There are two things to recall here: firstly HITLER was indubitably a socialist and secondly, none of the three listed above could compete with Cambodia's Pol Pot who, in purely percentage terms, killed between one third and one half of Cambodia's population!
In the 1980s, Le Figaro printed a rather fuller full list for socialist deaths worldwide during the twentieth century to that point, actually numbered some 184 million. (Their search for facts ran broader than the above!)
Every one started out like a good Corbynista!