• Eric Dumazet's avatar
    tcp: reduce out_of_order memory use · c8628155
    Eric Dumazet authored
    With increasing receive window sizes, but speed of light not improved
    that much, out of order queue can contain a huge number of skbs, waiting
    to be moved to receive_queue when missing packets can fill the holes.
    
    Some devices happen to use fat skbs (truesize of 4096 + sizeof(struct
    sk_buff)) to store regular (MTU <= 1500) frames. This makes highly
    probable sk_rmem_alloc hits sk_rcvbuf limit, which can be 4Mbytes in
    many cases.
    
    When limit is hit, tcp stack calls tcp_collapse_ofo_queue(), a true
    latency killer and cpu cache blower.
    
    Doing the coalescing attempt each time we add a frame in ofo queue
    permits to keep memory use tight and in many cases avoid the
    tcp_collapse() thing later.
    
    Tested on various wireless setups (b43, ath9k, ...) known to use big skb
    truesize, this patch removed the "packets collapsed in receive queue due
    to low socket buffer" I had before.
    
    This also reduced average memory used by tcp sockets.
    
    With help from Neal Cardwell.
    Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
    Cc: Neal Cardwell <ncardwell@google.com>
    Cc: Yuchung Cheng <ycheng@google.com>
    Cc: H.K. Jerry Chu <hkchu@google.com>
    Cc: Tom Herbert <therbert@google.com>
    Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
    Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    c8628155
tcp_input.c 172 KB