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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MSGID_FROM_MTA_HEADER,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4335BC433ED for ; Fri, 14 May 2021 20:50:19 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D9096613C9 for ; Fri, 14 May 2021 20:50:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D9096613C9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=oracle.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 66A7B6B0036; Fri, 14 May 2021 16:50:18 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 619346B006E; Fri, 14 May 2021 16:50:18 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 444D16B0070; Fri, 14 May 2021 16:50:18 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0122.hostedemail.com [216.40.44.122]) by kanga.kvack.org (Postfix) with ESMTP id 094B36B0036 for ; Fri, 14 May 2021 16:50:17 -0400 (EDT) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id A28C5BBEE for ; Fri, 14 May 2021 20:50:17 +0000 (UTC) X-FDA: 78141029274.26.71339B9 Received: from userp2130.oracle.com (userp2130.oracle.com [156.151.31.86]) by imf01.hostedemail.com (Postfix) with ESMTP id A6D26500152B for ; Fri, 14 May 2021 20:50:15 +0000 (UTC) Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 14EKj1f0058283; Fri, 14 May 2021 20:49:56 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : content-type : in-reply-to : mime-version; s=corp-2020-01-29; bh=f65agFedW/7FHmFwnLxf44LNQ9enwgW1NG+Erz7jeB0=; b=ZUhUroWv1t6rHwyN7N+BqfnSpVx4IYbrQMYEUdrvPJ0ogUzyRwEPBvO8ZuV8ZwoxNHfv 3vfVr9907XT9JHdLyGuljTqT8JgXl/qEC7JK8U2A5lW4sSJUZ60eOr4P0Ra5L8aqnkVl tjUvBjZWZHKSoeMI1IChameVdse4zcN7lM3nBTKw/X9uSijqpyLeQVceO5cv2NDO+i/h 16LxfOJzXCdWlFj9rAB7b1dxv37iH7TRQeSTePFULEUqBTbsGQsuncvO4uQr2HY82tLp dR/eQPYACv/XBE0oUgT4o09FaW/epRfqvHO+EL2A0eEMUo3vBSxjj9igQMiZTrrnbCXE dA== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by userp2130.oracle.com with ESMTP id 38gpnddb6f-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 14 May 2021 20:49:56 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 14EKnq2T075943; Fri, 14 May 2021 20:49:55 GMT Received: from nam11-co1-obe.outbound.protection.outlook.com (mail-co1nam11lp2174.outbound.protection.outlook.com [104.47.56.174]) by userp3030.oracle.com with ESMTP id 38gpq3e148-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 14 May 2021 20:49:55 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=NvHOFr0VLWIMr4bV0MyWsd3Z3fjK19f0M0ku9M+YvkLFwcfcHrdz+YEC3QxVggO0AAWEU+Vt5tyQEaAt+y77HBBHerDPYrId73xy905RpY1UhtB64jPGDAJtyMl/wxLaPucT80h3dapraD358DMr5vGDpu9uKI6F2vu43SlLvPaLGhut9EtlrBMY3KFjUPNe7tHznsnN6+K2QbRx/976XBejes0U5sFYKki+zi9zHZtDRlPhG1IKqGnf0pyDzDwISM8dtvjEwub/kH269yxMoMdmP+gpQbR/PiOalOUKpAB9bVhxp0qGw5ffaMYsba4lvjnp2XDpELKB/0Dr/YA2SQ== 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-SenderADCheck; bh=f65agFedW/7FHmFwnLxf44LNQ9enwgW1NG+Erz7jeB0=; b=L07QInMRj23K1ewRY0/Ap386SFK5vjZXfti3RYUOZFMN9ncGXJZAFfT98tNonup0wyjP6CH2NF5Ga9WaeCS3D71p37mDy5xaI3dcngp+Ci6LWKPTSCqqgKUlml9vOXFcJvL6tkcY+sViHs0L+/D3c776PSGfC5ZhNqroDgqZ4fJisGK+VIsw4xzagy5iFv4C+o176BWAr8woYO8hHkzTQgHRF7dv/TP6xtI9lpVm4hgX0N/zSZblOsPXkVjpgt/kHQ8v0gTgD6WVOgfVzhQoLyibeM9+pjUoRvBz1PhaMLBQFD+/B1ZH+zsc28hiHSmrxb203EE8FbgthVklgJaaAg== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=oracle.com; dmarc=pass action=none header.from=oracle.com; dkim=pass header.d=oracle.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.onmicrosoft.com; s=selector2-oracle-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=f65agFedW/7FHmFwnLxf44LNQ9enwgW1NG+Erz7jeB0=; b=F/Btn8yT+tEM5obyzrql5qFhsLqOMo1ivYpL5RI3sS5VUpnUzTqxrH7bmhN5K8spHfK8eASGqR4yQaHgrbQiJcafsmQ1YrYvXiXPOfgvUWmXIrFZzC4wFsQXFAHFWJvcu7+SOYQA/x7yX1KY6A/abYPxRqsJFPTUbQE0YlTTr28= Received: from BYAPR10MB2966.namprd10.prod.outlook.com (2603:10b6:a03:8c::27) by BYAPR10MB2693.namprd10.prod.outlook.com (2603:10b6:a02:b6::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4129.26; Fri, 14 May 2021 20:49:52 +0000 Received: from BYAPR10MB2966.namprd10.prod.outlook.com ([fe80::144d:392c:6407:169]) by BYAPR10MB2966.namprd10.prod.outlook.com ([fe80::144d:392c:6407:169%5]) with mapi id 15.20.4129.028; Fri, 14 May 2021 20:49:51 +0000 Date: Fri, 14 May 2021 16:49:47 -0400 From: Daniel Jordan To: "Huang, Ying" Cc: Peter Zijlstra , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dan Carpenter , Andrea Parri , Andi Kleen , Dave Hansen , Omar Sandoval , Paul McKenney , Tejun Heo , Will Deacon , Miaohe Lin Subject: Re: [PATCH] mm, swap: Remove unnecessary smp_rmb() in swap_type_to_swap_info() Message-ID: <20210514204947.g5nznqwo6gnt2vnu@oracle.com> References: <20210513064837.3949064-1-ying.huang@intel.com> <20210514015946.nivgnoobef4nqwmw@oracle.com> <878s4iezeq.fsf@yhuang6-desk1.ccr.corp.intel.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <878s4iezeq.fsf@yhuang6-desk1.ccr.corp.intel.com> X-Originating-IP: [98.229.125.203] X-ClientProxiedBy: MN2PR02CA0017.namprd02.prod.outlook.com (2603:10b6:208:fc::30) To BYAPR10MB2966.namprd10.prod.outlook.com (2603:10b6:a03:8c::27) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from oracle.com (98.229.125.203) by MN2PR02CA0017.namprd02.prod.outlook.com (2603:10b6:208:fc::30) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4108.32 via Frontend Transport; Fri, 14 May 2021 20:49:49 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 3f548e45-fccd-45b2-e230-08d91719d1fc X-MS-TrafficTypeDiagnostic: BYAPR10MB2693: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:10000; X-MS-Exchange-SenderADCheck: 1 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:BYAPR10MB2966.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(396003)(136003)(376002)(39860400002)(346002)(366004)(8676002)(8936002)(55016002)(66946007)(86362001)(26005)(4326008)(1076003)(6916009)(38100700002)(38350700002)(7416002)(2906002)(5660300002)(66556008)(54906003)(52116002)(66476007)(316002)(478600001)(83380400001)(956004)(2616005)(7696005)(186003)(8886007)(16526019)(36756003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData: =?us-ascii?Q?rvPq0n5yTPV4eZua0e0zSKwnlgZmtVZGeEknU0MTDsIvk5VpF3PXsXbalPUt?= =?us-ascii?Q?Wt0JSa7HH00i6gR4qzU2lzuV8fxfkMz/fGhnw9Zqs5Z3nQTxa5HWIKNZHhZs?= =?us-ascii?Q?1rtTi74iMOafZECMK55/2fFyAQG17+L++/80bBzvHxHoHX9sa0dd9MP4WXle?= =?us-ascii?Q?rTHnvWs+siYw8y9Tz1rg96DnnaOfHViHQutY3DLONHnYDXepYGNatteYLlu3?= =?us-ascii?Q?37xc9DtGel5/4j2LY7KbbM239J/BoEWgmCycuk63XP/waXqH9Af+O7X/VOVN?= =?us-ascii?Q?We9tj2VYnFbnfNzeggQGIgo0kLtsUQp9EySAd5plWDNBPtV9vZNYrEbUsmAl?= =?us-ascii?Q?+rwiw+o3k9Pxg245/HlIK1seGvj0NnMHehPornuBZegthdv7HUMfaXd/UOUu?= =?us-ascii?Q?1qYxa3wLl8d5eCuVDdte2qh2mu5gXgxBSsZaImMgT1aijqbfr0/WRFVcDKNC?= =?us-ascii?Q?RMSEhfYA4uM9sILKI7O5XQ60lFqX/nTXGchP1vzJzaZ7FqVFJ14Sag1mT1h6?= =?us-ascii?Q?E0oDaH9hUytNbpK0qRUfotCpF2szsOqZNarmT8lq2wehlB2EJs9sMV3MxZdP?= =?us-ascii?Q?OsMkzPKAqPUU2jQ/qs2n/hweZopoDTvRcCP2h0pVbq3Lr0oZbG00EHlEWrej?= =?us-ascii?Q?5u9usBxCDOqZ9cX5hmoybSDrTs1OVBHiF9RQHopZoQBwaegzOPvPDEo0X9PE?= =?us-ascii?Q?3VC6qm32WJjnLD/rxsGaLk8Xyup9kJsnpkfVYUn78n2fcSqwocyMqf4BNeLA?= =?us-ascii?Q?BXnSIJdjHfo1HAPgjcovOFjoYAyizLhHFtz7mzeSFvj7EZwoqinPJBIRuwyt?= =?us-ascii?Q?+Iz6cbBkCwcyZ7/ic7ShG1dJGcww+yAAsGZq7sX7Lsay+bX9Xgwcvz2pHAvl?= =?us-ascii?Q?oU6s4DCMpolIFYYnOiERra3GOxcPwZnmBaXymqF6wP+IFgahHtGJf1uudUxi?= =?us-ascii?Q?e3MGsCZx/s+K17Sldr/Zy1FqSQ2Bif+10BmnBZuv9FjgUDWS3XBqW97LO52m?= =?us-ascii?Q?t3aTIRrnLtOh2sWxzCZT5cExFEPKY3qWcIv4436Yl0bJsf+PwnAT40H66Ugt?= =?us-ascii?Q?R115TQS98EZ5qKVLQf1i5m31gRhljn8cIUAeqRnjyQNAwg69FS4KXcLuxhnh?= =?us-ascii?Q?VU9xJmSK+c8Rf5fItss7UIYjoArXIrNoHql86BcdO+kKky3Z2rosOZM8RZxI?= =?us-ascii?Q?nk751wSks0JXpIDdADNLJqqHL99BX0fXBJVuftpzT4CrqI0aphlbL7bDW09X?= =?us-ascii?Q?UhpqbfCXt0nlT1me/U3VZcPV1ptgfijaWcJn3MclUh7Nq9aVKyhkD+XwHY6m?= =?us-ascii?Q?HEd0Rjrqt7eoPM0vY/nPSi+h?= X-OriginatorOrg: oracle.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3f548e45-fccd-45b2-e230-08d91719d1fc X-MS-Exchange-CrossTenant-AuthSource: BYAPR10MB2966.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 May 2021 20:49:51.7996 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: ysSvPz/qh/JwOVVSeyxWXnNB0flEoMIudaLU2CzEtYE1DH6HQectET3d77qwc5399HNFuTrTDFp3JCwhnN/pDULyzS+cZxlKfdTV1ePAXbE= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR10MB2693 X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=9984 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 suspectscore=0 malwarescore=0 spamscore=0 mlxscore=0 adultscore=0 bulkscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2105140166 X-Proofpoint-ORIG-GUID: LqHy2X15MqhuxdsAN_pLuUdCdrSe_Pz7 X-Proofpoint-GUID: LqHy2X15MqhuxdsAN_pLuUdCdrSe_Pz7 X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=9984 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 impostorscore=0 phishscore=0 priorityscore=1501 suspectscore=0 spamscore=0 lowpriorityscore=0 adultscore=0 clxscore=1015 mlxscore=0 bulkscore=0 mlxlogscore=999 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2105140165 X-Rspamd-Queue-Id: A6D26500152B Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=oracle.com header.s=corp-2020-01-29 header.b=ZUhUroWv; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b="F/Btn8yT"; spf=none (imf01.hostedemail.com: domain of daniel.m.jordan@oracle.com has no SPF policy when checking 156.151.31.86) smtp.mailfrom=daniel.m.jordan@oracle.com; dmarc=pass (policy=none) header.from=oracle.com X-Rspamd-Server: rspam04 X-Stat-Signature: 957unqg65xatffpwff4aecgjwnetf9bx X-HE-Tag: 1621025415-772299 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 Fri, May 14, 2021 at 12:02:05PM +0800, Huang, Ying wrote: > Daniel Jordan writes: > > Yes, this does help, I didn't understand why smp_wmb stayed around in > > the original post. > > > > I think the only access smp_store_release() orders is p->type. Wouldn't > > it be kinda inconsistent to only initialize that one field before > > publishing when many others would be done at the end of > > alloc_swap_info() after the fact? > > In addition to p->type, *p is zeroed via kvzalloc(). So it is, good point. > > p->type doesn't seem special. For > > instance, get_swap_page_of_type() touches si->lock soon after it calls > > swap_type_to_swap_info(), so there could be a small window where there's > > a non-NULL si with an uninitialized lock. > > We usually check the state of swap_info_struct before other operations. > For example, we check si->swap_map in swap_start(). Yes, we usually do. > > It's not as if this is likely to be a problem in practice, it would just > > make it harder to understand why smp_store_release is there. Maybe all > > we need is a WRITE_ONCE, or if it's really necessary for certain fields > > to be set before publication then move them up and explain? > > I think we have initialized all fields before publication :-). Probably all the ones that matter in practice, yes :-) Still feeling slightly uneasy about the theoretical p->lock, but that was possible before this change too so it's out of scope. A comment explaining the pairing and that we care mostly about the zero init would be nice.