diff --git a/src/mm/balance.zig b/src/mm/balance.zig
new file mode 100644
index 0000000..30ee25e
--- /dev/null
+++ b/src/mm/balance.zig
@@ -0,0 +1,71 @@
+//! Balance manager.
+//! The balance manager is called periodically (or when memory is low) to do
+//! the following actions:
+//! 1. Reap unused kernel stacks
+//! 2. Zone trimming
+//! 3. Working-set trimming (eventually...)
+
+const r = @import("root");
+const std = @import("std");
+const ps = r.ps;
+const ke = r.ke;
+const mm = r.mm;
+const mi = mm.private;
+
+const balance_interval = ke.Tunable(u32, 1000, "mm.balance.interval_ms");
+
+const stack_reap_interval = 5;
+const zone_update_interval = mm.zone.update_interval_s;
+
+var stack_reap_time: u8 = stack_reap_interval;
+var zone_update_time: u8 = zone_update_interval;
+
+pub fn init() void {
+    const td = ps.thread.create_kernel(.LowRealtime, .{
+        .func = balance_manager,
+        .arg = null,
+    }, true) catch
+        @panic("Could not create balance manager thread");
+
+    ke.sched.enqueue(&td.kern);
+}
+
+fn balance_manager(_: ?*anyopaque) void {
+    while (true) {
+        var timer: ke.Timer = undefined;
+        timer.init();
+        ke.timer.set(
+            &timer,
+            .from(r.Milliseconds.init(balance_interval.load())),
+            .{},
+        );
+
+        _ = ke.wait.wait_one(&timer.hdr, "balmgr", .{}) catch unreachable;
+
+        stack_reap_time -= 1;
+        zone_update_time -= 1;
+
+        if (zone_update_time == 0) {
+            zone_update_time = zone_update_interval;
+            mm.zone.update();
+        }
+
+        if (stack_reap_time == 0) {
+            stack_reap_time = stack_reap_interval;
+
+            if (ke.thread.stack_cache_update()) |lst| {
+                // Reap all the excess stacks.
+                var entry: ?*ke.Stack = lst;
+
+                while (entry != null) {
+                    const next = entry.?.next;
+                    mm.heap.free(
+                        (@intFromPtr(entry) + @sizeOf(ke.Stack)) - ps.thread.kernel_thread_stack_size,
+                        ps.thread.kernel_thread_stack_size,
+                    );
+                    entry = next;
+                }
+            }
+        }
+    }
+}
diff --git a/src/mm/init.zig b/src/mm/init.zig
index e9e94c3..b9a6695 100644
--- a/src/mm/init.zig
+++ b/src/mm/init.zig
@@ -14,4 +14,5 @@ pub fn init() linksection(r.init) void {
 pub fn late_init() linksection(r.init) void {
     mi.zone.late_init();
     mi.tlb.init();
+    mi.balance.init();
 }
diff --git a/src/mm/private.zig b/src/mm/private.zig
index 5d6f5f7..04a5b8d 100644
--- a/src/mm/private.zig
+++ b/src/mm/private.zig
@@ -7,6 +7,7 @@ pub const heap = @import("heap.zig");
 pub const zone = @import("zone.zig");
 pub const PMap = pmap.PMap;
 pub const tlb = @import("tlb.zig");
+pub const balance = @import("balance.zig");
 
 const ke = @import("root").ke;
 
diff --git a/src/mm/zone.zig b/src/mm/zone.zig
index df7f14c..26ec5bc 100644
--- a/src/mm/zone.zig
+++ b/src/mm/zone.zig
@@ -118,9 +118,7 @@ const ex = r.ex;
 const mi = mm.private;
 
 /// Interval at which we do housekeeping (working set update, reaping, etc.)
-const update_interval_s = 15;
-const update_interval: r.Nanoseconds = .from(r.Seconds.init(update_interval_s));
-var update_work_item: ex.DelayedWorkItem = undefined;
+pub const update_interval_s = 15;
 
 /// Fixed point conversion for WMA computation.
 const wma_unit = 256;
@@ -1076,11 +1074,10 @@ pub const Zone = struct {
 
         self.lock.release();
 
-        while (true) {
+        while (entry != head) {
             const slab: *Slab = @fieldParentPtr("link", entry);
             const next = entry.next;
             self.slab_destroy(slab);
-            if (next == head) break;
             entry = next;
         }
     }
@@ -1332,6 +1329,7 @@ pub const Zone = struct {
 
             mm.heap.free(slab.base, self.slab_size);
         } else {
+            std.log.info("slab is {*}", .{slab});
             free_page(@ptrFromInt(
                 std.mem.alignBackward(usize, @intFromPtr(slab), mm.page_size),
             ));
@@ -1503,7 +1501,7 @@ pub const Zone = struct {
 };
 
 /// Called periodically to do housekeeping tasks on zones.
-fn update(_: ?*anyopaque) void {
+pub fn update() void {
     zone_list_lock.acquire();
 
     var zone = all_zones;
@@ -1513,9 +1511,6 @@ fn update(_: ?*anyopaque) void {
     }
 
     zone_list_lock.release();
-
-    // Do it again.
-    ex.work.enqueue_in(&update_work_item, update_interval);
 }
 
 /// Parameterized version of Zone, useful for object caches.
@@ -1605,8 +1600,6 @@ pub fn late_init() linksection(r.init) void {
     zone_list_lock.release();
 
     magazines_initialized = true;
-    update_work_item.init(.Normal, update, null);
-    ex.work.enqueue_in(&update_work_item, update_interval);
 
     smr_zone.init("SMR", .{});
     smr_cpu_zone.init("SMR CPU", @sizeOf(ke.smr.Cpu) * ke.ncpus, .{});