kernel - Cut buffer cache related pmap invalidations in half
* Do not bother to invalidate the TLB when tearing down a buffer
cache buffer. On the flip side, always invalidate the TLB
(the page range in question) when entering pages into a buffer
cache buffer. Only applicable to normal VMIO buffers.
* Significantly improves buffer cache / filesystem performance with
no real risk.
* Significantly improves performance for tmpfs teardowns on unmount
(which typically have to tear-down a lot of buffer cache buffers).