RFR(s): 8250627: Use -XX:+/-UseContainerSupport for enabling/disabling Java container metrics

[David Holmes]

Hi Severin,

On 28/07/2020 6:27 pm, Severin Gehwolf wrote:
> Hi,
> 
> Please review this patch which makes the Java container metrics adhere
> to -XX:+/-UseContainerSupport so they can be disabled if heuristics
> turn out to be wrong. The approach taken is to use JNI and call into
> the JVM in order to determine the setting of UseContainerSupport before
> Metrics are being instantiated.
> 
> The intention is for this patch to be backported to older JDKs so as to
> provide a means to disable container metrics should things go wrong
> with backports of the likes of JDK-8226575.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8250627
> webrev: https://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8250627/01/webrev/

Seems quite simple and clean.

One query though, I'm not clear on who the expected caller of 
Metrics.getInstance() is? (Coming from the perspective of "might we want 
to cache the fact container support is not enabled?".)

Also note that we no longer update JVM_INTERFACE_VERSION (last update 
was JDK 13) - it is meaningless now the JDK and hotspot are in sync 
version wise.

Thanks,
David

> Testing: New container test. Existing container tests. jdk/submit.
>           tier1 on Linux x86_64.
> 
> Thoughts?
> 
> Thanks,
> Severin
>