MAP_HUGE_SHIFT      6 arch/x86/include/uapi/asm/mman.h #define MAP_HUGE_2MB    (21 << MAP_HUGE_SHIFT)
MAP_HUGE_SHIFT      7 arch/x86/include/uapi/asm/mman.h #define MAP_HUGE_1GB    (30 << MAP_HUGE_SHIFT)