Hello, Michal, Glauber.
On Tue, Dec 04, 2012 at 09:45:44AM +0100, Michal Hocko wrote:
> Because such a helper might be useful in general? I didn't check if
> somebody does the same test elsewhere though.
The problem is that whether a cgroup has a child or not may differ
depending on the specific controller. You can't tell whether
something exists or not at a given time without synchronization and
synchronization is per-controller. IOW, if a controller cares about
when a cgroup comes online and goes offline, it should synchronize
those events in ->css_on/offline() and only consider cgroups marked
online as online.
> > If you really dislike doing a children count (I don't like as well, I
> > just don't dislike), maybe we can do something like:
> >
> > i = 0;
> > for_each_mem_cgroup_tree(iter, memcg) {
> > if (i++ == 1)
> > return false;
> > }
> > return true;
>
> I guess you meant:
> i = 0;
> for_each_mem_cgroup_tree(iter, memcg) {
> if (i++ == 1) {
> mem_cgroup_iter_break(iter);
> break;
> }
> }
> return i > 1;
Or sth like the following?
bool memcg_has_children(cgrp)
{
lockdep_assert_held(memcg_lock);
rcu_read_lock();
cgroup_for_each_children(pos, cgrp) {
if (memcg_is_online(pos)) {
rcu_read_unlock();
return true;
}
}
rcu_read_unlock();
return ret;
}
--
tejun
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