[PATCH v4 09/22] xfs: align args->minlen for forced allocation alignment

John Garry
2024-06-07T14:40:25Z

From: Dave Chinner <dchinner@redhat.com>

If args->minlen is not aligned to the constraints of forced
alignment, we may do minlen allocations that are not aligned when we
approach ENOSPC. Avoid this by always aligning args->minlen
appropriately. If alignment of minlen results in a value smaller
than the alignment constraint, fail the allocation immediately.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: John Garry <john.g.garry@oracle.com>
---
fs/xfs/libxfs/xfs_bmap.c | 45 +++++++++++++++++++++++++++-------------
1 file changed, 31 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 9131ba8113a6..c9cf138e13c4 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -3278,33 +3278,48 @@ xfs_bmap_longest_free_extent(
return 0;
}

-static xfs_extlen_t
+static int
xfs_bmap_select_minlen(
struct xfs_bmalloca *ap,
struct xfs_alloc_arg *args,
xfs_extlen_t blen)
{
-
/* Adjust best length for extent start alignment. */
if (blen > args->alignment)
blen -= args->alignment;

/*
* Since we used XFS_ALLOC_FLAG_TRYLOCK in _longest_free_extent(), it is
- * possible that there is enough contiguous free space for this request.
+ * possible that there is enough contiguous free space for this request
+ * even if best length is less that the minimum length we need.
+ *
+ * If the best length won't satisfy the maximum length we requested,
+ * then use it as the minimum length so we get as large an allocation
+ * as possible.
*/
if (blen < ap->minlen)
- return ap->minlen;
+ blen = ap->minlen;
+ else if (blen > args->maxlen)
+ blen = args->maxlen;

/*
- * If the best seen length is less than the request length,
- * use the best as the minimum, otherwise we've got the maxlen we
- * were asked for.
+ * If we have alignment constraints, round the minlen down to match the
+ * constraint so that alignment will be attempted. This may reduce the
+ * allocation to smaller than was requested, so clamp the minimum to
+ * ap->minlen to allow unaligned allocation to succeed. If we are forced
+ * to align the allocation, return ENOSPC at this point because we don't
+ * have enough contiguous free space to guarantee aligned allocation.
*/
- if (blen < args->maxlen)
- return blen;
- return args->maxlen;
-
+ if (args->alignment > 1) {
+ blen = rounddown(blen, args->alignment);
+ if (blen < ap->minlen) {
+ if (args->datatype & XFS_ALLOC_FORCEALIGN)
+ return -ENOSPC;
+ blen = ap->minlen;
+ }
+ }
+ args->minlen = blen;
+ return 0;
}

static int
@@ -3340,8 +3355,7 @@ xfs_bmap_btalloc_select_lengths(
if (pag)
xfs_perag_rele(pag);

- args->minlen = xfs_bmap_select_minlen(ap, args, blen);
- return error;
+ return xfs_bmap_select_minlen(ap, args, blen);
}

/* Update all inode and quota accounting for the allocation we just did. */
@@ -3661,7 +3675,10 @@ xfs_bmap_btalloc_filestreams(
goto out_low_space;
}

- args->minlen = xfs_bmap_select_minlen(ap, args, blen);
+ error = xfs_bmap_select_minlen(ap, args, blen);
+ if (error)
+ goto out_low_space;
+
if (ap->aeof && ap->offset)
error = xfs_bmap_btalloc_at_eof(ap, args);

--
2.31.1