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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4F93FC54EAA for ; Thu, 26 Jan 2023 22:49:35 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DFDB86B0071; Thu, 26 Jan 2023 17:49:34 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D88206B0072; Thu, 26 Jan 2023 17:49:34 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C0B7F8E0001; Thu, 26 Jan 2023 17:49:34 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id AEAF06B0071 for ; Thu, 26 Jan 2023 17:49:34 -0500 (EST) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 87F348061F for ; Thu, 26 Jan 2023 22:49:34 +0000 (UTC) X-FDA: 80398443468.06.2FF4AB8 Received: from NAM12-MW2-obe.outbound.protection.outlook.com (mail-mw2nam12on2079.outbound.protection.outlook.com [40.107.244.79]) by imf25.hostedemail.com (Postfix) with ESMTP id 4E891A0003 for ; Thu, 26 Jan 2023 22:49:31 +0000 (UTC) Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b="RtyK/11k"; spf=pass (imf25.hostedemail.com: domain of jhubbard@nvidia.com designates 40.107.244.79 as permitted sender) smtp.mailfrom=jhubbard@nvidia.com; arc=pass ("microsoft.com:s=arcselector9901:i=1"); dmarc=pass (policy=reject) header.from=nvidia.com ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1674773371; h=from:from:sender: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:dkim-signature; bh=72MlngrVJhO8vi22N2nyiNPWPhFojC+8hVnkjp9yON4=; b=AxmlqEbAo5VeLzfMY1NL32rVlit1DEQCq2VfKZxvjqExfVxdVr13FWgKfZg/kL9L8VrrgY GPhmTXD1jQS3iyv30PbIeWUhcZloKd0yRCBfJ2vfDOIUucU6dVHK1ewK+jiy9iB76nVkoL +YYuWdS7+8KfEqZsBePwLpMQVPVqdyQ= ARC-Authentication-Results: i=2; imf25.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b="RtyK/11k"; spf=pass (imf25.hostedemail.com: domain of jhubbard@nvidia.com designates 40.107.244.79 as permitted sender) smtp.mailfrom=jhubbard@nvidia.com; arc=pass ("microsoft.com:s=arcselector9901:i=1"); dmarc=pass (policy=reject) header.from=nvidia.com ARC-Seal: i=2; s=arc-20220608; d=hostedemail.com; t=1674773371; a=rsa-sha256; cv=pass; b=sPPWTO3HNzhybr4Bcof6TUhMRHq6wipRudJ2t4+6Qen9sP7dGNE1whu+6/6m7R7MATYNm9 HA1S58+ITCqzHKR3lbRUWzYhGr24zKMk55+pq0LwTAR1D6oZtIrFE5UixWCNnq9xLp8PMi eiR7eN+2q1E4nSwrE/2B3Xwe5czLam0= ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=eJ7JvpXsrwFjOt9+HpB6z9eH79sGY+0+PSzMcrTEcowNzgrWNuCj6C8ouyKqFJg5uGu8GjgYZRNpMIeOsZpcSXSYbanKZa412L1NQX35QMccyUrkwdv+ewLIctL1aiEA3V0DdR/CHL303cJgcHckG5wEi+cOcGBq53DsG1OYpQyMc40bdbr11lHQUSVxg2cKmE1NtoEF/XTtNN6vPDDfoZxnlFNWnNTnNpnZIh95jvSTthY0DOEVeEfo2O4mHqC4DMeuk9i0hmzz1Nn7rQjy7eVsKznyLbocXych8sk6UiJGfU2qBGPj81khNGhPQSrdHtFVTb9NWzVI2JyF5WAHVQ== 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=72MlngrVJhO8vi22N2nyiNPWPhFojC+8hVnkjp9yON4=; b=EUoX8164jG5JoMsrzktbsbI5rSeQTWC1pIixo4tJ/7CCRsvQ2BLx2KXW3DPG/fG0dbbsO4nAmu1yhKgmX76h04B5F0+FDgc7g7lTzorLtq+AdmvgUKeUHOtfTT5B5rVupSRcXjyUDD4mz/zKHtpLu1G7vt1RoWXf9L9iaDtJwNZp/VGVWsFl+b6Qc80G8iM+u8DCezUGHnYgcXfy/B9SCpf1l0Y35p30JIGUzteMjY9B6YpaZLE4bW70bXkp5IYxBYKiKjUGLUUp46oN0YAF66qkWigBYqYoFKyy4/SNSCPl18saAFzG6SOztheq2imAdSceb/ms7MmUuS/5s+pbGg== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass (sender ip is 216.228.117.160) smtp.rcpttodomain=zeniv.linux.org.uk smtp.mailfrom=nvidia.com; dmarc=pass (p=reject sp=reject pct=100) action=none header.from=nvidia.com; dkim=none (message not signed); 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=72MlngrVJhO8vi22N2nyiNPWPhFojC+8hVnkjp9yON4=; b=RtyK/11kkuP1qrdWTvco3wocOCGASsIKXoDnEJQMN1xKj1kh10Am1CcGbHDB6Y7DMAer813Sfr/6+0cMi2y+6bF9oDLpjZ4dZA+7gOb+mkRGuZ0IsOMcKFkq2qRm7BXjzMfGibdVxFEaRIxW1Cf1fIQe2nGp03CVU9zUzr44syAshLOtYilBrb+e4glmIioSir4HSw6Kjifusu3bHcNzYu2en4iIcFYl+FwpCHYk1HH75EAcCZaSIexlQE+5gOg1no/go3N7kQ93GdjYep2qKtJefvIukfiA/bwO4HIh45wCtsZSW4mL12it3ApLpDuiH1YPk3lOvKDuNsvB18lJIw== Received: from DM6PR13CA0032.namprd13.prod.outlook.com (2603:10b6:5:bc::45) by CY5PR12MB6370.namprd12.prod.outlook.com (2603:10b6:930:20::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6043.22; Thu, 26 Jan 2023 22:49:27 +0000 Received: from DM6NAM11FT009.eop-nam11.prod.protection.outlook.com (2603:10b6:5:bc:cafe::f4) by DM6PR13CA0032.outlook.office365.com (2603:10b6:5:bc::45) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6043.22 via Frontend Transport; Thu, 26 Jan 2023 22:49:27 +0000 X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 216.228.117.160) smtp.mailfrom=nvidia.com; dkim=none (message not signed) header.d=none;dmarc=pass action=none header.from=nvidia.com; Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates 216.228.117.160 as permitted sender) receiver=protection.outlook.com; client-ip=216.228.117.160; helo=mail.nvidia.com; pr=C Received: from mail.nvidia.com (216.228.117.160) by DM6NAM11FT009.mail.protection.outlook.com (10.13.173.20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6043.22 via Frontend Transport; Thu, 26 Jan 2023 22:49:27 +0000 Received: from rnnvmail201.nvidia.com (10.129.68.8) by mail.nvidia.com (10.129.200.66) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.36; Thu, 26 Jan 2023 14:49:18 -0800 Received: from [10.110.48.28] (10.126.231.37) by rnnvmail201.nvidia.com (10.129.68.8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.36; Thu, 26 Jan 2023 14:49:18 -0800 Message-ID: Date: Thu, 26 Jan 2023 14:49:17 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH v11 2/8] iov_iter: Add a function to extract a page list from an iterator Content-Language: en-US To: Al Viro , David Howells CC: Christoph Hellwig , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , David Hildenbrand , "Jason Gunthorpe" , Logan Gunthorpe , , , , , Christoph Hellwig References: <20230126141626.2809643-1-dhowells@redhat.com> <20230126141626.2809643-3-dhowells@redhat.com> From: John Hubbard In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.126.231.37] X-ClientProxiedBy: rnnvmail201.nvidia.com (10.129.68.8) To rnnvmail201.nvidia.com (10.129.68.8) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6NAM11FT009:EE_|CY5PR12MB6370:EE_ X-MS-Office365-Filtering-Correlation-Id: 6f665809-61e2-4588-6374-08daffef9443 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:216.228.117.160;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge1.nvidia.com;CAT:NONE;SFS:(13230025)(4636009)(396003)(136003)(376002)(346002)(39860400002)(451199018)(40470700004)(46966006)(36840700001)(16526019)(186003)(31686004)(26005)(478600001)(966005)(47076005)(336012)(2616005)(82310400005)(426003)(83380400001)(316002)(54906003)(41300700001)(8676002)(7636003)(356005)(70206006)(53546011)(82740400003)(16576012)(110136005)(86362001)(36756003)(5660300002)(40460700003)(7416002)(8936002)(4326008)(70586007)(31696002)(40480700001)(2906002)(36860700001)(43740500002);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Jan 2023 22:49:27.4651 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 6f665809-61e2-4588-6374-08daffef9443 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT009.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY5PR12MB6370 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4E891A0003 X-Stat-Signature: w788eabf4a5odet6nykerbdiipwi5rwx X-HE-Tag: 1674773371-66818 X-HE-Meta: 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 QKLKC7Nx 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 1/26/23 14:36, Al Viro wrote: ... >>> +static inline bool iov_iter_extract_will_pin(const struct iov_iter *iter) >>> +{ >>> + return user_backed_iter(iter); >>> +} >>> + >> >> Wait a sec; why would we want a pin for pages we won't be modifying? >> A reference - sure, but... > > After having looked through the earlier iterations of the patchset - > sorry, but that won't fly for (at least) vmsplice(). There we can't > pin those suckers; thankfully, we don't need to - they are used only > for fetches, so FOLL_GET is sufficient. With your "we'll just pin them, > source or destination" you won't be able to convert at least that > call of iov_iter_get_pages2(). And there might be other similar cases; > I won't swear there's more, but ISTR running into more than one of > the "pin won't be OK here, but fortunately it's a data source" places. Assuming that "page is a data source" means that we are writing out from the page to a block device (so, a WRITE operation, which of course actually *reads* from the page), then... ...one thing I'm worried about now is whether Jan's original problem report [1] can be fixed, because that involves page writeback. And it seems like we need to mark the pages involved as "maybe dma-pinned" via FOLL_PIN pins, in order to solve it. Or am I missing a key point (I hope)? [1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz/T/#u thanks, -- John Hubbard NVIDIA