epyc: nerf it

modules/nix-daemon.nix

@@ -1,6 +1,7 @@
 { lib
 , config
 , pkgs
+, inputs
 , ...
 }:
 
@@ -29,6 +30,17 @@ in
       { domain = "*"; item = "nofile"; type = "-"; value = "20480"; }
     ];
 
+    # Memory accounting techniques
+    systemd.services.nix-daemon.serviceConfig = {
+      MemoryAccounting = true;
+      MemoryMax = "225G";
+      MemoryHigh = "220G";
+      MemorySwapMax = "2G";
+      ManagedOOMSwap = "kill";
+      ManagedOOMMemoryPressure = "kill";
+      MemoryPressureWatch = "on";
+    };
+
     nix = {
       # Garbage-collect often
       gc.automatic = true;
@@ -38,23 +50,21 @@ in
       # Randomize GC to avoid thundering herd effects.
       gc.randomizedDelaySec = "1800";
 
-      # 2.11, 2.12 suffers from a bug with remote builders…
-      package = pkgs.nixVersions.nix_2_13;
+      # Inchallah, it works.
+      # package = lib.mkForce inputs.nixpkgs-unstable.legacyPackages.x86_64-linux.nixVersions.nix_2_17;
 
       # should be enough?
       nrBuildUsers = 128;
 
-      # https://github.com/NixOS/nix/issues/719
-      daemonCPUSchedPolicy = "batch";
-      daemonIOSchedClass = "best-effort";
-      daemonIOSchedPriority = 5;
-
       settings = {
         keep-outputs = true;
         keep-derivations = true;
-        max-jobs = 42; # 64 is too much, it will explode the RAM for now. Let's keep it serious.
-        # in zfs we trust
-        fsync-metadata = lib.boolToString (!config.boot.isContainer or config.fileSystems."/".fsType != "zfs");
+        use-cgroups = true;
+        http-connections = 0;
+        auto-allocate-uids = true;
+        cores = 64; # 128 is too much, it will explode the RAM for now. Let's keep it serious.
+        max-jobs = 2; # Do not build more than 2 derivations at once in the event, both of them are too big, yes this is stupid, fix it in Nix.
+        fsync-metadata = true;
         substituters = [
           "https://nix-community.cachix.org"
           "https://tum-dse.cachix.org"
@@ -64,6 +74,14 @@ in
           "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
           "tum-dse.cachix.org-1:v67rK18oLwgO0Z4b69l30SrV1yRtqxKpiHodG4YxhNM="
         ];
+        experimental-features = [
+          "auto-allocate-uids"
+          "ca-derivations"
+          "cgroups"
+          "discard-references"
+          "fetch-closure"
+          "impure-derivations"
+        ];
       };
     };