linux-kernel - Re: [PATCH 2/2] oom: give bonus to frozen processes

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Message-Id: <20110926183115.277afeb1.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 26 Sep 2011 18:31:15 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Michal Hocko <mhocko@...e.cz>, Oleg Nesterov <oleg@...hat.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH 2/2] oom: give bonus to frozen processes

On Mon, 26 Sep 2011 02:02:59 -0700 (PDT)
David Rientjes <rientjes@...gle.com> wrote:

> On Mon, 26 Sep 2011, Michal Hocko wrote:
> 
> > Let's try it with a heuristic change first. If you really do not like
> > it, we can move to oom_scode_adj. I like the heuristic change little bit
> > more because it is at the same place as the root bonus.
> 
> The problem with the bonus is that, as mentioned previously, it doesn't 
> protect against ANYTHING for the case you're trying to fix.  This won't 
> panic the machine because all killable threads are guaranteed to have a 
> non-zero badness score, but it's a very valid configuration to have either
> 
>  - all eligible threads (system-wide, shared cpuset, shared mempolicy 
>    nodes) are frozen, or
> 
>  - all eligible frozen threads use <5% of memory whereas all other 
>    eligible killable threads use 1% of available memory.
> 
> and that means the oom killer will repeatedly select those threads and the 
> livelock still exists unless you can guarantee that they are successfully 
> thawed, that thawing them in all situations is safe, and that once thawed 
> they will make a timely exit.
> 
> Additionally, I don't think biasing against frozen tasks makes sense from 
> a heusritic standpoint of the oom killer.  Why would we want give 
> non-frozen tasks that are actually getting work done a preference over a 
> task that is frozen and doing absolutely nothing?  It seems like that's 
> backwards and that we'd actually prefer killing the task doing nothing so 
> it can free its memory.
> 

I agree with David.
Why don't you set oom_score_adj as -1000 for processes which never should die ?
You don't freeze processes via user-land using cgroup ?

Thanks,
-Kame



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