If it is to be an address space operations sturcture then you'll need a
pseudo mapping structure for anonymous pages that are pinned by aio --
similar in principal to how swapper_space is used for managing PageSwapCache
or how anon_vma structures can be associated with a page.
However, I warn you that you may find that the address_space is the
wrong level to register such callbacks, it just seemed like the obvious
first choice. A potential alternative implementation is to create a 1:1
association between pages and a long-lived holder that is stored on a hash
table (similar style of arrangement as page_waitqueue). A page is looked up
in the hash table and if an entry exists, it points to an callback structure
to the subsystem holding the pin. It's up to the subsystem to register the
callbacks when it is about to pin a page (get_user_pages_longlived(....,
&release_ops) and figure out how to release the pin safely.