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

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Message-Id: <20110309145457.0400.A69D9226@jp.fujitsu.com>
Date:	Wed,  9 Mar 2011 15:17:01 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	avagin@...il.com
Cc:	kosaki.motohiro@...fujitsu.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...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 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.
> 
> 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...

Hi, 

Hmmm...
If I could observed your patch, I did support your opinion. but I didn't. so, now I'm 
curious why we got the different conclusion. tommorow, I'll try to construct a test 
environment to reproduce your system.

Unfortunatelly, zone->all_unreclamable is unreliable value while hibernation processing.
Then I doubt current your patch is enough acceptable. but I'm not against to make alternative
if we can observe the same phenomenon.

At minimum, I also dislike kernel hang up issue.

Thanks.

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