typedef enum _MM_PREEMPTIVE_TRIMS
{
         MmPreemptForNonPaged = 0,
         MmPreemptForPaged = 1,
         MmPreemptForNonPagedPriority = 2,
         MmPreemptForPagedPriority = 3,
         MmMaximumPreempt = 4
} MM_PREEMPTIVE_TRIMS;

Windows Vista Kernel Structures