RFR: Container Fixes (8219652, 8217766, 8212528)

[Bob Vandette]

I will be committing each change individually but thought I’d save some time testing/reviewing.

Thanks,
Bob.


> On Mar 18, 2019, at 10:12 AM, Severin Gehwolf <sgehwolf at redhat.com> wrote:
> 
> 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.
>