[PATCH v2 3/3] mm: Consider the number in local CPUs when *reads* NUMA stats

[Kemi Wang]

To avoid deviation, the per cpu number of NUMA stats in vm_numa_stat_diff[]
is included when a user *reads* the NUMA stats.

Since NUMA stats does not be read by users frequently, and kernel does not
need it to make a decision, it will not be a problem to make the readers
more expensive.

Changelog:
v2:
    a) new creation.

Signed-off-by: Kemi Wang <kemi.wang@xxxxxxxxx>
---
 include/linux/vmstat.h | 6 +++++-
 mm/vmstat.c            | 9 +++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index a29bd98..72e9ca6 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -125,10 +125,14 @@ static inline unsigned long global_numa_state(enum numa_stat_item item)
 	return x;
 }
 
-static inline unsigned long zone_numa_state(struct zone *zone,
+static inline unsigned long zone_numa_state_snapshot(struct zone *zone,
 					enum numa_stat_item item)
 {
 	long x = atomic_long_read(&zone->vm_numa_stat[item]);
+	int cpu;
+
+	for_each_online_cpu(cpu)
+		x += per_cpu_ptr(zone->pageset, cpu)->vm_numa_stat_diff[item];
 
 	return x;
 }
diff --git a/mm/vmstat.c b/mm/vmstat.c
index b015f39..abeab81 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -895,6 +895,10 @@ unsigned long sum_zone_node_page_state(int node,
 	return count;
 }
 
+/*
+ * Determine the per node value of a numa stat item. To avoid deviation,
+ * the per cpu stat number in vm_numa_stat_diff[] is also included.
+ */
 unsigned long sum_zone_numa_state(int node,
 				 enum numa_stat_item item)
 {
@@ -903,7 +907,7 @@ unsigned long sum_zone_numa_state(int node,
 	unsigned long count = 0;
 
 	for (i = 0; i < MAX_NR_ZONES; i++)
-		count += zone_numa_state(zones + i, item);
+		count += zone_numa_state_snapshot(zones + i, item);
 
 	return count;
 }
@@ -1534,7 +1538,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 	for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++)
 		seq_printf(m, "\n      %-12s %lu",
 				vmstat_text[i + NR_VM_ZONE_STAT_ITEMS],
-				zone_numa_state(zone, i));
+				zone_numa_state_snapshot(zone, i));
 #endif
 
 	seq_printf(m, "\n  pagesets");
@@ -1790,6 +1794,7 @@ static bool need_update(int cpu)
 #ifdef CONFIG_NUMA
 		BUILD_BUG_ON(sizeof(p->vm_numa_stat_diff[0]) != 2);
 #endif
+
 		/*
 		 * The fast way of checking if there are any vmstat diffs.
 		 * This works because the diffs are byte sized items.
-- 
2.7.4