f2fs: set flush_merge by default

This patch sets flush_merge by default.
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -86,6 +86,7 @@ enum {
 	Opt_inline_data,
 	Opt_inline_dentry,
 	Opt_flush_merge,
+	Opt_noflush_merge,
 	Opt_nobarrier,
 	Opt_fastboot,
 	Opt_extent_cache,
@@ -114,6 +115,7 @@ static match_table_t f2fs_tokens = {
 	{Opt_inline_data, "inline_data"},
 	{Opt_inline_dentry, "inline_dentry"},
 	{Opt_flush_merge, "flush_merge"},
+	{Opt_noflush_merge, "noflush_merge"},
 	{Opt_nobarrier, "nobarrier"},
 	{Opt_fastboot, "fastboot"},
 	{Opt_extent_cache, "extent_cache"},
@@ -482,6 +484,9 @@ static int parse_options(struct super_block *sb, char *options)
 		case Opt_flush_merge:
 			set_opt(sbi, FLUSH_MERGE);
 			break;
+		case Opt_noflush_merge:
+			clear_opt(sbi, FLUSH_MERGE);
+			break;
 		case Opt_nobarrier:
 			set_opt(sbi, NOBARRIER);
 			break;
@@ -946,6 +951,7 @@ static void default_options(struct f2fs_sb_info *sbi)
 	set_opt(sbi, INLINE_DATA);
 	set_opt(sbi, EXTENT_CACHE);
 	sbi->sb->s_flags |= MS_LAZYTIME;
+	set_opt(sbi, FLUSH_MERGE);
 
 #ifdef CONFIG_F2FS_FS_XATTR
 	set_opt(sbi, XATTR_USER);