Some estimates are that there are 20 million legal and illegal Chinese living in Eastern Russia. There is a huge section of Siberia that was originally Chinese and they have never accepted Russian dominance.
That's why Russian leader tries to make friendly gestures towards China. He knows that in a longer term Chinese will be the winners in that region (when they finally turn Japan multiplied by 10). He would gladly support Taiwan take over by China - it would cost him just about nothing.