linux-kernel - RE: [PATCH 2/5] vmevent: Convert from deferred timer to deferred work

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Message-ID: <84FF21A720B0874AA94B46D76DB98269045F7A24@008-AM1MPN1-004.mgdnok.nokia.com>
Date:	Fri, 8 Jun 2012 08:16:04 +0000
From:	<leonid.moiseichuk@...ia.com>
To:	<anton.vorontsov@...aro.org>
CC:	<kosaki.motohiro@...il.com>, <penberg@...nel.org>,
	<b.zolnierkie@...sung.com>, <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>
Subject: RE: [PATCH 2/5] vmevent: Convert from deferred timer to deferred
 work

> -----Original Message-----
> From: ext Anton Vorontsov [mailto:anton.vorontsov@...aro.org]
> Sent: 08 June, 2012 10:59
... 
> a) Two more context swtiches;
> b) Serialization/deserialization of /proc/vmstat.
> 
> > It also will cause page trashing because user-space code could be pushed
> out from cache if VM decide.
> 
> This can solved by moving a "watcher" to a separate (daemon) process, and
> mlocking it. We do this in ulmkd.

Right. It but it has drawbacks as well e.g. ensure that daemon scheduled properly and propagate reaction decision outside ulmkd.
Also I understand your statement about "watcher" as probably you use one timer for daemon. 
Btw, in my variant (memnotify.c) I used only one timer, it is enough.