readahead: 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 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>
Cc: Steven Pratt <slpratt@austin.ibm.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 731cd2a..709d92f 100644 (file)
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -83,6 +83,7 @@
 #define PG_private             11      /* If pagecache, has fs-private data */
 
 #define PG_writeback           12      /* Page is under writeback */
+#define PG_readahead           13      /* Reminder to do async read-ahead */
 #define PG_compound            14      /* Part of a compound page */
 #define PG_swapcache           15      /* Swap page: swp_entry_t in private */
 
@@ -226,6 +227,10 @@ static inline void SetPageUptodate(struct page *page)
 #define SetPageMappedToDisk(page) set_bit(PG_mappedtodisk, &(page)->flags)
 #define ClearPageMappedToDisk(page) clear_bit(PG_mappedtodisk, &(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)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e2a10b9..2165be9 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -617,7 +617,7 @@ static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
        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);