[RFC PATCH 2/3] topology: support node_numa_mem() for determining the fallback node

[Christoph Lameter]

On Tue, 18 Feb 2014, Nishanth Aravamudan wrote:

>
> Well, on powerpc, with the hypervisor providing the resources and the
> topology, you can have cpuless and memoryless nodes. I'm not sure how
> "fake" the NUMA is -- as I think since the resources are virtualized to
> be one system, it's logically possible that the actual topology of the
> resources can be CPUs from physical node 0 and memory from physical node
> 2. I would think with KVM on a sufficiently large (physically NUMA
> x86_64) and loaded system, one could cause the same sort of
> configuration to occur for a guest?

Ok but since you have a virtualized environment: Why not provide a fake
home node with fake memory that could be anywhere? This would avoid the
whole problem of supporting such a config at the kernel level.

Do not have a fake node that has no memory.

> In any case, these configurations happen fairly often on long-running
> (not rebooted) systems as LPARs are created/destroyed, resources are
> DLPAR'd in and out of LPARs, etc.

Ok then also move the memory of the local node somewhere?

> I might look into it, as it might have sped up testing these changes.

I guess that will be necessary in order to support the memoryless nodes
long term.