linux-kernel - Re: [RFC/T/D][PATCH 2/2] Linux/Guest cooperative unmapped page cache control

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Message-ID: <20100611044632.GD5191@balbir.in.ibm.com>
Date:	Fri, 11 Jun 2010 10:16:32 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>, Avi Kivity <avi@...hat.com>,
	kvm <kvm@...r.kernel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC/T/D][PATCH 2/2] Linux/Guest cooperative unmapped page cache
 control

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-06-11 10:54:41]:

> On Thu, 10 Jun 2010 17:07:32 -0700
> Dave Hansen <dave@...ux.vnet.ibm.com> wrote:
> 
> > On Thu, 2010-06-10 at 19:55 +0530, Balbir Singh wrote:
> > > > I'm not sure victimizing unmapped cache pages is a good idea.
> > > > Shouldn't page selection use the LRU for recency information instead
> > > > of the cost of guest reclaim?  Dropping a frequently used unmapped
> > > > cache page can be more expensive than dropping an unused text page
> > > > that was loaded as part of some executable's initialization and
> > > > forgotten.
> > > 
> > > We victimize the unmapped cache only if it is unused (in LRU order).
> > > We don't force the issue too much. We also have free slab cache to go
> > > after.
> > 
> > Just to be clear, let's say we have a mapped page (say of /sbin/init)
> > that's been unreferenced since _just_ after the system booted.  We also
> > have an unmapped page cache page of a file often used at runtime, say
> > one from /etc/resolv.conf or /etc/passwd.
> > 
> 
> Hmm. I'm not fan of estimating working set size by calculation
> based on some numbers without considering history or feedback.
> 
> Can't we use some kind of feedback algorithm as hi-low-watermark, random walk
> or GA (or somehing more smart) to detect the size ?
>

Could you please clarify at what level you are suggesting size
detection? I assume it is outside the OS, right? 

-- 
	Three Cheers,
	Balbir
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