"Computing quotient graph" takes lots of memory

On a huge `/nix/store` (11 TB) with many, many GC roots, `nix-du` uses hundreds of GB of memory to compute the quotient graph and gets OOMed. Can you recommend any potentially low-hanging fruit for reducing its memory usage? If not possible, would it be possible to give `nix-du` a directory of GC roots to consider instead of considering all of them?