[PATCH v2 3/5] mm: enlarge NUMA counters threshold size

[Kemi Wang]

We have seen significant overhead in cache bouncing caused by NUMA counters
update in multi-threaded page allocation. See 'commit 1d90ca897cb0 ("mm:
update NUMA counter threshold size")' for more details.

This patch updates NUMA counters to a fixed size of (MAX_S16 - 2) and deals
with global counter update using different threshold size for node page
stats.

Signed-off-by: Kemi Wang <kemi.wang@xxxxxxxxx>
---
 mm/vmstat.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 9c681cc..64e08ae 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -30,6 +30,8 @@
 
 #include "internal.h"
 
+#define VM_NUMA_STAT_THRESHOLD (S16_MAX - 2)
+
 #ifdef CONFIG_NUMA
 int sysctl_vm_numa_stat = ENABLE_NUMA_STAT;
 
@@ -394,7 +396,11 @@ void __inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
 	s16 v, t;
 
 	v = __this_cpu_inc_return(*p);
-	t = __this_cpu_read(pcp->stat_threshold);
+	if (item >= NR_VM_NUMA_STAT_ITEMS)
+		t = __this_cpu_read(pcp->stat_threshold);
+	else
+		t = VM_NUMA_STAT_THRESHOLD;
+
 	if (unlikely(v > t)) {
 		s16 overstep = t >> 1;
 
@@ -549,7 +555,10 @@ static inline void mod_node_state(struct pglist_data *pgdat,
 		 * Most of the time the thresholds are the same anyways
 		 * for all cpus in a node.
 		 */
-		t = this_cpu_read(pcp->stat_threshold);
+		if (item >= NR_VM_NUMA_STAT_ITEMS)
+			t = this_cpu_read(pcp->stat_threshold);
+		else
+			t = VM_NUMA_STAT_THRESHOLD;
 
 		o = this_cpu_read(*p);
 		n = delta + o;
-- 
2.7.4