linux-kernel - Re: [PATCH net-next v9 2/8] netmem: introduce utility APIs to use struct netmem

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Message-ID: <4a8b0a45-b829-462c-a655-af0bda10a246@gmail.com>
Date: Sat, 12 Jul 2025 12:59:34 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Byungchul Park <byungchul@...com>, willy@...radead.org,
 netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 kernel_team@...ynix.com, kuba@...nel.org, almasrymina@...gle.com,
 ilias.apalodimas@...aro.org, harry.yoo@...cle.com, hawk@...nel.org,
 akpm@...ux-foundation.org, davem@...emloft.net, john.fastabend@...il.com,
 andrew+netdev@...n.ch, toke@...hat.com, tariqt@...dia.com,
 edumazet@...gle.com, pabeni@...hat.com, saeedm@...dia.com, leon@...nel.org,
 ast@...nel.org, daniel@...earbox.net, david@...hat.com,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, vbabka@...e.cz,
 rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, horms@...nel.org,
 linux-rdma@...r.kernel.org, bpf@...r.kernel.org, vishal.moola@...il.com,
 hannes@...xchg.org, ziy@...dia.com, jackmanb@...gle.com
Subject: Re: [PATCH net-next v9 2/8] netmem: introduce utility APIs to use
 struct netmem_desc

On 7/10/25 09:28, Byungchul Park wrote:
...> +
>   static inline struct net_iov *netmem_to_net_iov(netmem_ref netmem)
>   {
>   	if (netmem_is_net_iov(netmem))
> @@ -314,6 +340,21 @@ static inline netmem_ref netmem_compound_head(netmem_ref netmem)
>   	return page_to_netmem(compound_head(netmem_to_page(netmem)));
>   }
>   
> +#define nmdesc_to_page(nmdesc)		(_Generic((nmdesc),		\
> +	const struct netmem_desc * :	(const struct page *)(nmdesc),	\
> +	struct netmem_desc * :		(struct page *)(nmdesc)))

Considering that nmdesc is going to be separated from pages and
accessed through indirection, and back reference to the page is
not needed (at least for net/), this helper shouldn't even exist.
And in fact, you don't really use it ...

> +static inline struct netmem_desc *page_to_nmdesc(struct page *page)
> +{
> +	VM_BUG_ON_PAGE(PageTail(page), page);
> +	return (struct netmem_desc *)page;
> +}
> +
> +static inline void *nmdesc_address(struct netmem_desc *nmdesc)
> +{
> +	return page_address(nmdesc_to_page(nmdesc));
> +}

... That's the only caller, and nmdesc_address() is not used, so
just nuke both of them. This helper doesn't even make sense.

Please avoid introducing functions that you don't use as a general
rule.

> +
>   /**
>    * __netmem_address - unsafely get pointer to the memory backing @netmem
>    * @netmem: netmem reference to get the pointer for

-- 
Pavel Begunkov