19. HWPOISON
20. NOPAGE
21. KSM
+ 22. THP
Short descriptions to the page flags:
21. KSM
identical memory pages dynamically shared between one or more processes
+22. THP
+ contiguous pages which construct transparent hugepages
+
[IO related page flags]
1. ERROR IO error occurred
3. UPTODATE page has up-to-date data