Re: [PATCH RFC v3 2/5] net: Add NETIF_F_GRO_LIST feature

[Steffen Klassert <steffen.klassert@secunet.com>]

On Wed, Sep 18, 2019 at 08:04:18PM -0600, Subash Abhinov Kasiviswanathan wrote:
> On 2019-09-18 10:10, Willem de Bruijn wrote:
> > On Wed, Sep 18, 2019 at 3:25 AM Steffen Klassert
> > <steffen.klassert@secunet.com> wrote:
> > > 
> > > This adds a new NETIF_F_GRO_LIST feature flag. I will be used
> > > to configure listfyed GRO what will be implemented with some
> > > followup paches.
> > 
> > This should probably simultaneously introduce SKB_GSO_FRAGLIST as well
> > as a BUILD_BUG_ON in net_gso_ok.
> > 
> > Please also in the commit describe the constraints of skbs that have
> > this type. If I'm not mistaken, an skb with either gso_size linear
> > data or one gso_sized frag, followed by a frag_list of the same. With
> > the exception of the last frag_list member, whose mss may be less than
> > gso_size. This will help when reasoning about all the types of skbs we
> > may see at segmentation, as we recently had to do [1]
> > 
> 
> Would it be preferrable to allow any size skbs for the listification.

We currently require a single gso_size because we adjust uh->len
on the head skb to the full size to do correct memory accounting
on the local input path. That is going to be restored with the
gso_size on segmentation.

> Since the original skbs are being restored, single gso_size shoudln't
> be a constraint here.

It might be possible to allow any sized skbs with some extra work, though.