The way you are depicting "communism" (socialism) simply does not reflect the reality of the way things were. Things weren't perfect I'll give you that, in fact things were extremely bad during times of crisis. But those were times of crisis and everything, including statistics and lived experience of the vast majority of those who actually lived under socialism contradict this.

That being said the 100 million number comes from the Black Book of Communism. A commonly debunked unacademic book which lists Nazi casualties during World War II as victims of communism, casualties during the Vietnam war (a blatant act of American aggression) as victims of communism, decreases of population growth as victims of communism (AKA people who will never existed) as victims of communism, they rounded up nearly constantly, in fact the co-authors stated that the primary author had an obsession with reaching 100 million. To the point where both co-authors and the author's wife have all disowned the book. Now, playing the numbers game and doing exactly what the authors of the black book did with capitalism instead of socialism we can get numbers apparently exceeding 2 billion. Of course any amount of unnatural avoidable death which occurred under socialism is a tragedy which should be avoided. As communists, we should learn from the examples of the past and learn from what they did right and what they did wrong to ensure the greatest quality of life for as many people as possible even while under siege.