memory hotplug: update zone pcp at memory online

In my test, 128M memory is hot added, but zone's pcp batch is 0, which is
an obvious error.  When pages are onlined, zone pcp should be updated
accordingly.

[akpm@linux-foundation.org: fix warnings]
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Yakui Zhao <yakui.zhao@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -422,6 +422,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages)
 	zone->present_pages += onlined_pages;
 	zone->zone_pgdat->node_present_pages += onlined_pages;
 
+	zone_pcp_update(zone);
 	setup_per_zone_wmarks();
 	calculate_zone_inactive_ratio(zone);
 	if (onlined_pages) {

mm/page_alloc.c

@@ -3142,6 +3142,32 @@ int zone_wait_table_init(struct zone *zone, unsigned long zone_size_pages)
 	return 0;
 }
 
+static int __zone_pcp_update(void *data)
+{
+	struct zone *zone = data;
+	int cpu;
+	unsigned long batch = zone_batchsize(zone), flags;
+
+	for (cpu = 0; cpu < NR_CPUS; cpu++) {
+		struct per_cpu_pageset *pset;
+		struct per_cpu_pages *pcp;
+
+		pset = zone_pcp(zone, cpu);
+		pcp = &pset->pcp;
+
+		local_irq_save(flags);
+		free_pages_bulk(zone, pcp->count, &pcp->list, 0);
+		setup_pageset(pset, batch);
+		local_irq_restore(flags);
+	}
+	return 0;
+}
+
+void zone_pcp_update(struct zone *zone)
+{
+	stop_machine(__zone_pcp_update, zone, NULL);
+}
+
 static __meminit void zone_pcp_init(struct zone *zone)
 {
 	int cpu;