Date: Wed, 25 Jun 2008 15:08:59 +0900
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: "MinChan Kim" <minchan.kim@gmail.com>
Subject: Re: [RFC][PATCH] prevent incorrect oom under split_lru
Cc: kosaki.motohiro@jp.fujitsu.com, "Rik van Riel" <riel@redhat.com>,
       linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
       "Lee Schermerhorn" <Lee.Schermerhorn@hp.com>, akpm@linux-foundation.org,
       "Takenori Nagano" <t-nagano@ah.jp.nec.com>
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References: <20080624092824.4f0440ca@bree.surriel.com> <28c262360806242259k3ac308c4n7cee29b72456e95b@mail.gmail.com>
Message-Id: <20080625150141.D845.KOSAKI.MOTOHIRO@jp.fujitsu.com>
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Hi Kim-san,

> >> So, if priority==0, We should try to reclaim all page for prevent OOM.
> >
> > You are absolutely right.  Good catch.
> 
> I have a concern about application latency.
> If lru list have many pages, it take a very long time to scan pages.
> More system have many ram, More many time to scan pages.

No problem.

priority==0 indicate emergency.
it doesn't happend on typical workload.


> Of course I know this is trade-off between memory efficiency VS latency.
> But In embedded, some application think latency is more important
> thing than memory efficiency.
> We need some mechanism to cut off scanning time.
> 
> I think Takenori Nagano's "memory reclaim more efficiently patch" is
> proper to reduce application latency in this case If we modify some
> code.

I think this is off-topic.

but Yes.
both my page reclaim throttle and nagano-san's patch provide 
reclaim cut off mechanism.


and more off-topic,
nagano-san's patch improve only priority==12.
So, typical embedded doesn't improve so big because 
embedded system does't have so large memory.


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