runtime: optimize markspan Increases throughput by 2x on a memory hungry program on 8-node NUMA machine.
runtime: optimize markspan
Increases throughput by 2x on a memory hungry program on 8-node NUMA machine.

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https://codereview.appspot.com/100230043

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang