Virtual Memory Size
The virtual memory map contains a lot of stuff. Some of it is read-only, some of it is shared, and some of it is allocated but never touched (eg, almost all of the 4Gb of heap in this example). But the operating system is smart enough to only load what it needs, so the virtual memory size is largely irrelevant.
But, given that 64-bit machines are ubiquitous, I don’t think it will be long before Virtual Memory Size is a completely irrelevant statistic.
Resident Set Size
Resident Set size is that portion of the virtual memory space that is actually in RAM. If your RSS grows to be a significant portion of your total physical memory, it might be time to start worrying. If your RSS grows to take up all your physical memory, and your system starts swapping, it’s well past time to start worrying.
Reference
Virtual Memory Usage from Java under Linux, too much memory used - Stack Overflow
what does anon-rss and total-vm mean - Stack Overflow