RFR: Account for humongous object waste

[Y. Srinivas Ramakrishna]

On Sat, 15 Apr 2023 00:27:13 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/shenandoahGeneration.hpp line 55:
>> 
>>> 53:   // Usage
>>> 54:   size_t _affiliated_region_count;
>>> 55:   size_t _humongous_waste;      // how much waste for padding in humongous objects
>> 
>> Could you document here whether this is included in `_used` below, or is explicitly excluded from it. From my cursory reading of the code doing the adjustments, it looked like `_used` includes `_humongous_waste`.
>> 
>> it would also be good to include a line of documentation about where this statistic might be useful (or, if it is, where it is used today).
>
> It isn't included in `used`, but is deducted from `available`. This gives the heuristics a more accurate view of how much memory remains for allocations. I will update the comment.

Makes sense. Thanks for updating the documentation.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/255#discussion_r1169166551