modules/hugepages: init

flake.nix

@@ -309,6 +309,7 @@
       bluemap = ./modules/bluemap.nix;
       drumknotty = ./modules/drumknotty;
       gickup = ./modules/gickup;
+      hugepages = ./modules/hugepages.nix;
       matrix-ooye = ./modules/matrix-ooye.nix;
       python-http-handlers = ./modules/python-http-handlers.nix;
       robots-txt = ./modules/robots-txt.nix;

modules/hugepages.nix

@@ -0,0 +1,38 @@
+{ config, lib, ... }:
+let
+  cfg = config.boot.kernel.hugepages;
+in
+{
+  options.boot.kernel.hugepages = {
+    size = lib.mkOption {
+      type = lib.types.enum [ 2 1024 ];
+      default = 2;
+      description = ''
+        Hugepage size in MB.
+
+        You can use this value to calculate the amount of memory you will have available as hugepages.
+      '';
+    };
+
+    reservations = lib.mkOption {
+      type = lib.types.attrsOf lib.types.ints.unsigned;
+      default = { };
+      description = ''
+        Number of hugepages each service wants reserved in vm.nr_hugepages,
+        keyed by service name.
+      '';
+    };
+  };
+
+  config = {
+    boot.kernelParams = let
+      num = {
+        "2" = "2M";
+        "1024" = "1G";
+      }.${toString cfg.size};
+    in [ "hugepagesz=${num}" ];
+
+    boot.kernel.sysctl."vm.nr_hugepages" =
+      lib.foldl' (a: b: a + b) 0 (lib.attrValues cfg.reservations);
+  };
+}