jcmd: separate metadata statistics from NMT?

[Zhengyu Gu]

On 02/14/2018 04:26 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?

Fine with me.

Thanks,

-Zhengyu



> 
> Thanks and Kind Regards, Thomas