diff a/src/hotspot/share/gc/shenandoah/shenandoahMarkingContext.inline.hpp b/src/hotspot/share/gc/shenandoah/shenandoahMarkingContext.inline.hpp
--- a/src/hotspot/share/gc/shenandoah/shenandoahMarkingContext.inline.hpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahMarkingContext.inline.hpp
@@ -1,7 +1,8 @@
 /*
  * Copyright (c) 2018, 2019, Red Hat, Inc. All rights reserved.
+ * 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.
@@ -24,12 +25,12 @@
 
 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHMARKINGCONTEXT_INLINE_HPP
 #define SHARE_GC_SHENANDOAH_SHENANDOAHMARKINGCONTEXT_INLINE_HPP
 
 #include "gc/shenandoah/shenandoahMarkingContext.hpp"
-
 #include "gc/shenandoah/shenandoahMarkBitMap.inline.hpp"
+#include "logging/log.hpp"
 
 inline bool ShenandoahMarkingContext::mark_strong(oop obj, bool& was_upgraded) {
   return !allocated_after_mark_start(obj) && _mark_bit_map.mark_strong(cast_from_oop<HeapWord*>(obj), was_upgraded);
 }
 
@@ -47,47 +48,66 @@
 
 inline bool ShenandoahMarkingContext::is_marked_weak(oop obj) const {
   return allocated_after_mark_start(obj) || _mark_bit_map.is_marked_weak(cast_from_oop<HeapWord *>(obj));
 }
 
-inline HeapWord* ShenandoahMarkingContext::get_next_marked_addr(HeapWord* start, HeapWord* limit) const {
+inline bool ShenandoahMarkingContext::is_marked_or_old(oop obj) const {
+  return is_marked(obj) || ShenandoahHeap::heap()->is_old(obj);
+}
+
+inline bool ShenandoahMarkingContext::is_marked_strong_or_old(oop obj) const {
+  return is_marked_strong(obj) || ShenandoahHeap::heap()->is_old(obj);
+}
+
+inline HeapWord* ShenandoahMarkingContext::get_next_marked_addr(const HeapWord* start, const HeapWord* limit) const {
   return _mark_bit_map.get_next_marked_addr(start, limit);
 }
 
 inline bool ShenandoahMarkingContext::allocated_after_mark_start(oop obj) const {
-  HeapWord* addr = cast_from_oop<HeapWord*>(obj);
+  const HeapWord* addr = cast_from_oop<HeapWord*>(obj);
   return allocated_after_mark_start(addr);
 }
 
-inline bool ShenandoahMarkingContext::allocated_after_mark_start(HeapWord* addr) const {
+inline bool ShenandoahMarkingContext::allocated_after_mark_start(const HeapWord* addr) const {
   uintx index = ((uintx) addr) >> ShenandoahHeapRegion::region_size_bytes_shift();
   HeapWord* top_at_mark_start = _top_at_mark_starts[index];
-  bool alloc_after_mark_start = addr >= top_at_mark_start;
+  const bool alloc_after_mark_start = addr >= top_at_mark_start;
   return alloc_after_mark_start;
 }
 
 inline void ShenandoahMarkingContext::capture_top_at_mark_start(ShenandoahHeapRegion *r) {
+  if (!r->is_affiliated()) {
+    // Non-affiliated regions do not need their TAMS updated
+    return;
+  }
+
   size_t idx = r->index();
   HeapWord* old_tams = _top_at_mark_starts_base[idx];
   HeapWord* new_tams = r->top();
 
   assert(new_tams >= old_tams,
          "Region " SIZE_FORMAT", TAMS updates should be monotonic: " PTR_FORMAT " -> " PTR_FORMAT,
          idx, p2i(old_tams), p2i(new_tams));
-  assert(is_bitmap_clear_range(old_tams, new_tams),
+  assert((new_tams == r->bottom()) || (old_tams == r->bottom()) || (new_tams >= _top_bitmaps[idx]),
+         "Region " SIZE_FORMAT", top_bitmaps updates should be monotonic: " PTR_FORMAT " -> " PTR_FORMAT,
+         idx, p2i(_top_bitmaps[idx]), p2i(new_tams));
+  assert(old_tams == r->bottom() || is_bitmap_clear_range(old_tams, new_tams),
          "Region " SIZE_FORMAT ", bitmap should be clear while adjusting TAMS: " PTR_FORMAT " -> " PTR_FORMAT,
          idx, p2i(old_tams), p2i(new_tams));
 
+  log_debug(gc)("Capturing TAMS for %s Region " SIZE_FORMAT ", was: " PTR_FORMAT ", now: " PTR_FORMAT,
+                r->affiliation_name(), idx, p2i(old_tams), p2i(new_tams));
+
   _top_at_mark_starts_base[idx] = new_tams;
   _top_bitmaps[idx] = new_tams;
 }
 
 inline void ShenandoahMarkingContext::reset_top_at_mark_start(ShenandoahHeapRegion* r) {
   _top_at_mark_starts_base[r->index()] = r->bottom();
 }
 
-inline HeapWord* ShenandoahMarkingContext::top_at_mark_start(ShenandoahHeapRegion* r) const {
+inline HeapWord* ShenandoahMarkingContext::top_at_mark_start(const ShenandoahHeapRegion* r) const {
   return _top_at_mark_starts_base[r->index()];
 }
 
 inline void ShenandoahMarkingContext::reset_top_bitmap(ShenandoahHeapRegion* r) {
   assert(is_bitmap_clear_range(r->bottom(), r->end()),
