8368015: Shenandoah: fix error in computation of average allocation rate

[pf0n]

Backport is not clean. Resolved conflict in shenandoahGeneration.cpp where we need to pass in the unaccounted bytes to provide a more accurate estimation for the allocation rate + there is no AtomicAccess class in JDK25, so resorted to using Atomic::store instead of AtomicAccess::store - pf0n@94b8d0b.

Testing (all passed):

• GHA
• Local tier1 tests with Linux x86_64 server fastdebug and release build

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Issue

• JDK-8368015: Shenandoah: fix error in computation of average allocation rate (Enhancement - P4 - Approved)

Reviewers

• Paul Hohensee (@phohensee - Reviewer)

Reviewing

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[openjdk]

@pf0n This change now passes all automated pre-integration checks.

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8368015: Shenandoah: fix error in computation of average allocation rate

Reviewed-by: phh

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At the time when this comment was updated there had been 25 new commits pushed to the master branch:

• 4a9608f: 8377512: AOT cache creation fails with invalid native pointer
• 8f1542c: Merge
• 2fce64f: 8382438: [25u] Remove designator DEFAULT_PROMOTED_VERSION_PRE=ea for release 25.0.3
• ... and 22 more: https://git.openjdk.org/jdk25u-dev/compare/01842310f75aa37ad07b8f7aa7ed53b4ee04365e...master

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Webrevs

• 00: Full (94b8d0b4)

[openjdk]

This backport pull request has now been updated with issue from the original commit.

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⚠️ @pf0n This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[pf0n]

/approval request This fixes an error that could cause Shenandoah heuristics to underestimate the allocation rate.

This is not a clean backport because the AtomicAccess class does not exist in JDK25, so I had to replace it with the Atomic class. The change does not introduce any new functionality beyond the original fix. The fix is straightforward and nearly identical with the mainline change. All existing tests passes. The risk is considered low.

[openjdk]

@pf0n
8368015: The approval request has been created successfully.