Hello, Lennart, Li.

Two things.

* Probably I'm missing something but isn't the systemd cgroup
  hierarchy already managed by systemd?  If so, I don't see how
  managing tmpfs on the side would noticeably make things more
  fragile.  It would take a bit more care after, for example, restart
  but it shouldn't be too complex, no?

* FS attributes already being used for userland information seems like
  a good argument, but we shouldn't add separate specialized xattr
  implementation to different pseudo filesystems.  For it to be
  acceptable, it should be a libfs thing easily applicable to any
  pseudo FS and definitely shouldn't be using kmem for storage.

Thanks.

-- 
tejun