Re: [PATCH 6/7] generic/774: reduce file size

[John Garry <john.g.garry@oracle.com>]

On 10/11/2025 18:27, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> We've gotten complaints about this test taking hours to run and
> producing stall warning on test VMs with a large number of cpu cores.  I
> think this is due to the maximum atomic write unit being very large on
> XFS where we can fall back to a software-based out of place write
> implementation.
> 
> On the victim machine, the atomic write max is 4MB and there are 24
> CPUs.  As a result, aw_bsize to be 1MB, so the file size is
> 1MB * 24 * 2 * 100 == 4.8GB.  I set up a test machine with fast storage
> and 24 CPUs, and the atomic writes poked along at 25MB/s and the total
> runtime was 300s.  On spinning rust those stats will be much worse.
> 
> Let's try backing the file size off by 10x and see if that eases the
> complaints.
> 

The awu max for xfs is still unbounded (so the file size could still be 
huge). For ext4, it is limited by HW constraints - the largest HW awu 
max I heard about is 256KB. How about also limiting awu max to something 
sane, like 1MB?

> Cc: <fstests@vger.kernel.org> # v2025.10.20
> Fixes: 9117fb93b41c38 ("generic: Add atomic write test using fio verify on file mixed mappings")
> Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
> ---
>   tests/generic/774 |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 
> diff --git a/tests/generic/774 b/tests/generic/774
> index 7a4d70167f9959..28886ed5b09ff7 100755
> --- a/tests/generic/774
> +++ b/tests/generic/774
> @@ -29,7 +29,7 @@ aw_bsize=$(_max "$awu_min_write" "$((awu_max_write/4))")
>   fsbsize=$(_get_block_size $SCRATCH_MNT)
>   
>   threads=$(_min "$(($(nproc) * 2 * LOAD_FACTOR))" "100")
> -filesize=$((aw_bsize * threads * 100))
> +filesize=$((aw_bsize * threads * 10))
>   depth=$threads
>   aw_io_size=$((filesize / threads))
>   aw_io_inc=$aw_io_size
>