There is insufficient memory for the Java Runtime Environment in elasticsearch

I'm facing following issue while starting my elasticsearch, can any one help me to resolve my issue.

Elastisearch version 2.2.1
java version 1.8

There is insufficient memory for the Java Runtime Environment to continue.
Native memory allocation (mmap) failed to map 8190689280 bytes for committing reserved memory.
Possible reasons:
The system is out of physical RAM or swap space
In 32 bit mode, the process size limit was hit
Possible solutions:
Reduce memory load on the system
Increase physical memory or swap space
Check if swap backing store is full
Use 64 bit Java on a 64 bit OS
Decrease Java heap size (-Xmx/-Xms)
Decrease number of Java threads
Decrease Java thread stack sizes (-Xss)
Set larger code cache with -XX:ReservedCodeCacheSize=
This output file may be truncated or incomplete.

Out of Memory Error (os_linux.cpp:2627), pid=5299, tid=140486350145280

JRE version: (8.0_71-b15) (build )
Java VM: Java HotSpot(TM) 64-Bit Server VM (25.71-b15 mixed mode linux-amd64 compressed oops)\ Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again

How much did you assign ES?

i assigned 6GB memory for ES