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authorEric Dumazet <eric.dumazet@gmail.com>2012-03-18 11:07:47 +0000
committerDavid S. Miller <davem@davemloft.net>2012-03-19 16:53:08 -0400
commitc8628155ece363487b57d33441ea0359018c0fa7 (patch)
treea3a4e89d3f66208f4145bb2ed401e464474a8d9f /net
parente86b291962cbf477e35d983d312428cf737bc0f8 (diff)
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')
-rw-r--r--net/ipv4/proc.c1
-rw-r--r--net/ipv4/tcp_input.c19
2 files changed, 19 insertions, 1 deletions
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 02d61079f08b..8af0d44e4e22 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -257,6 +257,7 @@ static const struct snmp_mib snmp4_net_list[] = {
SNMP_MIB_ITEM("TCPReqQFullDoCookies", LINUX_MIB_TCPREQQFULLDOCOOKIES),
SNMP_MIB_ITEM("TCPReqQFullDrop", LINUX_MIB_TCPREQQFULLDROP),
SNMP_MIB_ITEM("TCPRetransFail", LINUX_MIB_TCPRETRANSFAIL),
+ SNMP_MIB_ITEM("TCPRcvCoalesce", LINUX_MIB_TCPRCVCOALESCE),
SNMP_MIB_SENTINEL
};
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)