Why are the docs suggesting --ulimit memlock=-1:-1 for running docker image?

[karfau]

As far as I understand this tells the docker runtime to not limit the memory consumption of the container, right?
I would assume that this is not recommended in settings like kubernetes, where multiple containers run on the same node.

I tried to find any related issue, pull request or discussion, but couldn't find anything.

Why is this recommended in the docs and what would be the impact of not setting this?

[KeepALifeUS]

Why --ulimit memlock=-1:-1 for Bun Docker

This flag is about memory locking (mlock), not total memory consumption.

What it does

• memlock = max locked-in-memory address space
• -1:-1 = unlimited soft and hard limits
• This allows Bun to lock memory pages, preventing them from being swapped to disk

Why Bun needs it

Bun uses memory-mapped files and locked memory for:

1. JavaScriptCore JIT - JIT-compiled code needs locked pages
2. Fast file I/O - mmap for reading files
3. SQLite - uses mlock for database pages

Impact of NOT setting it

Without this flag, you may see:

• Slower performance (pages get swapped)
• Potential crashes if mlock fails
• Warning: failed to lock memory

For Kubernetes

You can set resource limits separately:

resources:
  limits:
    memory: "512Mi"  # Total memory limit still works

The memlock ulimit only affects how much can be locked, not total consumption. Its safe to use with K8s resource limits.

Alternative: Set a specific limit

docker run --ulimit memlock=67108864:67108864 bun-app
# 64MB locked memory limit

This is safer than unlimited if you have many containers.

[karfau]

Thx for the elaborate reply.
Do you think it makes sense to provide a short "note" about this in the docs directly?