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john.fastabend@gmail.com, andrew+netdev@lunn.ch, toke@redhat.com, tariqt@nvidia.com, edumazet@google.com, pabeni@redhat.com, saeedm@nvidia.com, leon@kernel.org, ast@kernel.org, daniel@iogearbox.net, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, horms@kernel.org, linux-rdma@vger.kernel.org, bpf@vger.kernel.org, vishal.moola@gmail.com Subject: Re: [PATCH 12/18] page_pool: use netmem APIs to access page->pp_magic in page_pool_page_is_pp() Message-ID: <20250528091416.GA54984@system.software.com> References: <20250523032609.16334-1-byungchul@sk.com> <20250523032609.16334-13-byungchul@sk.com> <20250526022307.GA27145@system.software.com> <20250528081403.GA28116@system.software.com> <06fca2f8-39f6-4abb-8e0d-bef373d9be0f@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 DyetA0vu MNOC9tfNcoleFtj7L6oe0LOHx4kMB0fu6aLtLmj0VweEp0RZ958NHc42coYTRichks9RfFiL1TH3HOTirMb9LA5lxTr0LKOv3uinGnPLfZt9dKEGenLN6yeOuPLu8EeIYdd/eO8ic1mJMvMTnbQ6owKub61xhuLuY63JccWl+VDNtS0VRF4tAlbb5iOMC7w6CccqgCLMFk3KfGJjrpdpx3Oc3RQ+E4G5sGzo1Ue3G8xjSc74= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, May 28, 2025 at 10:07:52AM +0100, Pavel Begunkov wrote: > On 5/28/25 09:14, Byungchul Park wrote: > > On Wed, May 28, 2025 at 08:51:47AM +0100, Pavel Begunkov wrote: > > > 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 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 > > > > > > --- > > > > > > 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; } > > > > Agree, but we need a temporary solution until then. I will use the > > following way for now: > > The question is what is the problem that you need another temporary > solution? If, for example, we go the placeholder way, page_pool_page_is_pp() I prefer using the place-holder, but Matthew does not. I explained it: https://lore.kernel.org/all/20250528013145.GB2986@system.software.com/ Now, I'm going with the same way as the other approaches e.g. ptdesc. Byungchul > can continue using page->netmem_desc->pp_magic as before, and mm folks > will fix it up to page->type when it's time for that. And the compiler > will help by failing compilation if forgotten. You should be able to do > the same with the overlay option. > > And, AFAIU, they want to remove/move the lru field in the same way? > In which case we'll get the same problem and need to re-alias it to > something else. > > -- > Pavel Begunkov