8257073: ZGC: Try forward object before retaining page

[pliden]

This is a follow up to @albertnetymk's comment in the review of #1228, where he suggested that we could try to forward the object before we go ahead and retain the page. This could be an optimization in two cases:

1. A mutator would avoid a relocation stall in case the page is claimed, but the object the mutator is interested in has already been relocated.
2. The worker thread detaching the page would not have to wait for a mutator that is just forwarding an object.

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Testing

	Linux x64	Linux x86	Windows x64	macOS x64
Build	❌ (6/6 failed)	❌ (2/2 failed)	✔️ (2/2 passed)	✔️ (2/2 passed)
Test (tier1)			✔️ (9/9 passed)	✔️ (9/9 passed)

Failed test tasks

• Linux x64 (build debug)
• Linux x64 (build hotspot minimal)
• Linux x64 (build hotspot no-pch)
• Linux x64 (build hotspot optimized)
• Linux x64 (build hotspot zero)
• Linux x64 (build release)
• Linux x86 (build debug)
• Linux x86 (build release)

Issue

• JDK-8257073: ZGC: Try forward object before retaining page

Reviewers

• Albert Mingkun Yang (@albertnetymk - Author)
• Erik Österlund (@fisk - Reviewer)
• Stefan Karlsson (@stefank - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jdk pull/1431/head:pull/1431
$ git checkout pull/1431

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[openjdk]

@pliden The following label will be automatically applied to this pull request:

• hotspot-gc

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[mlbridge]

Webrevs

• 00: Full (8fa6063)

[fisk]

Looks good.

[openjdk]

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

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8257073: ZGC: Try forward object before retaining page

Reviewed-by: ayang, eosterlund, stefank

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 42 new commits pushed to the master branch:

• 1b3aa3a: 8256831: MIPS Zero builds fail with undefined __atomic_compare_exchange_8
• 734d3c3: 8256862: Several java/foreign tests fail on x86_32 platforms
• 7946c94: 8257082: ZGC: Clean up ZRuntimeWorkers and ZWorkers
• f6d6a07: 8256938: Improve remembered set sampling task scheduling
• b823ad9: 8257072: ZGC: Rename roots iterators
• 973255c: 8196100: javax/swing/text/JTextComponent/5074573/bug5074573.java fails
• a8e3eab: 8245026: PsAdaptiveSizePolicy::_old_gen_policy_is_ready is unused
• b1d1499: 8256956: RegisterImpl::max_slots_per_register is incorrect on AMD64
• 20020d1: 8254360: Re-examine use of CodeBuffer::verify_section_allocation
• e56a8df: 8257042: [aix] Disable os.release_one_mapping_multi_commits_vm gtest
• ... and 32 more: https://git.openjdk.java.net/jdk/compare/7b3d0958c068c8f45c98ea0615ef8cd908fd408d...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[pliden]

Thanks for reviewing!

/integrate

[openjdk]

@pliden Since your change was applied there have been 42 commits pushed to the master branch:

• 1b3aa3a: 8256831: MIPS Zero builds fail with undefined __atomic_compare_exchange_8
• 734d3c3: 8256862: Several java/foreign tests fail on x86_32 platforms
• 7946c94: 8257082: ZGC: Clean up ZRuntimeWorkers and ZWorkers
• f6d6a07: 8256938: Improve remembered set sampling task scheduling
• b823ad9: 8257072: ZGC: Rename roots iterators
• 973255c: 8196100: javax/swing/text/JTextComponent/5074573/bug5074573.java fails
• a8e3eab: 8245026: PsAdaptiveSizePolicy::_old_gen_policy_is_ready is unused
• b1d1499: 8256956: RegisterImpl::max_slots_per_register is incorrect on AMD64
• 20020d1: 8254360: Re-examine use of CodeBuffer::verify_section_allocation
• e56a8df: 8257042: [aix] Disable os.release_one_mapping_multi_commits_vm gtest
• ... and 32 more: https://git.openjdk.java.net/jdk/compare/7b3d0958c068c8f45c98ea0615ef8cd908fd408d...master

Your commit was automatically rebased without conflicts.

Pushed as commit bf66d73.

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