You can now set 'evaluator_max_heap_size' to make hydra-eval-jobs
restart itself if the Boehm heap exceeds the specified size.
For example, with 'evaluator_max_heap_size = 256000000',
$ hydra-eval-jobs '<nixpkgs/pkgs/top-level/release.nix>' -I nixpkgs=channel:nixos-17.09
has a max RSS of .56 GiB rather than 4.7 GiB.
Unfortunately it doesn't help much for the NixOS jobsets because of
the "tested" job which requires a huge amount of memory all by itself.
0882519b10