builders: migrate tmpfs to new build-dir

Author: mweinelt

builders/common/system.nix

@@ -17,7 +17,4 @@
 
   # use memory more efficiently at the cost of some compute
   zramSwap.enable = true;
-
-  # enable huge pages for tmpfs on /tmp
-  boot.tmp.tmpfsHugeMemoryPages = "within_size";
 }

builders/profiles/hetzner-ax101r.nix

@@ -13,11 +13,23 @@
   boot.supportedFilesystems.zfs = true;
   networking.hostId = "91312b0a";
 
-  boot.tmp = {
-    useTmpfs = true;
-    # 128G tmpfs, 128G RAM for standard builders
-    # 160G tmpfs, 96G RAM for big parallel builders
-    tmpfsSize = if lib.elem "big-parallel" config.nix.settings.system-features then "160G" else "128G";
+  fileSystems."/nix/var/nix/builds" = {
+    device = "none";
+    fsType = "tmpfs";
+    options = [
+      "huge=within_size"
+      "mode=0700"
+      "nosuid"
+      "nodev"
+    ]
+    # 128G tmpfs, 128G RAM (+zram swap) for standard builders
+    # 160GB tmpfs, 96 GB RAM (+zram swap) for big-parallel builders
+    ++ (
+      if lib.elem "big-parallel" config.nix.settings.system-features then
+        [ "size=160G" ]
+      else
+        [ "size=128G" ]
+    );
   };
 
   boot.initrd.availableKernelModules = [