[openib-general] Reusing receive MADs

[Roland Dreier]

    Sean> Is there any interest among people to reuse receive MADs?
    Sean> I.e. once allocated and mapped, the receive MAD and work
    Sean> request would be re-posted to the QP when freed.

I'm not sure this is that useful...  MAD processing is not such a
super-hot path that we need to keep per-CPU lists of cache-hot buffers
(as is done for sk_buffs), and the kernel slab code should do a pretty
good job of reusing buffers anyway.

(The receive buffer needs to be unmapped before passing to the
consumer anyway so there's not a saving there)

 - R.