pagemap: document KPF_THP and make page-types aware of it

page-types, which is a common user of pagemap, gets aware of thp with this
patch. This helps system admins and kernel hackers know about how thp
works. Here is a sample output of page-types over a thp:

$ page-types -p <pid> --raw --list

voffset offset len flags
...
7f9d40200 3f8400 1 ___U_lA____Ma_bH______t____________
7f9d40201 3f8401 1ff ________________T_____t____________

flags page-count MB symbolic-flags long-symbolic-flags
0x0000000000410000 511 1 ________________T_____t____________ compound_tail,thp
0x000000000040d868 1 0 ___U_lA____Ma_bH______t____________ uptodate,lru,active,mmap,anonymous,swapbacked,compound_head,thp

Signed-off-by: Naoya Horiguchi <[e-mail]>
Acked-by: Wu Fengguang <[e-mail]>
Reviewed-by: KAMEZAWA Hiroyuki <[e-mail]>
Acked-by: KOSAKI Motohiro <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/vm/page-types.c

···
 #define KPF_HWPOISON		19
 #define KPF_NOPAGE		20
 #define KPF_KSM			21
+#define KPF_THP			22
 
 /* [32-] kernel hacking assistances */
 #define KPF_RESERVED		32
···
 	[KPF_HWPOISON]		= "X:hwpoison",
 	[KPF_NOPAGE]		= "n:nopage",
 	[KPF_KSM]		= "x:ksm",
+	[KPF_THP]		= "t:thp",
 
 	[KPF_RESERVED]		= "r:reserved",
 	[KPF_MLOCKED]		= "m:mlocked",

Documentation/vm/pagemap.txt

···
     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