Mmap's understanding

Mmap's Understanding

One obvious benefit of using shared memory communication is that it is efficient because the process can read and write directly to the memory without requiring any copy of the data. for communication methods such as pipelines and message queues, four copies of the data are required in the kernel and user space, while shared memory copies only two data [1]: One from the input file to the shared memory area, and the other from the shared memory area to the output file. in fact, when you share memory between processes, you do not always have to read and write small amounts of data, and then re-establish the shared memory area when there is new communication. instead, the shared area is maintained until the communication is complete, so that the data content is kept in shared memory and is not written back to the file. Content in shared memory is often written back to a file when it is de-mapped. Therefore, the use of shared memory communication mode is very efficient.

This allows us to understand that shared memory is the fastest way of IPC (interprocess communication) , and it is also described in the framebuffer display driver that mmap can map framebuffer memory to user space. This allows each AP of an Android device to manipulate the mapped memory to change what is displayed.

Mmap () system calls enable shared memory between processes by mapping the same common file. After the normal file is mapped to the process address space, the process can access the same file as the normal memory without having to call read (), write (), and so on.
Note: In fact, the mmap () system call is not designed entirely for shared memory. It itself provides a different way of accessing ordinary files than normal, and processes can operate on ordinary files like read-write memory. The shared memory IPC for POSIX or System V is purely for sharing purposes, and of course mmap () realizes shared memory is also one of its main applications .

Mmap's understanding