From patchwork Tue Dec 17 20:12:06 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mina Almasry X-Patchwork-Id: 13912452 X-Patchwork-Delegate: kuba@kernel.org Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A7B261F6671 for ; Tue, 17 Dec 2024 20:12:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734466330; cv=none; b=PN1IszYpJcxzmLfrrD83nTr8XKDHQ89QdwVM6a6dR0L0LQrFjOwAvV/ZJYYjy/bDqU+S82wKsD9CUjLkkJ6Wnp4HoS5/rO8bFi81arUwRjUb2c/Vk9S5zjgU6+cFceR7nuyIcIiWfSHdHVLIJcsZji6hsJKsfe6DEuSkH7hoLi8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734466330; c=relaxed/simple; bh=pVImGNEmG/zX77a+vhzi+si5GDL8xTOF4zHCM6KYXyM=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=TVqVCaMUuL2Qhi19KP2G9JUIa631tH15N+kdRLM/rGACHZglRmRVIAhuSceObt9ALM2XLowdVc4OPVa/7UIi6YQDDRldIkseXwhmxGwSaHXr7WLePUQBZ60LXEkV5TKau3zc8pk1iMa/OB6nF/bBvMYjl2xWPYZS1cwWer5KA+Q= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--almasrymina.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=ng7MEfjH; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--almasrymina.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ng7MEfjH" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-2ee5668e09bso5378188a91.3 for ; Tue, 17 Dec 2024 12:12:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1734466328; x=1735071128; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=S7CI+KsjLDAbysY8RsQOlNWjMrZ9ZlwbSEe2N6sprvE=; b=ng7MEfjH0oSBi72ygWvouldAuy8iUY0x6KB5iS0dZi25HgOfR2vO2HaONKYkjl6cy3 6C8dcZpxvDY5wJe4+HZyNSGEvKlDsDo+RZUsbOnRF8psusFKP68vn90TAE/cnNkVCCgj G6Nc0B9p/2kHRNMdlbxHM1OT+OLYq/U1hXxxQNxhKrVh/0lY/1ZUIYpswvONDQ+xC1aV NVoXZGr8g7HWEWNk6kbt0bGxAxerwgfWQ3U2POJh+Bs+YYm0wclldvMv45p2QVGrIAc/ jEjKWNrYMTk1x6mcpPiB3JAbcnxidFRZUPkncdJbaJTiA2XD4x087A7mX3rTtwNizINp LjXA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1734466328; x=1735071128; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=S7CI+KsjLDAbysY8RsQOlNWjMrZ9ZlwbSEe2N6sprvE=; b=CD8wHJ28M0OYBewquoa2mT+tMPWGuemah3Re7TA8soY5zMOxc0F1mk/qDz+CKatYBR m3IJ1j+7dvdJAPpanyZ1Lxl+d9fAIpCpIu+W11rcjwTS3tQk3HCPGq1hyV8riS8s0wQP GUDnMt8/xECNuI4D/HAg8xBzxy4Ky/H0CahYq9TF8WWvYurnulEWDY0SqcLQF+7AI95o ukRin5GlN4I5Am5niR1r+GqtyFKzvy9DX49YFb61koFAnjvxrBl6HlsnN4zs2Gcifr7S urN93mbZnCLFSyZujEgRn2c1WOBmL4b/YnTQcVXoQ/WqHsVIiWRCQPTxZK3OtrzvaqIr asBg== X-Gm-Message-State: AOJu0YzIyAznk2t5sAMyJM3z+r+Xa6x98ClIV5HxlWckQVsN3m8vuFU9 3v0a/117c8kolZeGUkzqBYBmy2bbfQKsvy39VOjNQZ5jPr2zb2hJu143NlghkKm6RY9GlUJvlap 16poTkkDgJ5NRyX0mf+NhdWkGNumlqZ/IZ33GVGX/99vppmRdGiKjTApFoa9upXTUMl9nfU2r0W jWvSposLa6VxopBwcgazBCI9Fm8PqXfk+XcB/8FV82J5Z7IMNuOwVlfdCRmog= X-Google-Smtp-Source: AGHT+IFsiV1/4XtIWEL3oEqqXsvoAtV5761RQFgsgkc/U1ZC9rkOBZSzJ+H2Zb6WjBufhYhAwO1A6CIR7ORB52npuQ== X-Received: from pjbsd7.prod.google.com ([2002:a17:90b:5147:b0:2ea:5469:76c2]) (user=almasrymina job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:51c4:b0:2ee:aa28:79aa with SMTP id 98e67ed59e1d1-2f2e91a9815mr307291a91.6.1734466327882; Tue, 17 Dec 2024 12:12:07 -0800 (PST) Date: Tue, 17 Dec 2024 20:12:06 +0000 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.47.1.613.gc27f4b7a9f-goog Message-ID: <20241217201206.2360389-1-almasrymina@google.com> Subject: [PATCH net-next v5] net: Document netmem driver support From: Mina Almasry To: netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Mina Almasry , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet X-Patchwork-Delegate: kuba@kernel.org Document expectations from drivers looking to add support for device memory tcp or other netmem based features. Signed-off-by: Mina Almasry --- v5 (forked from the merged series): - Describe benefits of netmem (Shannon). - Specify that netmem is for payload pages (Jakub). - Clarify what recycling the driver can do (Jakub). - Clarify why the driver needs to use DMA_SYNC and DMA_MAP pp flags (Shannon). v4: - Address comments from Randy. - Change docs to netmem focus (Jakub). - Address comments from Jakub. --- Documentation/networking/index.rst | 1 + Documentation/networking/netmem.rst | 79 +++++++++++++++++++++++++++++ 2 files changed, 80 insertions(+) create mode 100644 Documentation/networking/netmem.rst diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst index 46c178e564b3..058193ed2eeb 100644 --- a/Documentation/networking/index.rst +++ b/Documentation/networking/index.rst @@ -86,6 +86,7 @@ Contents: netdevices netfilter-sysctl netif-msg + netmem nexthop-group-resilient nf_conntrack-sysctl nf_flowtable diff --git a/Documentation/networking/netmem.rst b/Documentation/networking/netmem.rst new file mode 100644 index 000000000000..7de21ddb5412 --- /dev/null +++ b/Documentation/networking/netmem.rst @@ -0,0 +1,79 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================================== +Netmem Support for Network Drivers +================================== + +This document outlines the requirements for network drivers to support netmem, +an abstract memory type that enables features like device memory TCP. By +supporting netmem, drivers can work with various underlying memory types +with little to no modification. + +Benefits of Netmem : + +* Flexibility: Netmem can be backed by different memory types (e.g., struct + page, DMA-buf), allowing drivers to support various use cases such as device + memory TCP. +* Future-proof: Drivers with netmem support are ready for upcoming + features that rely on it. +* Simplified Development: Drivers interact with a consistent API, + regardless of the underlying memory implementation. + +Driver Requirements +=================== + +1. The driver must support page_pool. + +2. The driver must support the tcp-data-split ethtool option. + +3. The driver must use the page_pool netmem APIs for payload memory. The netmem + APIs currently 1-to-1 correspond with page APIs. Conversion to netmem should + be achievable by switching the page APIs to netmem APIs and tracking memory + via netmem_refs in the driver rather than struct page * : + + - page_pool_alloc -> page_pool_alloc_netmem + - page_pool_get_dma_addr -> page_pool_get_dma_addr_netmem + - page_pool_put_page -> page_pool_put_netmem + + Not all page APIs have netmem equivalents at the moment. If your driver + relies on a missing netmem API, feel free to add and propose to netdev@, or + reach out to the maintainers and/or almasrymina@google.com for help adding + the netmem API. + +4. The driver must use the following PP_FLAGS: + + - PP_FLAG_DMA_MAP: netmem is not dma-mappable by the driver. The driver + must delegate the dma mapping to the page_pool, which knows when + dma-mapping is (or is not) appropriate. + - PP_FLAG_DMA_SYNC_DEV: netmem dma addr is not necessarily dma-syncable + by the driver. The driver must delegate the dma syncing to the page_pool, + which knows when dma-syncing is (or is not) appropriate. + - PP_FLAG_ALLOW_UNREADABLE_NETMEM. The driver must specify this flag iff + tcp-data-split is enabled. + +5. The driver must not assume the netmem is readable and/or backed by pages. + The netmem returned by the page_pool may be unreadable, in which case + netmem_address() will return NULL. The driver must correctly handle + unreadable netmem, i.e. don't attempt to handle its contents when + netmem_address() is NULL. + + Ideally, drivers should not have to check the underlying netmem type via + helpers like netmem_is_net_iov() or convert the netmem to any of its + underlying types via netmem_to_page() or netmem_to_net_iov(). In most cases, + netmem or page_pool helpers that abstract this complexity are provided + (and more can be added). + +6. The driver must use page_pool_dma_sync_netmem_for_cpu() in lieu of + dma_sync_single_range_for_cpu(). For some memory providers, dma_syncing for + CPU will be done by the page_pool, for others (particularly dmabuf memory + provider), dma syncing for CPU is the responsibility of the userspace using + dmabuf APIs. The driver must delegate the entire dma-syncing operation to + the page_pool which will do it correctly. + +7. Avoid implementing driver-specific recycling on top of the page_pool. Drivers + cannot hold onto a struct page to do their own recycling as the netmem may + not be backed by a struct page. However, you may hold onto a page_pool + reference with page_pool_fragment_netmem() or page_pool_ref_netmem() for + that purpose, but be mindful that some netmem types might have longer + circulation times, such as when userspace holds a reference in zerocopy + scenarios.