netdev - Re: [PATCH v2 net-next 07/14] ipv6: add GRO_IPV6_MAX

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Message-ID: <CANn89i+DTORA9B4TPoqfZifCns4dChJAGFXtunU5yg8efBM5aA@mail.gmail.com>
Date:   Fri, 4 Mar 2022 09:16:32 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     David Ahern <dsahern@...nel.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>, Coco Li <lixiaoyan@...gle.com>,
        Alexander Duyck <alexanderduyck@...com>
Subject: Re: [PATCH v2 net-next 07/14] ipv6: add GRO_IPV6_MAX_SIZE

On Thu, Mar 3, 2022 at 8:37 PM David Ahern <dsahern@...nel.org> wrote:
>
> On 3/3/22 11:16 AM, Eric Dumazet wrote:
> > From: Coco Li <lixiaoyan@...gle.com>
> >
> > Enable GRO to have IPv6 specific limit for max packet size.
> >
> > This patch introduces new dev->gro_ipv6_max_size
> > that is modifiable through ip link.
> >
> > ip link set dev eth0 gro_ipv6_max_size 185000
> >
> > Note that this value is only considered if bigger than
> > gro_max_size, and for non encapsulated TCP/ipv6 packets.
> >
>
> What is the point of a max size for the Rx path that is per ingress
> device? If the stack understands the larger packets then the ingress
> device limits should not matter. (yes, I realize the existing code has
> it this way, so I guess this is a historical question)

The point is to opt-in for this feature really.

Some software stack might not be ready yet.

For example, maybe you do not want to let GRO build skbs with
frag_list, because you know these skbs might cause problems later.