f2fs: don't need to collect dirty sit entries and flush journal when there's no dirty sit entries

 Don't need to collect dirty sit entries and flush sit journal to sit
 entries when there's no dirty sit entries. This patch check dirty_sentries
 earlier just like flush_nat_entries.

Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 29c04ed..1e90934 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1733,6 +1733,9 @@
 	mutex_lock(&curseg->curseg_mutex);
 	mutex_lock(&sit_i->sentry_lock);
 
+	if (!sit_i->dirty_sentries)
+		goto out;
+
 	/*
 	 * add and account sit entries of dirty bitmap in sit entry
 	 * set temporarily
@@ -1747,9 +1750,6 @@
 	if (!__has_cursum_space(sum, sit_i->dirty_sentries, SIT_JOURNAL))
 		remove_sits_in_journal(sbi);
 
-	if (!sit_i->dirty_sentries)
-		goto out;
-
 	/*
 	 * there are two steps to flush sit entries:
 	 * #1, flush sit entries to journal in current cold data summary block.