From 5658505b8631d28a09fc1f75481397c192e6f0eb Mon Sep 17 00:00:00 2001
From: aszlig <aszlig@nix.build>
Date: Mon, 16 Jul 2018 02:22:21 +0200
Subject: Add module for zswap

Even though these options are rather opinionated rather than generally
useful, it makes sense to have an option for that because I'm going to
use it for my managed machines as well.

Signed-off-by: aszlig <aszlig@nix.build>
---
 modules/system/kernel/zswap.nix | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 modules/system/kernel/zswap.nix

(limited to 'modules/system')

diff --git a/modules/system/kernel/zswap.nix b/modules/system/kernel/zswap.nix
new file mode 100644
index 00000000..43b89ca6
--- /dev/null
+++ b/modules/system/kernel/zswap.nix
@@ -0,0 +1,38 @@
+{ config, lib, ... }:
+
+let
+  kernelVersion = config.boot.kernelPackages.kernel.version;
+  hasZstd = lib.versionAtLeast kernelVersion "4.18";
+in {
+  options.vuizvui.system.kernel.zswap.enable = lib.mkOption {
+    type = lib.types.bool;
+    default = false;
+    description = ''
+      Whether to enable support for zswap with the use of the
+      <literal>z3fold</literal> for pooling and <literal>zstd</literal> for
+      compression, if available (otherwise it falls back to
+      <literal>lzo</literal>).
+
+      Zswap is a compressed cache for swap pages, which is especially useful
+      for machines with limited RAM.
+    '';
+  };
+
+  config = lib.mkIf config.vuizvui.system.kernel.zswap.enable {
+    boot.kernelPatches = lib.singleton {
+      name = "zswap-config";
+      patch = null;
+      extraConfig = ''
+        CRYPTO_${if hasZstd then "ZSTD" else "LZO"} y
+        ZSWAP y
+        Z3FOLD y
+      '';
+    };
+
+    boot.kernelParams = [
+      "zswap.enabled=1"
+      "zswap.zpool=z3fold"
+      "zswap.compressor=${if hasZstd then "zstd" else "lzo"}"
+    ];
+  };
+}
-- 
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