1 files changed, 21 insertions, 3 deletions

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 9ea629c02a4b..d276a4e2f825 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -48,8 +48,20 @@
 
 /*
  * Don't use the *_dontuse flags.  Use the macros.  Otherwise you'll break
- * locked- and dirty-page accounting.  The top eight bits of page->flags are
- * used for page->zone, so putting flag bits there doesn't work.
+ * locked- and dirty-page accounting.
+ *
+ * The page flags field is split into two parts, the main flags area
+ * which extends from the low bits upwards, and the fields area which
+ * extends from the high bits downwards.
+ *
+ *  | FIELD | ... | FLAGS |
+ *  N-1     ^             0
+ *          (N-FLAGS_RESERVED)
+ *
+ * The fields area is reserved for fields mapping zone, node and SPARSEMEM
+ * section.  The boundry between these two areas is defined by
+ * FLAGS_RESERVED which defines the width of the fields section
+ * (see linux/mmzone.h).  New flags must _not_ overlap with this area.
  */
 #define PG_locked                0      /* Page is locked. Don't touch. */
 #define PG_error                 1
@@ -74,7 +86,9 @@
 #define PG_mappedtodisk         16      /* Has blocks allocated on-disk */
 #define PG_reclaim              17      /* To be reclaimed asap */
 #define PG_nosave_free          18      /* Free, should not be written */
-#define PG_uncached             19      /* Page has been mapped as uncached */
+#define PG_buddy                19      /* Page is free, on buddy lists */
+
+#define PG_uncached             20      /* Page has been mapped as uncached */
 
 /*
  * Global page accounting.  One instance per CPU.  Only unsigned longs are
@@ -317,6 +331,10 @@ extern void __mod_page_state_offset(unsigned long offset, unsigned long delta);
 #define SetPageNosaveFree(page) set_bit(PG_nosave_free, &(page)->flags)
 #define ClearPageNosaveFree(page)               clear_bit(PG_nosave_free, &(page)->flags)
 
+#define PageBuddy(page)         test_bit(PG_buddy, &(page)->flags)
+#define __SetPageBuddy(page)    __set_bit(PG_buddy, &(page)->flags)
+#define __ClearPageBuddy(page)  __clear_bit(PG_buddy, &(page)->flags)
+
 #define PageMappedToDisk(page)  test_bit(PG_mappedtodisk, &(page)->flags)
 #define SetPageMappedToDisk(page) set_bit(PG_mappedtodisk, &(page)->flags)
 #define ClearPageMappedToDisk(page) clear_bit(PG_mappedtodisk, &(page)->flags)