Node 0 not necessary for powerpc?

[David Rientjes]

On Wed, 21 May 2014, Nishanth Aravamudan wrote:

> For context: I was looking at why N_ONLINE was statically setting Node 0
> to be online, whether or not the topology is that way -- I've been
> getting several bugs lately where Node 0 is online, but has no CPUs and
> no memory on it, on powerpc. 
> 
> On powerpc, setup_per_cpu_areas calls into ___alloc_bootmem_node using
> NODE_DATA(cpu_to_node(cpu)).
> 
> Currently, cpu_to_node() in arch/powerpc/include/asm/topology.h does:
> 
>         /*
>          * During early boot, the numa-cpu lookup table might not have been
>          * setup for all CPUs yet. In such cases, default to node 0.
>          */
>         return (nid < 0) ? 0 : nid;
> 
> And so early at boot, if node 0 is not present, we end up accessing an
> unitialized NODE_DATA(). So this seems buggy (I'll contact the powerpc
> deveopers separately on that).
> 

I think what this really wants to do is NODE_DATA(cpu_to_mem(cpu)) and I 
thought ppc had the cpu-to-local-memory-node mappings correct?