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([2620:10d:c092:600::1:a4c1]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-611d8d54112sm6292085a12.1.2025.07.15.03.22.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Jul 2025 03:22:19 -0700 (PDT) Message-ID: <839d5486-a92a-4ae8-a536-b4a0e3d595ea@gmail.com> Date: Tue, 15 Jul 2025 11:23:47 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v7 1/7] netmem: introduce struct netmem_desc mirroring struct page To: Jakub Kicinski , Harry Yoo Cc: Vlastimil Babka , Byungchul Park , willy@infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, almasrymina@google.com, ilias.apalodimas@linaro.org, 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, 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, hannes@cmpxchg.org, ziy@nvidia.com, jackmanb@google.com References: <20250625043350.7939-1-byungchul@sk.com> <20250625043350.7939-2-byungchul@sk.com> <20250626174904.4a6125c9@kernel.org> <20250627035405.GA4276@system.software.com> <20250627173730.15b25a8c@kernel.org> <20250701164508.0738f00f@kernel.org> <92073822-ab60-40ca-9ff5-a41119c0ad3d@suse.cz> <20250714184743.4acd7ead@kernel.org> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <20250714184743.4acd7ead@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/15/25 02:47, Jakub Kicinski wrote: > On Mon, 14 Jul 2025 22:58:31 +0900 Harry Yoo wrote: >>>> Could you please share your thoughts on why it's hard to judge them and >>>> what's missing from the series, such as in the comments, changelog, or >>>> the cover letter? > > My main concern (as shared on earlier revisions) is the type hierarchy Quick overview. struct netmem_desc is a common denominator b/w pp pages and net_iov, and contains fields used by the pp generic path, e.g. refcount, dma_addr. Before, pp was using type casting hacks to keep code generic with some overhead on bit masking, now it'll be able to look up netmem_desc from a netmem and use it directly. That's pretty much what I was suggesting niov / page aliasing to be 1+ years ago, but unfortunately that didn't happen. It definitely removes some type casting hackiness. > exposed to the drivers. v10 adds a bunch of "pp_page_to_nmdesc(page)->pp" in the drivers, Not sure I have a strong opinion, but it can be turned into a helper. Converting things back and forth or blindly > downcasting to netmem and upcasting back to the CPU-readable type is > no good. -- Pavel Begunkov