typedef struct _HEAP_LOOKASIDE
{
     SLIST_HEADER ListHead;
     WORD Depth;
     WORD MaximumDepth;
     ULONG TotalAllocates;
     ULONG AllocateMisses;
     ULONG TotalFrees;
     ULONG FreeMisses;
     ULONG LastTotalAllocates;
     ULONG LastAllocateMisses;
     ULONG Counters[2];
} HEAP_LOOKASIDE, *PHEAP_LOOKASIDE;

Windows Vista Kernel Structures