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

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Message-Id: <20100611105441.ee657515.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 11 Jun 2010 10:54:41 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	balbir@...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

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 ?

Thanks,
-Kame




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