From: David Miller <davem@davemloft.net>
To: eric.dumazet@gmail.com
Cc: nbowler@elliptictech.com, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org
Subject: Re: [PATCH] ip : take care of last fragment in ip_append_data
Date: Tue, 21 Sep 2010 16:38:56 -0700 (PDT) [thread overview]
Message-ID: <20100921.163856.71124744.davem@davemloft.net> (raw)
In-Reply-To: <1285049787.2323.797.camel@edumazet-laptop>
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 21 Sep 2010 08:16:27 +0200
> [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 <eric.dumazet@gmail.com>
This patch largely looks fine, but:
1) I want to find out where that "17" tailer_len comes from before
applying this, that doesn't make any sense.
2) Even with #1 addressed, this function is tricky so I want to review
this patch some more.
next prev parent reply other threads:[~2010-09-21 23:38 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-20 17:44 Regression, bisected: reference leak with IPSec since ~2.6.31 Nick Bowler
2010-09-20 18:20 ` Eric Dumazet
2010-09-20 19:52 ` Nick Bowler
2010-09-20 20:00 ` David Miller
2010-09-20 21:23 ` Nick Bowler
2010-09-20 20:17 ` Eric Dumazet
2010-09-20 21:31 ` Eric Dumazet
2010-09-21 6:16 ` [PATCH] ip : take care of last fragment in ip_append_data Eric Dumazet
2010-09-21 23:38 ` David Miller [this message]
2010-09-22 4:44 ` Eric Dumazet
2010-09-22 4:53 ` David Miller
2010-09-24 21:42 ` David Miller
2010-09-21 9:12 ` Regression, bisected: reference leak with IPSec since ~2.6.31 Jarek Poplawski
2010-09-21 9:21 ` Eric Dumazet
2010-09-21 9:38 ` Jarek Poplawski
2010-09-21 9:55 ` Eric Dumazet
2010-09-21 10:07 ` Eric Dumazet
2010-09-21 10:48 ` Jarek Poplawski
2010-09-21 11:58 ` Eric Dumazet
2010-09-21 12:39 ` Jarek Poplawski
2010-09-21 14:05 ` Nick Bowler
2010-09-21 14:16 ` [PATCH] ip : fix truesize mismatch in ip fragmentation Eric Dumazet
2010-09-21 15:58 ` [PATCH v3] ip: " Eric Dumazet
2010-09-21 16:26 ` Henrique de Moraes Holschuh
2010-09-21 16:31 ` Eric Dumazet
2010-09-21 18:09 ` Henrique de Moraes Holschuh
2010-09-21 19:24 ` David Miller
2010-09-21 23:06 ` Henrique de Moraes Holschuh
2010-09-21 17:50 ` Jarek Poplawski
2010-09-21 18:47 ` Eric Dumazet
2010-09-21 19:21 ` Jarek Poplawski
2010-09-21 22:15 ` David Miller
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