linux-kernel - Re: [PATCH 6/8] cgroup: remove cgroup->name

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Date:	Wed, 29 Jan 2014 13:09:07 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	lizefan@...wei.com, containers@...ts.linux-foundation.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Balbir Singh <bsingharora@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 6/8] cgroup: remove cgroup->name

On Tue 28-01-14 18:59:43, Tejun Heo wrote:
> cgroup->name handling became quite complicated over time involving
> dedicated struct cgroup_name for RCU protection.  Now that cgroup is
> on kernfs, we can drop all of it and simply use kernfs_name/path() and
> friends.  Replace cgroup->name and all related code with kernfs
> name/path constructs.
> 
> * Reimplement cgroup_name() and cgroup_path() as thin wrappers on top
>   of kernfs counterparts, which involves semantic changes.
>   pr_cont_cgroup_name() and pr_cont_cgroup_path() added.
> 
> * cgroup->name handling dropped from cgroup_rename().
> 
> * All users of cgroup_name/path() updated to the new semantics.  Users
>   which were formatting the string just to printk them are converted
>   to use pr_cont_cgroup_name/path() instead, which simplifies things
>   quite a bit.  As cgroup_name() no longer requires RCU read lock
>   around it, RCU lockings which were protecting only cgroup_name() are
>   removed.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Li Zefan <lizefan@...wei.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.cz>
> Cc: Balbir Singh <bsingharora@...il.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Nice. I hated the way how we retrieved the name previously.
Acked-by: Michal Hocko <mhocko@...e.cz>

Btw. after this change we should drop part of the comment above
oom_info_lock:

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 19d5d4274e22..d998baec5deb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1684,8 +1684,7 @@ static void move_unlock_mem_cgroup(struct mem_cgroup *memcg,
 void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
 {
 	/*
-	 * protects memcg_name and makes sure that parallel ooms do not
-	 * interleave
+	 * Makes sure that parallel ooms do not interleave
 	 */
 	static DEFINE_SPINLOCK(oom_info_lock);
 	struct cgroup *task_cgrp;
-- 
Michal Hocko
SUSE Labs
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