netdev - Re: [PATCH net-next 4/4] net: introduce a config option to tweak MAX_SKB

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Date:   Fri, 11 Feb 2022 18:41:33 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>, Coco Li <lixiaoyan@...gle.com>
Subject: Re: [PATCH net-next 4/4] net: introduce a config option to tweak MAX_SKB_FRAGS

On Fri, Feb 11, 2022 at 2:16 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 10 Feb 2022 09:55:57 -0800 Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@...gle.com>
> >
> > Currently, MAX_SKB_FRAGS value is 17.
> >
> > For standard tcp sendmsg() traffic, no big deal because tcp_sendmsg()
> > attempts order-3 allocations, stuffing 32768 bytes per frag.
> >
> > But with zero copy, we use order-0 pages.
>
> If I read this right BIG TCP works but for zc cases, without this patch,
> but there's little point to applying this patch without BIG TCP.
>
> Shouldn't the BIG TCP work go in first and then we'll worry about how
> many frags can each skb carry?

This is orthogonal really.

My guess is that most people do not use TCP RX zerocopy, apart from Google ?