netdev - Re: [PATCH v2 net-next 1/2] net: veth: add page

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Date:   Tue, 25 Apr 2023 19:19:12 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>
CC:     Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <hawk@...nel.org>, <john.fastabend@...il.com>,
        <ast@...nel.org>, <daniel@...earbox.net>
Subject: Re: [PATCH v2 net-next 1/2] net: veth: add page_pool for page
 recycling

On 2023/4/24 21:10, Maciej Fijalkowski wrote:
>>> There was a discussion in the past to reduce XDP_PACKET_HEADROOM to 192B but
>>> this is not merged yet and it is not related to this series. We can address
>>> your comments in a follow-up patch when XDP_PACKET_HEADROOM series is merged.
> 
> Intel drivers still work just fine at 192 headroom and split the page but
> it makes it problematic for BIG TCP where MAX_SKB_FRAGS from shinfo needs

I am not sure why we are not enabling skb_shinfo(skb)->frag_list to support
BIG TCP instead of increasing MAX_SKB_FRAGS, perhaps there was some disscution
about this in the past I am not aware of?

> to be increased. So it's the tailroom that becomes the bottleneck, not the
> headroom. I believe at some point we will convert our drivers to page_pool
> with full 4k page dedicated for a single frame.

Can we use header splitting to ensure there is enough tailroom for
napi_build_skb() or xdp_frame with shinfo?