refactor into modules

nixos/modules/filesystems.nix

@@ -0,0 +1,27 @@
+{ ... }:
+
+{
+  fileSystems."/" = {
+    options = [ "subvol=@" "compress=zstd" "space_cache=v2" "noatime" "lazytime" "ssd" "discard=async" ];
+  };
+
+  fileSystems."/home" = {
+    options = [ "subvol=@home" "compress=zstd" "space_cache=v2" "noatime" "lazytime" "ssd" "discard=async" ];
+  };
+
+  fileSystems."/var/log" = {
+    options = [ "subvol=@log" "compress=zstd" "space_cache=v2" "noatime" "lazytime" "ssd" "discard=async" ];
+  };
+
+  fileSystems."/swap" = {
+    options = [ "subvol=@swap" "noatime" "ssd" "discard=async" ];
+  };
+
+  swapDevices = [{ device = "/swap/swapfile"; }];
+
+  boot.kernel.sysctl = {
+    "vm.dirty_ratio" = 10;
+    "vm.dirty_background_ratio" = 5;
+    "vm.swappiness" = 10;
+  };
+}