Re: [RFC] shrinking struct page (part of page pool)

["Vishal Moola (Oracle)" <vishal.moola@gmail.com>]

On Mon, Apr 14, 2025 at 10:36:27AM +0900, Byungchul Park wrote:
> Hi guys,
> 
> I'm looking at network's page pool code to help 'shrinking struct page'
> project by Matthew Wilcox.  See the following link:
> 
>    https://kernelnewbies.org/MatthewWilcox/Memdescs/Path

Thanks for looking at this!

> My first goal is to remove fields for page pool from struct page like:
> 
>    struct {	/* page_pool used by netstack */
> 	/**
> 	 * @pp_magic: magic value to avoid recycling non
> 	 * page_pool allocated pages.
> 	 */
> 	unsigned long pp_magic;
> 	struct page_pool *pp;
> 	unsigned long _pp_mapping_pad;
> 	unsigned long dma_addr;
> 	atomic_long_t pp_ref_count;
>    };
> 
> Fortunately, many prerequisite works have been done by Mina but I guess
> he or she has done it for other purpose than 'shrinking struct page'.
> 
> I'd like to just finalize the work so that the fields above can be
> removed from struct page.  However, I need to resolve a curiousity
> before starting.

I have a blog that walks you through what I focused on when making
ptdescs. It would benefit you to look at:

https://blogs.oracle.com/linux/post/introducing-memdesc

I'll need to start looking into the networking code before I can
offer any opinions about the specifics of the descriptor though.

>    Network guys already introduced a sperate strcut, struct net_iov,
>    to overlay the interesting fields.  However, another separate struct
>    for system memory might be also needed e.g. struct bump so that
>    struct net_iov and struct bump can be overlayed depending on the
>    source:
> 
>    struct bump {
> 	unsigned long _page_flags;
> 	unsigned long bump_magic;
> 	struct page_pool *bump_pp;
> 	unsigned long _pp_mapping_pad;
> 	unsigned long dma_addr;
> 	atomic_long_t bump_ref_count;
> 	unsigned int _page_type;
> 	atomic_t _refcount;
>    };
> 
> To netwrok guys, any thoughts on it?
> To Willy, do I understand correctly your direction?
> 
> Plus, it's a quite another issue but I'm curious, that is, what do you
> guys think about moving the bump allocator(= page pool) code from
> network to mm?  I'd like to start on the work once gathering opinion
> from both Willy and network guys.
> 
> 	Byungchul
>