RFR: 8342444: Shenandoah: Uncommit regions from a separate, STS aware thread

[William Kemper]

On Mon, 11 Nov 2024 17:31:58 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Currently, Shenandoah uncommits regions from its control thread. The control thread is responsible for starting GC cycles in a timely fashion. Uncommitting memory from this thread may introduce unwanted delays in the control thread's response to GC pressure.

I modified the testing pipelines to set `-Xms4g -Xmx10g -XX:+ShenandoahUncommit`. All performance and stress tests completed successfully on x86 and aarch64. Marking this as ready for review.

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PR Comment: https://git.openjdk.org/jdk/pull/22019#issuecomment-2471152157