[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: NPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

include/asm-i386/pgtable.h

@@ -86,9 +86,7 @@ void paging_init(void);
 #endif
 
 /*
- * The 4MB page is guessing..  Detailed in the infamous "Chapter H"
- * of the Pentium details, but assuming intel did the straightforward
- * thing, this bit set in the page directory entry just means that
+ * _PAGE_PSE set in the page directory entry just means that
  * the page directory entry points directly to a 4MB-aligned block of
  * memory. 
  */
@@ -119,8 +117,10 @@ void paging_init(void);
 #define _PAGE_UNUSED2	0x400
 #define _PAGE_UNUSED3	0x800
 
-#define _PAGE_FILE	0x040	/* set:pagecache unset:swap */
-#define _PAGE_PROTNONE	0x080	/* If not present */
+/* If _PAGE_PRESENT is clear, we use these: */
+#define _PAGE_FILE	0x040	/* nonlinear file mapping, saved PTE; unset:swap */
+#define _PAGE_PROTNONE	0x080	/* if the user mapped it with PROT_NONE;
+				   pte_present gives true */
 #ifdef CONFIG_X86_PAE
 #define _PAGE_NX	(1ULL<<_PAGE_BIT_NX)
 #else

include/asm-um/pgtable.h

@@ -16,13 +16,15 @@
 
 #define _PAGE_PRESENT	0x001
 #define _PAGE_NEWPAGE	0x002
-#define _PAGE_NEWPROT   0x004
-#define _PAGE_FILE	0x008   /* set:pagecache unset:swap */
-#define _PAGE_PROTNONE	0x010	/* If not present */
+#define _PAGE_NEWPROT	0x004
 #define _PAGE_RW	0x020
 #define _PAGE_USER	0x040
 #define _PAGE_ACCESSED	0x080
 #define _PAGE_DIRTY	0x100
+/* If _PAGE_PRESENT is clear, we use these: */
+#define _PAGE_FILE	0x008	/* nonlinear file mapping, saved PTE; unset:swap */
+#define _PAGE_PROTNONE	0x010	/* if the user mapped it with PROT_NONE;
+				   pte_present gives true */
 
 #ifdef CONFIG_3_LEVEL_PGTABLES
 #include "asm/pgtable-3level.h"

include/asm-x86_64/pgtable.h

@@ -143,7 +143,7 @@ extern inline void pgd_clear (pgd_t * pgd)
 #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 */