diff --git a/persistent-data/space-maps/careful_alloc.cc b/persistent-data/space-maps/careful_alloc.cc
index 9991430..4609883 100644
--- a/persistent-data/space-maps/careful_alloc.cc
+++ b/persistent-data/space-maps/careful_alloc.cc
@@ -58,18 +58,18 @@ namespace {
 			clear_freed();
 		}
 
-		virtual void inc(block_address b) {
+		virtual void inc(block_address b, ref_t count) override {
 			if (was_freed(b))
 				throw runtime_error("inc of block freed within current transaction");
 
-			sm_->inc(b);
+			sm_->inc(b, count);
 		}
 
-		virtual void dec(block_address b) {
-			if (sm_->get_count(b) == 1)
+		virtual void dec(block_address b, ref_t count) override {
+			if (sm_->get_count(b) == count)
 				mark_freed(b);
 
-			sm_->dec(b);
+			sm_->dec(b, count);
 		}
 
 		virtual maybe_block find_free(span_iterator &it) {
diff --git a/persistent-data/space-maps/core.h b/persistent-data/space-maps/core.h
index e2af33a..73b555c 100644
--- a/persistent-data/space-maps/core.h
+++ b/persistent-data/space-maps/core.h
@@ -63,15 +63,15 @@ namespace persistent_data {
 		void commit() {
 		}
 
-		void inc(block_address b) {
+		void inc(block_address b, ref_t count) override {
 			if (counts_[b] == 0)
 				nr_free_--;
 
-			counts_[b]++;
+			counts_[b] += count;
 		}
 
-		void dec(block_address b) {
-			counts_[b]--;
+		void dec(block_address b, ref_t count) override {
+			counts_[b] -= count;
 
 			if (counts_[b] == 0) {
 				if (b < search_start_)
diff --git a/persistent-data/space-maps/disk.cc b/persistent-data/space-maps/disk.cc
index df3ab5b..51a4b78 100644
--- a/persistent-data/space-maps/disk.cc
+++ b/persistent-data/space-maps/disk.cc
@@ -383,17 +383,6 @@ namespace {
 			indexes_->commit_ies();
 		}
 
-		void inc(block_address b) override {
-			if (b == search_start_)
-				search_start_++;
-
-			modify_count(b, [](ref_t c) {return c + 1;});
-		}
-
-		void dec(block_address b) override {
-			modify_count(b, [](ref_t c) {return c - 1;});
-		}
-
 		void inc(block_address b, uint32_t count) override {
 			if (b == search_start_)
 				search_start_++;
diff --git a/persistent-data/space-maps/noop.h b/persistent-data/space-maps/noop.h
index fdd58a4..925936c 100644
--- a/persistent-data/space-maps/noop.h
+++ b/persistent-data/space-maps/noop.h
@@ -51,11 +51,11 @@ namespace persistent_data {
 			fail();
 		}
 
-		void inc(block_address b) {
+		void inc(block_address b, ref_t count) {
 			fail();
 		}
 
-		void dec(block_address b) {
+		void dec(block_address b, ref_t count) {
 			fail();
 		}
 
diff --git a/persistent-data/space-maps/recursive.cc b/persistent-data/space-maps/recursive.cc
index d904b8c..634c530 100644
--- a/persistent-data/space-maps/recursive.cc
+++ b/persistent-data/space-maps/recursive.cc
@@ -106,21 +106,21 @@ namespace {
 			sm_->commit();
 		}
 
-		virtual void inc(block_address b) {
+		virtual void inc(block_address b, ref_t count) override {
 			if (depth_)
-				add_op(b, block_op(INC, 1));
+				add_op(b, block_op(INC, count));
 			else {
 				recursing_lock lock(*this);
-				return sm_->inc(b);
+				return sm_->inc(b, count);
 			}
 		}
 
-		virtual void dec(block_address b) {
+		virtual void dec(block_address b, ref_t count) override {
 			if (depth_)
-				add_op(b, block_op(INC, -1));
+				add_op(b, block_op(INC, -count));
 			else {
 				recursing_lock lock(*this);
-				return sm_->dec(b);
+				return sm_->dec(b, count);
 			}
 		}
 
diff --git a/persistent-data/space_map.h b/persistent-data/space_map.h
index eacc558..930626a 100644
--- a/persistent-data/space_map.h
+++ b/persistent-data/space_map.h
@@ -45,19 +45,8 @@ namespace persistent_data {
 		virtual void set_count(block_address b, ref_t c) = 0;
 		virtual void commit() = 0;
 
-		virtual void inc(block_address b) = 0;
-		virtual void dec(block_address b) = 0;
-
-		// slow default implementation
-		virtual void inc(block_address b, uint32_t count) {
-			for (uint32_t i = 0; i < count; i++)
-				inc(b);
-		}
-
-		virtual void dec(block_address b, uint32_t count) {
-			for (uint32_t i = 0; i < count; i++)
-				dec(b);
-		}
+		virtual void inc(block_address b, ref_t count = 1) = 0;
+		virtual void dec(block_address b, ref_t count = 1) = 0;
 
 		// FIXME: change these to return an optional, failure is
 		// not that rare if we're restricting the area that's