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Date: Thu, 26 Aug 2010 10:11:39 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: David Rientjes <rientjes@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, Minchan Kim <minchan.kim@gmail.com>
Subject: Re: [PATCH 1/2][BUGFIX] oom: remove totalpage normalization from
 oom_badness()
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On Wed, 25 Aug 2010 17:52:06 -0700 (PDT)
David Rientjes <rientjes@google.com> wrote:

> On Thu, 26 Aug 2010, KAMEZAWA Hiroyuki wrote:
> 
> > I'm now trying to write a userspace tool to calculate this, for me.
> > Then, could you update documentation ? 
> > ==
> > 3.2 /proc/<pid>/oom_score - Display current oom-killer score
> > -------------------------------------------------------------
> > 
> > This file can be used to check the current score used by the oom-killer is for
> > any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
> > process should be killed in an out-of-memory situation.
> > ==
> > 
> 
> You'll want to look at section 3.1 of Documentation/filesystems/proc.txt, 
> which describes /proc/pid/oom_score_adj, not 3.2.
> 
> > add a some documentation like:
> > ==
> > (For system monitoring tool developpers, not for usual users.)
> > oom_score calculation is implemnentation dependent and can be modified without
> > any caution. But current logic is
> > 
> > oom_score = ((proc's rss + proc's swap) / (available ram + swap)) + oom_score_adj
> > 
> 
> I'd hesitate to state the formula outside of the implementation and 
> instead focus on the semantics of oom_score_adj (as a proportion of 
> available memory compared to other tasks), which I tried doing in section 
> 3.1.  Then, the userspace tool only need be concerned about the units of 
> oom_score_adj rather than whether rss, swap, or later extentions such as 
> shm are added.
> 
Hmm. I'll add a text like following to cgroup/memory.txt. O.K. ?

==
Notes on oom_score and oom_score_adj.

oom_score is calculated as
	oom_score = (taks's proportion of memory) + oom_score_adj.

Then, when you use oom_score_adj to control the order of priority of oom,
you should know about the amount of memory you can use.
So, an approximate oom_score under memcg can be

 memcg_oom_score = (oom_score - oom_score_adj) * system_memory/memcg's limit
		+ oom_score_adj.

And yes, this can be affected by hierarchy control of memcg and calculation
will be more complicated. See, oom_disable feature also.
==

Thanks,
-Kame












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