netdev - Re: [PATCH net-next] page_pool: check if nmdesc->pp is !NULL to confirm its usage as pp for net

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Message-ID: <CAHS8izMdwiijk_15NgecSOi_VD3M7cx5M0XLAWxQqWnZgJksjg@mail.gmail.com>
Date: Fri, 17 Oct 2025 08:13:14 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: Byungchul Park <byungchul@...com>, axboe@...nel.dk, kuba@...nel.org, pabeni@...hat.com, 
	davem@...emloft.net, edumazet@...gle.com, horms@...nel.org, hawk@...nel.org, 
	ilias.apalodimas@...aro.org, sdf@...ichev.me, dw@...idwei.uk, 
	ap420073@...il.com, dtatulea@...dia.com, toke@...hat.com, 
	io-uring@...r.kernel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, kernel_team@...ynix.com, max.byungchul.park@...il.com
Subject: Re: [PATCH net-next] page_pool: check if nmdesc->pp is !NULL to
 confirm its usage as pp for net_iov

On Fri, Oct 17, 2025 at 5:32 AM Pavel Begunkov <asml.silence@...il.com> wrote:
>
> On 10/16/25 08:21, Byungchul Park wrote:
> > On Thu, Oct 16, 2025 at 03:36:57PM +0900, Byungchul Park 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.
> >
> > IIRC,
> >
> > Suggested-by: Pavel Begunkov <asml.silence@...il.com>
>
> Pointing out a problem in a patch with a fix doesn't qualify to
> me as "suggested-by", you don't need to worry about that.
>
> Did you get the PGTY bits merged? There is some uneasiness about
> this patch as it does nothing good by itself, it'd be much better
> to have it in a series finalising the page_pool conversion. And
> I don't think it simplify merging anyhow, hmm?
>

+1 honestly.

If you want to 'extract the networking bits' into its own patch,  let
it be a patch series where this is a patch doing pre-work, and the
next patches in the series are adding the page_flag.

I don't want added netmem_is_net_iov checks unnecessarily tbh. These
checks are bad and only used when absolutely necessary, so let the
patch series that adds them also do something useful (i.e. add the
page flag), if possible. But I honestly think this patch was almost
good as-is:

https://lore.kernel.org/all/20250729110210.48313-1-byungchul@sk.com/

You just need to address Jakub's review comments and resubmit? Not
sure why we want to split, but if you want let it be a patch series
that does something useful.

-- 
Thanks,
Mina