linux-kernel - Re: Memory overcommit

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Message-Id: <20091030084836.5428e085.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 30 Oct 2009 08:48:36 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	vedran.furac@...il.com, Hugh Dickins <hugh.dickins@...cali.co.uk>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	minchan.kim@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: Memory overcommit

On Thu, 29 Oct 2009 12:53:42 -0700 (PDT)
David Rientjes <rientjes@...gle.com> wrote:

> > If you have OOM situation and Xorg is the first, that means it's leaking
> > memory badly and the system is probably already frozen/FUBAR. Killing
> > krunner in that situation wouldn't do any good. From a user perspective,
> > nothing changes, system is still FUBAR and (s)he would probably reboot
> > cursing linux in the process.
> > 
> 
> It depends on what you're running, we need to be able to have the option 
> of protecting very large tasks on production servers.  Imagine if "test" 
> here is actually a critical application that we need to protect, its 
> not solely mlocked anonymous memory, but still kill if it is leaking 
> memory beyond your approximate 2.5GB.  How do you do that when using rss 
> as the baseline?

As I wrote repeatedly,

   - OOM-Killer itselfs is bad thing, bad situation.
   - The kernel can't know the program is bad or not. just guess it.
   - Then, there is no "correct" OOM-Killer other than fork-bomb killer.
   - User has a knob as oom_adj. This is very strong.

Then, there is only "reasonable" or "easy-to-understand" OOM-Kill.
"Current biggest memory eater is killed" sounds reasonable, easy to
understand. And if total_vm works well, overcommit_guess should catch it.
Please improve overcommit_guess if you want to stay on total_vm.


Thanks,
-Kame

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