linux-kernel - Re: [PATCH 1/5] cgroup: ID notification call back

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Date:	Tue, 24 Aug 2010 00:19:01 -0700
From:	Greg Thelen <gthelen@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	linux-mm@...ck.org,
	"nishimura\@mxp.nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"balbir\@linux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	m-ikeda@...jp.nec.com,
	"akpm\@linux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	kamezawa.hiroyuki@...il.com,
	"menage\@google.com" <menage@...gle.com>,
	"lizf\@cn.fujitsu.com" <lizf@...fujitsu.com>
Subject: Re: [PATCH 1/5] cgroup: ID notification call back

KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> writes:

> CC'ed to Paul Menage and Li Zefan.
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> When cgroup subsystem use ID (ss->use_id==1), each css's ID is assigned
> after successful call of ->create(). css_ID is tightly coupled with
> css struct itself but it is allocated by ->create() call, IOW,
> per-subsystem special allocations.
>
> To know css_id before creation, this patch adds id_attached() callback.
> after css_ID allocation. This will be used by memory cgroup's quick lookup
> routine.
>
> Maybe you can think of other implementations as
> 	- pass ID to ->create()
> 	or
> 	- add post_create()
> 	etc...
> But when considering dirtiness of codes, this straightforward patch seems
> good to me. If someone wants post_create(), this patch can be replaced.
>
> Changelog: 20100820
>  - new approarch.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>  Documentation/cgroups/cgroups.txt |   10 ++++++++++
>  include/linux/cgroup.h            |    1 +
>  kernel/cgroup.c                   |    5 ++++-
>  3 files changed, 15 insertions(+), 1 deletion(-)
>
> Index: mmotm-0811/Documentation/cgroups/cgroups.txt
> ===================================================================
> --- mmotm-0811.orig/Documentation/cgroups/cgroups.txt
> +++ mmotm-0811/Documentation/cgroups/cgroups.txt
> @@ -621,6 +621,16 @@ and root cgroup. Currently this will onl
>  the default hierarchy (which never has sub-cgroups) and a hierarchy
>  that is being created/destroyed (and hence has no sub-cgroups).
>  
> +void id_attached(struct cgroup_subsys *ss, struct cgroup *root)
> +(cgroup_mutex and ss->hierarchy_mutex held by caller)
> +(called only when ss->use_id=1)
> +
> +Called when css_id is attached to css. Because css_id is assigned
> +against "css", css_id is not available until ->create() is called.
> +If subsystem wants to make use of ID at createtion time, use

Minor spelling correction: s/createtion/creation/

> +this handler. This handler will be called after css_id is assigned
> +to css. Not necessary to be implemented in usual(see memcontrol.c)

Maybe this sounds better?

"This handler is not usually needed.  See memcontrol.c for an example."

> +
>  4. Questions
>  ============
>  
> Index: mmotm-0811/include/linux/cgroup.h
> ===================================================================
> --- mmotm-0811.orig/include/linux/cgroup.h
> +++ mmotm-0811/include/linux/cgroup.h
> @@ -475,6 +475,7 @@ struct cgroup_subsys {
>  			struct cgroup *cgrp);
>  	void (*post_clone)(struct cgroup_subsys *ss, struct cgroup *cgrp);
>  	void (*bind)(struct cgroup_subsys *ss, struct cgroup *root);
> +	void (*id_attached)(struct cgroup_subsys *ss, struct cgroup *cgrp);
>  
>  	int subsys_id;
>  	int active;
> Index: mmotm-0811/kernel/cgroup.c
> ===================================================================
> --- mmotm-0811.orig/kernel/cgroup.c
> +++ mmotm-0811/kernel/cgroup.c
> @@ -4618,6 +4618,8 @@ static int __init_or_module cgroup_init_
>  	newid->stack[0] = newid->id;
>  	newid->css = rootcss;
>  	rootcss->id = newid;
> +	if (ss->id_attached)
> +		ss->id_attached(ss, dummytop);
>  	return 0;
>  }
>  
> @@ -4646,7 +4648,8 @@ static int alloc_css_id(struct cgroup_su
>  	 * see cgroup_populate_dir()
>  	 */
>  	rcu_assign_pointer(child_css->id, child_id);
> -
> +	if (ss->id_attached)
> +		ss->id_attached(ss, child);
>  	return 0;
>  }
>  
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