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Subject[PATCH 16/27] sched: Select a preferred node with the most numa hinting faults
Date
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>
---
include/linux/sched.h | 1 +
kernel/sched/core.c | 1 +
kernel/sched/fair.c | 17 +++++++++++++++--
3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 702a5b6..d65e31c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1336,6 +1336,7 @@ 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 e6dda1b..194559e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1634,6 +1634,7 @@ 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 babac71..ee8da21 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 (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;
+ }
+ }
+
+ /* Update the tasks preferred node if necessary */
+ if (max_faults && max_nid != p->numa_preferred_nid)
+ p->numa_preferred_nid = max_nid;
}

/*
--
1.8.1.4


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