_MMVAD

incomplete layouts only for what the kernel debuggers decode; other types are named by the kernel's ASSERT text, without layouts

struct _MMVAD;/* named only */

Named, without a layout, by a pointer cast in NTOSKRNL.EXE's ASSERT text for this build (a debug build keeps each assertion's source text): Vad != (PMMVAD)NULL It says MMVAD; recorded builds name the struct _MMVAD (NT's typedef struct _X {…} X convention).