mm, thp: preventing hugepage creation for read-write file pages

mm, thp: preventing hugepage creation for read-write file pages

Sometimes, an user process incurs writes on file pages
which has VM_DENYWRITE flag in its vma->vm_flags (of
course, the vma has VM_WRITE flags too). In this case,
the kernel creates a new page by a COW fault, but it is
an unexpected behaviour for 64KB file hugepages.

This patch disallows scanning of read-write file pages
to prevent unexpected buggy behaviours.

Change-Id: I28c1da7f7ad4be55be5607316b29a2978896fcb9
Signed-off-by: Sung-hun Kim <sfoon.kim@samsung.com>