Re: [BUG] "Quota Ignored On write" problem still exist with 3.16-rc5

[Wang Shilong <wangsl.fnst@cn.fujitsu.com>]

Hi Satoru-san,

On 07/23/2014 08:53 AM, Satoru Takeuchi wrote:
> Hi Wang,
>
> (2014/07/18 19:29), Wang Shilong wrote:
>> On 07/18/2014 04:45 PM, Satoru Takeuchi wrote:
>>> Hi Josef, Chris,
>>>
>>> I found "Quota Ignored On write" problem still exist with 3.16-rc5,
>>> which Kevin reported before.
>>>
>>> Kevin's report:
>>> https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg35292.html
>>>
>>> The result of bisect:
>>> https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg35304.html
>> I guess this is because Josef's patch delayed qgroup accounting, it will
>> cause @refer and @excl updating very late...
>>
>> The patch maybe optimize to merge some delayed refs(for example), but
>> it updates qgroup accounting when commiting transaction which will be
>> very late,
>> we may have accumulated many data..
> Thank you for your comment. I know of the code logic which caused
> this problem. However, what I want to say here is that this
> problem should be fixed as soon as possible. It is a important
> regression problem and we've already know the root cause.
>
> If it's impossible to fix it by releasing 3.16, I consider this
> patch should be reverted.
Since Btrfs Quota function is under heavy development, and should be
considered as *broken*.

I think we'd better close Btrfs quota function(Like snapshot-aware function)
until we really sit down and solve everything.

Thanks,
Wang
>
> Thanks,
> Satoru
>
>> Thanks,
>> Wang
>>>> I bisected and found the bad commit is the following patch.
>>>>
>>>> ===============================================================================
>>>> commit fcebe4562dec83b3f8d3088d77584727b09130b2
>>>> Author: Josef Bacik <jba...@fb.com>
>>>> Date:   Tue May 13 17:30:47 2014 -0700
>>>>
>>>>      Btrfs: rework qgroup accounting
>>>> ===============================================================================
>>>>
>>>> Josef, please take a look at this patch.
>>> Reproducer:
>>> https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg35299.html
>>>
>>> Could you tell me the progress of fixing this bug?
>>> In addition, could you fix it by 3.16?
>>>
>>> command log:
>>> ===============================================================================
>>> # ./test.sh
>>> + uname -a
>>> Linux luna.soft.fujitsu.com 3.16.0-rc5 #2 SMP Tue Jul 15 13:39:46 JST 2014 x86_64 x86_64 x86_64 GNU/Linux
>>> + df -T /test7
>>> Filesystem     Type  1K-blocks  Used Available Use% Mounted on
>>> /dev/sdc7      btrfs  29296640  1536  27169536   1% /test7
>>> + btrfs quota ena /test7
>>> + cd /test7
>>> + btrfs sub cre test
>>> Create subvolume './test'
>>> + btrfs sub l -a /test7
>>> ID 270 gen 66 top level 5 path test
>>> + btrfs qg lim 1G test                          # limit test subvol to 1GB
>>> + btrfs qg show -pcre /test7
>>> qgroupid rfer  excl  max_rfer   max_excl parent  child
>>> -------- ----  ----  --------   -------- ------  -----
>>> 0/5      16384 16384 0          0        ---     ---
>>> 0/270    16384 16384 1073741824 0        ---     ---
>>> + dd if=/dev/zero of=test/file0 bs=1M count=2000
>>> 2000+0 records in
>>> 2000+0 records out
>>> 2097152000 bytes (2.1 GB) copied, 9.67876 s, 217 MB/s   # write 2GB. It's a bug!
>>> + sync
>>> + ls -lisaR /test7
>>> /test7:
>>> total 20
>>> 256 16 drwxr-xr-x   1 root root    8 Jul 18 15:12 .
>>>    2  4 drwxr-xr-x. 43 root root 4096 Jul 16 08:34 ..
>>> 256  0 drwxr-xr-x   1 root root   10 Jul 18 15:17 test
>>>
>>> /test7/test:
>>> total 2048016
>>> 256       0 drwxr-xr-x 1 root root         10 Jul 18 15:17 .
>>> 256      16 drwxr-xr-x 1 root root          8 Jul 18 15:12 ..
>>> 257 2048000 -rw-r--r-- 1 root root 2097152000 Jul 18 15:17 file0
>>> + btrfs qg show -pcre /test7
>>> qgroupid rfer       excl       max_rfer   max_excl parent  child
>>> -------- ----       ----       --------   -------- ------  -----
>>> 0/5      16384      16384      0          0        ---     ---
>>> 0/270    2097168384 2097168384 1073741824 0        ---     ---
>>> + btrfs quota dis /test7
>>> + btrfs sub del test
>>> Transaction commit: none (default)
>>> Delete subvolume '/test7/test'
>>> + set +x
>>> #
>>> ===============================================================================
>>>
>>>    NOTE:
>>>    The reproducer here (./test.sh) is a bit different from above-mentioned
>>>    one because of some reason.
>>>
>>> Thanks,
>>> Satoru
>>>
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> .
>