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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 24 Aug 2010 00:19:01 -0700
Greg Thelen <gthelen@google.com> wrote:

> 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/
> 
ok.

> > +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."
> 

Sure. will fix.

> > +
> >  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;
> >  }
> >  
> 

Thank you for review.

-Kame