netdev - 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: <20251107183712.36228f2a@kernel.org>
Date: Fri, 7 Nov 2025 18:37:12 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Byungchul Park <byungchul@...com>
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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 Sat, 8 Nov 2025 11:24:58 +0900 Byungchul Park wrote:
> On Fri, Nov 07, 2025 at 05:41:29PM -0800, Jakub Kicinski wrote:
> > On Fri, 7 Nov 2025 13:47:08 +0900 Byungchul Park wrote:  
> > > The offset of page_type in struct page cannot be used in struct net_iov
> > > for the same purpose, since the offset in struct net_iov is for storing
> > > (struct net_iov_area *)owner.  
> > 
> > owner does not have to be at a fixed offset. Can we not move owner
> > to _pp_mapping_pad ? Or reorder it with type, enum net_iov_type
> > only has 2 values we can smoosh it with page_type easily.  
> 
> I'm still confused.  I think you probably understand what this work is
> for.  (I've explained several times with related links.)  Or am I
> missing something from your questions?
> 
> I've answered your question directly since you asked, but the point is
> that, struct net_iov will no longer overlay on struct page.
> 
> Instead, struct netmem_desc will be responsible for keeping the pp
> fields while struct page will lay down the resonsibility, once the pp
> fields will be removed from struct page like:

I understand the end goal. I don't understand why patch 1 is a step 
in that direction, and you seem incapable of explaining it. So please
either follow my suggestion on how to proceed with patch 2 without
patch 1 in current form. Or come back when have the full conversion
ready.