RFR: 8230305: Cgroups v2: Container awareness

[Severin Gehwolf]

Hi,

Please review this update to the container detection code which adds
cgroup version 2 support. Initial review of this started in [1]. Bob
preferred one big patch and didn't like the other refactoring in
os_linux so this has been dropped.

This new patch includes both, the refactoring to move cgroup v1
specific implementation out of osContainer_linux.{h,c}pp files[2] as
well as updated detection code and the implementation for cgroups
v2[3]. After this patch, osContainer_linux{h,c}pp files are cgroups
version agnostic. Implementations for specific versions are in
cgroupV{1,2}Subsystem.{c,h}pp files. Some shared, cgroup version
agnostic code is in cgroupSubsystem.{c,h}pp.

Updated detection logic looks in /proc/cgroups first for hierarchy ids
of cpu/cpuset/cpuacct/memory controllers. If the hierarchy id for all
of them is 0 and they're all enabled, cgroups v2, unified hierarchy is
assumed. Otherwise it uses cgroups v1 controllers (also known as hybrid
or legacy hierarchy). Note that controllers can be only be mounted via
one or the other hierarchy, legacy (v1) or unified (v2) - exclusive[4].

Note that for the cgroups v2 cpu_shares() implementation a reverse
mapping is needed for the plain value exposed via cpu.weight.
Additionally, there doesn't seem to be an API exposed to use for an
implementation of memory_max_usage_in_bytes() in cgroups v2. Hence, it
returns OSCONTAINER_ERROR which is mapped to "not supported" elsewhere
in hotspot code.

Once reviewed, I intend to push this in two changesets/bugs. One for
the refactoring work (no-op) as JDK-8230848. Another for the cgroupv2
impl with JDK-8230305.

Bug: https://bugs.openjdk.java.net/browse/JDK-8230305
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/cgroupsv2-hotspot/02/webrev/

Testing: tier1 tests on Linux x86_64. Docker/podman hotspot tests on
F30 with hybrid cgroup v1 hierarchy. Hotspot container tests on F31
with unified hierarchy on Linux x86_64. jdk/submit. All pass.

Thoughts?

Thanks,
Severin

[1] http://mail.openjdk.java.net/pipermail/hotspot-dev/2019-September/039605.html
    http://mail.openjdk.java.net/pipermail/hotspot-dev/2019-October/039708.html
[2] http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8230848/04/webrev/
[3] http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8230305/06/webrev/
[4] https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#mounting
    "All controllers which support v2 and are not bound to a v1 hierarchy are
    automatically bound to the v2 hierarchy and show up at the root.
    Controllers which are not in active use in the v2 hierarchy can be
    bound to other hierarchies."