can't include headers

hi,
I need to write a device driver under linux. I am using slackware linux  kernel 2.4.18. 
I have problem to include headers, here is some of my code:

#define __KERNEL__
#include <linux/config.h>      (ok) 

#ifdef CONFIG_MODVERSIONS
#define MODVERSIONS
#include <linux/modversions.h> (ok)
#endif

#include <linux/module.h>      (ok)
#include <linux/stddef.h>      (ok) 
#include <linux/kernel.h>      (ok)               
#include <linux/mm.h>          <--- can't include this one
 
Any comments is greatly appreciated.
Thanks alot.

Ganda

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