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

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Page cache shared across domain
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Tue, 24 Jan 2006 15:58:08 +0000
Cc: Amit Patel <amitpate@xxxxxxxxx>
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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.

The most invasive approach is to implement a Xen-aware filesystem - I'm 
working on this too.  XenFS and the DCSS work require similar infrastructure 
(including an enhanced version of grant tables, and more functionality in the 
Xenstore to support more complicated "device" sharing relationships) so the 
two efforts are symbiotic.  The port of the dcssblk driver is less 
sophisticated and will likely be available substantially sooner.


On Tuesday 24 January 2006 07:38, Amit Patel wrote:
> Hi,
> I just got started using Xen. Is there any mechanism in Xen which
> allows pages shared across multiple domains? I was reading documents
> regarding grant tables but one limitation it states, is that a page
> using this mechanism  can only be shared between two domains and only
> one of them has control over pages at anytime. I was looking for
> something where any domain has access to this shared memory and can be
> accessed by any domain in read only mode. Any help if its possible to
> do with Xen and where can I look for information is appreciated.
> Siva
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel

Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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