	int mmap_flags = MAP_SHARED;
	int prot = PROT_READ;
#ifdef MAP_NOSYNC	/* Used on FreeBSD */
	if (flags & MDB_NOSYNC)
		mmap_flags |= MAP_NOSYNC;
#endif
	if (flags & MDB_WRITEMAP) {
		prot |= PROT_WRITE;
		if (ftruncate(env->me_fd, env->me_mapsize) < 0)
			return ErrCode();
	}
	env->me_map = mmap(addr, env->me_mapsize, prot, mmap_flags,
		env->me_fd, 0);
	if (env->me_map == MAP_FAILED) {
		env->me_map = NULL;
		return ErrCode();
	}

	if (flags & MDB_NORDAHEAD) {
		/* Turn off readahead. It's harmful when the DB is larger than RAM. */
#ifdef MADV_RANDOM
		madvise(env->me_map, env->me_mapsize, MADV_RANDOM);
#else
#ifdef POSIX_MADV_RANDOM
		posix_madvise(env->me_map, env->me_mapsize, POSIX_MADV_RANDOM);
#endif /* POSIX_MADV_RANDOM */
#endif /* MADV_RANDOM */
	}
#endif /* _WIN32 */

	/* Can happen because the address argument to mmap() is just a
	 * hint.  mmap() can pick another, e.g. if the range is in use.
	 * The MAP_FIXED flag would prevent that, but then mmap could
	 * instead unmap existing pages to make room for the new map.
	 */
	if (addr && env->me_map != addr)
		return EBUSY;	/* TODO: Make a new MDB_* error code? */

Warm-up