[Users] ploop on ext4 without journal - bug?

Wed Oct 7 11:57:44 PDT 2015

Do I understand right - after all patches (in a little bit future) ploop 
should work fine on ext4 without journal with any data= mount option?

And if I have journal - I should use data=ordered to avoid silent bugs?

If ext4 has journal - there is known "feature" with mysql - mysql is 
much faster (near two times in my tests) if mount options are 
"data=journal,journal_async_commit" (and may be with O_DIRECT flag) 
compared to data=ordered. How to configure (if it's possible) such setup 
in case when mysql is inside CT with ploop on ext4 with journal and 
data=ordered?

07.10.2015 21:05, Dmitry Monakhov пишет:
> Nick Knutov <mail at knutov.com> writes:
>
>
> yes, I'm using SSDs.
>
> Partition was
> tune2fs -O ^has_journal /dev/sdX
> so I thought the journal was removed completely and data= section is not
> important at all.
> WOW.. This is hilarious. Indeed even w/o journal ext4 show journal
> related options in /proc/mounts. This is bug(minor, but still). I'll
> prepare patch for mainstream.
>
>> Ok, what is the right way to fix it for me now?
> Ok. If you want to run your host w/o journal than it is ok. We do not
> test such configuration, but it does not contradict to any assumptions.
>> Will
>> remount with data=ordered (and still tune2fs -O ^has_journal)
>> be fine?
> No you do not have to modify /etc/fstab
>> Was that fixed bug already compiled and sent to yum repository (package
>> ploop I suppose) ?
> This was kernel's issue. Just update your kernel to most recent one
> (042stab112_3 or higher)
>
> #yum update vzkernel
>>
>> 07.10.2015 17:03, Dmitry Monakhov пишет:
>>> Sergey Bronnikov <sergeyb at openvz.org> writes:
>>>
>>>> Dima, could you help?
>>>>
>>>> On 02:08 Wed 30 Sep , Nick Knutov wrote:
>>>>> Hello all,
>>>>>
>>>>> I have an ext4 partition without journal (I need it so):
>>> First of all. The subject you mentioned is incorrect. This is not
>>> nojournal mode. Configuration you want to create is external journal
>> with data=journal.
>>> data=journal is full data journaling mode. Such mode assumes that it
>>> will pass through journal all data, but ploop directly issues bios to
>>> lower-fs(i.e. baypass journal). This done for performance reasons. That
>>> is why ploop is faster that any other solutions.
>>> All this means that full journaling for lower(/vz/private) fs is not
>>> compatible with ploop. So please do not use it, otherwise you'll get
>>> undefined behavior (most likely silent corruptions in guest-fs)
>>>
>>> The glitch you have mentioned most likely happen due to the fact that
>>> you use SSD. Recently we have found a bug in mm reclaim code which
>>> result in deadlock (swap on ssd in our case)
>> https://jira.sw.ru/browse/PSBM-39335
>>> Bug was fixed here:
>>> *diff-ms-mm-vmscan-do-not-wait-for-page-writeback-for-GFP_NOFS-allocations
>>> Added to 042stab112_3
>>>
>>> mm, vmscan: Do not wait for page writeback for GFP_NOFS
>>> Backport of mainline patch ecf5fc6e9654
>>>
>>>>> mount | grep vz2
>>>>> /dev/sde1 on /vz2 type ext4
>> (rw,relatime,discard,errors=remount-ro,commit=20,data=journal,journal_async_commit)
>>>>> debugfs -R features /dev/sde1
>>>>> debugfs 1.41.12 (17-May-2010)
>>>>> Filesystem features: ext_attr resize_inode dir_index filetype extent
>> flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
>>>>> When I'm trying to create CT with ploop layout - I've got
>>>>>
>>>>> Creating image: /vz2/private/2008.tmp/root.hdd/root.hdd size=10485760K
>>>>> Creating delta /vz2/private/2008.tmp/root.hdd/root.hdd bs=2048
>> size=20971520 sectors v2
>>>>> Storing /vz2/private/2008.tmp/root.hdd/DiskDescriptor.xml
>>>>> WARNING: /vz2 is mounted with data=writeback not recommended for
>> ploop; please use data=ordered instead
>>>>> Opening delta /vz2/private/2008.tmp/root.hdd/root.hdd
>>>>> Adding delta dev=/dev/ploop58376
>> img=/vz2/private/2008.tmp/root.hdd/root.hdd (rw)
>>>>> and now it freezes. (btw, vzctl says it's data=writeback, but it's
>>>>> data=journal and journal is removed - is it ok?)
>>>>>
>>>>>
>>>>> When ctrl+c I've got:
>>>>>
>>>>> ^C
>>>>> Cancelling...
>>>>> Cancelling...
>>>>> Destroying container private area: /vz2/private/2008.tmp
>>>>> ^C
>>>>> Cancelling...
>>>>> Cancelling...
>>>>>
>>>>> so I have to log in other ssh session and kill -9 it.
>>>>>
>>>>> Kernel: 042stab108.8
>>>>>
>>>>> Is it a bug or I'm doing something wrong?
>>>>>
>>>>> --
>>>>> Best Regards,
>>>>> Nick Knutov
>>>>> http://knutov.com
>>>>> ICQ: 272873706
>>>>> Voice: +7-904-84-23-130
>>>>>
>>>>> _______________________________________________
>>>>> Users mailing list
>>>>> Users at openvz.org
>>>>> https://lists.openvz.org/mailman/listinfo/users
>> - -- 
>> Best Regards,
>> Nick Knutov
>> http://knutov.com
>> ICQ: 272873706
>> Voice: +7-904-84-23-130
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-- 
Best Regards,
Nick Knutov
http://knutov.com
ICQ: 272873706
Voice: +7-904-84-23-130