Here’s a bit of work from Paul Cockshott on the Soviet population:
“There is a great deal of nonsense spread about the alleged number of deaths caused by the Soviet Government. The number of executions they carried out over the history of the country – somewhere between 600,000 and 900,000 is bad enough, but there is an upsurge of posts on the web claiming that ‘Jewish Bolsheviks’ executed 30 to 40 million Russian Christians. The only reason for these absurd exaggerations is to make the terrible soviet record of executions seem more than the even worse record of the German government. You can not hide 10s of millions of executions. They would have a lasting effect on the population of the country. In fact the Soviet population increased rapidly for all years of soviet rule other than those of the war. This did produce a huge demographic deficit, of the order of 40 million in the short term, growing to around 70 million by the fall of the USSR. I have in this graph projected back the population in 1945 from the censuses of the 1950s using the growth rate of the 1950s and 1930s, and projected forward the 1941 population. So yes there was a huge demographic loss, but it occurred 1941 to 1945 and the government of Germany not the Government of the USSR was responsible for it. Source Pockney with my own [Paul Cockshott] interpolations for the uppermost graph (Bertram Patrick Pockney. Soviet statistics since 1950. Aldershot (UK) Dart-mouth, 1991.)”
The actual demographic disaster in the former USSR started in the Gorbachev and Yeltsin period with a 30% rise in the death rate and an even steeper fall in the birthrate. There was nothing under Khrushchev or Stalin to compare with this.
Evolution of Russian birth and death rates in Soviet and post-Glasnost periods. Bezier plot. Shaded area post-Glasnost. Source Pockney 231 and UN Demographic Yearbooks.  Bertram Patrick Pockney. Soviet statistics since 1950. Aldershot (UK) Dartmouth, 1991.