• Daniel Borkmann's avatar
    net: sock: adapt SOCK_MIN_RCVBUF and SOCK_MIN_SNDBUF · eea86af6
    Daniel Borkmann authored
    The current situation is that SOCK_MIN_RCVBUF is 2048 + sizeof(struct sk_buff))
    while SOCK_MIN_SNDBUF is 2048. Since in both cases, skb->truesize is used for
    sk_{r,w}mem_alloc accounting, we should have both sizes adjusted via defining a
    TCP_SKB_MIN_TRUESIZE.
    
    Further, as Eric Dumazet points out, the minimal skb truesize in transmit path is
    SKB_TRUESIZE(2048) after commit f07d960d
    
     ("tcp: avoid frag allocation for
    small frames"), and tcp_sendmsg() tries to limit skb size to half the congestion
    window, meaning we try to build two skbs at minimum. Thus, having SOCK_MIN_SNDBUF
    as 2048 can hit a small regression for some applications setting to low
    SO_SNDBUF / SO_RCVBUF. Note that we define a TCP_SKB_MIN_TRUESIZE, because
    SKB_TRUESIZE(2048) adds SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), but in
    case of TCP skbs, the skb_shared_info is part of the 2048 bytes allocation for
    skb->head.
    
    The minor adaption in sk_stream_moderate_sndbuf() is to silence a warning by
    using a typed max macro, as similarly done in SOCK_MIN_RCVBUF occurences, that
    would appear otherwise.
    Suggested-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
    Signed-off-by: default avatarDaniel Borkmann <dborkman@redhat.com>
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    eea86af6