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>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 731cd2ac3227..709d92fd2877 100644
--- 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)