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Mon, 02 Nov 2026 15:38:06 -0800 (PST) Received: from localhost ([2a03:2880:9ff:41::]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-36a4239ca83sm1701518eec.0.2026.11.02.15.38.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Nov 2026 15:38:06 -0800 (PST) Date: Mon, 2 Nov 2026 15:27:23 -0800 From: Stanislav Fomichev To: Mina Almasry Cc: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, andrew+netdev@lunn.ch, edumazet@kernel.org, horms@kernel.org, corbet@lwn.net, skhan@linuxfoundation.org, rdunlap@infradead.org, michael.chan@broadcom.com, pavan.chebbi@broadcom.com, sdf@fomichev.me, bobbyeshleman@meta.com, asml.silence@gmail.com, daniel@iogearbox.net, razor@blackwall.org, leitao@debian.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH net-next 4/7] net: devmem: add a per-device netmem TX frag size limit Message-ID: References: <20261102191438.1059771-1-sdf@fomichev.me> <20261102191438.1059771-5-sdf@fomichev.me> X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On 11/02, Mina Almasry wrote: > On Mon, Nov 2, 2026 at 11:14 AM Stanislav Fomichev wrote: > > > > Devmem TX frags are bounded only by the net_iov size, which is about > > to grow up to 2MB, more than some devices can describe in a single TX > > descriptor. > > > > Add netmem_tx_max_frag_size, U32_MAX by default, and cap devmem TX > > frags to the limit of the device the binding is attached to. > > > > Signed-off-by: Stanislav Fomichev > > Abstractly LGTM but I'm not sure why this is TX-specific. Didn't we > add non-PAGE_SIZE rx net-iovs? This should have been a problem then. > Either you know what you're doing (maybe document in the commit > message) or we need some more alignment on RX and TX. > > TBH I was dissapointed when LLMs started reporting that > binding->vdev/dev are treated very differently for RX and TX and I > have to write a cleanup that consolidates this: > > https://github.com/mina/linux/compare/devmem-teardown-v4...devmem-lease-bind-map-dev > > I think maybe my reviews and yours maybe should be more mindful about > keeping these memory things consolidated and as much as possible not > RX/TX specific. This patch is mostly a bandaid for bnxt which can't express sizes longer than 2^16-1 in its tx descriptors. And rx is even more restricted I think? Up to 32K HW GRO aggregated?