Support for soft RAM limit?

[pete-woods]

Hello 👋🏻

Are there any plans to support the soft RAM limit introduced in Go 1.19?

(Either in this library or a new one)

[rabbbit]

Hey,

Just acknowledging here that we saw the question. We're discussing this, but we don't have an exact plan yet.

[StevenACoffman]

This is appears to be a quick attempt at doing that: https://github.com/KimMachineGun/automemlimit
it used containerd under the hood, but I've not tried using it under various container runtimes, non-Linux OSes like darwin, etc.

[StevenACoffman]

GOMAXPROCS and GOMEMLIMIT are environmental values that can help the application's Go Runtime to perform better.

In Kubernetes manifests, we could easily (and naively) set GOMEMLIMIT to be equal to the container limit like this:

apiVersion: v1
kind: Pod
metadata:
  name: go-k8s-memory
spec:
  containers:
  - name: go-k8s-memory
    image: ko://go-k8s-memory
    ports:
    - containerPort: 8080
    resources:
      limits:
        memory: 64Mi        // <--- limit on container memory
        cpu: "1"
      requests:
        memory: 62Mi
        cpu: "0.2"
    env:
    - name: GOMEMLIMIT
      valueFrom:            // <--- value taken from downwards API
        resourceFieldRef:
          resource: limits.memory

However, the Go documentation has this note:

In this case, a good rule of thumb is to leave an additional 5-10% of headroom to account for memory sources the Go runtime is unaware of.

Examples of these sources might include:

• OS kernel memory held on behalf of the process
• memory allocated by C code
• memory mapped by syscall.Mmap

As a result, it would be best if we could correctly introspect the container's memory limit and set GOMEMLIMIT to 90-90% of the container's memory limit.

Also, I believe the Kubernetes API expects values to omit the B like in "62Mi" but GOMEMLIMIT expects "62MiB", and GOMEMLIMIT does not allow decimal values (GOMEMLIMIT="6.2MiB" will cause an error), so it's awkward without a library to smooth this over.

[StevenACoffman]

@rabbbit any update on your internal discussions?

[sywhang]

hey folks, we've internally developed a system that automatically detects and sets GOMEMLIMIT and decided to not put that code on automaxprocs. The main rationale behind that decision is because this library, as its name suggests, detects max "procs", not memlimit.

We could open-source the internal library we're using, but we have a requirement of having to run something for over some period of time before we can open source them because we don't want to open source something that hasn't been battle-tested internally : )

Hope that makes sense, and we may reconsider open sourcing the internal library we're using in the future, but this is what we've decided for now. I won't close this issue as it's something we may still consider in the future.

Thanks.

[KyleSanderson]

hey folks, we've internally developed a system that automatically detects and sets GOMEMLIMIT and decided to not put that code on automaxprocs. The main rationale behind that decision is because this library, as its name suggests, detects max "procs", not memlimit.

We could open-source the internal library we're using, but we have a requirement of having to run something for over some period of time before we can open source them because we don't want to open source something that hasn't been battle-tested internally : )

Hope that makes sense, and we may reconsider open sourcing the internal library we're using in the future, but this is what we've decided for now. I won't close this issue as it's something we may still consider in the future.

Thanks.

Happy Holidays (and anniversary) 😉 how did it go?