xfs: improve busy extent sorting

Sort busy extents by the full block number instead of just the AGNO so
that we can issue consecutive discard requests that the block layer could
merge (although we'll need additional block layer fixes for fast devices).
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_extent_busy.c

@@ -656,9 +656,17 @@ xfs_extent_busy_wait_all(
 int
 xfs_extent_busy_ag_cmp(
 	void			*priv,
-	struct list_head	*a,
-	struct list_head	*b)
+	struct list_head	*l1,
+	struct list_head	*l2)
 {
-	return container_of(a, struct xfs_extent_busy, list)->agno -
-		container_of(b, struct xfs_extent_busy, list)->agno;
+	struct xfs_extent_busy	*b1 =
+		container_of(l1, struct xfs_extent_busy, list);
+	struct xfs_extent_busy	*b2 =
+		container_of(l2, struct xfs_extent_busy, list);
+	s32 diff;
+
+	diff = b1->agno - b2->agno;
+	if (!diff)
+		diff = b1->bno - b2->bno;
+	return diff;
 }