nixos/ksm: add option sleep

nixos/modules/hardware/ksm.nix

@@ -1,9 +1,24 @@
 { config, lib, ... }:
 
-{
+with lib;
-  options.hardware.enableKSM = lib.mkEnableOption "Kernel Same-Page Merging";
 
-  config = lib.mkIf config.hardware.enableKSM {
+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" ];
@@ -11,6 +26,7 @@
       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
       '';
     };

nixos/modules/rename.nix

@@ -241,6 +241,9 @@ with lib;
     # binfmt
     (mkRenamedOptionModule [ "boot" "binfmtMiscRegistrations" ] [ "boot" "binfmt" "registrations" ])
 
+    # KSM
+    (mkRenamedOptionModule [ "hardware" "enableKSM" ] [ "hardware" "ksm" "enable" ])
+
   ] ++ (flip map [ "blackboxExporter" "collectdExporter" "fritzboxExporter"
                    "jsonExporter" "minioExporter" "nginxExporter" "nodeExporter"
                    "snmpExporter" "unifiExporter" "varnishExporter" ]