[jdk21u-dev] RFR: 8354145: G1: UseCompressedOops boundary is calculated on maximum heap region size instead of maxiumum ergonomic heap region size

[Daniel Hu]

On Mon, 1 Dec 2025 19:55:55 GMT, Paul Hohensee <phh at openjdk.org> wrote:

>> Fixes UseCompressedOops ergonomics to use original limits for G1 GC; prior to JDK18, `-Xmx32736m` by default enables UseCompressedOops but in JDK21 `-Xmx32736m` default sets UseCompressedOops to false. New test passes with change, fails without. Change passes GHA. Backport not clean due to [JDK-8330694](https://bugs.openjdk.org/browse/JDK-8330694) renaming `HeapRegion` to `G1HeapRegion`; modifications to the change are minimal as only had to "un-rename" the refactor.
>
> What other testing have you done? We usually like to see at least jdk tier1, and tier2 if possible.

@phohensee Thanks for calling that out. I've updated the description, and since ran tests on internal pipelines confirming no regressions jtreg tier 1-4 for our supported platforms.

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PR Comment: https://git.openjdk.org/jdk21u-dev/pull/2497#issuecomment-3604268725