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

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

[kerayhuang]

Add periodic cond_resched() calls during large full_clusters
reclaim operations to prevent softlockup issues.

Signed-off-by: kerayhuang <kerayhuang@tencent.com>
Reviewed-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Hao Peng <flyingpeng@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();
 	}
 }
 
-- 
2.43.5

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

[Baoquan He]

Hi Keray,

On 04/24/26 at 08:37pm, kerayhuang wrote:
> Add periodic cond_resched() calls during large full_clusters
> reclaim operations to prevent softlockup issues.
> 
> Signed-off-by: kerayhuang <kerayhuang@tencent.com>
> Reviewed-by: Kairui Song <kasong@tencent.com>
> Reviewed-by: Hao Peng <flyingpeng@tencent.com>
> ---
>  mm/swapfile.c | 1 +
>  1 file changed, 1 insertion(+)

Thanks for the patch. The change looks good to me, however there are
still small concerns.

For patch log, it might be better to provide more details, e.g did you
observe this issue in a product environment, or just a code exploring?
If observed in a product environment, what does the backtrace look like 
when softlockup happened?

> 
> 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();

Besides, is it a little bit too aggressive to call cond_resched() for
each cluster reclaiming compared with the old code? Do you consider to
make it gentle, e.g calling cond_resched() every several clusters, 8, 16
or other number decided based on your testing performance statistics.

Thanks
Baoquan