netdev - Re: [RFC mm v4 1/2] page_pool: check if nmdesc->pp is !NULL to confirm its usage as pp for net

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Message-ID: <CAHS8izPM-s2sL_KyGyUyv37PfZxNLf029DrXpQe8fo637Rn+rw@mail.gmail.com>
Date: Mon, 27 Oct 2025 18:25:38 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Byungchul Park <byungchul@...com>
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Subject: Re: [RFC mm v4 1/2] page_pool: check if nmdesc->pp is !NULL to
 confirm its usage as pp for net_iov

On Thu, Oct 23, 2025 at 12:44 AM Byungchul Park <byungchul@...com> wrote:
>
> ->pp_magic field in struct page is current used to identify if a page
> belongs to a page pool.  However, ->pp_magic will be removed and page
> type bit in struct page e.g. PGTY_netpp should be used for that purpose.
>
> As a preparation, the check for net_iov, that is not page-backed, should
> avoid using ->pp_magic since net_iov doens't have to do with page type.
> Instead, nmdesc->pp can be used if a net_iov or its nmdesc belongs to a
> page pool, by making sure nmdesc->pp is NULL otherwise.
>
> For page-backed netmem, just leave unchanged as is, while for net_iov,
> make sure nmdesc->pp is initialized to NULL and use nmdesc->pp for the
> check.
>
> Signed-off-by: Byungchul Park <byungchul@...com>
> ---
>  net/core/devmem.c      |  1 +
>  net/core/netmem_priv.h |  8 ++++++++
>  net/core/page_pool.c   | 16 ++++++++++++++--
>  3 files changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/devmem.c b/net/core/devmem.c
> index d9de31a6cc7f..f81b700f1fd1 100644
> --- a/net/core/devmem.c
> +++ b/net/core/devmem.c
> @@ -291,6 +291,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
>                         niov = &owner->area.niovs[i];
>                         niov->type = NET_IOV_DMABUF;
>                         niov->owner = &owner->area;
> +                       niov->desc.pp = NULL;

Don't you also need to = NULL the niov allocations in io_uring zcrx,
or is that already done? Maybe mention in commit message.

Other than that, looks correct,

Reviewed-by: Mina Almasry <almasrymina@...gle.com>