[PATCH] mm: correct _PAGE_FILE comment

_PAGE_FILE does not indicate whether a file is in page / swap cache, it is
set just for non-linear PTE's.  Correct the comment for i386, x86_64, UML.
Also clearify _PAGE_NONE.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/asm-x86_64/pgtable.h b/include/asm-x86_64/pgtable.h
index 4e167b5..20476d1 100644
--- a/include/asm-x86_64/pgtable.h
+++ b/include/asm-x86_64/pgtable.h
@@ -143,7 +143,7 @@
 #define _PAGE_ACCESSED	0x020
 #define _PAGE_DIRTY	0x040
 #define _PAGE_PSE	0x080	/* 2MB page */
-#define _PAGE_FILE	0x040	/* set:pagecache, unset:swap */
+#define _PAGE_FILE	0x040	/* nonlinear file mapping, saved PTE; unset:swap */
 #define _PAGE_GLOBAL	0x100	/* Global TLB entry */
 
 #define _PAGE_PROTNONE	0x080	/* If not present */