linux-kernel - Re: [PATCH net-next 05/12] xdp: add generic xdp_build_skb_from

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Message-ID: <1fa637fd-c29e-42ef-9221-023693353d23@intel.com>
Date: Fri, 13 Dec 2024 18:25:45 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
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	<daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, "Andrii
 Nakryiko" <andrii@...nel.org>, Peter Zijlstra <peterz@...radead.org>, "Josh
 Poimboeuf" <jpoimboe@...nel.org>, "Jose E. Marchesi"
	<jose.marchesi@...cle.com>, Toke Høiland-Jørgensen
	<toke@...hat.com>, Magnus Karlsson <magnus.karlsson@...el.com>, "Maciej
 Fijalkowski" <maciej.fijalkowski@...el.com>, Przemek Kitszel
	<przemyslaw.kitszel@...el.com>, Jason Baron <jbaron@...mai.com>, "Casey
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Subject: Re: [PATCH net-next 05/12] xdp: add generic xdp_build_skb_from_buff()

From: Jakub Kicinski <kuba@...nel.org>
Date: Thu, 12 Dec 2024 18:11:29 -0800

> On Wed, 11 Dec 2024 18:26:42 +0100 Alexander Lobakin wrote:
>> +	if (rxq->mem.type == MEM_TYPE_PAGE_POOL && is_page_pool_compiled_in())
>> +		skb_mark_for_recycle(skb);
> 
> I feel like the check for mem.type is unnecessary. I can't think of 
> a driver that would build a skb out of pp pages, and not own pp

But there's no restriction that this function is limited to PP pages.

> refs on those pages. Setting pp_recycle on non-pp skb should be safe,
> even if slightly wasteful.
> 
> Also:
> 
> static inline void skb_mark_for_recycle(struct sk_buff *skb)
> {
> #ifdef CONFIG_PAGE_POOL
> 	skb->pp_recycle = 1;
> #endif
> }
> 
> You don't have to check if PP is complied in explicitly.

Ah I see ._. My idea was to compile-out this check/branch at all when
the PP is not compiled in, but I think that it would be optimized out
anyway by the compiler, so correct.

Thanks,
Olek