netdev - Re: [PATCH net-next v3 3/4] net: use skb->priority for overloading skb->dropcount and skb->reserved

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Date:	Tue, 24 Feb 2015 12:10:40 +0200
From:	Eyal Birger <eyal.birger@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Shmulik Ladkani <shmulik.ladkani@...il.com>,
	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3 3/4] net: use skb->priority for overloading
 skb->dropcount and skb->reserved_tailroom instead of skb->mark

On Tue, Feb 24, 2015 at 8:58 AM, Eyal Birger <eyal.birger@...il.com> wrote:
> On Mon, Feb 23, 2015 at 11:48 PM, David Miller <davem@...emloft.net> wrote:
>> From: Shmulik Ladkani <shmulik.ladkani@...il.com>
>> Date: Mon, 23 Feb 2015 20:56:33 +0200
>>
>>> May I suggest to unalias 'mark' out of the union?
>>
>> Only in exchange for finding a way to remove completely another object
>> of the same size from sk_buff.
>>
>> I refuse to let it grow any more, it's already way too big.
>
> I agree that aliasing skb->priority with skb->dropcount and
> skb->reserved_tailroom is
> less than optimal.
>
> I can suggest an alternative patch following Eric Dumazet's suggestion in which
> skb->dropcount is removed and skb->cb[] is used instead for keeping dropcount.
>
> That would require protocol family implementations to access skb->cb[]
> via a common
> accessor or use a common offset #define from the start of skb->cb[].
>

Well, gave it a shot... it looks like several protocol families
(packet, rxrpc, bluetooth) do not
have room in skb->cb[] for the dropcount - at least on my 64 bit machine.
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