Re: [PATCH RFC 1/6] skbuff: support per-page destructors in copy_ubufs

From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Fri, 11 May 2012 15:08:37 +0300

On Fri, May 11, 2012 at 11:58:12AM +0100, Ian Campbell wrote:

quoted

On Fri, 2012-05-11 at 10:00 +0100, Ian Campbell wrote:

quoted

I'm seeing copy_ubufs called in my remote NFS test, which I don't
think I expected -- I'll investigate why this is happening today. 

It's tcp_transmit_skb which can (conditionally) call skb_clone
(backtrace below)

Interesting. I didn't realise we clone skbs on data path:
tcp_write_xmit calls tcp_transmit_skb with clone_it flag.
Could someone comment on why we need to clone on good path
like this?

We can't send the original SKB that's linked into the retransmit
queue.  It's linkage must stay secure in that queue.