From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=74.125.229.7 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793901356; b=zUWM1okYCcaS5yiOvuRitPlmH1qXqiEtbhg3Ey/hoEkBQ/VrwWj1++HtNl+fdu7JxpzB zDh99BTvpaepGC4Knkbn0M9Wic8BJzHXzVJJgGA23Yt73P/uqvPonKuI/G7VQzS7Ng6FR eFYMI3HALXh/8ZFG8MuotMGJo4wMqZxosnCi4+8FPwguC2iwJpWwX7mE7n24NtT/GSexe O/DjJR+G3iyacE+MKHErdTkGIP/MdhK2F7aYETeQiogW0f/udQkZzMoZ87nEwZThwSzVO N/gknztu8r8yK5fS/CJ2AzJKuBmQW/OCTiy1xUzzN9CpRajVnIbGUe1HmzA+k8flVAA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793901356; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; bh=KJPkIDOAYDK93RB/9c0VDv3wKCD+7XkZXq4Nusu/JJ0=; b=0/3H6IwJVKTeakehfzu4CfMNTf6Tw3CULinzO2f9yyavFKruNpD+8d7rjh8jWFDgTycD FhNNB02Ozvi3A+uvz9e8XBLGLJbf+xBbv2R4NJh1puEPnrT5f1lLkPQjz0LyAnYlej0E9 bSABqnLFaNTYyfHb0FqX7DBSKGsILkOJaLiMthtzg2NKxGbO+ZH+JtF/hMcQmQ9ejaK6m 09c2Gcc0ybNza329J6NiHXsg/aeJPlnEgPYPHmy+O0kBTr5u03F2haBsQUJKDJq72fw0Z 0x52MymTvPnO1kMhbDlgvFtgHnbRFw6CQNTQaI4QkBduq1NkO0wn/1EWduf7RxqSeVA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=N1kTwUwv; arc=none smtp.remote-ip=74.125.229.7 Received: from mail-dy2-f7.google.com (mail-dy2-f7.google.com [74.125.229.7]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 043D9606A339 for ; Thu, 5 Nov 2026 17:55:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 043D9606A339 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=N1kTwUwv Received: by mail-dy2-f7.google.com with SMTP id 5a478bee46e88-36c9e2dfb29so280538eec.1 for ; Thu, 05 Nov 2026 09:55:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1793901355; x=1794506155; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=KJPkIDOAYDK93RB/9c0VDv3wKCD+7XkZXq4Nusu/JJ0=; b=N1kTwUwvpB9XGiNqY3oRRDkzMFpGtl/3/7auXAzY2if4gWRYBUHuPntVBU4+TUujkG W7jJELMjM/8dRVIN8nB3i2Rq/SIHnr6VLrFzvLb7rxQHGkwUoZZY33BfAt41D5M89+jH hxgRIA2vm1sRoXNbc5lwnZBzfH/NSIr0NAITPAVv7u5S7aeArsy8IefaR/+uMyx3XMBq mLyXgvolIQ8QbxRTvlRYD2RpHFWsFLg502wzz0gs2+mflVzlv1OyU2xJSxhpqsRql6JQ lzH3vQurUPNHdCD4wqRjKVppVCXRrwDctcJyqVt8TV+Bp7zj6pzbUE4ZfVvOb1N06HOI 0JWw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793901355; x=1794506155; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=KJPkIDOAYDK93RB/9c0VDv3wKCD+7XkZXq4Nusu/JJ0=; b=N3koqz/sDEumkj76v4YcU3UnjFDakeoJbYjZPGFn47+GCdxIRC/CuIxo1U6aIT3SFf 6cd7k6Bf+3RhyM93ENyMbYIhtVZCt5ozcIO3OTBOE307Td3AfFapYqz55bcVWjDCFdcF 8JgXvdM9g71w8LZbRyYzw3h0u319rMCqqQ5hubfAwLeVr/2fLR6uB7ShjyiMyDMJpi8b 1Oq72bZzkObww8W4USSV23Lm8g3GuFW/qED2AWa8FhSSrvqMA8W9JkWWOewtrvo/Nbm9 VBZEXcRkklXdIyOaPJAqs06+CJYLLvuIPsw9AatdW7pljdMMkUUEIP+yRWFemSKa9KZP 9r1Q== X-Forwarded-Encrypted: i=1; AKwUvBxQIuBcwKNp81zccv/S9udY9yNBKn2q3/vt/7HaDo9I+c2Sb5FfCG9u1LVj7yet49LN+h4WcoZvAqox7yo=@vger.kernel.org X-Gm-Message-State: APuU4Z9oo41SHl0GjBNWFfRFUYlBtJURnjbFqhZLlxoi2KQqVfx6x7br 2SIPgQrjD4XcVjOf9/QO1QB2aEFWbOtBJ6jgu/2ZOw/Sq9bMH07A15yO X-Gm-Gg: AYBFou1Vixb0ruMV31lQs6xtOB5CBQiSiqJuvtEm4Wz/MntKQT1Ibc/GLoSiWc6e9n2 vhjIDkmTAGbV/dEcPsdVsXPLjBFMjkxjb29L44r0vC1r0SWFhsCLOOd1Veus1nlbyqoAIBrr8oj 8N5DYA3D/GlFjoI4YM5tjAWXp+IE5ciMxIXHClpJ3Vro28CaYTWDxQoS+IESqvWf7Y795JSnGxM WGLzhwyrCoo9zB03ycVfLU1q9IoJ+l5m4OAZq1JwLt+OguwjZCgFbkM1rZTh7XiwMoq8QBIwiGm NiJoH80K2sha4AVuTqifyd8j/9NqcFw1hmT3iU1FCxQ5kxwrEq7qJiSy6mlEQALB0Ip7l0qAG7E w0yNkOU65k58EvgJbIurJXbw+OQGPmULnIh2iYEse3wSsFIfL3MKcBlFX5KK6Xm8ygrynhn1i8F XW8s1zOwEc2pJm7oyFpu64ZYI/xrlZkag34hTaqhMEiXZMs6JhPH6KbMcXooe5TB+1gXIPDzieN 29nVb17L/A+fOGhDmKV/3j94qauQCjqPjarCacdtgnw7bhF9VmtDkGISJVdGBbknBYs1VQcNqA6 ekVsMbIbh2vuW3kiIYOn5A== X-Received: by 2002:a05:7023:a5c:10b0:1a9:4d51:8c33 with SMTP id a92af1059eb24-1b24f460f1dmr4221448c88.18.1793901354912; Thu, 05 Nov 2026 09:55:54 -0800 (PST) Received: from localhost ([2a03:2880:9ff:65::]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1b245b86fbesm18947609c88.1.2026.11.05.09.55.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 09:55:54 -0800 (PST) Date: Thu, 5 Nov 2026 09:53:41 -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, razor@blackwall.org, daniel@iogearbox.net, leitao@debian.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH net-next v2 4/7] net: devmem: add a per-device netmem TX frag size limit Message-ID: References: <20261103235152.1904727-1-sdf@fomichev.me> <20261103235152.1904727-5-sdf@fomichev.me> <18e4e1daa184cadc.3137322e32382e36372e3935.ceab9.0000sendgmr@google.com> X-Mailing-List: linux-kernel@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 In-Reply-To: <18e4e1daa184cadc.3137322e32382e36372e3935.ceab9.0000sendgmr@google.com> On 11/04, Mina Almasry wrote: > On Tue, Nov 3, 2026 at 3:51 PM 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 > > --- > > Documentation/networking/net_cachelines/net_device.rst | 1 + > > Documentation/networking/netmem.rst | 6 ++++++ > > include/linux/netdevice.h | 2 ++ > > net/core/datagram.c | 1 + > > net/core/dev.c | 1 + > > net/core/devmem.c | 1 + > > net/core/devmem.h | 1 + > > 7 files changed, 13 insertions(+) > > > ... > > diff --git a/net/core/dev.c b/net/core/dev.c > > index 3ac700d37e59..ba2f887dcd39 100644 > > --- a/net/core/dev.c > > +++ b/net/core/dev.c > > @@ -12350,6 +12350,7 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name, > > dev->gro_ipv4_max_size = GRO_LEGACY_MAX_SIZE; > > dev->tso_max_size = TSO_LEGACY_MAX_SIZE; > > dev->tso_max_segs = TSO_MAX_SEGS; > > + dev->netmem_tx_max_frag_size = U32_MAX; > > I wonder if netmem_tx_max_frag_size should default to PAGE_SIZE instead > of U32_MAX, and have drivers opt in by raising it after verification > (e.g. SZ_32K for bnxt and U32_MAX for mlx5 in this series)? > > With U32_MAX as the default, large frags are enabled on all NETMEM_TX > drivers unless they opt out. For example, fbnic also has a 16-bit TX > descriptor length (FBNIC_TWD_LEN_MASK) and only avoids hitting > dma_error here because its tso_max_size happens to be 64KB today, and > gve hasn't been tested with >PAGE_SIZE devmem TX frags yet. Defaulting > to PAGE_SIZE (similar to tso_max_size = TSO_LEGACY_MAX_SIZE above) seems > safer for existing and future drivers. Hmm, I did not see fbnic :-/ That sounds fair, let me switch to an opt in, should be safer, agreed... Will only option mlx/bnxt and most likely fbnic.