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RE: [Xen-devel] Seamlessly sharing identical memory pages among domains

To: "Ian Pratt" <Ian.Pratt@xxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Seamlessly sharing identical memory pages among domains
From: "Scheer, Roque" <roque.scheer@xxxxxx>
Date: Fri, 21 May 2004 08:56:04 -0300
Cc: "ROQUE SCHEER (Scheer, Roque)" <roque.scheer@xxxxxx>
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Thread-index: AcQ+0XshQuNW7Hp1ROquEuTBvOjOCwAVzMqw
Thread-topic: [Xen-devel] Seamlessly sharing identical memory pages among domains
>> I'm not convinced there's that much sharing to be had between
>> VMs

In the paper Carl Waldspurger reports some worthwhile sharing under
certain real world workloads:

           | Total| Shared   |Reclaimed   |
Guest Types|  MB  | MB |  %  | MB  |   %  |
-----------+------+----+-----+-----+------+
A)10 WinNT | 2048 | 880| 42.9| 673 | 32.9 |
B) 9 Linux | 1846 | 539| 29.2| 345 | 18.7 |
C) 5 Linux | 1658 | 165| 10.0| 120 | 7.2  |

>> Doing a proper shared cache is slightly trickier given the
paravirtualised 
>> memory interface -- we'd have to introduce guests to a new kind of
write 
>> fault

Wouldn't it be possible for XEN to share the pages tranparently, without
the guest OSes needing to know it?

- Roque


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