Re: [PATCH 12/12] memcg: don't need to free memcg via RCU or workqueue

[Michal Hocko <mhocko@suse.cz>]

On Mon 08-04-13 14:36:32, Li Zefan wrote:
> Now memcg has the same life cycle with its corresponding cgroup, and
> a cgroup is freed via RCU and then mem_cgroup_css_free() is called
> in a work function, so we can simply call __mem_cgroup_free() in
> mem_cgroup_css_free().
> 
> This actually reverts 59927fb984de1703c67bc640c3e522d8b5276c73
> ("memcg: free mem_cgroup by RCU to fix oops").
> 
> Cc: Hugh Dickins <hughd@google.com>
> Signed-off-by: Li Zefan <lizefan@huawei.com>

OK, makes sense after the previous changes.
Acked-by: Michal Hocko <mhocko@suse.cz>

> ---
>  mm/memcontrol.c | 51 +++++----------------------------------------------
>  1 file changed, 5 insertions(+), 46 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a6d44bc..5aa6e91 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -261,28 +261,10 @@ struct mem_cgroup {
>  	 */
>  	struct res_counter res;
>  
> -	union {
> -		/*
> -		 * the counter to account for mem+swap usage.
> -		 */
> -		struct res_counter memsw;
> -
> -		/*
> -		 * rcu_freeing is used only when freeing struct mem_cgroup,
> -		 * so put it into a union to avoid wasting more memory.
> -		 * It must be disjoint from the css field.  It could be
> -		 * in a union with the res field, but res plays a much
> -		 * larger part in mem_cgroup life than memsw, and might
> -		 * be of interest, even at time of free, when debugging.
> -		 * So share rcu_head with the less interesting memsw.
> -		 */
> -		struct rcu_head rcu_freeing;
> -		/*
> -		 * We also need some space for a worker in deferred freeing.
> -		 * By the time we call it, rcu_freeing is no longer in use.
> -		 */
> -		struct work_struct work_freeing;
> -	};
> +	/*
> +	 * the counter to account for mem+swap usage.
> +	 */
> +	struct res_counter memsw;
>  
>  	/*
>  	 * the counter to account for kernel memory usage.
> @@ -6097,29 +6079,6 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
>  		vfree(memcg);
>  }
>  
> -
> -/*
> - * Helpers for freeing a kmalloc()ed/vzalloc()ed mem_cgroup by RCU,
> - * but in process context.  The work_freeing structure is overlaid
> - * on the rcu_freeing structure, which itself is overlaid on memsw.
> - */
> -static void free_work(struct work_struct *work)
> -{
> -	struct mem_cgroup *memcg;
> -
> -	memcg = container_of(work, struct mem_cgroup, work_freeing);
> -	__mem_cgroup_free(memcg);
> -}
> -
> -static void free_rcu(struct rcu_head *rcu_head)
> -{
> -	struct mem_cgroup *memcg;
> -
> -	memcg = container_of(rcu_head, struct mem_cgroup, rcu_freeing);
> -	INIT_WORK(&memcg->work_freeing, free_work);
> -	schedule_work(&memcg->work_freeing);
> -}
> -
>  /*
>   * Returns the parent mem_cgroup in memcgroup hierarchy with hierarchy enabled.
>   */
> @@ -6269,7 +6228,7 @@ static void mem_cgroup_css_free(struct cgroup *cont)
>  
>  	mem_cgroup_sockets_destroy(memcg);
>  
> -	call_rcu(&memcg->rcu_freeing, free_rcu);
> +	__mem_cgroup_free(memcg);
>  }
>  
>  #ifdef CONFIG_MMU
> -- 
> 1.8.0.2
> --
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-- 
Michal Hocko
SUSE Labs

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