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

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Message-ID: <20100614171624.GY5191@balbir.in.ibm.com>
Date:	Mon, 14 Jun 2010 22:46:24 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Dave Hansen <dave@...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

* Dave Hansen <dave@...ux.vnet.ibm.com> [2010-06-14 10:09:31]:

> On Mon, 2010-06-14 at 22:28 +0530, Balbir Singh wrote:
> > If you've got duplicate pages and you know
> > that they are duplicated and can be retrieved at a lower cost, why
> > wouldn't we go after them first?
> 
> I agree with this in theory.  But, the guest lacks the information about
> what is truly duplicated and what the costs are for itself and/or the
> host to recreate it.  "Unmapped page cache" may be the best proxy that
> we have at the moment for "easy to recreate", but I think it's still too
> poor a match to make these patches useful.
>

That is why the policy (in the next set) will come from the host. As
to whether the data is truly duplicated, my experiments show up to 60%
of the page cache is duplicated. The first patch today is again
enabled by the host. Both of them are expected to be useful in the
cache != none case.

The data I have shows more details including the performance and
overhead.

-- 
	Three Cheers,
	Balbir
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