linux-kernel - Re: [PATCH] mm: check zone->all_unreclaimable in all

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Date:	Wed, 9 Mar 2011 14:52:39 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	avagin@...il.com
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrey Vagin <avagin@...nvz.org>, Mel Gorman <mel@....ul.ie>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: check zone->all_unreclaimable in
 all_unreclaimable()

On Tue, 08 Mar 2011 22:02:27 +0300
"avagin@...il.com" <avagin@...il.com> wrote:

> On 03/08/2011 06:06 AM, KOSAKI Motohiro wrote:
> >>>> Hmm.. Although it solves the problem, I think it's not a good idea that
> >>>> depends on false alram and give up the retry.
> >>>
> >>> Any alternative proposals?  We should get the livelock fixed if possible..
> >>
> >> I agree with Minchan and can't think this is a real fix....
> >> Andrey, I'm now trying your fix and it seems your fix for oom-killer,
> >> 'skip-zombie-process' works enough good for my environ.
> >>
> >> What is your enviroment ? number of cpus ? architecture ? size of memory ?
> >
> > me too. 'skip-zombie-process V1' work fine. and I didn't seen this patch
> > improve oom situation.
> >
> > And, The test program is purely fork bomb. Our oom-killer is not silver
> > bullet for fork bomb from very long time ago. That said, oom-killer send
> > SIGKILL and start to kill the victim process. But, it doesn't prevent
> > to be created new memory hogging tasks. Therefore we have no gurantee
> > to win process exiting and creating race.
> 
> I think a live-lock is a bug, even if it's provoked by fork bomds.
> 

I tried to write fork-bomb-detector in oom-kill layer but I think
it should be co-operative with do_fork(), now.
IOW, some fork() should return -ENOMEM under OOM condition.

I'd like to try some but if you have some idea, please do.


> And now I want say some words about zone->all_unreclaimable. I think 
> this flag is "conservative". It is set when situation is bad and it's 
> unset when situation get better. If we have a small number of 
> reclaimable  pages, the situation is still bad. What do you mean, when 
> say that kernel is alive? If we have one reclaimable page, is the kernel 
> alive? Yes, it can work, it will generate many page faults and do 
> something, but anyone say that it is more dead than alive.
> 
> Try to look at it from my point of view. The patch will be correct and 
> the kernel will be more alive.
> 
> Excuse me, If I'm mistaken...
> 

Mayne something more casual interface than oom-kill should be provided.
I wonder I can add memory-reclaim-priority to memory cgroup and
allow control of page fault latency for applicaton...
Maybe "soft_limit" for memcg, it's implemented now, works to some extent.

Thanks,
-Kame

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