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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: Li Zefan <lizf@cn.fujitsu.com>
Reviewed-by: Paul 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Li Zefan 2008-04-29 01:00:13 -07:00 committed by Linus Torvalds
parent 472b1053f3
commit e8d55fdeb8
2 changed files with 10 additions and 28 deletions
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3
Documentation/cgroups.txt
View File

@ -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)

35
kernel/cgroup.c
View File

@ -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;
}