[PATCH 0/2] fstests: prevent dm-log-writes out of order replay issues

[PATCH 0/2] fstests: prevent dm-log-writes out of order replay issues

[Brian Foster]

Here's a stab at addressing the out-of-order write issues reproduced by
generic/482 on XFS v5 filesystems. Patch 1 refactors the code to allow
for use of an arbitrary device and patch 2 fixes up generic/482 to use a
thinly provisioned replay device.

This could be factored in different ways and/or be implemented across
the other tests, but the focus here is on generic/482.

Brian

Brian Foster (2):
  common/dmlogwrites: genericize log writes target device
  generic/482: use thin volume as data device

 common/dmlogwrites | 24 ++++++++++++++++++------
 tests/generic/455  |  8 ++++----
 tests/generic/457  |  8 ++++----
 tests/generic/470  |  4 ++--
 tests/generic/482  | 20 ++++++++++++++------
 5 files changed, 42 insertions(+), 22 deletions(-)

-- 
2.17.2

[PATCH 1/2] common/dmlogwrites: genericize log writes target device

[Brian Foster]

The dm-log-writes infrastructure is currently implemented to use
SCRATCH_DEV as a hardcoded data device. In preparation to allow use
of specialized devices in certain circumstances, genericize the code
to allow an arbitrary data device. This requires passing the target
device as a parameter to several helper functions from various
tests. No functional changes.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 common/dmlogwrites | 24 ++++++++++++++++++------
 tests/generic/455  |  8 ++++----
 tests/generic/457  |  8 ++++----
 tests/generic/470  |  4 ++--
 tests/generic/482  |  4 ++--
 5 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/common/dmlogwrites b/common/dmlogwrites
index b9cbae7a..ae2cbc6a 100644
--- a/common/dmlogwrites
+++ b/common/dmlogwrites
@@ -32,7 +32,7 @@ _require_log_writes_dax()
 	_require_test_program "log-writes/replay-log"
 
 	local ret=0
-	_log_writes_init
+	_log_writes_init $SCRATCH_DEV
 	_log_writes_mkfs > /dev/null 2>&1
 	_log_writes_mount -o dax > /dev/null 2>&1
 	# Check options to be sure. XFS ignores dax option
@@ -47,10 +47,15 @@ _require_log_writes_dax()
 
 _log_writes_init()
 {
-	local BLK_DEV_SIZE=`blockdev --getsz $SCRATCH_DEV`
+	blkdev=$1
+
+	[ -z "$blkdev" ] && _fail \
+	"block dev must be specified for _log_writes_init"
+
+	local BLK_DEV_SIZE=`blockdev --getsz $blkdev`
 	LOGWRITES_NAME=logwrites-test
 	LOGWRITES_DMDEV=/dev/mapper/$LOGWRITES_NAME
-	LOGWRITES_TABLE="0 $BLK_DEV_SIZE log-writes $SCRATCH_DEV $LOGWRITES_DEV"
+	LOGWRITES_TABLE="0 $BLK_DEV_SIZE log-writes $blkdev $LOGWRITES_DEV"
 	_dmsetup_create $LOGWRITES_NAME --table "$LOGWRITES_TABLE" || \
 		_fail "failed to create log-writes device"
 }
@@ -82,17 +87,21 @@ _log_writes_unmount()
 
 # _log_writes_replay_log <mark>
 #
-# This replays the log contained on $LOGWRITES_DEV onto $SCRATCH_DEV upto the
+# This replays the log contained on $LOGWRITES_DEV onto blkdev upto the
 # mark passed in.
 _log_writes_replay_log()
 {
 	_mark=$1
+	_blkdev=$2
+
+	[ -z "$_blkdev" ] && _fail \
+	"block dev must be specified for _log_writes_replay_log"
 
 	$here/src/log-writes/replay-log --log $LOGWRITES_DEV --find \
 		--end-mark $_mark >> $seqres.full 2>&1
 	[ $? -ne 0 ] && _fail "mark '$_mark' does not exist"
 
-	$here/src/log-writes/replay-log --log $LOGWRITES_DEV --replay $SCRATCH_DEV \
+	$here/src/log-writes/replay-log --log $LOGWRITES_DEV --replay $_blkdev \
 		--end-mark $_mark >> $seqres.full 2>&1
 	[ $? -ne 0 ] && _fail "replay failed"
 }
@@ -150,16 +159,19 @@ _log_writes_find_next_fua()
 _log_writes_replay_log_range()
 {
 	local end=$1
+	local blkdev=$2
 
 	[ -z "$end" ] && _fail \
 	"end entry must be specified for _log_writes_replay_log_range"
+	[ -z "$blkdev" ] && _fail \
+	"block dev must be specified for _log_writes_replay_log_range"
 
 	# To ensure we replay the last entry,
 	# we need to manually increase the end entry number to ensure
 	# it's played
 	echo "=== replay to $end ===" >> $seqres.full
 	$here/src/log-writes/replay-log --log $LOGWRITES_DEV \
-		--replay $SCRATCH_DEV --limit $(($end + 1)) \
+		--replay $blkdev --limit $(($end + 1)) \
 		>> $seqres.full 2>&1
 	[ $? -ne 0 ] && _fail "replay failed"
 }
diff --git a/tests/generic/455 b/tests/generic/455
index 6a87b99b..05621220 100755
--- a/tests/generic/455
+++ b/tests/generic/455
@@ -42,7 +42,7 @@ check_files()
 		local filename=$(basename $i)
 		local mark="${filename##*.}"
 		echo "checking $filename" >> $seqres.full
-		_log_writes_replay_log $filename
+		_log_writes_replay_log $filename $SCRATCH_DEV
 		_scratch_mount
 		local expected_md5=$(_md5_checksum $i)
 		local md5=$(_md5_checksum $SCRATCH_MNT/$name)
@@ -57,7 +57,7 @@ rm -rf $SANITY_DIR
 mkdir $SANITY_DIR
 
 # Create the log
-_log_writes_init
+_log_writes_init $SCRATCH_DEV
 
 _log_writes_mkfs >> $seqres.full 2>&1
 
@@ -92,7 +92,7 @@ _check_scratch_fs
 
 # check pre umount
 echo "checking pre umount" >> $seqres.full
-_log_writes_replay_log last
+_log_writes_replay_log last $SCRATCH_DEV
 _scratch_mount
 _scratch_unmount
 _check_scratch_fs
@@ -103,7 +103,7 @@ done
 
 # Check the end
 echo "checking post umount" >> $seqres.full
-_log_writes_replay_log end
+_log_writes_replay_log end $SCRATCH_DEV
 _scratch_mount
 for j in `seq 0 $((NUM_FILES-1))`; do
 	md5=$(_md5_checksum $SCRATCH_MNT/testfile$j)
diff --git a/tests/generic/457 b/tests/generic/457
index c4c0ca45..82367304 100755
--- a/tests/generic/457
+++ b/tests/generic/457
@@ -44,7 +44,7 @@ check_files()
 		local filename=$(basename $i)
 		local mark="${filename##*.}"
 		echo "checking $filename" >> $seqres.full
-		_log_writes_replay_log $filename
+		_log_writes_replay_log $filename $SCRATCH_DEV
 		_scratch_mount
 		local expected_md5=$(_md5_checksum $i)
 		local md5=$(_md5_checksum $SCRATCH_MNT/$name)
@@ -59,7 +59,7 @@ rm -rf $SANITY_DIR
 mkdir $SANITY_DIR
 
 # Create the log
-_log_writes_init
+_log_writes_init $SCRATCH_DEV
 
 _log_writes_mkfs >> $seqres.full 2>&1
 
@@ -96,7 +96,7 @@ _check_scratch_fs
 
 # check pre umount
 echo "checking pre umount" >> $seqres.full
-_log_writes_replay_log last
+_log_writes_replay_log last $SCRATCH_DEV
 _scratch_mount
 _scratch_unmount
 _check_scratch_fs
@@ -107,7 +107,7 @@ done
 
 # Check the end
 echo "checking post umount" >> $seqres.full
-_log_writes_replay_log end
+_log_writes_replay_log end $SCRATCH_DEV
 _scratch_mount
 for j in `seq 0 $((NUM_FILES-1))`; do
 	md5=$(_md5_checksum $SCRATCH_MNT/testfile$j)
diff --git a/tests/generic/470 b/tests/generic/470
index a970aa80..93691f4a 100755
--- a/tests/generic/470
+++ b/tests/generic/470
@@ -39,7 +39,7 @@ _require_log_writes_dax
 _require_xfs_io_command "mmap" "-S"
 _require_xfs_io_command "log_writes"
 
-_log_writes_init
+_log_writes_init $SCRATCH_DEV
 _log_writes_mkfs >> $seqres.full 2>&1
 _log_writes_mount -o dax
 
@@ -58,7 +58,7 @@ _check_scratch_fs
 _scratch_mkfs >> $seqres.full 2>&1
 
 # check pre-unmap state
-_log_writes_replay_log preunmap
+_log_writes_replay_log preunmap $SCRATCH_DEV
 _scratch_mount
 
 # We should see $SCRATCH_MNT/test as having 1 MiB in block allocations
diff --git a/tests/generic/482 b/tests/generic/482
index 7595aa59..3c2199d7 100755
--- a/tests/generic/482
+++ b/tests/generic/482
@@ -55,7 +55,7 @@ fsstress_args=$(_scale_fsstress_args -w -d $SCRATCH_MNT -n 512 -p $nr_cpus \
 		$FSSTRESS_AVOID)
 
 _test_unmount
-_log_writes_init
+_log_writes_init $SCRATCH_DEV
 _log_writes_mkfs >> $seqres.full 2>&1
 _log_writes_mark mkfs
 
@@ -70,7 +70,7 @@ cur=$(_log_writes_find_next_fua $prev)
 [ -z "$cur" ] && _fail "failed to locate next FUA write"
 
 while [ ! -z "$cur" ]; do
-	_log_writes_replay_log_range $cur >> $seqres.full
+	_log_writes_replay_log_range $cur $SCRATCH_DEV >> $seqres.full
 
 	# Here we need extra mount to replay the log, mainly for journal based
 	# fs, as their fsck will report dirty log as error.
-- 
2.17.2

[PATCH 2/2] generic/482: use thin volume as data device

[Brian Foster]

The dm-log-writes replay mechanism issues discards to provide
zeroing functionality to prevent out-of-order replay issues. These
discards don't always result in zeroing bevavior, however, depending
on the underlying physical device. In turn, this causes test
failures on XFS v5 filesystems that enforce metadata log recovery
ordering if the filesystem ends up with stale data from the future
with respect to the active log at a particular recovery point.

To ensure reliable discard zeroing behavior, use a thinly
provisioned volume as the data device instead of using the scratch
device directly. This slows the test down slightly, but provides
reliable functional behavior at a reduced cost from active snapshot
management or forced zeroing.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 tests/generic/482 | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/tests/generic/482 b/tests/generic/482
index 3c2199d7..3b93a7fc 100755
--- a/tests/generic/482
+++ b/tests/generic/482
@@ -22,12 +22,14 @@ _cleanup()
 	cd /
 	$KILLALL_PROG -KILL -q $FSSTRESS_PROG &> /dev/null
 	_log_writes_cleanup &> /dev/null
+	_dmthin_cleanup
 	rm -f $tmp.*
 }
 
 # get standard environment, filters and checks
 . ./common/rc
 . ./common/filter
+. ./common/dmthin
 . ./common/dmlogwrites
 
 # remove previous $seqres.full before test
@@ -44,6 +46,7 @@ _require_command "$KILLALL_PROG" killall
 _require_scratch
 # and we need extra device as log device
 _require_log_writes
+_require_dm_target thin-pool
 
 
 nr_cpus=$("$here/src/feature" -o)
@@ -53,9 +56,15 @@ if [ $nr_cpus -gt 8 ]; then
 fi
 fsstress_args=$(_scale_fsstress_args -w -d $SCRATCH_MNT -n 512 -p $nr_cpus \
 		$FSSTRESS_AVOID)
+devsize=$((1024*1024*200 / 512))	# 200m phys/virt size
+csize=$((1024*64 / 512))		# 64k cluster size
+lowspace=$((1024*1024 / 512))		# 1m low space threshold
 
+# Use a thin device to provide deterministic discard behavior. Discards are used
+# by the log replay tool for fast zeroing to prevent out-of-order replay issues.
 _test_unmount
-_log_writes_init $SCRATCH_DEV
+_dmthin_init $devsize $devsize $csize $lowspace
+_log_writes_init $DMTHIN_VOL_DEV
 _log_writes_mkfs >> $seqres.full 2>&1
 _log_writes_mark mkfs
 
@@ -70,16 +79,15 @@ cur=$(_log_writes_find_next_fua $prev)
 [ -z "$cur" ] && _fail "failed to locate next FUA write"
 
 while [ ! -z "$cur" ]; do
-	_log_writes_replay_log_range $cur $SCRATCH_DEV >> $seqres.full
+	_log_writes_replay_log_range $cur $DMTHIN_VOL_DEV >> $seqres.full
 
 	# Here we need extra mount to replay the log, mainly for journal based
 	# fs, as their fsck will report dirty log as error.
-	# We don't care to preserve any data on $SCRATCH_DEV, as we can replay
+	# We don't care to preserve any data on the replay dev, as we can replay
 	# back to the point we need, and in fact sometimes creating/deleting
 	# snapshots repeatedly can be slower than replaying the log.
-	_scratch_mount
-	_scratch_unmount
-	_check_scratch_fs
+	_dmthin_mount
+	_dmthin_check_fs
 
 	prev=$cur
 	cur=$(_log_writes_find_next_fua $(($cur + 1)))
-- 
2.17.2

Re: [PATCH 1/2] common/dmlogwrites: genericize log writes target device

[Amir Goldstein]

On Thu, Feb 28, 2019 at 4:41 PM Brian Foster <bfoster@redhat.com> wrote:
>
> The dm-log-writes infrastructure is currently implemented to use
> SCRATCH_DEV as a hardcoded data device. In preparation to allow use
> of specialized devices in certain circumstances, genericize the code
> to allow an arbitrary data device. This requires passing the target
> device as a parameter to several helper functions from various
> tests. No functional changes.
>
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks ok.
Reviewed-by: Amir Goldstein <amir73il@gmail.com>

> ---
>  common/dmlogwrites | 24 ++++++++++++++++++------
>  tests/generic/455  |  8 ++++----
>  tests/generic/457  |  8 ++++----
>  tests/generic/470  |  4 ++--
>  tests/generic/482  |  4 ++--
>  5 files changed, 30 insertions(+), 18 deletions(-)
>
> diff --git a/common/dmlogwrites b/common/dmlogwrites
> index b9cbae7a..ae2cbc6a 100644
> --- a/common/dmlogwrites
> +++ b/common/dmlogwrites
> @@ -32,7 +32,7 @@ _require_log_writes_dax()
>         _require_test_program "log-writes/replay-log"
>
>         local ret=0
> -       _log_writes_init
> +       _log_writes_init $SCRATCH_DEV
>         _log_writes_mkfs > /dev/null 2>&1
>         _log_writes_mount -o dax > /dev/null 2>&1
>         # Check options to be sure. XFS ignores dax option
> @@ -47,10 +47,15 @@ _require_log_writes_dax()
>
>  _log_writes_init()
>  {
> -       local BLK_DEV_SIZE=`blockdev --getsz $SCRATCH_DEV`
> +       blkdev=$1
> +
> +       [ -z "$blkdev" ] && _fail \
> +       "block dev must be specified for _log_writes_init"
> +
> +       local BLK_DEV_SIZE=`blockdev --getsz $blkdev`
>         LOGWRITES_NAME=logwrites-test
>         LOGWRITES_DMDEV=/dev/mapper/$LOGWRITES_NAME
> -       LOGWRITES_TABLE="0 $BLK_DEV_SIZE log-writes $SCRATCH_DEV $LOGWRITES_DEV"
> +       LOGWRITES_TABLE="0 $BLK_DEV_SIZE log-writes $blkdev $LOGWRITES_DEV"
>         _dmsetup_create $LOGWRITES_NAME --table "$LOGWRITES_TABLE" || \
>                 _fail "failed to create log-writes device"
>  }
> @@ -82,17 +87,21 @@ _log_writes_unmount()
>
>  # _log_writes_replay_log <mark>
>  #
> -# This replays the log contained on $LOGWRITES_DEV onto $SCRATCH_DEV upto the
> +# This replays the log contained on $LOGWRITES_DEV onto blkdev upto the
>  # mark passed in.
>  _log_writes_replay_log()
>  {
>         _mark=$1
> +       _blkdev=$2
> +
> +       [ -z "$_blkdev" ] && _fail \
> +       "block dev must be specified for _log_writes_replay_log"
>
>         $here/src/log-writes/replay-log --log $LOGWRITES_DEV --find \
>                 --end-mark $_mark >> $seqres.full 2>&1
>         [ $? -ne 0 ] && _fail "mark '$_mark' does not exist"
>
> -       $here/src/log-writes/replay-log --log $LOGWRITES_DEV --replay $SCRATCH_DEV \
> +       $here/src/log-writes/replay-log --log $LOGWRITES_DEV --replay $_blkdev \
>                 --end-mark $_mark >> $seqres.full 2>&1
>         [ $? -ne 0 ] && _fail "replay failed"
>  }
> @@ -150,16 +159,19 @@ _log_writes_find_next_fua()
>  _log_writes_replay_log_range()
>  {
>         local end=$1
> +       local blkdev=$2
>
>         [ -z "$end" ] && _fail \
>         "end entry must be specified for _log_writes_replay_log_range"
> +       [ -z "$blkdev" ] && _fail \
> +       "block dev must be specified for _log_writes_replay_log_range"
>
>         # To ensure we replay the last entry,
>         # we need to manually increase the end entry number to ensure
>         # it's played
>         echo "=== replay to $end ===" >> $seqres.full
>         $here/src/log-writes/replay-log --log $LOGWRITES_DEV \
> -               --replay $SCRATCH_DEV --limit $(($end + 1)) \
> +               --replay $blkdev --limit $(($end + 1)) \
>                 >> $seqres.full 2>&1
>         [ $? -ne 0 ] && _fail "replay failed"
>  }
> diff --git a/tests/generic/455 b/tests/generic/455
> index 6a87b99b..05621220 100755
> --- a/tests/generic/455
> +++ b/tests/generic/455
> @@ -42,7 +42,7 @@ check_files()
>                 local filename=$(basename $i)
>                 local mark="${filename##*.}"
>                 echo "checking $filename" >> $seqres.full
> -               _log_writes_replay_log $filename
> +               _log_writes_replay_log $filename $SCRATCH_DEV
>                 _scratch_mount
>                 local expected_md5=$(_md5_checksum $i)
>                 local md5=$(_md5_checksum $SCRATCH_MNT/$name)
> @@ -57,7 +57,7 @@ rm -rf $SANITY_DIR
>  mkdir $SANITY_DIR
>
>  # Create the log
> -_log_writes_init
> +_log_writes_init $SCRATCH_DEV
>
>  _log_writes_mkfs >> $seqres.full 2>&1
>
> @@ -92,7 +92,7 @@ _check_scratch_fs
>
>  # check pre umount
>  echo "checking pre umount" >> $seqres.full
> -_log_writes_replay_log last
> +_log_writes_replay_log last $SCRATCH_DEV
>  _scratch_mount
>  _scratch_unmount
>  _check_scratch_fs
> @@ -103,7 +103,7 @@ done
>
>  # Check the end
>  echo "checking post umount" >> $seqres.full
> -_log_writes_replay_log end
> +_log_writes_replay_log end $SCRATCH_DEV
>  _scratch_mount
>  for j in `seq 0 $((NUM_FILES-1))`; do
>         md5=$(_md5_checksum $SCRATCH_MNT/testfile$j)
> diff --git a/tests/generic/457 b/tests/generic/457
> index c4c0ca45..82367304 100755
> --- a/tests/generic/457
> +++ b/tests/generic/457
> @@ -44,7 +44,7 @@ check_files()
>                 local filename=$(basename $i)
>                 local mark="${filename##*.}"
>                 echo "checking $filename" >> $seqres.full
> -               _log_writes_replay_log $filename
> +               _log_writes_replay_log $filename $SCRATCH_DEV
>                 _scratch_mount
>                 local expected_md5=$(_md5_checksum $i)
>                 local md5=$(_md5_checksum $SCRATCH_MNT/$name)
> @@ -59,7 +59,7 @@ rm -rf $SANITY_DIR
>  mkdir $SANITY_DIR
>
>  # Create the log
> -_log_writes_init
> +_log_writes_init $SCRATCH_DEV
>
>  _log_writes_mkfs >> $seqres.full 2>&1
>
> @@ -96,7 +96,7 @@ _check_scratch_fs
>
>  # check pre umount
>  echo "checking pre umount" >> $seqres.full
> -_log_writes_replay_log last
> +_log_writes_replay_log last $SCRATCH_DEV
>  _scratch_mount
>  _scratch_unmount
>  _check_scratch_fs
> @@ -107,7 +107,7 @@ done
>
>  # Check the end
>  echo "checking post umount" >> $seqres.full
> -_log_writes_replay_log end
> +_log_writes_replay_log end $SCRATCH_DEV
>  _scratch_mount
>  for j in `seq 0 $((NUM_FILES-1))`; do
>         md5=$(_md5_checksum $SCRATCH_MNT/testfile$j)
> diff --git a/tests/generic/470 b/tests/generic/470
> index a970aa80..93691f4a 100755
> --- a/tests/generic/470
> +++ b/tests/generic/470
> @@ -39,7 +39,7 @@ _require_log_writes_dax
>  _require_xfs_io_command "mmap" "-S"
>  _require_xfs_io_command "log_writes"
>
> -_log_writes_init
> +_log_writes_init $SCRATCH_DEV
>  _log_writes_mkfs >> $seqres.full 2>&1
>  _log_writes_mount -o dax
>
> @@ -58,7 +58,7 @@ _check_scratch_fs
>  _scratch_mkfs >> $seqres.full 2>&1
>
>  # check pre-unmap state
> -_log_writes_replay_log preunmap
> +_log_writes_replay_log preunmap $SCRATCH_DEV
>  _scratch_mount
>
>  # We should see $SCRATCH_MNT/test as having 1 MiB in block allocations
> diff --git a/tests/generic/482 b/tests/generic/482
> index 7595aa59..3c2199d7 100755
> --- a/tests/generic/482
> +++ b/tests/generic/482
> @@ -55,7 +55,7 @@ fsstress_args=$(_scale_fsstress_args -w -d $SCRATCH_MNT -n 512 -p $nr_cpus \
>                 $FSSTRESS_AVOID)
>
>  _test_unmount
> -_log_writes_init
> +_log_writes_init $SCRATCH_DEV
>  _log_writes_mkfs >> $seqres.full 2>&1
>  _log_writes_mark mkfs
>
> @@ -70,7 +70,7 @@ cur=$(_log_writes_find_next_fua $prev)
>  [ -z "$cur" ] && _fail "failed to locate next FUA write"
>
>  while [ ! -z "$cur" ]; do
> -       _log_writes_replay_log_range $cur >> $seqres.full
> +       _log_writes_replay_log_range $cur $SCRATCH_DEV >> $seqres.full
>
>         # Here we need extra mount to replay the log, mainly for journal based
>         # fs, as their fsck will report dirty log as error.
> --
> 2.17.2
>

Re: [PATCH 2/2] generic/482: use thin volume as data device

[Amir Goldstein]

On Thu, Feb 28, 2019 at 4:41 PM Brian Foster <bfoster@redhat.com> wrote:
>
> The dm-log-writes replay mechanism issues discards to provide
> zeroing functionality to prevent out-of-order replay issues. These
> discards don't always result in zeroing bevavior, however, depending
> on the underlying physical device. In turn, this causes test
> failures on XFS v5 filesystems that enforce metadata log recovery
> ordering if the filesystem ends up with stale data from the future
> with respect to the active log at a particular recovery point.
>
> To ensure reliable discard zeroing behavior, use a thinly
> provisioned volume as the data device instead of using the scratch
> device directly. This slows the test down slightly, but provides
> reliable functional behavior at a reduced cost from active snapshot
> management or forced zeroing.
>
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks ok. Apart from minor nit below
Reviewed-by: Amir Goldstein <amir73il@gmail.com>


> ---
>  tests/generic/482 | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/tests/generic/482 b/tests/generic/482
> index 3c2199d7..3b93a7fc 100755
> --- a/tests/generic/482
> +++ b/tests/generic/482
> @@ -22,12 +22,14 @@ _cleanup()
>         cd /
>         $KILLALL_PROG -KILL -q $FSSTRESS_PROG &> /dev/null
>         _log_writes_cleanup &> /dev/null
> +       _dmthin_cleanup
>         rm -f $tmp.*
>  }
>
>  # get standard environment, filters and checks
>  . ./common/rc
>  . ./common/filter
> +. ./common/dmthin
>  . ./common/dmlogwrites
>
>  # remove previous $seqres.full before test
> @@ -44,6 +46,7 @@ _require_command "$KILLALL_PROG" killall
>  _require_scratch
_require_scratch_nocheck

>  # and we need extra device as log device
>  _require_log_writes
> +_require_dm_target thin-pool
>
>
>  nr_cpus=$("$here/src/feature" -o)
> @@ -53,9 +56,15 @@ if [ $nr_cpus -gt 8 ]; then
>  fi
>  fsstress_args=$(_scale_fsstress_args -w -d $SCRATCH_MNT -n 512 -p $nr_cpus \
>                 $FSSTRESS_AVOID)
> +devsize=$((1024*1024*200 / 512))       # 200m phys/virt size
> +csize=$((1024*64 / 512))               # 64k cluster size
> +lowspace=$((1024*1024 / 512))          # 1m low space threshold
>
> +# Use a thin device to provide deterministic discard behavior. Discards are used
> +# by the log replay tool for fast zeroing to prevent out-of-order replay issues.
>  _test_unmount
> -_log_writes_init $SCRATCH_DEV
> +_dmthin_init $devsize $devsize $csize $lowspace
> +_log_writes_init $DMTHIN_VOL_DEV
>  _log_writes_mkfs >> $seqres.full 2>&1
>  _log_writes_mark mkfs
>
> @@ -70,16 +79,15 @@ cur=$(_log_writes_find_next_fua $prev)
>  [ -z "$cur" ] && _fail "failed to locate next FUA write"
>
>  while [ ! -z "$cur" ]; do
> -       _log_writes_replay_log_range $cur $SCRATCH_DEV >> $seqres.full
> +       _log_writes_replay_log_range $cur $DMTHIN_VOL_DEV >> $seqres.full
>
>         # Here we need extra mount to replay the log, mainly for journal based
>         # fs, as their fsck will report dirty log as error.
> -       # We don't care to preserve any data on $SCRATCH_DEV, as we can replay
> +       # We don't care to preserve any data on the replay dev, as we can replay
>         # back to the point we need, and in fact sometimes creating/deleting
>         # snapshots repeatedly can be slower than replaying the log.
> -       _scratch_mount
> -       _scratch_unmount
> -       _check_scratch_fs
> +       _dmthin_mount
> +       _dmthin_check_fs
>
>         prev=$cur
>         cur=$(_log_writes_find_next_fua $(($cur + 1)))
> --
> 2.17.2
>