netdev - Re: [PATCH 12/18] page_pool: use netmem APIs to access page->pp_magic in page_pool_page_is

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Message-ID: <87ecwfn1om.fsf@toke.dk>
Date: Fri, 23 May 2025 10:58:33 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Byungchul Park <byungchul@...com>, 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, 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 12/18] page_pool: use netmem APIs to access
 page->pp_magic in page_pool_page_is_pp()

Byungchul Park <byungchul@...com> writes:

> To simplify struct page, the effort to seperate 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 accessing page pool members
> of struct page directly, but use safe APIs for the purpose.
>
> Use netmem_is_pp() instead of directly accessing page->pp_magic in
> page_pool_page_is_pp().
>
> Signed-off-by: Byungchul Park <byungchul@...com>
> ---
>  include/linux/mm.h   | 5 +----
>  net/core/page_pool.c | 5 +++++
>  2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8dc012e84033..3f7c80fb73ce 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4312,10 +4312,7 @@ 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;
> -}
> +bool page_pool_page_is_pp(struct page *page);

Here you're turning an inline function into a function call, which has
performance implications. Please try to avoid that.

-Toke