f2fs: introduce readahead mode of node pages

Previously, f2fs reads several node pages ahead when get_dnode_of_data is called
with RDONLY_NODE flag.
And, this flag is set by the following functions.
- get_data_block_ro
- get_lock_data_page
- do_write_data_page
- truncate_blocks
- truncate_hole

However, this readahead mechanism is initially introduced for the use of
get_data_block_ro to enhance the sequential read performance.

So, let's clarify all the cases with the additional modes as follows.

enum {
	ALLOC_NODE,	/* allocate a new node page if needed */
	LOOKUP_NODE,	/* look up a node without readahead */
	LOOKUP_NODE_RA,	/*
			 * look up a node with readahead called
			 * by get_datablock_ro.
			 */
}

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
Reviewed-by: Namjae Jeon <namjae.jeon@samsung.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 855e5e5..e777c7a 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -125,11 +125,15 @@ static inline int update_sits_in_cursum(struct f2fs_summary_block *rs, int i)
 					 * file keeping -1 as its node offset to
 					 * distinguish from index node blocks.
 					 */
-#define RDONLY_NODE		1	/*
-					 * specify a read-only mode when getting
-					 * a node block. 0 is read-write mode.
-					 * used by get_dnode_of_data().
+enum {
+	ALLOC_NODE,			/* allocate a new node page if needed */
+	LOOKUP_NODE,			/* look up a node without readahead */
+	LOOKUP_NODE_RA,			/*
+					 * look up a node with readahead called
+					 * by get_datablock_ro.
 					 */
+};
+
 #define F2FS_LINK_MAX		32000	/* maximum link count per file */
 
 /* for in-memory extent cache entry */