linux-kernel - Re: [PATCH] mm, page_pool: introduce a new page type for page pool in page type

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Message-ID: <CAHS8izM6h1_qoPnWDHmPiiFj5e_mcJqQFTTLJT9dgBymJuk8rw@mail.gmail.com>
Date: Tue, 22 Jul 2025 15:20:04 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: Byungchul Park <byungchul@...com>, linux-mm@...ck.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kernel_team@...ynix.com, harry.yoo@...cle.com, 
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	linux-rdma@...r.kernel.org
Subject: Re: [PATCH] mm, page_pool: introduce a new page type for page pool in
 page type

On Mon, Jul 21, 2025 at 4:11 AM Pavel Begunkov <asml.silence@...il.com> wrote:
>
> On 7/21/25 06:49, Byungchul Park wrote:
> > Hi,
> >
> > I focused on converting the existing APIs accessing ->pp_magic field to
> > page type APIs.  However, yes.  Additional works would better be
> > considered on top like:
> >
> >     1. Adjust how to store and retrieve dma index.  Maybe network guys
> >        can work better on top.
> >
> >     2. Move the sanity check for page pool in mm/page_alloc.c to on free.
>
> Don't be in a hurry, I've got a branch, but as mentioned before,
> it'll be for-6.18. And there will also be more time for testing.
>
> > This work was inspired by the following link by Pavel:
>
> The idea came from David, let's add
>
> Suggested-by: David Hildenbrand <david@...hat.com>
>
> ...> -
> >   static inline bool netmem_is_pp(netmem_ref netmem)
> >   {
> > -     return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE;
> > +     if (netmem_is_net_iov(netmem))
>
> This needs to return false for tx niovs. Seems like all callers are
> gated on ->pp_recycle, so maybe it's fine, but we can at least
> check pp. Mina, you've been checking tx doesn't mix with rx, any
> opinion on that?
>
> Question to net maintainers, can a ->pp_recycle marked skb contain
> not page pool originated pages or a mix?
>

IIRC last I looked at the code ->pp_recycle technically means it could
be a mix. Technically it means "consider this netmem for pp recycling
when the skb is freed." and non-pp netmems don't get recycled to the
pp obviously, because napi_pp_put_page rejects recycling them.


-- 
Thanks,
Mina