modules/builder: gc by percent used

hosts/build01/default.nix

@@ -7,8 +7,6 @@
     inputs.self.nixosModules.community-builder
   ];
 
-  nixCommunity.gc.gbFree = 500;
-
   # Emulate riscv64 until we have proper builders
   boot.binfmt.emulatedSystems = [ "riscv64-linux" ];
 

hosts/build02/default.nix

@@ -13,8 +13,6 @@
   # set in srvos, remove when reinstalling
   networking.hostId = "deadbeef";
 
-  nixCommunity.gc.gbFree = 500;
-
   boot.kernelParams = [ "zfs.zfs_arc_max=${toString (24 * 1024 * 1024 * 1024)}" ]; # 24GB, try to limit OOM kills / reboots
 
   networking.nameservers = [

hosts/build03/default.nix

@@ -16,8 +16,6 @@
     ./postgresql.nix
   ];
 
-  nixCommunity.gc.gbFree = 500;
-
   systemd.network.networks."10-uplink".networkConfig.Address = "2a01:4f8:2190:2698::2";
 
   system.stateVersion = "23.11";

modules/darwin/builder.nix

@@ -1,10 +1,23 @@
 {
-  imports = [ ../shared/builder.nix ];
+  config,
+  inputs,
+  pkgs,
+  ...
+}:
+{
+  nix.gc.automatic = false;
+
+  launchd.daemons.free-space = {
+    serviceConfig = {
+      StartCalendarInterval = [ { Minute = 15; } ];
+    };
+    path = [
+      config.nix.package
+      pkgs.coreutils
+    ];
+    script = import "${inputs.self}/modules/shared/free-space.nix";
+  };
 
   # https://github.com/LnL7/nix-darwin/blob/230a197063de9287128e2c68a7a4b0cd7d0b50a7/modules/nix/default.nix#L201
   nix.daemonProcessType = "Interactive";
-
-  nix.gc.interval = {
-    Minute = 15;
-  };
 }

modules/nixos/builder.nix

@@ -1,7 +1,21 @@
 {
-  imports = [ ../shared/builder.nix ];
+  config,
+  inputs,
+  pkgs,
+  ...
+}:
+{
+  nix.gc.automatic = false;
 
-  nix.gc.dates = "hourly";
+  systemd.services.free-space = {
+    serviceConfig.Type = "oneshot";
+    startAt = "hourly";
+    path = [
+      config.nix.package
+      pkgs.coreutils
+    ];
+    script = import "${inputs.self}/modules/shared/free-space.nix";
+  };
 
   # Bump the open files limit so that non-root users can run NixOS VM tests
   security.pam.loginLimits = [

modules/shared/builder.nix

@@ -1,17 +0,0 @@
-{
-  config,
-  lib,
-  pkgs,
-  ...
-}:
-{
-  options.nixCommunity.gc.gbFree = lib.mkOption {
-    type = lib.types.int;
-    default = 150;
-    description = "Amount of free space in GB to keep on disk.";
-  };
-
-  config.nix.gc.options = ''
-    --max-freed "$((${toString config.nixCommunity.gc.gbFree} * 1024**3 - 1024 * $(df -P -k /nix/store | tail -n 1 | ${pkgs.gawk}/bin/awk '{ print $4 }')))"
-  '';
-}

modules/shared/free-space.nix

@@ -0,0 +1,12 @@
+# https://git.lix.systems/the-distro/infra/commit/15a684c5d7e1ee25cdd6f2941ed17c01aa107781
+''
+  nix-env --delete-generations 1d --profile /nix/var/nix/profiles/system
+  while : ; do
+    used=$(($(stat -f --format="100-(100*%a/%b)" /)))
+    if [[ $used -gt "85" ]]; then
+      nix-store --gc --max-freed 100G
+    else
+      break
+    fi
+  done
+''

modules/shared/nix-daemon.nix

@@ -12,14 +12,14 @@ in
     settings.substituters = [ "https://nix-community.cachix.org" ];
 
     # auto-free the /nix/store
-    settings.min-free = asGB 10;
+    settings.min-free = asGB 1;
     settings.max-free = asGB 50;
 
     # useful for ad-hoc nix-shell's for debugging
     # use mkForce to avoid search path warnings with nix-darwin
     nixPath = pkgs.lib.mkForce [ "nixpkgs=${pkgs.path}" ];
 
-    gc.automatic = true;
+    gc.automatic = pkgs.lib.mkDefault true;
     gc.options = pkgs.lib.mkDefault "--delete-older-than 14d";
   };
 }