Re: [PATCH] xfs/014: try a few times to create speculative preallocations

[Zorro Lang <zlang@redhat.com>]

On Mon, Jan 03, 2022 at 06:04:17PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> This test checks that speculative file preallocations are transferred to
> threads writing other files when space is low.  Since we have background
> threads to clear those preallocations, it's possible that the test
> program might not get a speculative preallocation on the first try.
> 
> This problem has become more pronounced since the introduction of
> background inode inactivation since userspace no longer has direct
> control over the timing of file blocks being released from unlinked
> files.  As a result, the author has seen an increase in sporadic
> warnings from this test about speculative preallocations not appearing.
> 
> Therefore, modify the function to try up to five times to create the
> speculative preallocation before emitting warnings that then cause
> golden output failures.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  tests/xfs/014 |   41 +++++++++++++++++++++++++----------------
>  1 file changed, 25 insertions(+), 16 deletions(-)
> 
> diff --git a/tests/xfs/014 b/tests/xfs/014
> index a605b359..1f0ebac3 100755
> --- a/tests/xfs/014
> +++ b/tests/xfs/014
> @@ -33,27 +33,36 @@ _cleanup()
>  # failure.
>  _spec_prealloc_file()
>  {
> -	file=$1
> +	local file=$1
> +	local prealloc_size=0
> +	local i=0
>  
> -	rm -f $file
> +	# Now that we have background garbage collection processes that can be
> +	# triggered by low space/quota conditions, it's possible that we won't
> +	# succeed in creating a speculative preallocation on the first try.
> +	for ((tries = 0; tries < 5 && prealloc_size == 0; tries++)); do
> +		rm -f $file
>  
> -	# a few file extending open-write-close cycles should be enough to
> -	# trigger the fs to retain preallocation. write 256k in 32k intervals to
> -	# be sure
> -	for i in $(seq 0 32768 262144); do
> -		$XFS_IO_PROG -f -c "pwrite $i 32k" $file >> $seqres.full
> +		# a few file extending open-write-close cycles should be enough
> +		# to trigger the fs to retain preallocation. write 256k in 32k
> +		# intervals to be sure
> +		for i in $(seq 0 32768 262144); do
> +			$XFS_IO_PROG -f -c "pwrite $i 32k" $file >> $seqres.full
> +		done
> +
> +		# write a 4k aligned amount of data to keep the calculations
> +		# simple
> +		$XFS_IO_PROG -c "pwrite 0 128m" $file >> $seqres.full
> +
> +		size=`_get_filesize $file`
> +		blocks=`stat -c "%b" $file`
> +		blocksize=`stat -c "%B" $file`
> +
> +		prealloc_size=$((blocks * blocksize - size))

So we only try same pwrite operations 5 times, and only check the prealloc_size after 5
times done? Should we break from this loop once prealloc_size > 0?

Thanks,
Zorro

>  	done
>  
> -	# write a 4k aligned amount of data to keep the calculations simple
> -	$XFS_IO_PROG -c "pwrite 0 128m" $file >> $seqres.full
> -
> -	size=`_get_filesize $file`
> -	blocks=`stat -c "%b" $file`
> -	blocksize=`stat -c "%B" $file`
> -
> -	prealloc_size=$((blocks * blocksize - size))
>  	if [ $prealloc_size -eq 0 ]; then
> -		echo "Warning: No speculative preallocation for $file." \
> +		echo "Warning: No speculative preallocation for $file after $tries iterations." \
>  			"Check use of the allocsize= mount option."
>  	fi
>  
>