An important thing about USSR, which people often forget about, is there was no free movement.
Oversimplifying things a bit, you could only relocate when you're changing jobs and your new employer must have a special permission to hire workers from outside their region.
It’s the same in China today. They have the Hukou system. This is your family registration system and you need special permission to register somewhere new. Your benefits as a citizen are tied to this.
If you move to a city without approval, you work illegally and are not entitled to housing or educational facilities (which is why parents who’ve moved illegally need to send their kids to illegal schools).
The local government also can go raid these places from time to time depending on what quotas they need to align with.
So kind of sort of of like the four belt system in the USSR which limited internal movement and required internal passports.
Oversimplifying things a bit, you could only relocate when you're changing jobs and your new employer must have a special permission to hire workers from outside their region.
Very similar to H1B quotas.