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

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Message-Id: <1276214852.6437.1427.camel@nimitz>
Date:	Thu, 10 Jun 2010 17:07:32 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	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, 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.

Which page will be preferred for eviction with this patch set?

-- Dave

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