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: <20251107015902.GA3021@system.software.com>
Date: Fri, 7 Nov 2025 10:59:02 +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 Thu, Nov 06, 2025 at 05:33:20PM -0800, Jakub Kicinski wrote:
> On Mon,  3 Nov 2025 16:51:07 +0900 Byungchul Park wrote:
> > However, for net_iov not
			  ^
		*not* page-backed

> > page-backed, the identification cannot be based on the page_type.
> > Instead, nmdesc->pp can be used to see if it belongs to a page pool, by
> > making sure nmdesc->pp is NULL otherwise.
> 
> Please explain why. Isn't the type just a value in a field?
> Which net_iov could also set accordingly.. ?

page_type field is in 'struct page', so 'struct page' can check the type.

However, the field is not in 'struct net_iov', so 'struct net_iov' that
is not backed by page, cannot use the type checking to see if it's page
pool'ed instance.

I'm afraid I didn't get your questions.  I will try to explain again
properly if you give me more detail and example about your questions or
requirement.

	Byungchul