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 08:13:14AM -0700, Mina Almasry wrote:

On Fri, Oct 17, 2025 at 5:32 AM Pavel Begunkov [off-list ref] wrote:

quoted

On 10/16/25 08:21, Byungchul Park wrote:

quoted

On Thu, Oct 16, 2025 at 03:36:57PM +0900, Byungchul Park wrote:

quoted

->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@gmail.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.

Okay.  Then is it possible that one for mm tree and the other for
net-next in the same patch series?  I've never tried patches that way.

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:

Hm.. but the following patch includes both networking changes and mm
changes.  Jakub thinks it should go to mm and I don't know how Andrew
thinks it should be.  It's not clear even to me.

That's why I splitted it into two, and this is the networking part, and
I will post the mm part to mm folks later.  Any suggestions?

	Byungchul

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

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