[ofa-general] Memory registration redux

[Roland Dreier]

By the way, what's the desired behavior of the cache if a process
registers, say, address range 0x1000 ... 0x3fff, and then the same
process registers address range 0x2000 ... 0x2fff (with all the same
permissions, etc)?

The initial registration creates an MR that is still valid for the
smaller virtual address range, so the second registration is much
cheaper if we used the cached registration; but if we use the cache for
the second registration, and then deregister the first one, we're stuck
with a too-big range pinned in the cache because of the second
registration.

 - R.