Commit 32dd4f9c authored by Dave Chinner's avatar Dave Chinner Committed by Dave Chinner
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xfs: remove a superflous hash lookup when inserting new buffers 



Currently on the slow path insert we repeat the initial hash table
lookup before we attempt the insert, resulting in a two traversals
of the hash table to ensure the insert is valid. The rhashtable API
provides a method for an atomic lookup and insert operation, so we
can avoid one of the hash table traversals by using this method.

Adapted from a large patch containing this optimisation by Christoph
Hellwig.

Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDarrick J. Wong <djwong@kernel.org>
parent d8d9bbb0

fs/xfs/xfs_buf.c

+9 −4
Original line number Diff line number Diff line
@@ -623,8 +623,15 @@ xfs_buf_find_insert( 
	}



	spin_lock(&pag->pag_buf_lock);

	bp = rhashtable_lookup(&pag->pag_buf_hash, cmap, xfs_buf_hash_params);

	bp = rhashtable_lookup_get_insert_fast(&pag->pag_buf_hash,

			&new_bp->b_rhash_head, xfs_buf_hash_params);

	if (IS_ERR(bp)) {

		error = PTR_ERR(bp);

		spin_unlock(&pag->pag_buf_lock);

		goto out_free_buf;

	}

	if (bp) {

		/* found an existing buffer */

		atomic_inc(&bp->b_hold);

		spin_unlock(&pag->pag_buf_lock);

		error = xfs_buf_find_lock(bp, flags);
@@ -635,10 +642,8 @@ xfs_buf_find_insert( 
		goto out_free_buf;

	}



	/* The buffer keeps the perag reference until it is freed. */

	/* The new buffer keeps the perag reference until it is freed. */

	new_bp->b_pag = pag;

	rhashtable_insert_fast(&pag->pag_buf_hash, &new_bp->b_rhash_head,

			       xfs_buf_hash_params);

	spin_unlock(&pag->pag_buf_lock);

	*bpp = new_bp;

	return 0;