[PATCH 1/9] readahead: introduce PG_readahead

[Fengguang Wu <wfg@mail.ustc.edu.cn>]

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Introduce a new page flag: PG_readahead.

It acts as a look-ahead mark, which tells the page reader:
Hey, it's time to invoke the read-ahead logic.  For the sake of I/O pipelining,
don't wait until it runs out of cached pages!

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---

 include/linux/page-flags.h |    5 +++++
 mm/page_alloc.c            |    2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

--- linux-2.6.22-rc1-mm1.orig/include/linux/page-flags.h
+++ linux-2.6.22-rc1-mm1/include/linux/page-flags.h
@@ -92,6 +92,7 @@
 #define PG_lazyfree		20	/* MADV_FREE potential throwaway */
 
 #define PG_booked		21	/* Has blocks reserved on-disk */
+#define PG_readahead		22	/* Reminder to do async read-ahead */
 
 /* PG_owner_priv_1 users should have descriptive aliases */
 #define PG_checked		PG_owner_priv_1 /* Used by some filesystems */
@@ -206,6 +207,10 @@ static inline void SetPageUptodate(struc
 #define SetPageBooked(page)	set_bit(PG_booked, &(page)->flags)
 #define ClearPageBooked(page)	clear_bit(PG_booked, &(page)->flags)
 
+#define PageReadahead(page)	test_bit(PG_readahead, &(page)->flags)
+#define SetPageReadahead(page)	set_bit(PG_readahead, &(page)->flags)
+#define ClearPageReadahead(page) clear_bit(PG_readahead, &(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)
--- linux-2.6.22-rc1-mm1.orig/mm/page_alloc.c
+++ linux-2.6.22-rc1-mm1/mm/page_alloc.c
@@ -659,7 +659,7 @@ static int prep_new_page(struct page *pa
 	if (PageReserved(page))
 		return 1;
 
-	page->flags &= ~(1 << PG_uptodate | 1 << PG_error |
+	page->flags &= ~(1 << PG_uptodate | 1 << PG_error | 1 << PG_readahead |
 			1 << PG_referenced | 1 << PG_arch_1 |
 			1 << PG_owner_priv_1 | 1 << PG_mappedtodisk);
 	set_page_private(page, 0);

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