[CentOS] Sharing RAM between VM

John R Pierce pierce at hogranch.com
Tue Apr 14 17:15:08 UTC 2009

Jim Wildman wrote:
> 'over commit' of RAM is the phrase you are probably looking for.  And
> this is one of the limitations of Xen (it doesn't).

perhaps I am being naive here, but I'd guess that a hypervisor which 
allowed such would have to have its own page swapping mechanism, as it 
needs to present each guest OS with the appearance of having whatever 
"physical" memory it thinks it has...   meanwhile, each guest OS has 
*its* own page swapping to implement whatever VM scheme it supports.

since most modern virtual memory systems attempt to maximize their 
memory footprint by treating the bulk of otherwise unused ('free') pages 
as disk cache, I can't help but think this wouldn't work that well 
(having the hypervisor doing swapping on pages that are guest OS 
discardable cache pages just doesn't sound very effective)

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