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



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

Regards,
Daniel
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