jcmd: separate metadata statistics from NMT?

[coleen.phillimore at oracle.com]

On 2/14/18 4:26 AM, Thomas Stüfe wrote:
> Hi all,
>
> JDK-8189688 introduced metadata printing into NMT. This is a very useful
> feature. However, it is tied to NMT, which is unnecessary.
>
> Currently, we have to trigger metadata statistics with jcmd with the
> NMT-printing command "VM.native_memory metadata". In order for that to
> work, NMT must have been enabled first in the monitored VM - so, the VM
> must have been started with -XX:NativeMemoryTracking=... . If not, "jcmd
> VM.native_memory" will give us an error. This diminishes its usefulness. We
> have many customer scenarios where we cannot restart the VM to enable NMT
> but still would like to see metadata statistics.
>
> The metadata statistics do not need the NMT infrastructure, they work
> perfectly fine without it. I propose to remove metadata statistics
> from "VM.native_memory"
> and make it an own first-class diagnostic command. I have made a quick
> patch to check if that would work and it works just fine.
>
> What do you think?
>
> Thanks and Kind Regards, Thomas

This sounds good to me.   Will NMT still print the metadata statistics 
when you use -XX:+PrintNMTStatistics?
Coleen