RFR: Borrow from old gen

[Kelvin Nilsen]

On Mon, 7 Feb 2022 23:44:12 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/shenandoahCollectionSet.hpp line 50:
>> 
>>> 48:   size_t                _used;
>>> 49:   size_t                _region_count;
>>> 50:   size_t                _immediate_trash;
>> 
>> Might consider having collection set itself manage these new members through `add_region` API - rather than having similar looking code in each of the heuristics when the collection set is populated.
>
> This is a good idea.  I'll work on this change.

This change will be incorporated in next commit.

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PR: https://git.openjdk.java.net/shenandoah/pull/110