linux-kernel - Re: Misleading OOM messages

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Message-ID: <alpine.DEB.2.00.0905141412130.30300@chino.kir.corp.google.com>
Date:	Thu, 14 May 2009 14:12:23 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Nick Piggin <npiggin@...e.de>, Mel Gorman <mel@....ul.ie>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	San Mehat <san@...roid.com>, Arve Hj?nnev?g <arve@...roid.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Misleading OOM messages

On Thu, 14 May 2009, Dave Hansen wrote:

> On Thu, 2009-05-14 at 13:49 -0700, David Rientjes wrote:
> > I think switching all the oom killer messages to be "no available memory" 
> > as it is in the MPOL_BIND case would be the best alternative.  We 
> > currently use "out of memory" even for cpusets, for example, when it 
> > happens because it cannot accommodate any more hardwall allocations while 
> > there may be an abundance of memory elsewhere that it cannot access.  I 
> > also think "no available memory" makes more sense than "out of memory" 
> > when describing situations where we're at or below the minimum watermarks 
> > for all allowable zones.  Either that or "no allowable memory".
> 
> How about something like this to start?  We can "mv mm/oom_kill.c
> mm/nam_kill.c" later. ;)
> 

I don't think it's that easy, I think we need to indicate what the set of 
available memory is.  For instance, we need to show the nodes that 
MPOL_BIND is allowed to access, what the hard limit for the memory cgroup 
is, what current->mems_allowed is for cpuset ooms, why we can't allocate 
in ZONE_DMA or ZONE_DMA32 because of lowmem_reserve_ratio, etc.

oom_kill_allocating_task, for instance, can indicate all of the above 
scenarios but it doesn't show the cause for the oom like others do, even 
with your patch.  It simply shows that 
/proc/sys/vm/oom_kill_allocating_task was set to avoid the expensive 
tasklist scan.
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