Re: [PATCH v4 1/8] mm: list_lru: lock_list_lru_of_memcg() cannot return NULL if !skip_empty

[Liam R . Howlett]

On 26/05/21 11:02AM, 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>
> Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Reviewed-by: Liam R. Howlett (Oracle) <liam@xxxxxxxxxxxxx>

> ---
>  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 dd29bcf8eb5f..d3619961a7ac 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 */
> @@ -204,9 +202,8 @@ 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--;
> -- 
> 2.54.0
>