perldoc > PerlIO::mmap(3perl)

NAME
    PerlIO::mmap - Memory mapped IO

SYNOPSIS
     open my $fh, '<:mmap', $filename;

DESCRIPTION
    This layer does "read" and "write" operations by mmap()ing the file if possible, but falls back
    to the default behavior if not.

IMPLEMENTATION NOTE
    "PerlIO::mmap" only exists to use XSLoader to load C code that provides support for using memory
    mapped IO. One does not need to explicitly "use PerlIO::mmap;".