Re: [PATCH net-next 9/9] page_pool: access ->pp_magic through struct netmem_desc in page_pool_page_is_pp()

[Mina Almasry]

On Sun, Jun 8, 2025 at 9:32 PM Byungchul Park <byungchul@xxxxxx> wrote:
>
> To simplify struct page, the effort to separate its own descriptor from
> struct page is required and the work for page pool is on going.
>
> To achieve that, all the code should avoid directly accessing page pool
> members of struct page.
>
> Access ->pp_magic through struct netmem_desc instead of directly
> accessing it through struct page in page_pool_page_is_pp().  Plus, move
> page_pool_page_is_pp() from mm.h to netmem.h to use struct netmem_desc
> without header dependency issue.
>
> Signed-off-by: Byungchul Park <byungchul@xxxxxx>
> Reviewed-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> ---
>  include/linux/mm.h   | 12 ------------
>  include/net/netmem.h | 14 ++++++++++++++
>  mm/page_alloc.c      |  1 +
>  3 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e51dba8398f7..f23560853447 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4311,16 +4311,4 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
>   */
>  #define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL)
>
> -#ifdef CONFIG_PAGE_POOL
> -static inline bool page_pool_page_is_pp(struct page *page)
> -{
> -       return (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE;
> -}
> -#else
> -static inline bool page_pool_page_is_pp(struct page *page)
> -{
> -       return false;
> -}
> -#endif
> -
>  #endif /* _LINUX_MM_H */
> diff --git a/include/net/netmem.h b/include/net/netmem.h
> index d84ab624b489..8f354ae7d5c3 100644
> --- a/include/net/netmem.h
> +++ b/include/net/netmem.h
> @@ -56,6 +56,20 @@ NETMEM_DESC_ASSERT_OFFSET(pp_ref_count, pp_ref_count);
>   */
>  static_assert(sizeof(struct netmem_desc) <= offsetof(struct page, _refcount));
>
> +#ifdef CONFIG_PAGE_POOL
> +static inline bool page_pool_page_is_pp(struct page *page)
> +{
> +       struct netmem_desc *desc = (struct netmem_desc *)page;
> +
> +       return (desc->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE;
> +}
> +#else
> +static inline bool page_pool_page_is_pp(struct page *page)
> +{
> +       return false;
> +}
> +#endif
> +
>  /* net_iov */
>
>  DECLARE_STATIC_KEY_FALSE(page_pool_mem_providers);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4f29e393f6af..be0752c0ac92 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -55,6 +55,7 @@
>  #include <linux/delayacct.h>
>  #include <linux/cacheinfo.h>
>  #include <linux/pgalloc_tag.h>
> +#include <net/netmem.h>

mm files starting to include netmem.h is a bit interesting. I did not
expect/want dependencies outside of net. If anything the netmem stuff
include linux/mm.h

But I don't have a butter suggestion here and I don't see any huge
problems with this off the top of my head, so

Reviewed-by: Mina Almasry <almasrymina@xxxxxxxxxx>

Lets see if Jakub objects though. To be fair, we did put the netmem
private stuff in net/core/netmem_priv.h, so technically
include/net/netmem.h should be exportable indeed.

-- 
Thanks,
Mina