Commit f30a7d0c authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

writeback: restructure try_writeback_inodes_sb[_nr]() 



try_writeback_inodes_sb_nr() wraps writeback_inodes_sb_nr() so that it
handles s_umount locking and skips if writeback is already in
progress.  The in progress test is performed on the root wb
(bdi_writeback) which isn't sufficient for cgroup writeback support.
The test must be done per-wb.

To prepare for the change, this patch factors out
__writeback_inodes_sb_nr() from writeback_inodes_sb_nr() and adds
@skip_if_busy and moves the in progress test right before queueing the
wb_writeback_work.  try_writeback_inodes_sb_nr() now just grabs
s_umount and invokes __writeback_inodes_sb_nr() with asserted
@skip_if_busy.  This way, later addition of multiple wb handling can
skip only the wb's which already have writeback in progress.

This swaps the order between in progress test and s_umount test which
can flip the return value when writeback is in progress and s_umount
is being held by someone else but this shouldn't cause any meaningful
difference.  It's a fringe condition and the return value is an
unsynchronized hint anyway.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 98754bf7

fs/fs-writeback.c

+29 −23
Original line number Diff line number Diff line
@@ -1581,19 +1581,8 @@ static void wait_sb_inodes(struct super_block *sb) 
	iput(old_inode);

}



/**

 * writeback_inodes_sb_nr -	writeback dirty inodes from given super_block

 * @sb: the superblock

 * @nr: the number of pages to write

 * @reason: reason why some writeback work initiated

 *

 * Start writeback on some inodes on this super_block. No guarantees are made

 * on how many (if any) will be written, and this function does not wait

 * for IO completion of submitted IO.

 */

void writeback_inodes_sb_nr(struct super_block *sb,

			    unsigned long nr,

			    enum wb_reason reason)

static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,

				     enum wb_reason reason, bool skip_if_busy)

{

	DEFINE_WB_COMPLETION_ONSTACK(done);

	struct wb_writeback_work work = {
@@ -1609,9 +1598,30 @@ void writeback_inodes_sb_nr(struct super_block *sb, 
	if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)

		return;

	WARN_ON(!rwsem_is_locked(&sb->s_umount));



	if (skip_if_busy && writeback_in_progress(&bdi->wb))

		return;



	wb_queue_work(&bdi->wb, &work);

	wb_wait_for_completion(bdi, &done);

}



/**

 * writeback_inodes_sb_nr -	writeback dirty inodes from given super_block

 * @sb: the superblock

 * @nr: the number of pages to write

 * @reason: reason why some writeback work initiated

 *

 * Start writeback on some inodes on this super_block. No guarantees are made

 * on how many (if any) will be written, and this function does not wait

 * for IO completion of submitted IO.

 */

void writeback_inodes_sb_nr(struct super_block *sb,

			    unsigned long nr,

			    enum wb_reason reason)

{

	__writeback_inodes_sb_nr(sb, nr, reason, false);

}

EXPORT_SYMBOL(writeback_inodes_sb_nr);



/**
@@ -1638,19 +1648,15 @@ EXPORT_SYMBOL(writeback_inodes_sb); 
 * Invoke writeback_inodes_sb_nr if no writeback is currently underway.

 * Returns 1 if writeback was started, 0 if not.

 */

int try_to_writeback_inodes_sb_nr(struct super_block *sb,

				  unsigned long nr,

bool try_to_writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,

				   enum wb_reason reason)

{

	if (writeback_in_progress(&sb->s_bdi->wb))

		return 1;



	if (!down_read_trylock(&sb->s_umount))

		return 0;

		return false;



	writeback_inodes_sb_nr(sb, nr, reason);

	__writeback_inodes_sb_nr(sb, nr, reason, true);

	up_read(&sb->s_umount);

	return 1;

	return true;

}

EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
@@ -1662,7 +1668,7 @@ EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr); 
 * Implement by try_to_writeback_inodes_sb_nr()

 * Returns 1 if writeback was started, 0 if not.

 */

int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)

bool try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)

{

	return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);

}

include/linux/writeback.h

+3 −3
Original line number Diff line number Diff line
@@ -93,8 +93,8 @@ struct bdi_writeback; 
void writeback_inodes_sb(struct super_block *, enum wb_reason reason);

void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,

							enum wb_reason reason);

int try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);

int try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,

bool try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);

bool try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,

				   enum wb_reason reason);

void sync_inodes_sb(struct super_block *);

void wakeup_flusher_threads(long nr_pages, enum wb_reason reason);

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