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Thu, 29 May 2025 13:48:42 -0700 (PDT) Received: from [192.168.8.100] ([148.252.146.217]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-450cfbf40casm29286315e9.4.2025.05.29.13.48.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 May 2025 13:48:41 -0700 (PDT) Message-ID: Date: Thu, 29 May 2025 21:49:52 +0100 Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v3 18/18] page_pool: access ->pp_magic through struct netmem_desc in page_pool_page_is_pp() To: Mina Almasry , Byungchul Park Cc: willy@infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, kuba@kernel.org, ilias.apalodimas@linaro.org, harry.yoo@oracle.com, hawk@kernel.org, akpm@linux-foundation.org, davem@davemloft.net, 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 References: <20250529031047.7587-1-byungchul@sk.com> <20250529031047.7587-19-byungchul@sk.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/29/25 20:54, Mina Almasry wrote: ...>> #endif /* _LINUX_MM_H */ >> diff --git a/include/net/netmem.h b/include/net/netmem.h >> index f05a8b008d00..9e4ed3530788 100644 >> --- a/include/net/netmem.h >> +++ b/include/net/netmem.h >> @@ -53,6 +53,20 @@ 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 = (__force struct netmem_desc *)page; >> + > > Is it expected that page can be cast to netmem_desc freely? I know it > works now since netmem_desc and page have the same layout, but how is > it going to continue to work when page is shrunk and no longer has > 'pp_magic' inside of it? Is that series going to fixup all the places > where casts are done? It's expected the struct page will have a type field once it's shrunk. > Is it also allowed that we can static cast netmem_desc to page? > > Consider creating netmem_desc_page helper like ptdesc_page. > > I'm not sure the __force is needed too. > -- Pavel Begunkov