RCU reviews

I would be honoured to pre-view the next LWN article.
However, I believe I am mostly out of my league here. 
I hope to not disappoint you.

I understand memory barriers are quite expensive (on most current machines that implement
them), so I have some suggestions for optimizations in rcu_try_flip_waitmb_needed and
rcu_try_flip_waitack_needed. 

And I understand mb is both read and write barrier. I plan on looking into the possibility of
using (the potentially) less expensive read (or write) barriers, if you think they may
benefit.

I did not see your email anywhere on LWN - even in the new "GuestArticles index", so I will
look for your email on lkml. Having seen no other posts here, perhaps we are OK going private
correspondence.

Thanks again for these informative (and thought provoking) articles.