netdev - Re: [net-next, RFC, 4/8] net: core: add recycle capabilities on skbs via page

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Message-ID: <72f33f12-9222-cbe7-6ff2-e4b4f86fb17c@gmail.com>
Date:   Sat, 8 Dec 2018 04:29:17 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Florian Westphal <fw@...len.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        ard.biesheuvel@...aro.org, Jason Wang <jasowang@...hat.com>,
        ilias.apalodimas@...aro.org,
        BjörnTöpel <bjorn.topel@...el.com>, w@....eu,
        Saeed Mahameed <saeedm@...lanox.com>,
        mykyta.iziumtsev@...il.com,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [net-next, RFC, 4/8] net: core: add recycle capabilities on skbs
 via page_pool API



On 12/08/2018 01:57 AM, Florian Westphal wrote:
> Jesper Dangaard Brouer <brouer@...hat.com> wrote:
>> From: Ilias Apalodimas <ilias.apalodimas@...aro.org>
>>
>> This patch is changing struct sk_buff, and is thus per-definition
>> controversial.
>>
>> Place a new member 'mem_info' of type struct xdp_mem_info, just after
>> members (flags) head_frag and pfmemalloc, And not in between
>> headers_start/end to ensure skb_copy() and pskb_copy() work as-is.
>> Copying mem_info during skb_clone() is required.  This makes sure that
>> pages are correctly freed or recycled during the altered
>> skb_free_head() invocation.
> 
> I read this to mean that this 'info' isn't accessed/needed until skb
> is freed.  Any reason its not added at the end?
> 
> This would avoid moving other fields that are probably accessed
> more frequently during processing.
> 

But I do not get why the patch is needed.

Adding extra cost for each skb destruction is costly.

I though XDP was all about _not_ having skbs.

Please let's do not slow down the non XDP stack only to make XDP more appealing.