From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: [PATCH net-next] tcp: reduce memory needs of out of order queue Date: Fri, 14 Oct 2011 09:19:51 +0200 Message-ID: <1318576791.2533.99.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev To: David Miller Return-path: Received: from mail-wy0-f174.google.com ([74.125.82.174]:65190 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932100Ab1JNHT5 (ORCPT ); Fri, 14 Oct 2011 03:19:57 -0400 Received: by wyg34 with SMTP id 34so2674715wyg.19 for ; Fri, 14 Oct 2011 00:19:56 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: Many drivers allocates big skb to store a single TCP frame. (WIFI drivers, or NIC using PAGE_SIZE fragments) Its now common to get skb->truesize bigger than 4096 to store a ~1500 bytes TCP frame. TCP sessions with large RTT and packet losses can fill their Out Of Order queue with such oversized skbs, and hit their sk_rcvbuf limit, starting a pruning of complete OFO queue, without giving chance to receive the missing packet(s) and moving skbs from OFO to receive queue. This patch adds skb_reduce_truesize() helper, and uses it for all skbs queued into OFO queue. Spending some time to perform a copy is worth the pain, since it permits SACK processing to have a chance to complete over the RTT barrier. This greatly improves user experience, without added cost on fast path. Signed-off-by: Eric Dumazet --- net/ipv4/tcp_input.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index c1653fe..1d10edb 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4426,6 +4426,25 @@ static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size) return 0; } +/* + * Caller want to reduce memory needs before queueing skb + * The (expensive) copy should not be be done in fast path. + */ +static struct sk_buff *skb_reduce_truesize(struct sk_buff *skb) +{ + if (skb->truesize > 2 * SKB_TRUESIZE(skb->len)) { + struct sk_buff *nskb; + + nskb = skb_copy_expand(skb, skb_headroom(skb), 0, + GFP_ATOMIC | __GFP_NOWARN); + if (nskb) { + __kfree_skb(skb); + skb = nskb; + } + } + return skb; +} + static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) { struct tcphdr *th = tcp_hdr(skb); @@ -4553,6 +4572,11 @@ drop: SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n", tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); + /* Since this skb might stay on ofo a long time, try to reduce + * its truesize (if its too big) to avoid future pruning. + * Many drivers allocate large buffers even to hold tiny frames. + */ + skb = skb_reduce_truesize(skb); skb_set_owner_r(skb, sk); if (!skb_peek(&tp->out_of_order_queue)) {