• Eric Dumazet's avatar
    tcp/dccp: try to not exhaust ip_local_port_range in connect() · 07f4c900
    Eric Dumazet authored
    A long standing problem on busy servers is the tiny available TCP port
    range (/proc/sys/net/ipv4/ip_local_port_range) and the default
    sequential allocation of source ports in connect() system call.
    
    If a host is having a lot of active TCP sessions, chances are
    very high that all ports are in use by at least one flow,
    and subsequent bind(0) attempts fail, or have to scan a big portion of
    space to find a slot.
    
    In this patch, I changed the starting point in __inet_hash_connect()
    so that we try to favor even [1] ports, leaving odd ports for bind()
    users.
    
    We still perform a sequential search, so there is no guarantee, but
    if connect() targets are very different, end result is we leave
    more ports available to bind(), and we spread them all over the range,
    lowering time for both connect() and bind() to find a slot.
    
    This strategy only works well if /proc/sys/net/ipv4/ip_local_port_range
    is even, ie if start/end values have different parity.
    
    Therefore, default /proc/sys/net/ipv4/ip_local_port_range was changed to
    32768 - 60999 (instead of 32768 - 61000)
    
    There is no change on security aspects here, only some poor hashing
    schemes could be eventually impacted by this change.
    
    [1] : The odd/even property depends on ip_local_port_range values parity
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    07f4c900
inet_hashtables.c 16.7 KB