linux-kernel - Re: Regression associated with commit c8628155ece3

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Message-ID: <50369925.3050705@lwfinger.net>
Date:	Thu, 23 Aug 2012 15:57:09 -0500
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Neal Cardwell <ncardwell@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	John W Linville <linville@...driver.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Regression associated with commit c8628155ece3 - "tcp: reduce
 out_of_order memory use"

On 08/22/2012 11:03 PM, Eric Dumazet wrote:
>
> Changing the allocation size removes the problem ? thats really strange.
>
> If you try different sizes in the 9100-30720 range, can you pinpoint the
> failure threshold ?

The allocation size change did not fix the problem. It turned out that 10 tries 
from a secure web page were not enough to trigger this intermittent problem that 
particular test.

Based on DaveM's comment that skb->truesize could be wrong, I tried setting 
truesize after every netdev_alloc_skb() call. Of course, that had no effect. I 
then found https://lkml.org/lkml/2010/11/19/505I, which clearly states why this 
need not be done.

What skb modifications require that truesize be adjusted? The driver never 
resets skb->len or skb->data_len for any buffers, other than setting skb->len to 
zero.

Thanks,

Larry

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