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

[David Holmes]

On Tue, 14 Feb 2023 13:40:40 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> 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.

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?

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?

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PR: https://git.openjdk.org/jdk/pull/12556