netdev - Re: [PATCH net 0/9] rxrpc: Fix use of skb_cow

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Date:   Fri, 23 Aug 2019 09:52:28 +0100
From:   David Howells <dhowells@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     dhowells@...hat.com, netdev@...r.kernel.org,
        linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 0/9] rxrpc: Fix use of skb_cow_data()

David Miller <davem@...emloft.net> wrote:

> Why don't you just do an skb_unshare() at the beginning when you know that
> you'll need to do that?

I was trying to defer any copying to process context rather than doing it in
softirq context to spend less time in softirq context - plus that way I can
use GFP_NOIO (kafs) or GFP_KERNEL (direct AF_RXRPC socket) rather than
GFP_ATOMIC if the api supports it.

I don't remember now why I used skb_cow_data() rather than skb_unshare() - but
it was probably because the former leaves the sk_buff object itself intact,
whereas the latter replaces it.  I can switch to using skb_unshare() instead.

Question for you: how likely is a newly received buffer, through a UDP socket,
to be 'cloned'?

David