Re: [v7 PATCH 11/12] mm: memcontrol: reparent nr_deferred when memcg offline

[Roman Gushchin <guro@fb.com>]

On Tue, Feb 09, 2021 at 09:46:45AM -0800, Yang Shi wrote:
> Now shrinker's nr_deferred is per memcg for memcg aware shrinkers, add to parent's
> corresponding nr_deferred when memcg offline.
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> Signed-off-by: Yang Shi <shy828301@gmail.com>

Acked-by: Roman Gushchin <guro@fb.com>

> ---
>  include/linux/memcontrol.h |  1 +
>  mm/memcontrol.c            |  1 +
>  mm/vmscan.c                | 24 ++++++++++++++++++++++++
>  3 files changed, 26 insertions(+)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index c457fc7bc631..e1c4b93889ad 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1585,6 +1585,7 @@ static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
>  int alloc_shrinker_info(struct mem_cgroup *memcg);
>  void free_shrinker_info(struct mem_cgroup *memcg);
>  void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id);
> +void reparent_shrinker_deferred(struct mem_cgroup *memcg);
>  #else
>  #define mem_cgroup_sockets_enabled 0
>  static inline void mem_cgroup_sk_alloc(struct sock *sk) { };
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f64ad0d044d9..21f36b73f36a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5282,6 +5282,7 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
>  	page_counter_set_low(&memcg->memory, 0);
>  
>  	memcg_offline_kmem(memcg);
> +	reparent_shrinker_deferred(memcg);
>  	wb_memcg_offline(memcg);
>  
>  	drain_all_stock(memcg);
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index dfde6e7fd7f5..66163082cc6f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -389,6 +389,30 @@ static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
>  	return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
>  }
>  
> +void reparent_shrinker_deferred(struct mem_cgroup *memcg)
> +{
> +	int i, nid;
> +	long nr;
> +	struct mem_cgroup *parent;
> +	struct shrinker_info *child_info, *parent_info;
> +
> +	parent = parent_mem_cgroup(memcg);
> +	if (!parent)
> +		parent = root_mem_cgroup;
> +
> +	/* Prevent from concurrent shrinker_info expand */
> +	down_read(&shrinker_rwsem);
> +	for_each_node(nid) {
> +		child_info = shrinker_info_protected(memcg, nid);
> +		parent_info = shrinker_info_protected(parent, nid);
> +		for (i = 0; i < shrinker_nr_max; i++) {
> +			nr = atomic_long_read(&child_info->nr_deferred[i]);
> +			atomic_long_add(nr, &parent_info->nr_deferred[i]);
> +		}
> +	}
> +	up_read(&shrinker_rwsem);
> +}
> +
>  static bool cgroup_reclaim(struct scan_control *sc)
>  {
>  	return sc->target_mem_cgroup;
> -- 
> 2.26.2
>