linux-kernel - Re: [RFC mm v5 1/2] page_pool: check nmdesc->pp to see its usage as page pool for net

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Message-ID: <20251107174129.62a3f39c@kernel.org>
Date: Fri, 7 Nov 2025 17:41:29 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Byungchul Park <byungchul@...com>
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Subject: Re: [RFC mm v5 1/2] page_pool: check nmdesc->pp to see its usage as
 page pool for net_iov not page-backed

On Fri, 7 Nov 2025 13:47:08 +0900 Byungchul Park wrote:
> The offset of page_type in struct page cannot be used in struct net_iov
> for the same purpose, since the offset in struct net_iov is for storing
> (struct net_iov_area *)owner.

owner does not have to be at a fixed offset. Can we not move owner 
to _pp_mapping_pad ? Or reorder it with type, enum net_iov_type 
only has 2 values we can smoosh it with page_type easily.

> Yeah, you can tell 'why don't we add the field, page_type, to struct
> net_iov (or struct netmem_desc)' so as to be like:
> 
>   struct net_iov {
> 	union {
> 		struct netmem_desc desc;
> 		struct
> 		{
> 			unsigned long _flags;
> 			unsigned long pp_magic;
> 			struct page_pool *pp;
> 			unsigned long _pp_mapping_pad;
> 			unsigned long dma_addr;
> 			atomic_long_t pp_ref_count;
> +			unsigned int page_type; // add this field newly
> 		};
> 	};
> 	struct net_iov_area *owner; // the same offet of page_type
> 	enum net_iov_type type;
>   };
> 
> I think we can make it anyway but it makes less sense to add page_type
> to struct net_iov, only for PGTY_netpp.
> 
> It'd be better to use netmem_desc->pp for that purpose, IMO.