cleanup the walk_page_range interface v2

From: Christoph Hellwig
Date: Wed Aug 28 2019 - 10:20:07 EST

Hi all,

this series is based on a patch from Linus to split the callbacks
passed to walk_page_range and walk_page_vma into a separate structure
that can be marked const, with various cleanups from me on top.

This series is also available as a git tre here:

git:// pagewalk-cleanup



14 files changed, 291 insertions(+), 273 deletions(-)

Changes since v1:
- minor comment typo and checkpatch fixes
- fix a compile failure for !CONFIG_SHMEM
- rebased to the wip/jgg-hmm branch