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



On Tue, Feb 04, 2014 at 03:04:11PM -0700, Eric Blake wrote:
> On 02/04/2014 02:57 PM, Marcelo Tosatti wrote:
> > 
> >> 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 
> 
> Which feels a bit redundant (we're already under the <hugepages>
> element, after all).  Maybe:
> 
> <hugepages>
>   <size strict='yes' unit='G'>1</size>
> </hugepages>
> 
> where strict could be no if we are giving a hint but don't care if the
> hint cannot be honored (default yes if omitted), and where unit + value

Its awkward because you'd always want the largest hugepages size
possible, to reduce TLB pressure. So its hard to find use for 

<size strict='no' unit='G'>1</size>

So what about <size strict unit='K/G/M'>x</size> ?

> allows the user to input the size in a sensible unit (on output, we'd
> probably want to use unit='k' and spell out 1048576, for similarity with
> all our other memory interfaces that output in k for back-compat reasons).
> 
> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
> 



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