linux-kernel - Re: [PATCH v2 7/8] memcg: stop using css id

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Date:	Wed, 24 Jul 2013 16:30:00 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Glauber Costa <glommer@...allels.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH v2 7/8] memcg: stop using css id

On Wed 24-07-13 18:03:03, Li Zefan wrote:
> Now memcg uses cgroup id instead of css id. Update some comments and
> set mem_cgroup_subsys->use_id to 0.
> 
> Signed-off-by: Li Zefan <lizefan@...wei.com>

Acked-by: Michal Hocko <mhocko@...e.cz>

> ---
>  mm/memcontrol.c | 23 ++++++++---------------
>  1 file changed, 8 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 403c8d9..03c8bf7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -598,16 +598,11 @@ static void disarm_sock_keys(struct mem_cgroup *memcg)
>  #ifdef CONFIG_MEMCG_KMEM
>  /*
>   * This will be the memcg's index in each cache's ->memcg_params->memcg_caches.
> - * There are two main reasons for not using the css_id for this:
> - *  1) this works better in sparse environments, where we have a lot of memcgs,
> - *     but only a few kmem-limited. Or also, if we have, for instance, 200
> - *     memcgs, and none but the 200th is kmem-limited, we'd have to have a
> - *     200 entry array for that.
> - *
> - *  2) In order not to violate the cgroup API, we would like to do all memory
> - *     allocation in ->create(). At that point, we haven't yet allocated the
> - *     css_id. Having a separate index prevents us from messing with the cgroup
> - *     core for this
> + * The main reason for not using cgroup id for this:
> + *  this works better in sparse environments, where we have a lot of memcgs,
> + *  but only a few kmem-limited. Or also, if we have, for instance, 200
> + *  memcgs, and none but the 200th is kmem-limited, we'd have to have a
> + *  200 entry array for that.
>   *
>   * The current size of the caches array is stored in
>   * memcg_limited_groups_array_size.  It will double each time we have to
> @@ -622,14 +617,14 @@ int memcg_limited_groups_array_size;
>   * cgroups is a reasonable guess. In the future, it could be a parameter or
>   * tunable, but that is strictly not necessary.
>   *
> - * MAX_SIZE should be as large as the number of css_ids. Ideally, we could get
> + * MAX_SIZE should be as large as the number of cgrp_ids. Ideally, we could get
>   * this constant directly from cgroup, but it is understandable that this is
>   * better kept as an internal representation in cgroup.c. In any case, the
> - * css_id space is not getting any smaller, and we don't have to necessarily
> + * cgrp_id space is not getting any smaller, and we don't have to necessarily
>   * increase ours as well if it increases.
>   */
>  #define MEMCG_CACHES_MIN_SIZE 4
> -#define MEMCG_CACHES_MAX_SIZE 65535
> +#define MEMCG_CACHES_MAX_SIZE MEM_CGROUP_ID_MAX
>  
>  /*
>   * A lot of the calls to the cache allocation functions are expected to be
> @@ -6183,7 +6178,6 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
>  	size_t size = memcg_size();
>  
>  	mem_cgroup_remove_from_trees(memcg);
> -	free_css_id(&mem_cgroup_subsys, &memcg->css);
>  
>  	for_each_node(node)
>  		free_mem_cgroup_per_zone_info(memcg, node);
> @@ -6980,7 +6974,6 @@ struct cgroup_subsys mem_cgroup_subsys = {
>  	.bind = mem_cgroup_bind,
>  	.base_cftypes = mem_cgroup_files,
>  	.early_init = 0,
> -	.use_id = 1,
>  };
>  
>  #ifdef CONFIG_MEMCG_SWAP
> -- 
> 1.8.0.2

-- 
Michal Hocko
SUSE Labs
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