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



Hi
On Thu, Aug 16, 2018 at 12:48 PM Daniel P. Berrangé <berrange redhat com> wrote:
>
> On Fri, Jul 13, 2018 at 03:28:08PM +0200, 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.
>
>
> > diff --git a/tests/qemuxml2argvdata/fd-memory-no-numa-topology.args b/tests/qemuxml2argvdata/fd-memory-no-numa-topology.args
> > index bd88daaa3b..400fb39cc6 100644
> > --- a/tests/qemuxml2argvdata/fd-memory-no-numa-topology.args
> > +++ b/tests/qemuxml2argvdata/fd-memory-no-numa-topology.args
> > @@ -11,6 +11,10 @@ QEMU_AUDIO_DRV=none \
> >  -m 14336 \
> >  -mem-prealloc \
> >  -smp 8,sockets=8,cores=1,threads=1 \
> > +-object memory-backend-file,id=ram-node,\
> > +mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-instance-00000092/ram-node,\
> > +share=yes,size=15032385536 \
> > +-numa node,nodeid=0,memdev=ram-node \
>
> I'm not at all convinced it is safe todo this. We've been burnt in the
> past by adding  use of memory-backend objects causing migration to break
>
>
>   commit f309db1f4d51009bad0d32e12efc75530b66836b
>   Author: Michal Privoznik <mprivozn redhat com>
>   Date:   Thu Dec 18 12:36:48 2014 +0100
>
>     qemu: Create memory-backend-{ram,file} iff needed
>
>     Libvirt BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1175397
>     QEMU BZ:    https://bugzilla.redhat.com/show_bug.cgi?id=1170093
>
> This change doesn't really feel like it is required either. If the
> user wants NUMA, then the XML can just be written to request a NUMA
> topology with a single node.  Better to be explicit in the XML rather
> than silently adding things as a side effect

Ok, let's drop this patch then. I'll modify "qemu: use
memory-backend-memfd if possible" to make use of memfd differently,
with explicit NUMA.

>
> Regards,
> Daniel
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-- 
Marc-André Lureau


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