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SubjectRe: [PATCH 1/5] cgroup: ID notification call back
Date
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> writes:

> CC'ed to Paul Menage and Li Zefan.
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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@jp.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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