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[Xen-devel] Re: issue with domains having close to or more than 512G

  • To: Jan Beulich <jbeulich@xxxxxxxxxx>
  • From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
  • Date: Thu, 18 Dec 2008 11:20:25 +0000
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 18 Dec 2008 03:20:47 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AclhAp93ryh0jOrs4UOGGdIOmqEo2g==
  • Thread-topic: issue with domains having close to or more than 512G

I think we should keep the current layout up to the point that the required
address space wraps past zero. Beyond that we can flag a new layout.

Who's surprised that a domain won't boot with nearly 512GB of memory? It's
never been tested, and it's not immediately an argument for messing with the
memory layout, unless it clearly will not fit.

 -- Keir

On 18/12/2008 10:39, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> Keir,
> the ordering of elements in the initial virtual memory arrangement is part of
> the official ABI, yet I would think some parts of it may need changing:
> When the complete space occupied by the initial mapping exceeds 1G,
> Linux won't cope at present, and obviously as soon as it exceeds 2G it
> really never can't with the current layout. 1G is reached when there is
> close to 512G available to the domain. I think that the only way to deal
> with this is to move the initial p2m map out of that range, at least in the
> case where it would cause the entire mapping to exceed 1G (or, if
> moving start_info before p2m, then 2G could be considered the limit
> here, but it would require fixes to Linux anyway).
> Are you aware of kernel side dependencies on this layout other than the
> initial page table setup needing to be made aware of the possibility of
> the p2m map sitting other than between kernel start and initial page
> tables end?
> Thanks, Jan

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