linux-kernel - Re: ixgbe truesize underestimation fix missing?

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Date:	Mon, 13 Feb 2012 11:46:00 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christian Brunner <christian@...nner-muc.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: ixgbe truesize underestimation fix missing?

Le lundi 13 février 2012 à 10:57 +0100, Christian Brunner a écrit :
> 2012/2/13 Eric Dumazet <eric.dumazet@...il.com>:
> > Le lundi 13 février 2012 à 09:45 +0100, Christian Brunner a écrit :
> >> Back in Oktober, there was a patch by Eric Dumazet for the ixgbe
> >> driver to fix the skb truesize underestimation (commit
> >> 98130646770db42cd14c44ba0d7f2d0eb8078820). It changed only one line in
> >> ixgbe_main.c:
> >>
> >> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> >> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> >> @@ -1326,7 +1326,7 @@ static bool ixgbe_clean_rx_irq(struct
> >> ixgbe_q_vector *q_vector,
> >>                         skb->len += upper_len;
> >>                         skb->data_len += upper_len;
> >> -                       skb->truesize += upper_len;
> >> +                       skb->truesize += PAGE_SIZE / 2;
> >>                 }                 i++;
> >>
> >>
> >> But when I look at the current code (3.2.5 or 3.3rc), skb->truesize is
> >> still increased by the same value as skb->data_len.
> >>
> >> 1228         skb->data_len += frag_list_size;
> >> 1229         skb->truesize += frag_list_size;
> >>
> >> Is it posible that there was a merge conflict, or am I missing something here?
> >
> > Maybe a problem in your local tree ?
> >
> > I can see proper fix in current tree.
> 
> Ahh... Sorry. I Was looking at the wrong place -
> ixgbe_transform_rsc_queue() has code that is quite similar.
> 
> This however makes me wonder, why we are using "skb->len" for
> increasing the frag_list_size, as skb->len might be smaller than
> skb->truesize.
> 
> Shouldn't we add a frag_list_truesize counter in ixgbe_transform_rsc_queue() ?

Probably, but you should raise this discussion on netdev, not lkml, and
based on net-next tree, as ixgbe_transform_rsc_queue() doesnt exist
anymore ;)

Note that in this case (RSC) truesize underestimation is small since
typical segment size is very close to PAGE_SIZE/2



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