From: Breno Leitao <leitao@debian.org>
To: Stanislav Fomichev <sdf.kernel@gmail.com>
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, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org,
linux-kselftest@vger.kernel.org, leon@kernel.org
Subject: Re: [PATCH net-next v3 2/9] net: devmem: charge the frag length to TX skb truesize
Date: Mon, 9 Nov 2026 02:59:16 -0800 [thread overview]
Message-ID: <avGneUOQtUAMvpCq@gmail.com> (raw)
In-Reply-To: <20261105222058.944293-3-sdf@fomichev.me>
On Thu, Nov 05, 2026 at 02:20:51PM -0800, Stanislav Fomichev wrote:
> 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 <sdf@fomichev.me>
> Reviewed-by: Mina Almasry <almasrymina@google.com>
> Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
next prev parent reply other threads:[~2026-11-09 10:59 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-05 22:20 [PATCH net-next v3 0/9] net: devmem: size TX net_iovs from the dmabuf layout Stanislav Fomichev
2026-11-05 22:20 ` [PATCH net-next v3 1/9] bnxt_en: let the stack segment GSO skbs with too many frags Stanislav Fomichev
2026-11-09 1:22 ` netdev-bot+sashiko
2026-11-05 22:20 ` [PATCH net-next v3 2/9] net: devmem: charge the frag length to TX skb truesize Stanislav Fomichev
2026-11-09 1:22 ` netdev-bot+sashiko
2026-11-09 10:59 ` Breno Leitao [this message]
2026-11-05 22:20 ` [PATCH net-next v3 3/9] net: devmem: use niov_shift in net_devmem_get_niov_at() Stanislav Fomichev
2026-11-05 22:20 ` [PATCH net-next v3 4/9] net: devmem: add a per-device netmem TX frag size limit Stanislav Fomichev
2026-11-09 1:22 ` netdev-bot+sashiko
2026-11-05 22:20 ` [PATCH net-next v3 5/9] bnxt_en: set the netmem TX frag size limit to 32KB Stanislav Fomichev
2026-11-09 1:22 ` netdev-bot+sashiko
2026-11-05 22:20 ` [PATCH net-next v3 6/9] eth: fbnic: " Stanislav Fomichev
2026-11-05 22:20 ` [PATCH net-next v3 7/9] net/mlx5e: lift the netmem TX frag size limit Stanislav Fomichev
2026-11-09 1:23 ` netdev-bot+sashiko
2026-11-05 22:20 ` [PATCH net-next v3 8/9] net: devmem: size TX net_iovs from the dmabuf sg table Stanislav Fomichev
2026-11-09 1:23 ` netdev-bot+sashiko
2026-11-05 22:20 ` [PATCH net-next v3 9/9] selftests: drv-net: devmem: TX from a hugepage-backed dmabuf Stanislav Fomichev
2026-11-09 1:23 ` netdev-bot+sashiko
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