mmap problem, allocates huge amounts of memory

Question

I got some huge files I need to parse, and people have been recommending mmap because this should avoid having to allocate the entire file in-memory.

But looking at

Answer 1

You can also use fadvise(2) (and madvise(2), see also posix_fadvise & posix_madvise ) to mark mmaped file (or its parts) as read-once.

#include  

int madvise(void *start, size_t length, int advice);

The advice is indicated in the advice parameter which can be

MADV_SEQUENTIAL 

Expect page references in sequential order. (Hence, pages in the given range can be aggressively read ahead, and may be freed soon after they are accessed.)

Portability: posix_madvise and posix_fadvise is part of ADVANCED REALTIME option of IEEE Std 1003.1, 2004. And constants will be POSIX_MADV_SEQUENTIAL and POSIX_FADV_SEQUENTIAL.