netdev - [PATCH] net: sock: fix TCP_SKB_MIN

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Message-ID: <1372852942.4979.67.camel@edumazet-glaptop>
Date:	Wed, 03 Jul 2013 05:02:22 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, Daniel Borkmann <dborkman@...hat.com>,
	Neal Cardwell <ncardwell@...gle.com>
Subject: [PATCH] net: sock: fix TCP_SKB_MIN_TRUESIZE

From: Eric Dumazet <edumazet@...gle.com>

commit eea86af6b1e18d ("net: sock: adapt SOCK_MIN_RCVBUF and
SOCK_MIN_SNDBUF") forgot the sk_buff alignment taken into account
in __alloc_skb() : skb->truesize = SKB_TRUESIZE(size);

While above commit fixed the sender issue, the receiver is still
dropping the second packet (on loopback device), because the receiver
socket can not really hold two skbs :
First packet truesize already is above sk_rcvbuf, so even TCP coalescing
cannot help.

On a typical 64bit build, each tcp skb truesize is 2304, instead of 2272

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Daniel Borkmann <dborkman@...hat.com>
Cc: Neal Cardwell <ncardwell@...gle.com>
---
Google-Bug-Id: 8124810

 include/net/sock.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index ea6206c..95a5a2c 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2052,7 +2052,7 @@ static inline void sk_wake_async(struct sock *sk, int how, int band)
  * Note: for send buffers, TCP works better if we can build two skbs at
  * minimum.
  */
-#define TCP_SKB_MIN_TRUESIZE	(2048 + sizeof(struct sk_buff))
+#define TCP_SKB_MIN_TRUESIZE	(2048 + SKB_DATA_ALIGN(sizeof(struct sk_buff)))
 
 #define SOCK_MIN_SNDBUF		(TCP_SKB_MIN_TRUESIZE * 2)
 #define SOCK_MIN_RCVBUF		 TCP_SKB_MIN_TRUESIZE


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