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Date: Tue, 1 Dec 2009 14:20:08 -0800 (PST)
From: David Rientjes <rientjes@google.com>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
cc: Andrea Arcangeli <aarcange@redhat.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>, vedran.furac@gmail.com
Subject: Re: [PATCH] oom_kill: use rss value instead of vm size for badness
In-Reply-To: <20091201131509.5C19.A69D9226@jp.fujitsu.com>
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References: <20091127182607.GA30235@random.random> <alpine.DEB.2.00.0911301502160.12038@chino.kir.corp.google.com> <20091201131509.5C19.A69D9226@jp.fujitsu.com>
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On Tue, 1 Dec 2009, KOSAKI Motohiro wrote:

> > The purpose of /proc/pid/oom_adj is not always to polarize the heuristic 
> > for the task it represents, it allows userspace to define when a task is 
> > rogue.  Working with total_vm as a baseline, it is simple to use the 
> > interface to tune the heuristic to prefer a certain task over another when 
> > its memory consumption goes beyond what is expected.  With this interface, 
> > I can easily define when an application should be oom killed because it is 
> > using far more memory than expected.  I can also disable oom killing 
> > completely for it, if necessary.  Unless you have a consistent baseline 
> > for all tasks, the adjustment wouldn't contextually make any sense.  Using 
> > rss does not allow users to statically define when a task is rogue and is 
> > dependent on the current state of memory at the time of oom.
> > 
> > I would support removing most of the other heuristics other than the 
> > baseline and the nodes intersection with mems_allowed to prefer tasks in 
> > the same cpuset, though, to make it easier to understand and tune.
> 
> I feel you talked about oom_adj doesn't fit your use case. probably you need
> /proc/{pid}/oom_priority new knob. oom adjustment doesn't fit you.
> you need job severity based oom killing order. severity doesn't depend on any
> hueristic.
> server administrator should know job severity on his system.
> 

That's the complete opposite of what I wrote above, we use oom_adj to 
define when a user application is considered "rogue," meaning that it is 
using far more memory than expected and so we want it killed.  As you 
mentioned weeks ago, the kernel cannot identify a memory leaker; this is 
the user interface to allow the oom killer to identify a memory-hogging 
rogue task that will (probably) consume all system memory eventually.  
The way oom_adj is implemented, with a bit shift on a baseline of 
total_vm, it can also polarize the badness heuristic to kill an 
application based on priority by examining /proc/pid/oom_score, but that 
wasn't my concern in this case.  Using rss as a baseline reduces my 
ability to tune oom_adj appropriately to identify those rogue tasks 
because it is highly dynamic depending on the state of the VM at the time 
of oom.
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