From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7316ECAAD8 for ; Wed, 21 Sep 2022 14:10:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229990AbiIUOKy (ORCPT ); Wed, 21 Sep 2022 10:10:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43526 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230131AbiIUOKp (ORCPT ); Wed, 21 Sep 2022 10:10:45 -0400 Received: from NAM10-DM6-obe.outbound.protection.outlook.com (mail-dm6nam10on2045.outbound.protection.outlook.com [40.107.93.45]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C41868E0DA; Wed, 21 Sep 2022 07:10:38 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=HqUI+CHxcjCosoG3vd852mQqqV7qDy5CqqOBDbHRTK1uZUiRHlmNZzKMaAr6ZYaVSSxwCuNkDL8fbBEAhy2iscjhi3l2N5MvrhEupYwe1fMbyvTapHUOvdybD9JxZIOigX97l9TGyTFptNL5D/qmCN6VjaC6ME442JIb77mbiY2WgvCNgBAnx6qAP021+hB3Bfxap+WvZwo+Tch3JAixBGkabKEJe9h4/Bm/+dl1XkUmINIA0MWjadO+Im7oPH1OS6XL0ca2eZIbZegKQJH5+8b9eS0hUz812SHp3HZL8te4nILDjJFPFHQAV3O/hF9yje4AinUdp6ARB28TBeAWkA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; 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=uJS+Rrn+hgF13hGWR2dza3J6d5hy7BxMAKRiDc0GH/4=; b=G0mRK35JWQlhAC0QGp3/2MO1HyjRgSxsdt/vZHpeGpvAQ1RrU7nbu0WSPP2XOujeZpSB7SdwLwRM4Pzp2/Obl7K8z285SzwAWe9MekugcFVOKGP6gA0wzV5TjuFHVe+SMv0VGbvLYFyv30Pnoxb+vYXreqNVR6enjt8dc2JbLwLNaDmLBk1YQBtHJu5jnwTr7Jog/WpGVntIMwgc8ywex838PnuvjkZ95qh+6d5TYBvCNKw7WeOTM8nQBiX82kmkiLCgX94nhnqGPGC6ErMnRIMdOQOH9BeIBUeLrmt5BNpgg7A/WtJ9jmceUkUWLlSua9MR5tXA34tPzwWLqzUz/w== 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=uJS+Rrn+hgF13hGWR2dza3J6d5hy7BxMAKRiDc0GH/4=; b=Q8f2wcAW+yzSE3+2iiWlm+MrKITDeQ8QBfGeVNXDUrMTvTKND7l8zGyLRnv3vFVsnSssPKRCMluflr14VPQkscwIqMBPqeA4Rg3z5SNo49egZavUAJwnNB4JS1V/Jy+Lw9dLaDFidf8d+p7oXG+IJkk4dNe+j+z0M8r8Sj4A1r11qnfUVnZTXid1yw08bvzS0edwQvTVymeTQbLZ6kMZp0sgQogvELZgHkODMCkaDi2kKt3xoA05uO3iYBIoXs0BIcd2GiqPqEUFpW+dgLMdbvVnup4QWv6+gLLgPCpqCJ1HOPbnfwpmHjmMQf4Fh4NCFlsL8CQXW8Xi9HXayrsyPA== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from MN2PR12MB4192.namprd12.prod.outlook.com (2603:10b6:208:1d5::15) by CH2PR12MB4905.namprd12.prod.outlook.com (2603:10b6:610:64::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.5632.18; Wed, 21 Sep 2022 14:10:37 +0000 Received: from MN2PR12MB4192.namprd12.prod.outlook.com ([fe80::462:7fe:f04f:d0d5]) by MN2PR12MB4192.namprd12.prod.outlook.com ([fe80::462:7fe:f04f:d0d5%7]) with mapi id 15.20.5654.016; Wed, 21 Sep 2022 14:10:37 +0000 Date: Wed, 21 Sep 2022 11:10:36 -0300 From: Jason Gunthorpe To: Dan Williams Cc: akpm@linux-foundation.org, Matthew Wilcox , Jan Kara , "Darrick J. Wong" , Christoph Hellwig , John Hubbard , linux-fsdevel@vger.kernel.org, nvdimm@lists.linux.dev, linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-ext4@vger.kernel.org Subject: Re: [PATCH v2 15/18] devdax: Use dax_insert_entry() + dax_delete_mapping_entry() Message-ID: References: <166329930818.2786261.6086109734008025807.stgit@dwillia2-xfh.jf.intel.com> <166329939733.2786261.13946962468817639563.stgit@dwillia2-xfh.jf.intel.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <166329939733.2786261.13946962468817639563.stgit@dwillia2-xfh.jf.intel.com> X-ClientProxiedBy: BL1P223CA0007.NAMP223.PROD.OUTLOOK.COM (2603:10b6:208:2c4::12) To MN2PR12MB4192.namprd12.prod.outlook.com (2603:10b6:208:1d5::15) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MN2PR12MB4192:EE_|CH2PR12MB4905:EE_ X-MS-Office365-Filtering-Correlation-Id: b9b8a288-aa92-4995-6350-08da9bdb0e54 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:MN2PR12MB4192.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230022)(4636009)(39860400002)(376002)(346002)(396003)(136003)(366004)(451199015)(26005)(6512007)(2616005)(478600001)(6506007)(6486002)(41300700001)(38100700002)(86362001)(186003)(8936002)(36756003)(83380400001)(66476007)(66556008)(2906002)(316002)(66946007)(5660300002)(54906003)(6916009)(7416002)(4326008)(8676002);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?w8CyrvbyXu+/6j8KrRQK5Jk0St6G/2Tngt7AuLXFcA3d9mVsWtXRMCtpnF8C?= =?us-ascii?Q?iO3LET7tK1vhVVxGpepCJNS+7onKOdLwcI1AXE9wPfEpvIRufJ3EaXPsrN2w?= =?us-ascii?Q?kNGtv4OOD+nGoECrpAd+G2cKbSQ+VCL5nD3GhJXSV9OOEXa59C39veQguZ41?= =?us-ascii?Q?b7YYrGgZkjRmwJOa5Di05cm57ToRxncLn8/llPqQ0xI7UAerjUNLOOxnB2NP?= =?us-ascii?Q?0yCaT1FTt5aGEOyg9rTEgIyUdU5L66iDQsCP2yBNL2hYhOqt9gH+ylxyryVL?= =?us-ascii?Q?GJJWNpbYCUYIiDDB6CLVlqkfZjGU2JMhV3uGBePqAiGa2JVCOjnMGQLqTEjp?= =?us-ascii?Q?7AHKirWsXl6HyegZ2UnLSgHeQosKAlgicrsJdTKiuBcn3y2kjnmfK0MfOXvl?= =?us-ascii?Q?JIMVbZVsxXSKfiLUrhvYcgZndcx932DDF/qD7u5aQfFL648H2GhY533mGAY5?= =?us-ascii?Q?yByg81cnbhKbAPIg/6VR2JgqTxbhth4gYwfMvgnVpircfabkGdj/trT5OD/Y?= =?us-ascii?Q?cr3eKELHRhqUHRx0GbtQzcKxLJwq4/bDEaMlMw+GqTwGDmtak0cUWSeYO2us?= =?us-ascii?Q?S4pAx9Fb10kzVPXZZDZdGYlRLEwInpYZmurlWnMdma8ZyqA+GlYAjiFGcczC?= =?us-ascii?Q?tUyJ2NPznKkJ+peXAGvTGTs0h6r2HtOHmkNYPScNf62SHg33YDRB/bAmQdyC?= =?us-ascii?Q?mGbsJVgpEI4TUC89DyeiCRT4F5p0RSfgFH0fSqKY6vGWS73fTz1FHHsfsfzF?= =?us-ascii?Q?Wt/Dq6RKa8bTlzbS7hvv9lS9WH9ALEEEyeXdpPrTCA7bFvWBAhofSvESyhM/?= =?us-ascii?Q?YVnvPFR6+XQy9dV8gkbDuE0QIiVx2UWxxCXi0Rxg0607pWleeMsPaDbgtW4O?= =?us-ascii?Q?HjJPxWa6VALIrxE7iw7yv7BaKUwG35VhZVAwPyO6KEF5OVK4mO3Ck7/C4zKU?= =?us-ascii?Q?UDDZ0KH85VKP5/re/l2tsNjF2ekKYOV4+ZAdr88EOoF/74onetRNPGXdopm6?= =?us-ascii?Q?ysNKsTFaY5TUy7mQnMg9sBzsdI4+K1ATOE32W7f8qKsXQKMhiWeERZEDUGxs?= =?us-ascii?Q?gTBdjHCWr0S81On9PkRPrcT8seRjakGbbyH9EIsv0v4xOI5MpR28qYj90NO/?= =?us-ascii?Q?+z/1a+zrVZn5bFxYVrbsZwYpwuhUdwn/hfJ8zK9rnyiBnwsgP83gPd2Wpgbd?= =?us-ascii?Q?cBF+1TPvGx/vFa63MXqdJvE6tjDaC+YWFz6Pn6gD0wMr62GFpKfrbb8PI5E9?= =?us-ascii?Q?kCv/Jr59quWJVcGBOA/oKupT4bzkYG9anowtum7QeTTJL9yek4Jeiq0UjHFu?= =?us-ascii?Q?6fTdlxqaF0nwwe/73s03TAAPlf5SIQm81isDPJm63MuuyBSUqepCtFckDxnU?= =?us-ascii?Q?C0ti1Zp/pfFJc0mxt5XDBmQQuEkkOgvDIM6ev+6myKSmgZ8M9pkb+IgIkC1B?= =?us-ascii?Q?/DmluC7Wif67Vwc2Iygyu7YFurGV5/invVUrFg8icNeqLV6FHQ+1ndYskwcw?= =?us-ascii?Q?GNHU4NeOutFLVtXMCoS+EFUR6du1+tKUX8kCGeEDBc29wOTWAlqudMyrFnXw?= =?us-ascii?Q?9n3hgSN3l935vmz53sCbKSENNNOSVFYnIYnAi2ZY?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: b9b8a288-aa92-4995-6350-08da9bdb0e54 X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB4192.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Sep 2022 14:10:36.8619 (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: 4+XyaIlUb5kOxdf/eQX5XxXq02W8OHs6q47EcNg52hlLou87Dw73MIc+fCCCb8FN X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR12MB4905 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Sep 15, 2022 at 08:36:37PM -0700, Dan Williams wrote: > Track entries and take pgmap references at mapping insertion time. > Revoke mappings (dax_zap_mappings()) and drop the associated pgmap > references at device destruction or inode eviction time. With this in > place, and the fsdax equivalent already in place, the gup code no longer > needs to consider PTE_DEVMAP as an indicator to get a pgmap reference > before taking a page reference. > > In other words, GUP takes additional references on mapped pages. Until > now, DAX in all its forms was failing to take references at mapping > time. With that fixed there is no longer a requirement for gup to manage > @pgmap references. However, that cleanup is saved for a follow-on patch. A page->pgmap must be valid and stable so long as a page has a positive refcount. Once we fixed the refcount GUP is automatically fine. So this explanation seems confusing. If dax code needs other changes to maintain that invarient it should be spelled out what those are and why, but the instant we fix the refcount we can delete the stuff in gup.c and everywhere else. Jason