netdev - Re: [PATCH v3 net-next 2/2] xdp: add multi-buff support for xdp running in generic mode

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Date: Mon, 11 Dec 2023 09:00:53 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Lorenzo Bianconi <lorenzo@...nel.org>
Cc: Jesper Dangaard Brouer <hawk@...nel.org>, aleksander.lobakin@...el.com,
 netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com, lorenzo.bianconi@...hat.com, bpf@...r.kernel.org,
 toke@...hat.com, willemdebruijn.kernel@...il.com, jasowang@...hat.com,
 sdf@...gle.com
Subject: Re: [PATCH v3 net-next 2/2] xdp: add multi-buff support for xdp
 running in generic mode

On Sat, 9 Dec 2023 20:23:09 +0100 Lorenzo Bianconi wrote:
> Are we going to use these page_pools just for virtual devices (e.g. veth) or
> even for hw NICs? If we do not bound the page_pool to a netdevice I think we
> can't rely on it to DMA map/unmap the buffer, right?

Right, I don't think it's particularly useful for HW NICs.
Maybe for allocating skb heads? We could possibly kill
struct page_frag_1k and use PP page / frag instead.
But not sure how Eric would react :)

> Moreover, are we going to rework page_pool stats first? It seems a bit weird to
> have a percpu struct with a percpu pointer in it, right?

The per-CPU stuff is for recycling, IIRC. Even if PP is for a single
CPU we can still end up freeing packets which used its pages anywhere
in the system.

I don't disagree that we may end up with a lot of stats on a large
system, but seems tangential to per-cpu page pools.