RFR: 8331560: Refactor Hotspot container detection code so that subsystem delegates to controllers [v2]

[Jan Kratochvil]

On Tue, 21 May 2024 18:51:31 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> Please review this preparatory PR which is an enabler for some bugfix/alignment work (e.g. [JDK-8322420](https://bugs.openjdk.org/browse/JDK-8322420)). The idea is to delegate limit lookup to controllers (`memory`, `cpu`, etc.) from the overarching `CgroupSubsystem` class. This way we can - once the cg type has been detected - "adjust" a controller's path to the limit files when the controller is being created (on init) and then left alone. In this case, the two preparatory entry points are `CgroupUtil::processor_count()` taking a version-agnostic `CgroupCpuController` to do the actual look-up and `CgroupMemoryController::read_memory_limit_in_bytes()` for the same in terms of memory limits.
>> 
>> This enables setting the contoller's path to the interface files (wherever it might be in the hierarchy of it's original cgroup path), look up the limit and "freeze" the path once it found a - lower - limit.
>> 
>> It also ensures that both cgroup versions return `-1` or `-2` (`OSCONTAINER_ERROR`) - in both cases negative - for some notion of unlimited. I.e. it makes the upper bound by the host's physical memory apparent in the version agnostic classes.
>> 
>> Testing:
>> - [x] GHA
>> - [x] gtest:cgroupTest tests
>> - [x] container tests on Linux cgv1 and cgv2 on x86_64
>> 
>> Thoughts?
>
> Severin Gehwolf has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:
> 
>  - More fix-ups after merge
>  - Fix limit_from_str usages
>  - Merge branch 'pr/19060' into jdk-8331560-cgroup-controller-delegation
>  - Fix whitespace
>  - Refactor cgroup controller code

src/hotspot/os/linux/cgroupSubsystem_linux.cpp line 70:

> 68:     CgroupV2CpuController* cpu = new CgroupV2CpuController(cg_infos[CPU_IDX]._mount_path, cg_infos[CPU_IDX]._cgroup_path);
> 69:     log_debug(os, container)("Detected cgroups v2 unified hierarchy");
> 70:     cleanup(cg_infos);

Could this be a dtor?

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/19085#discussion_r1610062047