Re: Possible memory allocation deadlock in kmem_alloc and hung task in xfs_log_commit_cil and xlog_cil_push

From: juncheng bai <baijuncheng@unitedstack.com>
To: Gavin Guo <gavin.guo@canonical.com>, Dave Chinner <david@fromorbit.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>, xfs@oss.sgi.com
Subject: Re: Possible memory allocation deadlock in kmem_alloc and hung task in xfs_log_commit_cil and xlog_cil_push
Date: Wed, 08 Jul 2015 22:06:10 +0800	[thread overview]
Message-ID: <559D2E52.2070900@unitedstack.com> (raw)
In-Reply-To: <CA+eFSM2mSSW-BtP5-ArHREPu9sRRO3=J8acWJ-h_iZHfLPnhiw@mail.gmail.com>

Hi, All

As far as I know, the patch b3f03bac8132207a20286d5602eda64500c19724 
solves one case which big directory size.

I am not very familiar with xfs, but I think why can't we use vmalloc
when kmalloc fails?

Thanks.
--------------
juncheng bai

On 2015/7/8 20:34, Gavin Guo wrote:
> Hi Dave,
>
> On Wed, Jul 8, 2015 at 7:37 AM, Dave Chinner <david@fromorbit.com> wrote:
>> On Tue, Jul 07, 2015 at 05:29:43PM +0800, Gavin Guo wrote:
>>> Hi all,
>>>
>>> Recently, we observed that there is the error message in
>>> Ubuntu-3.13.0-48.80:
>>>
>>> "XFS: possible memory allocation deadlock in kmem_alloc (mode:0x8250)"
>>>
>>> repeatedly shows in the dmesg. Temporarily, our workaround is to tune the
>>> parameters, such as, vfs_cache_pressure, min_free_kbytes, and dirty_ratio.
>>>
>>> And we also found that there are different error messages regarding the
>>> hung tasks which happened in xfs_log_commit_cil and xlog_cil_push.
>>>
>>> The log is available at: http://paste.ubuntu.com/11835007/
>>>
>>> The following link seems the same problem we suffered:
>>>
>>> XFS hangs with XFS: possible memory allocation deadlock in kmem_alloc
>>> http://oss.sgi.com/archives/xfs/2015-03/msg00172.html
>>>
>>> I read the mail and found that there might be some modification regarding
>>> to move the memory allocation outside the ctx lock. And I also read the
>>> latest patch from February of 2015 to see if there is any new change
>>> about that. Unfortunately, I didn't find anything regarding the change (may
>>> be I'm not familiar with the XFS, so didn't find the commit). If it's
>>> possible for someone who is familiar with the code to point out the commits
>>> related to the bug if already exist or any status about the plan.
>>
>> No commits - the approach I thought we might be able to take to
>> avoid the problem didn't work out. I have another idea of how we
>> might solve the problem, but I haven't ad a chance to prototype it
>> yet.
>>
>> Cheers,
>>
>> Dave.
>> --
>> Dave Chinner
>> david@fromorbit.com
>
> Really thanks for your information, I'll keep watching out the status.
>
> Thanks,
> Gavin Guo
>
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