Re: 32bit xen and "claim"

[Dan Magenheimer <dan.magenheimer@oracle.com>]

> From: Jan Beulich [mailto:jbeulich@suse.com]
> Sent: Thursday, November 01, 2012 2:42 PM
> To: Dan Magenheimer; keir@xen.org
> Cc: xen-devel@lists.xen.org
> Subject: Re: 32bit xen and "claim"

> >If the CONFIG_X86/separation code will no longer be used,
> >shall I submit a patch to delete the code in page_alloc.c
> >and memory.c?  Or can you (Keir or Jan) just delete it?
> 
> Please don't.

OK.  I'm glad I asked rather than assuming.

> >when prototyping the "claim" hypercall/subop, can I assume
> >that the CONFIG_X86 code in the hypervisor and, specifically
> >any separation of the concepts of xen_heap from dom_heap,
> >can be ignored?
> 
> No, you shouldn't. Once adding support for memory amounts beyond 5Tb
> I expect the separation to become meaningful even for x86-64.

On quick scan, I don't see anything obvious in the archives
that explains why 5Tb is the limit (rather than, say, 4Tb
or 8Tb, or some other power of two).  Could you provide a
pointer to this info or, if you agree it is non-obvious and
undocumented, say a few words of explanation?

Also, just wondering, should exceeding 5Tb be on the 4.3
features list or is >5Tb physical memory still too far away?

Thanks,
Dan