[PATCH 04/32] mm: introduce PG_readahead

Wu Fengguang
2006-05-27T15:51:52Z

[-- Attachment #1: mm-PG_readahead.patch --]
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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 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>
---

include/linux/page-flags.h | 6 ++++++
mm/page_alloc.c | 2 +-
2 files changed, 7 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
@@ -90,6 +90,8 @@
#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 +374,10 @@ 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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