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Re: [libvirt] [RFC PATCH 01/17] qemu: setup shared memory without explicit numa configuration



On Thu, Aug 16, 2018 at 07:32:57AM -0400, John Ferlan wrote:
> 
> 
> On 08/16/2018 06:31 AM, Marc-André Lureau wrote:
> > Hi
> > 
> > On Thu, Aug 16, 2018 at 4:35 AM, John Ferlan <jferlan redhat com> wrote:
> >>
> >>
> >> On 07/13/2018 09:28 AM, marcandre lureau redhat com wrote:
> >>> From: Marc-André Lureau <marcandre lureau redhat com>
> >>>
> >>> When a domain is configured with 'shared' memory backing:
> >>>
> >>>   <memoryBacking>
> >>>     <access mode='shared'/>
> >>>   </memoryBacking>
> >>>
> >>> But no explicit NUMA configuration, let's configure a shared memory
> >>> backend associated with default -numa.
> >>>
> >>> Signed-off-by: Marc-André Lureau <marcandre lureau redhat com>
> >>> ---
> >>>  src/qemu/qemu_command.c                       | 100 ++++++++++++------
> >>>  .../fd-memory-no-numa-topology.args           |   4 +
> >>>  2 files changed, 73 insertions(+), 31 deletions(-)
> >>>
> >>
> >> NUMA, memory backends, and hugepages - not in my wheelhouse of
> >> knowledge. Hopefully Michal and/or Pavel will take a look!
> >>
> >> Is it possible someone may not want this type of thing to happen? Is
> > 
> > I assume someone that sets 'shared' memory mode may consider this as a bug fix.
> > 
> >> there an upside or downside to this?  What happens "today" when not
> > 
> > You get non-shared memory
> > 
> 
> So today someone asks for "shared" and then end up with "non-shared"? I
> don't think that's apparent from the "access" description in:
> 
> https://libvirt.org/formatdomain.html#elementsMemoryBacking
> 
> Then again, not in my wheelhouse of knowledge, so maybe that's just one
> of those givens. Of course that perhaps goes to your first answer of
> this being a "bug fix". Not something that's apparent from the existing
> documentation or commit description though. This probably should have
> been it's own separate patch and not included in this series.

If we can't honour the "shared" request, we should make sure libvirt
reports an error and aborts startup.

Regards,
Daniel
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