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Commit 9ecc2738 authored by Jens Axboe's avatar Jens Axboe
Browse files

writeback: make the super_block pinning more efficient 



Currently we pin the inode->i_sb for every single inode. This
increases cache traffic on sb->s_umount sem. Lets instead
cache the inode sb pin state and keep the super_block pinned
for as long as keep writing out inodes from the same
super_block.

Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent cf137307

fs/fs-writeback.c

+29 −17
Original line number Diff line number Diff line
@@ -540,6 +540,17 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc) 
	return ret;

}



static void unpin_sb_for_writeback(struct super_block **psb)

{

	struct super_block *sb = *psb;



	if (sb) {

		up_read(&sb->s_umount);

		put_super(sb);

		*psb = NULL;

	}

}



/*

 * For WB_SYNC_NONE writeback, the caller does not have the sb pinned

 * before calling writeback. So make sure that we do pin it, so it doesn't
@@ -549,10 +560,19 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc) 
 * 1 if we failed.

 */

static int pin_sb_for_writeback(struct writeback_control *wbc,

				   struct inode *inode)

				struct inode *inode, struct super_block **psb)

{

	struct super_block *sb = inode->i_sb;



	/*

	 * If this sb is already pinned, nothing more to do. If not and

	 * *psb is non-NULL, unpin the old one first

	 */

	if (sb == *psb)

		return 0;

	else if (*psb)

		unpin_sb_for_writeback(psb);



	/*

	 * Caller must already hold the ref for this

	 */
@@ -566,7 +586,7 @@ static int pin_sb_for_writeback(struct writeback_control *wbc, 
	if (down_read_trylock(&sb->s_umount)) {

		if (sb->s_root) {

			spin_unlock(&sb_lock);

			return 0;

			goto pinned;

		}

		/*

		 * umounted, drop rwsem again and fall through to failure
@@ -577,24 +597,15 @@ static int pin_sb_for_writeback(struct writeback_control *wbc, 
	sb->s_count--;

	spin_unlock(&sb_lock);

	return 1;

}



static void unpin_sb_for_writeback(struct writeback_control *wbc,

				   struct inode *inode)

{

	struct super_block *sb = inode->i_sb;



	if (wbc->sync_mode == WB_SYNC_ALL)

		return;



	up_read(&sb->s_umount);

	put_super(sb);

pinned:

	*psb = sb;

	return 0;

}



static void writeback_inodes_wb(struct bdi_writeback *wb,

				struct writeback_control *wbc)

{

	struct super_block *sb = wbc->sb;

	struct super_block *sb = wbc->sb, *pin_sb = NULL;

	const int is_blkdev_sb = sb_is_blkdev_sb(sb);

	const unsigned long start = jiffies;	/* livelock avoidance */
@@ -653,7 +664,7 @@ static void writeback_inodes_wb(struct bdi_writeback *wb, 
		if (inode_dirtied_after(inode, start))

			break;



		if (pin_sb_for_writeback(wbc, inode)) {

		if (pin_sb_for_writeback(wbc, inode, &pin_sb)) {

			requeue_io(inode);

			continue;

		}
@@ -662,7 +673,6 @@ static void writeback_inodes_wb(struct bdi_writeback *wb, 
		__iget(inode);

		pages_skipped = wbc->pages_skipped;

		writeback_single_inode(inode, wbc);

		unpin_sb_for_writeback(wbc, inode);

		if (wbc->pages_skipped != pages_skipped) {

			/*

			 * writeback is not making progress due to locked
@@ -682,6 +692,8 @@ static void writeback_inodes_wb(struct bdi_writeback *wb, 
			wbc->more_io = 1;

	}



	unpin_sb_for_writeback(&pin_sb);



	spin_unlock(&inode_lock);

	/* Leave any unwritten inodes on b_io */

}