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 BAD21C8303C for ; Mon, 7 Jul 2025 18:06:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3F9CB8D0003; Mon, 7 Jul 2025 14:06:40 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3AA0F8D0002; Mon, 7 Jul 2025 14:06:40 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 272328D0003; Mon, 7 Jul 2025 14:06:40 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 14EFB8D0002 for ; Mon, 7 Jul 2025 14:06:40 -0400 (EDT) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 7450E128391 for ; Mon, 7 Jul 2025 18:06:39 +0000 (UTC) X-FDA: 83638248918.20.88133FA Received: from NAM12-BN8-obe.outbound.protection.outlook.com (mail-bn8nam12on2070.outbound.protection.outlook.com [40.107.237.70]) by imf03.hostedemail.com (Postfix) with ESMTP id CE18420013 for ; Mon, 7 Jul 2025 18:06:36 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=gLU2csgG; spf=pass (imf03.hostedemail.com: domain of ziy@nvidia.com designates 40.107.237.70 as permitted sender) smtp.mailfrom=ziy@nvidia.com; dmarc=pass (policy=reject) header.from=nvidia.com; arc=pass ("microsoft.com:s=arcselector10001:i=1") ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1751911596; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=T49v6Wodb0ZYWWwT2oPBrMee5Cq1RuP62qT2RyLmtW8=; b=BsOrRKZ88g87nLm7xnHc/fwPGCWz0//EoY2aq6gwXQ42zx1jjUmgyTd5l4Q17WAg6ePNcT R/ar5oT1Z+h9VoZa9MLv5LUWLRdy1UFvkBnLZ8YQmaH58Xqw/5Ycrrpakfqc2ZWHjfd8rn b6rmij2ymuMcJDZkLPEaqX8zNZDwUNs= ARC-Authentication-Results: i=2; imf03.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=gLU2csgG; spf=pass (imf03.hostedemail.com: domain of ziy@nvidia.com designates 40.107.237.70 as permitted sender) smtp.mailfrom=ziy@nvidia.com; dmarc=pass (policy=reject) header.from=nvidia.com; arc=pass ("microsoft.com:s=arcselector10001:i=1") ARC-Seal: i=2; s=arc-20220608; d=hostedemail.com; t=1751911596; a=rsa-sha256; cv=pass; b=FuupGJ4btlftM8TB4UnZk82cn9FHeJCLW8QDDP7r1aeOxZs6A2oKBEc6mwQ2gSF+WaW4K2 S9dnoC2H8HTbJRJdGDWtgUfAD0UK6aVFGYfF9EEuvHwhxCyzu45dP4nLuBvi6q8ECxJ4Wa +h+LKpdplpVcW97eqpipmVmbPi8+808= ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=yxhIvA3TlXEloH0fZ+E6CiSpzP809F3Pw5wg/nlGGDVeGh7Cg9lziHkAI/6KGgMi/uJ2lLOBpk+LlyLkw9csT0X2vfAFOCjVJmu8WcU2V4+z1Vxrm1mPySYIAaSnWU7kM18m5MypnO9/r4SkMGXTb8KnfEDvGCndLJbOKNTDRLHGSeANf+Az5f+MIAAVvkcu91ec6Q60rIy8M340heqpcEPKDSLY9d5ETzFvlnY7cKT3mgGClTAoi0MR4ciYkUP3mcAFEBzvuluncDbEy7tHFGwzvIoE6nM4w1g0YSp7qJlroB/tU6s3NQLc7yGfiEgR6H+emDeJEdKdulb2ssvUyw== 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=T49v6Wodb0ZYWWwT2oPBrMee5Cq1RuP62qT2RyLmtW8=; b=Ioe1ft2nvu8vXwccaobTTbwYuBDspG1n7lFQ5Q0zt1TRqV/iM8NSRFzEpf+L8YntLIPfB5MyYevB625Hcf5bG3d2yv0seVUpKNVz42iqfOd3TaBb18ufgh/yezNB22/ZXWEAA7aWHIpDloqCCZIzOUmDumPqEzbO+isS3Z7MNEMigjRGsXhQhxkN5DdCQA+BwvF8TIJOMT8AEsnCLYi1oamuE+anjrH0SBySwwtOZg1hGpwk9vwyaKRXFDIoamqMIhIrYoVF2Lqr+n9Rrz4n6x2BecORdUXwQgXYyk/L0HqUifChdaaP8W+6tXjHu3qGxYtz3h9art9DRebVTaPUvQ== 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=T49v6Wodb0ZYWWwT2oPBrMee5Cq1RuP62qT2RyLmtW8=; b=gLU2csgGyUnaxeGkNHKenbwtZ0CmOTz8e0eQZfcuzq4PkSedYH+n4ttpxizwB5DkiXFUjnra4Fbcq8RFNjBqGhGnBGQa82HriwtUM9JW8gIK6KyXr7yQC+r0KtsdveVDqREUmhTrC+d9te0xSj8OPTAqbzYU0OCqskX9LVnsh20ZPmplN1XQfIcmIYyFSLazvrfwRYniPNStl3KGeGqy8x9JGHF3euPx4JMOHLBeqLMmQ8QFPZjSOIB4YQ2lHtM3/q9QXIo1NFJ7rnvHPvIQlRSMlcKbHVkaLAVcn5xybIiP50WQKwewY81pUjatFFosYvbULtPXFIJgLzgfQEZ5dg== Received: from DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) by DS2PR12MB9662.namprd12.prod.outlook.com (2603:10b6:8:27d::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8901.22; Mon, 7 Jul 2025 18:06:33 +0000 Received: from DS7PR12MB9473.namprd12.prod.outlook.com ([fe80::5189:ecec:d84a:133a]) by DS7PR12MB9473.namprd12.prod.outlook.com ([fe80::5189:ecec:d84a:133a%6]) with mapi id 15.20.8901.024; Mon, 7 Jul 2025 18:06:33 +0000 From: Zi Yan To: "Pankaj Raghav (Samsung)" Cc: Suren Baghdasaryan , Ryan Roberts , Baolin Wang , Borislav Petkov , Ingo Molnar , "H . Peter Anvin" , Vlastimil Babka , Mike Rapoport , Dave Hansen , Michal Hocko , David Hildenbrand , Lorenzo Stoakes , Andrew Morton , Thomas Gleixner , Nico Pache , Dev Jain , "Liam R . Howlett" , Jens Axboe , linux-kernel@vger.kernel.org, willy@infradead.org, linux-mm@kvack.org, x86@kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Darrick J . Wong" , mcgrof@kernel.org, gost.dev@samsung.com, hch@lst.de, Pankaj Raghav Subject: Re: [PATCH v2 0/5] add static PMD zero page support Date: Mon, 07 Jul 2025 14:06:22 -0400 X-Mailer: MailMate (2.0r6272) Message-ID: In-Reply-To: <20250707142319.319642-1-kernel@pankajraghav.com> References: <20250707142319.319642-1-kernel@pankajraghav.com> Content-Type: text/plain X-ClientProxiedBy: BL0PR05CA0018.namprd05.prod.outlook.com (2603:10b6:208:91::28) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB9473:EE_|DS2PR12MB9662:EE_ X-MS-Office365-Filtering-Correlation-Id: 20812098-a1ee-44b6-ac70-08ddbd8101c2 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|1800799024; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?Mbqcks+3QDN/acjWD7gbx6Iq9lZtz0yK7A34ZBHQKCnBa/1MUu3BgcHGCrXt?= =?us-ascii?Q?9xnrg9WyaFveIl+YmVL0MruOO0+nzRu4m6Gf7a6u7OfC2i6oPnq67SJ6yuJk?= =?us-ascii?Q?faGskZhCJIgwPuR/DQKib2wN17h5q3QMWPzZxity/RNq3RVS25to7C+8TgiM?= =?us-ascii?Q?qFa2QhA1vwLfoz0La+wprcwmfo/THVHYGmRjGyPjxWSnIuIJ+LwYsjjxqxD+?= =?us-ascii?Q?/YJIn1KMfE21YRf9Hd6nP56VFyoRtf63HKHf7NiP7U9MHGEdTSW66oI1xala?= =?us-ascii?Q?83jdLjvrdabvjiKWLCI7r5aBaJ4oxuOFr2hRW38BrMye6YJ1zB51lDHpO1gM?= =?us-ascii?Q?Hut46qxd1sv2+PLWWR1DkTS6ulFkQXbmU1STfSGncNVyL8/BCgAnFlgJ6b/5?= =?us-ascii?Q?WcftX9JwkiHT4jR/Xl5xKtOqhGjlb9zwJfQGzXX42ko05buVvXG56LHcRIIR?= =?us-ascii?Q?g1cKViUC2juJLlo+DMsYXu6Qi4qs0dlD0G75RQq1fmDDhmePYeQ/FznsU68f?= =?us-ascii?Q?DXVidg4fCElGZ2s84c/sTt+f3NvyZNPc4R/+xX826wa6VhByNaZtviyEvzL8?= =?us-ascii?Q?RuZVLUQVACQgnD19uUJbWI0wNnSIv9SJQfpD2IGwMz1V9qfb0AxO+zPa834T?= =?us-ascii?Q?58h0s4yp/sFCY4/4DXsOkOV+tmeniqQ3SoSeCKkT5gTpyGK3QV7z+4X//P6g?= =?us-ascii?Q?tVpw3L5eiN+1DygzNuqeXpT/awff0AownEwMrx1fGZks+6R4mh2N6QlHMPeM?= =?us-ascii?Q?RNhd0jR4PwrDr0daV4KsgJ8Zfdaeo7Dxh8Fz9WJnlaSoJnnuFV2Ge+z0QMMD?= =?us-ascii?Q?DF+cWEn85fcS78BFDd5n0reEq0mNzMQk6Wn4sxCNMJpS0An5GwpJTQVUUrxE?= =?us-ascii?Q?XZfTsw5K1RS0qrFhn6VKWbOi6YRPtNDt24KpG/rvtI+9tH8Pa8NxKX6dvjNc?= =?us-ascii?Q?A4ryYTxjWm/rTVdnFwLhVkG/H+l/OHO21qPGyhHgLvWsTvny7cPMkvxu+daA?= =?us-ascii?Q?EGioAkcIbjtYCVL57JjVVJPET5YJpxGlJITCeQNeOqnX+zoNdZRjNqKVR/DK?= =?us-ascii?Q?gATle/3N6c+lxRZrJxC4A54DbCRO0gS7m/BlXRv54aNZWICu8r77TqrwdXPx?= =?us-ascii?Q?K4Q9t3VEMK8N6XtC/Ir1om54yxVbZs19ohXpnQJReNDqWsLUIW4opN493yaz?= =?us-ascii?Q?RnG0zKrGPWjf7W/64EjWPu6MKMAtB6yL8JhUoM1QReUqrYfbAjRdw/7ras3w?= =?us-ascii?Q?N/XccuZ346EkSSvcvRliOfcZTSGwXRYxPpppcwto8g2Tte6gEKf7j19zUhst?= =?us-ascii?Q?Egel3qIMAFUz4q7ihFtSfxp+z/lw1ODjhZYr4TzzEDZcU9d3UziySHy/ICR5?= =?us-ascii?Q?Fz8Tn4vU1afK4/EwWpm0qm/5VaTZCC2rIMw2jEKWolLUHuoTDqxHpts5ZerB?= =?us-ascii?Q?1ht5o/5b5Fc=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DS7PR12MB9473.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(7416014)(366016)(1800799024);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?mqh8crd4iEwwPtLl1lcLFEGaeuxG3cOxTSucYfL9fcfiQbt+Oj/eccaPnhjl?= =?us-ascii?Q?HBOkolxPovqUP1lSXlHZybkEONIXCLx9lu1+iX8leBQ9U+mx6L+Qnc/FK8qX?= =?us-ascii?Q?9Rm5cYFss7P0b2nLh3t9zkMMgMIaSxZ9URvH3b+DZi92AkXdNsqYMIoc+T6i?= =?us-ascii?Q?4J+s0PD/qmlwd7rbnT63E0gVyFw+Akjvm8B1Ly7wyCm3+VOPo7PgSFtW5Xof?= =?us-ascii?Q?PAe2Gx0OQtO7qXfPTxRR5gmPLKRul3J3qp7uxUfAtOHcOfR6w73bf/SBfTve?= =?us-ascii?Q?95XQfxFF/LpGJCM9ATEphRIemcMeINZ3n2Q+zmqGWOcjMWlPufSmgtiKJ4p+?= =?us-ascii?Q?UTwdls6eJlHgV5ikQIjWgrg3cTmBUowhyBFAWuFAijIfBfDf8XsOMaLwL8gm?= =?us-ascii?Q?n9sCJ+XK6+6WYr259w8WlZb6fEwg8WQHixDG3kniGQhVtXW7iaUTXClDMPpc?= =?us-ascii?Q?E128wHR7lbXYu+mKO/BEkIv5SERGD71rAQVh9QL1wYwHHZVTTStZwp6/hhsp?= =?us-ascii?Q?+/FmaKfQdH/FA2SVXXJRvSFNyeIwUaTLDLTibxszgZTWKOxXhrb4NzQSyNFR?= =?us-ascii?Q?PbuwUndbq4EiyIT1j/KkFeX48tALbnKhFWD3sprz/XFwEZCFC4IdAM/1E7sO?= =?us-ascii?Q?PuSCy3W9HkkQwZiVTFXLEAHXmNh6mNMoXsn55Qxs4vau/HOOEriCUbBn9pto?= =?us-ascii?Q?RD0wmStgzW6C/gFkf0hsaKqvHFVwyrpLVhIIZ6sKfcSDeWQWaHlltrloYzlO?= =?us-ascii?Q?OTmzxTYNuKQiIO62mRI3480pB2wVZ/flDPi71Zg/tW1LU9JLxb7if/Is032e?= =?us-ascii?Q?znIiv7scEt465sgptexCgbmm8SWKi37cLtaz4K7JZ2xzOQ3VGOlf4nxzHluH?= =?us-ascii?Q?JdckTeG9WhtOwSj3INRIX4WCJJRAZSYKXO8rNbM9GAQEHbgWWgPbrUvCxCCk?= =?us-ascii?Q?JCsFcrNu3SDm2Vb7rPpZVJyDv7cmSsQgKAM6xcdxfB6aJc1oU8QCVlnlt8m1?= =?us-ascii?Q?AmrtzkWvaFi+5gTxSBd+RywhyeXW/O7A+R4QRd22jjdel2AIOs7gIP0FoS4K?= =?us-ascii?Q?cMgrHIcUW/y27IhXRZlFT8yqjtJW+7t5WSWS+c2inl6ECETs/J43GQNDgaSg?= =?us-ascii?Q?wUXL7I250OxXY6BaOSyzHaui8P+qGfuRutk2SHCfzLd6pSMuAEV+TrDCGHUS?= =?us-ascii?Q?IXodvI2du9Am7vYMuu/jmN6QQPy0hDB7BfJtIqDEOF8bnDcEWwv7/nOGzv1U?= =?us-ascii?Q?LLOVal89dOoOauTrLe4lZA7wcvOEVl+CGr5xvi/1BSvmXunRLNLV0Y1SdKYQ?= =?us-ascii?Q?SZlEJfpuinSPM7EO4yONRdifM3MpiAQZ0qJoD+KNgq+tCtEzQadMalflkFtI?= =?us-ascii?Q?u0tlstmMZfF1C6yaaVm2mwMRokJtNrVZVSipIfsqVl/x1eUvuG3Ny0qauxvJ?= =?us-ascii?Q?agi2vPqt3h9PfyTZZdV9+Uo/cVZk+KEnXlk3rA2vLmdP2LU4boJagiCFH0to?= =?us-ascii?Q?iILBA3s6MIWZTaNDCKlpVtjOy9GmG2W/YTHFat27+2O7UmA6y2CAatFJ6JYE?= =?us-ascii?Q?onvAfL2hDj0+MzH+pAmiSn7Fhu/qDfROVLtthd5N?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 20812098-a1ee-44b6-ac70-08ddbd8101c2 X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB9473.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Jul 2025 18:06:33.6655 (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: AUS2MkOlNaRUTSVpLqEfjukM9ATPCDb62rMJ35MrxXSWbPL0+ApYlIc3deALTRN0 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS2PR12MB9662 X-Stat-Signature: yg6yqxbwqg7jy7p49aar51recpeepnnc X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: CE18420013 X-HE-Tag: 1751911596-557284 X-HE-Meta: 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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: List-Subscribe: List-Unsubscribe: On 7 Jul 2025, at 10:23, Pankaj Raghav (Samsung) wrote: > From: Pankaj Raghav > > There are many places in the kernel where we need to zeroout larger > chunks but the maximum segment we can zeroout at a time by ZERO_PAGE > is limited by PAGE_SIZE. > > This concern was raised during the review of adding Large Block Size support > to XFS[1][2]. > > This is especially annoying in block devices and filesystems where we > attach multiple ZERO_PAGEs to the bio in different bvecs. With multipage > bvec support in block layer, it is much more efficient to send out > larger zero pages as a part of a single bvec. > > Some examples of places in the kernel where this could be useful: > - blkdev_issue_zero_pages() > - iomap_dio_zero() > - vmalloc.c:zero_iter() > - rxperf_process_call() > - fscrypt_zeroout_range_inline_crypt() > - bch2_checksum_update() > ... > > We already have huge_zero_folio that is allocated on demand, and it will be > deallocated by the shrinker if there are no users of it left. > > At moment, huge_zero_folio infrastructure refcount is tied to the process > lifetime that created it. This might not work for bio layer as the completions > can be async and the process that created the huge_zero_folio might no > longer be alive. > > Add a config option STATIC_PMD_ZERO_PAGE that will always allocate > the huge_zero_folio via memblock, and it will never be freed. Do the above users want a PMD sized zero page or a 2MB zero page? Because on systems with non 4KB base page size, e.g., ARM64 with 64KB base page, PMD size is different. ARM64 with 64KB base page has 512MB PMD sized pages. Having STATIC_PMD_ZERO_PAGE means losing half GB memory. I am not sure if it is acceptable. Best Regards, Yan, Zi