8344414: ZGC: Another division by zero in rule_major_allocation_rate

[xmas92]

This specific issue was known since #20888. As well as a more serious issue in calculate_extra_young_gc_time which may introduce a NaN. This specific issue is sane as long as we have IEEE 754 sans the C++ standard making division by zero UB.

As discussed in #21304 it is probably better to try and tackle the division by zero issue by making sure the input is never zero. This patch introduces a small offset to the average which will effectively leave the value unchanged unless it is zero, and behave as almost zero in calculations without causing actual division by zero.

There is still the issue with NaN, this patch adds a short circuit when this can occur and returns the analytical result of the calculation.

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Issue

• JDK-8344414: ZGC: Another division by zero in rule_major_allocation_rate (Bug - P4)

Reviewers

• Erik Österlund (@fisk - Reviewer)
• Stefan Karlsson (@stefank - Reviewer)

Reviewing

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[openjdk]

@xmas92 This change now passes all automated pre-integration checks.

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

8344414: ZGC: Another division by zero in rule_major_allocation_rate

Reviewed-by: eosterlund, stefank

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At the time when this comment was updated there had been 72 new commits pushed to the master branch:

• ec93cc5: 8343932: Error when parsing qualified generic type test pattern in switch
• c330b90: 8343780: Add since checker tests to the Tools area modules and add missing @SInCE to jdk.jfr
• 8dada73: 8345120: A likely bug in StringSupport::chunkedStrlenShort
• 659f70b: 8343418: Unnecessary Hashtable usage in CSS.htmlAttrToCssAttrMap
• 5c8cb2e: 8337199: Add jcmd Thread.vthread_scheduler and Thread.vthread_pollers diagnostic commands
• 3eb5461: 8343791: Socket.connect API should document whether the socket will be closed when hostname resolution fails or another error occurs
• 4ac2e47: 8343800: Cleanup definition of NULL_WORD
• a3b58ee: 8339983: [s390x] secondary_super_cache does not scale well: C1 and interpreter
• e023add: 8345297: test/jdk/javax/swing/Action/8133039/bug8133039.java fails in ubuntu22.04
• 40ae469: 8235786: Javadoc for com/sun/net/httpserver/HttpExchange.java#setAttribute is unclear
• ... and 62 more: https://git.openjdk.org/jdk/compare/8485cb1ca1fa4885ddaf8381ebf862bbb233f090...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.

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[openjdk]

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[mlbridge]

Webrevs

• 01: Full - Incremental (98c0acb8)
• 00: Full (3bc3ff4b)

[fisk]

Looks good.

[fisk]

Even better.

[xmas92]

Thanks for the reviews.
/integrate

[openjdk]

Going to push as commit 63af2f4.
Since your change was applied there have been 73 commits pushed to the master branch:

• 077b842: 8345074: java.net.InterfaceAddress constructor could be made private
• ec93cc5: 8343932: Error when parsing qualified generic type test pattern in switch
• c330b90: 8343780: Add since checker tests to the Tools area modules and add missing @SInCE to jdk.jfr
• 8dada73: 8345120: A likely bug in StringSupport::chunkedStrlenShort
• 659f70b: 8343418: Unnecessary Hashtable usage in CSS.htmlAttrToCssAttrMap
• 5c8cb2e: 8337199: Add jcmd Thread.vthread_scheduler and Thread.vthread_pollers diagnostic commands
• 3eb5461: 8343791: Socket.connect API should document whether the socket will be closed when hostname resolution fails or another error occurs
• 4ac2e47: 8343800: Cleanup definition of NULL_WORD
• a3b58ee: 8339983: [s390x] secondary_super_cache does not scale well: C1 and interpreter
• e023add: 8345297: test/jdk/javax/swing/Action/8133039/bug8133039.java fails in ubuntu22.04
• ... and 63 more: https://git.openjdk.org/jdk/compare/8485cb1ca1fa4885ddaf8381ebf862bbb233f090...master

Your commit was automatically rebased without conflicts.

[openjdk]

@xmas92 Pushed as commit 63af2f4.

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