From: Hugh Dickins <hugh@veritas.com>

First of a batch of three rmap patches: this initial batch of three paving
the way for a move to some form of object-based rmap (probably Andrea's, but
drawing from mine too), and making almost no functional change by itself.  A
few days will intervene before the next batch, to give the struct page
changes in the second patch some exposure before proceeding.

rmap 1 create include/linux/rmap.h

Start small: linux/rmap-locking.h has already gathered some declarations
unrelated to locking, and the rest of the rmap declarations were over in
linux/swap.h: gather them all together in linux/rmap.h, and rename the
pte_chain_lock to rmap_lock.