Re: [PATCH v3 1/7] mm: list_lru: lock_list_lru_of_memcg() cannot return NULL if !skip_empty

[Lorenzo Stoakes (Oracle)]

On Wed, Mar 18, 2026 at 03:53:19PM -0400, Johannes Weiner wrote:
> skip_empty is only for the shrinker to abort and skip a list that's
> empty or whose cgroup is being deleted.
>
> For list additions and deletions, the cgroup hierarchy is walked
> upwards until a valid list_lru head is found, or it will fall back to
> the node list. Acquiring the lock won't fail. Remove the NULL checks
> in those callers.
>
> Reviewed-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

LGTM, as !skip_empty and so that just isn't possible, so:

Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>

> ---
>  mm/list_lru.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 26463ae29c64..d96fd50fc9af 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -165,8 +165,6 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
>  	struct list_lru_one *l;
>
>  	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
> -	if (!l)
> -		return false;
>  	if (list_empty(item)) {
>  		list_add_tail(item, &l->list);
>  		/* Set shrinker bit if the first element was added */
> @@ -203,9 +201,8 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid,
>  {
>  	struct list_lru_node *nlru = &lru->node[nid];
>  	struct list_lru_one *l;
> +
>  	l = lock_list_lru_of_memcg(lru, nid, memcg, false, false);
> -	if (!l)
> -		return false;
>  	if (!list_empty(item)) {
>  		list_del_init(item);
>  		l->nr_items--;
> --
> 2.53.0
>

Cheers, Lorenzo