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

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> 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  |

I haven't got any figures for WinXP. The amount of sharing for
Linux instances will be very work load dependent. I'd bet that
almost all of it could be had through a shared buffer cache (from
a CoW file system).

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

Only for guests running in "shadow page table" mode, otherwise
the guest knows about real machine frame numbers.

Ian


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