[PATCH 04/33] readahead: page flag PG_readahead

Wu Fengguang
2006-05-24T11:19:01Z

[-- Attachment #1: readahead-page-flag-PG_readahead.patch --]
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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@mail.ustc.edu.cn>
---

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

--- linux-2.6.17-rc4-mm3.orig/include/linux/page-flags.h
+++ linux-2.6.17-rc4-mm3/include/linux/page-flags.h
@@ -89,6 +89,7 @@
#define PG_reclaim 17 /* To be reclaimed asap */
#define PG_nosave_free 18 /* Free, should not be written */
#define PG_buddy 19 /* Page is free, on buddy lists */
+#define PG_readahead 20 /* Reminder to do readahead */

#if (BITS_PER_LONG > 32)
@@ -372,6 +373,10 @@ 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-2.6.17-rc4-mm3.orig/mm/page_alloc.c
+++ linux-2.6.17-rc4-mm3/mm/page_alloc.c
@@ -564,7 +564,7 @@ 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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