This was discussed the PR of JDK-8372513. From the PR:
```
I realized that having an unconstrained flag like this can cause overflows and asserts because of that. If we want to fix that we could do something like the following:

https://github.com/stefank/jdk/compare/8372513_shenandoah_max_region_size...stefank:jdk:8372513_shenandoah_max_region_size_constraints

Then running

 java -XX:+UseShenandoahGC -XX:+UnlockExperimentalVMOptions -XX:ShenandoahMaxRegionSize=9223372036854775808 -version

Will give this error message instead of an assert:

$ java -XX:+UseShenandoahGC -XX:+UnlockExperimentalVMOptions -XX:ShenandoahMaxRegionSize=9223372036854775808 -version
ShenandoahMaxRegionSize 8589934592G should be lower than (8589934592G).
Improperly specified VM option 'ShenandoahMaxRegionSize=9223372036854775808'
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
```

It was decided to create a separate issue for the overflow.