1G huge pages in Linux guest VM

1G huge pages in Linux guest VM

[Sriram Murthy]

Hi,
   I wanted to know if we can pass a hugetlbfs with pagesize=1G created on the host to a Linux guest (The host is running RHEL 6.2 - x86_64 on Intel Westmere)?. 
   I am using RHEL 6.2 on the host and guest and the processor that has been passed by KVM to the guest is Intel Westmere and has the pdpe1gb flag set. Does this mean that the guest supports 1G huge pages?

Thanks, 
Sriram

Re: 1G huge pages in Linux guest VM

[Avi Kivity]

On 05/08/2012 09:38 PM, Sriram Murthy wrote:
> Hi,
>    I wanted to know if we can pass a hugetlbfs with pagesize=1G created on the host to a Linux guest (The host is running RHEL 6.2 - x86_64 on Intel Westmere)?. 

Yes, this is supported.

>    I am using RHEL 6.2 on the host and guest and the processor that has been passed by KVM to the guest is Intel Westmere and has the pdpe1gb flag set. Does this mean that the guest supports 1G huge pages?

Yes.  Note 1gb hugepages on the guest are supported even if not provided
by the host (of course the performance improvement will be smaller).

-- 
error compiling committee.c: too many arguments to function

Re: 1G huge pages in Linux guest VM

[Sriram Murthy]

If I have a mix of 2M and 1G pages on the host, how will I be able to pass the same to the guest?. Does KVM and Libvirtd allow multiple -mem-path options?. 
Also, where in the source can I find more info about hugepage support in KVM?
Thanks and regards,
Sriram

--- On Wed, 5/9/12, Avi Kivity <avi@redhat.com> wrote:

> From: Avi Kivity <avi@redhat.com>
> Subject: Re: 1G huge pages in Linux guest VM
> To: "Sriram Murthy" <sriramsm@yahoo.com>
> Cc: kvm@vger.kernel.org
> Date: Wednesday, May 9, 2012, 2:55 AM
> On 05/08/2012 09:38 PM, Sriram Murthy
> wrote:
> > Hi,
> >    I wanted to know if we can pass a
> hugetlbfs with pagesize=1G created on the host to a Linux
> guest (The host is running RHEL 6.2 - x86_64 on Intel
> Westmere)?. 
> 
> Yes, this is supported.
> 
> >    I am using RHEL 6.2 on the host and guest
> and the processor that has been passed by KVM to the guest
> is Intel Westmere and has the pdpe1gb flag set. Does this
> mean that the guest supports 1G huge pages?
> 
> Yes.  Note 1gb hugepages on the guest are supported
> even if not provided
> by the host (of course the performance improvement will be
> smaller).
> 
> -- 
> error compiling committee.c: too many arguments to function
> 
> 

Re: 1G huge pages in Linux guest VM

[Marcelo Tosatti]

On Thu, May 10, 2012 at 08:53:33AM -0700, Sriram Murthy wrote:
> If I have a mix of 2M and 1G pages on the host, how will I be able to pass the same to the guest?. Does KVM and Libvirtd allow multiple -mem-path options?. 
> Also, where in the source can I find more info about hugepage support in KVM?
> Thanks and regards,
> Sriram

You can't, only a single large page size is supported for guest RAM.