netdev - Re: [3.15-rc3] Bisected: xen-netback mangles packets between two guests on a bridge since merge of "TX grant mapping with SKBTX_DEV

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Date:	Thu, 01 May 2014 10:46:30 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sander Eikelenboom <linux@...elenboom.it>
Cc:	Zoltan Kiss <zoltan.kiss@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	xen-devel@...ts.xen.org
Subject: Re: [3.15-rc3] Bisected: xen-netback mangles packets between two
 guests on a bridge since merge of "TX grant mapping with SKBTX_DEV_ZEROCOPY
 instead of copy" series.

On Thu, 2014-05-01 at 19:39 +0200, Sander Eikelenboom wrote:

> Will run that for both the cases:
>         skb->truesize -= skb->data_len;
>         skb->truesize -= nskb->data_len;
> 
> Let's see what that does different and if that gives an insight in what is going 
> wrong.


Playing with skb->truesize only makes TCP stack reacts faster to bloat,
calling tcp collapse to save memory.

So you might prevent the bug from happening, not really fix root cause.


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