Here is an excerpt from example code that is known to work:
/* For various ports, try to guess a fixed spot in the vm space
that's probably free. */
#if defined(__sparc64__)
# define TRY_EMPTY_VM_SPACE 0x40000000000
#elif defined(_LP64)
# define TRY_EMPTY_VM_SPACE 0x400000000000
#elif defined(__mips__) || defined(__vax__) || defined (__arm__)
# define TRY_EMPTY_VM_SPACE 0x60000000
#else
# define TRY_EMPTY_VM_SPACE 0xb0000000
#endif
addr = mmap ((void *) TRY_EMPTY_VM_SPACE, size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_FIXED, fd, 0);
And size is allowed to be smaller than the page size.
Martin
