hydra: fix the hydra

hosts/hydra/hydra.nix

@@ -1,4 +1,4 @@
-{ hostRegistry, config, pkgs, ... }:
+{ hostRegistry, config, lib, pkgs, ... }:
 
 let
   nix-build = "client@${config.c3d2.hosts.nix-build.ip4}";
@@ -10,26 +10,13 @@ in {
     trustedUsers = [ "hydra" "root" ];
     buildMachines = [ {
       hostName = "localhost";
-      system = "x86_64-linux";
+      system = lib.concatStringsSep "," (
+        [ pkgs.system "i686-linux" ] ++
+        config.boot.binfmt.emulatedSystems
+      );
       supportedFeatures = [ "big-parallel" "benchmark" "kvm" "nixos-test" ];
       maxJobs = 4;
-    } {
-      hostName = nix-build;
-      system = "x86_64-linux";
-      supportedFeatures = [ "kvm" "nixos-test" "big-parallel" "benchmark" ];
-      maxJobs = 4;
-    } {
-      hostName = nix-build;
-      system = "aarch64-linux";
-      supportedFeatures = [ "nixos-test" "big-parallel" "benchmark" ];
-      maxJobs = 4;
-    } ] ++
-    map (system: {
-      hostName = "localhost";
-      inherit system;
-      supportedFeatures = [ "nixos-test" "big-parallel" "benchmark" ];
-      maxJobs = 4;
-    }) config.boot.binfmt.emulatedSystems;
+    } ];
 
     daemonCPUSchedPolicy = "idle";
     daemonIOSchedClass = "idle";
@@ -55,6 +42,12 @@ in {
       max_output_size = 4294967296
     '';
   };
+  systemd.services.hydra-evaluator.serviceConfig = {
+    MemoryAccounting = true;
+    MemoryHigh = "32G";
+    MemoryMax = "40G";
+    MemorySwapMax = "8G";
+  };
 
   services.nginx =
     let