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

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Message-ID: <AANLkTi=q=YMrT7Uta+wGm47VZ5N6meybAQTgjKGsDWFw@mail.gmail.com>
Date:	Thu, 10 Mar 2011 15:58:29 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrew Vagin <avagin@...il.com>,
	Andrey Vagin <avagin@...nvz.org>, Mel Gorman <mel@....ul.ie>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: check zone->all_unreclaimable in all_unreclaimable()

Hi Kame,

Sorry for late response.
I had a time to test this issue shortly because these day I am very busy.
This issue was interesting to me.
So I hope taking a time for enough testing when I have a time.
I should find out root cause of livelock.

I will answer your comment after it. :)
Thanks!

On Wed, Mar 9, 2011 at 2:37 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Tue, 8 Mar 2011 08:45:51 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
>
>> On Tue, Mar 8, 2011 at 6:58 AM, Andrew Morton <akpm@...ux-foundation.org> wrote:
>> > On Sun, 6 Mar 2011 02:07:59 +0900
>> > Minchan Kim <minchan.kim@...il.com> wrote:
>> > Any alternative proposals?  We should get the livelock fixed if possible..
>> >
>>
>> And we should avoid unnecessary OOM kill if possible.
>>
>> I think the problem is caused by (zone->pages_scanned <
>> zone_reclaimable_pages(zone) * 6). I am not sure (* 6) is a best. It
>> would be rather big on recent big DRAM machines.
>>
>
> It means 3 times full-scan from the highest priority to the lowest
> and cannot freed any pages. I think big memory machine tend to have
> more cpus, so don't think it's big.
>
>> I think it is a trade-off between latency and OOM kill.
>> If we decrease the magic value, maybe we should prevent the almost
>> livelock but happens unnecessary OOM kill.
>>
>
> Hmm, should I support a sacrifice feature 'some signal(SIGINT?) will be sent by
> the kernel when it detects system memory is in short' in cgroup ?
> (For example, if full LRU scan is done in a zone, notifier
>  works and SIGINT will be sent.)
>
>> And I think zone_reclaimable not fair.
>> For example, too many scanning makes reclaimable state to
>> unreclaimable state. Maybe it takes a very long time. But just some
>> page free makes unreclaimable state to reclaimabe with very easy. So
>> we need much painful reclaiming for changing reclaimable state with
>> unreclaimabe state. it would affect latency very much.
>>
>> Maybe we need more smart zone_reclaimabe which is adaptive with memory pressure.
>>
> I agree.
>
> Thanks,
> -Kame
>
>



-- 
Kind regards,
Minchan Kim
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