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

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Message-Id: <20160803191310.GB28305@arbab-laptop.austin.ibm.com>
Date:	Wed, 3 Aug 2016 14:13:10 -0500
From:	Reza Arbab <arbab@...ux.vnet.ibm.com>
To:	Mel Gorman <mgorman@...hsingularity.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>, Rik van Riel <riel@...riel.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/34] mm, vmstat: add infrastructure for per-node vmstats

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