Linux mmap()

The call maps content of file, started from an offset passed over from the caller, into a memory location. The unit of mapping is page.  The call will round the size up to page boundary.  The caller can specify if the mapping are PRIVATE or or SHARED.

The advantage of mmap over normal read/write call is that mmap transfers data directly to user space without keeping a copy in the kernel buffer.  Once the file is map, no system calls are required to manipulate the data except potential page fault and context switching overhead.  The mapped file can be shared by multiple processes.

mmap() is typically used for large file to avoid wasting memory.  The mapping is terminated using the unmmap() call.