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Subject: Re: [RFC PATCH] powerpc/numa: reset node_possible_map to only
 node_online_map
From: Michael Ellerman <mpe@ellerman.id.au>
To: David Rientjes <rientjes@google.com>
Date: Fri, 06 Mar 2015 08:48:52 +1100
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Cc: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>,
 Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
 Paul Mackerras <paulus@samba.org>, Anton Blanchard <anton@samba.org>,
 Tejun Heo <tj@kernel.org>, linuxppc-dev@lists.ozlabs.org
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On Thu, 2015-03-05 at 13:16 -0800, David Rientjes wrote:
> On Thu, 5 Mar 2015, Nishanth Aravamudan wrote:
> 
> > diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> > index 0257a7d659ef..24de29b3651b 100644
> > --- a/arch/powerpc/mm/numa.c
> > +++ b/arch/powerpc/mm/numa.c
> > @@ -958,9 +958,17 @@ void __init initmem_init(void)
> >  
> >  	memblock_dump_all();
> >  
> > +	/*
> > +	 * zero out the possible nodes after we parse the device-tree,
> > +	 * so that we lower the maximum NUMA node ID to what is actually
> > +	 * present.
> > +	 */
> > +	nodes_clear(node_possible_map);
> > +
> >  	for_each_online_node(nid) {
> >  		unsigned long start_pfn, end_pfn;
> >  
> > +		node_set(nid, node_possible_map);
> >  		get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
> >  		setup_node_data(nid, start_pfn, end_pfn);
> >  		sparse_memory_present_with_active_regions(nid);
> 
> This seems a bit strange, node_possible_map is supposed to be a superset 
> of node_online_map and this loop is iterating over node_online_map to set 
> nodes in node_possible_map.
 
Yeah. Though at this point in boot I don't think it matters that the two maps
are out-of-sync temporarily.

But it would simpler to just set the possible map to be the online map. That
would also maintain the invariant that the possible map is always a superset of
the online map.

Or did I miss a detail there (sleep deprived parent mode).

cheers