Re: [Xen-devel] [PATCH net-next] xen-netfront: try linearizing SKB if it occupies too many slots

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 16/05/14 17:47, Eric Dumazet wrote:
> On Fri, 2014-05-16 at 17:29 +0100, Zoltan Kiss wrote:
> > On 16/05/14 16:34, Wei Liu wrote:
> > > It works, at least in this Redis testcase. Could you explain a bit where
> > > this 56000 magic number comes from? :-)
> > >
> > > Presumably I can derive it from some constant in core network code?
> > I guess it just makes more unlikely to have packets with problematic layout. 
> > But the following packet would still fail:
> > linear buffer : 80 bytes, on 2 pages
> > 17 frags, 80 bytes each, each spanning over page boundary.
> How would you build such skbs ? Its _very_ difficult, you have to be
> very very smart to hit this.
I wouldn't build such skbs, I would expect the network stack to create 
such weird things sometimes :)
The goal here is to prepare and handle the worst case scenarios as well.
> Also reducing gso_max_size made sure order-5 allocations would not be
> attempted in this unlikely case.
But reducing the gso_max_size would have a bad impact on the general 
network throughput, right?
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