Help, I want to reinstall NixOS with btrfs subvolumes

[SherlockXia]

I just found a much better way of crrating swap.

https://discourse.nixos.org/t/how-to-add-a-swap-after-nixos-installation/41742

@lelgenio

I think the easiest thing for you to do now would be to create a swapfile:

{
  swapDevices = [{
    device = "/swapfile";
    size = 16 * 1024; # 16GB
  }];
}

Just switch configurations and it should be created automatically.

No need for partition or subvolume, it will just create a swap file under root at the top level.