RFR: Container Fixes (8219652, 8217766, 8212528)

[Severin Gehwolf]

Hi Bob,

Changes look OK to me.

I'd prefer if those issues would get addressed separately, though. 3
webrevs for 3 bugs, over lumping 3 bugs into 1 webrev. This makes it
A) easier to review B) easier to backport to older releases if/when the
time comes. Some of those issues are rather unrelated after all.

Thanks,
Severin

On Thu, 2019-03-14 at 10:15 -0400, Bob Vandette wrote:
> Ping ...
> 
> 
> Please review these three fixes for Linux Docker/cgroup container
> support.
> 
> WEBREV:
> 
> http://cr.openjdk.java.net/~bobv/8217766/webrev.0
> 
> ISSUE1:
> 
> https://bugs.openjdk.java.net/browse/JDK-8219562 - Line of code in
> osContainer_linux.cpp#L102 appears unreachable
> 
> This change corrects a rarely used hotspot code path making it
> compatible with the Java based Metrics.
> 
> ISSUE2:
> 
> https://bugs.openjdk.java.net/browse/JDK-8212528 - Wrong cgroup
> subsystem being used for some CPU Container Metrics
> 
> Most Linux distros provide symbolic links for cpuacct and cpu
> controller directories.  Docker on the Mac does not.
> This causes some of the cpu statistics to be unreported since the
> directory name was incorrect.
> 
> ISSUE3:
> 
> https://bugs.openjdk.java.net/browse/JDK-8217766 - Container Support
> doesn't work for some Join Controllers combinations
> 
> The cgroup identification -implemented by parsing
> /proc/self/mountinfo
> and /proc/self/cgroup- assumed each cgroup controller was mounted
> disjoint from the others (except for "cpu" and "cpuacct"
> controllers).
> Which means, we expected one single controller per mountinfo line.
> 
> This matches the way most Linux distributions currently configure
> cgroupsv1 by default. Yet controllers can be grouped arbitrarily.
> For instance, using the  systemd directive.
> One use case for that is to let Kubernetes' kubelet discover his own
> dedicated and reserved cgroup hierarchy. In that situation, the JVM
> fails to discover the expected cgroup controllers set, and, when
> running
> containerized, default to a suboptimal understanding of available
> resources.
> 
> Supporting arbitrarily controllers groups per mountpoint actually
> allows for simpler and easier to follow code, as we don't need nested
> if/else for every controller.
> 
> This fix also updates the Containers Metrics, to support joint
> controllers.
> 
> 
> Bob.