While reviewing an earlier series [1], Andrew asked why we carefully
initialize node_possible_map at compile time, then zero it within __init
code anyway.

node_possible_map, aliased by node_states[N_POSSIBLE], is initialized to
NODE_MASK_ALL at compile time, unlike the other entries, which are
initialized with only node 0 set.

Architectures that use numa_memblks set node_possible_map from
numa_nodes_parsed, so the compile-time value is meaningless for them.

However, a few architectures that do not use numa_memblks do not set
node_possible_map on their own. Once these architectures set
node_possible_map to match their own topology, the NODE_MASK_ALL
initialization can be removed.

Patches 1-2 handle sparc64 and sh, which do not set node_possible_map
themselves. Both set node_online_map from their topology, so set
node_possible_map from node_online_map.

Patch 3 handles powerpc, which sets node_possible_map by intersecting it
with node_online_map. Nothing sets node_possible_map before this, so it is
still NODE_MASK_ALL and the intersection is just node_online_map. Once
patch 4 changes that initial value, the intersection would no longer be
node_online_map, so assign node_online_map directly.

Patch 4 initializes node_possible_map with only node 0 set, like the other
node_states[] entries. NODE_MASK_ALL is then no longer used, so remove it
and its only helper NODE_MASK_LAST_WORD.

[1] https://lore.kernel.org/all/20260624204030.3c8baa67713b6ca1d537baba@linux-foundation.org/ (local)

Sang-Heon Jeon (4):
  sparc64: set node_possible_map in bootmem_init_numa()
  sh: set node_possible_map in do_init_bootmem()
  powerpc/numa: set node_possible_map from node_online_map
  mm/page_alloc: initialize node_possible_map like the other node maps

 arch/powerpc/mm/numa.c   |  2 +-
 arch/sh/mm/init.c        |  2 ++
 arch/sparc/mm/init_64.c  |  2 ++
 include/linux/nodemask.h | 20 --------------------
 mm/page_alloc.c          |  2 +-
 5 files changed, 6 insertions(+), 22 deletions(-)

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2.43.0