linux-kernel - Re: [v7 PATCH 06/12] mm: vmscan: add shrinker_info

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Date:   Wed, 10 Feb 2021 15:12:39 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Yang Shi <shy828301@...il.com>, guro@...com, vbabka@...e.cz,
        shakeelb@...gle.com, david@...morbit.com, hannes@...xchg.org,
        mhocko@...e.com, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v7 PATCH 06/12] mm: vmscan: add shrinker_info_protected() helper

On 09.02.2021 20:46, Yang Shi wrote:
> The shrinker_info is dereferenced in a couple of places via rcu_dereference_protected
> with different calling conventions, for example, using mem_cgroup_nodeinfo helper
> or dereferencing memcg->nodeinfo[nid]->shrinker_info.  And the later patch
> will add more dereference places.
> 
> So extract the dereference into a helper to make the code more readable.  No
> functional change.
> 
> Signed-off-by: Yang Shi <shy828301@...il.com>

Acked-by: Kirill Tkhai <ktkhai@...tuozzo.com>

> ---
>  mm/vmscan.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 9436f9246d32..273efbf4d53c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -190,6 +190,13 @@ static int shrinker_nr_max;
>  #define NR_MAX_TO_SHR_MAP_SIZE(nr_max) \
>  	(DIV_ROUND_UP(nr_max, BITS_PER_LONG) * sizeof(unsigned long))
>  
> +static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
> +						     int nid)
> +{
> +	return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
> +					 lockdep_is_held(&shrinker_rwsem));
> +}
> +
>  static void free_shrinker_info_rcu(struct rcu_head *head)
>  {
>  	kvfree(container_of(head, struct shrinker_info, rcu));
> @@ -202,8 +209,7 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
>  	int nid;
>  
>  	for_each_node(nid) {
> -		old = rcu_dereference_protected(
> -			mem_cgroup_nodeinfo(memcg, nid)->shrinker_info, true);
> +		old = shrinker_info_protected(memcg, nid);
>  		/* Not yet online memcg */
>  		if (!old)
>  			return 0;
> @@ -234,7 +240,7 @@ void free_shrinker_info(struct mem_cgroup *memcg)
>  
>  	for_each_node(nid) {
>  		pn = mem_cgroup_nodeinfo(memcg, nid);
> -		info = rcu_dereference_protected(pn->shrinker_info, true);
> +		info = shrinker_info_protected(memcg, nid);
>  		kvfree(info);
>  		rcu_assign_pointer(pn->shrinker_info, NULL);
>  	}
> @@ -674,8 +680,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
>  	if (!down_read_trylock(&shrinker_rwsem))
>  		return 0;
>  
> -	info = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
> -					 true);
> +	info = shrinker_info_protected(memcg, nid);
>  	if (unlikely(!info))
>  		goto unlock;
>  
>