[RFC PATCH 3/4] build per numa_group active node mask from faults_from statistics

[riel]

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

The faults_from statistics are used to maintain an active_nodes nodemask
per numa_group. This allows us to be smarter about when to do numa migrations.

Signed-off-by: Rik van Riel <r...@redhat.com>
---
 kernel/sched/fair.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 89b5217..91b8f11 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -869,6 +869,7 @@ struct numa_group {
        struct list_head task_list;
 
        struct rcu_head rcu;
+       nodemask_t active_nodes;
        unsigned long total_faults;
        unsigned long *faults_from;
        unsigned long faults[0];
@@ -1228,6 +1229,34 @@ static void numa_migrate_preferred(struct task_struct *p)
        task_numa_migrate(p);
 }
 
+static void update_numa_active_node_mask(struct task_struct *p)
+{
+       unsigned long faults, max_faults = 0;
+       struct numa_group *numa_group = p->numa_group;
+       int nid;
+
+       for_each_online_node(nid) {
+               faults = numa_group->faults_from[task_faults_idx(nid, 0)] +
+                        numa_group->faults_from[task_faults_idx(nid, 1)];
+               if (faults > max_faults)
+                       max_faults = faults;
+       }
+
+       /*
+        * Mark any node where more than 40% of the faults
+        * (half minus some hysteresis) as part of this
+        * group's active nodes.
+        */
+       for_each_online_node(nid) {
+               faults = numa_group->faults_from[task_faults_idx(nid, 0)] +
+                        numa_group->faults_from[task_faults_idx(nid, 1)];
+               if (faults > max_faults * 4 / 10)
+                       node_set(nid, numa_group->active_nodes);
+               else
+                       node_clear(nid, numa_group->active_nodes);
+       }
+}
+
 /*
  * When adapting the scan rate, the period is divided into NUMA_PERIOD_SLOTS
  * increments. The more local the fault statistics are, the higher the scan
@@ -1387,6 +1416,8 @@ static void task_numa_placement(struct task_struct *p)
                        }
                }
 
+               update_numa_active_node_mask(p);
+
                spin_unlock(group_lock);
        }
 
@@ -1433,6 +1464,8 @@ static void task_numa_group(struct task_struct *p, int 
cpupid, int flags,
                /* Second half of the array tracks where faults come from */
                grp->faults_from = grp->faults + 2 * nr_node_ids;
 
+               node_set(task_node(current), grp->active_nodes);
+
                for (i = 0; i < 4*nr_node_ids; i++)
                        grp->faults[i] = p->numa_faults[i];
 
-- 
1.8.3.1

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