From ed0a29c88dfe32f3121474ce5cad7df02e28c2cc Mon Sep 17 00:00:00 2001
From: rnhmjoj <rnhmjoj@inventati.org>
Date: Fri, 26 Feb 2021 13:06:18 +0100
Subject: [PATCH 1/2] nixos/test/ksm: add simple test

---
 nixos/tests/all-tests.nix |  1 +
 nixos/tests/ksm.nix       | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 nixos/tests/ksm.nix

diff --git a/nixos/tests/all-tests.nix b/nixos/tests/all-tests.nix
index bf094dbe984..625eb54403d 100644
--- a/nixos/tests/all-tests.nix
+++ b/nixos/tests/all-tests.nix
@@ -195,6 +195,7 @@ in
   keymap = handleTest ./keymap.nix {};
   knot = handleTest ./knot.nix {};
   krb5 = discoverTests (import ./krb5 {});
+  ksm = handleTest ./ksm.nix {};
   kubernetes.dns = handleTestOn ["x86_64-linux"] ./kubernetes/dns.nix {};
   # kubernetes.e2e should eventually replace kubernetes.rbac when it works
   #kubernetes.e2e = handleTestOn ["x86_64-linux"] ./kubernetes/e2e.nix {};
diff --git a/nixos/tests/ksm.nix b/nixos/tests/ksm.nix
new file mode 100644
index 00000000000..8feccbe6df5
--- /dev/null
+++ b/nixos/tests/ksm.nix
@@ -0,0 +1,22 @@
+import ./make-test-python.nix ({ pkgs, ...} :
+
+{
+  name = "ksm";
+  meta = with pkgs.lib.maintainers; {
+    maintainers = [ rnhmjoj ];
+  };
+
+  machine = { ... }: {
+    imports = [ ../modules/profiles/minimal.nix ];
+
+    hardware.ksm.enable = true;
+    hardware.ksm.sleep = 300;
+  };
+
+  testScript =
+    ''
+      machine.start()
+      machine.wait_until_succeeds("test $(</sys/kernel/mm/ksm/run) -eq 1")
+      machine.wait_until_succeeds("test $(</sys/kernel/mm/ksm/sleep_millisecs) -eq 300")
+    '';
+})

From 48052ca0dd1939beed30dc8c65f541cfa05704fa Mon Sep 17 00:00:00 2001
From: rnhmjoj <rnhmjoj@inventati.org>
Date: Fri, 26 Feb 2021 21:37:33 +0100
Subject: [PATCH 2/2] nixos/ksm: remove udev-settle dependency

The sysfs file /sys/kernel/mm/ksm/run seems to be available as soon as
the kernel has started, so no point in waiting for udev to "settle". If
for some reason it doesn't, we let the unit fail explicitly.
---
 nixos/modules/hardware/ksm.nix | 12 ++++++------
 nixos/tests/ksm.nix            |  4 ++--
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/nixos/modules/hardware/ksm.nix b/nixos/modules/hardware/ksm.nix
index 0938dbdc110..829c3532c45 100644
--- a/nixos/modules/hardware/ksm.nix
+++ b/nixos/modules/hardware/ksm.nix
@@ -26,13 +26,13 @@ in {
     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
+      script =
+        ''
           echo 1 > /sys/kernel/mm/ksm/run
-          ${optionalString (cfg.sleep != null) ''echo ${toString cfg.sleep} > /sys/kernel/mm/ksm/sleep_millisecs''}
-        fi
-      '';
+        '' + optionalString (cfg.sleep != null)
+        ''
+          echo ${toString cfg.sleep} > /sys/kernel/mm/ksm/sleep_millisecs
+        '';
     };
   };
 }
diff --git a/nixos/tests/ksm.nix b/nixos/tests/ksm.nix
index 8feccbe6df5..8f84b32020a 100644
--- a/nixos/tests/ksm.nix
+++ b/nixos/tests/ksm.nix
@@ -1,8 +1,8 @@
-import ./make-test-python.nix ({ pkgs, ...} :
+import ./make-test-python.nix ({ lib, ...} :
 
 {
   name = "ksm";
-  meta = with pkgs.lib.maintainers; {
+  meta = with lib.maintainers; {
     maintainers = [ rnhmjoj ];
   };