RFR: 8157023: Integrate NMT with JFR

[Stefan Johansson]

On Thu, 1 Dec 2022 17:44:53 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Please review this enhancement to include NMT information in JFR recordings.
>> 
>> **Summary**
>> Native Memory Tracking summary information can be obtained from a running VM using `jcmd` if started with `-XX:NativeMemoryTracking=summary/detail`. Using `jcmd` requires you to run a separate process and to parse the output to get the needed information. This change adds JFR events for NMT information to enable additional ways to consume the NMT data.
>> 
>> There are two new events added:
>> * _NativeMemoryUsage_ - The total native memory usage.
>> * _NativeMemoryUsagePart_ - The native memory usage for each component.
>> 
>> These events are sent periodically and by default the interval is 1s. This can of course be discussed, but that is the staring point. When NMT is not enabled on events will be sent.
>> 
>> **Testing**
>> * Added a simple test to verify that the events are sent as expected depending on if NMT is enabled or not.
>> * Mach5 sanity testing
>
> src/hotspot/share/jfr/metadata/metadata.xml line 711:
> 
>> 709:   <Event name="NativeMemoryUsagePart" category="Java Virtual Machine, Memory" label="Component Native Memory Usage" description="Native memory usage for a component" stackTrace="false" thread="false"
>> 710:     startTime="false" period="everyChunk">
>> 711:     <Field type="string" name="type" label="Memory Type" description="Component allocating the native memory" />
> 
> Is there a better way than to re-transmit the category name with every event?

There is a way to create special JFR types and instead just send an ID. This might make sense to save some extra memory. @egahlin, is there any drawback with creating custom type? Apart from the parsing needing an extra step.

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PR: https://git.openjdk.org/jdk/pull/11449