Re: [PATCH 3/4] powerpc/numa: set node_possible_map from node_online_map

[Sang-Heon Jeon]

Hi Yury,

On Thu, Jul 2, 2026 at 5:55 AM Yury Norov <yury.norov@xxxxxxxxx> wrote:
>
> On Thu, Jul 02, 2026 at 02:18:50AM +0900, Sang-Heon Jeon wrote:
> > mem_topology_setup() intersects node_possible_map with node_online_map.
> > Nothing sets node_possible_map before this, so it is NODE_MASK_ALL and
> > the result is just node_online_map.
> >
> > In preparation for changing node_possible_map's initial value,
> > mem_topology_setup() no longer depends on it.
> >
> > No functional change.
> >
> > Signed-off-by: Sang-Heon Jeon <ekffu200098@xxxxxxxxx>
> > ---
> >  arch/powerpc/mm/numa.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> > index f4cf3ae036de..2fdecae90a01 100644
> > --- a/arch/powerpc/mm/numa.c
> > +++ b/arch/powerpc/mm/numa.c
> > @@ -1179,7 +1179,7 @@ void __init mem_topology_setup(void)
> >        * that we expect to make use of for this platform's affinity
> >        * calculations.
> >        */
> > -     nodes_and(node_possible_map, node_possible_map, node_online_map);
> > +     node_possible_map = node_online_map;
> >
> >       find_possible_nodes();
>
> And in find_possible_nodes():
>
>          for (i = 0; i < max_nodes; i++) {
>                  if (!node_possible(i))
>                          node_set(i, node_possible_map);
>          }
>
> So, assuming the code reaches to that point, you unconditionally
> online all the offlined nodes.

This loop only sets bits in node_possible_map, not in node_online_map,
so I can't find how it onlines the offlined nodes unexpectedly. Please
correct me if I'm wrong or missing something.

Or are you talking about the case where max_nodes exceeds
MAX_NUMNODES, which was also noticed by sashiko? I think it is a
pre-existing issue, and this patch does not affect it.

> This doesn't look correct at the first glance, and definitely it's not
> a "No functional change" type of things.

Best Regards,
Sang-Heon Jeon