RFR: 8292984: Refactor internal container-related interfaces for clarity [v2]

[Casper Norrbin]

> Hi everyone,
> 
> The current memory-related code paths in Linux are unclear and convoluted, with responsibilities and data flow crossing between `os::Linux` and various container-related layers.
> 
> For example, consider the call sequence for `os::available_memory()`:
> 
> os::available_memory()
>         |
>         v
> os::Linux::available_memory()
>         |--------------------------------------------
>         v                                           v    
> OSContainer::memory_limit_in_bytes()       or return host physical memory
>         |
>         v
> CgroupSubsystem::memory_limit_in_bytes()
>         |--------------------------------------------
>         v                                           v
> return os::Linux::physical_memory()        or return cgroup v1/v2 limit
> 
> 
> This structure is difficult to follow. Calls move between `os::Linux` and container subsystems in a confusing manner. Ideally, each component should be responsible only for its relevant functionality:
> * `os::Linux` should focus solely on actual machine memory values.
> * `CgroupSubsystem` should focus exclusively on cgroup memory limits.
> * The selection of which value to use should occur at the `os` layer, based on whether the environment is containerized.
> 
> 
> A revised structure separates these responsibilities:
> 
> os::available_memory()
>         |--------------------------------------------
>         v                                           v
> OSContainer::memory_limit_in_bytes()       or os::Linux::available_memory()                       
>         |--------------------------------------------
>         v                                           v
> CgroupSubsystem::memory_limit_in_bytes()   os::Linux::physical_memory()
>         |
>         v
> return bounded cgroup v1/v2 limit
> 
> 
> With these changes:
> * `os::Linux` only retrieves machine values.
> * `CgroupSubsystem` works exclusively with cgroup limits.
> * `OSContainer` fetches and passes bounds for the cgroup values.
> * The decision of container or machine value is done in the `os` layer.
> 
> The concrete code changes include:
> * Moving container selection logic from `os::Linux::{available/free}_memory()` to `os:{available/free}_memory()`, so `os::Linux` now only deals with machine values (was already the case for `os::physical_memory()`).
> * Moving `os::Linux::available_memory_in_container()` to `OSContainer` instead, removing container-specific logic from `os::Linux`. Also refactored to use the new bool and reference interface introduced in [JDK-8357086](https://bugs.openjdk...

Casper Norrbin has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'master' into linux-container-mem-restructure
 - keep cgroupsubsystem separate
 - keep os::linux separate

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

Changes: https://git.openjdk.org/jdk/pull/27470/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27470&range=01
  Stats: 135 lines in 9 files changed: 32 ins; 27 del; 76 mod
  Patch: https://git.openjdk.org/jdk/pull/27470.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27470/head:pull/27470

PR: https://git.openjdk.org/jdk/pull/27470