This well written given link
https://blog.csdn.net/ljianhui/article/details/10253345
The figure is a schematic view of the use of shared memory communication between two processes:
processes A and B os operating system has its own virtual memory space
of the virtual memory space and corresponding to each section of physical memory space on the disk, and they are each independent nothing in common.
1, call the API, allow the operating system to open up a large section of the buffer space (that is, the pen in space) in the physical memory
2, processes A and B each for the process to open up the space to create the actual physical space cache of correspondence mapping relation
3, two processes operate their own virtual memory to read and write data, in order to achieve inter-process communication.
4, in fact, the size of the virtual memory address, and each process has such a large virtual address, the process itself is part of the virtual address corresponding to the actual physical address, and a large portion of the virtual address is not there, you can using a portion to achieve mapped virtual address
