Add ZGC generational memory managers

[DanielThomas]

Add ZGC generational memory manager labels.

genshen uses the same memory managers, but different pools and will go into a hybrid collection when necessary, so other than checking pool size changes, I'm not sure we can do anything there:

https://github.com/openjdk/shenandoah/blob/998f68b26b8d2a5178a30a6c5b596194961e3821/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp#L2928-L2935

[brharrington]

With generational ZGC is there still just a single pool name of ZHeap? We had to do some hacks to make allocation/promotion rate tracking work with the non-generational collectors (#847). Would that logic need to be revisited?

Similarly for generational Shenandoah is the only pool name Shenandoah?

[DanielThomas]

Oh yes indeed, found them:

• https://github.com/openjdk/zgc/blob/zgc_generational/src/hotspot/share/gc/z/zServiceability.cpp#L180-L181
• https://github.com/openjdk/shenandoah/blob/0dfb0a3eede0f8a20286ff0edf4d50349633bff5/src/hotspot/share/gc/shenandoah/shenandoahMemoryPool.cpp#L77-L104

[brharrington]

It looks like it is Shenandoah Young Gen and Shenandoah Old Gen (code). So the old gen should be fine, but we'll probably need a check for Young Gen, right now it looks for Eden Space:

https://github.com/Netflix/spectator/blob/main/spectator-ext-gc/src/main/java/com/netflix/spectator/gc/HelperFunctions.java#L72

[DanielThomas]

Made it a contains check.