not sure but on the 64M duo (the only one I have so far…) the memory is shared and the amount can be adjusted like was done with some (most) of the distros like ARCH. the info is HERE somewhere, maybe try this post 【Arch Linux On Milkv-duo】Milkv-duo 运行 Arch Linux 系统 - #17 by Judehahh
PS have a duo 256 on the way, will try your nix on it for sure, when it get here that is…