Monoblocks: optimize blocks that contain a single type of node

src/mapblock.cpp

@@ -102,11 +102,9 @@ static const char *modified_reason_strings[] = {
 MapBlock::MapBlock(v3s16 pos, IGameDef *gamedef):
 		m_pos(pos),
 		m_pos_relative(pos * MAP_BLOCKSIZE),
-		data(new MapNode[nodecount]),
 		m_gamedef(gamedef)
 {
-	reallocate();
+	reallocate(nodecount, MapNode(CONTENT_IGNORE));
-	assert(m_modified > MOD_STATE_CLEAN);
 }
 
 MapBlock::~MapBlock()
@@ -212,6 +210,10 @@ void MapBlock::copyTo(VoxelManipulator &dst)
 	v3s16 data_size(MAP_BLOCKSIZE, MAP_BLOCKSIZE, MAP_BLOCKSIZE);
 	VoxelArea data_area(v3s16(0,0,0), data_size - v3s16(1,1,1));
 
+	if (m_is_mono_block) {
+		reallocate(nodecount, data[0]);
+		m_is_mono_block = false;
+	}
 	// Copy from data to VoxelManipulator
 	dst.copyFrom(data, data_area, v3s16(0,0,0),
 			getPosRelative(), data_size);
@@ -222,6 +224,10 @@ void MapBlock::copyFrom(const VoxelManipulator &src)
 	v3s16 data_size(MAP_BLOCKSIZE, MAP_BLOCKSIZE, MAP_BLOCKSIZE);
 	VoxelArea data_area(v3s16(0,0,0), data_size - v3s16(1,1,1));
 
+	if (m_is_mono_block) {
+		reallocate(nodecount, data[0]);
+		m_is_mono_block = false;
+	}
 	// Copy from VoxelManipulator to data
 	src.copyTo(data, data_area, v3s16(0,0,0),
 			getPosRelative(), data_size);
@@ -232,6 +238,10 @@ void MapBlock::actuallyUpdateIsAir()
 	// Running this function un-expires m_is_air
 	m_is_air_expired = false;
 
+	if (m_is_mono_block) {
+		m_is_air = data[0].getContent() == CONTENT_AIR;
+		return;
+	}
 	bool only_air = true;
 	for (u32 i = 0; i < nodecount; i++) {
 		MapNode &n = data[i];
@@ -259,12 +269,12 @@ void MapBlock::expireIsAirCache()
 // Note that there's no technical reason why we *have to* renumber the IDs,
 // but we do it anyway as it also helps compressability.
 static void getBlockNodeIdMapping(NameIdMapping *nimap, MapNode *nodes,
-	const NodeDefManager *nodedef)
+	const NodeDefManager *nodedef, bool is_mono_block)
 {
 	IdIdMapping &mapping = IdIdMapping::giveClearedThreadLocalInstance();
 
 	content_t id_counter = 0;
-	for (u32 i = 0; i < MapBlock::nodecount; i++) {
+	for (u32 i = 0; i < (is_mono_block ? 1 : MapBlock::nodecount); i++) {
 		content_t global_id = nodes[i].getContent();
 		content_t id = CONTENT_IGNORE;
 
@@ -377,12 +387,19 @@ void MapBlock::serialize(std::ostream &os_compressed, u8 version, bool disk, int
 	const u8 params_width = 2;
 	if(disk)
 	{
-		MapNode *tmp_nodes = new MapNode[nodecount];
+		MapNode *tmp_nodes;
-		memcpy(tmp_nodes, data, nodecount * sizeof(MapNode));
+		if (m_is_mono_block) {
-		getBlockNodeIdMapping(&nimap, tmp_nodes, m_gamedef->ndef());
+			tmp_nodes = new MapNode[1];
+			tmp_nodes[0] = data[0];
+		}
+		else {
+			tmp_nodes = new MapNode[nodecount];
+			memcpy(tmp_nodes, data, nodecount * sizeof(MapNode));
+		}
+		getBlockNodeIdMapping(&nimap, tmp_nodes, m_gamedef->ndef(), m_is_mono_block);
 
 		buf = MapNode::serializeBulk(version, tmp_nodes, nodecount,
-				content_width, params_width);
+				content_width, params_width, m_is_mono_block);
 		delete[] tmp_nodes;
 
 		// write timestamp and node/id mapping first
@@ -395,7 +412,7 @@ void MapBlock::serialize(std::ostream &os_compressed, u8 version, bool disk, int
 	else
 	{
 		buf = MapNode::serializeBulk(version, data, nodecount,
-				content_width, params_width);
+				content_width, params_width, m_is_mono_block);
 	}
 
 	writeU8(os, content_width);
@@ -592,9 +609,15 @@ void MapBlock::deSerialize(std::istream &in_compressed, u8 version, bool disk)
 			m_node_timers.deSerialize(is, version);
 		}
 
-		u16 dummy;
+		if (nimap.size() == 1) {
-		m_is_air = nimap.size() == 1 && nimap.getId("air", dummy);
+			m_is_mono_block = true;
-		m_is_air_expired = false;
+			reallocate(1, data[0]);
+			u16 dummy;
+			if (nimap.getId("air", dummy)) {
+				m_is_air = true;
+				m_is_air_expired = false;
+			}
+		}
 	}
 
 	TRACESTREAM(<<"MapBlock::deSerialize "<<getPos()

src/mapblock.h

@@ -73,15 +73,12 @@ public:
 		m_orphan = true;
 	}
 
-	void reallocate()
-	{
-		for (u32 i = 0; i < nodecount; i++)
-			data[i] = MapNode(CONTENT_IGNORE);
-		raiseModified(MOD_STATE_WRITE_NEEDED, MOD_REASON_REALLOCATE);
-	}
-
 	MapNode* getData()
 	{
+		if (m_is_mono_block) {
+			reallocate(nodecount, data[0]);
+			m_is_mono_block = false;
+		}
 		return data;
 	}
 
@@ -236,7 +233,10 @@ public:
 		if (!*valid_position)
 			return {CONTENT_IGNORE};
 
-		return data[z * zstride + y * ystride + x];
+		if (m_is_mono_block)
+			return data[0];
+		else
+			return data[z * zstride + y * ystride + x];
 	}
 
 	inline MapNode getNode(v3s16 p, bool *valid_position)
@@ -255,6 +255,10 @@ public:
 		if (!isValidPosition(x, y, z))
 			throw InvalidPositionException();
 
+		if (m_is_mono_block) {
+			reallocate(nodecount, data[0]);
+			m_is_mono_block = false;
+		}
 		data[z * zstride + y * ystride + x] = n;
 		raiseModified(MOD_STATE_WRITE_NEEDED, MOD_REASON_SET_NODE);
 	}
@@ -270,7 +274,10 @@ public:
 
 	inline MapNode getNodeNoCheck(s16 x, s16 y, s16 z)
 	{
-		return data[z * zstride + y * ystride + x];
+		if (m_is_mono_block)
+			return data[0];
+		else
+			return data[z * zstride + y * ystride + x];
 	}
 
 	inline MapNode getNodeNoCheck(v3s16 p)
@@ -280,6 +287,10 @@ public:
 
 	inline void setNodeNoCheck(s16 x, s16 y, s16 z, MapNode n)
 	{
+		if (m_is_mono_block) {
+			reallocate(nodecount, data[0]);
+			m_is_mono_block = false;
+		}
 		data[z * zstride + y * ystride + x] = n;
 		raiseModified(MOD_STATE_WRITE_NEEDED, MOD_REASON_SET_NODE);
 	}
@@ -439,6 +450,14 @@ private:
 
 	void deSerialize_pre22(std::istream &is, u8 version, bool disk);
 
+	void reallocate(u32 c, MapNode n)
+	{
+		delete[] data;
+		data = new MapNode[c];
+		for (u32 i = 0; i < c; i++)
+			data[i] = n;
+	}
+
 	/*
 	 * PLEASE NOTE: When adding something here be mindful of position and size
 	 * of member variables! This is also the reason for the weird public-private
@@ -457,6 +476,7 @@ public:
 private:
 	// see isOrphan()
 	bool m_orphan = false;
+	bool m_is_mono_block = false;
 
 	// Position in blocks on parent
 	v3s16 m_pos;
@@ -480,7 +500,7 @@ private:
 	 * heap fragmentation (the array is exactly 16K), CPU caches and/or
 	 * optimizability of algorithms working on this array.
 	 */
-	MapNode *const data; // of `nodecount` elements
+	MapNode * data = nullptr; // of `nodecount` elements
 
 	// provides the item and node definitions
 	IGameDef *m_gamedef;

src/mapnode.cpp

@@ -589,7 +589,7 @@ void MapNode::deSerialize(const u8 *source, u8 version)
 
 Buffer<u8> MapNode::serializeBulk(int version,
 		const MapNode *nodes, u32 nodecount,
-		u8 content_width, u8 params_width)
+		u8 content_width, u8 params_width, bool is_mono_block)
 {
 	if (!ser_ver_supported_write(version))
 		throw VersionMismatchException("ERROR: MapNode format not supported");
@@ -602,13 +602,13 @@ Buffer<u8> MapNode::serializeBulk(int version,
 	// Writing to the buffer linearly is faster
 	u8 *p = &databuf[0];
 	for (u32 i = 0; i < nodecount; i++, p += 2)
-		writeU16(p, nodes[i].param0);
+		writeU16(p, nodes[is_mono_block ? 0 : i].param0);
 
 	for (u32 i = 0; i < nodecount; i++, p++)
-		writeU8(p, nodes[i].param1);
+		writeU8(p, nodes[is_mono_block ? 0 : i].param1);
 
 	for (u32 i = 0; i < nodecount; i++, p++)
-		writeU8(p, nodes[i].param2);
+		writeU8(p, nodes[is_mono_block ? 0 : i].param2);
 
 	return databuf;
 }

src/mapnode.h

@@ -307,7 +307,7 @@ struct alignas(u32) MapNode
 	//   compressed = true to zlib-compress output
 	static Buffer<u8> serializeBulk(int version,
 			const MapNode *nodes, u32 nodecount,
-			u8 content_width, u8 params_width);
+			u8 content_width, u8 params_width, bool is_mono_block = false);
 	static void deSerializeBulk(std::istream &is, int version,
 			MapNode *nodes, u32 nodecount,
 			u8 content_width, u8 params_width);