RFR: Expand old on demand [v42]

[Kelvin Nilsen]

On Wed, 10 May 2023 23:46:46 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.cpp line 362:
>> 
>>> 360:   size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
>>> 361:   collection_set->set_immediate_trash(immediate_garbage);
>>> 362: 
>> 
>> If we could introduce a new phase to do promote-in-place (indepedent of evacuation phase), then we could avoid some redundancy.  What's not implemented currently is that if the only reason we did evacuation was for promote in place, we SHOULD not have to update refs.
>
> Ideal: for abreviated cycles, we introduce a new phase that processes promote-in-palce regions and does not do update refs.

Development on this improvement is underway.  The improvement will be incorporated after this PR is integrated.

-------------

PR Review Comment: https://git.openjdk.org/shenandoah/pull/248#discussion_r1205914834