Re: [PATCH net-next v12 00/12] Split netmem from struct page

[Byungchul Park <byungchul@sk.com>]

On Mon, Jul 21, 2025 at 11:18:23AM +0900, Byungchul Park 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 that removes the page pool fields will be posted once
> all the conversions are completed.
> 
> 	Byungchul
> ---
> Changes from v11:
> 	1. Rebase on net-next/main as of Jul 21.
> 	2. Change page_pool_page_is_pp() to check for const type of
> 	   page.  For now that it's called along with every
> 	   pp_page_to_nmdesc() call as Pavel suggested,
> 	   page_pool_page_is_pp() should also cover const type of page.

I believe the curretn version is good enough.

	Byungchul

> Changes from v10:
> 	1. Introduce __netmem_to_nmdesc() and use it in
> 	   __netmem_get_pp(). (feedbacked by Mina)
> 	2. Fix a bug that fails on casting 'const page -> const
> 	   netmem_desc', by using macros and _Generic. (feedbacked by
> 	   test robot)
> 	3. Add comment on pp_page_to_nmdesc() to ask for more attention
> 	   before using the helper. (feedbacked by Mina)
> 
> Changes from v9:
> 	1. Remove the patch 'page_pool: access ->pp_magic through
> 	   netmem_desc in page_pool_page_is_pp()' and decide to wait for
> 	   Pavel's work of PageNetpp() to identify page type for page
> 	   pool, that doesn't need to access ->pp_magic.
> 	2. Rename page_to_nmdesc() to pp_page_to_nmdesc() and add
> 	   DEBUG_NET_WARN_ON_ONCE(!page_pool_page_is_pp(page)) in it,
> 	   just in case. (feedbacked by Pavel)
> 	3. Apply just simple casting from page to netmem_desc for
> 	   accessing ->pp and ->pp_ref_count, instead of full converting
> 	   page to netmem_ref for network drivers e.g. mlx4, netdevsim,
> 	   and mt76.
> 	4. Expand the support for drivers to access ->pp and
> 	   ->pp_ref_count to fec, octeontx2-pf, iavf, idpf, mlx5, ti,
> 	   and xdp.
> 	5. Squash each helper with its first user. (feedbacked by Mina)
> 
> Changes from v8:
> 	1. Rebase on net-next/main as of Jul 10.
> 	2. Exclude non-controversial patches that have already been
> 	   merged to net-next.
> 	3. Re-add the patches that focus on removing accessing the page
> 	   pool fields in struct page.
> 	4. Add utility APIs e.g. casting, to use struct netmem_desc as
> 	   descriptor, to support __netmem_get_pp() that has started to
> 	   be used again e.g. by libeth.
> 
> Changes from v7 (no actual updates):
> 	1. Exclude "netmem: introduce struct netmem_desc mirroring
> 	   struct page" that might be controversial.
> 	2. Exclude "netmem: introduce a netmem API,
> 	   virt_to_head_netmem()" since there are no users.
> 
> Changes from v6 (no actual updates):
> 	1. Rebase on net-next/main as of Jun 25.
> 	2. Supplement a comment describing struct net_iov.
> 	3. Exclude a controversial patch, "page_pool: access ->pp_magic
> 	   through struct netmem_desc in page_pool_page_is_pp()".
> 	4. Exclude "netmem: remove __netmem_get_pp()" since the API
> 	   started to be used again by libeth.
> 
> Changes from v5 (no actual updates):
> 	1. Rebase on net-next/main as of Jun 20.
> 	2. Add given 'Reviewed-by's and 'Acked-by's, thanks to all.
> 	3. Add missing cc's.
> 
> Changes from v4:
> 	1. Add given 'Reviewed-by's, thanks to all.
> 	2. Exclude potentially controversial patches.
> 
> Changes from v3:
> 	1. Relocates ->owner and ->type of net_iov out of netmem_desc
> 	   and make them be net_iov specific.
> 	2. Remove __force when casting struct page to struct netmem_desc.
> 
> Changes from v2:
> 	1. Introduce a netmem API, virt_to_head_netmem(), and use it
> 	   when it's needed.
> 	2. Introduce struct netmem_desc as a new struct and union'ed
> 	   with the existing fields in struct net_iov.
> 	3. Make page_pool_page_is_pp() access ->pp_magic through struct
> 	   netmem_desc instead of struct page.
> 	4. Move netmem alloc APIs from include/net/netmem.h to
> 	   net/core/netmem_priv.h.
> 	5. Apply trivial feedbacks, thanks to Mina, Pavel, and Toke.
> 	6. Add given 'Reviewed-by's, thanks to Mina.
> 
> Changes from v1:
> 	1. Rebase on net-next's main as of May 26.
> 	2. Check checkpatch.pl, feedbacked by SJ Park.
> 	3. Add converting of page to netmem in mt76.
> 	4. Revert 'mlx5: use netmem descriptor and APIs for page pool'
> 	   since it's on-going by Tariq Toukan.  I will wait for his
> 	   work to be done.
> 	5. Revert 'page_pool: use netmem APIs to access page->pp_magic
> 	   in page_pool_page_is_pp()' since we need more discussion.
> 	6. Revert 'mm, netmem: remove the page pool members in struct
> 	   page' since there are some prerequisite works to remove the
> 	   page pool fields from struct page.  I can submit this patch
> 	   separatedly later.
> 	7. Cancel relocating a page pool member in struct page.
> 	8. Modify static assert for offests and size of struct
> 	   netmem_desc.
> 
> Changes from rfc:
> 	1. Rebase on net-next's main branch.
> 	   https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/
> 	2. Fix a build error reported by kernel test robot.
> 	   https://lore.kernel.org/all/202505100932.uzAMBW1y-lkp@intel.com/
> 	3. Add given 'Reviewed-by's, thanks to Mina and Ilias.
> 	4. Do static_assert() on the size of struct netmem_desc instead
> 	   of placing place-holder in struct page, feedbacked by
> 	   Matthew.
> 	5. Do struct_group_tagged(netmem_desc) on struct net_iov instead
> 	   of wholly renaming it to strcut netmem_desc, feedbacked by
> 	   Mina and Pavel.
> 
> Byungchul Park (12):
>   netmem: introduce struct netmem_desc mirroring struct page
>   netmem: use netmem_desc instead of page to access ->pp in
>     __netmem_get_pp()
>   netmem, mlx4: access ->pp_ref_count through netmem_desc instead of
>     page
>   netdevsim: access ->pp through netmem_desc instead of page
>   mt76: access ->pp through netmem_desc instead of page
>   net: fec: access ->pp through netmem_desc instead of page
>   octeontx2-pf: access ->pp through netmem_desc instead of page
>   iavf: access ->pp through netmem_desc instead of page
>   idpf: access ->pp through netmem_desc instead of page
>   mlx5: access ->pp through netmem_desc instead of page
>   net: ti: icssg-prueth: access ->pp through netmem_desc instead of page
>   libeth: xdp: access ->pp through netmem_desc instead of page
> 
>  drivers/net/ethernet/freescale/fec_main.c     |  10 +-
>  drivers/net/ethernet/intel/iavf/iavf_txrx.c   |   2 +-
>  drivers/net/ethernet/intel/idpf/idpf_txrx.c   |   8 +-
>  .../marvell/octeontx2/nic/otx2_txrx.c         |   2 +-
>  drivers/net/ethernet/mellanox/mlx4/en_rx.c    |   4 +-
>  .../net/ethernet/mellanox/mlx5/core/en/xdp.c  |   3 +-
>  .../net/ethernet/ti/icssg/icssg_prueth_sr1.c  |   4 +-
>  drivers/net/netdevsim/netdev.c                |   6 +-
>  drivers/net/wireless/mediatek/mt76/mt76.h     |   3 +-
>  include/linux/mm.h                            |   4 +-
>  include/net/libeth/xdp.h                      |   2 +-
>  include/net/netmem.h                          | 153 +++++++++++++++---
>  12 files changed, 161 insertions(+), 40 deletions(-)
> 
> 
> base-commit: 4701ee5044fb3992f1c910630a9673c2dc600ce5
> -- 
> 2.17.1