netdev - Re: [PATCH v2 net-next] net: make skb_set_owner

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Message-Id: <20151102.152610.2091248201809813226.davem@davemloft.net>
Date:	Mon, 02 Nov 2015 15:26:10 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	haiyangz@...rosoft.com, edumazet@...gle.com,
	netdev@...r.kernel.org, kys@...rosoft.com
Subject: Re: [PATCH v2 net-next] net: make skb_set_owner_w() more robust

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 02 Nov 2015 12:09:25 -0800

> On Mon, 2015-11-02 at 20:05 +0000, Haiyang Zhang wrote:
> 
>> Thanks for the fix!
>> For some driver, like ours, this condition may not be "unlikely".
>> So could you remove the "unlikely"?
> 
> No, I wont remove the unlikely.
> 
> Look, your main issue is about reallocating skbs, because of excessive
> dev->needed_headroom.
> 
> An unlikely() mismatch is 1000 times less expensive, why would you
> care ?
> 
> If you really care, fix your driver to not abuse skb->head to store 220
> bytes of private data.

+1

And I've been saying this from the beginning.  This driver must place
it's private per-packet data in another location if it wants optimal
behavior inside of the Linux networking stack.
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