linux-kernel - Re: [PATCH v4] vmevent: Implement greater-than attribute state and one-shot mode

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Date:	Wed, 02 May 2012 16:41:31 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Anton Vorontsov <anton.vorontsov@...aro.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Leonid Moiseichuk <leonid.moiseichuk@...ia.com>,
	John Stultz <john.stultz@...aro.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, kernel-team@...roid.com,
	Glauber Costa <glommer@...allels.com>,
	kamezawa.hiroyu@...fujitsu.com,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH v4] vmevent: Implement greater-than attribute state and
 one-shot mode

On 05/02/2012 03:57 PM, Pekka Enberg wrote:

> On Wed, May 2, 2012 at 8:04 AM, Minchan Kim <minchan@...nel.org> wrote:
>> I think hardest problem in low mem notification is how to define _lowmem situation_.
>> We all guys (server, desktop and embedded) should reach a conclusion on define lowmem situation
>> before progressing further implementation because each part can require different limits.
>> Hopefully, I want it.
>>
>> What is the best situation we can call it as "low memory"?
> 
> Looking at real-world scenarios, it seems to be totally dependent on
> userspace policy.


That's why I insist on defining low memory state in user space, not kernel.

> 
> On Wed, May 2, 2012 at 8:04 AM, Minchan Kim <minchan@...nel.org> wrote:
>> As a matter of fact, if we can define it well, I think even we don't neead vmevent ABI.
>> In my opinion, it's not easy to generalize each use-cases so we can pass it to user space and
>> just export low attributes of vmstat in kernel by vmevent.
>> Userspace program can determine low mem situation well on his environment with other vmstats
>> when notification happens. Of course, it has a drawback that userspace couples kernel's vmstat
>> but at least I think that's why we need vmevent for triggering event when we start watching carefully.
> 
> Please keep in mind that VM events is not only about "low memory"
> notification. The ABI might be useful for other kinds of VM events as
> well.


Fully agreed but we should prove why such event is useful in real scenario before adding more features.


> 
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-- 
Kind regards,
Minchan Kim
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