sched/numa: Select a preferred node with the most numa hinting faults

This patch selects a preferred node for a task to run on based on the
NUMA hinting faults. This information is later used to migrate tasks
towards the node during balancing.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-21-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 17 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a810e95bca2b..b1fc75e7187b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1344,6 +1344,7 @@ struct task_struct {
         struct callback_head numa_work;
 
         unsigned long *numa_faults;
+        int numa_preferred_nid;
 #endif /* CONFIG_NUMA_BALANCING */
 
         struct rcu_head rcu;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6808d35fd7ed..d15cd70f85b5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1633,6 +1633,7 @@ static void __sched_fork(struct task_struct *p)
         p->numa_scan_seq = p->mm ? p->mm->numa_scan_seq : 0;
         p->numa_migrate_seq = p->mm ? p->mm->numa_scan_seq - 1 : 0;
         p->numa_scan_period = sysctl_numa_balancing_scan_delay;
+        p->numa_preferred_nid = -1;
         p->numa_work.next = &p->numa_work;
         p->numa_faults = NULL;
 #endif /* CONFIG_NUMA_BALANCING */
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0bb3e0aa110b..9efd34f63e81 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -879,7 +879,8 @@ static unsigned int task_scan_max(struct task_struct *p)
 
 static void task_numa_placement(struct task_struct *p)
 {
-        int seq;
+        int seq, nid, max_nid = -1;
+        unsigned long max_faults = 0;
 
         if (!p->mm)     /* for example, ksmd faulting in a user's mm */
                 return;
@@ -889,7 +890,19 @@ static void task_numa_placement(struct task_struct *p)
         p->numa_scan_seq = seq;
         p->numa_scan_period_max = task_scan_max(p);
 
-        /* FIXME: Scheduling placement policy hints go here */
+        /* Find the node with the highest number of faults */
+        for_each_online_node(nid) {
+                unsigned long faults = p->numa_faults[nid];
+                p->numa_faults[nid] >>= 1;
+                if (faults > max_faults) {
+                        max_faults = faults;
+                        max_nid = nid;
+                }
+        }
+
+        /* Update the tasks preferred node if necessary */
+        if (max_faults && max_nid != p->numa_preferred_nid)
+                p->numa_preferred_nid = max_nid;
 }
 
 /*