Fix resource detection for unset CPU and memory limits in cgroup v2

[mobratil]

Address the issue where /sys/fs/cgroup/cpu.max and /sys/fs/cgroup/memory.max report "max", indicating unset limits in cgroup v2.

Changes Made:

• When /sys/fs/cgroup/cpu.max reads "max", the number of CPU cores is now derived from the host's /proc/stat file.
• Similarly, available memory is determined from the host's /proc/meminfo file if /sys/fs/cgroup/memory.max contains "max".

Microsoft Reviewers: Open in CodeFlow

[gitmln]

Unfortunately, this pull request does not fix either of the two issues.

1. CPU limits
   LinuxUtilizationProvider can't handle 'max' in /sys/fs/cgroup/memory.max #5241
   Could not parse '/sys/fs/cgroup/cpu.max'. Expected an integer but got: 'max 100000'.
   if (quotaBuffer.Equals("max", StringComparison.InvariantCulture))
   quotaBuffer in the above case contains "max 100000", not "max" string,
2. Memory limits
   This one is more tricky.
   System.InvalidOperationException : Could not parse '/sys/fs/cgroup/memory.max' content. Expected to find available memory in bytes but got 'max ' instead #5161
   Could not parse '/sys/fs/cgroup/memory.max' content. Expected to find available memory in bytes but got 'max
   ' instead.
   if (memoryBuffer.Equals("max", StringComparison.InvariantCulture))
   Again, you are comparing the wrong strings. The correct one is "max\n" (note the new line at the end!).

[mobratil]

@gitmln thanks for pointing that out. The PR was just a draft because i didn't have a real installation of Linux with cgroup v2 on which I could test it.
Now I finally tested the PR with proper modifications.

[RussKie]

@gitmln how does the current implementation look to you?

[gitmln]

@RussKie It looks perfect to me. This is the code that I've already thought about and tested successfully using a generic web app with mcr.microsoft.com/dotnet/runtime-deps:8.0 image on my AKS cluster.

[mobratil]

@gitmln thanks for checking. Do not hesitate to create a PR next time 😊

[RussKie]

Thank you @mobratil