/sys$common/syshlp/helplib.hlb Sys Parameters, MPW_HILIMIT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    MPW_HILIMIT sets an upper limit for the modified-page list. When
    the list accumulates the number of pages specified by this limit,
    writing of the list begins. The pages that are written are then
    transferred to the free-page list.

    If MPW_HILIMIT is too low, excessive page faulting can occur from
    the page file. If it is too high, too many physical pages can be
    consumed by the modified-page list.

    If you increase MPW_HILIMIT, you might also need to increase
    MPW_WAITLIMIT. Note that if MPW_WAITLIMIT is less than
    MPW_HILIMIT, a system deadlock occurs. The values for the two
    parameters are usually equal.

    MPW_HILIMIT has the AUTOGEN and GEN attributes.