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Re: [Xen-devel] yanked share, round 2

To: "King, Steven R" <steven.r.king@xxxxxxxxx>
Subject: Re: [Xen-devel] yanked share, round 2
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sat, 14 Jan 2006 00:21:09 +0000
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 13 Jan 2006, at 23:02, King, Steven R wrote:

We get these features:
1) A domU can never cause the Xen share pool to shrink.
2) The number of pages mappable by a DomU is bounded only by the DomU
3) No page ownership problems.
4) We can have a nice share key ala SysV IPC semantics.
5) When no shares exist, the memory pool consumes no pages.
6) We leave Xen's heap alone.

The first benefit is critical since DomU's are untrusted. A downside is
that a platform with many DomU mappings will have many idle pages
sitting in the pool.  Given all the benefits above, a very reasonable
price to pay.

This is similar to ideas people have had for shared buffer cache without memory overcommitment. Seems to me that the Xen-level mechanism for doing the sharing could easily be identical, and the differences in interface, access control and other policy could be hidden in a share manager in a suitably-privileged domain.

 -- Keir

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