mb                 18 arch/x86/include/asm/barrier.h #define mb() alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2)
mb                 22 arch/x86/include/asm/barrier.h #define mb() 	asm volatile("mfence":::"memory")
mb                 34 include/asm-generic/barrier.h #define mb()	barrier()