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

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Message-ID: <84FF21A720B0874AA94B46D76DB98269045F7B01@008-AM1MPN1-004.mgdnok.nokia.com>
Date:	Fri, 8 Jun 2012 08:57:13 +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 11:41
...
> > Right. It but it has drawbacks as well e.g. ensure that daemon scheduled
> properly and propagate reaction decision outside ulmkd.
> 
> No, ulmkd itself propagates the decision (i.e. it kills processes).

That is a decision "select & kill" :)
Propagation of this decision required time. Not all processes could be killed. You may stuck in killing in some cases.
...
> In ulmkd I don't use timers at all, and by "watcher" I mean the some
> userspace daemon that receives lowmemory/pressure events (in our case it
> is ulmkd).

Thanks for info.

> If we start "polling" on /proc/vmstat via userland deferred timers, that would
> be a single timer, just like in vmevent case. So, I'm not sure what is the
> difference?..

Context switches, parsing, activity in userspace even memory situation is not changed. In kernel space you can use sliding timer (increasing interval) + shinker.