Case study of virtual memory management

Need to understand virtual memory concept. When a process requesting for 2GB mapping onto the virutal memory in Linux environment of 4GB ( 1GB Kernel : 3GB Userspace), when already another process already holds the mapping for 2 GB. How does the mapping of the stack, heap, data segments all going to happen? I am not able to find any example for my understanding. Text book only mentions separately for each mapping but not a practical approach.