diff --git a/vm/aging_collector.cpp b/vm/aging_collector.cpp
index 49b1c520ec..2972528cb3 100644
--- a/vm/aging_collector.cpp
+++ b/vm/aging_collector.cpp
@@ -25,7 +25,7 @@ void factor_vm::collect_aging()
 		collector.trace_cards(data->tenured,
 			card_points_to_aging,
 			simple_unmarker(card_mark_mask));
-		collector.cheneys_algorithm();
+		collector.tenure_reachable_objects();
 	}
 	{
 		/* If collection fails here, do a to_tenured collection. */
diff --git a/vm/aging_collector.hpp b/vm/aging_collector.hpp
index 8f2677c8b6..a04261d826 100644
--- a/vm/aging_collector.hpp
+++ b/vm/aging_collector.hpp
@@ -15,6 +15,10 @@ struct aging_policy {
 	{
 		return !(aging->contains_p(untagged) || tenured->contains_p(untagged));
 	}
+
+	void promoted_object(object *obj) {}
+
+	void visited_object(object *obj) {}
 };
 
 struct aging_collector : copying_collector<aging_space,aging_policy> {
diff --git a/vm/aging_space.hpp b/vm/aging_space.hpp
index 20e2506539..99efd44de5 100644
--- a/vm/aging_space.hpp
+++ b/vm/aging_space.hpp
@@ -1,20 +1,29 @@
 namespace factor
 {
 
-struct aging_space : bump_allocator {
+struct aging_space : bump_allocator<object> {
 	object_start_map starts;
 
 	aging_space(cell size, cell start) :
-		bump_allocator(size,start), starts(size,start) {}
+		bump_allocator<object>(size,start), starts(size,start) {}
 
 	object *allot(cell size)
 	{
 		if(here + size > end) return NULL;
 
-		object *obj = bump_allocator::allot(size);
+		object *obj = bump_allocator<object>::allot(size);
 		starts.record_object_start_offset(obj);
 		return obj;
 	}
+
+	cell next_object_after(cell scan)
+	{
+		cell size = ((object *)scan)->size();
+		if(scan + size < here)
+			return scan + size;
+		else
+			return 0;
+	}
 };
 
 }
diff --git a/vm/bump_allocator.hpp b/vm/bump_allocator.hpp
index 64011e0bb6..b41613b540 100644
--- a/vm/bump_allocator.hpp
+++ b/vm/bump_allocator.hpp
@@ -1,7 +1,7 @@
 namespace factor
 {
 
-struct bump_allocator {
+template<typename Block> struct bump_allocator {
 	/* offset of 'here' and 'end' is hardcoded in compiler backends */
 	cell here;
 	cell start;
@@ -9,27 +9,18 @@ struct bump_allocator {
 	cell size;
 
 	bump_allocator(cell size_, cell start_) :
-		here(0), start(start_), end(start_ + size_), size(size_) {}
+		here(start_), start(start_), end(start_ + size_), size(size_) {}
 
-	inline bool contains_p(object *pointer)
+	inline bool contains_p(Block *block)
 	{
-		return ((cell)pointer - start) < size;
+		return ((cell)block - start) < size;
 	}
 
-	inline object *allot(cell size)
+	inline Block *allot(cell size)
 	{
 		cell h = here;
 		here = h + align(size,data_alignment);
-		return (object *)h;
-	}
-
-	cell next_allocated_block_after(cell scan)
-	{
-		cell size = ((object *)scan)->size();
-		if(scan + size < here)
-			return scan + size;
-		else
-			return 0;
+		return (Block *)h;
 	}
 };
 
diff --git a/vm/code_heap.cpp b/vm/code_heap.cpp
index 2a466857f9..5ae55cb760 100755
--- a/vm/code_heap.cpp
+++ b/vm/code_heap.cpp
@@ -8,7 +8,7 @@ code_heap::code_heap(cell size)
 	if(size > (1L << (sizeof(cell) * 8 - 6))) fatal_error("Heap too large",size);
 	seg = new segment(align_page(size),true);
 	if(!seg) fatal_error("Out of memory in heap allocator",size);
-	allocator = new free_list_allocator<heap_block>(seg->start,size);
+	allocator = new free_list_allocator<heap_block>(size,seg->start);
 }
 
 code_heap::~code_heap()
diff --git a/vm/collector.hpp b/vm/collector.hpp
index 9200d95399..bc04ee4de7 100644
--- a/vm/collector.hpp
+++ b/vm/collector.hpp
@@ -40,7 +40,10 @@ template<typename TargetGeneration, typename Policy> struct collector {
 
 		object *untagged = parent->untag<object>(pointer);
 		if(!policy.should_copy_p(untagged))
+		{
+			policy.visited_object(untagged);
 			return;
+		}
 
 		object *forwarding = resolve_forwarding(untagged);
 
@@ -49,7 +52,10 @@ template<typename TargetGeneration, typename Policy> struct collector {
 		else if(policy.should_copy_p(forwarding))
 			untagged = promote_object(forwarding);
 		else
+		{
 			untagged = forwarding;
+			policy.visited_object(untagged);
+		}
 
 		*handle = RETAG(untagged,TAG(pointer));
 	}
@@ -79,6 +85,8 @@ template<typename TargetGeneration, typename Policy> struct collector {
 		stats->object_count++;
 		stats->bytes_copied += size;
 
+		policy.promoted_object(newpointer);
+
 		return newpointer;
 	}
 
@@ -145,6 +153,141 @@ template<typename TargetGeneration, typename Policy> struct collector {
 			ctx = ctx->next;
 		}
 	}
+
+	inline cell first_card_in_deck(cell deck)
+	{
+		return deck << (deck_bits - card_bits);
+	}
+
+	inline cell last_card_in_deck(cell deck)
+	{
+		return first_card_in_deck(deck + 1);
+	}
+
+	inline cell card_deck_for_address(cell a)
+	{
+		return addr_to_deck(a - this->data->start);
+	}
+
+	inline cell card_start_address(cell card)
+	{
+		return (card << card_bits) + this->data->start;
+	}
+
+	inline cell card_end_address(cell card)
+	{
+		return ((card + 1) << card_bits) + this->data->start;
+	}
+
+	void trace_partial_objects(cell start, cell end, cell card_start, cell card_end)
+	{
+		if(card_start < end)
+		{
+			start += sizeof(cell);
+
+			if(start < card_start) start = card_start;
+			if(end > card_end) end = card_end;
+
+			cell *slot_ptr = (cell *)start;
+			cell *end_ptr = (cell *)end;
+
+			if(slot_ptr != end_ptr)
+			{
+				for(; slot_ptr < end_ptr; slot_ptr++)
+					this->trace_handle(slot_ptr);
+			}
+		}
+	}
+
+	template<typename SourceGeneration, typename Unmarker>
+	void trace_cards(SourceGeneration *gen, card mask, Unmarker unmarker)
+	{
+		u64 start_time = current_micros();
+	
+		card_deck *decks = this->data->decks;
+		card_deck *cards = this->data->cards;
+	
+		cell gen_start_card = addr_to_card(gen->start - this->data->start);
+
+		cell first_deck = card_deck_for_address(gen->start);
+		cell last_deck = card_deck_for_address(gen->end);
+	
+		cell start = 0, binary_start = 0, end = 0;
+	
+		for(cell deck_index = first_deck; deck_index < last_deck; deck_index++)
+		{
+			if(decks[deck_index] & mask)
+			{
+				this->parent->gc_stats.decks_scanned++;
+
+				cell first_card = first_card_in_deck(deck_index);
+				cell last_card = last_card_in_deck(deck_index);
+	
+				for(cell card_index = first_card; card_index < last_card; card_index++)
+				{
+					if(cards[card_index] & mask)
+					{
+						this->parent->gc_stats.cards_scanned++;
+
+						if(end < card_start_address(card_index))
+						{
+							start = gen->starts.find_object_containing_card(card_index - gen_start_card);
+							binary_start = start + this->parent->binary_payload_start((object *)start);
+							end = start + ((object *)start)->size();
+						}
+	
+#ifdef FACTOR_DEBUG
+						assert(addr_to_card(start - this->data->start) <= card_index);
+						assert(start < card_end_address(card_index));
+#endif
+
+scan_next_object:				{
+							trace_partial_objects(
+								start,
+								binary_start,
+								card_start_address(card_index),
+								card_end_address(card_index));
+							if(end < card_end_address(card_index))
+							{
+								start = gen->next_object_after(start);
+								if(start)
+								{
+									binary_start = start + this->parent->binary_payload_start((object *)start);
+									end = start + ((object *)start)->size();
+									goto scan_next_object;
+								}
+							}
+						}
+	
+						unmarker(&cards[card_index]);
+	
+						if(!start) goto end;
+					}
+				}
+	
+				unmarker(&decks[deck_index]);
+			}
+		}
+
+end:		this->parent->gc_stats.card_scan_time += (current_micros() - start_time);
+	}
+
+	/* Trace all literals referenced from a code block. Only for aging and nursery collections */
+	void trace_literal_references(code_block *compiled)
+	{
+		this->trace_handle(&compiled->owner);
+		this->trace_handle(&compiled->literals);
+		this->trace_handle(&compiled->relocation);
+		this->parent->gc_stats.code_blocks_scanned++;
+	}
+
+	void trace_code_heap_roots(std::set<code_block *> *remembered_set)
+	{
+		std::set<code_block *>::const_iterator iter = remembered_set->begin();
+		std::set<code_block *>::const_iterator end = remembered_set->end();
+
+		for(; iter != end; iter++) trace_literal_references(*iter);
+	}
 };
 
 }
diff --git a/vm/copying_collector.hpp b/vm/copying_collector.hpp
index ea7faf2423..012aa4ec10 100644
--- a/vm/copying_collector.hpp
+++ b/vm/copying_collector.hpp
@@ -18,147 +18,12 @@ struct copying_collector : collector<TargetGeneration,Policy> {
 	explicit copying_collector(factor_vm *parent_, generation_statistics *stats_, TargetGeneration *target_, Policy policy_) :
 		collector<TargetGeneration,Policy>(parent_,stats_,target_,policy_), scan(target_->here) {}
 
-	inline cell first_card_in_deck(cell deck)
-	{
-		return deck << (deck_bits - card_bits);
-	}
-
-	inline cell last_card_in_deck(cell deck)
-	{
-		return first_card_in_deck(deck + 1);
-	}
-
-	inline cell card_deck_for_address(cell a)
-	{
-		return addr_to_deck(a - this->data->start);
-	}
-
-	inline cell card_start_address(cell card)
-	{
-		return (card << card_bits) + this->data->start;
-	}
-
-	inline cell card_end_address(cell card)
-	{
-		return ((card + 1) << card_bits) + this->data->start;
-	}
-
-	void trace_partial_objects(cell start, cell end, cell card_start, cell card_end)
-	{
-		if(card_start < end)
-		{
-			start += sizeof(cell);
-
-			if(start < card_start) start = card_start;
-			if(end > card_end) end = card_end;
-
-			cell *slot_ptr = (cell *)start;
-			cell *end_ptr = (cell *)end;
-
-			if(slot_ptr != end_ptr)
-			{
-				for(; slot_ptr < end_ptr; slot_ptr++)
-					this->trace_handle(slot_ptr);
-			}
-		}
-	}
-
-	template<typename SourceGeneration, typename Unmarker>
-	void trace_cards(SourceGeneration *gen, card mask, Unmarker unmarker)
-	{
-		u64 start_time = current_micros();
-	
-		card_deck *decks = this->data->decks;
-		card_deck *cards = this->data->cards;
-	
-		cell gen_start_card = addr_to_card(gen->start - this->data->start);
-
-		cell first_deck = card_deck_for_address(gen->start);
-		cell last_deck = card_deck_for_address(gen->end);
-	
-		cell start = 0, binary_start = 0, end = 0;
-	
-		for(cell deck_index = first_deck; deck_index < last_deck; deck_index++)
-		{
-			if(decks[deck_index] & mask)
-			{
-				this->parent->gc_stats.decks_scanned++;
-
-				cell first_card = first_card_in_deck(deck_index);
-				cell last_card = last_card_in_deck(deck_index);
-	
-				for(cell card_index = first_card; card_index < last_card; card_index++)
-				{
-					if(cards[card_index] & mask)
-					{
-						this->parent->gc_stats.cards_scanned++;
-
-						if(end < card_start_address(card_index))
-						{
-							start = gen->starts.find_object_containing_card(card_index - gen_start_card);
-							binary_start = start + this->parent->binary_payload_start((object *)start);
-							end = start + ((object *)start)->size();
-						}
-	
-#ifdef FACTOR_DEBUG
-						assert(addr_to_card(start - this->data->start) <= card_index);
-						assert(start < card_end_address(card_index));
-#endif
-
-scan_next_object:				{
-							trace_partial_objects(
-								start,
-								binary_start,
-								card_start_address(card_index),
-								card_end_address(card_index));
-							if(end < card_end_address(card_index))
-							{
-								start = gen->next_allocated_block_after(start);
-								if(start)
-								{
-									binary_start = start + this->parent->binary_payload_start((object *)start);
-									end = start + ((object *)start)->size();
-									goto scan_next_object;
-								}
-							}
-						}
-	
-						unmarker(&cards[card_index]);
-	
-						if(!start) goto end;
-					}
-				}
-	
-				unmarker(&decks[deck_index]);
-			}
-		}
-
-end:		this->parent->gc_stats.card_scan_time += (current_micros() - start_time);
-	}
-
-	/* Trace all literals referenced from a code block. Only for aging and nursery collections */
-	void trace_literal_references(code_block *compiled)
-	{
-		this->trace_handle(&compiled->owner);
-		this->trace_handle(&compiled->literals);
-		this->trace_handle(&compiled->relocation);
-		this->parent->gc_stats.code_blocks_scanned++;
-	}
-
-	void trace_code_heap_roots(std::set<code_block *> *remembered_set)
-	{
-		std::set<code_block *>::const_iterator iter = remembered_set->begin();
-		std::set<code_block *>::const_iterator end = remembered_set->end();
-
-		for(; iter != end; iter++) trace_literal_references(*iter);
-	}
-
 	void cheneys_algorithm()
 	{
 		while(scan && scan < this->target->here)
 		{
 			this->trace_slots((object *)scan);
-			scan = this->target->next_allocated_block_after(scan);
+			scan = this->target->next_object_after(scan);
 		}
 	}
 };
diff --git a/vm/data_heap.cpp b/vm/data_heap.cpp
index 5a8f4d6b36..7c887c7419 100755
--- a/vm/data_heap.cpp
+++ b/vm/data_heap.cpp
@@ -19,7 +19,7 @@ data_heap::data_heap(cell young_size_, cell aging_size_, cell tenured_size_)
 	aging_size = aging_size_;
 	tenured_size = tenured_size_;
 
-	cell total_size = young_size + 2 * aging_size + 2 * tenured_size;
+	cell total_size = young_size + 2 * aging_size + tenured_size;
 
 	total_size += deck_size;
 
@@ -29,20 +29,21 @@ data_heap::data_heap(cell young_size_, cell aging_size_, cell tenured_size_)
 
 	cards = new card[cards_size];
 	cards_end = cards + cards_size;
+	memset(cards,0,cards_size);
 
 	cell decks_size = addr_to_deck(total_size);
 	decks = new card_deck[decks_size];
 	decks_end = decks + decks_size;
+	memset(decks,0,decks_size);
 
 	start = align(seg->start,deck_size);
 
 	tenured = new tenured_space(tenured_size,start);
-	tenured_semispace = new tenured_space(tenured_size,tenured->end);
 
-	aging = new aging_space(aging_size,tenured_semispace->end);
+	aging = new aging_space(aging_size,tenured->end);
 	aging_semispace = new aging_space(aging_size,aging->end);
 
-	nursery = new bump_allocator(young_size,aging_semispace->end);
+	nursery = new nursery_space(young_size,aging_semispace->end);
 
 	assert(seg->end - nursery->end <= deck_size);
 }
@@ -54,7 +55,6 @@ data_heap::~data_heap()
 	delete aging;
 	delete aging_semispace;
 	delete tenured;
-	delete tenured_semispace;
 	delete[] cards;
 	delete[] decks;
 }
@@ -71,8 +71,6 @@ void factor_vm::set_data_heap(data_heap *data_)
 	nursery = *data->nursery;
 	nursery.here = nursery.start;
 	init_card_decks();
-	data->reset_generation(data->aging);
-	data->reset_generation(data->tenured);
 }
 
 void factor_vm::init_data_heap(cell young_size, cell aging_size, cell tenured_size)
@@ -185,8 +183,11 @@ void factor_vm::primitive_data_room()
 	a.add(tag_fixnum((data->aging->end - data->aging->here) >> 10));
 	a.add(tag_fixnum((data->aging->size) >> 10));
 
-	a.add(tag_fixnum((data->tenured->end - data->tenured->here) >> 10));
-	a.add(tag_fixnum((data->tenured->size) >> 10));
+	//XXX
+	cell used, total_free, max_free;
+	data->tenured->usage(&used,&total_free,&max_free);
+	a.add(tag_fixnum(total_free >> 10));
+	a.add(tag_fixnum(used >> 10));
 
 	a.trim();
 	dpush(a.elements.value());
@@ -195,7 +196,7 @@ void factor_vm::primitive_data_room()
 /* Disables GC and activates next-object ( -- obj ) primitive */
 void factor_vm::begin_scan()
 {
-	heap_scan_ptr = data->tenured->start;
+	heap_scan_ptr = data->tenured->first_object();
 	gc_off = true;
 }
 
@@ -214,12 +215,14 @@ cell factor_vm::next_object()
 	if(!gc_off)
 		general_error(ERROR_HEAP_SCAN,false_object,false_object,NULL);
 
-	if(heap_scan_ptr >= data->tenured->here)
+	if(heap_scan_ptr)
+	{
+		cell current = heap_scan_ptr;
+		heap_scan_ptr = data->tenured->next_object_after(heap_scan_ptr);
+		return tag_dynamic((object *)current);
+	}
+	else
 		return false_object;
-
-	object *obj = (object *)heap_scan_ptr;
-	heap_scan_ptr += obj->size();
-	return tag_dynamic(obj);
 }
 
 /* Push object at heap scan cursor and advance; pushes f when done */
diff --git a/vm/data_heap.hpp b/vm/data_heap.hpp
index 526a5eb9ae..fe714b91b0 100755
--- a/vm/data_heap.hpp
+++ b/vm/data_heap.hpp
@@ -10,11 +10,10 @@ struct data_heap {
 
 	segment *seg;
 
-	bump_allocator *nursery;
+	nursery_space *nursery;
 	aging_space *aging;
 	aging_space *aging_semispace;
 	tenured_space *tenured;
-	tenured_space *tenured_semispace;
 
 	card *cards;
 	card *cards_end;
@@ -49,7 +48,6 @@ their allocation pointers and cards reset. */
 template<typename Generation> void data_heap::reset_generation(Generation *gen)
 {
 	gen->here = gen->start;
-
 	clear_cards(gen);
 	clear_decks(gen);
 	gen->starts.clear_object_start_offsets();
diff --git a/vm/debug.cpp b/vm/debug.cpp
index 31164e972b..afc0b43f7a 100755
--- a/vm/debug.cpp
+++ b/vm/debug.cpp
@@ -209,19 +209,21 @@ void factor_vm::dump_memory(cell from, cell to)
 		dump_cell(from);
 }
 
-void factor_vm::dump_zone(const char *name, bump_allocator *z)
+template<typename Generation>
+void factor_vm::dump_generation(const char *name, Generation *gen)
 {
 	print_string(name); print_string(": ");
-	print_string("Start="); print_cell(z->start);
-	print_string(", size="); print_cell(z->size);
-	print_string(", here="); print_cell(z->here - z->start); nl();
+	print_string("Start="); print_cell(gen->start);
+	print_string(", size="); print_cell(gen->size);
+	print_string(", end="); print_cell(gen->end);
+	nl();
 }
 
 void factor_vm::dump_generations()
 {
-	dump_zone("Nursery",&nursery);
-	dump_zone("Aging",data->aging);
-	dump_zone("Tenured",data->tenured);
+	dump_generation("Nursery",&nursery);
+	dump_generation("Aging",data->aging);
+	dump_generation("Tenured",data->tenured);
 
 	print_string("Cards: base=");
 	print_cell((cell)data->cards);
diff --git a/vm/free_list_allocator.hpp b/vm/free_list_allocator.hpp
index da2622bb0b..c8f3bd6f47 100644
--- a/vm/free_list_allocator.hpp
+++ b/vm/free_list_allocator.hpp
@@ -9,29 +9,17 @@ struct free_list {
 };
 
 template<typename Block> struct free_list_allocator {
-	cell start;
 	cell size;
+	cell start;
 	cell end;
 	free_list free_blocks;
 	mark_bits<Block> state;
 
-	explicit free_list_allocator(cell start, cell size);
-
-	inline Block *first_block()
-	{
-		return (Block *)start;
-	}
-
-	inline Block *last_block()
-	{
-		return (Block *)end;
-	}
-
-	Block *next_block_after(heap_block *block)
-	{
-		return (Block *)((cell)block + block->size());
-	}
-
+	explicit free_list_allocator(cell size, cell start);
+	bool contains_p(Block *block);
+	Block *first_block();
+	Block *last_block();
+	Block *next_block_after(Block *block);
 	void clear_free_list();
 	void add_to_free_list(free_heap_block *block);
 	void build_free_list(cell size);
@@ -42,35 +30,42 @@ template<typename Block> struct free_list_allocator {
 	void free(Block *block);
 	void usage(cell *used, cell *total_free, cell *max_free);
 	cell occupied();
-
+	void sweep();
 	template<typename Iterator> void sweep(Iterator &iter);
 	template<typename Iterator> void compact(Iterator &iter);
-
-	template<typename Iterator> void iterate(Iterator &iter)
-	{
-		Block *scan = first_block();
-		Block *end = last_block();
-
-		while(scan != end)
-		{
-			cell size = scan->size();
-			Block *next = (Block *)((cell)scan + size);
-			if(!scan->free_p()) iter(scan,size);
-			scan = next;
-		}
-	}
+	template<typename Iterator> void iterate(Iterator &iter);
 };
 
+template<typename Block>
+free_list_allocator<Block>::free_list_allocator(cell size_, cell start_) :
+	size(size_), start(start_), end(start_ + size_), state(mark_bits<Block>(size_,start_))
+{
+	clear_free_list();
+}
+
 template<typename Block> void free_list_allocator<Block>::clear_free_list()
 {
 	memset(&free_blocks,0,sizeof(free_list));
 }
 
-template<typename Block>
-free_list_allocator<Block>::free_list_allocator(cell start_, cell size_) :
-	start(start_), size(size_), end(start_ + size_), state(mark_bits<Block>(start_,size_))
+template<typename Block> bool free_list_allocator<Block>::contains_p(Block *block)
 {
-	clear_free_list();
+	return ((cell)block - start) < size;
+}
+
+template<typename Block> Block *free_list_allocator<Block>::first_block()
+{
+	return (Block *)start;
+}
+
+template<typename Block> Block *free_list_allocator<Block>::last_block()
+{
+	return (Block *)end;
+}
+
+template<typename Block> Block *free_list_allocator<Block>::next_block_after(Block *block)
+{
+	return (Block *)((cell)block + block->size());
 }
 
 template<typename Block> void free_list_allocator<Block>::add_to_free_list(free_heap_block *block)
@@ -234,8 +229,56 @@ template<typename Block> cell free_list_allocator<Block>::occupied()
 		return size;
 }
 
-/* After code GC, all live code blocks are marked, so any
-which are not marked can be reclaimed. */
+template<typename Block>
+void free_list_allocator<Block>::sweep()
+{
+	this->clear_free_list();
+
+	Block *prev = NULL;
+	Block *scan = this->first_block();
+	Block *end = this->last_block();
+
+	while(scan != end)
+	{
+		cell size = scan->size();
+
+		if(scan->free_p())
+		{
+			if(prev && prev->free_p())
+			{
+				free_heap_block *free_prev = (free_heap_block *)prev;
+				free_prev->set_size(free_prev->size() + size);
+			}
+			else
+				prev = scan;
+		}
+		else if(this->state.marked_p(scan))
+		{
+			if(prev && prev->free_p())
+				this->add_to_free_list((free_heap_block *)prev);
+			prev = scan;
+		}
+		else
+		{
+			if(prev && prev->free_p())
+			{
+				free_heap_block *free_prev = (free_heap_block *)prev;
+				free_prev->set_size(free_prev->size() + size);
+			}
+			else
+			{
+				((free_heap_block *)scan)->set_free();
+				prev = scan;
+			}
+		}
+
+		scan = (Block *)((cell)scan + size);
+	}
+
+	if(prev && prev->free_p())
+		this->add_to_free_list((free_heap_block *)prev);
+}
+
 template<typename Block>
 template<typename Iterator>
 void free_list_allocator<Block>::sweep(Iterator &iter)
@@ -302,4 +345,20 @@ void free_list_allocator<Block>::compact(Iterator &iter)
 	this->build_free_list((cell)compactor.address - this->start);
 }
 
+template<typename Block>
+template<typename Iterator>
+void free_list_allocator<Block>::iterate(Iterator &iter)
+{
+	Block *scan = first_block();
+	Block *end = last_block();
+
+	while(scan != end)
+	{
+		cell size = scan->size();
+		Block *next = (Block *)((cell)scan + size);
+		if(!scan->free_p()) iter(scan,size);
+		scan = next;
+	}
+}
+
 }
diff --git a/vm/full_collector.cpp b/vm/full_collector.cpp
index 924cad6777..9191823d75 100644
--- a/vm/full_collector.cpp
+++ b/vm/full_collector.cpp
@@ -4,7 +4,7 @@ namespace factor
 {
 
 full_collector::full_collector(factor_vm *parent_) :
-	copying_collector<tenured_space,full_policy>(
+	collector<tenured_space,full_policy>(
 		parent_,
 		&parent_->gc_stats.full_stats,
 		parent_->data->tenured,
@@ -89,18 +89,22 @@ void full_collector::trace_literal_references(code_block *compiled)
 collections */
 void full_collector::mark_code_block(code_block *compiled)
 {
-	this->code->set_marked_p(compiled);
-	trace_literal_references(compiled);
+	if(!this->code->marked_p(compiled))
+	{
+		this->code->set_marked_p(compiled);
+		trace_literal_references(compiled);
+	}
 }
 
-void full_collector::cheneys_algorithm()
+void full_collector::mark_reachable_objects()
 {
-	while(scan && scan < target->here)
+	std::vector<object *> *mark_stack = &this->target->mark_stack;
+	while(!mark_stack->empty())
 	{
-		object *obj = (object *)scan;
+		object *obj = mark_stack->back();
+		mark_stack->pop_back();
 		this->trace_slots(obj);
 		this->mark_object_code_block(obj);
-		scan = target->next_allocated_block_after(scan);
 	}
 }
 
@@ -109,6 +113,7 @@ void factor_vm::collect_full_impl(bool trace_contexts_p)
 	full_collector collector(this);
 
 	code->clear_mark_bits();
+	data->tenured->clear_mark_bits();
 
 	collector.trace_roots();
         if(trace_contexts_p)
@@ -118,8 +123,9 @@ void factor_vm::collect_full_impl(bool trace_contexts_p)
 		collector.trace_callbacks();
 	}
 
-	collector.cheneys_algorithm();
+	collector.mark_reachable_objects();
 
+	data->tenured->sweep();
 	data->reset_generation(data->aging);
 	nursery.here = nursery.start;
 }
@@ -144,9 +150,6 @@ void factor_vm::collect_growing_heap(cell requested_bytes,
 
 void factor_vm::collect_full(bool trace_contexts_p, bool compact_code_heap_p)
 {
-	/* Copy all live objects to the tenured semispace. */
-	std::swap(data->tenured,data->tenured_semispace);
-	data->reset_generation(data->tenured);
 	collect_full_impl(trace_contexts_p);
 
 	if(compact_code_heap_p)
diff --git a/vm/full_collector.hpp b/vm/full_collector.hpp
index 5298f56637..9aef352b4b 100644
--- a/vm/full_collector.hpp
+++ b/vm/full_collector.hpp
@@ -11,9 +11,20 @@ struct full_policy {
 	{
 		return !tenured->contains_p(untagged);
 	}
+
+	void promoted_object(object *obj)
+	{
+		tenured->mark_and_push(obj);
+	}
+
+	void visited_object(object *obj)
+	{
+		if(!tenured->marked_p(obj))
+			tenured->mark_and_push(obj);
+	}
 };
 
-struct full_collector : copying_collector<tenured_space,full_policy> {
+struct full_collector : collector<tenured_space,full_policy> {
 	bool trace_contexts_p;
 
 	full_collector(factor_vm *parent_);
@@ -22,7 +33,7 @@ struct full_collector : copying_collector<tenured_space,full_policy> {
 	void trace_callbacks();
 	void trace_literal_references(code_block *compiled);
 	void mark_code_block(code_block *compiled);
-	void cheneys_algorithm();
+	void mark_reachable_objects();
 };
 
 }
diff --git a/vm/gc.cpp b/vm/gc.cpp
index c8ba57b7f2..6cb99b6da0 100755
--- a/vm/gc.cpp
+++ b/vm/gc.cpp
@@ -235,11 +235,13 @@ object *factor_vm::allot_object(header header, cell size)
 	else
 	{
 		/* If tenured space does not have enough room, collect */
-		if(data->tenured->here + size > data->tenured->end)
+		//XXX
+		//if(data->tenured->here + size > data->tenured->end)
 			primitive_full_gc();
 
 		/* If it still won't fit, grow the heap */
-		if(data->tenured->here + size > data->tenured->end)
+		//XXX
+		//if(data->tenured->here + size > data->tenured->end)
 		{
 			gc(collect_growing_heap_op,
 				size, /* requested size */
diff --git a/vm/image.cpp b/vm/image.cpp
index b47fe4e86a..ee0a1064ed 100755
--- a/vm/image.cpp
+++ b/vm/image.cpp
@@ -39,7 +39,7 @@ void factor_vm::load_data_heap(FILE *file, image_header *h, vm_parameters *p)
 		fatal_error("load_data_heap failed",0);
 	}
 
-	data->tenured->here = data->tenured->start + h->data_size;
+	data->tenured->build_free_list(h->data_size);
 }
 
 void factor_vm::load_code_heap(FILE *file, image_header *h, vm_parameters *p)
@@ -203,7 +203,7 @@ void factor_vm::relocate_data(cell data_relocation_base, cell code_relocation_ba
 	{
 		relocate_object((object *)obj,data_relocation_base,code_relocation_base);
 		data->tenured->starts.record_object_start_offset((object *)obj);
-		obj = data->tenured->next_allocated_block_after(obj);
+		obj = data->tenured->next_object_after(obj);
 	}
 }
 
@@ -289,7 +289,7 @@ bool factor_vm::save_image(const vm_char *filename)
 	h.magic = image_magic;
 	h.version = image_version;
 	h.data_relocation_base = data->tenured->start;
-	h.data_size = data->tenured->here - data->tenured->start;
+	h.data_size = data->tenured->occupied();
 	h.code_relocation_base = code->seg->start;
 	h.code_size = code->allocator->occupied();
 
diff --git a/vm/master.hpp b/vm/master.hpp
index 293923ca7b..0282a0597d 100755
--- a/vm/master.hpp
+++ b/vm/master.hpp
@@ -53,6 +53,7 @@ namespace factor
 #include "free_list_allocator.hpp"
 #include "write_barrier.hpp"
 #include "object_start_map.hpp"
+#include "nursery_space.hpp"
 #include "aging_space.hpp"
 #include "tenured_space.hpp"
 #include "data_heap.hpp"
diff --git a/vm/nursery_collector.hpp b/vm/nursery_collector.hpp
index f9d2172929..778efab138 100644
--- a/vm/nursery_collector.hpp
+++ b/vm/nursery_collector.hpp
@@ -6,10 +6,14 @@ struct nursery_policy {
 
 	nursery_policy(factor_vm *parent_) : parent(parent_) {}
 
-	bool should_copy_p(object *untagged)
+	bool should_copy_p(object *obj)
 	{
-		return parent->nursery.contains_p(untagged);
+		return parent->nursery.contains_p(obj);
 	}
+
+	void promoted_object(object *obj) {}
+
+	void visited_object(object *obj) {}
 };
 
 struct nursery_collector : copying_collector<aging_space,nursery_policy> {
diff --git a/vm/nursery_space.hpp b/vm/nursery_space.hpp
new file mode 100644
index 0000000000..4425c1612b
--- /dev/null
+++ b/vm/nursery_space.hpp
@@ -0,0 +1,9 @@
+namespace factor
+{
+
+struct nursery_space : bump_allocator<object>
+{
+	nursery_space(cell size, cell start) : bump_allocator<object>(size,start) {}
+};
+
+}
diff --git a/vm/tenured_space.hpp b/vm/tenured_space.hpp
index 1162bb5fd3..c0c12d3f58 100644
--- a/vm/tenured_space.hpp
+++ b/vm/tenured_space.hpp
@@ -1,19 +1,65 @@
 namespace factor
 {
 
-struct tenured_space : bump_allocator {
+struct tenured_space : free_list_allocator<object> {
 	object_start_map starts;
+	std::vector<object *> mark_stack;
 
 	tenured_space(cell size, cell start) :
-		bump_allocator(size,start), starts(size,start) {}
+		free_list_allocator<object>(size,start), starts(size,start) {}
 
 	object *allot(cell size)
 	{
-		if(here + size > end) return NULL;
+		object *obj = free_list_allocator<object>::allot(size);
+		if(obj)
+		{
+			starts.record_object_start_offset(obj);
+			return obj;
+		}
+		else
+			return NULL;
+	}
 
-		object *obj = bump_allocator::allot(size);
-		starts.record_object_start_offset(obj);
-		return obj;
+	object *first_allocated_block_after(object *block)
+	{
+		while(block != this->last_block() && block->free_p())
+		{
+			free_heap_block *free_block = (free_heap_block *)block;
+			block = (object *)((cell)free_block + free_block->size());
+		}
+
+		if(block == this->last_block())
+			return NULL;
+		else
+			return block;
+	}
+
+	cell first_object()
+	{
+		return (cell)first_allocated_block_after(this->first_block());
+	}
+
+	cell next_object_after(cell scan)
+	{
+		cell size = ((object *)scan)->size();
+		object *next = (object *)(scan + size);
+		return (cell)first_allocated_block_after(next);
+	}
+
+	void clear_mark_bits()
+	{
+		state.clear_mark_bits();
+	}
+
+	bool marked_p(object *obj)
+	{
+		return this->state.marked_p(obj);
+	}
+
+	void mark_and_push(object *obj)
+	{
+		this->state.set_marked_p(obj);
+		this->mark_stack.push_back(obj);
 	}
 };
 
diff --git a/vm/to_tenured_collector.cpp b/vm/to_tenured_collector.cpp
index 3676324ce2..3150647cd2 100644
--- a/vm/to_tenured_collector.cpp
+++ b/vm/to_tenured_collector.cpp
@@ -4,12 +4,23 @@ namespace factor
 {
 
 to_tenured_collector::to_tenured_collector(factor_vm *myvm_) :
-	copying_collector<tenured_space,to_tenured_policy>(
+	collector<tenured_space,to_tenured_policy>(
 		myvm_,
 		&myvm_->gc_stats.aging_stats,
 		myvm_->data->tenured,
 		to_tenured_policy(myvm_)) {}
 
+void to_tenured_collector::tenure_reachable_objects()
+{
+	std::vector<object *> *mark_stack = &this->target->mark_stack;
+	while(!mark_stack->empty())
+	{
+		object *obj = mark_stack->back();
+		mark_stack->pop_back();
+		this->trace_slots(obj);
+	}
+}
+
 void factor_vm::collect_to_tenured()
 {
 	/* Copy live objects from aging space to tenured space. */
@@ -21,7 +32,7 @@ void factor_vm::collect_to_tenured()
 		card_points_to_aging,
 		dummy_unmarker());
 	collector.trace_code_heap_roots(&code->points_to_aging);
-	collector.cheneys_algorithm();
+	collector.tenure_reachable_objects();
 	update_code_heap_for_minor_gc(&code->points_to_aging);
 
 	nursery.here = nursery.start;
diff --git a/vm/to_tenured_collector.hpp b/vm/to_tenured_collector.hpp
index 9a4cf3764b..e87ba5ee29 100644
--- a/vm/to_tenured_collector.hpp
+++ b/vm/to_tenured_collector.hpp
@@ -11,10 +11,18 @@ struct to_tenured_policy {
 	{
 		return !tenured->contains_p(untagged);
 	}
+
+	void promoted_object(object *obj)
+	{
+		tenured->mark_stack.push_back(obj);
+	}
+
+	void visited_object(object *obj) {}
 };
 
-struct to_tenured_collector : copying_collector<tenured_space,to_tenured_policy> {
+struct to_tenured_collector : collector<tenured_space,to_tenured_policy> {
 	to_tenured_collector(factor_vm *myvm_);
+	void tenure_reachable_objects();
 };
 
 }
diff --git a/vm/vm.hpp b/vm/vm.hpp
index 0509127918..615efe35ed 100755
--- a/vm/vm.hpp
+++ b/vm/vm.hpp
@@ -11,7 +11,7 @@ struct factor_vm
 	context *ctx;
 	
 	/* New objects are allocated here */
-	bump_allocator nursery;
+	nursery_space nursery;
 
 	/* Add this to a shifted address to compute write barrier offsets */
 	cell cards_offset;
@@ -308,7 +308,7 @@ struct factor_vm
 	void print_callstack();
 	void dump_cell(cell x);
 	void dump_memory(cell from, cell to);
-	void dump_zone(const char *name, bump_allocator *z);
+	template<typename Generation> void dump_generation(const char *name, Generation *gen);
 	void dump_generations();
 	void dump_objects(cell type);
 	void find_data_references_step(cell *scan);