cleanup

services/minecraft.nix

@@ -21,6 +21,19 @@
     ])
   ];
 
+  boot.kernel.sysctl = {
+    # Disable autogroup for better scheduling of game server threads
+    "kernel.sched_autogroup_enabled" = 0;
+
+    # We want to determine the number of hugepages based on how many minecraft needs.
+    # This can be determined by dividing the heap size by the size of a large page.
+    # Doing this gives us how many large pages are needed.
+    # Then we add 300 to give some headroom.
+    "vm.nr_hugepages" =
+      (service_configs.minecraft.memory.heap_size_m / service_configs.minecraft.memory.large_page_size_m)
+      + 300;
+  };
+
   services.minecraft-servers = {
     enable = true;
     eula = true;
@@ -31,42 +44,38 @@
       enable = true;
       package = pkgs.fabricServers.fabric-1_21_11;
 
-      jvmOpts =
-        let
-          heap_size = "4000M";
-        in
-        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"
-        ];
+      jvmOpts = lib.concatStringsSep " " [
+        # Memory
+        "-Xmx${builtins.toString service_configs.minecraft.memory.heap_size_m}M"
+        "-Xms${builtins.toString service_configs.minecraft.memory.heap_size_m}M"
+        # 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=${builtins.toString service_configs.minecraft.memory.large_page_size_m}M"
+      ];
 
       serverProperties = {
         server-port = service_configs.ports.minecraft;

services/wg.nix

@@ -17,4 +17,36 @@
       # "192.168.0.0/24"
     ];
   };
+
+  boot = {
+    # BBR congestion control handles variable-latency VPN connections much
+    # better than CUBIC by probing bandwidth continuously rather than
+    # reacting to packet loss.
+    kernelModules = [ "tcp_bbr" ];
+
+    kernel.sysctl = {
+      # Use BBR + fair queuing for smooth throughput through the WireGuard VPN
+      "net.core.default_qdisc" = "fq";
+      "net.ipv4.tcp_congestion_control" = "bbr";
+
+      # Disable slow-start after idle: prevents TCP from resetting window
+      # size on each burst cycle (the primary cause of the 0 -> 40 MB/s spikes)
+      "net.ipv4.tcp_slow_start_after_idle" = 0;
+
+      # Larger socket buffers to accommodate the VPN bandwidth-delay product
+      # (22ms RTT * target throughput). Current 2.5MB max is too small.
+      "net.core.rmem_max" = 16777216;
+      "net.core.wmem_max" = 16777216;
+      "net.ipv4.tcp_rmem" = "4096 87380 16777216";
+      "net.ipv4.tcp_wmem" = "4096 65536 16777216";
+
+      # Higher backlog for the large number of concurrent torrent connections
+      "net.core.netdev_max_backlog" = 5000;
+      # Faster cleanup of dead connections from torrent peer churn
+      "net.ipv4.tcp_fin_timeout" = 15; # default 60
+      "net.ipv4.tcp_tw_reuse" = 1;
+    };
+  };
+
+  networking.firewall.trustedInterfaces = [ "wg-br" ];
 }