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

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Date:	Fri, 8 Jun 2012 12:25:11 +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 15:14
> To: Moiseichuk Leonid (Nokia-MP/Espoo)
...
> Hm. I would expect that avg value for meminfo will be much worse than
> vmstat (meminfo grabs some locks).
> 
> OK, if we consider 100ms interval, then this would be like 0.1% overhead?
> Not great, but still better than memcg:
> 
> http://lkml.org/lkml/2011/12/21/487

That is difficult to win over memcg :)
But in comparison to one syscall like read() for small structure for particular device the generation of meminfo is about 1000x times more expensive.

> So, I guess the right approach would be to find ways to not depend on
> frequent vm_stat updates (and thus reads).

Agree.

> userland deferred timers (and infrequent reads from vmstat) + "userland vm
> pressure notifications" looks promising for the userland solution.