From 59104f062435c7816e39ee5ed504a69cb8037f10 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 20 Sep 2010 20:16:27 +0000 Subject: [PATCH] ip: take care of last fragment in ip_append_data While investigating a bit, I found ip_fragment() slow path was taken because ip_append_data() provides following layout for a send(MTU + N*(MTU - 20)) syscall : - one skb with 1500 (mtu) bytes - N fragments of 1480 (mtu-20) bytes (before adding IP header) last fragment gets 17 bytes of trail data because of following bit: if (datalen == length + fraggap) alloclen += rt->dst.trailer_len; Then esp4 adds 16 bytes of data (while trailer_len is 17... hmm... another bug ?) In ip_fragment(), we notice last fragment is too big (1496 + 20) > mtu, so we take slow path, building another skb chain. In order to avoid taking slow path, we should correct ip_append_data() to make sure last fragment has real trail space, under mtu... Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/ip_output.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c index e42762023c27..3551b6dc7419 100644 --- a/net/ipv4/ip_output.c +++ b/net/ipv4/ip_output.c @@ -926,16 +926,19 @@ alloc_new_skb: !(rt->dst.dev->features&NETIF_F_SG)) alloclen = mtu; else - alloclen = datalen + fragheaderlen; + alloclen = fraglen; /* The last fragment gets additional space at tail. * Note, with MSG_MORE we overallocate on fragments, * because we have no idea what fragment will be * the last. */ - if (datalen == length + fraggap) + if (datalen == length + fraggap) { alloclen += rt->dst.trailer_len; - + /* make sure mtu is not reached */ + if (datalen > mtu - fragheaderlen - rt->dst.trailer_len) + datalen -= ALIGN(rt->dst.trailer_len, 8); + } if (transhdrlen) { skb = sock_alloc_send_skb(sk, alloclen + hh_len + 15, -- 2.20.1