High Memcached Wasted Space
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We're using a fairly large (20GB), very active (>92% hit rate) Memcache cluster and seeing more than 10% wasted space. 

The eviction rate is extremely low (0.1/sec), and the reclaimed rate is flat - 0. 

Is this cause for concern, and is there anything that can be done - even periodically - to ensure that is doesn't eat as much usable space as it currently is? 