linux-kernel - Re: Memory overcommit

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Date:	Tue, 3 Nov 2009 12:49:52 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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 Fri, 30 Oct 2009, KAMEZAWA Hiroyuki wrote:

> > >    - The kernel can't know the program is bad or not. just guess it.
> > 
> > Totally irrelevant, given your fourth point about /proc/pid/oom_adj.  We 
> > can tell the kernel what we'd like the oom killer behavior should be if 
> > the situation arises.
> > 
> 
> My point is that the server cannot distinguish memory leak from intentional
> memory usage. No other than that.
> 

That's a different point.  Today, we can influence the badness score of 
any user thread to prioritize oom killing from userspace and that can be 
done regardless of whether there's a memory leaker, a fork bomber, etc.  
The priority based oom killing is important to production scenarios and 
cannot be replaced by a heuristic that works everytime if it cannot be 
influenced by userspace.

A spike in memory consumption when a process is initially forked would be 
defined as a memory leaker in your quiet_time model.

> In this summer, at lunch with a daily linux user, I was said
> "you, enterprise guys, don't consider desktop or laptop problem at all."
> yes, I use only servers. My customer uses server, too. My first priority
> is always on server users.
> But, for this time, I wrote reply to Vedran and try to fix desktop problem.
> Even if current logic works well for servers, "KDE/GNOME is killed" problem
> seems to be serious. And this may be a problem for EMBEDED people, I guess.
> 

You argued before that the problem wasn't specific to X (after I said you 
could protect it very trivially with /proc/pid/oom_adj set to 
OOM_DISABLE), but that's now your reasoning for rewriting the oom killer 
heuristics?

> I can say the same thing to total_vm size. total_vm size doesn't include any
> good information for oom situation. And tweaking based on that not-useful
> parameter will make things worse.
> 

Tweaking on the heuristic will probably make it more convoluted and 
overall worse, I agree.  But it's a more stable baseline than rss from 
which we can set oom killing priorities from userspace.
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