CC'ed to Paul Menage and Li Zefan.
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
---
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
+this handler. This handler will be called after css_id is assigned
+to css. Not necessary to be implemented in usual(see memcontrol.c)
+
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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