diff mbox

overlay: test concurrent copy up

Message ID 1484492478-13883-1-git-send-email-amir73il@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Amir Goldstein Jan. 15, 2017, 3:01 p.m. UTC
Run 4 process pairs, each competing over copy up of 1K files
in 1 directory. One opponent touches all files in the directory
and the other truncates all files in the directory.

This test does NOT check for concurrent copy up support. It only
fails on unexpected errors of any of the touch/truncate operations.

The test full output should demonstrate the expected results -
for kernel with concurrent copy up support, truncate workers are
not delayed by touch workers. As a result, truncate workers will
finish their work much sooner than a test run without concurrent
copy up support.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 tests/overlay/021     | 163 ++++++++++++++++++++++++++++++++++++++++++++++++++
 tests/overlay/021.out |   2 +
 tests/overlay/group   |   1 +
 3 files changed, 166 insertions(+)
 create mode 100755 tests/overlay/021
 create mode 100644 tests/overlay/021.out

Eryu,

I wrote this test to excercise "ovl: concurrent copy up", but it does not
require concurrent copy up support to run, nor does it fail due to lack of
concurrent copy up support (it may run a bit slower), so there is nothing
blocking from merging this test for kernel 4.9.

Note that although I used fsstress to create/truncate a bunch of files,
this is by no means a stress test, so I did not add it to stress group.
It is rather 'quick', less than half the time of the 'quick' overlay/001.

Amir.

Comments

Eryu Guan Jan. 16, 2017, 9:11 a.m. UTC | #1
On Sun, Jan 15, 2017 at 05:01:18PM +0200, Amir Goldstein wrote:
> Run 4 process pairs, each competing over copy up of 1K files
> in 1 directory. One opponent touches all files in the directory
> and the other truncates all files in the directory.
> 
> This test does NOT check for concurrent copy up support. It only
> fails on unexpected errors of any of the touch/truncate operations.
> 
> The test full output should demonstrate the expected results -
> for kernel with concurrent copy up support, truncate workers are
> not delayed by touch workers. As a result, truncate workers will
> finish their work much sooner than a test run without concurrent
> copy up support.
> 
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  tests/overlay/021     | 163 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/overlay/021.out |   2 +
>  tests/overlay/group   |   1 +
>  3 files changed, 166 insertions(+)
>  create mode 100755 tests/overlay/021
>  create mode 100644 tests/overlay/021.out
> 
> Eryu,
> 
> I wrote this test to excercise "ovl: concurrent copy up", but it does not
> require concurrent copy up support to run, nor does it fail due to lack of
> concurrent copy up support (it may run a bit slower), so there is nothing
> blocking from merging this test for kernel 4.9.

Agreed.

> 
> Note that although I used fsstress to create/truncate a bunch of files,
> this is by no means a stress test, so I did not add it to stress group.
> It is rather 'quick', less than half the time of the 'quick' overlay/001.

Agreed.

> 
> Amir.
> 
> diff --git a/tests/overlay/021 b/tests/overlay/021
> new file mode 100755
> index 0000000..405d3d0
> --- /dev/null
> +++ b/tests/overlay/021
> @@ -0,0 +1,163 @@
> +#! /bin/bash
> +# FS QA Test 021
> +#
> +# test concurrent copy up
> +#
> +#-----------------------------------------------------------------------
> +# Copyright (C) 2016 CTERA Networks. All Rights Reserved.
> +# Author: Amir Goldstein <amir73il@gmail.com>
> +#
> +# This program is free software; you can redistribute it and/or
> +# modify it under the terms of the GNU General Public License as
> +# published by the Free Software Foundation.
> +#
> +# This program is distributed in the hope that it would be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program; if not, write the Free Software Foundation,
> +# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
> +#-----------------------------------------------------------------------
> +#
> +
> +seq=`basename $0`
> +seqres=$RESULT_DIR/$seq
> +echo "QA output created by $seq"
> +
> +here=`pwd`
> +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
> +
> +# remove previous $seqres.full before test
> +rm -f $seqres.full
> +
> +# real QA test starts here
> +_supported_fs overlay
> +_supported_os Linux
> +_require_scratch
> +
> +# Remove all files from previous tests
> +_scratch_mkfs
> +
> +# overlay copy_up doesn't deal with sparse file well, holes will be filled by
> +# zeros, so for the worst case of hitting all the copy up bomb files, we need
> +# (64*(16+32+64+128)M) free space on $SCRATCH_DEV.
> +# However, triggering more than a total of 16 copy up bombs would require
> +# really fast data copy (clone up doesn't take up space at all), so let's be
> +# conservative and reserve space for 16 data copy ups per directory.
> +_require_fs_space $SCRATCH_DEV $((16*(16+32+64+128)*1024))
> +
> +lowerdir=$SCRATCH_DEV/$OVERLAY_LOWER_DIR
> +mkdir -p $lowerdir
> +
> +_scratch_mount
> +
> +echo "Silence is golden"
> +
> +testdir=arena
> +d_low=$lowerdir/$testdir
> +d_top=$SCRATCH_MNT/$testdir
> +mkdir -p $d_low
> +
> +# Create 4K empty files in 4 directories
> +echo $FSSTRESS_PROG -d $d_low -p 4 -z -f creat=1 -n 1024 -v >> $seqres.full
> +$FSSTRESS_PROG -d $d_low -p 4 -z -f creat=1 -n 1024 -v >> $seqres.full 2>&1
> +echo "--------------------------------------"       >> $seqres.full
> +echo "Created 1K files in lower directory.  "       >> $seqres.full
> +
> +# Plant 64 copy up bombs in each directory
> +for f in $d_low/p0/*0; do truncate -s 128M $f ;done
> +for f in $d_low/p1/*4; do truncate -s 64M $f ;done
> +for f in $d_low/p2/*8; do truncate -s 32M $f ;done
> +for f in $d_low/p3/*b; do truncate -s 16M $f ;done

Better to use $XFS_IO_PROG -c "truncate <size>" $f, some distros like
RHEL5 don't have truncate command. RHEL5 is really old and should not be
a big problem, but we have better choice, so why not :)

> +echo "Created 64*4 copy up bombs.           "       >> $seqres.full
> +echo "--------------------------------------"       >> $seqres.full

All these setups should be done before overlay is mounted, because we're
writing to the lowerdir directly, which is undefined behavior when
overlay is mounted. i.e. call _scratch_mount only after all these setups.

> +
> +#
> +# Run 2 process teams - 4 pairs of rival processes
> +# Each process pair competing on copy up of 1K files in 1 directory.
> +# Team 'touch' players touch all files in readdir order.
> +# Team 'truncate' players truncates all files in numeric (name) order.
> +#
> +# If player from team 'touch' reaches a copy up bomb before player
> +# from team 'truncate' does, the copy up of (sparse) data will delay
> +# the end of the process pair match.
> +#
> +# If copy up of bomb is not concurrent with other copy ups, then
> +# 'touch' player p0 with the largest copy up bombs will delay players
> +# of both teams and all matches will take longer.
> +#
> +# If copy up is concurrent with copy ups in different directories,
> +# process pair 3 match will be over first and process pair 0 match
> +# will be over last.
> +#
> +# If copy up of data is concurrent with other copy ups on the same directory,
> +# then all the 'touch' team players will finish far behind their 'truncate'
> +# opponenets.
> +#
> +# This test doesn't verify any of those conditions, it will only fail
> +# on unexpected errors of any of the touch/truncate operations.
> +# The test full output should demonstrate the expected game results,
> +# as described above and depending on concurrent copy up support in kernel.
> +#
> +cd $d_top
> +echo "--------------------------------------"       >> $seqres.full
> +echo "Go team touch!!                       "       >> $seqres.full
> +find p0 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
> +find p1 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
> +find p2 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
> +find p3 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &

find seems not returning non-zero if touch fails. I did this experiment
and find always returned 0.

# create 16 empty files
./ltp/fsstress -d testdir -p 1 -z -f creat=1 -n 16

# make all files immutable
find testdir -type f -exec chattr +i {} \;

# touch all files, touch should report "Operation not permitted", and
# check return status of find
find testdir -type f -print -exec touch {} \;
echo $?


So how about letting stderr break golden image when touch error happens?

find p0 -type f -print -exec touch {} \; >> $seqres.full &

> +cd - > /dev/null
> +
> +# Give team 'touch' a 1 second head start.
> +# Team 'truncate' players should catch up after few copy up bombs.
> +sleep 1
> +echo "--------------------------------------"       >> $seqres.full
> +echo "Go team truncate!!                    "       >> $seqres.full
> +# Give team 'touch' a 1 second head start.
> +# Team 'truncate' players should catch up after few copy up bombs.
> +sleep 1

Redundant "sleep 1" and comments?

> +$FSSTRESS_PROG -d $d_top -p 4 -z -f creat=1 -n 1024 -v >> $seqres.full 2>&1 &
> +
> +err=0
> +if ! wait %1; then
> +	echo "Player p0/touch returned $? - see $seqres.full"
> +	err=1
> +fi
> +
> +if ! wait %2; then
> +	echo "Player p1/touch returned $? - see $seqres.full"
> +	err=1
> +fi
> +
> +if ! wait %3; then
> +	echo "Player p2/touch returned $? - see $seqres.full"
> +	err=1
> +fi
> +
> +if ! wait %4; then
> +	echo "Player p3/touch returned $? - see $seqres.full"
> +	err=1
> +fi

Then no need to check job %1-4 status, if we rely on stderr of find.

Thanks,
Eryu

> +
> +if ! wait %5; then
> +	echo "Team truncate returned $? - see $seqres.full"
> +	err=1
> +fi
> +
> +status=$err
> +
> +exit $status
> diff --git a/tests/overlay/021.out b/tests/overlay/021.out
> new file mode 100644
> index 0000000..09f4062
> --- /dev/null
> +++ b/tests/overlay/021.out
> @@ -0,0 +1,2 @@
> +QA output created by 021
> +Silence is golden
> diff --git a/tests/overlay/group b/tests/overlay/group
> index 684ed45..5bcc25e 100644
> --- a/tests/overlay/group
> +++ b/tests/overlay/group
> @@ -23,3 +23,4 @@
>  018 auto quick copyup
>  019 auto stress
>  020 auto quick copyup perms
> +021 auto quick copyup
> -- 
> 2.7.4
> 
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Amir Goldstein Jan. 16, 2017, 10:20 a.m. UTC | #2
On Mon, Jan 16, 2017 at 11:11 AM, Eryu Guan <eguan@redhat.com> wrote:
> On Sun, Jan 15, 2017 at 05:01:18PM +0200, Amir Goldstein wrote:
>> Run 4 process pairs, each competing over copy up of 1K files
>> in 1 directory. One opponent touches all files in the directory
>> and the other truncates all files in the directory.
>>
>> This test does NOT check for concurrent copy up support. It only
>> fails on unexpected errors of any of the touch/truncate operations.
>>
>> The test full output should demonstrate the expected results -
>> for kernel with concurrent copy up support, truncate workers are
>> not delayed by touch workers. As a result, truncate workers will
>> finish their work much sooner than a test run without concurrent
>> copy up support.
>>
>> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
>> ---
>>  tests/overlay/021     | 163 ++++++++++++++++++++++++++++++++++++++++++++++++++
>>  tests/overlay/021.out |   2 +
>>  tests/overlay/group   |   1 +
>>  3 files changed, 166 insertions(+)
>>  create mode 100755 tests/overlay/021
>>  create mode 100644 tests/overlay/021.out
>>
>> Eryu,
>>
>> I wrote this test to excercise "ovl: concurrent copy up", but it does not
>> require concurrent copy up support to run, nor does it fail due to lack of
>> concurrent copy up support (it may run a bit slower), so there is nothing
>> blocking from merging this test for kernel 4.9.
>
> Agreed.
>
>>
>> Note that although I used fsstress to create/truncate a bunch of files,
>> this is by no means a stress test, so I did not add it to stress group.
>> It is rather 'quick', less than half the time of the 'quick' overlay/001.
>
> Agreed.
>
>>
>> Amir.
>>
>> diff --git a/tests/overlay/021 b/tests/overlay/021
>> new file mode 100755
>> index 0000000..405d3d0
>> --- /dev/null
>> +++ b/tests/overlay/021
>> @@ -0,0 +1,163 @@
>> +#! /bin/bash
>> +# FS QA Test 021
>> +#
>> +# test concurrent copy up
>> +#
>> +#-----------------------------------------------------------------------
>> +# Copyright (C) 2016 CTERA Networks. All Rights Reserved.
>> +# Author: Amir Goldstein <amir73il@gmail.com>
>> +#
>> +# This program is free software; you can redistribute it and/or
>> +# modify it under the terms of the GNU General Public License as
>> +# published by the Free Software Foundation.
>> +#
>> +# This program is distributed in the hope that it would be useful,
>> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> +# GNU General Public License for more details.
>> +#
>> +# You should have received a copy of the GNU General Public License
>> +# along with this program; if not, write the Free Software Foundation,
>> +# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
>> +#-----------------------------------------------------------------------
>> +#
>> +
>> +seq=`basename $0`
>> +seqres=$RESULT_DIR/$seq
>> +echo "QA output created by $seq"
>> +
>> +here=`pwd`
>> +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
>> +
>> +# remove previous $seqres.full before test
>> +rm -f $seqres.full
>> +
>> +# real QA test starts here
>> +_supported_fs overlay
>> +_supported_os Linux
>> +_require_scratch
>> +
>> +# Remove all files from previous tests
>> +_scratch_mkfs
>> +
>> +# overlay copy_up doesn't deal with sparse file well, holes will be filled by
>> +# zeros, so for the worst case of hitting all the copy up bomb files, we need
>> +# (64*(16+32+64+128)M) free space on $SCRATCH_DEV.
>> +# However, triggering more than a total of 16 copy up bombs would require
>> +# really fast data copy (clone up doesn't take up space at all), so let's be
>> +# conservative and reserve space for 16 data copy ups per directory.
>> +_require_fs_space $SCRATCH_DEV $((16*(16+32+64+128)*1024))
>> +
>> +lowerdir=$SCRATCH_DEV/$OVERLAY_LOWER_DIR
>> +mkdir -p $lowerdir
>> +
>> +_scratch_mount
>> +
>> +echo "Silence is golden"
>> +
>> +testdir=arena
>> +d_low=$lowerdir/$testdir
>> +d_top=$SCRATCH_MNT/$testdir
>> +mkdir -p $d_low
>> +
>> +# Create 4K empty files in 4 directories
>> +echo $FSSTRESS_PROG -d $d_low -p 4 -z -f creat=1 -n 1024 -v >> $seqres.full
>> +$FSSTRESS_PROG -d $d_low -p 4 -z -f creat=1 -n 1024 -v >> $seqres.full 2>&1
>> +echo "--------------------------------------"       >> $seqres.full
>> +echo "Created 1K files in lower directory.  "       >> $seqres.full
>> +
>> +# Plant 64 copy up bombs in each directory
>> +for f in $d_low/p0/*0; do truncate -s 128M $f ;done
>> +for f in $d_low/p1/*4; do truncate -s 64M $f ;done
>> +for f in $d_low/p2/*8; do truncate -s 32M $f ;done
>> +for f in $d_low/p3/*b; do truncate -s 16M $f ;done
>
> Better to use $XFS_IO_PROG -c "truncate <size>" $f, some distros like
> RHEL5 don't have truncate command. RHEL5 is really old and should not be
> a big problem, but we have better choice, so why not :)
>

Oh. That's good to know.

>> +echo "Created 64*4 copy up bombs.           "       >> $seqres.full
>> +echo "--------------------------------------"       >> $seqres.full
>
> All these setups should be done before overlay is mounted, because we're
> writing to the lowerdir directly, which is undefined behavior when
> overlay is mounted. i.e. call _scratch_mount only after all these setups.
>

ok.

>> +
>> +#
>> +# Run 2 process teams - 4 pairs of rival processes
>> +# Each process pair competing on copy up of 1K files in 1 directory.
>> +# Team 'touch' players touch all files in readdir order.
>> +# Team 'truncate' players truncates all files in numeric (name) order.
>> +#
>> +# If player from team 'touch' reaches a copy up bomb before player
>> +# from team 'truncate' does, the copy up of (sparse) data will delay
>> +# the end of the process pair match.
>> +#
>> +# If copy up of bomb is not concurrent with other copy ups, then
>> +# 'touch' player p0 with the largest copy up bombs will delay players
>> +# of both teams and all matches will take longer.
>> +#
>> +# If copy up is concurrent with copy ups in different directories,
>> +# process pair 3 match will be over first and process pair 0 match
>> +# will be over last.
>> +#
>> +# If copy up of data is concurrent with other copy ups on the same directory,
>> +# then all the 'touch' team players will finish far behind their 'truncate'
>> +# opponenets.
>> +#
>> +# This test doesn't verify any of those conditions, it will only fail
>> +# on unexpected errors of any of the touch/truncate operations.
>> +# The test full output should demonstrate the expected game results,
>> +# as described above and depending on concurrent copy up support in kernel.
>> +#
>> +cd $d_top
>> +echo "--------------------------------------"       >> $seqres.full
>> +echo "Go team touch!!                       "       >> $seqres.full
>> +find p0 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
>> +find p1 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
>> +find p2 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
>> +find p3 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
>
> find seems not returning non-zero if touch fails. I did this experiment
> and find always returned 0.
>
> # create 16 empty files
> ./ltp/fsstress -d testdir -p 1 -z -f creat=1 -n 16
>
> # make all files immutable
> find testdir -type f -exec chattr +i {} \;
>
> # touch all files, touch should report "Operation not permitted", and
> # check return status of find
> find testdir -type f -print -exec touch {} \;
> echo $?
>
>
> So how about letting stderr break golden image when touch error happens?
>
> find p0 -type f -print -exec touch {} \; >> $seqres.full &
>

Yes. Good idea.

>> +cd - > /dev/null
>> +
>> +# Give team 'touch' a 1 second head start.
>> +# Team 'truncate' players should catch up after few copy up bombs.
>> +sleep 1
>> +echo "--------------------------------------"       >> $seqres.full
>> +echo "Go team truncate!!                    "       >> $seqres.full
>> +# Give team 'touch' a 1 second head start.
>> +# Team 'truncate' players should catch up after few copy up bombs.
>> +sleep 1
>
> Redundant "sleep 1" and comments?
>

oops.

>> +$FSSTRESS_PROG -d $d_top -p 4 -z -f creat=1 -n 1024 -v >> $seqres.full 2>&1 &
>> +
>> +err=0
>> +if ! wait %1; then
>> +     echo "Player p0/touch returned $? - see $seqres.full"
>> +     err=1
>> +fi
>> +
>> +if ! wait %2; then
>> +     echo "Player p1/touch returned $? - see $seqres.full"
>> +     err=1
>> +fi
>> +
>> +if ! wait %3; then
>> +     echo "Player p2/touch returned $? - see $seqres.full"
>> +     err=1
>> +fi
>> +
>> +if ! wait %4; then
>> +     echo "Player p3/touch returned $? - see $seqres.full"
>> +     err=1
>> +fi
>
> Then no need to check job %1-4 status, if we rely on stderr of find.
>

Yes, that would be cleaner.
Thank!

> Thanks,
> Eryu
>
>> +
>> +if ! wait %5; then
>> +     echo "Team truncate returned $? - see $seqres.full"
>> +     err=1
>> +fi
>> +
>> +status=$err
>> +
>> +exit $status
>> diff --git a/tests/overlay/021.out b/tests/overlay/021.out
>> new file mode 100644
>> index 0000000..09f4062
>> --- /dev/null
>> +++ b/tests/overlay/021.out
>> @@ -0,0 +1,2 @@
>> +QA output created by 021
>> +Silence is golden
>> diff --git a/tests/overlay/group b/tests/overlay/group
>> index 684ed45..5bcc25e 100644
>> --- a/tests/overlay/group
>> +++ b/tests/overlay/group
>> @@ -23,3 +23,4 @@
>>  018 auto quick copyup
>>  019 auto stress
>>  020 auto quick copyup perms
>> +021 auto quick copyup
>> --
>> 2.7.4
>>
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diff mbox

Patch

diff --git a/tests/overlay/021 b/tests/overlay/021
new file mode 100755
index 0000000..405d3d0
--- /dev/null
+++ b/tests/overlay/021
@@ -0,0 +1,163 @@ 
+#! /bin/bash
+# FS QA Test 021
+#
+# test concurrent copy up
+#
+#-----------------------------------------------------------------------
+# Copyright (C) 2016 CTERA Networks. All Rights Reserved.
+# Author: Amir Goldstein <amir73il@gmail.com>
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it would be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write the Free Software Foundation,
+# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#-----------------------------------------------------------------------
+#
+
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+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
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+_supported_fs overlay
+_supported_os Linux
+_require_scratch
+
+# Remove all files from previous tests
+_scratch_mkfs
+
+# overlay copy_up doesn't deal with sparse file well, holes will be filled by
+# zeros, so for the worst case of hitting all the copy up bomb files, we need
+# (64*(16+32+64+128)M) free space on $SCRATCH_DEV.
+# However, triggering more than a total of 16 copy up bombs would require
+# really fast data copy (clone up doesn't take up space at all), so let's be
+# conservative and reserve space for 16 data copy ups per directory.
+_require_fs_space $SCRATCH_DEV $((16*(16+32+64+128)*1024))
+
+lowerdir=$SCRATCH_DEV/$OVERLAY_LOWER_DIR
+mkdir -p $lowerdir
+
+_scratch_mount
+
+echo "Silence is golden"
+
+testdir=arena
+d_low=$lowerdir/$testdir
+d_top=$SCRATCH_MNT/$testdir
+mkdir -p $d_low
+
+# Create 4K empty files in 4 directories
+echo $FSSTRESS_PROG -d $d_low -p 4 -z -f creat=1 -n 1024 -v >> $seqres.full
+$FSSTRESS_PROG -d $d_low -p 4 -z -f creat=1 -n 1024 -v >> $seqres.full 2>&1
+echo "--------------------------------------"       >> $seqres.full
+echo "Created 1K files in lower directory.  "       >> $seqres.full
+
+# Plant 64 copy up bombs in each directory
+for f in $d_low/p0/*0; do truncate -s 128M $f ;done
+for f in $d_low/p1/*4; do truncate -s 64M $f ;done
+for f in $d_low/p2/*8; do truncate -s 32M $f ;done
+for f in $d_low/p3/*b; do truncate -s 16M $f ;done
+echo "Created 64*4 copy up bombs.           "       >> $seqres.full
+echo "--------------------------------------"       >> $seqres.full
+
+#
+# Run 2 process teams - 4 pairs of rival processes
+# Each process pair competing on copy up of 1K files in 1 directory.
+# Team 'touch' players touch all files in readdir order.
+# Team 'truncate' players truncates all files in numeric (name) order.
+#
+# If player from team 'touch' reaches a copy up bomb before player
+# from team 'truncate' does, the copy up of (sparse) data will delay
+# the end of the process pair match.
+#
+# If copy up of bomb is not concurrent with other copy ups, then
+# 'touch' player p0 with the largest copy up bombs will delay players
+# of both teams and all matches will take longer.
+#
+# If copy up is concurrent with copy ups in different directories,
+# process pair 3 match will be over first and process pair 0 match
+# will be over last.
+#
+# If copy up of data is concurrent with other copy ups on the same directory,
+# then all the 'touch' team players will finish far behind their 'truncate'
+# opponenets.
+#
+# This test doesn't verify any of those conditions, it will only fail
+# on unexpected errors of any of the touch/truncate operations.
+# The test full output should demonstrate the expected game results,
+# as described above and depending on concurrent copy up support in kernel.
+#
+cd $d_top
+echo "--------------------------------------"       >> $seqres.full
+echo "Go team touch!!                       "       >> $seqres.full
+find p0 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
+find p1 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
+find p2 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
+find p3 -type f -print -exec touch {} \; >> $seqres.full 2>&1 &
+cd - > /dev/null
+
+# Give team 'touch' a 1 second head start.
+# Team 'truncate' players should catch up after few copy up bombs.
+sleep 1
+echo "--------------------------------------"       >> $seqres.full
+echo "Go team truncate!!                    "       >> $seqres.full
+# Give team 'touch' a 1 second head start.
+# Team 'truncate' players should catch up after few copy up bombs.
+sleep 1
+$FSSTRESS_PROG -d $d_top -p 4 -z -f creat=1 -n 1024 -v >> $seqres.full 2>&1 &
+
+err=0
+if ! wait %1; then
+	echo "Player p0/touch returned $? - see $seqres.full"
+	err=1
+fi
+
+if ! wait %2; then
+	echo "Player p1/touch returned $? - see $seqres.full"
+	err=1
+fi
+
+if ! wait %3; then
+	echo "Player p2/touch returned $? - see $seqres.full"
+	err=1
+fi
+
+if ! wait %4; then
+	echo "Player p3/touch returned $? - see $seqres.full"
+	err=1
+fi
+
+if ! wait %5; then
+	echo "Team truncate returned $? - see $seqres.full"
+	err=1
+fi
+
+status=$err
+
+exit $status
diff --git a/tests/overlay/021.out b/tests/overlay/021.out
new file mode 100644
index 0000000..09f4062
--- /dev/null
+++ b/tests/overlay/021.out
@@ -0,0 +1,2 @@ 
+QA output created by 021
+Silence is golden
diff --git a/tests/overlay/group b/tests/overlay/group
index 684ed45..5bcc25e 100644
--- a/tests/overlay/group
+++ b/tests/overlay/group
@@ -23,3 +23,4 @@ 
 018 auto quick copyup
 019 auto stress
 020 auto quick copyup perms
+021 auto quick copyup