Re: [PATCH 12/18] page_pool: use netmem APIs to access page->pp_magic in page_pool_page_is_pp()

Pavel Begunkov
2025-05-28T07:50:39Z

On 5/26/25 03:23, Byungchul Park wrote:
> On Fri, May 23, 2025 at 10:21:17AM -0700, Mina Almasry wrote:
>> On Thu, May 22, 2025 at 8:26 PM Byungchul Park <byungchul@sk.com> wrote:
>>>
>>> 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@sk.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;
>>> -}
>>
>> I vote for keeping this function as-is (do not convert it to netmem),
>> and instead modify it to access page->netmem_desc->pp_magic.
>
> Once the page pool fields are removed from struct page, struct page will
> have neither struct netmem_desc nor the fields..
>
> So it's unevitable to cast it to netmem_desc in order to refer to
> pp_magic. Again, pp_magic is no longer associated to struct page.
>
> Thoughts?

Once the indirection / page shrinking is realized, the page is
supposed to have a type field, isn't it? And all pp_magic trickery
will be replaced with something like

page_pool_page_is_pp() { return page->type == PAGE_TYPE_PP; }

--
Pavel Begunkov