linux-kernel - Re: [PATCH v3] oom-kill: add lowmem usage aware oom kill handling

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Message-Id: <20100201090140.116cc704.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 1 Feb 2010 09:01:40 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, vedran.furac@...il.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, minchan.kim@...il.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3] oom-kill: add lowmem usage aware oom kill handling

On Fri, 29 Jan 2010 13:07:01 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:

> On Sat, 30 Jan 2010, KAMEZAWA Hiroyuki wrote:
> 
> > okay...I guess the cause of the problem Vedran met came from
> > this calculation.
> > ==
> >  109         /*
> >  110          * Processes which fork a lot of child processes are likely
> >  111          * a good choice. We add half the vmsize of the children if they
> >  112          * have an own mm. This prevents forking servers to flood the
> >  113          * machine with an endless amount of children. In case a single
> >  114          * child is eating the vast majority of memory, adding only half
> >  115          * to the parents will make the child our kill candidate of
> > choice.
> >  116          */
> >  117         list_for_each_entry(child, &p->children, sibling) {
> >  118                 task_lock(child);
> >  119                 if (child->mm != mm && child->mm)
> >  120                         points += child->mm->total_vm/2 + 1;
> >  121                 task_unlock(child);
> >  122         }
> >  123
> > ==
> > This makes task launcher(the fist child of some daemon.) first victim.
> 
> That "victim", p, is passed to oom_kill_process() which does this:
> 
> 	/* Try to kill a child first */
> 	list_for_each_entry(c, &p->children, sibling) {
> 		if (c->mm == p->mm)
> 			continue;
> 		if (!oom_kill_task(c))
> 			return 0;
> 	}
> 	return oom_kill_task(p);
> 

Then, finally, per-process oom_adj(!=OOM_DISABLE) control is ignored ?
Seems broken.

I think all this children-parent logic is bad.

Thanks,
-Kame



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