[libvirt] [PATCH] add flag to enforce hugepage backing of guest RAM

[Marcelo Tosatti]

On Tue, Feb 04, 2014 at 05:26:31PM +0000, Daniel P. Berrange wrote:
> On Tue, Feb 04, 2014 at 12:22:00PM -0500, Marcelo Tosatti wrote:
> > 
> > You're OK with StrictHugePageSize=N element ?
> 
> I'm not entirely sure what that would do ? Is that for when people want
> to have a specific size of hugepages ? If so, then I guess we might
> actually need some kind of granularity here.

Yes, they want to enforce a specific hugepage size (so as to fail guest
initialization if guest RAM cannot be backed by the particular size).

> eg if the user has a 1200 MB guest, and they want to use 1 GB huge
> pages, then there's a choice between 2 * 1GB huge pages, or 1 x 1GB
> and n * 4M huge pages, or an error requiring that their guest RAM is
> a multiple of requested huge page size.

ATM QEMU does not support different huge page sizes, so the only 
option would be 2 * 1GB pages.

> So perhaps we do need some "policy" attribute on the <hugepages/>
> element to indicate desired behaviour here.

What about the following new element under <hugepages/> ?

enforce_hugepage_size=integer