linux-kernel - Re: [PATCH v2 8/8] rcu/kfree: Fix kfree_rcu_shrink

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Message-ID: <20220626041738.GO1790663@paulmck-ThinkPad-P17-Gen-1>
Date:   Sat, 25 Jun 2022 21:17:38 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        rushikesh.s.kadam@...el.com, urezki@...il.com,
        neeraj.iitr10@...il.com, frederic@...nel.org, rostedt@...dmis.org,
        vineeth@...byteword.org
Subject: Re: [PATCH v2 8/8] rcu/kfree: Fix kfree_rcu_shrink_count() return
 value

On Wed, Jun 22, 2022 at 10:51:02PM +0000, Joel Fernandes (Google) wrote:
> As per the comments in include/linux/shrinker.h, .count_objects callback
> should return the number of freeable items, but if there are no objects
> to free, SHRINK_EMPTY should be returned. The only time 0 is returned
> should be when we are unable to determine the number of objects, or the
> cache should be skipped for another reason.

Good catch!

							Thanx, Paul

> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> ---
>  kernel/rcu/tree.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 711679d10cbb..935788e8d2d7 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -3722,7 +3722,7 @@ kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
>  		atomic_set(&krcp->backoff_page_cache_fill, 1);
>  	}
>  
> -	return count;
> +	return count == 0 ? SHRINK_EMPTY : count;
>  }
>  
>  static unsigned long
> -- 
> 2.37.0.rc0.104.g0611611a94-goog
>