Re: [Xen-users] SMP and Memory Limits

[Gordan Bobic <gordan@xxxxxxxxxx>]

Petersson, Mats wrote:
> > -----Original Message-----
> > From: Gordan Bobic [mailto:gordan@xxxxxxxxxx] 
> > Sent: 20 September 2005 12:34
> > To: Petersson, Mats
> > Subject: Re: [Xen-users] SMP and Memory Limits
> >
> >
> > > > What are the limits on how many CPUs and how much memory 
> > Xen supports? 
> >
> > > > I am interested in this for both the host (0) kernel and the client 
> > > > (U) kernel.
> > > > I am looking at getting some 16-way (8-way dual-core) 
> > Opteron systems 
> >
> > > > with about 64 GB of RAM for prototyping, so I would like to 
> > make sure 
> >
> > > > that Xen can use up all of the resources of such a machine.
> > > In Xen-unstable (to become 3.0) I believe there is no 
> > software limits
> >
> > > for CPU count or memory amount, only whatever limits the hardware
> > > dictates (i.e. 40 bits of hardware address, 48 bits 
> > available in virtual
> >
> > > space). If there are any other limitations, it's probably fair to
> > > consider it a bug, and report such failings on the Xen-Devel mailing
> > > list. 
> > >
> > > Obviously, 2.0.x, only supporting 32-bit in non-PAE mode 
> > would not be
> >
> > > able to use more than about 3.5GB of RAM.
> > Is that 3.5 GB per dom-U/dom-0, or the total between dom-0 and all 
> > dom-Us put together?
> That would be 3.5 GB in total, since the only way to access more than
> this amount of memory would involve using address extended page table,
> which isn't supported by Xen 2.0.x. 64-bit x86 actually uses the
> exisiting PAE, but with an added page-table level so that a bigger than
> 36-bit address can be supported. 
How stable is the "unstable/64-bit" version of Xen? Is it usable?

Gordan

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