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

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Message-ID: <1313046422.18195.YahooMailNeo@web111711.mail.gq1.yahoo.com>
Date:	Thu, 11 Aug 2011 00:07:02 -0700 (PDT)
From:	Mahmood Naderan <nt_mahmood@...oo.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	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

>The default behavior is to kill all eligible and unkillable threads until 
>there are none left to sacrifice (i.e. all kthreads and OOM_DISABLE).
 
In a simple test with virtualbox, I reduced the amount of ram to 300MB. 
Then I ran "swapoff -a" and opened some applications. I noticed that the free
spaces is kept around 2-3MB and "kswapd" is running. Also I saw that disk
activity was very high. 
That mean although "swap" partition is turned off, "kswapd" was trying to do
something. I wonder how that behavior can be explained?

>Ok, so you don't have a /proc/pid/oom_score_adj, so you're using a kernel 
>that predates 2.6.36.
Yes, the srv machine that I posted those results, has kernel before 2.6.36



// Naderan *Mahmood;


----- Original Message -----
From: David Rientjes <rientjes@...gle.com>
To: Mahmood Naderan <nt_mahmood@...oo.com>
Cc: Randy Dunlap <rdunlap@...otime.net>; ""linux-kernel@...r.kernel.org"" <linux-kernel@...r.kernel.org>; "linux-mm@...ck.org" <linux-mm@...ck.org>
Sent: Thursday, August 11, 2011 8:39 AM
Subject: Re: running of out memory => kernel crash

On Wed, 10 Aug 2011, Mahmood Naderan wrote:

> >If you're using cpusets or mempolicies, you must ensure that all tasks 
> >attached to either of them are not set to OOM_DISABLE.  It seems unlikely 
> >that you're using those, so it seems like a system-wide oom condition.
>  
> I didn't do that manually. What is the default behaviour? Does oom
> working or not?
> 

The default behavior is to kill all eligible and unkillable threads until 
there are none left to sacrifice (i.e. all kthreads and OOM_DISABLE).

> For a user process:
> 
> root@srv:~# cat /proc/18564/oom_score
> 9198
> root@srv:~# cat /proc/18564/oom_adj
> 0
> 

Ok, so you don't have a /proc/pid/oom_score_adj, so you're using a kernel 
that predates 2.6.36.

> And for "init" process:
> 
> root@srv:~# cat /proc/1/oom_score
> 17509
> root@srv:~# cat /proc/1/oom_adj
> 0
> 
> Based on my understandings, in an out of memory condition (oom),
> the init process is more eligible to be killed!!!!!!! Is that right?
> 

init is exempt from oom killing, it's oom_score is meaningless.

> Again I didn't get my answer yet:
> What is the default behavior of linux in an oom condition? If the default is,
> crash (kernel panic), then how can I change that in such a way to kill
> the hungry process?
> 

You either have /proc/sys/vm/panic_on_oom set or it's killing a thread 
that is taking down the entire machine.  If it's the latter, then please 
capture the kernel log and post it as Randy suggested.
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