Commit 6e6938b6 authored by Wu Fengguang's avatar Wu Fengguang
Browse files

writeback: introduce .tagged_writepages for the WB_SYNC_NONE sync stage 



sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
WB_SYNC_ALL sync. Identify the first stage with .tagged_writepages and
do livelock prevention for it, too.

Jan's commit f446daae ("mm: implement writeback livelock avoidance
using page tagging") is a partial fix in that it only fixed the
WB_SYNC_ALL phase livelock.

Although ext4 is tested to no longer livelock with commit f446daae,
it may due to some "redirty_tail() after pages_skipped" effect which
is by no means a guarantee for _all_ the file systems.

Note that writeback_inodes_sb() is called by not only sync(), they are
treated the same because the other callers also need livelock prevention.

Impact:  It changes the order in which pages/inodes are synced to disk.
Now in the WB_SYNC_NONE stage, it won't proceed to write the next inode
until finished with the current inode.

Acked-by: default avatarJan Kara <jack@suse.cz>
CC: Dave Chinner <david@fromorbit.com>
Signed-off-by: default avatarWu Fengguang <fengguang.wu@intel.com>
parent 59c5f46f

fs/ext4/inode.c

+2 −2
Original line number Diff line number Diff line
@@ -2741,7 +2741,7 @@ static int write_cache_pages_da(struct address_space *mapping, 
	index = wbc->range_start >> PAGE_CACHE_SHIFT;

	end = wbc->range_end >> PAGE_CACHE_SHIFT;



	if (wbc->sync_mode == WB_SYNC_ALL)

	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)

		tag = PAGECACHE_TAG_TOWRITE;

	else

		tag = PAGECACHE_TAG_DIRTY;
@@ -2973,7 +2973,7 @@ static int ext4_da_writepages(struct address_space *mapping, 
	}



retry:

	if (wbc->sync_mode == WB_SYNC_ALL)

	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)

		tag_pages_for_writeback(mapping, index, end);



	while (!ret && wbc->nr_to_write > 0) {

fs/fs-writeback.c

+9 −8
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ struct wb_writeback_work { 
	long nr_pages;

	struct super_block *sb;

	enum writeback_sync_modes sync_mode;

	unsigned int tagged_writepages:1;

	unsigned int for_kupdate:1;

	unsigned int range_cyclic:1;

	unsigned int for_background:1;
@@ -650,6 +651,7 @@ static long wb_writeback(struct bdi_writeback *wb, 
{

	struct writeback_control wbc = {

		.sync_mode		= work->sync_mode,

		.tagged_writepages	= work->tagged_writepages,

		.older_than_this	= NULL,

		.for_kupdate		= work->for_kupdate,

		.for_background		= work->for_background,
@@ -657,7 +659,7 @@ static long wb_writeback(struct bdi_writeback *wb, 
	};

	unsigned long oldest_jif;

	long wrote = 0;

	long write_chunk;

	long write_chunk = MAX_WRITEBACK_PAGES;

	struct inode *inode;



	if (wbc.for_kupdate) {
@@ -683,9 +685,7 @@ static long wb_writeback(struct bdi_writeback *wb, 
	 *                   (quickly) tag currently dirty pages

	 *                   (maybe slowly) sync all tagged pages

	 */

	if (wbc.sync_mode == WB_SYNC_NONE)

		write_chunk = MAX_WRITEBACK_PAGES;

	else

	if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_writepages)

		write_chunk = LONG_MAX;



	wbc.wb_start = jiffies; /* livelock avoidance */
@@ -1190,6 +1190,7 @@ void writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr) 
	struct wb_writeback_work work = {

		.sb			= sb,

		.sync_mode		= WB_SYNC_NONE,

		.tagged_writepages	= 1,

		.done			= &done,

		.nr_pages		= nr,

	};

include/linux/writeback.h

+1 −0
Original line number Diff line number Diff line
@@ -47,6 +47,7 @@ struct writeback_control { 
	unsigned encountered_congestion:1; /* An output: a queue is full */

	unsigned for_kupdate:1;		/* A kupdate writeback */

	unsigned for_background:1;	/* A background writeback */

	unsigned tagged_writepages:1;	/* tag-and-write to avoid livelock */

	unsigned for_reclaim:1;		/* Invoked from the page allocator */

	unsigned range_cyclic:1;	/* range_start is cyclic */

	unsigned more_io:1;		/* more io to be dispatched */

mm/page-writeback.c

+2 −2
Original line number Diff line number Diff line
@@ -892,12 +892,12 @@ int write_cache_pages(struct address_space *mapping, 
			range_whole = 1;

		cycled = 1; /* ignore range_cyclic tests */

	}

	if (wbc->sync_mode == WB_SYNC_ALL)

	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)

		tag = PAGECACHE_TAG_TOWRITE;

	else

		tag = PAGECACHE_TAG_DIRTY;

retry:

	if (wbc->sync_mode == WB_SYNC_ALL)

	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)

		tag_pages_for_writeback(mapping, index, end);

	done_index = index;

	while (!done && (index <= end)) {

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