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Wed, 11 Nov 2026 14:47:44 -0800 (PST) Received: from localhost ([2a03:2880:9ff:70::]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-375215d8889sm20837742eec.27.2026.11.11.14.47.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Nov 2026 14:47:44 -0800 (PST) From: Stanislav Fomichev X-Google-Original-From: Stanislav Fomichev To: netdev@vger.kernel.org Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, michael.chan@broadcom.com, pavan.chebbi@broadcom.com, andrew+netdev@lunn.ch, edumazet@kernel.org, horms@kernel.org, shuah@kernel.org, almasrymina@google.com, sdf@fomichev.me, leitao@debian.org, dtatulea@nvidia.com, asml.silence@gmail.com, bobbyeshleman@meta.com, daniel@iogearbox.net, razor@blackwall.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH net-next v4 2/5] net: devmem: charge the frag length to TX skb truesize Date: Wed, 11 Nov 2026 14:47:37 -0800 Message-ID: <20261111224740.2744522-3-sdf@fomichev.me> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261111224740.2744522-1-sdf@fomichev.me> References: <20261111224740.2744522-1-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-Transfer-Encoding: 8bit Devmem TX charges each frag the net_iov size, PAGE_SIZE today: zerocopy_fill_skb_from_devmem() adds PAGE_SIZE to skb->truesize per frag and __zerocopy_sg_from_iter() charges it to sk_wmem_queued. TCP uncharges in bytes as acked data is trimmed from the skb (tcp_trim_head()) and uncharges the rest when the skb is freed. A frag shorter than a page leaves the difference charged until then, which is small with PAGE_SIZE net_iovs. TX net_iovs are about to grow up to 2MB, while frags stay bounded by the skb and many frags share a net_iov. Charging the net_iov size would charge up to 2MB per frag: a 64KB skb with two frags would charge 4MB and fill the default 4MB send buffer on its own. Charge the frag length instead, which also matches what TCP uncharges. Signed-off-by: Stanislav Fomichev Reviewed-by: Mina Almasry Reviewed-by: Dragos Tatulea Reviewed-by: Breno Leitao --- net/core/datagram.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/core/datagram.c b/net/core/datagram.c index ecc30a6f8302..489d92fe6dae 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -737,7 +737,7 @@ zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from, netmem_inc_ref(net_iov_to_netmem(niov)); skb_add_rx_frag_netmem(skb, i, net_iov_to_netmem(niov), off, - size, PAGE_SIZE); + size, size); iov_iter_advance(from, size); length -= size; i++; -- 2.53.0-Meta