diff --git a/ruby/unpack.c b/ruby/unpack.c
index 2a6614f7..f61fe6db 100644
--- a/ruby/unpack.c
+++ b/ruby/unpack.c
@@ -24,7 +24,7 @@ static ID s_sysread;
 static ID s_readpartial;
 
 struct unpack_buffer {
-	size_t size;
+	size_t used;
 	size_t free;
 	char* ptr;
 };
@@ -37,6 +37,7 @@ typedef struct {
 	VALUE stream;
 	VALUE streambuf;
 	ID stream_append_method;
+	size_t buffer_free_size;
 } unpack_user;
 
 
@@ -241,6 +242,13 @@ static VALUE eUnpackError;
 #define MSGPACK_UNPACKER_BUFFER_RESERVE_SIZE (8*1024)
 #endif
 
+/*
+#ifndef MSGPACK_BUFFER_FREE_SIZE
+#define MSGPACK_BUFFER_FREE_SIZE (1024*1024)
+#endif
+*/
+#define MSGPACK_BUFFER_FREE_SIZE 0
+
 static void MessagePack_Unpacker_free(void* data)
 {
 	if(data) {
@@ -273,7 +281,7 @@ static VALUE MessagePack_Unpacker_alloc(VALUE klass)
 
 	mp->user.finished = 0;
 	mp->user.offset = 0;
-	mp->user.buffer.size = 0;
+	mp->user.buffer.used = 0;
 	mp->user.buffer.free = 0;
 	mp->user.buffer.ptr = NULL;
 
@@ -326,6 +334,7 @@ static VALUE MessagePack_Unpacker_initialize(int argc, VALUE *argv, VALUE self)
 	mp->user.stream = stream;
 	mp->user.streambuf = rb_str_buf_new(MSGPACK_UNPACKER_BUFFER_RESERVE_SIZE);
 	mp->user.stream_append_method = append_method_of(stream);
+	mp->user.buffer_free_size = MSGPACK_BUFFER_FREE_SIZE;
 
 	return self;
 }
@@ -366,22 +375,27 @@ static void reserve_buffer(msgpack_unpack_t* mp, size_t require)
 {
 	struct unpack_buffer* buffer = &mp->user.buffer;
 
-	if(buffer->size == 0) {
-		size_t nsize = MSGPACK_UNPACKER_BUFFER_INIT_SIZE;
+	if(buffer->used == 0) {
+		if(require <= buffer->free) {
+			/* enough free space */
+			return;
+		}
+		/* no used buffer: realloc only */
+		size_t nsize = buffer->free == 0 ?
+			MSGPACK_UNPACKER_BUFFER_INIT_SIZE : buffer->free*2;
 		while(nsize < require) {
 			nsize *= 2;
 		}
-		char* tmp = ALLOC_N(char, nsize);
-		buffer->ptr = tmp;
+		char* tmp = REALLOC_N(buffer->ptr, char, nsize);
 		buffer->free = nsize;
-		buffer->size = 0;
+		buffer->ptr = tmp;
 		return;
 	}
 
-	if(buffer->size <= mp->user.offset) {
+	if(buffer->used <= mp->user.offset) {
 		/* clear buffer and rewind offset */
-		buffer->free += buffer->size;
-		buffer->size = 0;
+		buffer->free += buffer->used;
+		buffer->used = 0;
 		mp->user.offset = 0;
 	}
 
@@ -390,41 +404,91 @@ static void reserve_buffer(msgpack_unpack_t* mp, size_t require)
 		return;
 	}
 
-	size_t nsize = (buffer->size + buffer->free) * 2;
+	size_t nsize = (buffer->used + buffer->free) * 2;
 
-	if(mp->user.offset <= buffer->size / 2) {
+	if(mp->user.offset <= buffer->used / 2) {
 		/* parsed less than half: realloc only */
-		while(nsize < buffer->size + require) {
+		while(nsize < buffer->used + require) {
 			nsize *= 2;
 		}
 		char* tmp = REALLOC_N(buffer->ptr, char, nsize);
-		buffer->free = nsize - buffer->size;
+		buffer->free = nsize - buffer->used;
 		buffer->ptr = tmp;
 
 	} else {
 		/* parsed more than half: realloc and move */
-		size_t not_parsed = buffer->size - mp->user.offset;
+		size_t not_parsed = buffer->used - mp->user.offset;
 		while(nsize < not_parsed + require) {
 			nsize *= 2;
 		}
 		char* tmp = REALLOC_N(buffer->ptr, char, nsize);
 		memcpy(tmp, tmp + mp->user.offset, not_parsed);
-		buffer->free = nsize - buffer->size;
-		buffer->size = not_parsed;
+		buffer->free = nsize - not_parsed;
+		buffer->used = not_parsed;
 		buffer->ptr = tmp;
 		mp->user.offset = 0;
 	}
 }
 
-static inline void feed_buffer(msgpack_unpack_t* mp, const char* ptr, size_t len)
+static inline void try_free_buffer(msgpack_unpack_t* mp, size_t require)
+{
+	if(mp->user.buffer_free_size == 0) {
+		return;
+	}
+
+	struct unpack_buffer* buffer = &mp->user.buffer;
+	size_t csize = buffer->used + buffer->free;
+
+	if(csize <= mp->user.buffer_free_size) {
+		return;
+	}
+
+	if(mp->user.offset <= buffer->used / 2) {
+		/* parsed less than half: do nothing */
+
+	} else if(mp->user.offset < buffer->used) {
+		/* parsed more than half but not all: realloc and move */
+		size_t nsize = MSGPACK_UNPACKER_BUFFER_INIT_SIZE;
+		size_t not_parsed = buffer->used - mp->user.offset;
+		while(nsize < not_parsed + require) {
+			nsize *= 2;
+		}
+
+		if(nsize >= csize) {
+			return;
+		}
+
+		char* tmp;
+		if(mp->user.offset == 0) {
+			tmp = ALLOC_N(char, nsize);
+			memcpy(tmp, buffer->ptr + mp->user.offset, not_parsed);
+			free(buffer->ptr);
+		} else {
+			tmp = REALLOC_N(buffer->ptr, char, nsize);
+		}
+		buffer->free = nsize - not_parsed;
+		buffer->used = not_parsed;
+		buffer->ptr = tmp;
+		mp->user.offset = 0;
+
+	} else {
+		/* all parsed: free all */
+		free(buffer->ptr);
+		buffer->free = 0;
+		buffer->used = 0;
+		buffer->ptr = NULL;
+		mp->user.offset = 0;
+	}
+}
+
+static void feed_buffer(msgpack_unpack_t* mp, const char* ptr, size_t len)
 {
 	struct unpack_buffer* buffer = &mp->user.buffer;
 
-	//if(buffer->free < len) {
-		reserve_buffer(mp, len);
-	//}
-	memcpy(buffer->ptr + buffer->size, ptr, len);
-	buffer->size += len;
+	reserve_buffer(mp, len);
+
+	memcpy(buffer->ptr + buffer->used, ptr, len);
+	buffer->used += len;
 	buffer->free -= len;
 }
 
@@ -498,7 +562,7 @@ static VALUE MessagePack_Unpacker_each(VALUE self)
 #endif
 
 	while(1) {
-		if(mp->user.buffer.size <= mp->user.offset) {
+		if(mp->user.buffer.used <= mp->user.offset) {
 			do_fill:
 			{
 				VALUE len = MessagePack_Unpacker_fill(self);
@@ -509,7 +573,7 @@ static VALUE MessagePack_Unpacker_each(VALUE self)
 		}
 
 		ret = template_execute_wrap_each(mp,
-				mp->user.buffer.ptr, mp->user.buffer.size,
+				mp->user.buffer.ptr, mp->user.buffer.used,
 				&mp->user.offset);
 
 		if(ret < 0) {
@@ -525,6 +589,8 @@ static VALUE MessagePack_Unpacker_each(VALUE self)
 		}
 	}
 
+	try_free_buffer(mp, 0);
+
 	return Qnil;
 }
 
@@ -539,10 +605,10 @@ static VALUE feed_each_impl(VALUE args)
 	const char* ptr = RSTRING_PTR(data);
 	size_t len = RSTRING_LEN(data);
 
-	if(mp->user.buffer.size > 0) {
+	if(mp->user.buffer.used > 0) {
 		while(1) {
 			ret = template_execute_wrap_each(mp,
-					mp->user.buffer.ptr, mp->user.buffer.size,
+					mp->user.buffer.ptr, mp->user.buffer.used,
 					&mp->user.offset);
 
 			if(ret < 0) {
@@ -563,7 +629,7 @@ static VALUE feed_each_impl(VALUE args)
 		return Qnil;
 	}
 
-	if(mp->user.buffer.size <= mp->user.offset) {
+	if(mp->user.buffer.used <= mp->user.offset) {
 		// wrap & execute & feed
 		while(1) {
 			ret = template_execute_wrap_each(mp,
@@ -589,7 +655,7 @@ static VALUE feed_each_impl(VALUE args)
 
 		while(1) {
 			ret = template_execute_wrap_each(mp,
-					mp->user.buffer.ptr, mp->user.buffer.size,
+					mp->user.buffer.ptr, mp->user.buffer.used,
 					&mp->user.offset);
 
 			if(ret < 0) {
@@ -614,17 +680,26 @@ static VALUE feed_each_ensure(VALUE args) {
 	VALUE data = ((VALUE*)args)[1];
 	size_t* pconsumed = (size_t*)((VALUE*)args)[2];
 
-	UNPACKER(self, mp);
-	const char* ptr = RSTRING_PTR(data);
-	size_t len = RSTRING_LEN(data);
+	const char* dptr = RSTRING_PTR(data) + *pconsumed;
+	size_t dlen = RSTRING_LEN(data) - *pconsumed;
 
-	if(len > *pconsumed) {
-		feed_buffer(mp, ptr+*pconsumed, len-*pconsumed);
+	if(dlen > 0) {
+		UNPACKER(self, mp);
+		try_free_buffer(mp, dlen);
+		feed_buffer(mp, dptr, dlen);
 	}
 
 	return Qnil;
 }
 
+/**
+ * Document-method: MessagePack::Unpacker#feed_each
+ *
+ * call-seq:
+ *   unpacker.feed_each(data) {|object| }
+ *
+ * Same as feed(data) + each {|object| }, but tries to avoid copying of the buffer.
+ */
 static VALUE MessagePack_Unpacker_feed_each(VALUE self, VALUE data)
 {
 	size_t consumed = 0;
@@ -731,7 +806,7 @@ static VALUE MessagePack_Unpacker_execute_impl(VALUE self, VALUE data,
  *
  * This method doesn't use the internal buffer.
  *
- * Call *reset()* method before calling this method again.
+ * Call *reset* method before calling this method again.
  *
  * UnpackError is throw when parse error is occured.
  */
@@ -753,7 +828,7 @@ static VALUE MessagePack_Unpacker_execute_limit(VALUE self, VALUE data,
  *
  * This method doesn't use the internal buffer.
  *
- * Call *reset()* method before calling this method again.
+ * Call *reset* method before calling this method again.
  *
  * This returns offset that was parsed to.
  * Use *finished?* method to check an object is deserialized and call *data*
@@ -816,6 +891,7 @@ static VALUE MessagePack_Unpacker_reset(VALUE self)
 	UNPACKER(self, mp);
 	template_init(mp);
 	mp->user.finished = 0;
+	try_free_buffer(mp, 0);
 	return self;
 }