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

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Message-ID: <20220211141624.14d6f4ac@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 11 Feb 2022 14:16:24 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Coco Li <lixiaoyan@...gle.com>
Subject: Re: [PATCH net-next 4/4] net: introduce a config option to tweak
 MAX_SKB_FRAGS

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?