RFR: Track promotion rate into old generation [v2]

[Roman Kennke]

On Fri, 17 Sep 2021 21:25:39 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> The member `_bytes_allocated_since_last_gc` has been moved into the `ShenandoahGeneration` abstraction and is updated accordingly. Evacuations into the old generation (i.e., promotion) are counted as allocations against the old generation. Promotion of entire regions is not recorded in the promotion rate.
>
> William Kemper has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Only register successful old evacuations
>  - Only treat promotions as old gen allocations

Looks good to me, thanks!

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Marked as reviewed by rkennke (Lead).

PR: https://git.openjdk.java.net/shenandoah/pull/70