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

Fri Dec 12 17:57:08 UTC 2025

On Fri, 28 Nov 2025 18:48:13 GMT, Daniel Hu <duke 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 ran on internal Amazon pipeline and passes jtreg tier1-4 on platforms linux x64, aarch64, aarch32; windows x64; macos x64, aarch64. 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.

This pull request has now been integrated.

Changeset: 7c993206
Author:    Daniel Hu <costmuch at amazon.com>
Committer: Paul Hohensee <phh at openjdk.org>
URL:       https://git.openjdk.org/jdk21u-dev/commit/7c99320610f4a743c3cf94be6ebc3685a2612241
Stats:     94 lines in 4 files changed: 94 ins; 0 del; 0 mod

8354145: G1: UseCompressedOops boundary is calculated on maximum heap region size instead of maxiumum ergonomic heap region size

Reviewed-by: phh
Backport-of: 526951dba731f0e733e22a3bff7ac7a18ce9dece

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PR: https://git.openjdk.org/jdk21u-dev/pull/2497