netdev - Re: LRO num of frags limit

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Date:	Tue, 16 Sep 2008 11:40:17 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Eli Cohen <eli@....mellanox.co.il>
Cc:	netdev@...r.kernel.org, themann@...ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: LRO num of frags limit

On Tue, 2008-09-16 at 10:36 +0300, Eli Cohen wrote:
> Hi,
> 
> looking at the LRO code, at __lro_proc_segment(), it seems that the
> network driver can configure lro_mgr->max_aggr to any value it wants
> while the number of fragments aggregated must not exceed MAX_SKB_FRAGS

Correct.

> (since we only use a single SKB to aggregate fragments, allocated by
> lro_gen_skb()). Moreover, even if the driver does limit
> lro_mgr->max_aggr to MAX_SKB_FRAGS, it might still cause overflow
> since subsequent aggregations are done at lro_add_frags() which is
> called before checking whether we overflow.

So you must set max_aggr to
MAX_SKB_FRAGS - max number of frags added at once + 1.

> If the above observation is correct, I can send a patch.

I would be interested to see that, anyway.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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