linux-kernel - Re: [PATCH v3 1/2] gro: decrease size of CB

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Date:   Mon, 13 Mar 2023 10:01:01 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Richard Gobert <richardbgobert@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        dsahern@...nel.org, alexanderduyck@...com, lucien.xin@...il.com,
        lixiaoyan@...gle.com, iwienand@...hat.com, leon@...nel.org,
        ye.xingchen@....com.cn, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] gro: decrease size of CB

On Mon, Mar 13, 2023 at 9:30 AM Richard Gobert <richardbgobert@...il.com> wrote:
>
> The GRO control block (NAPI_GRO_CB) is currently at its maximum size.  This
> commit reduces its size by putting two groups of fields that are used only
> at different times into a union.
>
> Specifically, the fields frag0 and frag0_len are the fields that make up
> the frag0 optimisation mechanism, which is used during the initial parsing
> of the SKB.

Note that these fields could also be stored in some auto variable,
instead of skb.

>
> The fields last and age are used after the initial parsing, while the SKB
> is stored in the GRO list, waiting for other packets to arrive.
>
> There was one location in dev_gro_receive that modified the frag0 fields
> after setting last and age. I changed this accordingly without altering the
> code behaviour.
>
> Signed-off-by: Richard Gobert <richardbgobert@...il.com>
> ---

SGTM, thanks.

Reviewed-by: Eric Dumazet <edumazet@...gle.com>