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Commit e8d55fde authored by Li Zefan's avatar Li Zefan Committed by Linus Torvalds
Browse files

cgroups: 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 no processes have 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: default avatarLi Zefan <lizf@cn.fujitsu.com>
Reviewed-by: default avatarPaul Menage <menage@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 472b1053

Documentation/cgroups.txt

+1 −2
Original line number Diff line number Diff line
@@ -500,8 +500,7 @@ post-attachment activity that requires memory allocations or blocking. 


void fork(struct cgroup_subsy *ss, struct task_struct *task)



Called when a task is forked into a cgroup. Also called during

registration for all existing tasks.

Called when a task is forked into a cgroup.



void exit(struct cgroup_subsys *ss, struct task_struct *task)

kernel/cgroup.c

+9 −26
Original line number Diff line number Diff line
@@ -2477,7 +2477,6 @@ 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);
@@ -2488,35 +2487,19 @@ 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;



	/* At system boot, before all subsystems have been

	 * registered, no tasks have been forked, so we don't

	 * need to invoke fork callbacks here. */

	BUG_ON(!list_empty(&init_task.tasks));



	ss->active = 1;

}