linux-kernel - RE: [PATCH 0/5] Some vmevent fixes...

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Message-ID: <84FF21A720B0874AA94B46D76DB98269045EBBD8@008-AM1MPN1-003.mgdnok.nokia.com>
Date:	Tue, 5 Jun 2012 08:16:12 +0000
From:	<leonid.moiseichuk@...ia.com>
To:	<penberg@...nel.org>, <minchan@...nel.org>
CC:	<cbouatmailru@...il.com>, <kosaki.motohiro@...il.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 0/5] Some vmevent fixes...

> -----Original Message-----
> From: penberg@...il.com [mailto:penberg@...il.com] On Behalf Of ext
> Pekka Enberg
> Sent: 05 June, 2012 11:02
> To: Minchan Kim
...
> > Next concern is that periodic timer of implementation.
> > I think it would add direct hook in vmscan.c rather than peeking raw
> > vmstat periodically by timer so we can control more fine-grained way
> without unnecessary overhead.
> 
> If the hooks are clean and it doesn't hurt the  !CONFIG_VMEVENT case, I'm
> completely OK with that.

On the previous iteration hooking vm was pointed as very bad idea, so in my version I installed shrinker to handle cases when we have memory pressure.
Using deferred timer with adequate timeout (0.250 ms or larger) fully suitable for userspace and produce adequate overhead 
-> by nature such API should not be 100% accurate, anyhow applications cannot handle situation as good as kernel can provide, 0.5MB space accuracy, 100ms is maximum user-space require for 64-1024MB devices.
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