Somehow, in the long chain of shell variable fiddling that creates the
command line in bin/daemon.sh, there is a small mistake. The command
line for tasktracker comes out (shorn of many other items) with two
memory allocation requests:
--Xmx1000m -Xmx512m org.apache.hadoop.mapred.TaskTracker
This is in Cloudera CH3, but is probably in regular 0.20.