f2fs: fix equation of has_not_enough_free_secs()

Practically, has_not_enough_free_secs() should calculate with the numbers of
current node and directory data blocks together.
Actually the equation was implemented in need_to_flush().

So, this patch removes need_flush() and moves the equation into
has_not_enough_free_secs().

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 0948405..66a288a 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -459,7 +459,20 @@
 
 static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi)
 {
-	return free_sections(sbi) <= reserved_sections(sbi);
+	unsigned int pages_per_sec = (1 << sbi->log_blocks_per_seg) *
+			sbi->segs_per_sec;
+	int node_secs = ((get_pages(sbi, F2FS_DIRTY_NODES) + pages_per_sec - 1)
+			>> sbi->log_blocks_per_seg) / sbi->segs_per_sec;
+	int dent_secs = ((get_pages(sbi, F2FS_DIRTY_DENTS) + pages_per_sec - 1)
+			>> sbi->log_blocks_per_seg) / sbi->segs_per_sec;
+
+	if (sbi->por_doing)
+		return false;
+
+	if (free_sections(sbi) <= (node_secs + 2 * dent_secs +
+						reserved_sections(sbi)))
+		return true;
+	return false;
 }
 
 static inline int utilization(struct f2fs_sb_info *sbi)