linux-kernel - Re: [PATCH net-next v9 0/8] Split netmem from struct page

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Message-ID: <CAHS8izMie=XQcVUhW9CmydTqYEscp5soeOT4nwvFj2T+8X1ypA@mail.gmail.com>
Date: Thu, 10 Jul 2025 11:35:33 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Byungchul Park <byungchul@...com>
Cc: willy@...radead.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, kernel_team@...ynix.com, kuba@...nel.org, 
	ilias.apalodimas@...aro.org, harry.yoo@...cle.com, hawk@...nel.org, 
	akpm@...ux-foundation.org, davem@...emloft.net, john.fastabend@...il.com, 
	andrew+netdev@...n.ch, asml.silence@...il.com, toke@...hat.com, 
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	hannes@...xchg.org, ziy@...dia.com, jackmanb@...gle.com
Subject: Re: [PATCH net-next v9 0/8] Split netmem from struct page

On Thu, Jul 10, 2025 at 1:28 AM Byungchul Park <byungchul@...com> wrote:
>
> Hi all,
>
> The MM subsystem is trying to reduce struct page to a single pointer.
> See the following link for your information:
>
>    https://kernelnewbies.org/MatthewWilcox/Memdescs/Path
>
> The first step towards that is splitting struct page by its individual
> users, as has already been done with folio and slab.  This patchset does
> that for page pool.
>
> Matthew Wilcox tried and stopped the same work, you can see in:
>
>    https://lore.kernel.org/linux-mm/20230111042214.907030-1-willy@infradead.org/
>
> I focused on removing the page pool members in struct page this time,
> not moving the allocation code of page pool from net to mm.  It can be
> done later if needed.
>
> The final patch removing the page pool fields will be posted once all
> the converting of page to netmem are done:
>
>    1. converting use of the pp fields in struct page in prueth_swdata.
>    2. converting use of the pp fields in struct page in freescale driver.
>
> For our discussion, I'm sharing what the final patch looks like, in this
> cover letter.
>
>         Byungchul
> --8<--
> commit 1847d9890f798456b21ccb27aac7545303048492
> Author: Byungchul Park <byungchul@...com>
> Date:   Wed May 28 20:44:55 2025 +0900
>
>     mm, netmem: remove the page pool members in struct page
>
>     Now that all the users of the page pool members in struct page have been
>     gone, the members can be removed from struct page.
>
>     However, since struct netmem_desc still uses the space in struct page,
>     the important offsets should be checked properly, until struct
>     netmem_desc has its own instance from slab.
>
>     Remove the page pool members in struct page and modify static checkers
>     for the offsets.
>
>     Signed-off-by: Byungchul Park <byungchul@...com>
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 32ba5126e221..db2fe0d0ebbf 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -120,17 +120,6 @@ struct page {
>                          */
>                         unsigned long private;
>                 };
> -               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;
> -               };
>                 struct {        /* Tail pages of compound page */
>                         unsigned long compound_head;    /* Bit zero is set */
>                 };
> diff --git a/include/net/netmem.h b/include/net/netmem.h
> index 8f354ae7d5c3..3414f184d018 100644
> --- a/include/net/netmem.h
> +++ b/include/net/netmem.h
> @@ -42,11 +42,8 @@ struct netmem_desc {
>         static_assert(offsetof(struct page, pg) == \
>                       offsetof(struct netmem_desc, desc))
>  NETMEM_DESC_ASSERT_OFFSET(flags, _flags);
> -NETMEM_DESC_ASSERT_OFFSET(pp_magic, pp_magic);
> -NETMEM_DESC_ASSERT_OFFSET(pp, pp);
> -NETMEM_DESC_ASSERT_OFFSET(_pp_mapping_pad, _pp_mapping_pad);
> -NETMEM_DESC_ASSERT_OFFSET(dma_addr, dma_addr);
> -NETMEM_DESC_ASSERT_OFFSET(pp_ref_count, pp_ref_count);
> +NETMEM_DESC_ASSERT_OFFSET(lru, pp_magic);
> +NETMEM_DESC_ASSERT_OFFSET(mapping, _pp_mapping_pad);
>  #undef NETMEM_DESC_ASSERT_OFFSET
>
>  /*


Can you remove the above patch/diff from the cover letter?

-- 
Thanks,
Mina