Re: [PATCH] generic/301: skip extent count check on btrfs

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Mar 24, 2026 at 01:40:00PM -0700, Leo Martins wrote:
> The 2/3 fragmentation threshold was designed for XFS's cowextsize
> mechanism and is not applicable to btrfs. After commit 0dc118b3c327
> ("btrfs: be less aggressive with metadata overcommit when we can do
> full flushing"), btrfs commits transactions more frequently during
> writeback, reducing the extent allocator's opportunity to coalesce
> adjacent CoW extents. This causes the extent count to sometimes cross
> the threshold, making the test flaky on btrfs.
> 
> Skip only the extent count assertion for btrfs while keeping the CoW
> write + remount + md5sum data integrity checks, which remain useful.
> 
> Signed-off-by: Leo Martins <loemra.dev@gmail.com>

Seems reasonable to me,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  tests/generic/301 | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/generic/301 b/tests/generic/301
> index 0303f25d..985d943a 100755
> --- a/tests/generic/301
> +++ b/tests/generic/301
> @@ -62,7 +62,12 @@ new_extents=$(_count_extents $testdir/file2)
>  echo "old extents: $old_extents" >> $seqres.full
>  echo "new extents: $new_extents" >> $seqres.full
>  echo "maximum extents: $internal_blks" >> $seqres.full
> -test $new_extents -lt $((internal_blks * 2 / 3)) || echo "file2 badly fragmented"
> +# btrfs CoW extent allocation depends on transaction commit frequency and
> +# metadata reservation behavior, so the 2/3 fragmentation threshold (designed
> +# for XFS cowextsize) is not applicable.
> +if [ "$FSTYP" != "btrfs" ]; then
> +	test $new_extents -lt $((internal_blks * 2 / 3)) || echo "file2 badly fragmented"
> +fi
>  
>  # success, all done
>  status=0
> -- 
> 2.52.0
> 
>