netdev - Re: [PATCH net] net: sched: shrink struct qdisc_skb

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Message-ID: <20140918092628.566eae2b@urahara>
Date:	Thu, 18 Sep 2014 09:26:28 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Or Gerlitz <or.gerlitz@...il.com>,
	Govindarajulu Varadarajan <_govind@....com>,
	Yinghai Lu <yinghai@...nel.org>,
	David Miller <davem@...emloft.net>,
	NetDev <netdev@...r.kernel.org>, ssujith@...co.com,
	gvaradar@...co.com, "Christian Benvenuti (benve)" <benve@...co.com>
Subject: Re: [PATCH net] net: sched: shrink struct qdisc_skb_cb to 28 bytes

On Thu, 18 Sep 2014 08:02:05 -0700
Eric Dumazet <eric.dumazet@...il.com> wrote:

> From: Eric Dumazet <edumazet@...gle.com>
> 
> We cannot make struct qdisc_skb_cb bigger without impacting IPoIB,
> or increasing skb->cb[] size.
> 
> Commit e0f31d849867 ("flow_keys: Record IP layer protocol in
> skb_flow_dissect()") broke IPoIB.
> 
> Only current offender is sch_choke, and this one do not need an
> absolutely precise flow key.
> 
> If we store 17 bytes of flow key, its more than enough. (Its the actual
> size of flow_keys if it was a packed structure, but we might add new
> fields at the end of it later)
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Can we add BUILD_BUG to stop next time something smacks this.
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