From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from CH5PR02CU005.outbound.protection.outlook.com (mail-northcentralusazon11012023.outbound.protection.outlook.com [40.107.200.23]) (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 DB4E737F8D6; Mon, 24 Aug 2026 17:38:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.200.23 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787593114; cv=fail; b=KENof371p4kmBuKSWFA1PPCVlalQWTP32HNEV1kpiRXa9zCPSoXoecC7hb/anJuHE3iU0LZoLAKVxufAm9J0TXd4vZIZ0If+BJZf/wPvWEm2h74qaXW3bTCaeBp6vIb8oOfejtDo4T64sDhNH+Q4bmJrEtqC1p355z20ZC44v6U= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787593114; c=relaxed/simple; bh=Da02aj3Y4SCKgu/h2DDL02fR2kiwrhB/fIB9LhNW+Fg=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=BiDH3qVmPMRfirwfvai4xdXrSxK8M0EVUnTJZtH+izi9nIojsUnXvMJ41emtYOn9DIjJPeN5HOF66SNyptpVQT3QQ91+euSLYrzxQ52p9/psw2m+XvhDv8/N++fR960W1V/AueILlYRPmYCA7IiX0dkPyIKl6dvWcZrS/uyrGUQ= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; spf=fail smtp.mailfrom=nvidia.com; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b=nqJLptia; arc=fail smtp.client-ip=40.107.200.23 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nvidia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b="nqJLptia" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=Jhze1EDMWaOkzRnmdorug4obgWyjW3NwhNyW/qSL/806hMvF4XwRzhW3C47KRCX/3lFmVctNo9Le/20iohGW81v5e7+D9t44X/ctjk/VphKpdEFflwBAIgyQob5s09NgbIIULVYhOaCdSAve4hqzmaHDLIOJsNyP66zRWxh7w3vPtvREKjk2wo9VpLTE4MgKoIdyWY6+gwx/kdHMhwEnC8h6r8iwyUG4tUPe5ZAQjXe2Q6qQ2/ZpS1f7aurR6fw3VOSGsWz5XiVlS3ENwRyxNSSwbkiEQ19FHD/QJncLYoeG7wYF2NCLN8pcMcwOHahda1aJdK42/t4X/9NW8hIJYA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=hm3h8e+sMh+d/mdJtHeW5XUau1BL5R/3hDeAxrWkbdw=; b=SfCTihQJ82uCpg9plc9LRdy0Yxdh1XsoW3JiSx+0ieV2KxL/ct+hRjF9axzPLdL44yMItWNxIuoeXedgbM+JG446uJ79GFXW0iRNhewJTS77OVu8DfayCqIM+J7uYb097Ry84i5JC9xUxicBpKr58u7Tqvzkjw7e+nI9HjwlDCk8fdQ9l6LzIqqnUW/WzSbQAWe3yhYN3/HYuJfhx+7cRjTTo6ltVhOCjMf+jNYolqhwfQhr8kw1+1j4gAg8quWw2HnuFeGZJIKw94ICDowas8jD8QhMKFK9lwfaRABvizVVsMh1geu687NvVJCXYY8eHfNInAhln6N57/yAYqmv+A== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nvidia.com; dmarc=pass action=none header.from=nvidia.com; dkim=pass header.d=nvidia.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Nvidia.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=hm3h8e+sMh+d/mdJtHeW5XUau1BL5R/3hDeAxrWkbdw=; b=nqJLptiaYj7W7mMAg13+HndIzTn//6xtY4uJiCwZk5hs1iuAokvvUhCQYN2gyzYh+mGs+8B9AAIigHE3+kyEdi8vn7W8GMVMbmV7cS+iAihLLDsI9F/XDCRtyAz4p84Ouw1CK9SXee5JQX0mvuNln+nRz8Jbok/nlKuvT/7kiZL/dQNkjVeQNAm3bQFcokfP5V2yCu0McgojLln/3UCA1xgycVD7XT3xKKMk8CIEy4weXM+YQRS/7fCJMUdbfVX2fODjBgS5nisdu1AnuOSrsuwL+ek+x5gauAcDVKkn3mlt/NBpTZ/UfwC5YUmDE4srBznx8ZirtZ+ujcMzH9cPiQ== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from CH3PR12MB8728.namprd12.prod.outlook.com (2603:10b6:610:171::12) by SN7PR12MB8820.namprd12.prod.outlook.com (2603:10b6:806:341::5) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.339.12; Mon, 24 Aug 2026 17:38:11 +0000 Received: from CH3PR12MB8728.namprd12.prod.outlook.com ([fe80::2641:1046:bdf3:93d7]) by CH3PR12MB8728.namprd12.prod.outlook.com ([fe80::2641:1046:bdf3:93d7%6]) with mapi id 15.21.0339.012; Mon, 24 Aug 2026 17:38:11 +0000 Message-ID: <472d9fe1-0044-4e47-af5f-cb03618d77b0@nvidia.com> Date: Mon, 24 Aug 2026 19:38:05 +0200 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH v2 2/5] swiotlb/mm: Implement SWIOTLB nocopy page allocator To: Luigi Rizzo , Robin Murphy Cc: Marek Szyprowski , Willem de Bruijn , Kuniyuki Iwashima , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Luigi Rizzo , Greg Kroah-Hartman , "Rafael J . Wysocki" , Andrew Morton , David Hildenbrand , netdev@vger.kernel.org, linux-mm@kvack.org, iommu@lists.linux.dev, driver-core@lists.linux.dev, linux-kernel@vger.kernel.org References: <20260615234220.3946885-1-lrizzo@google.com> <20260824152932.1583506-1-lrizzo@google.com> <20260824152932.1583506-3-lrizzo@google.com> Content-Language: en-US From: Dragos Tatulea In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR0P281CA0204.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:ad::13) To CH3PR12MB8728.namprd12.prod.outlook.com (2603:10b6:610:171::12) Precedence: bulk X-Mailing-List: driver-core@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PR12MB8728:EE_|SN7PR12MB8820:EE_ X-MS-Office365-Filtering-Correlation-Id: 959c2f8f-e659-4e41-15d5-08df020677e3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|7416014|23010399003|376014|4143699003|10067099003|11063799006|56012099006|22082099003|18002099003; X-Microsoft-Antispam-Message-Info: cshxjT6SKBA5VDevf7UY09Eg8mBJfiegjEmH4LD3yEvX9LSRcUVhGm+WA/vZtZNRG0a/6544DpySqlb/AeboEX1li9HcdZUdSXGyyze9xBjuF655YH62slrsg02zAFHptFMtZG+7TQap/7ekw4k1okYXgw5kXbcUqnFCJrdx4RBboKXbgk1CSRjxHwBeFmgFmZBBIGTK5V3vhcUEPlCFHiD/HVii/6JpQK/ow9sb61xgMR2IoZnBzA76YzHcrzczHQ6ZlwxEYtvuJdaq1j4vt4r3n3DAJqZKe/E5v5/clcUnhZ7dJDnewNPa6kkM514GfDafIbh/u4ZwDx4oDq34qAXSKz9s0DgcTzGFF35pyCorjoh6AXMdIXX9HN1zjnZDp2fvKvAhHrNrw96IInXSfCIVwcoWc7vDNNsp5jEL7ZVRd/lEIwliVoKBcfsoIVZcY11pvnuFA81W+taQ7j8smWWlCi1zvvLgg2F0NnlZiTBa7RwRbEOwBsOCx7Wg+GmoAR8VJP01/ULcwwdklRCuvEcV5fsJaKGlxaBvaNCKlbDSFz5oNseuMWBE2Jr2Xyq12DQ1XJ3ayJ6w3Er5Az73d1SiOB2bsInTJWgxWIy8w1OJvuFz12J6FQiTHD3ehK1QJfcykIDSa1gsRO0Usq1sTb5GnKIq5GDK+g7tVY529lc= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH3PR12MB8728.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(1800799024)(7416014)(23010399003)(376014)(4143699003)(10067099003)(11063799006)(56012099006)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?dTd2b3FMdlVWS2tZMzlXTXJnczhueVNkem5Xa0hiMUpiTHNsb3h1U240THBZ?= =?utf-8?B?WXNLYnJMUGx5Zm80N2FiVlJ1SWwrZDBYNEtBbXJZeHJUYmJoV2J5Y1hVUXE5?= =?utf-8?B?cG1ML1Q1QUc1NXhBclFFaFBJN3B2N3BpRFBYV2ZmU0hRWloxTUVVa0FtWUla?= =?utf-8?B?SXFmcVI5YS9ubjhUMDNRdmFHSHJuZGhmd2EyTDRZWTBYanBtN1VSdTdyMk5I?= =?utf-8?B?ZWY4RVVwUFZscUZCQUxObVFCMmtnNkQ5NEVRZEpIWUlPK3J3ZVpic0RVSEJS?= =?utf-8?B?THNpQ0R6T1ZNTWZjdkFQZER1MmMvdkZqZUJNRXZveFRoQ3o5Y3pXY0ZJMG1D?= =?utf-8?B?VFl4TlFlR2tRZ3VRVElpbFJ3RGppMXYrakRZQmFuS011S2J6UU1QdXZoek9r?= =?utf-8?B?azlEakRvUVZyUWtNdUFLMXU5YjJETDFZbVFRajdyTHQ0dWd1VFk0MGNtdXpy?= =?utf-8?B?NUhrL2pST0VXZzNXaWRLRjlRQkhTTVlHWWw0T2V4Z3ltQm9TRWRvRlF6YUVB?= =?utf-8?B?bGMyMXZhS0NUMXVBTFFlTmFLU1V2Q0tUcDV4T1gvMncwRWw1WThwdW1jYlZE?= =?utf-8?B?a3dtR09tbHRCUGdjbHVKRWFjT0JEYUlYUVhzc2swdjdtMVhFdDBsWml4VFo1?= =?utf-8?B?cmhDdnpIRnRKK0hhbXZTRmxEcHFzb2tkSUVSUklpeVljWThvY0RVQkxmemZK?= =?utf-8?B?aTg0ZVE2ckVjeFA3bzQ1bFQzK3BBNlBNajZyaVhNYU9rYXNkZ2RyZ0c5ck9N?= =?utf-8?B?cG1TNXdyU3JBQ0ZwVXdyb2Q0UGNaMkZ0aFJVMHBybk9pMU1yYmZnd3lEeUZ2?= =?utf-8?B?MkFPa1lJaXN6WE0vUzVCNDA4SU9EY0FUSHVZem9laTU2ejF4aGFtUy80MHdP?= =?utf-8?B?K3kxem5MV0NvRzlUMWRjbHBXQUs0N1ZEQWpPNVl1Y1ozRkZDNVlOSkJYNjBY?= =?utf-8?B?Z2YzL3R0NFhxQVgxeGJQYmdFUUMxNzcvR3pnRnY1MStrMnM0SWx4OWJPVUhm?= =?utf-8?B?RDhMSjZDaXA4eTVjQmxjMEFKdEgrZDZRZzFheC9tUUNSdjU0UUxCaC9jNE9k?= =?utf-8?B?U0R5VE82WGJVeGVQc1VLSWdrcldRb3ppSk8rTHhzdjkrc0xxRG9pRW1udXhV?= =?utf-8?B?NDZoVTlzRGR3VVV1SlFsYjdnZjJEVjc1dkdVUDhBbForNWhCdEJvdFUrZ3Ru?= =?utf-8?B?SU8rRmUzRE1hdU1GYzJJV1ZLaGFNdndibDUwN0kxSEFNRXpadVR4eXpEVEV3?= =?utf-8?B?cFNLYVNSN1M0RjMwam9BdlRXaXpMMVBDQnZQNWo5Zk80M1RYZlRQZGhKYThi?= =?utf-8?B?RUczbjlnM3RMczFjUjFTM2gvS2NycWVJd2owUzAzWVdWMkxxV3BRV2llSzBx?= =?utf-8?B?eVdreExLazk5MUJ2cWdPdXRucG5uK0tEaE04V1ZmK1Q3b2ZxTWVVd3RJREtT?= =?utf-8?B?Rm1VUzBzcFFDK0xoZk9Ta0NGVjhjeTV5aXFsRWZFbk1HMzVkdDdPOVZ4eVFU?= =?utf-8?B?SnZQazU0NEZxOTNVem1IQVBhc1NvNnhyVm44eWdyTHFUZm95U205UWp0RERt?= =?utf-8?B?blJCNEtJUVFLdHZxcUR0bE9JcHJUVFgvdUxwamtLbmNZbDlrS3RuUDBlMXJT?= =?utf-8?B?aUEzNmQ2U3hVZGV4MzgyeWxJWmZCVEdnQkgzWEk0SFgwQlIzdUhpWXplTkEx?= =?utf-8?B?WS9vRklwdVpza25uWHp2Y2p5NDZFWlQvV1p1eHBpQVc3bVlORVZnYjl6K28v?= =?utf-8?B?YXlKUU1nNjlpb1hQRWljcE5JNXZ3RW1IUzVlaXhnb0JjeXhVbkMrMDBHV2xn?= =?utf-8?B?TkJtRkJFc2JIRGtacUE2Wko0Tk5Bc3pYRUdxUHYwT2VLZnlxL3JUZ0FxbW5R?= =?utf-8?B?RWJQSC9RdEpXYjg3QTByeXBuTGtuYkpJSDlVRzRjQzUwZGY5TG5lTEVrb3d0?= =?utf-8?B?QXJxMEdUZnltMmFqWEhERC9PWnl0WnI1eU9nc3RJUU9oMFN4V3BaOUxOYlBU?= =?utf-8?B?dmVnMStzTUVCZ2x4akZkdytFaXRkYlVWWm9RWndFMU5peXNFTmtHd3c0TmI2?= =?utf-8?B?SStsZ1ZNWXM5TWJNMksrV2hlWWlpRkp4b0RMalh1aVpURW1FeWdmR1pXS1ky?= =?utf-8?B?cUNzWnVGcDdoZzJIRlI1SG91dVNmV2NRY0hKRjZsMlhpSHQvaWdTNnVhN3FM?= =?utf-8?B?MzhCdXBsUktTYis0ejU1TXhKcmxQZENtbmdNRi9tMzY1dTR6UjN4UkxqbHlm?= =?utf-8?B?c2tMLzd1SkdRNjdCOVhtZ3l5RjIxaGdXelpIOXBkR29aVHVYWUt3RzFuekpI?= =?utf-8?B?S2s2bHRSOS9RS1FBSXF1bE1relk3VmVtS3BIQnd2TlFuNEV5WjlkZz09?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 959c2f8f-e659-4e41-15d5-08df020677e3 X-MS-Exchange-CrossTenant-AuthSource: CH3PR12MB8728.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Aug 2026 17:38:11.6550 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: md0Zn1yei7aJBqgTuVk+9LNllLK+xUdiBfjIaeVNvunz33vlXGdezRCnrdVRqXb+nx/iwaN3YX9cgmfwDwLh5g== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB8820 On 24.08.26 18:30, Luigi Rizzo wrote: > On Mon, Aug 24, 2026 at 6:06 PM Robin Murphy wrote: >> >> On 2026-08-24 4:29 pm, Luigi Rizzo wrote: >>> Introduce swiotlb_alloc_pages() and swiotlb_free_pages() to allocate >>> and release compound pages directly from the default SWIOTLB pool. >> >> Huh? The sole intended purpose of SWIOTLB is for bounce-buffering data >> which already exists in some other memory that is unsuitable for DMA for >> whatever reason. If you want to allocate directly from some kind of >> pre-shared DMA page pool to avoid bounce-buffering, set up some kind of >> pre-shared DMA page pool and allocate from that in a manner which can >> avoid bouncing entirely (see DMA_ATTR_CC_SHARED). The idea of getting as >> far as calling swiotlb_bounce() to then have a special case saying "haha >> not really" seems entirely absurd. Don't hack stuff into the SWIOTLB >> code which has no business being there. > > Ah I see DMA_ATTR_CC_SHARED did not exist when I implemented the > swiotlb allocator. Cool, one less piece, it should be possible to replace > this chunk witth the DMA_ATTR_CC_SHARED. > I agree with Robin's point (if I understood it correctly): Why should it at all pass through the SWIOTLB? Why can't it be a standalone DMA pool? > The other pieces are still relevant though ? > > - use these dma-able pages for page pool allocations (small) > - [PATCH v2 3/5] net/swiotlb: Track bounce device per socket > or one would have to unconditionally allocate from that pool, > even for e.g. local sockets > - divert socket allocations for eligible sockets to a DMA-able pool > Thanks, Dragos