Re: [Xen-devel] Memory oversubscription

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

Yes, that will work. The total current memory reservation across all
domains must always be smaller than the amount of RAM. However, the
upper limit that Xen will allow the reservations to increase to can
sum to larger than available RAM.

However, beware that Linux won't be happy if it fails to increase its
reservation when it believes it ought to be able to -- the net driver
in particular will barf spectacularly. Fixing this is really a small
matter of cleaning up the code that I ought to get round to.

Within Xen, nothing smart happens when you run low on RAM (e.g.,
failing one guest's memory request in favour of other more important
guests). I guess this could be smarter!

 -- Keir

> Hi.  First of all, thanks for Xen.  It's terrific!
> 
> I'm interested in doing memory oversubscription and am wondering if Xen 
> can do this (now or in the future). 
> 
> For example, on a machine with 100MB available physical memory, can I:
> 1. Create a domain with a 90MB allocation
> 2. Inflate a balloon in that domain and return say 40MB back to Xen
> 
> I know there are mechanisms for doing 1 and 2...
> 
> 3. Allocate a second domain with an allocation of 50MB?
> 
> Thanks,
> 
> --Todd
> 
> 
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