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 E5B3BC47422 for ; Wed, 17 Jan 2024 05:25:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 51A466B0096; Wed, 17 Jan 2024 00:25:01 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4CA5B6B009D; Wed, 17 Jan 2024 00:25:01 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 391366B00A8; Wed, 17 Jan 2024 00:25:01 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 279DC6B0096 for ; Wed, 17 Jan 2024 00:25:01 -0500 (EST) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id E219AC06C2 for ; Wed, 17 Jan 2024 05:25:00 +0000 (UTC) X-FDA: 81687663960.16.9829C61 Received: from NAM04-MW2-obe.outbound.protection.outlook.com (mail-mw2nam04on2045.outbound.protection.outlook.com [40.107.101.45]) by imf13.hostedemail.com (Postfix) with ESMTP id 168C220007 for ; Wed, 17 Jan 2024 05:24:57 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=memverge.com header.s=selector2 header.b=mOuof8l3; spf=pass (imf13.hostedemail.com: domain of gregory.price@memverge.com designates 40.107.101.45 as permitted sender) smtp.mailfrom=gregory.price@memverge.com; dmarc=pass (policy=none) header.from=memverge.com; arc=pass ("microsoft.com:s=arcselector9901:i=1") ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1705469098; 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=bZ2nYC+1HNKPI4LD2c1bHGCWFXE7sBgGLFsG+sRvMio=; b=POV+2x77gCNFYP551AsN28a4JW8hjpV6v9TCPWxuYN6jv/lLC5/uvdGj+QGQdAmjVOwjDO i7mLrJJSBMoD1jfuCppnKIo5rqFhbHnvFSFtoEJbLUl/0fV5tNdx0fq5AEZmHEWVvCZoBv nqEiAEyM9qq8Xt0yVvIOaJ0TPtdYbME= ARC-Seal: i=2; s=arc-20220608; d=hostedemail.com; t=1705469098; a=rsa-sha256; cv=pass; b=ylO9qpFqfqGvqzy251HNHPVPa5GRcobWjl/uBn+J/iEX48urUEOcVWDaULYTZzmiQYc5Gl wfmpnD2junklSKekGfdDT4laDfhSppekkeUx5B3RjZ7APZGoExwoqe2dMaCYmRjuiFxn/b DMSlei8XQdtI9ijKT7XcdEBUqKrB38M= ARC-Authentication-Results: i=2; imf13.hostedemail.com; dkim=pass header.d=memverge.com header.s=selector2 header.b=mOuof8l3; spf=pass (imf13.hostedemail.com: domain of gregory.price@memverge.com designates 40.107.101.45 as permitted sender) smtp.mailfrom=gregory.price@memverge.com; dmarc=pass (policy=none) header.from=memverge.com; arc=pass ("microsoft.com:s=arcselector9901:i=1") ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=ZDnP1Uv/W36cD9O8Zx4jkKi57P7j+/dZ5KTVorkOWAR2SDwVrYH5jIppxLvecZHqXoi+/h9x4n9PF5yUKdt7cDApNEIwLF6ufnOX/cbgbwn56oK3IFd5riRn4uNA1JQecm7F61hMx47buQI59a9Jqrwk2FpksgBVyZpJYisg9LswM2AzulBSnmZ1Utk16nn4jcRSDNBAkOOV+tMsikTVAZbWT4puyAWlqr7BL2zDhscLTUsAUir7WCVuMMsbr9vJ9X0QSVuEkearrA8PW17lzRyx08JR2bNIH3pTartvLPvh8OnxWI8MdwgfTmktEgZOa29UoP2faeYVvNEvYFj5Zg== 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=bZ2nYC+1HNKPI4LD2c1bHGCWFXE7sBgGLFsG+sRvMio=; b=YD45LX3fm+eMzfSvmJc7MJCaWOr7VLzAjw5CMeRJ/vGDUAAJ8QISoYYFmjwzj7P3gLblznoScl8BteoM0aAmvneLDSJi87HsoYahijiN3gMvrET68yEFgyqU1Y7s425aYm2Uaodrbf0ZH3xAGuNdYwJp7PW6iRewn5/aStn294axAiMUIUQVQWUbkDDPOPSWeq3FhCfDC36HEWwLEfLM+ORyiOvmjRzp+2USIoTPnX4urx829u8KmksvXkIjCYsfIJqm/4MB+oktoydRTrXDE4itDEJU1t4a/YdIml8rNgmaw+VytyfGoSlT4dFSfIOmtVvxENojuqjeROjwo+WGIg== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=memverge.com; dmarc=pass action=none header.from=memverge.com; dkim=pass header.d=memverge.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=memverge.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=bZ2nYC+1HNKPI4LD2c1bHGCWFXE7sBgGLFsG+sRvMio=; b=mOuof8l36nSo2aE4bXgBshhZp6KUr7Tnk8daTvyLNkRdlicT6JcLEzX/ylAaY6mOyjIUXVxeFZh7T6QBU9yU2CyavC3Sb3cr8+wl16KXve6UmJV+y18gI8HitoNvPDJcavJoqm7DrwyeXnnWd0gUygTGD1iyeO8W0uF4cspxAR0= Received: from SJ0PR17MB5512.namprd17.prod.outlook.com (2603:10b6:a03:394::19) by SN7PR17MB6514.namprd17.prod.outlook.com (2603:10b6:806:323::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7181.30; Wed, 17 Jan 2024 05:24:50 +0000 Received: from SJ0PR17MB5512.namprd17.prod.outlook.com ([fe80::7a04:dc86:2799:2f15]) by SJ0PR17MB5512.namprd17.prod.outlook.com ([fe80::7a04:dc86:2799:2f15%5]) with mapi id 15.20.7181.027; Wed, 17 Jan 2024 05:24:50 +0000 Date: Wed, 17 Jan 2024 00:24:41 -0500 From: Gregory Price To: "Huang, Ying" Cc: Gregory Price , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, corbet@lwn.net, akpm@linux-foundation.org, honggyu.kim@sk.com, rakie.kim@sk.com, hyeongtak.ji@sk.com, mhocko@kernel.org, vtavarespetr@micron.com, jgroves@micron.com, ravis.opensrc@micron.com, sthanneeru@micron.com, emirakhur@micron.com, Hasan.Maruf@amd.com, seungjun.ha@samsung.com, hannes@cmpxchg.org, dan.j.williams@intel.com Subject: Re: [PATCH 1/3] mm/mempolicy: implement the sysfs-based weighted_interleave interface Message-ID: References: <20240112210834.8035-1-gregory.price@memverge.com> <20240112210834.8035-2-gregory.price@memverge.com> <87le8r1dzr.fsf@yhuang6-desk2.ccr.corp.intel.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87le8r1dzr.fsf@yhuang6-desk2.ccr.corp.intel.com> X-ClientProxiedBy: PH7PR10CA0016.namprd10.prod.outlook.com (2603:10b6:510:23d::8) To SJ0PR17MB5512.namprd17.prod.outlook.com (2603:10b6:a03:394::19) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ0PR17MB5512:EE_|SN7PR17MB6514:EE_ X-MS-Office365-Filtering-Correlation-Id: fad66eec-3654-4b87-bbb9-08dc171ca09e 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:SJ0PR17MB5512.namprd17.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(346002)(396003)(376002)(136003)(39840400004)(366004)(230922051799003)(1800799012)(64100799003)(186009)(451199024)(4326008)(8936002)(8676002)(7416002)(66476007)(5660300002)(66556008)(2906002)(6486002)(26005)(2616005)(36756003)(86362001)(6916009)(66946007)(316002)(44832011)(478600001)(6666004)(6506007)(6512007)(41300700001)(38100700002)(83380400001)(16393002);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?BQDbqw2BvFnX90OuMt0wZhakFUnNeQ2+OqAgtwkM3lCsU2VlKaIG/0QSUV3E?= =?us-ascii?Q?nqBku8CeV/dasfTzugXrIdtLT2UpDJ4iIVALx7SjjJ6hHdzD6eVqjAOMYbXI?= =?us-ascii?Q?athLR0tk1HO4wogA/LRoIcbHhGuyZQSMuINCr/n1aJlMVMnpW5ks1P6FxG1A?= =?us-ascii?Q?6dXaDRHuZCnEIl7E6PBpgNlSdIwiXe4rVYFq0vWXuMIsJeAU6GQfXBzdv26G?= =?us-ascii?Q?WCHPJLStNLB9x6OhRh82CDpu2mI48c6bC/hg16Oic9xkhgrsY+pQN6tQjvP5?= =?us-ascii?Q?hUEWRQ4iCktubhPdjDQskjCnCmkKeAdBXckPUhfyi3o2w8+eoHIt/kfnGIGR?= =?us-ascii?Q?cWJYawSQScO0Jl1R5z21NixNrMnqC26iSmObq9R1Y4ykKqrJ1SnuhRXgDnnb?= =?us-ascii?Q?ETT4cYWctHk3seg3kqZO7c7GbttqTq+kfBHaXeBxRUAjkwHzcz9ZqKn1PCHE?= =?us-ascii?Q?5bz0QuMv6mzUh22v6oDxgz+cKt77JZTw8XrcsqgCKfmuS53/H3dV1VqYB9Fn?= =?us-ascii?Q?Yc6OhlT3v7DxtmwqFcsAxFa4QTKc0W45Bumw4tQJ8VXvnJ3hkdb+Fl3qNN2e?= =?us-ascii?Q?p0IHqfoGE1lFfdDz5Hl35R/8d19owfVi9jp0zSkDMo6yPKH/dAuLWZ565w5m?= =?us-ascii?Q?TbhBzLEZB34jJJh+y7bl9pnIBxk54MjGwbSE5QqoL96JmJTUz0J4qQ30m7wV?= =?us-ascii?Q?rtMTYNWbWkHfI0BUlq79i073pWcbrYD0ElnMJEHB7brZJ/1n5bKyaFk0JH8b?= =?us-ascii?Q?lVv+adTiqF4jz5RXDXIlbGr4QORhbufzD906Wj038YfesM8bR5Dlxge1PZ/c?= =?us-ascii?Q?SlBfchJveFXKLOM44MYvnSYZq6hcyfkw0xoLrbPzyPWMpI+lYhS4imQ0EX9y?= =?us-ascii?Q?eOt/8bZmlVQ+u3rG+/DG5bgZt0l3ZGQZ/xHgSj0Wpiuqn2bxa/ZUImjHTBJt?= =?us-ascii?Q?bDoD2cYTCUcinMju+/Kgs5Ohq6EFBJNnOBfVMjN6NIqrBWYM0RITsPStH4tT?= =?us-ascii?Q?KsgZGfyjcHEQ7O97O3oEOz5OCCoZ3ZHNKdclC3Ky9fuFQfyvVjP6irQUWaEg?= =?us-ascii?Q?nc0pm2dPC3gx0+faGlWP1gdNU4tl2KsXX+LsYUPlvSms/SQH/3q1ABbQSSG1?= =?us-ascii?Q?7L0M8GheDUFFWXiplWY5gc5nFglyHd/79GU8HZwYBjqrdp7RwBThLMxgzva5?= =?us-ascii?Q?c2HqTlMEVjromU5lmDQeifo7MUGaEOWtu5/Km9sZSoAyR1INbz8PUi7/WxT6?= =?us-ascii?Q?1DXmmWrufonMAXRthnqOHj1KGeqZ5uZ8XoVoNsYwVn6Pp9WsQjIDBpXy2aaE?= =?us-ascii?Q?dY4Z1TUZN8R8583rjYhytsHgu3W1V2iTQLFKi6y3cEdCmAP23lG/O3tCMlxv?= =?us-ascii?Q?o8QMQ+g9gBQ1g8cTHT5djTnUwytkjArSc1wwEqxtMtrzFLHsBP1tyeB77O30?= =?us-ascii?Q?EhnCMh9c+/PSAGmuM+FWfAuXNsqoF5d05iREWBJDN/Kfz9WnTtHhm+WIl0Qn?= =?us-ascii?Q?2Qm0Pgw/PfWb2LckrNOSupye+nTnUOdDXwECYv4BzXVoCUaAexnZsS/EVbPF?= =?us-ascii?Q?pV0YVM1KEGoZfIwI84+Jm6fz1Sj467y5WvKKO32tMh1FlHlIB8+jC54Nkn2q?= =?us-ascii?Q?NQ=3D=3D?= X-OriginatorOrg: memverge.com X-MS-Exchange-CrossTenant-Network-Message-Id: fad66eec-3654-4b87-bbb9-08dc171ca09e X-MS-Exchange-CrossTenant-AuthSource: SJ0PR17MB5512.namprd17.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Jan 2024 05:24:50.2015 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 5c90cb59-37e7-4c81-9c07-00473d5fb682 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: NxtQDhuYmxARNWVJvKcwNpakCZRS6axH2jq0VIauLj7omHVoiz4lQ7xZSjvo4z2gOC01Wioz8wsiSAFStDi7IwsxiLBi0sSCNc591sL/+ps= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR17MB6514 X-Rspamd-Queue-Id: 168C220007 X-Rspam-User: X-Stat-Signature: ks7ic4731hq6y4iqqtrx68rfkhgfj7o5 X-Rspamd-Server: rspam03 X-HE-Tag: 1705469097-982261 X-HE-Meta: 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 hw6EwyMd ewkNRu/3+UFdBGf33L5v/wyaEU79GjT53MznhtrAMYpN7UHStAsof9QTTW6gugoSi9j+c9HgltsiemvKW7llJCEiB88rjVN2UoVTaHaLSxsKJgIANLNgeibkF75TSPg/Nk+EoP8TjFOxvMQY946MHBeZxnWD0kLPp7AljL4C71Q5/t47EdsWKZE3g4UocAI9gcqts3q1T9p5Qc2WtwKskmJi98UNIuaS8o1m0WdjOeLEUWx2DmR8zTfU1Y5up6pGBNyFPcsWToz5NMsaONhbCo0S3mmPqvXbZkQAW2h3xnhemKrORV05M2juvPmSxPdXkDuT+kUr/8Hc4vmAO9Wfk13Mv63DGHlTD+Mf7+79Vh7XUPBM= 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 Mon, Jan 15, 2024 at 11:18:00AM +0800, Huang, Ying wrote: > Gregory Price writes: > > > +static struct iw_table default_iw_table; > > +/* > > + * iw_table is the sysfs-set interleave weight table, a value of 0 > > + * denotes that the default_iw_table value should be used. > > + * > > + * iw_table is RCU protected > > + */ > > +static struct iw_table __rcu *iw_table; > > +static DEFINE_MUTEX(iw_table_mtx); > > I greped "mtx" in kernel/*.c and mm/*.c and found nothing. To following > the existing coding convention, better to name this as iw_table_mutex or > iw_table_lock? > ack. > And, I think this is used to protect both iw_table and default_iw_table? > If so, it deserves some comments. > Right now default_iw_table cannot be updated, and so it is neither protected nor requires protection. I planned to add the protection comment in the next patch series, which would implement the kernel-side interface for updating the default weights during boot/hotplug. We haven't had the discussion on how/when this should happen yet, though, and there's some research to be done. (i.e. when should DRAM weights be set? should the entire table be reweighted on hotplug? etc) > > +static ssize_t node_store(struct kobject *kobj, struct kobj_attribute *attr, > > + const char *buf, size_t count) > > +{ > > + struct iw_node_attr *node_attr; > > + struct iw_table __rcu *new; > > + struct iw_table __rcu *old; > > + u8 weight = 0; > > + > > + node_attr = container_of(attr, struct iw_node_attr, kobj_attr); > > + if (count == 0 || sysfs_streq(buf, "")) > > + weight = 0; > > + else if (kstrtou8(buf, 0, &weight)) > > + return -EINVAL; > > + > > + new = kmalloc(sizeof(*new), GFP_KERNEL); > > + if (!new) > > + return -ENOMEM; > > + > > + mutex_lock(&iw_table_mtx); > > + old = rcu_dereference_protected(iw_table, > > + lockdep_is_held(&iw_table_mtx)); > > + /* If value is 0, revert to default weight */ > > + weight = weight ? weight : default_iw_table.weights[node_attr->nid]; > > If we change the default weight in default_iw_table.weights[], how do we > identify whether the weight has been customized by users via sysfs? So, > I suggest to use 0 in iw_table for not-customized weight. > > And if so, we need to use RCU to access default_iw_table too. > Dumb simplification on my part, I'll walk this back and add the if (!weight) weight = default_iw_table[node] logic back into the allocator paths accordinly. > > + memcpy(&new->weights, &old->weights, sizeof(new->weights)); > > + new->weights[node_attr->nid] = weight; > > + rcu_assign_pointer(iw_table, new); > > + mutex_unlock(&iw_table_mtx); > > + kfree_rcu(old, rcu); > > synchronize_rcu() should be OK here. It's fast enough in this cold > path. This make it good to define iw_table as > I'll take a look. > u8 __rcu *iw_table; > > Then, we only need to allocate nr_node_ids elements now. > We need nr_possible_nodes to handle hotplug correctly. I decided to simplify this down to MAX_NUMNODES *juuuuuust in case* "true node hotplug" ever becomes a reality. If that happens, then only allocating space for possible nodes creates a much bigger headache on hotplug. For the sake of that simplification, it seemed better to just eat the 1KB. If you really want me to do that, I will, but the MAX_NUMNODES choice was an explicitly defensive choice. > > +static int __init mempolicy_sysfs_init(void) > > +{ > > + /* > > + * if sysfs is not enabled MPOL_WEIGHTED_INTERLEAVE defaults to > > + * MPOL_INTERLEAVE behavior, but is still defined separately to > > + * allow task-local weighted interleave and system-defaults to > > + * operate as intended. > > + * > > + * In this scenario iw_table cannot (presently) change, so > > + * there's no need to set up RCU / cleanup code. > > + */ > > + memset(&default_iw_table.weights, 1, sizeof(default_iw_table)); > > This depends on sizeof(default_iw_table.weights[0]) == 1, I think it's > better to use explicit loop here to make the code more robust a little. > oh hm, you're right. rookie mistake on my part. Thanks, Gregory