linux-kernel - Re: [RFC][PATCH] prevent incorrect oom under split

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Message-ID: <486327F9.6030004@ah.jp.nec.com>
Date:	Thu, 26 Jun 2008 14:24:09 +0900
From:	Takenori Nagano <t-nagano@...jp.nec.com>
To:	MinChan Kim <minchan.kim@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	akpm@...ux-foundation.org
Subject: Re: [RFC][PATCH] prevent incorrect oom under split_lru

MinChan Kim wrote:
> On Thu, Jun 26, 2008 at 10:49 AM, Takenori Nagano
> <t-nagano@...jp.nec.com> wrote:
>> MinChan Kim wrote:
>>> Hi peter,
>>>
>>> I agree with you.  but if application's virtual address space is big,
>>> we have a hard problem with mlockall since memory pressure might be a
>>> big.
>>> Of course, It will be a RT application design problem.
>>>
>>>> The much more important case is desktop usage - that is where we run non
>>>> real-time code, but do expect 'low' latency due to user-interaction.
>>>>
>>>> >From hitting swap on my 512M laptop (rather frequent occurance) I know
>>>> we can do better here,..
>>>>
>>> Absolutely. It is another example. So, I suggest following patch.
>>> It's based on idea of Takenori Nagano's memory reclaim more efficiently.
>> Hi Kim-san,
>>
>> Thank you for agreeing with me.
>>
>> I have one question.
>> My patch don't mind priority. Why do you need "priority == 0"?
> 
> Hi, Takenori-san.
> 
> Now, Kosaiki-san's patch didn't consider application latency.
> That patch scan all lru[x] pages when memory pressure is very high.
> (ie, priority == 0)
> It will cause application latency to high as peter and me notice that.
> We need a idea which prevent big scanning overhead
> I modified your idea to prevent big scanning overhead only when memory
> pressure is very big.

Hi, Kim-san.

Thank you for your explanation.
I understand your opinion.

But...your patch is not enough for me. :-(
Our Xeon box has 128GB memory, application latency will be very large if
priority goes to be zero.
So, I would like to use "cut off" on every priority.

I would like to delete "priority == 0", Can you?

Thanks,
  Takenori
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