[PATCH]

* struct file cleanup : the very large file_ra_state is now allocated only on demand, using a dedicated "filp_ra_cache" slab.
     machines handling lot of sockets or pipes can save about 80 bytes (or 40 bytes on 32bits platforms) per file.

* private_data : The field is moved close to f_count and f_op fields to speedup sockfd_lookups

Thank you

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>