monitor IO to tmpfs partition?

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http://serverfault.com – How can I monitor the write speed to a tmpfs partition. It does not appear in the output of vmstat or iostat. I am running several python processes that are writing heavily to tmpfs and contributing to load. The load is high but the CPU, memory, disk IO, etc is all nominal. The load seems to be taking this heavy tmpfs IO into account indirectly somehow. I'd love to know the write speed to have an idea of upper limits per host. I'm running blind any help would be appreciated. (HowTos)