Re: [RFC PATCH 15/20] mm: Make kswapd use kthread's preferred affinity

[Vlastimil Babka <vbabka@suse.cz>]

On 7/26/24 11:56 PM, Frederic Weisbecker wrote:
> Now that kthreads have an infrastructure to handle preferred affinity
> against CPU hotplug and housekeeping cpumask, convert kswapd to use
> it instead of handling halfway all the constraints by itself.
> 
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/vmscan.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2e34de9cd0d4..94359a893b4f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -7116,10 +7116,6 @@ static int kswapd(void *p)
>  	unsigned int highest_zoneidx = MAX_NR_ZONES - 1;
>  	pg_data_t *pgdat = (pg_data_t *)p;
>  	struct task_struct *tsk = current;
> -	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
> -
> -	if (!cpumask_empty(cpumask))
> -		set_cpus_allowed_ptr(tsk, cpumask);
>  
>  	/*
>  	 * Tell the memory management that we're a "memory allocator",
> @@ -7288,7 +7284,7 @@ void __meminit kswapd_run(int nid)
>  
>  	pgdat_kswapd_lock(pgdat);
>  	if (!pgdat->kswapd) {
> -		pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
> +		pgdat->kswapd = kthread_create(kswapd, pgdat, "kswapd%d", nid);
>  		if (IS_ERR(pgdat->kswapd)) {
>  			/* failure at boot is fatal */
>  			pr_err("Failed to start kswapd on node %d，ret=%ld\n",
> @@ -7296,6 +7292,8 @@ void __meminit kswapd_run(int nid)
>  			BUG_ON(system_state < SYSTEM_RUNNING);
>  			pgdat->kswapd = NULL;
>  		}
> +		kthread_affine_preferred(pgdat->kswapd, cpumask_of_node(pgdat->node_id));
> +		wake_up_process(pgdat->kswapd);
>  	}
>  	pgdat_kswapd_unlock(pgdat);
>  }