From 7baba7111bffbf3dafc41c66d7cc138526294f53 Mon Sep 17 00:00:00 2001
From: Seth Flynn <getchoo@tuta.io>
Date: Thu, 6 Feb 2025 21:01:11 -0500
Subject: modules: better tune `nix.gc` settings

---
 modules/nixos/profiles/server.nix | 14 +++++++++++---
 modules/shared/defaults/nix.nix   |  2 +-
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/modules/nixos/profiles/server.nix b/modules/nixos/profiles/server.nix
index a4eae44..fe369ef 100644
--- a/modules/nixos/profiles/server.nix
+++ b/modules/nixos/profiles/server.nix
@@ -6,6 +6,11 @@
 }:
 let
   cfg = config.profiles.server;
+
+  # 2^30
+  # Why doesn't nix have a `pow`???
+  gb = 1024 * 1024 * 1024;
+  minimumStorageKb = 15 * gb;
 in
 {
   options.profiles.server = {
@@ -35,9 +40,12 @@ in
         };
 
         nix.gc = {
-          # Every ~2 days
-          dates = "Mon,Wed,Fri *-*-* 00:00:00";
-          options = "-d --delete-older-than 2d";
+          dates = "*:0/30"; # Every 30 minutes
+          # GC to stay above minimumStorageBytes
+          options = toString [
+            "--delete-older-than 5d"
+            "--max-freed \"$((${toString minimumStorageKb} - 1024 * $(df -k --output=avail /nix/store | tail -n 1)))\""
+          ];
         };
 
         traits = {
diff --git a/modules/shared/defaults/nix.nix b/modules/shared/defaults/nix.nix
index 23becf9..6cc896d 100644
--- a/modules/shared/defaults/nix.nix
+++ b/modules/shared/defaults/nix.nix
@@ -35,7 +35,7 @@ in
 
         gc = {
           automatic = lib.mkDefault true;
-          options = lib.mkDefault "--delete-older-than 2d";
+          options = lib.mkDefault "--delete-older-than 5d";
         };
 
         registry = lib.mapAttrs (lib.const (
-- 
cgit v1.2.3