Re: [PATCH 5/7] generic/563: Increase the write tolerance to 6% for larger nodesize

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2025/7/29 15:51, Nirjhar Roy (IBM) 写道:
> When tested with blocksize/nodesize 64K on powerpc
> with 64k  pagesize on btrfs, then the test fails
> with the folllowing error:
>       QA output created by 563
>       read/write
>       read is in range
>      -write is in range
>      +write has value of 8855552
>      +write is NOT in range 7969177.6 .. 8808038.4

I can reproduce the failure, although it's not 100% reliable, and indeed 
with one tree block's size removed, it's back into the tolerance range.

>       write -> read/write
>      ...
> The slight increase in the amount of bytes that
> are written is because of the increase in the
> the nodesize(metadata) and hence it exceeds the tolerance limit slightly.
> Fix this by increasing the write tolerance limit from 5% from 6%
> for 64k blocksize btrfs.
> 
> Reported-by: Disha Goel <disgoel@linux.ibm.com>
> Signed-off-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@gmail.com>
> ---
>   tests/generic/563 | 17 ++++++++++++++++-
>   1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/generic/563 b/tests/generic/563
> index 89a71aa4..efcac1ec 100755
> --- a/tests/generic/563
> +++ b/tests/generic/563
> @@ -119,7 +119,22 @@ $XFS_IO_PROG -c "pread 0 $iosize" -c "pwrite -b $blksize 0 $iosize" -c fsync \
>   	$SCRATCH_MNT/file >> $seqres.full 2>&1
>   switch_cg $cgdir
>   $XFS_IO_PROG -c fsync $SCRATCH_MNT/file
> -check_cg $cgdir/$seq-cg $iosize $iosize 5% 5%
> +blksz=`_get_block_size $SCRATCH_MNT`
> +
> +# On higher node sizes on btrfs, we observed slightly more
> +# writes, due to increased metadata sizes.
> +# Hence have a higher write tolerance for btrfs and when
> +# node size is greater than 4k.
> +if [[ "$FSTYP" == "btrfs" ]]; then
> +	nodesz=$(_get_btrfs_node_size "$SCRATCH_DEV")
> +	if [[ "$nodesz" -gt 4096 ]]; then
> +		check_cg $cgdir/$seq-cg $iosize $iosize 5% 6%
> +	else
> +		check_cg $cgdir/$seq-cg $iosize $iosize 5% 5%
> +	fi
> +else
> +	check_cg $cgdir/$seq-cg $iosize $iosize 5% 5%
> +fi

Instead of the btrfs specific hack, I'd recommend to just enlarge iosize.

Double the iosize will easily make it to cover the tolerance of even 
btrfs, but you still need a proper explanation of the change.

Thanks,
Qu

>   
>   # Write from one cgroup then read and write from a second. Writes are charged to
>   # the first group and nothing to the second.