linux-kernel - Re: running of out memory => kernel crash

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Date:	Fri, 19 Aug 2011 15:19:34 -0600
From:	Chris Friesen <chris.friesen@...band.com>
To:	Bryan Donlan <bdonlan@...il.com>
CC:	Pavel Ivanov <paivanof@...il.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Mahmood Naderan <nt_mahmood@...oo.com>,
	David Rientjes <rientjes@...gle.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: running of out memory => kernel crash

On 08/19/2011 01:29 PM, Bryan Donlan wrote:
> On Thu, Aug 18, 2011 at 10:26, Pavel Ivanov<paivanof@...il.com>  wrote:

>> Could you elaborate on this? We have a completely unusable server
>> which can be revived only by hard power cycling (administrators won't
>> be able to log in because sshd and shell will fall victims of the same
>> unending disk reading). And as an alternative we can kill some process
>> and at least allow administrator to log in and check if something else
>> can be done to make server feel better. Why is it worse?
>>
>> I understand that it could be very hard to detect such situation but
>> at least it's worth trying I think.
>
> Deciding when to call the server unusable is a policy decision that
> the kernel can't make very easily on its own; the point when the
> system is considered unusable may be different depending on workload.
> You could create a userspace daemon, however, that mlockall()s, then
> monitors memory usage, load average, etc and kills processes when
> things start to go south. You could also use the memory resource
> cgroup controller to set hard limits on memory usage.

Indeed.  From the point of view of the OS, it's running everything on 
the system without a problem.  It's deep into swap, but it's running.

If there are application requirements on grade-of-service, it's up to 
the application to check whether those are being met and if not to do 
something about it.

Chris

-- 
Chris Friesen
Software Developer
GENBAND
chris.friesen@...band.com
www.genband.com
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