Re: [PATCH v2] mm/swap: Add cond_resched() in swap_reclaim_full_clusters to prevent softlockup

[Baoquan He <baoquan.he@linux.dev>]

On 05/06/26 at 09:09pm, Zijiang Huang wrote:
> We hit a real softlockup in an internal stress test environment.
> The workload was LTP memory/swap stress on a large arm64 machine,
> with 320 CPUs, about 1TB memory and an 8.6GB swap device.
> The system was under heavy load and the swap device had a large
> number of full clusters. The softlockup was triggered during
> a stress test after about 3 days.
> 
> So, add periodic cond_resched() calls during large full_clusters
> reclaim operations to prevent softlockup issues.
> 
> Detailed call trace as follow:
> 
> PID: 3817773  TASK: ffff0883bb28b780  CPU: 48   COMMAND: "kworker/48:7"
>    #0 [ffff800080183d10] __crash_kexec at ffffa4c1361e5de4
>    #1 [ffff800080183d90] panic at ffffa4c1360d5e9c
>    #2 [ffff800080183e20] watchdog_timer_fn at ffffa4c136231fa8
>    ...
>   #16 [ffff8000c4ad3cb0] swap_cache_del_folio at ffffa4c1363e1614
>   #17 [ffff8000c4ad3ce0] __try_to_reclaim_swap at ffffa4c1363e4bfc
>   #18 [ffff8000c4ad3d40] swap_reclaim_full_clusters at ffffa4c1363e5474
>   #19 [ffff8000c4ad3da0] swap_reclaim_work at ffffa4c1363e550c
>   #20 [ffff8000c4ad3dc0] process_one_work at ffffa4c136102edc
>   #21 [ffff8000c4ad3e10] worker_thread at ffffa4c136103398
>   #22 [ffff8000c4ad3e70] kthread at ffffa4c13610d95c
> 
> Fixes: 5168a68eb78f ("mm, swap: avoid over reclaim of full clusters")
> Signed-off-by: Zijiang Huang <kerayhuang@tencent.com>
> Reviewed-by: Kairui Song <kasong@tencent.com>
> Reviewed-by: Hao Peng <flyingpeng@tencent.com>
> Reviewed-by: albinwyang <albinwyang@tencent.com>
> ---
>  mm/swapfile.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 9174f1eeffb0..74a1e324449d 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1054,6 +1054,7 @@ static void swap_reclaim_full_clusters(struct swap_info_struct *si, bool force)
>  		swap_cluster_unlock(ci);
>  		if (to_scan <= 0)
>  			break;
> +		cond_resched();
>  	}
>  }

LGTM,

Reviewed-by: Baoquan He <baoquan.he@linux.dev>