RFR: 8333926: Shenandoah: Lower default immediate garbage threshold

[Kelvin Nilsen]

On Mon, 10 Jun 2024 22:53:07 GMT, William Kemper <wkemper at openjdk.org> wrote:

> After marking, when Shenandoah finds a certain percentage threshold of garbage within regions that contain no live objects it will skip the evacuation phase. This threshold is currently 90%, but we (Amazon) have found that many internal workloads benefit significantly by reducing this threshold to 70%. We have also seen improvements on dacapo/sunflow and specjbb2015. We have also not seen any performance degradation caused by lowering this threshold.

Marked as reviewed by kdnilsen (no project role).

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PR Review: https://git.openjdk.org/jdk/pull/19641#pullrequestreview-2110886323