Re: [PATCH net-next 02/13] sk_buff: add skb extension infrastructure

Eric Dumazet [off-list ref] wrote:

On 12/13/2018 03:03 AM, Florian Westphal wrote:

quoted

Eric Dumazet [off-list ref] wrote:

quoted

So, cloning would do an refcount_inc(), and deleting the extension would do an refcount_dec_and_test() ?

That is what I called an extra pair of atomic operations.

If it replaces 1:1 current mptcp skb->private out-of-tree storage, then
yes.

One day I will write a book on the number of atomic operations done on a TCP sendmsg() system call :/

Just to clarify: mptcp skb->private out-of-tree storage is maintened
using atomic_ops too, so if its converted 1:1 nothing changes in the
*mptcp tree*.

If its possible to re-arrange the out-of-tree so that it doesn't need
that (only used while skb is not cloned), then the same applies to the
extension conversion.

So this, as far as *this series* is concerened, a "future problem" that
may or may not exist.