RFR: 8322255: Generational ZGC: Improve heuristics about page size

[Thomas Schatzl]

On Sun, 17 Dec 2023 15:37:25 GMT, Guoxiong Li <gli at openjdk.org> wrote:

> Hi all,
> 
> This patch fixes several issues about heuristics.
> 
> 1. Move `ZHeuristics::set_medium_page_size` to `ZArguments::initialize` so that the setting of `MaxTenuringThreshold` can use `ZPageSizeMedium` correctly.
> 2. Fix `ZHeuristics::use_per_cpu_shared_small_pages` to meet its comment.
> 3. Fix `ZHeuristics::significant_heap_overhead` and `ZHeuristics::significant_young_overhead` to use `ZFragmentationLimit` and `ZYoungCompactionLimit` as percentages instead of multiples.
> 
> Thanks for the review.
> 
> Best Regards,
> -- Guoxiong

That is the point - put unrelated changes into different PRs so that new, unexpected behavior can be (if necessary) easily traced back to that particular issue (e.g. when bisecting).

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PR Comment: https://git.openjdk.org/jdk/pull/17137#issuecomment-1860026029