http://structureddata.org/2012/06/18/linux-6-transparent-huge-pages-and-hadoop-workloads/
http://underthehood.meltwater.com/blog/2015/04/14/riak-elasticsearch-and-numad-walk-into-a-red-hat/
https://blogs.oracle.com/linuxkernel/entry/performance_impact_of_transparent_huge
http://www.cloudera.com/content/cloudera/en/documentation/core/latest/topics/cdh_admin_performance.html
compaction の defrag 問題。