Re: [PATCH 01/34] mm, vmstat: add infrastructure for per-node vmstats

[Reza Arbab]

On Fri, Jul 08, 2016 at 10:34:37AM +0100, Mel Gorman wrote:
void refresh_zone_stat_thresholds(void)
{
[...]
+       /* Zero current pgdat thresholds */
+       for_each_online_pgdat(pgdat) {
+               for_each_online_cpu(cpu) {
+                       per_cpu_ptr(pgdat->per_cpu_nodestats, 
cpu)->stat_threshold = 0;
+               }
+       }

I am oopsing here, for a node whose pgdat->per_cpu_nodestats is NULL.

The node in question is memoryless, so in setup_per_cpu_pageset(), the 
loop over its populated zones doesn't run, and the per_cpu_nodestat 
struct isn't allocated.

This patch fixes things for me:

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ea759b9..5221e17 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5271,9 +5271,17 @@ static void __meminit setup_zone_pageset(struct zone 
*zone)
 void __init setup_per_cpu_pageset(void)
 {
        struct zone *zone;
+       struct pglist_data *pgdat;
 
 	for_each_populated_zone(zone)
                setup_zone_pageset(zone);
+
+       for_each_online_pgdat(pgdat) {
+               if (!pgdat->per_cpu_nodestats) {
+                       pgdat->per_cpu_nodestats =
+                               alloc_percpu(struct per_cpu_nodestat);
+               }
+       }
 }
 
 static noinline __init_refok


--
Reza Arbab