Re: [Xen-devel] Future support of 5-level paging in Xen

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 12/08/2016 05:21 PM, Andrew Cooper wrote:
> On 08/12/2016 19:18, Stefano Stabellini wrote:
> > Of course even the largest virtual machine today (2TB on Amazon AFAIK)
> > is not close to reaching the current memory limit, but it's just a
> > matter of time.
> /me things Oracle will have something to say about this.  I'm sure there
> was talk about VMs larger than this at previous hackathons.  XenServer
> functions (ish, so long as you don't migrate) with 6TB VMs, although
> starting and shutting them down feels like treacle.


I've been working (on and off) with SGI to get one of their 32TB boxes 
to boot and I don't think that works. We've fixed a couple of bugs but I 
don't think Xen can boot with that much memory. We successfully booted 
with just under 8TB but couldn't do it with the full system. The machine 
has been taken from us for now so this work is on hold.
This is on OVM, which is 4.4-based, we haven't tried (IIRC) latest bits.

(BTW, speaking of slow starting and shutting down very large guests ---
have you or anyone else had a chance to look at this? My investigation 
initially pointed to scrubbing and then to an insane number of hypercall 
preemptions in relinquish_memory()).
-boris

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