Virtual Memory higher for logstash 1.5.3

I have logstash 1.5.3 running on one of the server where the process details of it are as follows:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
13194 logstash 39 19 2181m 233m 12m S 1.3 4.0 1:09.79 java

The virtual memory as shown is 2181m which is very large. Although I have set the following parameters -Xmx256m -Xms256m -Xss2048k but it not helpful on this server which worked on other server.

The VIRT column shows how much is mapped into the address space of the process. This isn't the same as the RAM usage in the RES column which, in turn, isn't the same thing as the maximum heap size. Numbers that are more interesting then VM size are a) the Java heap utilization (not visible in top(1)) and b) the RES column.

Thank you Magnus!!

Can you please suggest a way we can control the VIRT column.
Also does this high value affect other processes?

How can I view the JAVA heap utilization specific to logstash process?

Can you please suggest a way we can control the VIRT column.
Also does this high value affect other processes?

How much memory is mapped into a process's address space rarely matters. Don't worry about it. No, other processes aren't affected.

How can I view the JAVA heap utilization specific to logstash process?

VisualVM or the jstat tool should be able to help.