RFR: Add generations to freeset [v21]

[William Kemper]

On Sat, 29 Apr 2023 14:22:53 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> ShenandoahFreeSet has not yet been modified to deal efficiently with the combination of old-gen and young-gen collection set reserves.  This PR makes changes so that we can distinguish between collector_is_free, old_collector_is_free, and mutator_is_free.  Further, it endeavors to keep each set of free regions tightly packed, so the range of regions representing each set is small.
>> 
>> In its current form, this no longer fails existing regression tests (except for known problems that are being addressed independently)
>
> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Respond to reviewer feedback

Changes requested by wkemper (Committer).

src/hotspot/share/gc/shenandoah/shenandoahFreeSet.hpp line 32:

> 30: #include "gc/shenandoah/shenandoahHeap.hpp"
> 31: 
> 32: enum FreeMemoryType : uint8_t {

Globally visible type should `Shenandoah` prefix.

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PR Review: https://git.openjdk.org/shenandoah/pull/250#pullrequestreview-1407945260
PR Review Comment: https://git.openjdk.org/shenandoah/pull/250#discussion_r1181794878