From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta1.migadu.com (out-177.mta1.migadu.com [95.215.58.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 35858392838 for ; Thu, 22 Jan 2026 20:21:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769113321; cv=none; b=UmttREwMylOuAGLjpJMGiExHt2D+Arrft6hIeMHtZojLkEjxgmCrgzbE76aKpuaR0X7mBHilP33qk/ULUq3sOT9xlwgnZW1wNcoDg12aRVwZ7abwTjB8qA30i/XLvVq2WEZn4AIExcYT3wfpF+EtYvEuL3qPozEwmhd3NXOEeZo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769113321; c=relaxed/simple; bh=MBz9V95XIV9RSXmKmjbflPIhLxIbuc9EdkzrUGIegkg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=m7ZqImWc2+Wt+esZrNHezHB0LyUHMn4mU5+QoA5W2P95tHjbzvmo7RNhNRLmGI26xLbu4y7XkKboJ/h1qVy7SlUHFKdJfm7VNHDLCiSNPDICOadPODqtY6vE7XIgm/H44DVCXKWsudkQ8hNKQRmP7H+00Gt8htNf1bZU8grnEMU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=PwXNemkS; arc=none smtp.client-ip=95.215.58.177 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="PwXNemkS" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1769113307; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=SmsPbxD4P2U6cfRhimAmDFnoSDOJmyA6gTw2jvjRFQo=; b=PwXNemkSVY+ky4LEOmfP2pan4B5MDwzZCRi6xu+xEhtfhvYzFZS7qTQxmSfgbVn8p7vAse 8kz6jbK06oD70NIh5+furf0Dm3ao8i8vlft2osWnUQKB38nwgSp1lE6TquDLMrCmz/M5rm 4RgcUg9CBFSFRB9bO8oReErZOUz3QeI= Date: Thu, 22 Jan 2026 12:21:21 -0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH net-next 00/10] Call skb_metadata_set when skb->data points past metadata To: Jakub Sitnicki Cc: netdev@vger.kernel.org, "David S. Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Michael Chan , Pavan Chebbi , Andrew Lunn , Tony Nguyen , Przemek Kitszel , Saeed Mahameed , Leon Romanovsky , Tariq Toukan , Mark Bloch , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , intel-wired-lan@lists.osuosl.org, bpf@vger.kernel.org, kernel-team@cloudflare.com, Jakub Kicinski , Amery Hung References: <20260110-skb-meta-fixup-skb_metadata_set-calls-v1-0-1047878ed1b0@cloudflare.com> <20260112190856.3ff91f8d@kernel.org> <87bjixwv41.fsf@cloudflare.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau In-Reply-To: <87bjixwv41.fsf@cloudflare.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 1/13/26 4:33 AM, Jakub Sitnicki wrote: > Good point. I'm hoping we don't have to allocate from > skb_metadata_set(), which does sound prohibitively expensive. Instead > we'd allocate the extension together with the skb if we know upfront > that metadata will be used. [ Sorry for being late. Have been catching up after holidays. ] For the sk local storage (which was mentioned in other replies as making skb metadata to look more like sk local storage), there is a plan (Amery has been looking into it) to allocate the storage together with sk for performance reason. This means allocating a larger 'struct sock'. The extra space will be at the front of sk instead of the end of sk because of how the 'struct sock' is embedded in tcp_sock/udp_sock/... If skb is going in the same direction, it should be useful to have a similar scheme on: upfront allocation and then shared by multiple BPF progs. The current thinking is to built upon the existing bpf_sk_local_storage usage. A boot param decides how much BPF space should be allocated for 'struct sock'. When a bpf_sk_storage_map is created (with a new use_reserve flag), the space will be allocated permanently from the head space of every sk for this map. The read (from a BPF prog) will be at one stable offset before a sk. If there is no more head space left, the map creation will fail. User can decide if it wants to retry without the 'use_reserve' flag.