[PATCH RFCv2 1/3] xfs: refactor small allocation helper to skip cntbt attempt

[Brian Foster <bfoster@redhat.com>]

The small allocation helper is implemented in a way that is fairly
tightly integrated to the existing allocation algorithms. It expects
a cntbt cursor beyond the end of the tree, attempts to locate the
last record in the tree and only attempts an AGFL allocation if the
cntbt is empty.

The generic algorithm doesn't guarantee state or pass along context
for this helper to determine the state of the cntbt. It will only
call this function when the cntbt doesn't have a big enough extent
or is empty. Therefore, tweak xfs_alloc_ag_vextent_small() to allow
for a NULL cntbt cursor and skip the cntbt logic. Instead, consider
allocation from the AGFL or fail the allocation.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/libxfs/xfs_alloc.c | 52 +++++++++++++++++++--------------------
 1 file changed, 26 insertions(+), 26 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index bc3367b8b7bb..10a6e22b764d 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -1589,33 +1589,36 @@ xfs_alloc_ag_vextent_size(
  */
 STATIC int			/* error */
 xfs_alloc_ag_vextent_small(
-	xfs_alloc_arg_t	*args,	/* allocation argument structure */
-	xfs_btree_cur_t	*ccur,	/* by-size cursor */
-	xfs_agblock_t	*fbnop,	/* result block number */
-	xfs_extlen_t	*flenp,	/* result length */
-	int		*stat)	/* status: 0-freelist, 1-normal/none */
+	struct xfs_alloc_arg	*args,	/* allocation argument structure */
+	struct xfs_btree_cur	*ccur,	/* optional by-size cursor */
+	xfs_agblock_t		*fbnop,	/* result block number */
+	xfs_extlen_t		*flenp,	/* result length */
+	int			*stat)	/* status: 0-freelist, 1-normal/none */
 {
-	int		error;
-	xfs_agblock_t	fbno;
-	xfs_extlen_t	flen;
-	int		i;
+	int			error = 0;
+	xfs_agblock_t		fbno;
+	xfs_extlen_t		flen;
+	int			i = 0;
 
-	if ((error = xfs_btree_decrement(ccur, 0, &i)))
+	/*
+	 * If a cntbt cursor is provided, try to allocate the largest record in
+	 * the tree. Try the AGFL if the cntbt is empty, otherwise fail the
+	 * allocation. Make sure to respect minleft even when pulling from the
+	 * freelist.
+	 */
+	if (ccur)
+		error = xfs_btree_decrement(ccur, 0, &i);
+	if (error)
 		goto error0;
 	if (i) {
-		if ((error = xfs_alloc_get_rec(ccur, &fbno, &flen, &i)))
+		error = xfs_alloc_get_rec(ccur, &fbno, &flen, &i);
+		if (error)
 			goto error0;
 		XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
-	}
-	/*
-	 * Nothing in the btree, try the freelist.  Make sure
-	 * to respect minleft even when pulling from the
-	 * freelist.
-	 */
-	else if (args->minlen == 1 && args->alignment == 1 &&
-		 args->resv != XFS_AG_RESV_AGFL &&
-		 (be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_flcount)
-		  > args->minleft)) {
+	} else if (args->minlen == 1 && args->alignment == 1 &&
+		   args->resv != XFS_AG_RESV_AGFL &&
+		   (be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_flcount) >
+		    args->minleft)) {
 		error = xfs_alloc_get_freelist(args->tp, args->agbp, &fbno, 0);
 		if (error)
 			goto error0;
@@ -1661,14 +1664,11 @@ xfs_alloc_ag_vextent_small(
 		 */
 		else
 			flen = 0;
-	}
-	/*
-	 * Can't allocate from the freelist for some reason.
-	 */
-	else {
+	} else {
 		fbno = NULLAGBLOCK;
 		flen = 0;
 	}
+
 	/*
 	 * Can't do the allocation, give up.
 	 */
-- 
2.17.2