f2fs: avoid writing inode redundantly when creating a file

In f2fs_write_inode, updating inode after f2fs_balance_fs is not
a optimized way in the case that f2fs_gc is performed ahead. The
inode page will be unnecessarily written out twice, one of which
is in f2fs_gc->...->sync_node_pages and the other is in
update_inode_page.

Let's update the inode page in prior to f2fs_balance_fs to avoid
this.

To reproduce it,
$ touch file (before this step, should make the device need f2fs_gc)
$ sync (or wait the bdi to write dirty inode)
Signed-off-by: NJin Xu <jinuxstyle@gmail.com>
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/inode.c

@@ -221,9 +221,6 @@ int f2fs_write_inode(struct inode *inode, struct writeback_control *wbc)
 	if (!is_inode_flag_set(F2FS_I(inode), FI_DIRTY_INODE))
 		return 0;
 
-	if (wbc)
-		f2fs_balance_fs(sbi);
-
 	/*
 	 * We need to lock here to prevent from producing dirty node pages
 	 * during the urgent cleaning time when runing out of free sections.
@@ -231,6 +228,10 @@ int f2fs_write_inode(struct inode *inode, struct writeback_control *wbc)
 	ilock = mutex_lock_op(sbi);
 	ret = update_inode_page(inode);
 	mutex_unlock_op(sbi, ilock);
+
+	if (wbc)
+		f2fs_balance_fs(sbi);
+
 	return ret;
 }