object_pool, O(N) destroy?

Hi, I am considering using boost::object_pool for fast allocation and deallocation of likkle container/token objects. I need to make this as fast as possible, to this end I wonder why object_pool seems to use boost::pool::ordered_free() (O(N)) rather than the faster free() (O(1))? There must be a reason, but I can't seem to find it in the Lib's documentation. I would be interested in hearing if peoples experiences/comments on using object_pool. Thanks for reading! Kevin\