RAM, disk. Functions are often written in high level JITd languages, they may need to load large reference datasets from disk, they may require a lot of code to be transferred over the network before they can begin running, and because nobody trusts the security of the Linux kernel you also have to pay the VM startup time.
An idle process on Linux isn't much different: it consumes RAM, disk and a kernel. If you trust the software you're running enough you can amortize the kernel cost but the others remain.
An idle process on Linux isn't much different: it consumes RAM, disk and a kernel. If you trust the software you're running enough you can amortize the kernel cost but the others remain.