f2fs: introduce struct flush_cmd_control to wrap the flush_merge fields

Split the flush_merge fields from sm_i, and use the new struct flush_cmd_control
to wrap it, so that we can igonre these fileds if flush_merge is disable, and
it alse can the structs more neat.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 97da71d..fa0ec81 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -325,6 +325,15 @@
 	int ret;
 };
 
+struct flush_cmd_control {
+	struct task_struct *f2fs_issue_flush;	/* flush thread */
+	wait_queue_head_t flush_wait_queue;	/* waiting queue for wake-up */
+	struct flush_cmd *issue_list;		/* list for command issue */
+	struct flush_cmd *dispatch_list;	/* list for command dispatch */
+	spinlock_t issue_lock;			/* for issue list lock */
+	struct flush_cmd *issue_tail;		/* list tail of issue list */
+};
+
 struct f2fs_sm_info {
 	struct sit_info *sit_info;		/* whole segment information */
 	struct free_segmap_info *free_info;	/* free segment information */
@@ -355,12 +364,8 @@
 	unsigned int min_ipu_util;	/* in-place-update threshold */
 
 	/* for flush command control */
-	struct task_struct *f2fs_issue_flush;	/* flush thread */
-	wait_queue_head_t flush_wait_queue;	/* waiting queue for wake-up */
-	struct flush_cmd *issue_list;		/* list for command issue */
-	struct flush_cmd *dispatch_list;	/* list for command dispatch */
-	spinlock_t issue_lock;			/* for issue list lock */
-	struct flush_cmd *issue_tail;		/* list tail of issue list */
+	struct flush_cmd_control *cmd_control_info;
+
 };
 
 /*