Re: [PATCH net-next] tcp: add tcp_add_backlog()

On Mon, Aug 29, 2016 at 12:22:37PM -0700, Eric Dumazet wrote:

On Mon, 2016-08-29 at 15:51 -0300, Marcelo Ricardo Leitner wrote:

quoted

	skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));

Shouldn't __pskb_pull_tail() already fix this? As it seems the expected
behavior and it would have a more global effect then. For drivers not
using copybreak, that's needed here anyway, but maybe this help other
protocols/situations too.

That would be difficult, because some callers do their own truesize
tacking (skb might be attached/charged to a socket, so changing
skb->truesize would need to adjust the amount that was charged)

This is why pskb_expand_head() is not allowed to mess with skb->truesize
(but in the opposite way, since we probably are increasing
skb->truesize)

Ok, makes sense.

Not sure it is worth the pain in fast path, where packets are consumed
so fast that their skb->truesize being slightly over estimated is not an
issue.

Good point, thanks.