While searching for __exit use in kernel code . I came across https://www.kernel.org/doc/htmldocs/kernel-hacking/routines-init.html where it is written as "__exit is used to declare a function which is only required on exit: the function will be dropped if this file is not compiled as a module."
I don't know what does dropping of function mean. It would be great help if anyone delineate.
This means the memory used for the __exit executable code is reclaimed and the __exit will not be available in memory (since it will never be called for things which are not modules.)