netdev - Re: gso: Attempt to handle mega-GRO packets

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Message-ID: <1383809490.9412.50.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 06 Nov 2013 23:31:30 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>,
	christoph.paasch@...ouvain.be, netdev@...r.kernel.org,
	hkchu@...gle.com, mwdalton@...gle.com
Subject: Re: gso: Attempt to handle mega-GRO packets

On Thu, 2013-11-07 at 15:15 +0800, Herbert Xu wrote:

> So what in our stack violates this assumption? We've never handled
> arbitrary frag_lists in GSO and I see no reason why we need to start
> doing that now.

I do see this, skb_segment() is generic.

> 
> Also GRO was designed to only merge packets that satisfy these
> assumptions so that through GSO the original packets can be
> recovered without losing end-to-end connectivity.  This is really
> important for routers/switches.

I think we all agree on this, and we should keep this property.

The point is : skb_segment() is not tied to GRO anymore.

My patch handles virtio_net just fine, I see nothing really malicious in
virtio_net.

In particular, each skb found in the frag_list can be of any size,
and not an exact MSS multiple.

I see frag_list as a way to extend skb capacity, not as something
tied to GRO/GSO.

I worked last year so that we no longer had the frag_list being used in
GRO stack. frag_list was no longer needed, thanks to skb->head_frag

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