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

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Message-ID: <48634DD5.5050200@ah.jp.nec.com>
Date:	Thu, 26 Jun 2008 17:05:41 +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 2:24 PM, Takenori Nagano <t-nagano@...jp.nec.com> wrote:
>> 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 am not sure it will be a regression.
> We don't have any enough data.
> 
> My intention is just to prevent kosaki-san's patch's corner case.

OK.
I'll try to test to make enough data. :-)

Thanks,
  Takenori
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