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Mon, 09 Nov 2026 10:29:22 -0800 (PST) Received: from localhost ([2a03:2880:9ff:73::]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3752060c4b6sm117168eec.15.2026.11.09.10.29.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Nov 2026 10:29:21 -0800 (PST) Date: Mon, 09 Nov 2026 10:29:21 -0800 Message-ID: <86219505a92ebc720950d87dc76662f3@gmail.com> From: Stanislav Fomichev To: netdev-bot+sashiko@kernel.org 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, saeedm@nvidia.com, tariqt@nvidia.com, mbloch@nvidia.com, alexanderduyck@fb.com, kernel-team@meta.com, sdf@fomichev.me, dimitri.daskalakis1@gmail.com, almasrymina@google.com, dtatulea@nvidia.com, 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-rdma@vger.kernel.org, linux-kselftest@vger.kernel.org, leon@kernel.org In-Reply-To: <179418737701.994134.5100743053640770189@kernel.org> Subject: Re: [PATCH net-next v3 4/9] net: devmem: add a per-device netmem TX frag size limit Content-Type: text/plain; charset="utf-8" X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list > > @@ -734,6 +734,7 @@ zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from, > > > > size = min_t(size_t, size, length); > > size = min_t(size_t, size, iter_iov_len(from)); > > + size = min_t(size_t, size, binding->tx_max_frag_size); > > [Severity: Medium] > Is this the only place the new cap is enforced? The netmem.rst text added > by this patch says "Devmem TX frags are capped at > netdev->netmem_tx_max_frag_size". TCP MTU probing looks like it can merge > the capped frags back together later. [..] > Could tcp_clone_payload() compare skb_frag_netmem() and stop merging once > the binding cap is reached? Another option is to skip MTU probe > coalescing for unreadable skbs. Hmm, let me comment on Mina's patches, might be easier not to merge netmems in tcp_clone_payload at all? > [Severity: High] > This isn't a bug introduced by this patch, but the same merge check in > tcp_clone_payload() looks like it can also combine frags from different > net_iovs. skb_frag_page() returns NULL for both frags, so the page > comparison always passes and only the offsets are compared. [..] > Should the merge test compare skb_frag_netmem(), the way > skb_can_coalesce_netmem() does? Nothing later in the series changes > tcp_output.c. Mina is gonna take care of this: https://lore.kernel.org/netdev/20261108013838.1454450-3-almasrymina@google.com/