[PATCH 3/8] sched: Select a preferred node with the most numa hinting faults

[Mel Gorman]

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@xxxxxxx>
---
 include/linux/sched.h |  1 +
 kernel/sched/core.c   | 10 ++++++++++
 kernel/sched/fair.c   | 16 ++++++++++++++--
 kernel/sched/sched.h  |  2 +-
 4 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 72861b4..ba46a64 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1507,6 +1507,7 @@ 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 f332ec0..019baae 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1593,6 +1593,7 @@ 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 */
@@ -5713,6 +5714,15 @@ enum s_alloc {
 
 struct sched_domain_topology_level;
 
+#ifdef CONFIG_NUMA_BALANCING
+
+/* Set a tasks preferred NUMA node */
+void sched_setnuma(struct task_struct *p, int nid)
+{
+	p->numa_preferred_nid = nid;
+}
+#endif /* CONFIG_NUMA_BALANCING */
+
 typedef struct sched_domain *(*sched_domain_init_f)(struct sched_domain_topology_level *tl, int cpu);
 typedef const struct cpumask *(*sched_domain_mask_f)(int cpu);
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 904fd6f..f8c3f61 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -793,7 +793,8 @@ unsigned int sysctl_numa_balancing_scan_delay = 1000;
 
 static void task_numa_placement(struct task_struct *p)
 {
-	int seq;
+	int seq, nid, max_nid = 0;
+	unsigned long max_faults = 0;
 
 	if (!p->mm)	/* for example, ksmd faulting in a user's mm */
 		return;
@@ -802,7 +803,18 @@ static void task_numa_placement(struct task_struct *p)
 		return;
 	p->numa_scan_seq = seq;
 
-	/* FIXME: Scheduling placement policy hints go here */
+	/* Find the node with the highest number of faults */
+	for (nid = 0; nid < nr_node_ids; nid++) {
+		unsigned long faults = p->numa_faults[nid];
+		p->numa_faults[nid] >>= 1;
+		if (faults > max_faults) {
+			max_faults = faults;
+			max_nid = nid;
+		}
+	}
+
+	if (max_faults && max_nid != p->numa_preferred_nid)
+		sched_setnuma(p, max_nid);
 }
 
 /*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9c26d88..65a0cf0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -504,7 +504,7 @@ DECLARE_PER_CPU(struct rq, runqueues);
 #define raw_rq()		(&__raw_get_cpu_var(runqueues))
 
 #ifdef CONFIG_NUMA_BALANCING
-extern void sched_setnuma(struct task_struct *p, int node, int shared);
+extern void sched_setnuma(struct task_struct *p, int nid);
 static inline void task_numa_free(struct task_struct *p)
 {
 	kfree(p->numa_faults);
-- 
1.8.1.4

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