nixpkgs/nixos/modules/hardware/ksm.nix

{ config, lib, ... }:

with lib;

let
  cfg = config.hardware.ksm;

in {
  options.hardware.ksm = {
    enable = mkEnableOption "Kernel Same-Page Merging";
    sleep = mkOption {
      type = types.nullOr types.int;
      default = null;
      description = ''
        How many milliseconds ksmd should sleep between scans.
        Setting it to <literal>null</literal> uses the kernel's default time.
      '';
    };
  };

  config = mkIf cfg.enable {
    systemd.services.enable-ksm = {
      description = "Enable Kernel Same-Page Merging";
      wantedBy = [ "multi-user.target" ];
      after = [ "systemd-udev-settle.service" ];
      script = ''
        if [ -e /sys/kernel/mm/ksm ]; then
          echo 1 > /sys/kernel/mm/ksm/run
          ${optionalString (cfg.sleep != null) ''echo ${toString cfg.sleep} > /sys/kernel/mm/ksm/sleep_millisecs''}
        fi
      '';
    };
  };
}