nixos-config/lib/fudo/system.nix

{ pkgs, lib, config, ... }:

with lib;
let
  cfg = config.fudo.system;
in {
  options.fudo.system = {
    disableTransparentHugePages = mkOption {
      type = types.bool;
      description = ''
        Disable transparent huge pages (recommended for database loads, in
        particular for Redis.
      '';
      default = false;
    };

    postHugePageServices = mkOption {
      type = with types; listOf str;
      description = "List of systemd services that should wait until after THP are disabled.";
      default = [];
      example = ["redis.service"];
    };

    tmpOnTmpfs = mkOption {
      type = types.bool;
      description = "Put tmp filesystem on tmpfs (needs enough RAM).";
      default = true;
    };
  };

  config = mkIf cfg.disableTransparentHugePages {
    systemd.services.disableHugePages = {
      description = "Turn off Transparent Huge Pages (https://www.kernel.org/doc/Documentation/vm/transhuge.txt)";
      after = [ "sysinit.target" "localfs-target" ];
      before = cfg.postHugePageServices;
      enable = true;
      serviceConfig = {
        ExecStart = "/bin/sh -c 'echo never | tee /sys/kernel/mm/transparent_hugepage/enabled > /dev/null";
        Type = "oneshot";
      };
    };
  };
}