sched/numa: Retry placement more frequently when misplaced

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>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1397235629-16328-3-git-send-email-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f6457b63c95c..ecea8d9f957c 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)