final long getBitmapUsedSpace(int from, int till) {
		long allocated = 0;

		while (from < till) {
			Page pg = getGCPage(from);

			for (int j = 0; j < Page.pageSize; j++) {
				int mask = pg.data[j] & 0xFF;

				while (mask != 0) {
					if ((mask & 1) != 0) {
						allocated += dbAllocationQuantum;
					}

					mask >>= 1;
				}
			}

			pool.unfix(pg);
			from += 1;
		}

		return allocated;
	}