8381871: GenShen: ShenandoahGCHeuristics flag not reset after ignoring non-adaptive value

[pf0n]

Reset ShenandoahGCHeuristics flag to "adaptive" after a non-adaptive value is set for ShenandoahGCHeuristics when using Generational Shenandoah.

Testing

Created a test file TestGenerationalHeuristics.java that checks if ShenandoahGCHeuristics flag is always adaptive for Generational Shenandoah.

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Progress

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Issue

• JDK-8381871: GenShen: ShenandoahGCHeuristics flag not reset after ignoring non-adaptive value (Bug - P5)

Reviewers

• William Kemper (@earthling-amzn - Reviewer) 🔄 Re-review required (review applies to 3f636be2)
• Xiaolong Peng (@pengxiaolong - Committer) 🔄 Re-review required (review applies to 94eb0d7d)
• Kelvin Nilsen (@kdnilsen - Reviewer) 🔄 Re-review required (review applies to 94eb0d7d)
• Y. Srinivas Ramakrishna (@ysramakrishna - Reviewer)
• Sergey Bylokhov (@mrserb - Reviewer)

Reviewing

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[openjdk]

@pf0n The following labels will be automatically applied to this pull request:

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[mlbridge]

Webrevs

• 04: Full - Incremental (d3d6dcb5)
• 03: Full - Incremental (3f636be2)
• 02: Full - Incremental (ab8c77bb)
• 01: Full - Incremental (6a19ca01)
• 00: Full (94eb0d7d)

[kdnilsen]

Thanks for this fix.

[mrserb]

/reviewers 4

[openjdk]

@mrserb
The total number of required reviews for this PR (including the jcheck configuration and the last /reviewers command) is now set to 4 (with at least 1 Reviewer, 3 Authors).

[ysramakrishna]

Fix looks fine.

Can you verify the result of "PrintFlagsInitial"?

[pf0n]

Fix looks fine.

Can you verify the result of "PrintFlagsInitial"?

Yes, here's the result:

$ ./build/linux-x86_64-server-release/images/jdk/bin/java -XX:+UseShenandoahGC \
    -XX:ShenandoahGCMode=generational -XX:ShenandoahGCHeuristics=static \
    -XX:+PrintFlagsFinal -version | grep ShenandoahGCHeuristics

[0.001s][warning][gc] Ignoring -XX:ShenandoahGCHeuristics input: static, because generational shenandoah only supports adaptive heuristics
    ccstr ShenandoahGCHeuristics                   = adaptive                                  {product} {command line}

[mrserb]

I think FLAG_SET_ERGO should be used here. The FLAG_SET_DEFAULT will just assign the flag(I did not find a place where this macro is used with strings?). As far as I understand the FLAG_SET_ERGO will additionally clean the heap allocated for the string passed by the user.

[mrserb]

It would be good to add a test for this issue. grep the current tests for usage of "PrintFlagsFinal", you will find a few that call java via ProcessTools and check the results, for ex ProcessToolsExecuteLimitedTestJavaTest.

[mrserb]

another example of the test: gc/shenandoah/options/TestThreadCountsOverride.java

[ysramakrishna]

Fix looks fine.
Can you verify the result of "PrintFlagsInitial"?

Yes, here's the result:

$ ./build/linux-x86_64-server-release/images/jdk/bin/java -XX:+UseShenandoahGC \
    -XX:ShenandoahGCMode=generational -XX:ShenandoahGCHeuristics=static \
    -XX:+PrintFlagsFinal -version | grep ShenandoahGCHeuristics

[0.001s][warning][gc] Ignoring -XX:ShenandoahGCHeuristics input: static, because generational shenandoah only supports adaptive heuristics
    ccstr ShenandoahGCHeuristics                   = adaptive                                  {product} {command line}

How about -XX:+PrintFlagsInitial ?

[pf0n]

I think FLAG_SET_ERGO should be used here. The FLAG_SET_DEFAULT will just assign the flag(I did not find a place where this macro is used with strings?). As far as I understand the FLAG_SET_ERGO will additionally clean the heap allocated for the string passed by the user.

@mrserb good to note, I'll make that change.

[pf0n]

@ysramakrishna Here is -XX:+PrintFlagsInitial. The results are the same before my change.

$ ./build/linux-x86_64-server-release/jdk/bin/java -XX:+UseShenandoahGC \                          
    -XX:ShenandoahGCMode=generational -XX:ShenandoahGCHeuristics=static \
    -XX:+PrintFlagsInitial -version | grep ShenandoahGCHeuristics

    ccstr ShenandoahGCHeuristics                   = adaptive                                  {product} {default}

[ysramakrishna]

Fix looks fine.
Can you verify the result of "PrintFlagsInitial"?

Yes, here's the result:

$ ./build/linux-x86_64-server-release/images/jdk/bin/java -XX:+UseShenandoahGC \
    -XX:ShenandoahGCMode=generational -XX:ShenandoahGCHeuristics=static \
    -XX:+PrintFlagsFinal -version | grep ShenandoahGCHeuristics

[0.001s][warning][gc] Ignoring -XX:ShenandoahGCHeuristics input: static, because generational shenandoah only supports adaptive heuristics
    ccstr ShenandoahGCHeuristics                   = adaptive                                  {product} {command line}

I assume that, after the change suggested by @mrserb , above you now get ergonomic instead of command line as the last field in the output?

[pf0n]

I assume that, after the change suggested by @mrserb , above you now get ergonomic instead of command line as the last field in the output?

This is the result after the change:

[0.001s][warning][gc] Ignoring -XX:ShenandoahGCHeuristics input: static, because generational shenandoah only supports adaptive heuristics
    ccstr ShenandoahGCHeuristics                   = adaptive                                  {product} {command line, ergonomic}