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Date:   Tue, 15 May 2018 07:08:32 +0300
From:   Vladimir Davydov <vdavydov.dev@gmail.com>
To:     Kirill Tkhai <ktkhai@virtuozzo.com>
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        viro@zeniv.linux.org.uk, hannes@cmpxchg.org, mhocko@kernel.org,
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Subject: Re: [PATCH v5 10/13] mm: Set bit in memcg shrinker bitmap on first
 list_lru item apearance
Message-ID: <20180515040832.ukmrcdl5czqpldgv@esperanza>
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On Thu, May 10, 2018 at 12:53:45PM +0300, Kirill Tkhai wrote:
> Introduce set_shrinker_bit() function to set shrinker-related
> bit in memcg shrinker bitmap, and set the bit after the first
> item is added and in case of reparenting destroyed memcg's items.
> 
> This will allow next patch to make shrinkers be called only,
> in case of they have charged objects at the moment, and
> to improve shrink_slab() performance.
> 
> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> ---
>  include/linux/memcontrol.h |   15 +++++++++++++++
>  mm/list_lru.c              |   22 ++++++++++++++++++++--
>  2 files changed, 35 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index e5e7e0fc7158..82f892e77637 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1274,6 +1274,21 @@ static inline void memcg_put_cache_ids(void)
>  
>  extern int memcg_shrinker_nr_max;
>  extern int memcg_expand_shrinker_maps(int old_id, int id);
> +
> +static inline void memcg_set_shrinker_bit(struct mem_cgroup *memcg, int nid, int nr)

Nit: too long line (> 80 characters)
Nit: let's rename 'nr' to 'shrinker_id'

> +{
> +	if (nr >= 0 && memcg && memcg != root_mem_cgroup) {
> +		struct memcg_shrinker_map *map;
> +
> +		rcu_read_lock();
> +		map = MEMCG_SHRINKER_MAP(memcg, nid);

Missing rcu_dereference.

> +		set_bit(nr, map->map);
> +		rcu_read_unlock();
> +	}
> +}
> +#else
> +static inline void memcg_set_shrinker_bit(struct mem_cgroup *memcg,
> +					  int node, int id) { }

Nit: please keep the signature (including argument names) the same as in
MEMCG-enabled definition, namely 'node' => 'nid', 'id' => 'shrinker_id'.

Thanks.