• Eric Dumazet's avatar
    tcp: avoid frag allocation for small frames · f07d960d
    Eric Dumazet authored
    
    
    tcp_sendmsg() uses select_size() helper to choose skb head size when a
    new skb must be allocated.
    
    If GSO is enabled for the socket, current strategy is to force all
    payload data to be outside of headroom, in PAGE fragments.
    
    This strategy is not welcome for small packets, wasting memory.
    
    Experiments show that best results are obtained when using 2048 bytes
    for skb head (This includes the skb overhead and various headers)
    
    This patch provides better len/truesize ratios for packets sent to
    loopback device, and reduce memory needs for in-flight loopback packets,
    particularly on arches with big pages.
    
    If a sender sends many 1-byte packets to an unresponsive application,
    receiver rmem_alloc will grow faster and will stop queuing these packets
    sooner, or will collapse its receive queue to free excess memory.
    
    netperf -t TCP_RR results are improved by ~4 %, and many workloads are
    improved as well (tbench, mysql...)
    Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    f07d960d