linux-kernel - Re: [v5 PATCH 02/11] mm: vmscan: consolidate shrinker

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Date:   Thu, 28 Jan 2021 17:10:05 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Yang Shi <shy828301@...il.com>, guro@...com, ktkhai@...tuozzo.com,
        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: [v5 PATCH 02/11] mm: vmscan: consolidate shrinker_maps handling
 code

On 1/28/21 12:33 AM, Yang Shi wrote:
> The shrinker map management is not purely memcg specific, it is at the intersection
> between memory cgroup and shrinkers.  It's allocation and assignment of a structure,
> and the only memcg bit is the map is being stored in a memcg structure.  So move the
> shrinker_maps handling code into vmscan.c for tighter integration with shrinker code,
> and remove the "memcg_" prefix.  There is no functional change.
> 
> Signed-off-by: Yang Shi <shy828301@...il.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

Nits below:

> @@ -1581,10 +1581,10 @@ static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
>  	return false;
>  }
>  
> -extern int memcg_expand_shrinker_maps(int new_id);
> -
> -extern void memcg_set_shrinker_bit(struct mem_cgroup *memcg,
> -				   int nid, int shrinker_id);
> +extern int alloc_shrinker_maps(struct mem_cgroup *memcg);
> +extern void free_shrinker_maps(struct mem_cgroup *memcg);
> +extern void set_shrinker_bit(struct mem_cgroup *memcg,
> +			     int nid, int shrinker_id);

"extern" is unnecessary and people seem to be removing them nowadays when
touching the code

>  /*
>   * We allow subsystems to populate their shrinker-related
>   * LRU lists before register_shrinker_prepared() is called
> @@ -212,7 +338,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
>  		goto unlock;
>  
>  	if (id >= shrinker_nr_max) {
> -		if (memcg_expand_shrinker_maps(id)) {
> +		if (expand_shrinker_maps(id)) {
>  			idr_remove(&shrinker_idr, id);
>  			goto unlock;
>  		}
> @@ -601,7 +727,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,

Above this is a comment about barriers in memcg_set_shrinker_bit() that should
be updated.

>  			if (ret == SHRINK_EMPTY)
>  				ret = 0;
>  			else
> -				memcg_set_shrinker_bit(memcg, nid, i);
> +				set_shrinker_bit(memcg, nid, i);
>  		}
>  		freed += ret;
>  
>