xfs: get rid of unnecessary xfs_perag_{get,put} pairs

In the course of some operations, we look up the perag from
the mount multiple times to get or change perag information.
These are often very short pieces of code, so while the
lookup cost is generally low, the cost of the lookup is far
higher than the cost of the operation we are doing on the
perag.

Since we changed buffers to hold references to the perag
they are cached in, many modification contexts already hold
active references to the perag that are held across these
operations. This is especially true for any operation that
is serialised by an allocation group header buffer.

In these cases, we can just use the buffer's reference to
the perag to avoid needing to do lookups to access the
perag. This means that many operations don't need to do
perag lookups at all to access the perag because they've
already looked up objects that own persistent references
and hence can use that reference instead.

Cc: Dave Chinner <dchinner@redhat.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 11 insertions, 27 deletions

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 5c07bf491d9f..407d6299606d 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -2265,7 +2265,6 @@ xfs_iunlink(
 	}
 
 	if (next_agino != NULLAGINO) {
-		struct xfs_perag	*pag;
 		xfs_agino_t		old_agino;
 
 		/*
@@ -2282,9 +2281,7 @@ xfs_iunlink(
 		 * agino has been unlinked, add a backref from the next inode
 		 * back to agino.
 		 */
-		pag = xfs_perag_get(mp, agno);
-		error = xfs_iunlink_add_backref(pag, agino, next_agino);
-		xfs_perag_put(pag);
+		error = xfs_iunlink_add_backref(agibp->b_pag, agino, next_agino);
 		if (error)
 			return error;
 	}
@@ -2420,7 +2417,6 @@ xfs_iunlink_remove(
 	struct xfs_buf		*agibp;
 	struct xfs_buf		*last_ibp;
 	struct xfs_dinode	*last_dip = NULL;
-	struct xfs_perag	*pag = NULL;
 	xfs_agnumber_t		agno = XFS_INO_TO_AGNO(mp, ip->i_ino);
 	xfs_agino_t		agino = XFS_INO_TO_AGINO(mp, ip->i_ino);
 	xfs_agino_t		next_agino;
@@ -2464,32 +2460,22 @@ xfs_iunlink_remove(
 	 * this inode's backref to point from the next inode.
 	 */
 	if (next_agino != NULLAGINO) {
-		pag = xfs_perag_get(mp, agno);
-		error = xfs_iunlink_change_backref(pag, next_agino,
+		error = xfs_iunlink_change_backref(agibp->b_pag, next_agino,
 				NULLAGINO);
 		if (error)
-			goto out;
+			return error;
 	}
 
-	if (head_agino == agino) {
-		/* Point the head of the list to the next unlinked inode. */
-		error = xfs_iunlink_update_bucket(tp, agno, agibp, bucket_index,
-				next_agino);
-		if (error)
-			goto out;
-	} else {
+	if (head_agino != agino) {
 		struct xfs_imap	imap;
 		xfs_agino_t	prev_agino;
 
-		if (!pag)
-			pag = xfs_perag_get(mp, agno);
-
 		/* We need to search the list for the inode being freed. */
 		error = xfs_iunlink_map_prev(tp, agno, head_agino, agino,
 				&prev_agino, &imap, &last_dip, &last_ibp,
-				pag);
+				agibp->b_pag);
 		if (error)
-			goto out;
+			return error;
 
 		/* Point the previous inode on the list to the next inode. */
 		xfs_iunlink_update_dinode(tp, agno, prev_agino, last_ibp,
@@ -2503,15 +2489,13 @@ xfs_iunlink_remove(
 		 * change_backref takes care of deleting the backref if
 		 * next_agino is NULLAGINO.
 		 */
-		error = xfs_iunlink_change_backref(pag, agino, next_agino);
-		if (error)
-			goto out;
+		return xfs_iunlink_change_backref(agibp->b_pag, agino,
+				next_agino);
 	}
 
-out:
-	if (pag)
-		xfs_perag_put(pag);
-	return error;
+	/* Point the head of the list to the next unlinked inode. */
+	return xfs_iunlink_update_bucket(tp, agno, agibp, bucket_index,
+			next_agino);
 }
 
 /*