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Subject[PATCH 04/28] mm: introduce PG_readahead
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 adaptive read-ahead logic!
For the sake of I/O pipelining, don't wait until it runs out of
cached pages. ;-)

Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
Signed-off-by: Andrew Morton <akpm@osdl.org>
--- linux-2.6.19-rc5-mm2.orig/include/linux/page-flags.h
+++ linux-2.6.19-rc5-mm2/include/linux/page-flags.h
@@ -91,6 +91,8 @@
#define PG_nosave_free 18 /* Used for system suspend/resume */
#define PG_buddy 19 /* Page is free, on buddy lists */

+#define PG_readahead 20 /* Reminder to do read-ahead */
+

#if (BITS_PER_LONG > 32)
/*
@@ -247,6 +249,10 @@ static inline void SetPageUptodate(struc
#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 ClearPageReadahead(page) clear_bit(PG_readahead, &(page)->flags)
+
struct page; /* forward declaration */

int test_clear_page_dirty(struct page *page);
--- linux-2.6.19-rc5-mm2.orig/mm/page_alloc.c
+++ linux-2.6.19-rc5-mm2/mm/page_alloc.c
@@ -598,7 +598,7 @@ 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_fs_misc | 1 << PG_mappedtodisk);
set_page_private(page, 0);
--
-
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