[PATCH 2/3] sched,numa: retry placement more frequently when misplaced

[riel@redhat.com]

From: Rik van Riel <riel@redhat.com>

When tasks have not converged on their preferred nodes yet, we want
to retry fairly often, to make sure we do not migrate a task's memory
to an undesirable location, only to have to move it again later.

This patch reduces the interval at which migration is retried,
when the task's numa_scan_period is small.

Signed-off-by: Rik van Riel <riel@redhat.com>
Tested-by: Vinod Chegu <chegu_vinod@hp.com>
---
 kernel/sched/fair.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 12de50a..babd316 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1326,12 +1326,15 @@ static int task_numa_migrate(struct task_struct *p)
 /* Attempt to migrate a task to a CPU on the preferred node. */
 static void numa_migrate_preferred(struct task_struct *p)
 {
+	unsigned long interval = HZ;
+
 	/* This task has no NUMA fault statistics yet */
 	if (unlikely(p->numa_preferred_nid == -1 || !p->numa_faults_memory))
 		return;
 
 	/* Periodically retry migrating the task to the preferred node */
-	p->numa_migrate_retry = jiffies + HZ;
+	interval = min(interval, msecs_to_jiffies(p->numa_scan_period) / 16);
+	p->numa_migrate_retry = jiffies + interval;
 
 	/* Success if task is already running on preferred CPU */
 	if (task_node(p) == p->numa_preferred_nid)
-- 
1.8.5.3