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