Please add some more memory by editing the mapred-site.xml

<property>
    <name>mapred.child.java.opts</name>
    <value>-Xmx4096m</value>
</property>

The above tag i have used 5gb.

Let me know if that helped you

alternatively you can also edit the hadoop-env.sh file 

add 

export HADOOP_OPTS="-Xmx5096m"