RFR: DRAFT: Expand old on demand [v42]

[Kelvin Nilsen]

On Mon, 8 May 2023 18:41:49 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> This PR describes several proposed changes to dynamically adjust the sizes of old-gen and young-gen.  In general, the objective is to keep old-gen as small as possible so that there is an abundance of memory available for the young-gen allocation runway.
>> 
>> As currently drafted, there are regression failures.  This DRAFT PR is published for the purpose of facilitating a careful code review.
>
> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix whitespace

src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.cpp line 133:

> 131:     }
> 132:     if (r->age() >= InitialTenuringThreshold) {
> 133:       r->save_top_before_promote();

We have to save top before promote, even if we do not  promote in place, because evacuator asks "what was garbage before top was saved"?  Need to think about tis...

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/248#discussion_r1190459207