linux-kernel - Re: [RFC v3 0/3] vmpressure_fd: Linux VM pressure notifications

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Date:	Wed, 07 Nov 2012 09:20:35 -0800
From:	Greg Thelen <gthelen@...gle.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Mel Gorman <mgorman@...e.de>,
	Pekka Enberg <penberg@...nel.org>,
	Leonid Moiseichuk <leonid.moiseichuk@...ia.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.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,
	linux-man@...r.kernel.org
Subject: Re: [RFC v3 0/3] vmpressure_fd: Linux VM pressure notifications

On Wed, Nov 07 2012, Kirill A. Shutemov wrote:

> On Wed, Nov 07, 2012 at 02:53:49AM -0800, Anton Vorontsov wrote:
>> Hi all,
>> 
>> This is the third RFC. As suggested by Minchan Kim, the API is much
>> simplified now (comparing to vmevent_fd):
>> 
>> - As well as Minchan, KOSAKI Motohiro didn't like the timers, so the
>>   timers are gone now;
>> - Pekka Enberg didn't like the complex attributes matching code, and so it
>>   is no longer there;
>> - Nobody liked the raw vmstat attributes, and so they were eliminated too.
>> 
>> But, conceptually, it is the exactly the same approach as in v2: three
>> discrete levels of the pressure -- low, medium and oom. The levels are
>> based on the reclaimer inefficiency index as proposed by Mel Gorman, but
>> userland does not see the raw index values. The description why I moved
>> away from reporting the raw 'reclaimer inefficiency index' can be found in
>> v2: http://lkml.org/lkml/2012/10/22/177
>> 
>> While the new API is very simple, it is still extensible (i.e. versioned).
>
> Sorry, I didn't follow previous discussion on this, but could you
> explain what's wrong with memory notifications from memcg?
> As I can see you can get pretty similar functionality using memory
> thresholds on the root cgroup. What's the point?

Related question: are there plans to extend this system call to provide
per-cgroup vm pressure notification?
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