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Re: [Xen-devel] xen pv hugepages

On Thu, Feb 06, 2014 at 07:12:24PM -0500, Elena Ufimtseva wrote:
> On Thu, Feb 6, 2014 at 6:59 PM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> > On February 6, 2014 5:17:44 PM EST, Elena Ufimtseva <ufimtseva@xxxxxxxxx> 
> > wrote:
> >>Hello
> >>
> >>As I can see there is no support for hugepages in Xen for PV kernels.
> >>Is this something in the future plans or there is no really need to
> >>have this implemented?
> >
> > It was implemented. The UEK2 kernel (Oracle's) and SLES (I think) has this 
> > implemented. But making it upstream means adding some Xen specific code in 
> > the generic code which is a no-go.
> >
> > If you use PVH you get it for free. With the patches that Mukesh posted to 
> > enable some cpuid flags I was able to boot a guest with 2MB and 1GB pages 
> > without any trouble.
> Ok, I see. Well, I would think then that the kernel then should not
> provide any possibility to use it? Otherwise there are oopses and some
> other unpleasant things happening when trying to use huge pages. I am
> not sure, maybe if its clearly states that there is no hugetlb support
> for pv, then there is no need for this?

I was under the impression that the hugetlb option only gets enabled
if the 'cpu_has_pse' bit is set. And for PV that is cleared so it won't
be set.

> >>
> >>I came across this paper
> >>https://www.kernel.org/doc/ols/2011/ols2011-gadre.pdf,
> >>not sure if this was somehow presented to xen community, I can't find
> >>any code related to this.
> >>
> >>Thank you!
> >
> >
> -- 
> Elena

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