nilfs2: avoid readahead on metadata file for create mode

This turns off readhead action of metadata file if nilfs_mdt_get_block
function was called with a create flag.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/mdt.c

@@ -186,7 +186,7 @@ nilfs_mdt_submit_block(struct inode *inode, unsigned long blkoff,
 }
 
 static int nilfs_mdt_read_block(struct inode *inode, unsigned long block,
-				struct buffer_head **out_bh)
+				int readahead, struct buffer_head **out_bh)
 {
 	struct buffer_head *first_bh, *bh;
 	unsigned long blkoff;
@@ -200,16 +200,18 @@ static int nilfs_mdt_read_block(struct inode *inode, unsigned long block,
 	if (unlikely(err))
 		goto failed;
 
-	blkoff = block + 1;
-	for (i = 0; i < nr_ra_blocks; i++, blkoff++) {
-		err = nilfs_mdt_submit_block(inode, blkoff, READA, &bh);
-		if (likely(!err || err == -EEXIST))
-			brelse(bh);
-		else if (err != -EBUSY)
-			break; /* abort readahead if bmap lookup failed */
-
-		if (!buffer_locked(first_bh))
-			goto out_no_wait;
+	if (readahead) {
+		blkoff = block + 1;
+		for (i = 0; i < nr_ra_blocks; i++, blkoff++) {
+			err = nilfs_mdt_submit_block(inode, blkoff, READA, &bh);
+			if (likely(!err || err == -EEXIST))
+				brelse(bh);
+			else if (err != -EBUSY)
+				break;
+				/* abort readahead if bmap lookup failed */
+			if (!buffer_locked(first_bh))
+				goto out_no_wait;
+		}
 	}
 
 	wait_on_buffer(first_bh);
@@ -263,7 +265,7 @@ int nilfs_mdt_get_block(struct inode *inode, unsigned long blkoff, int create,
 
 	/* Should be rewritten with merging nilfs_mdt_read_block() */
  retry:
-	ret = nilfs_mdt_read_block(inode, blkoff, out_bh);
+	ret = nilfs_mdt_read_block(inode, blkoff, !create, out_bh);
 	if (!create || ret != -ENOENT)
 		return ret;
 
@@ -371,7 +373,7 @@ int nilfs_mdt_mark_block_dirty(struct inode *inode, unsigned long block)
 	struct buffer_head *bh;
 	int err;
 
-	err = nilfs_mdt_read_block(inode, block, &bh);
+	err = nilfs_mdt_read_block(inode, block, 0, &bh);
 	if (unlikely(err))
 		return err;
 	nilfs_mark_buffer_dirty(bh);