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

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Message-ID: <2f1509fa-649f-cfc8-7c41-94cd9979ccae@gmail.com>
Date:   Thu, 13 Dec 2018 03:16:25 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Florian Westphal <fw@...len.de>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org, cpaasch@...le.com, peter.krystad@...el.com,
        mathew.j.martineau@...ux.intel.com
Subject: Re: [PATCH net-next 02/13] sk_buff: add skb extension infrastructure



On 12/13/2018 03:03 AM, Florian Westphal wrote:
> Eric Dumazet <eric.dumazet@...il.com> wrote:
>>
>>
>> On 12/13/2018 02:39 AM, Florian Westphal wrote:
>>>
>>> Thats whats done in the MPTCP out-of-tree implementation, but I don't
>>> think its needed.
>>>
>>> It could just delete the extension before ->queue_xmit() AFAIU.
>>
>> 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 :/