Subject: Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and
 `mem_cgroup_shrink_node`
To: Michal Hocko <mhocko@kernel.org>
References: <20161108170340.GB4127@linux.vnet.ibm.com>
 <6c717122-e671-b086-77ed-4b3c26398564@molgen.mpg.de>
 <20161108183938.GD4127@linux.vnet.ibm.com>
 <9f87f8f0-9d0f-f78f-8dca-993b09b19a69@molgen.mpg.de>
 <20161116173036.GK3612@linux.vnet.ibm.com>
 <20161121134130.GB18112@dhcp22.suse.cz>
 <20161121140122.GU3612@linux.vnet.ibm.com>
 <20161121141818.GD18112@dhcp22.suse.cz>
 <20161121142901.GV3612@linux.vnet.ibm.com>
 <68025f6c-6801-ab46-b0fc-a9407353d8ce@molgen.mpg.de>
 <20161124101525.GB20668@dhcp22.suse.cz>
Cc: dvteam@molgen.mpg.de, Paul Menzel <pmenzel@molgen.mpg.de>,
        linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        Josh Triplett <josh@joshtriplett.org>
From: Donald Buczek <buczek@molgen.mpg.de>
Message-ID: <918a163c-52af-3c5e-85db-9829cce9ae2b@molgen.mpg.de>
Date: Thu, 24 Nov 2016 19:50:51 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101
 Thunderbird/45.4.0
MIME-Version: 1.0
In-Reply-To: <20161124101525.GB20668@dhcp22.suse.cz>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1861
Lines: 49

On 24.11.2016 11:15, Michal Hocko wrote:

> On Mon 21-11-16 16:35:53, Donald Buczek wrote:
> [...]
>> Hello,
>>
>> thanks a lot for looking into this!
>>
>> Let me add some information from the reporting site:
>>
>> * We've tried the patch from Paul E. McKenney (the one posted Wed, 16 Nov
>> 2016)  and it doesn't shut up the rcu stall warnings.
>>
>> * Log file from a boot with the patch applied ( grep kernel
>> /var/log/messages ) is here :
>> http://owww.molgen.mpg.de/~buczek/321322/2016-11-21_syslog.txt
>>
>> * This system is a backup server and walks over thousands of files sometimes
>> with multiple parallel rsync processes.
>>
>> * No rcu_* warnings on that machine with 4.7.2, but with 4.8.4 , 4.8.6 ,
>> 4.8.8 and now 4.9.0-rc5+Pauls patch
> I assume you haven't tried the Linus 4.8 kernel without any further
> stable patches? Just to be sure we are not talking about some later
> regression which found its way to the stable tree.
>
>> * When the backups are actually happening there might be relevant memory
>> pressure from inode cache and the rsync processes. We saw the oom-killer
>> kick in on another machine with same hardware and similar (a bit higher)
>> workload. This other machine also shows a lot of rcu stall warnings since
>> 4.8.4.
>>
>> * We see "rcu_sched detected stalls" also on some other machines since we
>> switched to 4.8 but not as frequently as on the two backup servers. Usually
>> there's "shrink_node" and "kswapd" on the top of the stack. Often
>> "xfs_reclaim_inodes" variants on top of that.
> I would be interested to see some reclaim tracepoints enabled. Could you
> try that out? At least mm_shrink_slab_{start,end} and
> mm_vmscan_lru_shrink_inactive. This should tell us more about how the
> reclaim behaved.

We'll try that tomorrow!

Donald

-- 
Donald Buczek
buczek@molgen.mpg.de
Tel: +49 30 8413 1433