Re: [Xen-devel] Is: SKB_MAX_LEN bites again. Was: Re: bug disabling guest interface

[ANNIE LI <annie.li@xxxxxxxxxx>]

On 2013-3-9 20:53, Sander Eikelenboom wrote:
> Saturday, March 9, 2013, 3:57:16 AM, you wrote:
>
> > > > - change MAX_SKB_FRAGS to 19 to accommodate all guests
> > Changing MAX_SKB_FRAGS is *not* an option upstream. This might be a
> > useful local hack but we need to drop the idea as a long term fix.
> > > Ugh. The negotiations between host and guest is probably the best
> > > choice. The issues you are going to hit are that you might need
> > > to redo the skbs to match what the frontend's max is.
> > IMHO the right fix is for netback to coalesce as it copies from the
> > frontend if it needs to do so, it is copying anyway so it should be
> > cheap enough. I thought we had discussed this and someone was working on
> > implementing it. If not Annie then perhaps it was Matt or Siva (both now
> > CC'd)
> > If necessary netback could even allocate a larger order head in order to
> > accommodate very large packets, but I don't expect that to be required
> > to fix the immediate issue we are seeing (but gives flexibility)
> > This should get us past the immediate issue of the upstream change from
> 18->>16  frags thing. Longer term the negotiation will allow us to avoid
> > future incompatible changes in guest and host network stacks, as well as
> > allowing frontends on other OSes (in particular Windows) to havea better
> > chance of to DTRT.
> >
> > > Annie, Wei, Ian - were there some RFC patches floating around
> > > for this?
> I think you refer to this thread ?
>
> http://lists.xen.org/archives/html/xen-devel/2013-01/msg00198.html
>
> And i see the annie's patch and my response haven't made the list because annie 
> dropped xen-devel from the response.
> I will forward them ..
Hi Sander,

This is a patch in which I tried to do some fix in netfront, the thread 
you mentioned is facing the same issue with this one.
Thanks
Annie
> --
> Sander
>
>
>
>
>
> > > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > > > index 821c7f4..82de0f5 100644
> > > > --- a/include/linux/skbuff.h
> > > > +++ b/include/linux/skbuff.h
> > > > @@ -143,8 +143,8 @@ struct sk_buff;
> > > >    * Since GRO uses frags we allocate at least 16 regardless of page
> > > >    * size.
> > > >    */
> > > > -#if (65536/PAGE_SIZE + 1)<  16
> > > > -#define MAX_SKB_FRAGS 16UL
> > > > +#if (65536/PAGE_SIZE + 1)<  19
> > > > +#define MAX_SKB_FRAGS 19UL
> > > >   #else
> > > >   #define MAX_SKB_FRAGS (65536/PAGE_SIZE + 1)
> > > >   #endif
> > > >
> > > >
> > > > _______________________________________________
> > > > Xen-devel mailing list
> > > > Xen-devel@xxxxxxxxxxxxx
> > > > http://lists.xen.org/xen-devel
>
>
>
>
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