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Message-ID: <20250609064955.GA57249@system.software.com>
Date: Mon, 9 Jun 2025 15:49:55 +0900
From: Byungchul Park <byungchul@...com>
To: willy@...radead.org, netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
kernel_team@...ynix.com, kuba@...nel.org, almasrymina@...gle.com,
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, tariqt@...dia.com,
edumazet@...gle.com, pabeni@...hat.com, saeedm@...dia.com,
leon@...nel.org, ast@...nel.org, daniel@...earbox.net,
david@...hat.com, lorenzo.stoakes@...cle.com,
Liam.Howlett@...cle.com, vbabka@...e.cz, rppt@...nel.org,
surenb@...gle.com, mhocko@...e.com, horms@...nel.org,
linux-rdma@...r.kernel.org, bpf@...r.kernel.org,
vishal.moola@...il.com
Subject: Re: [PATCH net-next 0/9] Split netmem from struct page
On Mon, Jun 09, 2025 at 01:32:16PM +0900, Byungchul Park wrote:
> Hi all,
I'm so sorry.. I missed to add v5 into the prefix..
Byungchul
> In this version, I'm posting non-controversial patches first. I will
> post the rest more carefully later. In this version, no update has been
> applied except excluding some patches from the previous version. See
> the changes below.
>
> --8<---
> The MM subsystem is trying to reduce struct page to a single pointer.
> 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 netmem which is used for page pools.
>
> Matthew Wilcox tried and stopped the same work, you can see in:
>
> https://lore.kernel.org/linux-mm/20230111042214.907030-1-willy@infradead.org/
>
> Mina Almasry already has done a lot fo prerequisite works by luck. I
> stacked my patches on the top of his work e.i. netmem.
>
> 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 submitted once
> all the converting work of page to netmem are done:
>
> 1. converting of libeth_fqe by Tony Nguyen.
> 2. converting of mlx5 by Tariq Toukan.
> 3. converting of prueth_swdata (on me).
> 4. converting of freescale driver (on me).
>
> For our discussion, I'm sharing what the final patch looks like the
> following.
>
> 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
>
> /*
> ---
> 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 (9):
> netmem: introduce struct netmem_desc mirroring struct page
> page_pool: rename page_pool_return_page() to page_pool_return_netmem()
> page_pool: rename __page_pool_release_page_dma() to
> __page_pool_release_netmem_dma()
> page_pool: rename __page_pool_alloc_pages_slow() to
> __page_pool_alloc_netmems_slow()
> netmem: use _Generic to cover const casting for page_to_netmem()
> netmem: remove __netmem_get_pp()
> page_pool: make page_pool_get_dma_addr() just wrap
> page_pool_get_dma_addr_netmem()
> netmem: introduce a netmem API, virt_to_head_netmem()
> page_pool: access ->pp_magic through struct netmem_desc in
> page_pool_page_is_pp()
>
> include/linux/mm.h | 12 ---
> include/net/netmem.h | 138 ++++++++++++++++++++++----------
> include/net/page_pool/helpers.h | 7 +-
> mm/page_alloc.c | 1 +
> net/core/page_pool.c | 36 ++++-----
> 5 files changed, 117 insertions(+), 77 deletions(-)
>
>
> base-commit: 90b83efa6701656e02c86e7df2cb1765ea602d07
> --
> 2.17.1
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