[PATCH v4 1/3] powerpc/numa: Set numa_node for all possible cpus

[Srikar Dronamraju]

A Powerpc system with multiple possible nodes and with CONFIG_NUMA
enabled always used to have a node 0, even if node 0 does not any cpus
or memory attached to it. As per PAPR, node affinity of a cpu is only
available once its present / online. For all cpus that are possible but
not present, cpu_to_node() would point to node 0.

To ensure a cpuless, memoryless dummy node is not online, powerpc need
to make sure all possible but not present cpu_to_node are set to a
proper node.

Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Christopher Lameter <cl@xxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Gautham R Shenoy <ego@xxxxxxxxxxxxxxxxxx>
Cc: Satheesh Rajendran <sathnaga@xxxxxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
---
Changelog v3:->v4:
- Resolved comments from Christopher.
Link v3: http://lore.kernel.org/lkml/20200501031128.19584-1-srikar@xxxxxxxxxxxxxxxxxx/t/#u

Changelog v1:->v2:
- Rebased to v5.7-rc3

 arch/powerpc/mm/numa.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 9fcf2d1..5b7918c 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -506,6 +506,11 @@ static int numa_setup_cpu(unsigned long lcpu)
 	int fcpu = cpu_first_thread_sibling(lcpu);
 	int nid = NUMA_NO_NODE;
 
+	if (!cpu_present(lcpu)) {
+		set_cpu_numa_node(lcpu, first_online_node);
+		return first_online_node;
+	}
+
 	/*
 	 * If a valid cpu-to-node mapping is already available, use it
 	 * directly instead of querying the firmware, since it represents
@@ -931,8 +936,17 @@ void __init mem_topology_setup(void)
 
 	reset_numa_cpu_lookup_table();
 
-	for_each_present_cpu(cpu)
+	for_each_possible_cpu(cpu) {
+		/*
+		 * Powerpc with CONFIG_NUMA always used to have a node 0,
+		 * even if it was memoryless or cpuless. For all cpus that
+		 * are possible but not present, cpu_to_node() would point
+		 * to node 0. To remove a cpuless, memoryless dummy node,
+		 * powerpc need to make sure all possible but not present
+		 * cpu_to_node are set to a proper node.
+		 */
 		numa_setup_cpu(cpu);
+	}
 }
 
 void __init initmem_init(void)
-- 
1.8.3.1