diff options
| author | Eric Dumazet <eric.dumazet@gmail.com> | 2012-03-18 11:07:47 +0000 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2012-03-19 16:53:08 -0400 |
| commit | c8628155ece363487b57d33441ea0359018c0fa7 (patch) | |
| tree | a3a4e89d3f66208f4145bb2ed401e464474a8d9f /net/ipv4/tcp_input.c | |
| parent | e86b291962cbf477e35d983d312428cf737bc0f8 (diff) | |
| download | linux-c8628155ece363487b57d33441ea0359018c0fa7.tar.bz2 | |
tcp: reduce out_of_order memory use
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: Eric 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: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_input.c')
| -rw-r--r-- | net/ipv4/tcp_input.c | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index fa7de12c4a52..e886e2f7fa8d 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4484,7 +4484,24 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb) end_seq = TCP_SKB_CB(skb)->end_seq; if (seq == TCP_SKB_CB(skb1)->end_seq) { - __skb_queue_after(&tp->out_of_order_queue, skb1, skb); + /* Packets in ofo can stay in queue a long time. + * Better try to coalesce them right now + * to avoid future tcp_collapse_ofo_queue(), + * probably the most expensive function in tcp stack. + */ + if (skb->len <= skb_tailroom(skb1) && !tcp_hdr(skb)->fin) { + NET_INC_STATS_BH(sock_net(sk), + LINUX_MIB_TCPRCVCOALESCE); + BUG_ON(skb_copy_bits(skb, 0, + skb_put(skb1, skb->len), + skb->len)); + TCP_SKB_CB(skb1)->end_seq = end_seq; + TCP_SKB_CB(skb1)->ack_seq = TCP_SKB_CB(skb)->ack_seq; + __kfree_skb(skb); + skb = NULL; + } else { + __skb_queue_after(&tp->out_of_order_queue, skb1, skb); + } if (!tp->rx_opt.num_sacks || tp->selective_acks[0].end_seq != seq) |