oom-reaper: use madvise_dontneed() logic to decide if unmap the VMA

Logic on whether we can reap pages from the VMA should match what we
have in madvise_dontneed().  In particular, we should skip, VM_PFNMAP
VMAs, but we don't now.

Let's just extract condition on which we can shoot down pagesi from a
VMA with MADV_DONTNEED into separate function and use it in both places.

Change-Id: I4e5daca9ec7ffc0606cba32471b27fa2eaba3c9a
Link: http://lkml.kernel.org/r/20170118122429.43661-4-kirill.shutemov@linux.intel.com


Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-Commit: 235190738aba7c5c94300c8d882842a535280e5a
Git-Repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>