builders: configure a swapfile + zswap

services/baremetal-builder/default.nix

@@ -51,6 +51,18 @@ in
       options = [ "fmask=0022" "dmask=0022" ];
     };
 
+    swapDevices = [
+      {
+        device = "/swapfile";
+        size = 50 * 1024;  # 50GiB
+      }
+    ];
+
+    zramSwap = {
+      enable = true;
+      memoryPercent = 25;
+    };
+
     boot.kernelParams = [
       "console=ttyS0,115200"
       "console=tty1"

services/hydra/default.nix

@@ -13,15 +13,15 @@ let
 
   # XXX: to support Nix's dumb public host key syntax (base64'd), this outputs
   # a string with shell-style command interpolations: $(...).
-  mkBaremetalBuilder = { nrCores, publicHostKey, host, speedFactor ? 1, user ? "builder", supportedSystems ? [ "i686-linux" "x86_64-linux" ], supportedFeatures ? [ "big-parallel" "kvm" "nixos-test" ] }:
-  "ssh://${user}@${host} ${lib.concatStringsSep "," supportedSystems} ${config.age.secrets.hydra-ssh-key-priv.path} ${toString nrCores} ${toString speedFactor} ${lib.concatStringsSep "," supportedFeatures} - $(echo -n '${publicHostKey}' | base64 -w0)";
+  mkBaremetalBuilder = { parallelBuilds, publicHostKey, host, speedFactor ? 1, user ? "builder", supportedSystems ? [ "i686-linux" "x86_64-linux" ], supportedFeatures ? [ "big-parallel" "kvm" "nixos-test" ] }:
+  "ssh://${user}@${host} ${lib.concatStringsSep "," supportedSystems} ${config.age.secrets.hydra-ssh-key-priv.path} ${toString parallelBuilds} ${toString speedFactor} ${lib.concatStringsSep "," supportedFeatures} - $(echo -n '${publicHostKey}' | base64 -w0)";
 
   # TODO:
   # - generalize to new architectures
   # - generalize to new features
   baremetalBuilders = lib.concatStringsSep "\n"
     (map (n: mkBaremetalBuilder {
-      nrCores = 40; # TODO: do not hardcode this, use the node's builder configuration.
+      parallelBuilds = 8; # TODO: do not hardcode this, use the node's builder configuration.
       publicHostKey = ssh-keys.machines.${n};
       host = nodes.${n}.config.networking.fqdn;
     }) cfg.builders);