jcmd: separate metadata statistics from NMT?

[Thomas Stüfe]

On Wed, Feb 14, 2018 at 3:11 PM, <coleen.phillimore at oracle.com> wrote:

>
>
> 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
>
>
Yes, you are right, that should be preserved.

..Thomas