Re: [PATCH] btrfs: test whether fallocate(2) can preallocate half of the whole fs space

[Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>]

hello,

On 07/20/2016 05:25 PM, Filipe Manana wrote:
> On Wed, Jul 20, 2016 at 8:34 AM, Wang Xiaoguang
> <wangxg.fnst@cn.fujitsu.com> wrote:
>> Currently in btrfs, there is something wrong with data space reservation.
>> For example, if we try to preallocate more than haf of whole fs space,
>> ENOSPC will occur, but indeed fs still has free space to satisfy this
>> request.
>>
>> To easily reproduce this bug, this test case needs fs is mixed mode(btrfs
>> specific), so put this test case in btrfs group, not generic group.
> Why does it need to be in mixed mode (why is it easier)? As far as I
> can see from the corresponding btrfs patch (and its description),
> the problem affects non-mixed mode, therefore it could be a generic test.
In btrfs mixed mode, as you know, data and metadata share the same
btrfs_space_info. In btrfs_fallocate(), if we try to pre-allocate 64M data,
it first makes bytes_may_use += 64M,  later btrfs_reserve_extent()
only makes bytes_reserved += 64M, but does not decrease bytes_may_use.
Assume our fs is 128M, now bytes_may_use + bytes_reserved is already
greater than 128M, so any later transaction operations in 
btrfs_fallocate() will
fail for ENOSPC reason. But note, byte_may_use will only be decreased in end
of btrfs_fallocate(). So I think this bug is easy to reproduce in mixed 
mode  :)

For non-mixed mode, still assume fs is 128M. For data's btrfs_space_info,
before we call  btrfs_free_reserved_data_space() in end of 
btrfs_fallocate(), though
bytes_may_use +=64M, bytes_reserved += 64M, and bytes_may_use +
bytes_reserved > 128M, there is no other process to allocating data 
space, so
there will still be no ENOSPC error.

I have rewritten a test case which do write(2) and fallocate(2) in 
parallel and
put this test case to generic group, thanks.


Regards,
Xiaoguang Wang

>
>> Signed-off-by: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>
>> ---
>>   tests/btrfs/127     | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   tests/btrfs/127.out |  2 ++
>>   tests/btrfs/group   |  1 +
>>   3 files changed, 64 insertions(+)
>>   create mode 100755 tests/btrfs/127
>>   create mode 100644 tests/btrfs/127.out
>>
>> diff --git a/tests/btrfs/127 b/tests/btrfs/127
>> new file mode 100755
>> index 0000000..f95c72f
>> --- /dev/null
>> +++ b/tests/btrfs/127
>> @@ -0,0 +1,61 @@
>> +#! /bin/bash
>> +# FS QA Test 127
>> +#
>> +# Test whether fallocate(2) can preallocate half of the whole fs space.
>> +#
>> +#-----------------------------------------------------------------------
>> +# Copyright (c) 2016 Fujitsu.  All Rights Reserved.
>> +#
>> +# 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
>> +
>> +# Modify as appropriate.
>> +_supported_fs btrfs
>> +_supported_os Linux
>> +_require_scratch
>> +
>> +MKFS_OPTIONS="-M"
> This now overrides any specific mkfs options specified in the command
> line, doesn't it?
>
>> +_scratch_mkfs_sized $((256 * 1024 * 1024)) >> $seqres.full 2>&1
>> +_scratch_mount
>> +
>> +$XFS_IO_PROG -f -c "falloc 0 128M" $SCRATCH_MNT/testfile | _filter_xfs_io
> No need for the filter here.
>
>> +
>> +echo "Silence is golden"
>> +status=0
>> +exit
>> diff --git a/tests/btrfs/127.out b/tests/btrfs/127.out
>> new file mode 100644
>> index 0000000..0af84c0
>> --- /dev/null
>> +++ b/tests/btrfs/127.out
>> @@ -0,0 +1,2 @@
>> +QA output created by 127
>> +Silence is golden
>> diff --git a/tests/btrfs/group b/tests/btrfs/group
>> index a21a80a..4c3ac00 100644
>> --- a/tests/btrfs/group
>> +++ b/tests/btrfs/group
>> @@ -129,3 +129,4 @@
>>   124 auto replace
>>   125 auto replace
>>   126 auto quick qgroup
>> +127 auto quick metadata enospc
>> --
>> 2.9.0
>>
>>
>>
>> --
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>
>