While investigating the following VisualVM bug https://github.com/oracle/visualvm/issues/494 that this problem is caused by fix for JDK-8268265.

Looking at jvmstat counters I see the following values for 'used' jvmstat counters:
INFO [org.graalvm.visualvm.tools.jvmstat.JvmJvmstatModel]: sun.gc.generation.0.space.0.used = 88202184
INFO [org.graalvm.visualvm.tools.jvmstat.JvmJvmstatModel]: sun.gc.generation.0.space.1.used = 88202184
INFO [org.graalvm.visualvm.tools.jvmstat.JvmJvmstatModel]: sun.gc.generation.0.space.2.used = 88202184
INFO [org.graalvm.visualvm.tools.jvmstat.JvmJvmstatModel]: sun.gc.generation.1.space.0.used = 88202184
INFO [org.graalvm.visualvm.tools.jvmstat.JvmJvmstatModel]: Sum 352808736
- note all 'used' counters have the same value.

Normal case looks similar to this:
INFO [org.graalvm.visualvm.tools.jvmstat.JvmJvmstatModel]: sun.gc.generation.0.space.0.used = 9069768
INFO [org.graalvm.visualvm.tools.jvmstat.JvmJvmstatModel]: sun.gc.generation.0.space.1.used = 0
INFO [org.graalvm.visualvm.tools.jvmstat.JvmJvmstatModel]: sun.gc.generation.0.space.2.used = 1062200
INFO [org.graalvm.visualvm.tools.jvmstat.JvmJvmstatModel]: sun.gc.generation.1.space.0.used = 80296096
INFO [org.graalvm.visualvm.tools.jvmstat.JvmJvmstatModel]: Sum 90428064

It looks to me that last_used_in_bytes should be instance variable of SpaceCounters , since there are four instances of SpaceCounters and all those instances need to remember last_used_in_bytes.