书里关于Simple Segregated Storage的疑问

goodier

Computer Systems -- A Programmer’s Perspective书里：
Simple Segregated Storage
To allocate a block of some given size, we check the appropriate free list. If the list is not empty, we simply
allocate the first block in its entirety. Free blocks are never split to satisfy allocation requests. If the list is
empty, the allocator requests a fixed-sized chunk of additional memory from the operating system (typically
a multiple of the page size), divides the chunk into equal-sized blocks, and links the blocks together to form
the new free list. To free a block, the allocator simply inserts the block at the front of the appropriate free
list.

Further, the combination of the same-sized blocks in each chunk, no splitting,
and no coalescing means that there is very little per-block memory overhead. Since each chunk has only
same-sized blocks, the size of an allocated block can be inferred from its address.

可是我还是想不明白怎么通过address来推断size,比如一个address是0x8000FF00，那它block size即可以是8bytes,也可以是16，32？ 还是有什么其他的限制？