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Date:	Tue, 27 Oct 2009 17:52:43 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	vedran.furac@...il.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	rientjes@...gle.com
Subject: Re: [RFC][PATCH] oom_kill: avoid depends on total_vm and use real
 RSS/swap value for oom_score (Re: Memory overcommit

On Tue, 27 Oct 2009 17:33:08 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> On Tue, 27 Oct 2009 17:14:41 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
> 
> > On Tue, 27 Oct 2009 16:56:28 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > 
> > > On Tue, 27 Oct 2009 16:45:26 +0900
> > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > >   	/*
> > > >  	 * After this unlock we can no longer dereference local variable `mm'
> > > > @@ -92,8 +93,13 @@ unsigned long badness(struct task_struct
> > > >  	 */
> > > >  	list_for_each_entry(child, &p->children, sibling) {
> > > >  		task_lock(child);
> > > > -		if (child->mm != mm && child->mm)
> > > > -			points += child->mm->total_vm/2 + 1;
> > > > +		if (child->mm != mm && child->mm) {
> > > > +			unsigned long cpoint;
> > > > +			/* At considering child, we don't count swap */
> > > > +			cpoint = get_mm_counter(child->mm, anon_rss) +
> > > > +				 get_mm_counter(child->mm, file_rss);
> > > > +			points += cpoint/2 + 1;
> > > > +		}
> > > >  		task_unlock(child);
> > > 
> > > BTW, I'd like to get rid of this code.
> > > 
> > > Can't we use other techniques for detecting fork-bomb ?
> > > 
> > > This check can't catch following type, anyway.
> > > 
> > >    fork()
> > >      -> fork()
> > >           -> fork()
> > >                -> fork()
> > >                     ....
> > > 
> > > but I have no good idea.
> > > What is the difference with task-launcher and fork bomb()...
> > > 
> > 
> > I think it's good as-is. 
> > Kernel is hard to know it by effiecient method.
> > It depends on applications. so Doesnt's task-launcher 
> > like gnome-session have to control his oom_score? 
> > 
> > Welcome to any ideas if kernel can do it well.
> > 
> Hmmm, check system-wide fork/sec and fork-depth ? Maybe not difficult to calculate..

Yes. We can do anything to achieve the goal in kernel. 
Maybe check the time or fork-depth counting. 
What I have a concern is how we can do it nicely if it is a serious
problem in kernel. ;)

I think most of program which have many child are victims of OOM killing.
It make sense to me. There is some cases to not make sense like task-launcher.
So I think if task-launcher which is very rare and special program can change
oom_adj by itself, it's good than thing that add new heuristic in kernel.

It's just my opinon. :)

> Regards,
> -Kame
> 


-- 
Kind regards,
Minchan Kim
--
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