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[Xen-devel] copy on write memory

To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] copy on write memory
From: Peri Hankey <mpah@xxxxxxxxxxxxxx>
Date: Mon, 15 Nov 2004 22:01:26 +0000
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UML has developed a SKAS mode of operation, in which (as far as I understand it) a process can be created much in the same way as any other Linux process, except that it runs (under an UML kernel) with a separate kernel address space.

It occurred to me that the equivalent in the Xen world would be to use one Linux xenU domain purely as a page-table manager for a collection of separate xenU domains that are expected or known have similar process populations. The process creation domain would have a large allocation of memory which it would use to populate page tables applying standard copy on write semantics, but the processes to which these page tables belong would effectively run in the separate execution domains to which they belong.

A similar arrangement of one page-table management domain with multiple separate execution domains could be used for other kernels such as netbsd, which have similar copy on write semantics.

Xen itself would only need to provide a mechanism for managing the trade between a page-manager domain and its execution domains, and would not need to replicate the functionality of any particular system.

As the page-table manager domain also knows which disk pages are clean, and which have been written to, it is also in a good position to manage copy on write semantics for filesystem storage.

Is this a feasible way of looking at it?

Peri Hankey

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