Re: [PATCH v4 3/8] mm: list_lru: move list dead check to lock_list_lru_of_memcg()

[Liam R . Howlett]

On 26/05/21 11:02AM, Johannes Weiner wrote:
> Only the MEMCG variant of lock_list_lru() needs to check if there is a
> race with cgroup deletion and list reparenting. Move the check to the
> caller, so that the next patch can unify the lock_list_lru() variants.
> 
> 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 | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 9a68177619bf..9da6fce19832 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -68,17 +68,12 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
>  	return &lru->node[nid].lru;
>  }
>  
> -static inline bool lock_list_lru(struct list_lru_one *l, bool irq)
> +static inline void lock_list_lru(struct list_lru_one *l, bool irq)
>  {
>  	if (irq)
>  		spin_lock_irq(&l->lock);
>  	else
>  		spin_lock(&l->lock);
> -	if (unlikely(READ_ONCE(l->nr_items) == LONG_MIN)) {
> -		unlock_list_lru(l, irq);
> -		return false;
> -	}
> -	return true;
>  }
>  
>  static inline struct list_lru_one *
> @@ -90,9 +85,13 @@ lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
>  	rcu_read_lock();
>  again:
>  	l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
> -	if (likely(l) && lock_list_lru(l, irq)) {
> -		rcu_read_unlock();
> -		return l;
> +	if (likely(l)) {
> +		lock_list_lru(l, irq);
> +		if (likely(READ_ONCE(l->nr_items) != LONG_MIN)) {
> +			rcu_read_unlock();
> +			return l;
> +		}
> +		unlock_list_lru(l, irq);
>  	}
>  	/*
>  	 * Caller may simply bail out if raced with reparenting or
> -- 
> 2.54.0
>