[PING] RFR: 8231111: Cgroups v2: Rework Metrics in java.base so as to recognize unified hierarchy

[Mandy Chung]

On 1/17/20 5:31 AM, Severin Gehwolf wrote:
>
> If I understand you correctly, then we'd have to change how
> -XshowSettings:system works currently with it. Not all metrics as
> currently printed via LauncherHelper.java are supported in both worlds
> (cgroup v1 & v2). It would make handling of cgroup v1 and cgroup v2
> specific metrics a little more awkward. Adding instanceof checks and
> downcasting as you suggest the consequence for a client would be.
> See:
> http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8231111/08/webrev/src/java.base/share/classes/sun/launcher/LauncherHelper.java.sdiff.html
>
> Also, in order to not break cross platform promises we'd also have to
> make the version specific interfaces available in shared code (or we'd
> risk requiring the user to use reflection) to get the proper sub-
> interface logic called.

-XshowSettings:system output is implementation detail [1] and also 
linux-only option.   jdk.internal.platform.Metrics is an internal API 
and there is no promise that it supports the union of all cgroups v1 and 
v2 metrics.  As you see, 1/3 of the metrics in v1 are not supported in 
v2.   It's reasonable for -XshowSettings:system showing the metrics 
valid to the container.

thanks
Mandy
[1] https://bugs.openjdk.java.net/browse/JDK-8204107