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

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Date:	Thu, 07 Jun 2012 23:35:20 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	leonid.moiseichuk@...ia.com
CC:	penberg@...nel.org, minchan@...nel.org, 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...

(6/5/12 4:16 AM), leonid.moiseichuk@...ia.com wrote:
>> -----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.

I believe that's bad idea. In fact, An "adequate" timeout depend on hardware, not application performance tendency. Thus, applications can't know "adequate" value.

  
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