From: Hugh Dickins <hugh@veritas.com>

The previous patches of this prio_tree batch have been to generic only.  Now
the arm and parisc __flush_dcache_page are converted to using
vma_prio_tree_next, and benefit from its selection of relevant vmas.  They're
still accessing the tree without i_shared_lock or any other, that's not
forgotten but still under investigation.  Include pagemap.h for the definition
of PAGE_CACHE_SHIFT.  s390 and x86_64 no longer initialize vma's shared field
(whose type has changed), done later.