Bug ID: JDK-8198553 jcmd: separate Metaspace statistics from NMT

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JDK 11
11 b03Fixed

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. We should remove metadata statistics from "VM.native_memory" and make it an own first-class diagnostic command.

(Prior discussion on hotspot-runtime: http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2018-February/026354.html)

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Update: The final form of this patch adds the new diagnostic command "VM.metaspace".

Ah, thanks! Then my fix should be fine.
22-02-2018
My mistake; I was talking about this snippet from this discussion: On Wed, Feb 14, 2018 at 3:19 PM, Thomas St��fe <thomas.stuefe at gmail.com> wrote: > On Wed, Feb 14, 2018 at 3:11 PM, <coleen.phillimore at oracle.com> wrote: > >> 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 And I confused -XX:+PrintNMTStatistics with a diagnostic command.
22-02-2018
>> We should remove metadata statistics from "VM.native_memory" and >> make it an own first-class diagnostic command. > >I believe the decision was to report metadata statistics via both >diagnostic commands. Which both commands? I only see one (VM.native_memory, sub command "metadata").
22-02-2018
> We should remove metadata statistics from "VM.native_memory" and > make it an own first-class diagnostic command. I believe the decision was to report metadata statistics via both diagnostic commands.
22-02-2018

Relates :	JDK-8203455 - jcmd: VM.metaspace: print loader name for anonymous CLDs.
Relates :	JDK-8204440 - jcmd: VM.metaspace: print loader name for anonymous CLDs.
Relates :	JDK-8189688 - NMT: Report per-class load metadata information
Relates :	JDK-8203219 - VM.metaspace jcmd should optionally show loaded classes for loaders
Relates :	JDK-8203343 - VM.{metaspace\|classloaders\|classhierarchy...} jcmd should show invocation targets for Generated{Method\|Constructor}AccessorImpl classes
Relates :	JDK-8201572 - Improve Metaspace reporting