Aside from the two small comments, the pipe side looked reasonable,
but I stopped looking when the patches moved on to the notificaiton
part, and maybe I missed something in the earlier ones too.

Which does bring me to the meat of this email: can we please keep the
pipe cleanups and prepwork (and benchmarking) as a separate patch
series? I'd like that to be done separately from the notification
code, since it's re-organization and cleanup - while the eventual goal
is to be able to add messages to the pipe atomically, I think the
series makes sense (and should make sense) on its own.

          Linus