linux-kernel - Re: [PATCH 1/2] mm, memcontrol: Add memcg_iterate

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Date:   Thu, 27 Jun 2019 17:07:46 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 1/2] mm, memcontrol: Add memcg_iterate_all()

On Mon 24-06-19 13:42:18, Waiman Long wrote:
> Add a memcg_iterate_all() function for iterating all the available
> memory cgroups and call the given callback function for each of the
> memory cgruops.

Why is a trivial wrapper any better than open coded usage of the
iterator?

> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  include/linux/memcontrol.h |  3 +++
>  mm/memcontrol.c            | 13 +++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 1dcb763bb610..0e31418e5a47 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1268,6 +1268,9 @@ static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
>  struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep);
>  void memcg_kmem_put_cache(struct kmem_cache *cachep);
>  
> +extern void memcg_iterate_all(void (*callback)(struct mem_cgroup *memcg,
> +					       void *arg), void *arg);
> +
>  #ifdef CONFIG_MEMCG_KMEM
>  int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order);
>  void __memcg_kmem_uncharge(struct page *page, int order);
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ba9138a4a1de..c1c4706f7696 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -443,6 +443,19 @@ static int memcg_alloc_shrinker_maps(struct mem_cgroup *memcg)
>  static void memcg_free_shrinker_maps(struct mem_cgroup *memcg) { }
>  #endif /* CONFIG_MEMCG_KMEM */
>  
> +/*
> + * Iterate all the memory cgroups and call the given callback function
> + * for each of the memory cgroups.
> + */
> +void memcg_iterate_all(void (*callback)(struct mem_cgroup *memcg, void *arg),
> +		       void *arg)
> +{
> +	struct mem_cgroup *memcg;
> +
> +	for_each_mem_cgroup(memcg)
> +		callback(memcg, arg);
> +}
> +
>  /**
>   * mem_cgroup_css_from_page - css of the memcg associated with a page
>   * @page: page of interest
> -- 
> 2.18.1

-- 
Michal Hocko
SUSE Labs