typedef struct _MSUBSECTION
{
     PCONTROL_AREA ControlArea;
     PMMPTE SubsectionBase;
     union
     {
          PSUBSECTION NextSubsection;
          PMSUBSECTION NextMappedSubsection;
     };
     ULONG PtesInSubsection;
     union
     {
          ULONG UnusedPtes;
          PMM_AVL_TABLE GlobalPerSessionHead;
     };
     ULONG u;
     ULONG StartingSector;
     ULONG NumberOfFullSectors;
     ULONG u1;
     PMMSUBSECTION_NODE LeftChild;
     PMMSUBSECTION_NODE RightChild;
     LIST_ENTRY DereferenceList;
     ULONG NumberOfMappedViews;
} MSUBSECTION, *PMSUBSECTION;

Windows Vista Kernel Structures