diff a/src/hotspot/share/gc/shenandoah/shenandoahOldGC.cpp b/src/hotspot/share/gc/shenandoah/shenandoahOldGC.cpp
--- /dev/null
+++ b/src/hotspot/share/gc/shenandoah/shenandoahOldGC.cpp
@@ -0,0 +1,170 @@
+/*
+ * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+
+#include "gc/shenandoah/heuristics/shenandoahYoungHeuristics.hpp"
+#include "gc/shenandoah/shenandoahFreeSet.hpp"
+#include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
+#include "gc/shenandoah/shenandoahHeap.inline.hpp"
+#include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
+#include "gc/shenandoah/shenandoahOldGC.hpp"
+#include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
+#include "gc/shenandoah/shenandoahGeneration.hpp"
+#include "gc/shenandoah/shenandoahOldGeneration.hpp"
+#include "gc/shenandoah/shenandoahYoungGeneration.hpp"
+#include "prims/jvmtiTagMap.hpp"
+#include "utilities/events.hpp"
+
+
+ShenandoahOldGC::ShenandoahOldGC(ShenandoahOldGeneration* generation, ShenandoahSharedFlag& allow_preemption) :
+    ShenandoahConcurrentGC(generation, false), _old_generation(generation), _allow_preemption(allow_preemption) {
+}
+
+// Final mark for old-gen is different than for young or old, so we
+// override the implementation.
+void ShenandoahOldGC::op_final_mark() {
+
+  ShenandoahGenerationalHeap* const heap = ShenandoahGenerationalHeap::heap();
+  assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Should be at safepoint");
+  assert(!heap->has_forwarded_objects(), "No forwarded objects on this path");
+
+  if (ShenandoahVerify) {
+    heap->verifier()->verify_roots_no_forwarded();
+  }
+
+  if (!heap->cancelled_gc()) {
+    assert(_mark.generation()->is_old(), "Generation of Old-Gen GC should be OLD");
+    _mark.finish_mark();
+    assert(!heap->cancelled_gc(), "STW mark cannot OOM");
+
+    // Old collection is complete, the young generation no longer needs this
+    // reference to the old concurrent mark so clean it up.
+    heap->young_generation()->set_old_gen_task_queues(nullptr);
+
+    // We need to do this because weak root cleaning reports the number of dead handles
+    JvmtiTagMap::set_needs_cleaning();
+
+    _generation->prepare_regions_and_collection_set(true);
+
+    heap->set_unload_classes(false);
+    heap->prepare_concurrent_roots();
+
+    // Believe verification following old-gen concurrent mark needs to be different than verification following
+    // young-gen concurrent mark, so am commenting this out for now:
+    //   if (ShenandoahVerify) {
+    //     heap->verifier()->verify_after_concmark();
+    //   }
+
+    if (VerifyAfterGC) {
+      Universe::verify();
+    }
+  }
+}
+
+bool ShenandoahOldGC::collect(GCCause::Cause cause) {
+  auto heap = ShenandoahGenerationalHeap::heap();
+  assert(!_old_generation->is_doing_mixed_evacuations(), "Should not start an old gc with pending mixed evacuations");
+  assert(!_old_generation->is_preparing_for_mark(), "Old regions need to be parsable during concurrent mark.");
+
+  // Enable preemption of old generation mark.
+  _allow_preemption.set();
+
+  // Continue concurrent mark, do not reset regions, do not mark roots, do not collect $200.
+  entry_mark();
+
+  // If we failed to unset the preemption flag, it means another thread has already unset it.
+  if (!_allow_preemption.try_unset()) {
+    // The regulator thread has unset the preemption guard. That thread will shortly cancel
+    // the gc, but the control thread is now racing it. Wait until this thread sees the
+    // cancellation.
+    while (!heap->cancelled_gc()) {
+      SpinPause();
+    }
+  }
+
+  if (heap->cancelled_gc()) {
+    return false;
+  }
+
+  // Complete marking under STW
+  vmop_entry_final_mark();
+
+  if (_generation->is_concurrent_mark_in_progress()) {
+    assert(heap->cancelled_gc(), "Safepoint operation observed gc cancellation");
+    // GC may have been cancelled before final mark, but after the preceding cancellation check.
+    return false;
+  }
+
+  // We aren't dealing with old generation evacuation yet. Our heuristic
+  // should not have built a cset in final mark.
+  assert(!heap->is_evacuation_in_progress(), "Old gen evacuations are not supported");
+
+  // Process weak roots that might still point to regions that would be broken by cleanup
+  if (heap->is_concurrent_weak_root_in_progress()) {
+    entry_weak_refs();
+    entry_weak_roots();
+  }
+
+  // Final mark might have reclaimed some immediate garbage, kick cleanup to reclaim
+  // the space. This would be the last action if there is nothing to evacuate.
+  entry_cleanup_early();
+
+  heap->free_set()->log_status_under_lock();
+
+
+  // TODO: Old marking doesn't support class unloading yet
+  // Perform concurrent class unloading
+  // if (heap->unload_classes() &&
+  //     heap->is_concurrent_weak_root_in_progress()) {
+  //   entry_class_unloading();
+  // }
+
+
+  assert(!heap->is_concurrent_strong_root_in_progress(), "No evacuations during old gc.");
+
+  // We must execute this vm operation if we completed final mark. We cannot
+  // return from here with weak roots in progress. This is not a valid gc state
+  // for any young collections (or allocation failures) that interrupt the old
+  // collection.
+  vmop_entry_final_roots();
+
+  // We do not rebuild_free following increments of old marking because memory has not been reclaimed. However, we may
+  // need to transfer memory to OLD in order to efficiently support the mixed evacuations that might immediately follow.
+  size_t allocation_runway = heap->young_generation()->heuristics()->bytes_of_allocation_runway_before_gc_trigger(0);
+  heap->compute_old_generation_balance(allocation_runway, 0);
+
+  ShenandoahGenerationalHeap::TransferResult result;
+  {
+    ShenandoahHeapLocker locker(heap->lock());
+    result = heap->balance_generations();
+  }
+
+  LogTarget(Info, gc, ergo) lt;
+  if (lt.is_enabled()) {
+    LogStream ls(lt);
+    result.print_on("Old Mark", &ls);
+  }
+  return true;
+}
