mm/page_alloc: don't re-init pageset in zone_pcp_update()

When memory hotplug is triggered, we call pageset_init() on
per-cpu-pagesets which both contain pages and are in use, causing both the
leakage of those pages and (potentially) bad behaviour if a page is
allocated from a pageset while it is being cleared.

Avoid this by factoring out pageset_set_high_and_batch() (which contains
all needed logic too set a pageset's ->high and ->batch inrespective of
system state) from zone_pageset_init() and using the new
pageset_set_high_and_batch() instead of zone_pageset_init() in
zone_pcp_update().
Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -4104,11 +4104,9 @@ static void pageset_set_high(struct per_cpu_pageset *p,
 	pageset_update(&p->pcp, high, batch);
 }
 
-static void __meminit zone_pageset_init(struct zone *zone, int cpu)
+static void __meminit pageset_set_high_and_batch(struct zone *zone,
+		struct per_cpu_pageset *pcp)
 {
-	struct per_cpu_pageset *pcp = per_cpu_ptr(zone->pageset, cpu);
-
-	pageset_init(pcp);
 	if (percpu_pagelist_fraction)
 		pageset_set_high(pcp,
 			(zone->managed_pages /
@@ -4117,6 +4115,14 @@ static void __meminit zone_pageset_init(struct zone *zone, int cpu)
 		pageset_set_batch(pcp, zone_batchsize(zone));
 }
 
+static void __meminit zone_pageset_init(struct zone *zone, int cpu)
+{
+	struct per_cpu_pageset *pcp = per_cpu_ptr(zone->pageset, cpu);
+
+	pageset_init(pcp);
+	pageset_set_high_and_batch(zone, pcp);
+}
+
 static void __meminit setup_zone_pageset(struct zone *zone)
 {
 	int cpu;
@@ -6100,7 +6106,8 @@ void __meminit zone_pcp_update(struct zone *zone)
 	unsigned cpu;
 	mutex_lock(&pcp_batch_high_lock);
 	for_each_possible_cpu(cpu)
-		zone_pageset_init(zone, cpu);
+		pageset_set_high_and_batch(zone,
+				per_cpu_ptr(zone->pageset, cpu));
 	mutex_unlock(&pcp_batch_high_lock);
 }
 #endif