Re: [PATCH] generic: test cloning large exents to a file with many small extents

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Jun 27, 2019 at 06:00:30PM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> Test that if we clone a file with some large extents into a file that has
> many small extents, when the fs is nearly full, the clone operation does
> not fail and produces the correct result.
> 
> This is motivated by a bug found in btrfs wich is fixed by the following
> patches for the linux kernel:
> 
>  [PATCH 1/2] Btrfs: factor out extent dropping code from hole punch handler
>  [PATCH 2/2] Btrfs: fix ENOSPC errors, leading to transaction aborts, when
>              cloning extents
> 
> The test currently passes on xfs.
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
>  tests/generic/558     | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/558.out |  5 ++++
>  tests/generic/group   |  1 +
>  3 files changed, 81 insertions(+)
>  create mode 100755 tests/generic/558
>  create mode 100644 tests/generic/558.out
> 
> diff --git a/tests/generic/558 b/tests/generic/558
> new file mode 100755
> index 00000000..ee16cdf7
> --- /dev/null
> +++ b/tests/generic/558
> @@ -0,0 +1,75 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2019 SUSE Linux Products GmbH. All Rights Reserved.
> +#
> +# FSQA Test No. 558
> +#
> +# Test that if we clone a file with some large extents into a file that has
> +# many small extents, when the fs is nearly full, the clone operation does
> +# not fail and produces the correct result.
> +#
> +seq=`basename $0`
> +seqres=$RESULT_DIR/$seq
> +echo "QA output created by $seq"
> +tmp=/tmp/$$
> +status=1	# failure is the default!
> +trap "_cleanup; exit \$status" 0 1 2 3 15
> +
> +_cleanup()
> +{
> +	cd /
> +	rm -f $tmp.*
> +}
> +
> +# get standard environment, filters and checks
> +. ./common/rc
> +. ./common/filter
> +. ./common/reflink
> +
> +# real QA test starts here
> +_supported_fs generic
> +_supported_os Linux
> +_require_scratch_reflink
> +
> +rm -f $seqres.full
> +
> +_scratch_mkfs_sized $((512 * 1024 * 1024)) >>$seqres.full 2>&1
> +_scratch_mount
> +
> +file_size=$(( 128 * 1024 * 1024 )) # 128Mb
> +extent_size=4096

What if the fs block size is 64k?

> +num_extents=$(( $file_size / $extent_size ))
> +
> +# Create a file with many small extents.
> +for ((i = 0; i < $num_extents; i++)); do
> +	offset=$(( $i * $extent_size ))
> +	$XFS_IO_PROG -f -s -c "pwrite -S 0xe5 $offset $extent_size" \
> +		$SCRATCH_MNT/foo >>/dev/null
> +done

I wouldn't have thought that this would actually succeed on xfs because
you could lay extents down one after the other, but then started seeing
this in the filefrag output:

File size of /opt/foo is 528384 (129 blocks of 4096 bytes)
 ext:     logical_offset:        physical_offset: length:   expected: flags:
   3:       17..      17:         52..        52:      1:         37:
   4:       18..      18:         67..        67:      1:         53:
   5:       19..      19:         81..        81:      1:         68:
   6:       20..      20:         94..        94:      1:         82:
   7:       21..      21:        106..       106:      1:         95:
   8:       22..      22:        117..       117:      1:        107:
   9:       23..      23:        127..       127:      1:        118:
  10:       24..      24:        136..       136:      1:        128:
  11:       25..      25:        144..       144:      1:        137:
  12:       26..      26:        151..       151:      1:        145:
  13:       27..      27:        157..       157:      1:        152:
  14:       28..      28:        162..       162:      1:        158:
  15:       29..      29:        166..       166:      1:        163:
  16:       30..      30:        169..       169:      1:        167:
  17:       31..      32:        171..       172:      2:        170:
  18:       33..      33:        188..       188:      1:        173:

52, 67, 81, 94, 106, 117, 127, 136, 44, 151, 157, 162, 166, 169, 171...

 +15 +14 +13 +12  +11  +10   +9   +8  +7   +6   +5   +4   +3   +2...

Hm, I wonder what quirk of the xfs allocator this might be?

> +
> +# Create file bar with the same size that file foo has but with large extents.
> +$XFS_IO_PROG -f -c "pwrite -S 0xc7 -b $file_size 0 $file_size" \
> +	$SCRATCH_MNT/bar >>/dev/null
> +
> +# Fill the fs (for btrfs we are interested in filling all unallocated space
> +# and most of the existing metadata block group(s), so that after this there
> +# will be no unallocated space and metadata space will be mostly full but with
> +# more than enough free space for the clone operation below to succeed).
> +i=1
> +while true; do
> +	$XFS_IO_PROG -f -c "pwrite 0 2K" $SCRATCH_MNT/filler_$i &> /dev/null
> +	[ $? -ne 0 ] && break
> +	i=$(( i + 1 ))
> +done

_fill_fs?

> +
> +# Now clone file bar into file foo. This is supposed to succeed and not fail
> +# with ENOSPC for example.
> +$XFS_IO_PROG -c "reflink $SCRATCH_MNT/bar" $SCRATCH_MNT/foo >>/dev/null

_reflink $SCRATCH_MNT/bar $SCRATCH_MNT/foo ?

--D

> +
> +_scratch_remount
> +
> +echo "File foo data after cloning and remount:"
> +od -A d -t x1 $SCRATCH_MNT/foo
> +
> +status=0
> +exit
> diff --git a/tests/generic/558.out b/tests/generic/558.out
> new file mode 100644
> index 00000000..d1e8e70f
> --- /dev/null
> +++ b/tests/generic/558.out
> @@ -0,0 +1,5 @@
> +QA output created by 558
> +File foo data after cloning and remount:
> +0000000 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7
> +*
> +134217728
> diff --git a/tests/generic/group b/tests/generic/group
> index 543c0627..c06c1cd1 100644
> --- a/tests/generic/group
> +++ b/tests/generic/group
> @@ -560,3 +560,4 @@
>  555 auto quick cap
>  556 auto quick casefold
>  557 auto quick log
> +558 auto clone
> -- 
> 2.11.0
>