f2fs: make clean inodes when flushing inode page

This patch tries to make more clean inodes when flushing dirty inodes in
checkpoint.
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -921,6 +921,10 @@ int f2fs_sync_inode_meta(struct f2fs_sb_info *sbi)
 		inode = igrab(&fi->vfs_inode);
 		spin_unlock(&sbi->inode_lock[DIRTY_META]);
 		if (inode) {
+			sync_inode_metadata(inode, 0);
+
+			/* it's on eviction */
+			if (is_inode_flag_set(inode, FI_DIRTY_INODE))
 				update_inode_page(inode);
 			iput(inode);
 		}

fs/f2fs/inode.c

@@ -339,7 +339,7 @@ int f2fs_write_inode(struct inode *inode, struct writeback_control *wbc)
 	 * We need to balance fs here to prevent from producing dirty node pages
 	 * during the urgent cleaning time when runing out of free sections.
 	 */
-	if (update_inode_page(inode))
+	if (update_inode_page(inode) && wbc && wbc->nr_to_write)
 		f2fs_balance_fs(sbi, true);
 	return 0;
 }