		nr_pages = wbs.nr_dirty + wbs.nr_unstable;
+	}
+	return pdflush_operation(background_writeout, nr_pages);
+}
+
+static void wb_timer_fn(unsigned long unused);
+static void laptop_timer_fn(unsigned long unused);
+
+static struct timer_list wb_timer =
+			TIMER_INITIALIZER(wb_timer_fn, 0, 0);
+static struct timer_list laptop_mode_wb_timer =
+			TIMER_INITIALIZER(laptop_timer_fn, 0, 0);
+
+/*
+ * Periodic writeback of "old" data.
+ *
+ * Define "old": the first time one of an inode's pages is dirtied, we mark the
+ * dirtying-time in the inode's address_space.  So this periodic writeback code
+ * just walks the superblock inode list, writing back any inodes which are
+ * older than a specific point in time.
+ *
+ * Try to run once per dirty_writeback_centisecs.  But if a writeback event
+ * takes longer than a dirty_writeback_centisecs interval, then leave a
+ * one-second gap.
+ *
+ * older_than_this takes precedence over nr_to_write.  So we'll only write back
+ * all dirty pages if they are all attached to "old" mappings.
+ */
+static void wb_kupdate(unsigned long arg)
+{
+	unsigned long oldest_jif;
+	unsigned long start_jif;
+	unsigned long next_jif;
+	long nr_to_write;
+	struct writeback_state wbs;
+	struct writeback_control wbc = {
+		.bdi		= NULL,
+		.sync_mode	= WB_SYNC_NONE,
+		.older_than_this = &oldest_jif,
+		.nr_to_write	= 0,
+		.nonblocking	= 1,
+		.for_kupdate	= 1,
+	};
+
+	sync_supers();
+
+	get_writeback_state(&wbs);
+	oldest_jif = jiffies - (dirty_expire_centisecs * HZ) / 100;
+	start_jif = jiffies;
+	next_jif = start_jif + (dirty_writeback_centisecs * HZ) / 100;
+	nr_to_write = wbs.nr_dirty + wbs.nr_unstable +
+			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
+	while (nr_to_write > 0) {
+		wbc.encountered_congestion = 0;
+		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
+		writeback_inodes(&wbc);
+		if (wbc.nr_to_write > 0) {
+			if (wbc.encountered_congestion)
+				blk_congestion_wait(WRITE, HZ/10);
+			else
+				break;	/* All the old data is written */
+		}
+		nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+	}
+	if (time_before(next_jif, jiffies + HZ))
+		next_jif = jiffies + HZ;
+	if (dirty_writeback_centisecs)
+		mod_timer(&wb_timer, next_jif);
+}
+
+/*
+ * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
+ */
+int dirty_writeback_centisecs_handler(ctl_table *table, int write,
+		struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
+{
+	proc_dointvec(table, write, file, buffer, length, ppos);
+	if (dirty_writeback_centisecs) {
+		mod_timer(&wb_timer,
+			jiffies + (dirty_writeback_centisecs * HZ) / 100);
+	} else {
+		del_timer(&wb_timer);
+	}
+	return 0;
+}
+
+static void wb_timer_fn(unsigned long unused)
+{
+	if (pdflush_operation(wb_kupdate, 0) < 0)
+		mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
+}
+
+static void laptop_flush(unsigned long unused)
+{
+	sys_sync();
+}
+
+static void laptop_timer_fn(unsigned long unused)
+{
+	pdflush_operation(laptop_flush, 0);
+}
+
+/*
+ * We've spun up the disk and we're in laptop mode: schedule writeback
+ * of all dirty data a few seconds from now.  If the flush is already scheduled
+ * then push it back - the user is still using the disk.
+ */
+void laptop_io_completion(void)
+{
+	mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode * HZ);
+}
+
+/*
+ * We're in laptop mode and we've just synced. The sync's writes will have
+ * caused another writeback to be scheduled by laptop_io_completion.
+ * Nothing needs to be written back anymore, so we unschedule the writeback.
+ */
+void laptop_sync_completion(void)
+{
+	del_timer(&laptop_mode_wb_timer);
+}
+
+/*
+ * If ratelimit_pages is too high then we can get into dirty-data overload
+ * if a large number of processes all perform writes at the same time.
+ * If it is too low then SMP machines will call the (expensive)
+ * get_writeback_state too often.
+ *
+ * Here we set ratelimit_pages to a level which ensures that when all CPUs are
+ * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
+ * thresholds before writeback cuts in.
+ *
+ * But the limit should not be set too high.  Because it also controls the
+ * amount of memory which the balance_dirty_pages() caller has to write back.
+ * If this is too large then the caller will block on the IO queue all the
+ * time.  So limit it to four megabytes - the balance_dirty_pages() caller
+ * will write six megabyte chunks, max.
+ */
+
+static void set_ratelimit(void)
+{
+	ratelimit_pages = total_pages / (num_online_cpus() * 32);
+	if (ratelimit_pages < 16)
+		ratelimit_pages = 16;
+	if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
+		ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
+}
+
+static int
+ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
+{
+	set_ratelimit();
+	return 0;
+}
+
+static struct notifier_block ratelimit_nb = {
+	.notifier_call	= ratelimit_handler,
+	.next		= NULL,
+};
+
+/*
+ * If the machine has a large highmem:lowmem ratio then scale back the default
+ * dirty memory thresholds: allowing too much dirty highmem pins an excessive
+ * number of buffer_heads.
+ */
+void __init page_writeback_init(void)
+{
+	long buffer_pages = nr_free_buffer_pages();
+	long correction;
+
+	total_pages = nr_free_pagecache_pages();
+
+	correction = (100 * 4 * buffer_pages) / total_pages;
+
+	if (correction < 100) {
+		dirty_background_ratio *= correction;
+		dirty_background_ratio /= 100;
+		vm_dirty_ratio *= correction;
+		vm_dirty_ratio /= 100;
+
+		if (dirty_background_ratio <= 0)
+			dirty_background_ratio = 1;
+		if (vm_dirty_ratio <= 0)
+			vm_dirty_ratio = 1;
+	}
+	mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100);
+	set_ratelimit();
+	register_cpu_notifier(&ratelimit_nb);
+}
+
+int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
+{
+	if (wbc->nr_to_write <= 0)
+		return 0;
+	if (mapping->a_ops->writepages)
+		return mapping->a_ops->writepages(mapping, wbc);
+	return generic_writepages(mapping, wbc);
+}
+
+/**
+ * write_one_page - write out a single page and optionally wait on I/O
+ *
+ * @page - the page to write
+ * @wait - if true, wait on writeout
+ *
+ * The page must be locked by the caller and will be unlocked upon return.
+ *
+ * write_one_page() returns a negative error code if I/O failed.
+ */
+int write_one_page(struct page *page, int wait)
+{
+	struct address_space *mapping = page->mapping;
+	int ret = 0;
+	struct writeback_control wbc = {
+		.sync_mode = WB_SYNC_ALL,
+		.nr_to_write = 1,
+	};
+
+	BUG_ON(!PageLocked(page));
+
+	if (wait)
+		wait_on_page_writeback(page);
+
+	if (clear_page_dirty_for_io(page)) {
+		page_cache_get(page);
+		ret = mapping->a_ops->writepage(page, &wbc);
+		if (ret == 0 && wait) {
+			wait_on_page_writeback(page);
+			if (PageError(page))
+				ret = -EIO;
+		}
+		page_cache_release(page);
+	} else {
+		unlock_page(page);
+	}
+	return ret;
+}
+EXPORT_SYMBOL(write_one_page);
+
+/*
+ * For address_spaces which do not use buffers.  Just tag the page as dirty in
+ * its radix tree.
+ *
+ * This is also used when a single buffer is being dirtied: we want to set the
+ * page dirty in that case, but not all the buffers.  This is a "bottom-up"
+ * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
+ *
+ * Most callers have locked the page, which pins the address_space in memory.
+ * But zap_pte_range() does not lock the page, however in that case the
+ * mapping is pinned by the vma's ->vm_file reference.
+ *
+ * We take care to handle the case where the page was truncated from the
+ * mapping by re-checking page_mapping() insode tree_lock.
+ */
+int __set_page_dirty_nobuffers(struct page *page)
+{
+	int ret = 0;
+
+	if (!TestSetPageDirty(page)) {
+		struct address_space *mapping = page_mapping(page);
+		struct address_space *mapping2;
+
+		if (mapping) {
+			write_lock_irq(&mapping->tree_lock);
+			mapping2 = page_mapping(page);
+			if (mapping2) { /* Race with truncate? */
+				BUG_ON(mapping2 != mapping);
+				if (mapping_cap_account_dirty(mapping))
+					inc_page_state(nr_dirty);
+				radix_tree_tag_set(&mapping->page_tree,
+					page_index(page), PAGECACHE_TAG_DIRTY);
+			}
+			write_unlock_irq(&mapping->tree_lock);
+			if (mapping->host) {
+				/* !PageAnon && !swapper_space */
+				__mark_inode_dirty(mapping->host,
+							I_DIRTY_PAGES);
+			}
+		}
+	}
+	return ret;
+}
+EXPORT_SYMBOL(__set_page_dirty_nobuffers);
+
+/*
+ * When a writepage implementation decides that it doesn't want to write this
+ * page for some reason, it should redirty the locked page via
+ * redirty_page_for_writepage() and it should then unlock the page and return 0
+ */
+int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
+{
+	wbc->pages_skipped++;
+	return __set_page_dirty_nobuffers(page);
+}
+EXPORT_SYMBOL(redirty_page_for_writepage);
+
+/*
+ * If the mapping doesn't provide a set_page_dirty a_op, then
+ * just fall through and assume that it wants buffer_heads.
+ */
+int fastcall set_page_dirty(struct page *page)
+{
+	struct address_space *mapping = page_mapping(page);
+
+	if (likely(mapping)) {
+		int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
+		if (spd)
+			return (*spd)(page);
+		return __set_page_dirty_buffers(page);
+	}
+	if (!PageDirty(page))
+		SetPageDirty(page);
+	return 0;
+}
+EXPORT_SYMBOL(set_page_dirty);
+
+/*
+ * set_page_dirty() is racy if the caller has no reference against
+ * page->mapping->host, and if the page is unlocked.  This is because another
+ * CPU could truncate the page off the mapping and then free the mapping.
+ *
+ * Usually, the page _is_ locked, or the caller is a user-space process which
+ * holds a reference on the inode by having an open file.
+ *
+ * In other cases, the page should be locked before running set_page_dirty().
+ */
+int set_page_dirty_lock(struct page *page)
+{
+	int ret;
+
+	lock_page(page);
+	ret = set_page_dirty(page);
+	unlock_page(page);
+	return ret;
+}
+EXPORT_SYMBOL(set_page_dirty_lock);
+
+/*
+ * Clear a page's dirty flag, while caring for dirty memory accounting. 
+ * Returns true if the page was previously dirty.
+ */
+int test_clear_page_dirty(struct page *page)
+{
+	struct address_space *mapping = page_mapping(page);
+	unsigned long flags;
+
+	if (mapping) {
+		write_lock_irqsave(&mapping->tree_lock, flags);
+		if (TestClearPageDirty(page)) {
+			radix_tree_tag_clear(&mapping->page_tree,
+						page_index(page),
+						PAGECACHE_TAG_DIRTY);
+			write_unlock_irqrestore(&mapping->tree_lock, flags);
+			if (mapping_cap_account_dirty(mapping))
+				dec_page_state(nr_dirty);
+			return 1;
+		}
+		write_unlock_irqrestore(&mapping->tree_lock, flags);
+		return 0;
+	}
+	return TestClearPageDirty(page);
+}
+EXPORT_SYMBOL(test_clear_page_dirty);
+
+/*
+ * Clear a page's dirty flag, while caring for dirty memory accounting.
+ * Returns true if the page was previously dirty.
+ *
+ * This is for preparing to put the page under writeout.  We leave the page
+ * tagged as dirty in the radix tree so that a concurrent write-for-sync
+ * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
+ * implementation will run either set_page_writeback() or set_page_dirty(),
+ * at which stage we bring the page's dirty flag and radix-tree dirty tag
+ * back into sync.
+ *
+ * This incoherency between the page's dirty flag and radix-tree tag is
+ * unfortunate, but it only exists while the page is locked.
+ */
+int clear_page_dirty_for_io(struct page *page)
+{
+	struct address_space *mapping = page_mapping(page);
+
+	if (mapping) {
+		if (TestClearPageDirty(page)) {
+			if (mapping_cap_account_dirty(mapping))
+				dec_page_state(nr_dirty);
+			return 1;
+		}
+		return 0;
+	}
+	return TestClearPageDirty(page);
+}
+EXPORT_SYMBOL(clear_page_dirty_for_io);
+
+int test_clear_page_writeback(struct page *page)
+{
+	struct address_space *mapping = page_mapping(page);
+	int ret;
+
+	if (mapping) {
+		unsigned long flags;
+
+		write_lock_irqsave(&mapping->tree_lock, flags);
+		ret = TestClearPageWriteback(page);
+		if (ret)
+			radix_tree_tag_clear(&mapping->page_tree,
+						page_index(page),
+						PAGECACHE_TAG_WRITEBACK);
+		write_unlock_irqrestore(&mapping->tree_lock, flags);
+	} else {
+		ret = TestClearPageWriteback(page);
+	}
+	return ret;
+}
+
+int test_set_page_writeback(struct page *page)
+{
+	struct address_space *mapping = page_mapping(page);
+	int ret;
+
+	if (mapping) {
+		unsigned long flags;
+
+		write_lock_irqsave(&mapping->tree_lock, flags);
+		ret = TestSetPageWriteback(page);
+		if (!ret)
+			radix_tree_tag_set(&mapping->page_tree,
+						page_index(page),
+						PAGECACHE_TAG_WRITEBACK);
+		if (!PageDirty(page))
+			radix_tree_tag_clear(&mapping->page_tree,
+						page_index(page),
+						PAGECACHE_TAG_DIRTY);
+		write_unlock_irqrestore(&mapping->tree_lock, flags);
+	} else {
+		ret = TestSetPageWriteback(page);
+	}
+	return ret;
+
+}
+EXPORT_SYMBOL(test_set_page_writeback);
+
+/*
+ * Return true if any of the pages in the mapping are marged with the
+ * passed tag.
+ */
+int mapping_tagged(struct address_space *mapping, int tag)
+{
+	unsigned long flags;
+	int ret;
+
+	read_lock_irqsave(&mapping->tree_lock, flags);
+	ret = radix_tree_tagged(&mapping->page_tree, tag);
+	read_unlock_irqrestore(&mapping->tree_lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL(mapping_tagged);