Some of the core G1 state variables in G1CollectorState are ambiguously named:

gcs_are_young, last_young_gc, last_gc_was_young

Problems:
 - All gcs include the young gen, so "young" is meaningless.
 - "young" is shorthand for "fully young" (which confusing with "full
 gc"), or "young only", but the "only" is both silent and invisible.
 "last" is used in one variable to mean "previous", and in another to mean
 "ultimate, maybe". "last_gc_was_young" vs. "last_young_gc".

JDK-8080226 (Replace collector state booleans with explicit state variable(s)?) depends on this.