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

[Severin Gehwolf]

Hi David,

Thanks for the review.

On Tue, 2020-07-28 at 23:49 +1000, David Holmes wrote:
> Hi Severin,
> 
> On 28/07/2020 11:23 pm, Severin Gehwolf wrote:
> > Hi David,
> > 
> > On Tue, 2020-07-28 at 21:17 +1000, David Holmes wrote:
> > > 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?".)
> > 
> > I know of two uses so far:
> > 
> > 1) Launcher (-XshowSettings:system):
> > http://hg.openjdk.java.net/jdk/jdk/file/89fe9e02a522/src/java.base/share/classes/sun/launcher/LauncherHelper.java#l318
> > 
> > 2) OperatingSystemMXBean:
> > http://hg.openjdk.java.net/jdk/jdk/file/89fe9e02a522/src/jdk.management/unix/classes/com/sun/management/internal/OperatingSystemImpl.java#l48
> > 
> > Both uses seem OK as is. Is it worth caching something here?
> 
> No that looks fine. I didn't find them because of the reflective 
> invocation in Metrics.systemMetrics().
> 
> > > 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.
> > 
> > OK. Does that mean I should revert the version increment, then?
> 
> I would leave it unchanged, yes.

Here you go:
https://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8250627/02/webrev/

OK?

Thanks,
Severin