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: <20251117042558.GA18510@system.software.com>
Date: Mon, 17 Nov 2025 13:25:58 +0900
From: Byungchul Park <byungchul@...com>
To: Jakub Kicinski <kuba@...nel.org>
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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, Nov 14, 2025 at 05:23:18PM -0800, Jakub Kicinski wrote:
> 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.

Sure.  Better reorder them.  I will.  Thanks.

	Byungchul

> 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 */
> };