quitte: enable memory resource control

Limits the Memory of some important slices via systemd cgroup management.

- nix-daemon may not use more than 32 GB of Memory
- all users together may not use more than 32GB of Memory

See man systemd.resource-control(5) for more detailed information.

hosts/quitte/configuration.nix

@@ -33,6 +33,17 @@
   services.openssh.enable = true;
   services.openssh.settings.PermitRootLogin = "yes";
 
+  systemd = {
+    services.nix-daemon.serviceConfig = {
+      MemoryMax = "32G";
+    };
+    # all users together may not use more than $MemoryMax of RAM
+    slices."user".sliceConfig = {
+      MemoryMax = "32G";
+    };
+  };
+
+
   # Open ports in the firewall.
   networking.firewall.allowedTCPPorts = [ 443 80 ];
   # networking.firewall.allowedUDPPorts = [ ... ];