[PATCH 04/23] readahead: page flag PG_readahead

[Wu Fengguang]

An new page flag PG_readahead is introduced as a look-ahead mark, which
reminds the caller to give the adaptive read-ahead logic a chance to do
read-ahead ahead of time for I/O pipelining.

It roughly corresponds to `ahead_start' of the stock read-ahead logic.

Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
---

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

--- linux-2.6.16-rc6-mm2.orig/include/linux/page-flags.h
+++ linux-2.6.16-rc6-mm2/include/linux/page-flags.h
@@ -76,6 +76,7 @@
 #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_readahead		20	/* Reminder to do readahead */
 
 /*
  * Global page accounting.  One instance per CPU.  Only unsigned longs are
@@ -343,6 +344,10 @@ extern void __mod_page_state_offset(unsi
 #define SetPageUncached(page)	set_bit(PG_uncached, &(page)->flags)
 #define ClearPageUncached(page)	clear_bit(PG_uncached, &(page)->flags)
 
+#define PageReadahead(page)	test_bit(PG_readahead, &(page)->flags)
+#define __SetPageReadahead(page) __set_bit(PG_readahead, &(page)->flags)
+#define TestClearPageReadahead(page) test_and_clear_bit(PG_readahead, &(page)->flags)
+
 struct page;	/* forward declaration */
 
 int test_clear_page_dirty(struct page *page);
--- linux-2.6.16-rc6-mm2.orig/mm/page_alloc.c
+++ linux-2.6.16-rc6-mm2/mm/page_alloc.c
@@ -549,7 +549,7 @@ 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_checked | 1 << PG_mappedtodisk);
 	set_page_private(page, 0);

--
-
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