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: <20251114172318.3aafc438@kernel.org>
Date: Fri, 14 Nov 2025 17:23:18 -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 Wed, 12 Nov 2025 16:41:18 +0900 Byungchul Park wrote:
> diff --git a/include/net/netmem.h b/include/net/netmem.h
> index 651e2c62d1dd..b42d75ecd411 100644
> --- a/include/net/netmem.h
> +++ b/include/net/netmem.h
> @@ -114,10 +114,21 @@ struct net_iov {
>  			atomic_long_t pp_ref_count;
>  		};
>  	};
> +
> +	unsigned int page_type;
>  	struct net_iov_area *owner;
>  	enum net_iov_type type;

type is 4B already in net-next, so you may want to reorder @type 
with @owner to avoid a hole and increasing the struct size. 
Other than that LGTM!

struct net_iov {
	union {
		struct netmem_desc desc;                 /*     0    48 */
		struct {
			long unsigned int _flags;        /*     0     8 */
			long unsigned int pp_magic;      /*     8     8 */
			struct page_pool * pp;           /*    16     8 */
			long unsigned int _pp_mapping_pad; /*    24     8 */
			long unsigned int dma_addr;      /*    32     8 */
			atomic_long_t pp_ref_count;      /*    40     8 */
		};                                       /*     0    48 */
	};                                               /*     0    48 */
	struct net_iov_area *      owner;                /*    48     8 */
	enum net_iov_type          type;                 /*    56     4 */

	/* size: 64, cachelines: 1, members: 3 */
	/* padding: 4 */
};