[PATCH] autonuma: Fix scan period updating

[Huang Ying]

>From the commit log and comments of commit 37ec97deb3a8 ("sched/numa:
Slow down scan rate if shared faults dominate"), the autonuma scan
period should be increased (scanning is slowed down) if the majority
of the page accesses are shared with other processes.  But in current
code, the scan period will be decreased (scanning is speeded up) in
that situation.

The commit log and comments make more sense.  So this patch fixes the
code to make it match the commit log and comments.  And this has been
verified via tracing the scan period changing and /proc/vmstat
numa_pte_updates counter when running a multi-threaded memory
accessing program (most memory areas are accessed by multiple
threads).

Fixes: 37ec97deb3a8 ("sched/numa: Slow down scan rate if shared faults dominate")
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: jhladky@xxxxxxxxxx
Cc: lvenanci@xxxxxxxxxx
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/sched/fair.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 036be95a87e9..468a1c5038b2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1940,7 +1940,7 @@ static void update_task_scan_period(struct task_struct *p,
 			unsigned long shared, unsigned long private)
 {
 	unsigned int period_slot;
-	int lr_ratio, ps_ratio;
+	int lr_ratio, sp_ratio;
 	int diff;
 
 	unsigned long remote = p->numa_faults_locality[0];
@@ -1971,22 +1971,22 @@ static void update_task_scan_period(struct task_struct *p,
 	 */
 	period_slot = DIV_ROUND_UP(p->numa_scan_period, NUMA_PERIOD_SLOTS);
 	lr_ratio = (local * NUMA_PERIOD_SLOTS) / (local + remote);
-	ps_ratio = (private * NUMA_PERIOD_SLOTS) / (private + shared);
+	sp_ratio = (shared * NUMA_PERIOD_SLOTS) / (private + shared);
 
-	if (ps_ratio >= NUMA_PERIOD_THRESHOLD) {
+	if (sp_ratio >= NUMA_PERIOD_THRESHOLD) {
 		/*
-		 * Most memory accesses are local. There is no need to
-		 * do fast NUMA scanning, since memory is already local.
+		 * Most memory accesses are shared with other tasks.
+		 * There is no point in continuing fast NUMA scanning,
+		 * since other tasks may just move the memory elsewhere.
 		 */
-		int slot = ps_ratio - NUMA_PERIOD_THRESHOLD;
+		int slot = sp_ratio - NUMA_PERIOD_THRESHOLD;
 		if (!slot)
 			slot = 1;
 		diff = slot * period_slot;
 	} else if (lr_ratio >= NUMA_PERIOD_THRESHOLD) {
 		/*
-		 * Most memory accesses are shared with other tasks.
-		 * There is no point in continuing fast NUMA scanning,
-		 * since other tasks may just move the memory elsewhere.
+		 * Most memory accesses are local. There is no need to
+		 * do fast NUMA scanning, since memory is already local.
 		 */
 		int slot = lr_ratio - NUMA_PERIOD_THRESHOLD;
 		if (!slot)
@@ -1998,7 +1998,7 @@ static void update_task_scan_period(struct task_struct *p,
 		 * yet they are not on the local NUMA node. Speed up
 		 * NUMA scanning to get the memory moved over.
 		 */
-		int ratio = max(lr_ratio, ps_ratio);
+		int ratio = max(lr_ratio, sp_ratio);
 		diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot;
 	}
 
-- 
2.20.1