memory-hotplug: fix zone stat mismatch

During memory-hotplug, I found NR_ISOLATED_[ANON|FILE] are increasing,
causing the kernel to hang.  When the system doesn't have enough free
pages, it enters reclaim but never reclaim any pages due to
too_many_isolated()==true and loops forever.

The cause is that when we do memory-hotadd after memory-remove,
__zone_pcp_update() clears a zone's ZONE_STAT_ITEMS in setup_pageset()
although the vm_stat_diff of all CPUs still have values.

In addtion, when we offline all pages of the zone, we reset them in
zone_pcp_reset without draining so we loss some zone stat item.
Reviewed-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/vmstat.h

@@ -198,6 +198,8 @@ extern void __dec_zone_state(struct zone *, enum zone_stat_item);
 void refresh_cpu_vm_stats(int);
 void refresh_zone_stat_thresholds(void);
 
+void drain_zonestat(struct zone *zone, struct per_cpu_pageset *);
+
 int calculate_pressure_threshold(struct zone *zone);
 int calculate_normal_threshold(struct zone *zone);
 void set_pgdat_percpu_threshold(pg_data_t *pgdat,
@@ -251,6 +253,8 @@ static inline void __dec_zone_page_state(struct page *page,
 static inline void refresh_cpu_vm_stats(int cpu) { }
 static inline void refresh_zone_stat_thresholds(void) { }
 
+static inline void drain_zonestat(struct zone *zone,
+			struct per_cpu_pageset *pset) { }
 #endif		/* CONFIG_SMP */
 
 static inline void __mod_zone_freepage_state(struct zone *zone, int nr_pages,

mm/page_alloc.c

@@ -5916,6 +5916,7 @@ static int __meminit __zone_pcp_update(void *data)
 		local_irq_save(flags);
 		if (pcp->count > 0)
 			free_pcppages_bulk(zone, pcp->count, pcp);
+		drain_zonestat(zone, pset);
 		setup_pageset(pset, batch);
 		local_irq_restore(flags);
 	}
@@ -5932,10 +5933,16 @@ void __meminit zone_pcp_update(struct zone *zone)
 void zone_pcp_reset(struct zone *zone)
 {
 	unsigned long flags;
+	int cpu;
+	struct per_cpu_pageset *pset;
 
 	/* avoid races with drain_pages()  */
 	local_irq_save(flags);
 	if (zone->pageset != &boot_pageset) {
+		for_each_online_cpu(cpu) {
+			pset = per_cpu_ptr(zone->pageset, cpu);
+			drain_zonestat(zone, pset);
+		}
 		free_percpu(zone->pageset);
 		zone->pageset = &boot_pageset;
 	}

mm/vmstat.c

@@ -495,6 +495,18 @@ void refresh_cpu_vm_stats(int cpu)
 			atomic_long_add(global_diff[i], &vm_stat[i]);
 }
 
+void drain_zonestat(struct zone *zone, struct per_cpu_pageset *pset)
+{
+	int i;
+
+	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
+		if (pset->vm_stat_diff[i]) {
+			int v = pset->vm_stat_diff[i];
+			pset->vm_stat_diff[i] = 0;
+			atomic_long_add(v, &zone->vm_stat[i]);
+			atomic_long_add(v, &vm_stat[i]);
+		}
+}
 #endif
 
 #ifdef CONFIG_NUMA