Xen max supported memory per guest VM?

Xen max supported memory per guest VM?

[Pasi Kärkkäinen]

Hello,

In http://wiki.xensource.com/xenwiki/Xen4.0 we mention the following:
"Better performance and scalability: 128 vcpus per guest, 1 TB of RAM per host, 128 physical CPUs per host (as a default, can be compile-time increased to lots more)."

But what's the max supported amount of memory for a (64bit) guest? 

-- Pasi

Re: Xen max supported memory per guest VM?

[Keir Fraser]

On 14/08/2010 19:42, "Pasi Kärkkäinen" <pasik@iki.fi> wrote:

> Hello,
> 
> In http://wiki.xensource.com/xenwiki/Xen4.0 we mention the following:
> "Better performance and scalability: 128 vcpus per guest, 1 TB of RAM per
> host, 128 physical CPUs per host (as a default, can be compile-time increased
> to lots more)."
> 
> But what's the max supported amount of memory for a (64bit) guest?

Allocating the whole 1TB should work. It's unlikely to have been tested
though.

 -- Keir

> -- Pasi
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

Re: Xen max supported memory per guest VM?

[Pasi Kärkkäinen]

On Sat, Aug 14, 2010 at 10:18:11PM +0100, Keir Fraser wrote:
> On 14/08/2010 19:42, "Pasi Kärkkäinen" <pasik@iki.fi> wrote:
> 
> > Hello,
> > 
> > In http://wiki.xensource.com/xenwiki/Xen4.0 we mention the following:
> > "Better performance and scalability: 128 vcpus per guest, 1 TB of RAM per
> > host, 128 physical CPUs per host (as a default, can be compile-time increased
> > to lots more)."
> > 
> > But what's the max supported amount of memory for a (64bit) guest?
> 
> Allocating the whole 1TB should work. It's unlikely to have been tested
> though.
> 

Ok. I guess it might also have a difference if it's a PV or HVM guest..

-- Pasi

Re: Xen max supported memory per guest VM?

[Keir Fraser]

On 14/08/2010 22:30, "Pasi Kärkkäinen" <pasik@iki.fi> wrote:

>>> In http://wiki.xensource.com/xenwiki/Xen4.0 we mention the following:
>>> "Better performance and scalability: 128 vcpus per guest, 1 TB of RAM per
>>> host, 128 physical CPUs per host (as a default, can be compile-time
>>> increased
>>> to lots more)."
>>> 
>>> But what's the max supported amount of memory for a (64bit) guest?
>> 
>> Allocating the whole 1TB should work. It's unlikely to have been tested
>> though.
>> 
> 
> Ok. I guess it might also have a difference if it's a PV or HVM guest..

I can't think of a reason we'd be limited to less for HVM or PV.

 -- Keir

Re: Xen max supported memory per guest VM?

[Jan Beulich]

>>> On 14.08.10 at 23:18, Keir Fraser <keir.fraser@eu.citrix.com> wrote:
> On 14/08/2010 19:42, "Pasi Kärkkäinen" <pasik@iki.fi> wrote:
> 
>> Hello,
>> 
>> In http://wiki.xensource.com/xenwiki/Xen4.0 we mention the following:
>> "Better performance and scalability: 128 vcpus per guest, 1 TB of RAM per
>> host, 128 physical CPUs per host (as a default, can be compile-time increased
>> to lots more)."
>> 
>> But what's the max supported amount of memory for a (64bit) guest?
> 
> Allocating the whole 1TB should work. It's unlikely to have been tested
> though.

Not everything will work with more than 512G: Anything that wants
to access the guest's pfn_to_mfn_frame_list_list won't work, as
there's no specification of how more than a page worth of these top
level pointers should be expressed. Affected would be (afaict) save/
restore/migrate, kexec, and dumping of a crashed guest.

Jan

Re: Xen max supported memory per guest VM?

[Keir Fraser]

On 16/08/2010 10:04, "Jan Beulich" <JBeulich@novell.com> wrote:

>>> But what's the max supported amount of memory for a (64bit) guest?
>> 
>> Allocating the whole 1TB should work. It's unlikely to have been tested
>> though.
> 
> Not everything will work with more than 512G: Anything that wants
> to access the guest's pfn_to_mfn_frame_list_list won't work, as
> there's no specification of how more than a page worth of these top
> level pointers should be expressed. Affected would be (afaict) save/
> restore/migrate, kexec, and dumping of a crashed guest.

Okay, so that's a further restriction on PV guests. HVM guests should
theoretically still be good up to 1TB.

 -- Keir

Re: Xen max supported memory per guest VM?

[Pasi Kärkkäinen]

On Mon, Aug 16, 2010 at 10:18:53AM +0100, Keir Fraser wrote:
> On 16/08/2010 10:04, "Jan Beulich" <JBeulich@novell.com> wrote:
> 
> >>> But what's the max supported amount of memory for a (64bit) guest?
> >> 
> >> Allocating the whole 1TB should work. It's unlikely to have been tested
> >> though.
> > 
> > Not everything will work with more than 512G: Anything that wants
> > to access the guest's pfn_to_mfn_frame_list_list won't work, as
> > there's no specification of how more than a page worth of these top
> > level pointers should be expressed. Affected would be (afaict) save/
> > restore/migrate, kexec, and dumping of a crashed guest.
> 
> Okay, so that's a further restriction on PV guests. HVM guests should
> theoretically still be good up to 1TB.
> 

Ok, I updated this info to:
http://wiki.xensource.com/xenwiki/Xen4.0

-- Pasi