RFR: Add generations to freeset [v5]

[William Kemper]

On Wed, 12 Apr 2023 15:08:29 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:
> 
>   Remove debug instrumentation

src/hotspot/share/gc/shenandoah/shenandoahFreeSet.cpp line 1044:

> 1042:       uint idx = i % 64;
> 1043:       if ((i != 0) && (idx == 0)) {
> 1044:         log_info(gc, ergo)(" %6u: %s", i-64, buffer);

Can we use the `gc, free` tags here as is done for the other messages in this class?

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/250#discussion_r1165860385