Re: [PATCH 2/3] mm: memcontrol: fix memcg id ref counter on swap charge move

[Michal Hocko <mhocko@kernel.org>]

On Mon 01-08-16 16:26:25, Vladimir Davydov wrote:
> Since commit 73f576c04b941 swap entries do not pin memcg->css.refcnt
> directly. Instead, they pin memcg->id.ref. So we should adjust the
> reference counters accordingly when moving swap charges between cgroups.
> 
> Fixes: 73f576c04b941 ("mm: memcontrol: fix cgroup creation failure after many small jobs")

Same as the previous patch. It should be marked for stable along with
73f576c04b941.

> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  mm/memcontrol.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5fe285f27ea7..58c229071fb1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4030,9 +4030,9 @@ static struct cftype mem_cgroup_legacy_files[] = {
>  
>  static DEFINE_IDR(mem_cgroup_idr);
>  
> -static void mem_cgroup_id_get(struct mem_cgroup *memcg)
> +static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
>  {
> -	atomic_inc(&memcg->id.ref);
> +	atomic_add(n, &memcg->id.ref);
>  }
>  
>  static struct mem_cgroup *mem_cgroup_id_get_active(struct mem_cgroup *memcg)
> @@ -4042,9 +4042,9 @@ static struct mem_cgroup *mem_cgroup_id_get_active(struct mem_cgroup *memcg)
>  	return memcg;
>  }
>  
> -static void mem_cgroup_id_put(struct mem_cgroup *memcg)
> +static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n)
>  {
> -	if (atomic_dec_and_test(&memcg->id.ref)) {
> +	if (atomic_sub_and_test(n, &memcg->id.ref)) {
>  		idr_remove(&mem_cgroup_idr, memcg->id.id);
>  		memcg->id.id = 0;
>  
> @@ -4053,6 +4053,16 @@ static void mem_cgroup_id_put(struct mem_cgroup *memcg)
>  	}
>  }
>  
> +static inline void mem_cgroup_id_get(struct mem_cgroup *memcg)
> +{
> +	mem_cgroup_id_get_many(memcg, 1);
> +}
> +
> +static inline void mem_cgroup_id_put(struct mem_cgroup *memcg)
> +{
> +	mem_cgroup_id_put_many(memcg, 1);
> +}
> +
>  /**
>   * mem_cgroup_from_id - look up a memcg from a memcg id
>   * @id: the memcg id to look up
> @@ -4687,6 +4697,8 @@ static void __mem_cgroup_clear_mc(void)
>  		if (!mem_cgroup_is_root(mc.from))
>  			page_counter_uncharge(&mc.from->memsw, mc.moved_swap);
>  
> +		mem_cgroup_id_put_many(mc.from, mc.moved_swap);
> +
>  		/*
>  		 * we charged both to->memory and to->memsw, so we
>  		 * should uncharge to->memory.
> @@ -4694,9 +4706,9 @@ static void __mem_cgroup_clear_mc(void)
>  		if (!mem_cgroup_is_root(mc.to))
>  			page_counter_uncharge(&mc.to->memory, mc.moved_swap);
>  
> -		css_put_many(&mc.from->css, mc.moved_swap);
> +		mem_cgroup_id_get_many(mc.to, mc.moved_swap);
> +		css_put_many(&mc.to->css, mc.moved_swap);
>  
> -		/* we've already done css_get(mc.to) */
>  		mc.moved_swap = 0;
>  	}
>  	memcg_oom_recover(from);
> -- 
> 2.1.4
> 
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-- 
Michal Hocko
SUSE Labs

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