On Thu, 2012-10-04 at 18:50 +0200, Eric Dumazet wrote: > > Since skb_recycle() resets skb->data using (skb->head + NET_SKB_PAD), a > > recycled skb going multiple times through a path that needs to expand > > skb head will get bigger and bigger each time, and you eventually end up > > with an allocation failure. > > > > Because there is not enough headroom ?
yes, on ipv6 forward path the default NET_SKB_PAD is too small, so each packet forwarded has its headroom expanded, it is then recycled and gets its original default headroom back, then it gets forwarded, expanded, ... > > An idea to fix this would be to pass needed skb size to skb_resize() and > > set skb->data to MIN(NET_SKB_PAD, (skb->end - skb->head - skb_size) / 2) > > I am trying to decode this but I cant ;) > > What is skb_resize() ? > and what do you mean setting skb->data to MIN(NET_SKB_PAD, (skb->end - > skb->head - skb_size) / 2) > > Care to explain again your idea ? damn typo, I meant skb_recycle(), and my formula is probably wrong. skb_size is passed to skb_recycle_check() to ensure the skb is at least that big. The idea is it to pass the same value to skb_recycle(), allowing it to set skb->data somewhat at the middle of skb head space (after honoring NET_SKB_PAD), that way the recycled skb won't have its head expanded again if it takes the same path. -- Maxime -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
