[RFC] Backport cgroups v2 support to 11u?

[Thomas Stüfe]

I think this makes a lot of sense.

Cheers, Thomas

p.s. I had just glimpsed at Zhengyus backport PR for 8230305 and it does
not look too bad. But tool-wise, I wish we had an easy way to see where
backport patches were modified for the target release. That would make
reviews of unclean patches so much easier.


On Fri, Feb 25, 2022 at 11:15 AM Severin Gehwolf <sgehwolf at redhat.com>
wrote:

> Hi,
>
> We, Red Hat, think that getting cgroups v2 support backported to JDK
> 11u (and perhaps 8u) would be good at this point since systems which
> use cgroups v2 by default become more an more widely used. For example
> Red Hat Enterprise Linux 9[1] will have that turned on by default.
> Recent Fedora and Ubuntu distributions have it on by default.
> Similarly, container technology such as Docker and Kubernetes support
> cgroups v2 as well.
>
> The risk of NOT backporting those patches is that the JVM would wrongly
> detect resource limits. Even though, -XX:+UseContainerSupport is on by
> default in 11u, container detection code would just give up early and
> would use the host systems' resource limits instead. That gets us back
> to pre-JDK-8146115[2] behaviour of the JDK when running on such
> systems. I.e. random OOM kills and other strange behaviour. IMHO, that
> would be bad.
>
> Cgroups v2 support has been available in the JDK since version 15 and
> up and, I believe, most bugs have been shaken out in due course.
> Support code has been pretty stable over the last couple of major JDK
> releases. The code is Linux-only and is pretty self-contained. It is
> our belief that the risks of introducing those patches to 11u is
> manageable.
>
> We propose to backport the following patch-set from JDK 15+:
>
> Cgroups v2: Container awareness
> https://bugs.openjdk.java.net/browse/JDK-8230305
>
> Cgroups v2: Rework Metrics in java.base so as to recognize unified
> hierarchy
> https://bugs.openjdk.java.net/browse/JDK-8231111
>
> 8230305 causes slowdebug build failure
> https://bugs.openjdk.java.net/browse/JDK-8237479
>
> [cgroups v2] Soft memory limit incorrectly using memory.high
> https://bugs.openjdk.java.net/browse/JDK-8253714
>
> Cgroups: Incorrect detection logic on old systems in hotspot
> https://bugs.openjdk.java.net/browse/JDK-8239785
>
> Cgroups: Incorrect detection logic on some systems
> https://bugs.openjdk.java.net/browse/JDK-8239559
>
> jtreg test error in
> test/hotspot/jtreg/containers/docker/TestMemoryAwareness.java
> https://bugs.openjdk.java.net/browse/JDK-8244500
>
> containers/cgroup/PlainRead.java fails on Ubuntu 21.10
> https://bugs.openjdk.java.net/browse/JDK-8278951
>
> [cgroups v2] Account for the fact that swap accounting is disabled on some
> systems
> https://bugs.openjdk.java.net/browse/JDK-8253797
>
> Cgroups: Incorrect detection logic on some systems (still reproducible)
> https://bugs.openjdk.java.net/browse/JDK-8245543
>
> [Metrics] Enhance parsing of cgroup interface files for version detection
> https://bugs.openjdk.java.net/browse/JDK-8254001
>
> HotSpot Not Identifying it is Running in a Container
> https://bugs.openjdk.java.net/browse/JDK-8252359
>
> Cgroup: 'stomping of _mount_path' crash if manually mounted cpusets exist
> https://bugs.openjdk.java.net/browse/JDK-8253435
>
> [TESTBUG] Increase coverage of the cgroups detection code
> https://bugs.openjdk.java.net/browse/JDK-8253939
>
> Thoughts? What do other 11u maintainers think?
>
> Thanks,
> Severin
>
> [1] https://www.redhat.com/en/blog/whats-new-rhel-90-beta
> [2] https://bugs.openjdk.java.net/browse/JDK-8146115
>
>