Initialization functions and data in Linux Kernel

- Macros exist that are used to mark some functions or intialized data as 'initialization functions'.
N.B. This does not apply to uninitialized data.

- The kernel can take this as hint that the function is used only during the initialization
phase and free up used memory resources after usage.


1) For functions:

You should add __init immediately before the function name, like:

static void __init initme(int x, int y)
{
extern int z; z = x * y;
}

If the function has a prototype somewhere, you can also add
__init between closing brace of the prototype and semicolon:

extern int initialize_foobar_device(int, int, int) __init;


2) For initialized data:
You should insert __initdata between the variable name and equal
sign followed by value, e.g.:

static int init_variable __initdata = 0;
static char linux_logo[] __initdata = { 0x32, 0x36, ... };

IMP!! Don't forget to initialize data not at file scope, i.e. within a function,
as gcc otherwise puts the data into the bss section and not into the init
section.

IMP!! Also note, that this data cannot be "const".


Source : Linux Kernel Documentation
Refer file include/linux/init.h
Line No. 8