Re: [Xen-devel] [PATCH V3] xen: eliminate scalability issues from initial mapping setup

[Juergen Gross <jgross@xxxxxxxx>]

On 09/24/2014 03:20 PM, David Vrabel wrote:
> On 17/09/14 15:59, Juergen Gross wrote:
> > Direct Xen to place the initial P->M table outside of the initial
> > mapping, as otherwise the 1G (implementation) / 2G (theoretical)
> > restriction on the size of the initial mapping limits the amount
> > of memory a domain can be handed initially.
> >
> > As the initial P->M table is copied rather early during boot to
> > domain private memory and it's initial virtual mapping is dropped,
> > the easiest way to avoid virtual address conflicts with other
> > addresses in the kernel is to use a user address area for the
> > virtual address of the initial P->M table. This allows us to just
> > throw away the page tables of the initial mapping after the copy
> > without having to care about address invalidation.
> >
> > It should be noted that this patch won't enable a pv-domain to USE
> > more than 512 GB of RAM. It just enables it to be started with a
> > P->M table covering more memory. This is especially important for
> > being able to boot a Dom0 on a system with more than 512 GB memory.
> This doesn't seem to work.  It crashes when attempting to construct
> the page tables.  Have these patches been tested on a host with > 512 GiB?
Not yet. I did a code review and was pretty sure the memory above 512GB
would be ignored - seems as if I was wrong.

I'll have access to a machine with 1TB RAM soon, so I'll try to test a
patch which really does what I thought should be done: ignoring the
memory above 512GB.

Thanks for testing!


Juergen

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