ZGC Improvements

[jlittle-ptc]

This is mostly to make sure I'm not stepping on any toes, but @j-bahr @kcpeppe, is there anything coming down the pipe from you two around ZGC?

I will likely want to try and address issues as I start looking into ZGC further, but I want to make sure I'm not jumping the gun (AKA: ZGC is not quite finished yet) by posting issues for areas that have known problems.

Thanks!

[kcpeppe]

I'm happy for you to take the lead on Z while I focus on fixing some legacy issues. For example, I've moved the SurvivorRecords that were for historical reasons that are long gone, into the GC event. So do feel free to fluff out ZGC. I may want to come back to revisit some of the ways information is currently being bundled. I've been adjusting queries in my tooling and as I'm using it, I feel that some small adjustments in how information is bundled might make things a bit more intuitive to use. For example, the young generation statistics table is something to look at.

[j-bahr]

I think the work I've submitted so far covers the vast majority of gc+info log statements for Generational ZGC. There is probably more work that could be done to handle debug and more detailed output but I don't have a huge need for it a this time so I don't have any plans to implement it at the moment.

[jlittle-ptc]

Thanks for the feedback.

@kcpeppe @karianna Is there a preferred way that you'd want me to document these changes? Should I just do a monolithic PR with various fixes and provide a summary, or would it be preferred to post issues for each thing that I end up fixing and send a separate PR for each?

Also, for questions along the way, are discussions the way to go, or is there a better way?

[dsgrieve]

@jlittle-ptc - Smaller is easier to manage. I don't think you need to create a separate issue for everything, but you can manage that as you see fit. I'd create a jlittle-ptc/zgc branch where all of your changes would merge into, then we can merge that more easily once your work is done.