From: Hugh Dickins <hugh@veritas.com>

tmpfs pages should be surfing the LRUs in the company of their filemap
friends: I was expecting the rules to change, but they've been stable so
long, let's sprinkle mark_page_accessed in the equivalent places here; but
(don't ask me why) SetPageReferenced in shmem_file_write.  Ooh, and
shmem_populate was missing a flush_page_to_ram.