How was Russia during the Holocaust?

Russia (or the U.S.S.R. as it was known then) was under the rule of Stalin, a cruel dictator, and was communist at the time. Stalin was in the process of murdering his peasants at a rapid rate at the time, and actually killed more than the estimated 6 million Jews and 5 million non-Jews that Hitler killed. Plus, the Soviet Union of course joined in WWII, and was the Allied country with the most casualties during the war.