RFR: 8367473: Shenandoah: Make the detailed evacuation metrics a runtime diagnostic option [v5]

[William Kemper]

On Thu, 18 Sep 2025 17:31:19 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Non-product builds currently have a feature to produce detailed metrics about evacuations (number of objects, number of bytes, split out by age (young, old, promotion) and thread (mutator or worker). This change makes this feature accessible in release builds as a diagnostic option.
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Only print promotion/old evacuation metrics in generational mode

It's only suppressed in the non-generational mode, in which case there will _always_ be zero promotions/old evacuations. In the _generational_ mode, it will show the zeros to reinforce the notion that no promotions or old evacuations happened on _this_ cycle.

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PR Comment: https://git.openjdk.org/jdk/pull/27238#issuecomment-3309136169