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Subject[PATCH -mm 2/3] cgroup: simplify init_subsys()
We are at system boot and there is only 1 cgroup group (i,e,
init_css_set), so we don't need to run through the css_set
linked list. Neither do we need to run through the task list,
since the init process hasn't been created yet.

Also referring to a comment in cgroup.h:

struct css_set
{
...
/*
* Set of subsystem states, one for each subsystem. This array
* is immutable after creation apart from the init_css_set
* during subsystem registration (at boot time).
*/
struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
}

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
kernel/cgroup.c | 30 ++++--------------------------
1 files changed, 4 insertions(+), 26 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 78e5bde..2b72346 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2467,7 +2467,6 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
{
struct cgroup_subsys_state *css;
- struct list_head *l;

printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);

@@ -2478,32 +2477,11 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
BUG_ON(IS_ERR(css));
init_cgroup_css(css, ss, dummytop);

- /* Update all cgroup groups to contain a subsys
+ /* Update the init_css_set to contain a subsys
* pointer to this state - since the subsystem is
- * newly registered, all tasks and hence all cgroup
- * groups are in the subsystem's top cgroup. */
- write_lock(&css_set_lock);
- l = &init_css_set.list;
- do {
- struct css_set *cg =
- list_entry(l, struct css_set, list);
- cg->subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];
- l = l->next;
- } while (l != &init_css_set.list);
- write_unlock(&css_set_lock);
-
- /* If this subsystem requested that it be notified with fork
- * events, we should send it one now for every process in the
- * system */
- if (ss->fork) {
- struct task_struct *g, *p;
-
- read_lock(&tasklist_lock);
- do_each_thread(g, p) {
- ss->fork(ss, p);
- } while_each_thread(g, p);
- read_unlock(&tasklist_lock);
- }
+ * newly registered, all tasks and hence the
+ * init_css_set is in the subsystem's top cgroup. */
+ init_css_set.subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];

need_forkexit_callback |= ss->fork || ss->exit;

--
1.5.4.rc3

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