On Thu, May 29, 2025 at 12:10:29PM +0900, Byungchul Park wrote: > 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@xxxxxxxxxxxxx/ > > Mina Almasry already has done a lot fo prerequisite works by luck, he > said :). 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. +cc Tony Nguyen +cc Tariq Toukan Byungchul > 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 86be39ea488df859cff6bc398a364f1dc486f2f9 > Author: Byungchul Park <byungchul@xxxxxx> > 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@xxxxxx> > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 56d07edd01f9..5a7864eb9d76 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -119,17 +119,6 @@ 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 9e4ed3530788..e88e299dd0f0 100644 > --- a/include/net/netmem.h > +++ b/include/net/netmem.h > @@ -39,11 +39,8 @@ 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 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@xxxxxxxxx/ > 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 (18): > netmem: introduce struct netmem_desc mirroring struct page > netmem: introduce netmem alloc APIs to wrap page alloc APIs > page_pool: use netmem alloc/put APIs in __page_pool_alloc_page_order() > page_pool: rename __page_pool_alloc_page_order() to > __page_pool_alloc_netmem_order() > page_pool: use netmem alloc/put APIs in __page_pool_alloc_pages_slow() > page_pool: rename page_pool_return_page() to page_pool_return_netmem() > page_pool: use netmem put API in page_pool_return_netmem() > page_pool: rename __page_pool_release_page_dma() to > __page_pool_release_netmem_dma() > page_pool: rename __page_pool_put_page() to __page_pool_put_netmem() > page_pool: rename __page_pool_alloc_pages_slow() to > __page_pool_alloc_netmems_slow() > mlx4: use netmem descriptor and APIs for page pool > 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() > netdevsim: use netmem descriptor and APIs for page pool > netmem: introduce a netmem API, virt_to_head_netmem() > mt76: use netmem descriptor and APIs for page pool > page_pool: access ->pp_magic through struct netmem_desc in > page_pool_page_is_pp() > > drivers/net/ethernet/mellanox/mlx4/en_rx.c | 48 +++--- > drivers/net/ethernet/mellanox/mlx4/en_tx.c | 8 +- > drivers/net/ethernet/mellanox/mlx4/mlx4_en.h | 4 +- > drivers/net/netdevsim/netdev.c | 19 +-- > drivers/net/netdevsim/netdevsim.h | 2 +- > drivers/net/wireless/mediatek/mt76/dma.c | 6 +- > drivers/net/wireless/mediatek/mt76/mt76.h | 12 +- > .../net/wireless/mediatek/mt76/sdio_txrx.c | 24 +-- > drivers/net/wireless/mediatek/mt76/usb.c | 10 +- > include/linux/mm.h | 12 -- > include/net/netmem.h | 145 +++++++++++++----- > include/net/page_pool/helpers.h | 7 +- > mm/page_alloc.c | 1 + > net/core/netmem_priv.h | 14 ++ > net/core/page_pool.c | 101 ++++++------ > 15 files changed, 239 insertions(+), 174 deletions(-) > > > base-commit: d09a8a4ab57849d0401d7c0bc6583e367984d9f7 > -- > 2.17.1
