This came up in D79183:

nika mentioned that the POSIX version should be able to stack-allocate the buffers when calling recvmsg, instead of needing per-channel allocations, because they're written only during that system call and the contents don't need to be preserved across calls. (This is not the case on Windows — the buffers are written to asynchronously and then userspace is notified, so they need to be per-channel.) So this will work, but you could also save another 5k per channel endpoint on Linux/Mac.

Clearing assignee because Kashav is no longer at Mozilla.