RFR: Add generations to freeset [v20]

[Kelvin Nilsen]

On Sat, 29 Apr 2023 00:10:39 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix white space
>
> src/hotspot/share/gc/shenandoah/shenandoahFreeSet.hpp line 44:
> 
>> 42: 
>> 43: private:
>> 44:   size_t _max;
> 
> What does `_max` hold?

Adding a comment: num_regions

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/250#discussion_r1181927673