[RFC] delayed allocation for ext4

booked-page-flag.patch

adds PG_booked bit to page->flags. it's used in delayed
allocation to mark space is already reserved for page
(including possible metadata)

From: Alex Tomas <alex@clusterfs.com>
---
Index: linux-2.6.21-rc7/include/linux/page-flags.h
===================================================================
--- linux-2.6.21-rc7.orig/include/linux/page-flags.h	2007-04-17 18:04:17.000000000 -0700
+++ linux-2.6.21-rc7/include/linux/page-flags.h	2007-04-17 18:04:54.000000000 -0700
@@ -90,6 +90,7 @@
 #define PG_reclaim		17	/* To be reclaimed asap */
 #define PG_nosave_free		18	/* Used for system suspend/resume */
 #define PG_buddy		19	/* Page is free, on buddy lists */
+#define PG_booked		20	/* Has blocks reserved on-disk */
 
 /* PG_owner_priv_1 users should have descriptive aliases */
 #define PG_checked		PG_owner_priv_1 /* Used by some filesystems */
@@ -232,6 +233,10 @@
 #define SetPageMappedToDisk(page) set_bit(PG_mappedtodisk, &(page)->flags)
 #define ClearPageMappedToDisk(page) clear_bit(PG_mappedtodisk, &(page)->flags)
 
+#define PageBooked(page)	test_bit(PG_booked, &(page)->flags)
+#define SetPageBooked(page)	set_bit(PG_booked, &(page)->flags)
+#define ClearPageBooked(page)	clear_bit(PG_booked, &(page)->flags)
+
 #define PageReclaim(page)	test_bit(PG_reclaim, &(page)->flags)
 #define SetPageReclaim(page)	set_bit(PG_reclaim, &(page)->flags)
 #define ClearPageReclaim(page)	clear_bit(PG_reclaim, &(page)->flags)