linux-kernel - Re: [RFC][PATCH 0/7] memcg: make memcg's life cycle the same as cgroup

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Message-ID: <20130407202130.GB12678@dhcp22.suse.cz>
Date:	Sun, 7 Apr 2013 22:21:30 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Li Zefan <lizefan@...wei.com>
Cc:	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
	Glauber Costa <glommer@...allels.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [RFC][PATCH 0/7] memcg: make memcg's life cycle the same as
 cgroup

On Sun 07-04-13 14:00:24, Li Zefan wrote:
> On 2013/4/4 20:00, Michal Hocko wrote:
> > On Wed 03-04-13 17:11:15, Li Zefan wrote:
> >> (I'll be off from my office soon, and I won't be responsive in the following
> >> 3 days.)
> >>
> >> I'm working on converting memcg to use cgroup->id, and then we can kill css_id.
> >>
> >> Now memcg has its own refcnt, so when a cgroup is destroyed, the memcg can
> >> still be alive. This patchset converts memcg to always use css_get/put, so
> >> memcg will have the same life cycle as its corresponding cgroup, and then
> >> it's always safe for memcg to use cgroup->id.
> >>
> >> The historical reason that memcg didn't use css_get in some cases, is that
> >> cgroup couldn't be removed if there're still css refs. The situation has
> >> changed so that rmdir a cgroup will succeed regardless css refs, but won't
> >> be freed until css refs goes down to 0.
> >>
> >> This is an early post, and it's NOT TESTED. I just want to see if the changes
> >> are fine in general.
> > 
> > yes, I like the approach and it looks correct as well (some minor things
> > mentioned in the patches). Thanks a lot Li! This will make our lifes much
> > easier. The separate ref counting was PITA especially after
> > introduction of kmem accounting which made its usage even more trickier.
> > 
> >> btw, after this patchset I think we don't need to free memcg via RCU, because
> >> cgroup is already freed in RCU callback.
> > 
> > But this depends on changes waiting in for-3.10 branch, right?
> 
> What changes? memcg changes or cgroup core changes? I don't think this depends
> on anything in cgroup 3.10 branch.

cgroup (be445626 e.g.) but now I've noticed that those are already
merged in Linus tree.

FYI: I've cherry-picked themo my -mm git tree.
-- 
Michal Hocko
SUSE Labs
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