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

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

On Thu, Jan 06, 2022 at 12:19:05AM +0800, Zorro Lang wrote:
> 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?

The second clause of the for loop tests for that, does it not?

--D

> 
> 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
> >  
> > 
>