RFR: Initial sizing refactor [v2]

[Y. Srinivas Ramakrishna]

On Tue, 20 Dec 2022 19:16:45 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp line 459:
>> 
>>> 457:   _young_generation = new ShenandoahYoungGeneration(_max_workers, max_capacity_young, initial_capacity_young);
>>> 458:   _old_generation = new ShenandoahOldGeneration(_max_workers, max_capacity_old, initial_capacity_old);
>>> 459:   _global_generation = new ShenandoahGlobalGeneration(_max_workers, soft_max_capacity(), soft_max_capacity());
>> 
>> A single line of comment here would be helpful here. It sounds as if the idea is that for the so-called global generation (which I assume is identified with the entirety of the committed heap at any time), the initial and max (floor and ceiling) are both set at `soft_max_capacity` ? What does that mean? I might have naively expected this to be, respectivley, `max_old + max_young` and `initial_old + initial_young` like you had it before.
>
> I've been thinking of the max capacity as the maximum _allowed_ capacity. For example, the maximum _allowed_ capacity for old would be `total heap - minimum capacity of young`. So, the sum of the maximum allowed for old and young could exceed the total. If that makes sense, I will put the explanation in a comment here.

Makes sense; thanks for the updated comments!

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PR: https://git.openjdk.org/shenandoah/pull/185