readahead is the file prefetching technology used in the Linux operating system. It is a system call that loads a file's contents into the page cache. When a file is subsequently accessed, its contents are read from physical memory rather than from disk, which is much faster.
Many distributions of Linux use readahead on a list of commonly used files to speed up booting. In such a setup, if the kernel is booted with the profile parameter, it will record all file accesses during bootup and write a new list of files to be read before booting. This will make additional installed services start faster, because they are not included in the default readahead list.