netdev - Re: [PATCH bpf 6/6] net: enetc: use truesize as XDP RxQ info frag

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Message-ID: <20260206185735.787fb0e5@kernel.org>
Date: Fri, 6 Feb 2026 18:57:35 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Larysa Zaremba <larysa.zaremba@...el.com>
Cc: Vladimir Oltean <vladimir.oltean@....com>, <bpf@...r.kernel.org>,
 "Claudiu Manoil" <claudiu.manoil@....com>, Wei Fang <wei.fang@....com>,
 Clark Wang <xiaoning.wang@....com>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, "Paolo Abeni" <pabeni@...hat.com>, Tony Nguyen
 <anthony.l.nguyen@...el.com>, "Przemek Kitszel"
 <przemyslaw.kitszel@...el.com>, Alexei Starovoitov <ast@...nel.org>, Daniel
 Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, "Stanislav Fomichev"
 <sdf@...ichev.me>, Andrii Nakryiko <andrii@...nel.org>, "Martin KaFai Lau"
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu
 <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP Singh
 <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>, Simon Horman <horms@...nel.org>, Shuah Khan
 <shuah@...nel.org>, Alexander Lobakin <aleksander.lobakin@...el.com>,
 "Maciej Fijalkowski" <maciej.fijalkowski@...el.com>, "Bastien Curutchet
 (eBPF Foundation)" <bastien.curutchet@...tlin.com>, Tushar Vyavahare
 <tushar.vyavahare@...el.com>, Jason Xing <kernelxing@...cent.com>, "Ricardo
 B. Marli√®re" <rbm@...e.com>, Eelco Chaudron
 <echaudro@...hat.com>, Lorenzo Bianconi <lorenzo@...nel.org>, "Toke
 Hoiland-Jorgensen" <toke@...hat.com>, <imx@...ts.linux.dev>,
 <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <intel-wired-lan@...ts.osuosl.org>, <linux-kselftest@...r.kernel.org>,
 Aleksandr Loktionov <aleksandr.loktionov@...el.com>
Subject: Re: [PATCH bpf 6/6] net: enetc: use truesize as XDP RxQ info
 frag_size

On Fri, 6 Feb 2026 09:36:21 +0100 Larysa Zaremba wrote:
> > FWIW my feeling is that instead of nickel and diming leftover space 
> > in the frags if someone actually cared about growing mbufs we should
> > have the helper allocate a new page from the PP and append it to the
> > shinfo. Much simpler, "infinite space", and works regardless of the
> > driver. I don't mean that to suggest you implement it, purely to point
> > out that I think nobody really uses positive offsets.. So we can as
> > well switch more complicated drivers back to xdp_rxq_info_reg().
> 
> As Vladimir has mentioned, if the driver does not use header split, frags will 
> have a tailroom of a size of skb_shared_info, so tail growing does work in 
> practice.
> 
> Allocating a page_pool buffer (given XDP queue has one attached) is certainly an 
> option, although I am not sure if anyone needs it. Furthermore, growing tail 
> would still fail for a single-buf case.

sbuf is a different code path, sbuf has precise frame_sz per frame,
not a single value in rxq, no? Don't mean to argue, just making sure
my mental model is correct ;)