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

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Date:	Fri, 22 Jan 2010 08:48:56 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	rientjes@...gle.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] oom-kill: add lowmem usage aware oom kill handling

On Fri, 22 Jan 2010 00:18:44 +0900
Minchan Kim <minchan.kim@...il.com> wrote:

> Hi, Kame. 
> 
> On Thu, 2010-01-21 at 14:59 +0900, KAMEZAWA Hiroyuki wrote:
> > A patch for avoiding oom-serial-killer at lowmem shortage.
> > Patch is onto mmotm-2010/01/15 (depends on mm-count-lowmem-rss.patch)
> > Tested on x86-64/SMP + debug module(to allocated lowmem), works well.
> > 
> > ==
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > 
> > One cause of OOM-Killer is memory shortage in lower zones.
> > (If memory is enough, lowmem_reserve_ratio works well. but..)
> > 
> > In lowmem-shortage oom-kill, oom-killer choses a vicitim process
> > on their vm size. But this kills a process which has lowmem memory
> > only if it's lucky. At last, there will be an oom-serial-killer.
> > 
> > Now, we have per-mm lowmem usage counter. We can make use of it
> > to select a good? victim.
> > 
> > This patch does
> >   - add CONSTRAINT_LOWMEM to oom's constraint type.
> >   - pass constraint to __badness()
> >   - change calculation based on constraint. If CONSTRAINT_LOWMEM,
> >     use low_rss instead of vmsize.
> 
> As far as low memory, it would be better to consider lowmem counter.
> But as you know, {vmsize VS rss} is debatable topic.
> Maybe someone doesn't like this idea. 
> 
About lowmem, vmsize never work well.

> So don't we need any test result at least?
My test result was very artificial, so I didn't attach the result.

 - Before this patch, sshd was killed at first.
 - After this patch, memory consumer of low-rss was killed.

> If we don't have this patch, it happens several innocent process
> killing. but we can't prevent it by this patch. 
> 
I can't catch what you mean.

> Sorry for bothering you.
> 

Hmm, boot option or CONFIG ? (CONFIG_OOMKILLER_EXTENSION ?)

I'm now writing fork-bomb detector again and want to remove current
"gathering child's vm_size" heuristics. I'd like to put that under
the same config, too.

Thanks,
-Kame






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