linux-kernel - Re: [patch 0/7] improve memcg oom killer robustness v2

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Date:	Mon, 16 Sep 2013 20:02:44 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	azurIt <azurit@...ox.sk>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org, cgroups@...r.kernel.org, x86@...nel.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 0/7] improve memcg oom killer robustness v2

On Mon, Sep 16, 2013 at 10:52:46PM +0200, azurIt wrote:
> > CC: "Johannes Weiner" <hannes@...xchg.org>, "Andrew Morton" <akpm@...ux-foundation.org>, "David Rientjes" <rientjes@...gle.com>, "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>, "KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>, linux-mm@...ck.org, cgroups@...r.kernel.org, x86@...nel.org, linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
> >On Mon 16-09-13 17:05:43, azurIt wrote:
> >> > CC: "Johannes Weiner" <hannes@...xchg.org>, "Andrew Morton" <akpm@...ux-foundation.org>, "David Rientjes" <rientjes@...gle.com>, "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>, "KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>, linux-mm@...ck.org, cgroups@...r.kernel.org, x86@...nel.org, linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
> >> >On Mon 16-09-13 16:13:16, azurIt wrote:
> >> >[...]
> >> >> >You can use sysrq+l via serial console to see tasks hogging the CPU or
> >> >> >sysrq+t to see all the existing tasks.
> >> >> 
> >> >> 
> >> >> Doesn't work here, it just prints 'l' resp. 't'.
> >> >
> >> >I am using telnet for accessing my serial consoles exported by
> >> >the multiplicator or KVM and it can send sysrq via ctrl+t (Send
> >> >Break). Check your serial console setup.
> >> 
> >> 
> >> 
> >> I'm using Raritan KVM and i created keyboard macro 'sysrq + l' resp.
> >> 'sysrq + t'. I'm also unable to use it on my local PC. Maybe it needs
> >> to be enabled somehow?
> >
> >Probably yes. echo 1 > /proc/sys/kernel/sysrq should enable all sysrq
> >commands. You can select also some of them (have a look at
> >Documentation/sysrq.txt for more information)
> 
> 
> Now it happens again and i was just looking on the server's
> htop. I'm sure that this time it was only one process (apache)
> running under user account (not root). It was taking about 100% CPU
> (about 100% of one core). I was able to kill it by hand inside htop
> but everything was very slow, server load was immediately on
> 500. I'm sure it must be related to that Johannes kernel patches
> because i'm also using i/o throttling in cgroups via Block IO
> controller so users are unable to create such a huge I/O. I will try
> to take stacks of processes but i'm not able to identify the
> problematic process so i will have to take them from *all* apache
> processes while killing them.

It would be fantastic if you could capture those stacks.  sysrq+t
captures ALL of them in one go and drops them into your syslog.

/proc/<pid>/stack for individual tasks works too.
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