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



On Tue, Feb 04, 2014 at 12:18:34PM -0500, Marcelo Tosatti wrote:
> On Tue, Feb 04, 2014 at 05:10:13PM +0000, Daniel P. Berrange wrote:
> > > Because there is no guarantee with -mem-prealloc. For instance, if the
> > > hugepage path is not actually hugetlbfs backed, QEMU falls back to
> > > malloc().
> > 
> > Well if you can't fix -mem-prealloc to properly report errors for reasons
> > of back compat, then it is certainly possible to add a further 'strict=yes|no'
> > option to the CLI arg request that it verify this. I don't see any reason
> > why this checking code should be in libvirt rather than QEMU.
> > 
> > Regards,
> > Daniel
> 
> OK, do you want the StrictHugepage element to exist, and default
> libvirt behaviour to remain as it is today (fallback to malloc), 
> 
> or
> 
> do you want libvirt to pass strict mode to -mem-prealloc as default
> when using hugepages element? (which would change behaviour of libvirt
> for existing guests)

I'd say the latter - if the user is requesting hugepages they should
be guaranteed to get them. Libvirt doesn't ever use -mem-path with
a non-hugetlbfs filesystem path AFAIR, so the fallback to malloc
doesn't really make any sense for our needs.

Daniel
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