RFR: 8304074: [JMX] Add an approximation of total bytes allocated on the Java heap by the JVM [v5]

[Paul Hohensee]

On Fri, 5 May 2023 15:11:26 GMT, Volker Simonis <simonis at openjdk.org> wrote:

>> Paul Hohensee has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8304074: [JMX] Add an approximation of total bytes allocated on the Java heap by the JVM
>
> src/hotspot/share/include/jmm.h line 55:
> 
>> 53:   JMM_VERSION_2   = 0x20020000, // JDK 10
>> 54:   JMM_VERSION_3   = 0x20030000, // JDK 14
>> 55:   JMM_VERSION_3_0 = 0x20030000,
> 
> Why do we need `JMM_VERSION_3_0`? We haven't defined `JMM_VERSION_2_0` either.

Removed.

> src/hotspot/share/include/jmm.h line 321:
> 
>> 319:                                                   jstring flag_name,
>> 320:                                                   jvalue  new_value);
>> 321:   jlong        (JNICALL *GetAllThreadAllocatedMemory)
> 
> I'm not sure here, but I think there's no need to "overwrite" a *reserved* slot if you add this functionality to a new major release as you do. You also haven't done it when you've added `GetOneThreadAllocatedMemory()` with [JDK-8231209](https://bugs.openjdk.org/browse/JDK-8231209).
> 
> I think we should keep these *reserved* slots for the case when we eventually have to downport new functionality from a later release.

Done.

> src/hotspot/share/services/management.cpp line 2282:
> 
>> 2280:   jmm_FindDeadlockedThreads,
>> 2281:   jmm_SetVMGlobal,
>> 2282:   jmm_GetAllThreadAllocatedMemory,
> 
> See comment on overwriting the `reserved6` slot above.

Done.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/13814#discussion_r1186515133
PR Review Comment: https://git.openjdk.org/jdk/pull/13814#discussion_r1186515257
PR Review Comment: https://git.openjdk.org/jdk/pull/13814#discussion_r1186515422