Re: [PATCH] mm/slub: remove useless kmem_cache_debug

[David Rientjes]

On Mon, 10 Aug 2020, wuyun.wu@xxxxxxxxxx wrote:

> From: Abel Wu <wuyun.wu@xxxxxxxxxx>
> 
> The commit below is incomplete, as it didn't handle the add_full() part.
> commit a4d3f8916c65 ("slub: remove useless kmem_cache_debug() before remove_full()")
> 
> Signed-off-by: Abel Wu <wuyun.wu@xxxxxxxxxx>
> ---
>  mm/slub.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index fe81773..0b021b7 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2182,7 +2182,8 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
>  		}
>  	} else {
>  		m = M_FULL;
> -		if (kmem_cache_debug(s) && !lock) {
> +#ifdef CONFIG_SLUB_DEBUG
> +		if (!lock) {
>  			lock = 1;
>  			/*
>  			 * This also ensures that the scanning of full
> @@ -2191,6 +2192,7 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
>  			 */
>  			spin_lock(&n->list_lock);
>  		}
> +#endif
>  	}
> 
>  	if (l != m) {

This should be functionally safe, I'm wonder if it would make sense to 
only check for SLAB_STORE_USER here instead of kmem_cache_debug(), 
however, since that should be the only context in which we need the 
list_lock for add_full()?  It seems more explicit.