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

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Date:   Sat, 8 Dec 2018 10:57:58 +0100
From:   Florian Westphal <fw@...len.de>
To:     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

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.