8373023: [REDO] Remove the default value of InitialRAMPercentage

[jsikstro]

Hello,

We backed out this change in #28617 after issues in found in testing. Moving forward, we've decided to problem list a few tests that assumes that a GC does not run during their execution. When the initial heap size becomes very low with this change, it may trigger additional GCs, which may interfere with a few tests.

We are planning to follow up on the problem lists with test fixes in:
#28638, #28637

From the original RFE:

This RFE changes the default of InitialRAMPercentage to 0, effectively removing its default value. Please see the CSR for specific details on this change.

Changing the default value to 0 results in the behavior that the initial heap size (InitialHeapSize) is set to the minimum heap size (MinHeapSize). This is because of the following lines in Arguments::set_heap_size(), which takes the MAX value of MinHeapSize as well:

uint64_t initial_memory = (uint64_t)(((double)MaxRAM * InitialRAMPercentage) / 100);
...

reasonable_initial = MAX3(reasonable_initial, reasonable_minimum, MinHeapSize);
reasonable_initial = MIN2(reasonable_initial, MaxHeapSize);

This change improves startup performance for all GCs, but affects the time-to-peak performance in some out-of-the-box configurations for some GCs. This is mainly visible in ParallelGC.

Testing:

• Oracle's tier1-3

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change requires CSR request JDK-8371987 to be approved

Issues

• JDK-8373023: [REDO] Remove the default value of InitialRAMPercentage (Enhancement - P4)
• JDK-8371987: Remove the default value of InitialRAMPercentage (CSR)

Reviewers

• Stefan Karlsson (@stefank - Reviewer)
• Stefan Johansson (@kstefanj - Reviewer)
• Axel Boldt-Christmas (@xmas92 - Reviewer)

Reviewing

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[openjdk]

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

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

8373023: [REDO] Remove the default value of InitialRAMPercentage

Reviewed-by: stefank, sjohanss, aboldtch

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At the time when this comment was updated there had been 1 new commit pushed to the master branch:

• c432150: 8372809: Test vmTestbase/nsk/jdi/ThreadReference/isSuspended/issuspended001/TestDescription.java failed: JVMTI_ERROR_THREAD_NOT_ALIVE

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[AlanBateman]

What about java/lang/management/MemoryPoolMXBean/ThresholdTest.java, that was the test that started failing for me yesterday.

[jsikstro]

The test failure in java/lang/management/MemoryPoolMXBean/ThresholdTest.java is fixed in #28630

This was a pre-existing issue that is not directly tied to this change.

[AlanBateman]

Thanks, I didn't see that change go by.

[kstefanj]

Looks good

[openjdk]

@jsikstro Please do not rebase or force-push to an active PR as it invalidates existing review comments. Note for future reference, the bots always squash all changes into a single commit automatically as part of the integration. See OpenJDK Developers’ Guide for more information.

[jsikstro]

Thank you for the reviews everyone!
/integrate

[openjdk]

Going to push as commit 8d80778.
Since your change was applied there have been 3 commits pushed to the master branch:

• fa6ca0b: 8362428: Update IANA Language Subtag Registry to Version 2025-08-25
• 0bcef61: 8372957: After JDK-8282441 JDWP might allow some invalid FrameIDs to be used
• c432150: 8372809: Test vmTestbase/nsk/jdi/ThreadReference/isSuspended/issuspended001/TestDescription.java failed: JVMTI_ERROR_THREAD_NOT_ALIVE

Your commit was automatically rebased without conflicts.

[openjdk]

@jsikstro Pushed as commit 8d80778.

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