VMS Help Sys Parameters, FREELIM  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    FREELIM sets the minimum number of pages that must be on the
    free-page list.

    The system writes pages from the modified-page list, swaps out
    working sets, or reduces the size of the working sets to maintain
    the minimum count.

    While the larger free-page list generally means less page I/O, it
    also means less space for the balance set, which tends to result
    in more swap I/O. You can monitor the size of the free-page list,
    the amount of page, and the amount of swap with the MONITOR IO
    command of the Monitor utility.

    FREELIM has the AUTOGEN and MAJOR attributes.