From: Libo Chen <libo.chen@xxxxxxxxxx> Task swapping is triggered when there are no idle CPUs in task A's preferred node. In this case, the NUMA load balancer chooses a task B on A's preferred node and swaps B with A. This helps improve NUMA locality without introducing load imbalance between nodes. In the current implementation, B's NUMA node preference is not mandatory, and it aims not to increase load imbalance. That is to say, a kernel thread might be chosen as B. However, kernel threads are not supposed to be covered by NUMA balancing because NUMA balancing only considers user pages via VMAs. Fix this by not considering kernel threads as swap targets in task_numa_compare(). This can be extended beyond kernel threads in the future by checking if a swap candidate has a valid NUMA preference through checking the candidate's numa_preferred_nid and numa_faults. For now, keep the code simple. Suggested-by: Michal Koutny <mkoutny@xxxxxxxx> Tested-by: Ayush Jain <Ayush.jain3@xxxxxxx> Signed-off-by: Libo Chen <libo.chen@xxxxxxxxxx> Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx> --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0fb9bf995a47..d1af2e084a2a 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2273,7 +2273,8 @@ static bool task_numa_compare(struct task_numa_env *env, rcu_read_lock(); cur = rcu_dereference(dst_rq->curr); - if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur))) + if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur) || + !cur->mm)) cur = NULL; /* -- 2.25.1
