JDK-8302455: VM.classloader_stats memory size values are wrong

[tstuefe]

VM.classloader_stats shows metaspace consumption in words, but should show bytes.

Patch fixes that, and adjusts the associated jtreg test to catch regressions like this.

I manually tested the test with the unpatched hotspot to see if the regression shows up, it does.

Tested the patch on x64 (fastdebug, release) and x86.

Note: "calculate_jfr_stats" is misnamed, actually only ever used by this dcmd, not by jfr. I will clear this up in a separate RFE.

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Issue

• JDK-8302455: VM.classloader_stats memory size values are wrong

Reviewers

• Coleen Phillimore (@coleenp - Reviewer) ⚠️ Review applies to 2be3a810
• David Holmes (@dholmes-ora - Reviewer)

Reviewing

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Webrevs

• 02: Full - Incremental (7ed3951a)
• 01: Full - Incremental (0bbbcc15)
• 00: Full (2be3a810)

[coleenp]

Looks good.

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8302455: VM.classloader_stats memory size values are wrong

Reviewed-by: coleenp, dholmes

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At the time when this comment was updated there had been 25 new commits pushed to the master branch:

• 3ba1560: 8302026: Port fdlibm inverse trig functions (asin, acos, atan) to Java
• 861e302: 8302163: Speed up various String comparison methods with ArraysSupport.mismatch
• 50dcc2a: 8301460: Clean up LambdaForm to reference BasicType enums directly
• 28f5250: 8302127: Remove unused arg in write_ref_field_post
• 0c96584: 8301225: Replace NULL with nullptr in share/gc/shenandoah/
• 26b111d: 8301700: Increase the default TLS Diffie-Hellman group size from 1024-bit to 2048-bit
• 5238817: 8301463: Code in DatagramSocket still refers to resolved JDK-8237352
• 11194e8: 8302325: Wrong comment in java.base/share/native/libjimage/imageFile.hpp
• 33bec20: 8300808: Accelerate Base64 on x86 for AVX2
• 46bcc49: 8302147: Speed up compiler/jvmci/compilerToVM/IterateFramesNative.java
• ... and 15 more: https://git.openjdk.org/jdk/compare/7dfe75cf553193faf709cff6b8b2505680d7cebc...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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[dholmes-ora]

So in addition to the poor name, the declaration is wrong:

 void calculate_jfr_stats(size_t* p_used_bytes, size_t* p_capacity_bytes) const;

as it refers to bytes not words. Perhaps better to clean this up completely in this issue rather than a separate RFE?

[dholmes-ora]

That said, given:

// This only exists for JFR and jcmd VM.classloader_stats. We may want to
//  change this. Capacity as a stat is of questionable use since it may
//  contain committed and uncommitted areas. For now we do this to maintain
//  backward compatibility with JFR.

and the fact this is not used by JFR then maybe it should all just be removed?

[tstuefe]

That said, given:

// This only exists for JFR and jcmd VM.classloader_stats. We may want to
//  change this. Capacity as a stat is of questionable use since it may
//  contain committed and uncommitted areas. For now we do this to maintain
//  backward compatibility with JFR.

and the fact this is not used by JFR then maybe it should all just be removed?

That's my plan, but I'd like to do this in a follow-up RFE. The patch I'd like to keep minimal for easy downport. I'd like to keep cleanups separate.

[dholmes-ora]

Given the reason this bug likely arose is the fact the parameters to calculate_jfr_stats say they are "bytes" then fixing that is not a mere cleanup IMO. Can we at least fix that in this PR?

[tstuefe]

Given the reason this bug likely arose is the fact the parameters to calculate_jfr_stats say they are "bytes" then fixing that is not a mere cleanup IMO. Can we at least fix that in this PR?

Hi David, I reformed the ill-named function and renamed it to "usage_numbers", because that name and prototype is used in other places in Metaspace as well (e.g. MetaspaceArena), so its a uniform scheme.

[dholmes-ora]

Looks good. The usage_numbers changes were a bit more involved then I had expected but they seem fine.

Thanks.

[tstuefe]

Thanks David!

/integrate

[openjdk]

Going to push as commit 6e2d3c6.
Since your change was applied there have been 27 commits pushed to the master branch:

• 1480d41: 8208470: Type annotations on inner type that is an array component
• 573c316: 8224980: FLAG_SET_ERGO silently ignores invalid values
• 3ba1560: 8302026: Port fdlibm inverse trig functions (asin, acos, atan) to Java
• 861e302: 8302163: Speed up various String comparison methods with ArraysSupport.mismatch
• 50dcc2a: 8301460: Clean up LambdaForm to reference BasicType enums directly
• 28f5250: 8302127: Remove unused arg in write_ref_field_post
• 0c96584: 8301225: Replace NULL with nullptr in share/gc/shenandoah/
• 26b111d: 8301700: Increase the default TLS Diffie-Hellman group size from 1024-bit to 2048-bit
• 5238817: 8301463: Code in DatagramSocket still refers to resolved JDK-8237352
• 11194e8: 8302325: Wrong comment in java.base/share/native/libjimage/imageFile.hpp
• ... and 17 more: https://git.openjdk.org/jdk/compare/7dfe75cf553193faf709cff6b8b2505680d7cebc...master

Your commit was automatically rebased without conflicts.

[openjdk]

@tstuefe Pushed as commit 6e2d3c6.

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