[PATCH 2.6.32] memcg: warn on deeper hierarchies with use_hierarchy==0

[David Rientjes]

On Thu, 20 Sep 2012, Michal Hocko wrote:

> Yes printk_once is an alternative but I really wanted to have this as
> much visible as possible. People tend to react to stack traceces more
> and this one will trigger only if somebody is either doing something
> wrong or the configuration is the one we are looking for.
> 

That's the complete opposite of what Linus has said he wants, he said very 
specifically that he doesn't want WARN_ONCE() or WARN_ON_ONCE() for 
deprecation of tunables.  If you want to have this merged, then please get 
him to ack it.

> Comparing to oom_adj, that one was used much more often so the WARN_ONCE
> was too verbose especially when you usually had to wait for an userspace
> update which is not the case here.

How is WARN_ONCE() too verbose for oom_adj?  It's printed once!  And how 
can you claim that userspace doesn't need to change if it's creating a 
hierarchy while use_hierarchy == 0?