linux-kernel - [PATCH v2 02/10] mm/page_alloc: prevent concurrent updaters of pcp ->batch and ->high

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Date:	Tue,  9 Apr 2013 16:28:11 -0700
From:	Cody P Schafer <cody@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Gilad Ben-Yossef <gilad@...yossef.com>,
	Simon Jeons <simon.jeons@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Mel Gorman <mgorman@...e.de>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>
Subject: [PATCH v2 02/10] mm/page_alloc: prevent concurrent updaters of pcp ->batch and ->high

Because we are going to rely upon a careful transision between old and
new ->high and ->batch values using memory barriers and will remove
stop_machine(), we need to prevent multiple updaters from interweaving
their memory writes.

Add a simple mutex to protect both update loops.

Signed-off-by: Cody P Schafer <cody@...ux.vnet.ibm.com>
---
 mm/page_alloc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5877cf0..d259599 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -64,6 +64,9 @@
 #include <asm/div64.h>
 #include "internal.h"
 
+/* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
+static DEFINE_MUTEX(pcp_batch_high_lock);
+
 #ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
 DEFINE_PER_CPU(int, numa_node);
 EXPORT_PER_CPU_SYMBOL(numa_node);
@@ -5491,6 +5494,8 @@ int percpu_pagelist_fraction_sysctl_handler(ctl_table *table, int write,
 	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
 	if (!write || (ret < 0))
 		return ret;
+
+	mutex_lock(&pcp_batch_high_lock);
 	for_each_populated_zone(zone) {
 		for_each_possible_cpu(cpu) {
 			unsigned long  high;
@@ -5499,6 +5504,7 @@ int percpu_pagelist_fraction_sysctl_handler(ctl_table *table, int write,
 				per_cpu_ptr(zone->pageset, cpu), high);
 		}
 	}
+	mutex_unlock(&pcp_batch_high_lock);
 	return 0;
 }
 
@@ -6012,7 +6018,9 @@ static int __meminit __zone_pcp_update(void *data)
 
 void __meminit zone_pcp_update(struct zone *zone)
 {
+	mutex_lock(&pcp_batch_high_lock);
 	stop_machine(__zone_pcp_update, zone, NULL);
+	mutex_unlock(&pcp_batch_high_lock);
 }
 #endif
 
-- 
1.8.2

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