linux-kernel - Re: [PATCH 04/19] sched/numa: Set preferred_node based on best

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Message-ID: <20180604121800.GR12217@hirez.programming.kicks-ass.net>
Date:   Mon, 4 Jun 2018 14:18:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 04/19] sched/numa: Set preferred_node based on best_cpu

On Mon, Jun 04, 2018 at 03:30:13PM +0530, Srikar Dronamraju wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ea32a66..94091e6 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1725,8 +1725,9 @@ static int task_numa_migrate(struct task_struct *p)
>  	 * Tasks that are "trapped" in such domains cannot be migrated
>  	 * elsewhere, so there is no point in (re)trying.
>  	 */
> -	if (unlikely(!sd)) {
> -		p->numa_preferred_nid = task_node(p);
> +	if (unlikely(!sd) && p->numa_preferred_nid != task_node(p)) {
> +		/* Set the new preferred node */
> +		sched_setnuma(p, task_node(p));
>  		return -EINVAL;
>  	}
>  

That looks dodgy.. this would allow things to continue with !sd.