From 2c0811cfe99725ff80717c4569201b7012be1012 Mon Sep 17 00:00:00 2001
From: Simon Gardling <titaniumtown@proton.me>
Date: Fri, 27 Feb 2026 00:04:07 -0500
Subject: [PATCH] minecraft: make more responsive

---
 configuration.nix      |  6 ++++++
 flake.nix              | 22 +++++++++++-----------
 services/minecraft.nix | 41 ++++++++++++++++++++++++++++++++++++++++-
 tests/minecraft.nix    |  4 ++++
 4 files changed, 61 insertions(+), 12 deletions(-)

diff --git a/configuration.nix b/configuration.nix
index aad090a..6212c0c 100644
--- a/configuration.nix
+++ b/configuration.nix
@@ -158,6 +158,12 @@
 
       # Higher backlog for the large number of concurrent torrent connections
       "net.core.netdev_max_backlog" = 5000;
+
+      # Minecraft server optimizations
+      # Disable autogroup for better scheduling of game server threads
+      "kernel.sched_autogroup_enabled" = 0;
+      # Huge pages for Minecraft JVM (4000MB heap / 2MB per page + ~200 overhead)
+      "vm.nr_hugepages" = 2200;
     };
   };
 
diff --git a/flake.nix b/flake.nix
index 5251504..2285cc2 100644
--- a/flake.nix
+++ b/flake.nix
@@ -326,16 +326,16 @@
       checks.${system} = testSuite;
 
       packages.${system} = {
-          tests = pkgs.linkFarm "all-tests" (
-            pkgs.lib.mapAttrsToList (name: test: {
-              name = name;
-              path = test;
-            }) testSuite
-          );
-        }
-        // (pkgs.lib.mapAttrs' (name: test: {
-          name = "test-${name}";
-          value = test;
-        }) testSuite);
+        tests = pkgs.linkFarm "all-tests" (
+          pkgs.lib.mapAttrsToList (name: test: {
+            name = name;
+            path = test;
+          }) testSuite
+        );
+      }
+      // (pkgs.lib.mapAttrs' (name: test: {
+        name = "test-${name}";
+        value = test;
+      }) testSuite);
     };
 }
diff --git a/services/minecraft.nix b/services/minecraft.nix
index 78eefa9..3b94e8c 100644
--- a/services/minecraft.nix
+++ b/services/minecraft.nix
@@ -35,7 +35,38 @@
         let
           heap_size = "4000M";
         in
-        "-Xmx${heap_size} -Xms${heap_size} -XX:+UseZGC -XX:+ZGenerational";
+        lib.concatStringsSep " " [
+          # Memory
+          "-Xmx${heap_size}"
+          "-Xms${heap_size}"
+          # GC
+          "-XX:+UseZGC"
+          "-XX:+ZGenerational"
+          # Base JVM optimizations (brucethemoose/Minecraft-Performance-Flags-Benchmarks)
+          "-XX:+UnlockExperimentalVMOptions"
+          "-XX:+UnlockDiagnosticVMOptions"
+          "-XX:+AlwaysActAsServerClassMachine"
+          "-XX:+AlwaysPreTouch"
+          "-XX:+DisableExplicitGC"
+          "-XX:+UseNUMA"
+          "-XX:+PerfDisableSharedMem"
+          "-XX:+UseFastUnorderedTimeStamps"
+          "-XX:+UseCriticalJavaThreadPriority"
+          "-XX:ThreadPriorityPolicy=1"
+          "-XX:AllocatePrefetchStyle=3"
+          "-XX:-DontCompileHugeMethods"
+          "-XX:MaxNodeLimit=240000"
+          "-XX:NodeLimitFudgeFactor=8000"
+          "-XX:ReservedCodeCacheSize=400M"
+          "-XX:NonNMethodCodeHeapSize=12M"
+          "-XX:ProfiledCodeHeapSize=194M"
+          "-XX:NonProfiledCodeHeapSize=194M"
+          "-XX:NmethodSweepActivity=1"
+          "-XX:+UseVectorCmov"
+          # Large pages (requires vm.nr_hugepages sysctl)
+          "-XX:+UseLargePages"
+          "-XX:LargePageSizeInBytes=2m"
+        ];
 
       serverProperties = {
         server-port = service_configs.ports.minecraft;
@@ -116,6 +147,14 @@
     };
   };
 
+  systemd.services.minecraft-server-main = {
+    serviceConfig = {
+      Nice = -5;
+      IOSchedulingPriority = 0;
+      LimitMEMLOCK = "infinity"; # Required for large pages
+    };
+  };
+
   services.caddy.virtualHosts = lib.mkIf (config.services.caddy.enable) {
     "map.${service_configs.https.domain}".extraConfig = ''
       root * ${service_configs.minecraft.parent_dir}/${service_configs.minecraft.server_name}/squaremap/web
diff --git a/tests/minecraft.nix b/tests/minecraft.nix
index b2e0956..7a27d21 100644
--- a/tests/minecraft.nix
+++ b/tests/minecraft.nix
@@ -60,6 +60,10 @@ testPkgs.testers.runNixOSTest {
         wants = lib.mkForce [ ];
         after = lib.mkForce [ ];
         requires = lib.mkForce [ ];
+        serviceConfig = {
+          Nice = lib.mkForce 0;
+          LimitMEMLOCK = lib.mkForce "infinity";
+        };
       };
 
       # Test-specific overrides only - reduce memory for testing