+ * MADV_DONTFORK - omit this area from child's address space when forking:
+ * typically, to avoid COWing pages pinned by get_user_pages().
+ * MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
+ * MADV_MERGEABLE - the application recommends that KSM try to merge pages in
+ * this area with pages of identical content from other such areas.
+ * MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.