8349906: G1: Improve initial survivor rate for newly used young regions

[tschatzl]

Hi all,

please review this change that tries to improve the survivor rate initial values for newly expanded regions.

Currently G1 uses InitialSurvivorRate as survivor rate for such regions, but it is typically a pretty bad choice because

• it's rather conservative, estimating that 40% of region contents will survive
• such a conservative value is kind of bad particularly in cases for regions that are expanded late in the mutator phase because they are not frequently updated (and with our running weights changes get propagated over a very long time), i.e. this 40% sticks for a long time (*)
• it is a random value, i.e. not particularly specific to the application.

The suggestion is to use the survivor rate for the last region we know the survivor rate already.

(*) to clarify this a little: G1 keeps track of [0...m] survivor rate predictors. For a given garbage collection, [0...n] of those are updated (n is the number of eden/survivor regions depending on the rate group). However those for ]n...m] are not, particularly those in that range that are seldom allocated, the predictors are not updated very frequently. Now the young gen sizing uses these predictions "at the end" of the predictor anyway, and since they are infrequently updated and their values are very conservative, G1 won't expand young gen as much as it could/should.

Testing: gha, tier1-7 (with other changes)

Hth,
Thomas

---

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Issue

• JDK-8349906: G1: Improve initial survivor rate for newly used young regions (Enhancement - P4)

Reviewers

• Ivan Walulya (@walulyai - Reviewer) Review applies to 5c4ded01
• Kim Barrett (@kimbarrett - Reviewer)

Reviewing

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[openjdk]

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

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

8349906: G1: Improve initial survivor rate for newly used young regions

Reviewed-by: kbarrett, iwalulya

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At the time when this comment was updated there had been 170 new commits pushed to the master branch:

• a70eba8: 8330174: Protection zone for easier detection of accidental zero-nKlass use
• f529bf7: 8350483: AArch64: turn on signum intrinsics by default on Ampere CPUs
• 037e471: 8350666: cmp-baseline builds fail after JDK-8280682
• c8a521f: 8345213: JVM Prefers /etc/timezone Over /etc/localtime on Debian 12
• 86024eb: 8348426: Generate binary file for -XX:AOTMode=record -XX:AOTConfiguration=file
• 267d69b: 8326447: jpackage creates Windows installers that cannot be signed
• 2efb033: 8350601: Miscellaneous updates to jpackage test lib
• d4fdc79: 8344981: [REDO] JDK-6672644 JComboBox still scrolling if switch to another window and return back
• b78043f: 8320220: Compilation of cyclic hierarchy causes infinite recursion
• a3188e0: 8349991: GraphUtils.java can use String.replace() instead of String.replaceAll()
• ... and 160 more: https://git.openjdk.org/jdk/compare/8e8582949669d5f3dcb68886ccb6a719393d1a9e...master

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[mlbridge]

Webrevs

• 02: Full - Incremental (fc2dde0c)
• 01: Full - Incremental (a09bc25e)
• 00: Full (5c4ded01)

[kimbarrett]

Looks good.

[tschatzl]

Thanks @kimbarrett @walulyai for your reviews

/integrate

[openjdk]

Going to push as commit aac9cb4.
Since your change was applied there have been 171 commits pushed to the master branch:

• a431046: 8350518: org.openjdk.bench.java.util.TreeMapUpdate.compute fails with "java.lang.IllegalArgumentException: key out of range"
• a70eba8: 8330174: Protection zone for easier detection of accidental zero-nKlass use
• f529bf7: 8350483: AArch64: turn on signum intrinsics by default on Ampere CPUs
• 037e471: 8350666: cmp-baseline builds fail after JDK-8280682
• c8a521f: 8345213: JVM Prefers /etc/timezone Over /etc/localtime on Debian 12
• 86024eb: 8348426: Generate binary file for -XX:AOTMode=record -XX:AOTConfiguration=file
• 267d69b: 8326447: jpackage creates Windows installers that cannot be signed
• 2efb033: 8350601: Miscellaneous updates to jpackage test lib
• d4fdc79: 8344981: [REDO] JDK-6672644 JComboBox still scrolling if switch to another window and return back
• b78043f: 8320220: Compilation of cyclic hierarchy causes infinite recursion
• ... and 161 more: https://git.openjdk.org/jdk/compare/8e8582949669d5f3dcb68886ccb6a719393d1a9e...master

Your commit was automatically rebased without conflicts.

[openjdk]

@tschatzl Pushed as commit aac9cb4.

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