config: control cgroup isolation

src/apprt/gtk/App.zig

@@ -44,6 +44,9 @@ config: Config,
 app: *c.GtkApplication,
 ctx: *c.GMainContext,
 
+/// True if the app was launched with single instance mode.
+single_instance: bool,
+
 /// The "none" cursor. We use one that is shared across the entire app.
 cursor_none: ?*c.GdkCursor,
 
@@ -269,6 +272,7 @@ pub fn init(core_app: *CoreApp, opts: Options) !App {
         .ctx = ctx,
         .cursor_none = cursor_none,
         .x11_xkb = x11_xkb,
+        .single_instance = single_instance,
         // If we are NOT the primary instance, then we never want to run.
         // This means that another instance of the GTK app is running and
         // our "activate" call above will open a window.
@@ -388,17 +392,25 @@ pub fn run(self: *App) !void {
     // If we are running, then we proceed to setup our app.
 
     // Setup our cgroup configurations for our surfaces.
-    if (cgroup.init(self)) |cgroup_path| {
-        self.transient_cgroup_base = cgroup_path;
-    } else |err| {
-        // If we can't initialize cgroups then that's okay. We
-        // want to continue to run so we just won't isolate surfaces.
-        // NOTE(mitchellh): do we want a config to force it?
-        log.warn(
-            "failed to initialize cgroups, terminals will not be isolated err={}",
-            .{err},
-        );
-    }
+    if (switch (self.config.@"linux-cgroup") {
+        .never => false,
+        .always => true,
+        .@"single-instance" => self.single_instance,
+    }) cgroup: {
+        const path = cgroup.init(self) catch |err| {
+            // If we can't initialize cgroups then that's okay. We
+            // want to continue to run so we just won't isolate surfaces.
+            // NOTE(mitchellh): do we want a config to force it?
+            log.warn(
+                "failed to initialize cgroups, terminals will not be isolated err={}",
+                .{err},
+            );
+            break :cgroup;
+        };
+
+        log.info("cgroup isolation enabled base={s}", .{path});
+        self.transient_cgroup_base = path;
+    } else log.debug("cgroup isoation disabled config={}", .{self.config.@"linux-cgroup"});
 
     // Setup our menu items
     self.initActions();

src/build/fish_completions.zig

@@ -12,7 +12,7 @@ pub const fish_completions = comptimeGenerateFishCompletions();
 
 fn comptimeGenerateFishCompletions() []const u8 {
     comptime {
-        @setEvalBranchQuota(13000);
+        @setEvalBranchQuota(15000);
         var counter = std.io.countingWriter(std.io.null_writer);
         try writeFishCompletions(&counter.writer());
 

src/config/Config.zig

@@ -988,6 +988,30 @@ keybind: Keybinds = .{},
 /// This does not work with GLFW builds.
 @"macos-option-as-alt": OptionAsAlt = .false,
 
+/// Put every surface (tab, split, window) into a dedicated Linux cgroup.
+///
+/// This makes it so that resource management can be done on a per-surface
+/// granularity. For example, if a shell program is using too much memory,
+/// only that shell will be killed by the oom monitor instead of the entire
+/// Ghostty process. Similarly, if a shell program is using too much CPU,
+/// only that surface will be CPU-throttled.
+///
+/// This will cause startup times to be slower (a hundred milliseconds or so),
+/// so the default value is "single-instance." In single-instance mode, only
+/// one instance of Ghostty is running (see gtk-single-instance) so the startup
+/// time is a one-time cost. Additionally, single instance Ghostty is much
+/// more likely to have many windows, tabs, etc. so cgroup isolation is a
+/// big benefit.
+///
+/// Valid values are:
+///
+///   * `never` - Never use cgroups.
+///   * `always` - Always use cgroups.
+///   * `single-instance` - Enable cgroups only for Ghostty instances launched
+///     as single-instance applications (see gtk-single-instance).
+///
+@"linux-cgroup": LinuxCgroup = .@"single-instance",
+
 /// If true, the Ghostty GTK application will run in single-instance mode:
 /// each new `ghostty` process launched will result in a new window if there
 /// is already a running process.
@@ -3495,3 +3519,10 @@ pub const GraphemeWidthMethod = enum {
     legacy,
     unicode,
 };
+
+/// See linux-cgroup
+pub const LinuxCgroup = enum {
+    never,
+    always,
+    @"single-instance",
+};