Re: [RFC][-mm] Add an owner to the mm_struct (v4)

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

On Tue, 01 Apr 2008 18:13:12 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> +	/*
> +	 * Search in the children
> +	 */
> +	list_for_each_entry(c, &p->children, sibling) {
> +		if (c->mm == mm)
> +			goto assign_new_owner;
> +	}
> +
This finds new owner when "current" is multi-threaded and
"current" called pthread_create(), right ?

> +	/*
> +	 * Search in the siblings
> +	 */
> +	list_for_each_entry(c, &p->parent->children, sibling) {
> +		if (c->mm == mm)
> +			goto assign_new_owner;
> +	}
> +
This finds new owner when "current" is multi-threaded and
"current" is just a child (means it doesn't call pthread_create()) ?


> +	/*
> +	 * Search through everything else. We should not get
> +	 * here often
> +	 */
> +	do_each_thread(g, c) {
> +		if (c->mm == mm)
> +			goto assign_new_owner;
> +	} while_each_thread(g, c);

Doing above in synchronized manner seems too heavy.
When this happen ? or Can this be done in lazy "on-demand" manner ?

+assign_new_owner:
+	rcu_read_unlock();
+	BUG_ON(c == p);
+	task_lock(c);
+	if (c->mm != mm) {
+		task_unlock(c);
+		goto retry;
+	}
+	cgroup_mm_owner_callbacks(mm->owner, c);
+	mm->owner = c;
+	task_unlock(c);
+}
Why rcu_read_unlock() before changing owner ? Is it safe ?

Thanks,
-Kame