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Subject[PATCH 2/3] sched/fair: Move task_numa_work() init to init_numa_balancing()
Date
We only need to set the callback_head worker function once, do it
during sched_fork().

While at it, move the comment regarding double task_work addition to
init_numa_balancing(), since the double add sentinel is first set there.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
kernel/sched/fair.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 476b0201a8fb..74faa55bc52a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2441,7 +2441,7 @@ void task_numa_work(struct callback_head *work)

SCHED_WARN_ON(p != container_of(work, struct task_struct, numa_work));

- work->next = work; /* protect against double add */
+ work->next = work;
/*
* Who cares about NUMA placement when they're dying.
*
@@ -2585,12 +2585,15 @@ void init_numa_balancing(unsigned long clone_flags, struct task_struct *p)
p->node_stamp = 0;
p->numa_scan_seq = mm ? mm->numa_scan_seq : 0;
p->numa_scan_period = sysctl_numa_balancing_scan_delay;
+ /* Protect against double add, see task_tick_numa and task_numa_work */
p->numa_work.next = &p->numa_work;
p->numa_faults = NULL;
p->numa_group = NULL;
p->last_task_numa_placement = 0;
p->last_sum_exec_runtime = 0;

+ init_task_work(&p->numa_work, task_numa_work);
+
/* New address space, reset the preferred nid */
if (!(clone_flags & CLONE_VM)) {
p->numa_preferred_nid = NUMA_NO_NODE;
@@ -2639,10 +2642,8 @@ static void task_tick_numa(struct rq *rq, struct task_struct *curr)
curr->numa_scan_period = task_scan_start(curr);
curr->node_stamp += period;

- if (!time_before(jiffies, curr->mm->numa_next_scan)) {
- init_task_work(work, task_numa_work); /* TODO: move this into sched_fork() */
+ if (!time_before(jiffies, curr->mm->numa_next_scan))
task_work_add(curr, work, true);
- }
}
}

--
2.22.0
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