RFR: Expand old on demand [v65]

[Y. Srinivas Ramakrishna]

On Thu, 25 May 2023 20:15:05 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.
>> 
>> This PR now passes all GHA pre-integration tests and other internal CI tests.
>
> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Respond to reviewer feedback
>   
>   This is mostly tidy and cleanup.

Let's get this integrated as is, without doing any further extensive refactorings at this stage, and we can deal with more detailed or low-level review feedback in the fullness of time.

Such review comments may appear in the future and can be fixed later.

Thanks for the improvements in performance that these changes provided!

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Marked as reviewed by ysr (Committer).

PR Review: https://git.openjdk.org/shenandoah/pull/248#pullrequestreview-1440821330