[PATCH] mm/vmscan.c: only adjust related kswapd cpu affinity when online cpu

[Wei Yang]

When onlining a cpu, kswapd_cpu_online() is called to adjust kswapd cpu
affinity.

Current routine does like this:

  * Iterate all the numa node
  * Adjust cpu affinity when node has an online cpu

Actually we could improve this by:

  * Just adjust the numa node to which current online cpu belongs

Because we know which numa node the cpu belongs to and this cpu would
not affect other node.

Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
---
 mm/vmscan.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 572fb17c6273..19c92d35045c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4049,18 +4049,19 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
    restore their cpu bindings. */
 static int kswapd_cpu_online(unsigned int cpu)
 {
-	int nid;
+	int nid = cpu_to_node(cpu);
+	pg_data_t *pgdat;
+	const struct cpumask *mask;
 
-	for_each_node_state(nid, N_MEMORY) {
-		pg_data_t *pgdat = NODE_DATA(nid);
-		const struct cpumask *mask;
+	if (!node_state(nid, N_MEMORY))
+		return 0;
 
-		mask = cpumask_of_node(pgdat->node_id);
+	pgdat = NODE_DATA(nid);
+	mask = cpumask_of_node(nid);
+
+	/* One of our CPUs online: restore mask */
+	set_cpus_allowed_ptr(pgdat->kswapd, mask);
 
-		if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
-			/* One of our CPUs online: restore mask */
-			set_cpus_allowed_ptr(pgdat->kswapd, mask);
-	}
 	return 0;
 }
 
-- 
2.17.1