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Re: [Xen-devel] Page cache shared across domain

To: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] Page cache shared across domain
From: Jacob Gorm Hansen <jacobg@xxxxxxx>
Date: Tue, 31 Jan 2006 11:17:31 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Amit Patel <amitpate@xxxxxxxxx>
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On 1/24/06, Mark Williamson <mark.williamson@xxxxxxxxxxxx> wrote:
> There are a number of routes for this.  The most obvious is to implement
> content-based page sharing mechanisms for the hypervisor itself - I believe
> people are working on this already.  This is what VMware ESX does when
> running multiple guests, and can unify storage for pages when they have the
> same content.
> Another approach is to use a shared interdomain ramdisk and do Execute In
> Place (XIP) on the contents.  It's not a full shared page cache, but it gives
> you sharing for program text, etc.  I'm implementing infrastructure to
> support the dcssblk driver used on IBM zSeries mainframes, which will give us
> this functionality.

Would it make sense to have a Read-Only page type in Xen (if it's not
already there), so that pages coming from the blockdev-backend could
be made RO by the backend, and the domain would have to CoW them if it
needed to modify the contents?

Seems this would allow a shared buffer cache, and also open the door
to a voluntary page sharing mechanism.


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