Userdata memory is not freed

[Shmuel Zeigerman <shmuz@...>]

I've got a case where the memory occupied by a userdatum
is not freed, even though Lua calls its __gc method.
I'm failing to understand that, any help is appreciated!
(Lua 5.1.2)

testlib.c and test.lua follow:

/* testlib.c */
#include <stdio.h>
#include "lua.h"
#include "lauxlib.h"

static int new_udata (lua_State *L) {
  int size = luaL_optinteger (L, 1, 32768);
  lua_newuserdata (L, size);
  lua_pushvalue(L, LUA_ENVIRONINDEX);
  lua_setmetatable (L, -2);
  return 1;
}

static int udata_gc (lua_State *L) {
  (void)L;
  printf("inside __gc\n");
  return 0;
}

static const luaL_reg meta[] = {
  { "__gc", udata_gc },
  { NULL, NULL }
};

static const luaL_reg lib[] = {
  { "new",  new_udata },
  { NULL, NULL }
};

LUALIB_API int luaopen_testlib (lua_State *L) {
  /* create a new function environment */
  lua_newtable (L);
  lua_pushvalue (L, -1);
  lua_replace (L, LUA_ENVIRONINDEX);
  luaL_register (L, NULL, meta);
  /* register functions */
  luaL_register (L, "testlib", lib);
  return 1;
}

-- test.lua
require "testlib"
print("1:", collectgarbage"count") --> 22 KB
testlib.new(2^20)
print("2:", collectgarbage"count") --> 1046 KB
collectgarbage"collect"
print("3:", collectgarbage"count") --> 1044 KB

--
Shmuel