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

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Message-ID: <84FF21A720B0874AA94B46D76DB98269045D2AC9@008-AM1MPN1-003.mgdnok.nokia.com>
Date:	Wed, 2 May 2012 06:46:15 +0000
From:	<leonid.moiseichuk@...ia.com>
To:	<minchan@...nel.org>, <anton.vorontsov@...aro.org>
CC:	<kosaki.motohiro@...il.com>, <riel@...hat.com>,
	<penberg@...nel.org>, <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>, <glommer@...allels.com>,
	<kamezawa.hiroyu@...fujitsu.com>, <suleiman@...gle.com>
Subject: RE: [PATCH v4] vmevent: Implement greater-than attribute state and
 one-shot mode

> -----Original Message-----
> From: ext Minchan Kim [mailto:minchan@...nel.org]
> Sent: 02 May, 2012 08:04
> To: Anton Vorontsov
> Cc: KOSAKI Motohiro; Rik van Riel; Pekka Enberg; Moiseichuk Leonid (Nokia-
...
> 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"?

That depends on what user-space can do. In n9 case [1] we can handle some OOM/slowness-prevention and actions e.g. close background applications, stop prestarted apps, 
flush browser/graphics caches in applications and do all the things kernel even don't know about. This set of activities usually comes as memory management design.

From another side, polling by re-scan vmstat data using procfs might be performance heavy and for sure - use-time disaster.

Leonid
[1] http://maemo.gitorious.org/maemo-tools/libmemnotify - yes, not ideal but it works and quite well isolated code.