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 3AB5BE77184 for ; Thu, 19 Dec 2024 03:40:59 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 54B636B0083; Wed, 18 Dec 2024 22:40:59 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4D33F6B0085; Wed, 18 Dec 2024 22:40:59 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2FD636B0088; Wed, 18 Dec 2024 22:40:59 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 0F14C6B0083 for ; Wed, 18 Dec 2024 22:40:59 -0500 (EST) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 742201413CB for ; Thu, 19 Dec 2024 03:40:58 +0000 (UTC) X-FDA: 82910306388.23.E95ABAA Received: from NAM11-BN8-obe.outbound.protection.outlook.com (mail-bn8nam11on2041.outbound.protection.outlook.com [40.107.236.41]) by imf16.hostedemail.com (Postfix) with ESMTP id 2B5B4180004 for ; Thu, 19 Dec 2024 03:40:22 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=QVn4u7Vx; spf=pass (imf16.hostedemail.com: domain of jhubbard@nvidia.com designates 40.107.236.41 as permitted sender) smtp.mailfrom=jhubbard@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=1734579625; a=rsa-sha256; cv=pass; b=17LI02siyAK+S+v/dsZrXRlIC2aai7STvi1HFqyPHZ0m/rMr7EUoB7z3SB58Syq9SLmVTa tOL82EOoPk0gPyiPJUpXUYYQR1AeGmaMBM2PAUy4UT3/kPaPiQeXlWI6G0fFXbKL46QIp+ xHQ470lupA7cKVlwtVnoTRVsRbZlIgg= ARC-Authentication-Results: i=2; imf16.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=QVn4u7Vx; spf=pass (imf16.hostedemail.com: domain of jhubbard@nvidia.com designates 40.107.236.41 as permitted sender) smtp.mailfrom=jhubbard@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=1734579625; 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=HoADcOH6YHmRt14bxjqcKaYfUxdbCLQvwftx3q6X6Z0=; b=AeQjG1zyxFWjyM0A+1zGU2FrfbKuMFv02EcSNQTBDqiphMZek+uesyvbsGCVff6pTgxE+Z Se/44uBXsFaEs5URT78XPQvOSAUGuMstQ7bbtXsG8Nd2S0eh8TedAI4nytABd/ZzS9xy3/ o93zHwxibRldI/7RDkgmX/UbFpIHr0g= ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=j8gnYMu7qZI0X7mQ+2yCOklUGo6Nb4C1i+PqWJu9DIIBN8Mtdi/DcfXBVfZkXsy48cMTZZPl0qbCfxS1N5YSrQ5xu/3Hai3gucX+0xw8O1jCRYcotJuiG1byrnB8eLSR9WNz5a6hnZIijwn7Z/ojnKSDcn3DppIRcucmJvpnBVOfr4flVNtsE9UlmMEi64H2ISREuiApWSoZTHUhkiTsCyQK9AbP9Aiw5nfKRAKeuzHM2kmk/IPpNsqGHEM0B7P/+gN0+iwlRwFiHna97zwDOS/w5HafFYAydG0U8TKxuhQ0loWKHGGDesGLojuul13sJFPoYxqGJhvuWy7im5CcdA== 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=HoADcOH6YHmRt14bxjqcKaYfUxdbCLQvwftx3q6X6Z0=; b=zQY/g27IURiz2paljLC4+x21bKx6yOKm8YkTjEASMszo8tVNyO0hRdaAsG8XuUrlZNnktICn942DGMuoEHiDPapWZXG3tY7lEDpzIcq9kh8vcwPU8Ahd5B/+UqKtQ0bBsraXuRq3fK0g2JjdkfO4D7SpYg7csM7h9E6qRyGuJA9kMDzy0axzoRXVNHw5hrZG3hYWoJgSzcscawil4EFQxdJLE0G1BRcGhX/hALGJ31VwM8QbF67PBGTPFl6g9jZkG2d9vR3QU/l/BI+kkIvcD0zWhNHcV5sadDurzYYuEsaRr1GuaLjDuJCp/UtFRWtYrgo63gkixnAmFch/lmxYXw== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass (sender ip is 216.228.117.161) smtp.rcpttodomain=arm.com 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 (0) 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=HoADcOH6YHmRt14bxjqcKaYfUxdbCLQvwftx3q6X6Z0=; b=QVn4u7VxXF85VGuCLNlDWD3LAGNxXsR5F3zUUNR82U6LjlG3vdLLVa96m5MkyAMbNSX8ddB/HvhQIDKNaZaqaCWdsi6s4QJ1j+l1D3kmelln8Vxagjldqaa40SrSu3u8JrjRH4hjbPszrB4pdCo9/xKtRMjaWGZdsykyPzH58AopeRGJxELS0aVffhbqlz7U/q0kwf1+H1GeMyruwlMJGnj3zS9v8RN99rE4i3nZ5U0vYIbKMoDdhsdfxidzE5mNH659TZVJyWQ5WaELJ9UvISBfLe8Pk0WsXg8XQJ+b1Zc6fbyeMLrXeJs5iUoAmrCkWY6i8AJo+MFJ8i+VbFwUTg== Received: from MN0PR03CA0026.namprd03.prod.outlook.com (2603:10b6:208:52f::23) by IA1PR12MB6283.namprd12.prod.outlook.com (2603:10b6:208:3e5::9) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8272.13; Thu, 19 Dec 2024 03:40:49 +0000 Received: from BN2PEPF0000449E.namprd02.prod.outlook.com (2603:10b6:208:52f:cafe::8b) by MN0PR03CA0026.outlook.office365.com (2603:10b6:208:52f::23) with Microsoft SMTP Server (version=TLS1_3, cipher=TLS_AES_256_GCM_SHA384) id 15.20.8251.24 via Frontend Transport; Thu, 19 Dec 2024 03:40:49 +0000 X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 216.228.117.161) 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 216.228.117.161 as permitted sender) receiver=protection.outlook.com; client-ip=216.228.117.161; helo=mail.nvidia.com; pr=C Received: from mail.nvidia.com (216.228.117.161) by BN2PEPF0000449E.mail.protection.outlook.com (10.167.243.149) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8251.15 via Frontend Transport; Thu, 19 Dec 2024 03:40:48 +0000 Received: from rnnvmail201.nvidia.com (10.129.68.8) by mail.nvidia.com (10.129.200.67) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.4; Wed, 18 Dec 2024 19:40:31 -0800 Received: from [10.110.48.28] (10.126.230.35) 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 15.2.1544.4; Wed, 18 Dec 2024 19:40:30 -0800 Message-ID: <00d429c9-6ade-42c9-a1f3-a7519375324f@nvidia.com> Date: Wed, 18 Dec 2024 19:40:29 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 10/12] khugepaged: Skip PTE range if a larger mTHP is already mapped To: Dev Jain , Ryan Roberts , , , , CC: , , , , , , , , , , , , , , , , , , , , , , , , <21cnbao@gmail.com>, , References: <20241216165105.56185-1-dev.jain@arm.com> <20241216165105.56185-11-dev.jain@arm.com> <7cc1840b-6f6c-4f82-86b8-41bb6fbc1b81@arm.com> Content-Language: en-US From: John Hubbard In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.126.230.35] 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: BN2PEPF0000449E:EE_|IA1PR12MB6283:EE_ X-MS-Office365-Filtering-Correlation-Id: 76714b4e-49c6-4f79-8cc4-08dd1fdeede6 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|376014|7416014|1800799024|82310400026; X-Microsoft-Antispam-Message-Info: =?utf-8?B?NHJOMXk3UHlhdk5rVENxN1JJSWl2dDEybVE4cWs3Q2JmT0VOTGRSc3ZDL2Yz?= =?utf-8?B?a1dHb1pydlQxc09PUzYxRXZYWm5WN25IeGltMUhFTTNLRHpDeWthRXFQUVhT?= =?utf-8?B?RkJOeFZKL0dQdnRPVGFZbHB1M25ENy9NSDlZS1FHczhYQ0MzVFZrOUtjaHl3?= =?utf-8?B?UmRudHVjNHZURUZiaGoxdmJiVFUvaENIREllcTZQcW9TL3RlN3JjY2toTU9H?= =?utf-8?B?NWJtR0xNVTU2VHdtRExJSUlLQy82bWw2WTY5dEFVUVIrd3pOVytBOWs3MUtN?= =?utf-8?B?UEFtSGtENjBrS0wwVnc5OUNNcVo2RTVLdENEaW9ROUlBZVpKQnBmRSs4cDBp?= =?utf-8?B?NVRHbU1VWkU4V2ZyRjF1cGVhODZaVXh5R2d4cWF1QXV5YzFsb3BQU2hsQWs0?= =?utf-8?B?R1VHb01XQ0gwY1A2Vk96YklnQzY0ck1CWEhnTllRd2lUVWNxbjF5WEhXakRa?= =?utf-8?B?RTBVYklQNFhRVVBXelJ6NnkxRVoxd2FsdFhRT2Y1MzZKUC9xWkd0cDNwWjdP?= =?utf-8?B?ZWRLdmVGNlA5ajVUUEprMFRlK0c2SzZncjRMZURqcDFMUlAxQjArWUNTSVcv?= =?utf-8?B?Z2dqYXBZamhUY1JyUmc0bTR6YTJoTld1TisycDlxQkRUV1VXZTVEWWEvblR3?= =?utf-8?B?a2xiTzN6V2RickRLMWR1RTRUdW1xNGUvbFE1RnVUc3k1emZ3cVRRakp2empH?= =?utf-8?B?ejRMaHBIZzQ0T28wa2tKU3pkSnEyUmNaRjJERTY0RDBFYXRrQWU3QlZmWXY2?= =?utf-8?B?N3U2VXhoMDh0YjdHMHBJYjBxWkpoQ2NVaVR5NEg2b284TVc2V2xPRlpQbjZj?= =?utf-8?B?SmVsVzJPZ2hGdGJGYzZRTnFzMlo0T1JBVFdCSEwvQzA0ZHJqdW44MmFtMDBY?= =?utf-8?B?cmUvLzU3NDRSZm9yQ0tnUnppN2dsdGVlL0Z0Qk1VUU9lUnVocnRzUVAySkxB?= =?utf-8?B?cWN2ZEVRYm5HSTJKYW5IdzUvMnpFVDdqV1B3Y3o2ZHJJM05INnpMVmNwMUNW?= =?utf-8?B?ZHFtWXA0Z29WNXFMbkFkd3lVOXdMWktCZnpwRndiZkxwemc2MUx3QVlvWmRS?= =?utf-8?B?QUo1WVV1d2JoRGplSnpFTm9uSFQyWkVhdm0vS0hwYVJkREhDRTBXUmVVOEVD?= =?utf-8?B?alJMWXo4SjJIU05LRWNYNVZtaGx1RTd1U2l5NDZRdTQ2a3NMT2NkVnNobitI?= =?utf-8?B?WitZa3ZyNlFMeG53WjMzcjMyYzJ5d2pBWmhpUnhoY0F0dnJCR0NDMHpzZm5T?= =?utf-8?B?MnRnWi9MRWx6YjBZMTluK0VrdU5iM2NWK3Yya3lTQ0k4WWt0dXUzeC9HbU1z?= =?utf-8?B?R2hEWUVsZWdBVUxRblM5bGZ2WmZnMTYxWjVIbCs2eC9vOUNmWngyczdWNVpQ?= =?utf-8?B?UVZIdXkrdU9nV2JDQ3dneGRSKzZ2UXFZQ3d6aVduWU1ENkhWV1FrZXhFQWpU?= =?utf-8?B?RE9JWStWMWZZanp6bEZUcGhSVmdjYjk5cEY3aTA0V1NLdHdUd09abmN6YURo?= =?utf-8?B?aGxNdkROQlBFNjhYbkVjMFoxcDl4eHpaVGNvZnNnemsrUkxpbzRZdTg3YmVX?= =?utf-8?B?Zm90Tm5yWUVCMk9ING41eDJ4clc4M0pSYkU2MjV4K3VuM1BCMGxuZWQzUDZ5?= =?utf-8?B?TGw4RTFxR0RCREREakNtVzV2SFZNNmpuYzlIYlh4WGhlNTN4ck9PdmNUUGVY?= =?utf-8?B?LytITXFzR3FlNEE4Y0FUN0xYYlNYTG5TTVZqS2J6TlFKM0x2ald5bjkvU256?= =?utf-8?B?dmxjN3VRbGJHUGRpVXpaQmZVWnE5YXV1cFhwaC95SjgybTArQkhpNTBIQVlx?= =?utf-8?B?SEdPeElnb1owWDRRdTM5WktKMjA4N0ttbFo0UnBISHRRTWZLUTNhODhwVGVO?= =?utf-8?B?QUFSK01GalVpVExoU2lLa0o3cG5YcTdnUW9XOEVWSUswOGVLU3BoRWh6d3VB?= =?utf-8?B?MUpLaUZYTHBQRjZRQnAwNnltTHVoNXdRdHY1czUxeTBpU3hPVFZNVEQxQ3ZJ?= =?utf-8?Q?Tmcn7gZk/AHRIQ/SGoeS5j4f8VBMgY=3D?= X-Forefront-Antispam-Report: CIP:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230040)(36860700013)(376014)(7416014)(1800799024)(82310400026);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Dec 2024 03:40:48.9113 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 76714b4e-49c6-4f79-8cc4-08dd1fdeede6 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN2PEPF0000449E.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB6283 X-Rspamd-Queue-Id: 2B5B4180004 X-Stat-Signature: xy8m3reqciw6ygkjnpqwh5x4c5pqdphs X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1734579622-99786 X-HE-Meta: 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 lH706PIC 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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 12/18/24 1:34 AM, Dev Jain wrote: > On 18/12/24 1:06 pm, Ryan Roberts wrote: >> On 16/12/2024 16:51, Dev Jain wrote: >>> We may hit a situation wherein we have a larger folio mapped. It is incorrect >>> to go ahead with the collapse since some pages will be unmapped, leading to >>> the entire folio getting unmapped. Therefore, skip the corresponding range. ... >> It would be good if you can spell out the desired policy when khugepaged hits >> partially unmapped large folios and unaligned large folios. I think the simple >> approach is to always collapse them to fully mapped, aligned folios even if the >> resulting order is smaller than the original. But I'm not sure that's definitely >> going to always be the best thing. >> >> Regardless, I'm struggling to understand the logic in this patch. Taking the >> order of a folio based on having hit one of it's pages says anything about >> whether the whole of that folio is mapped or not or it's alignment. And it's not >> clear to me how we would get to a situation where we are scanning for a lower >> order and find a (fully mapped, aligned) folio of higher order in the first place. >> >> Let's assume the desired policy is that khugepaged should always collapse to >> naturally aligned large folios. If there happens to be an existing aligned >> order-4 folio that is fully mapped, we will identify that for collapse as part >> of the scan for order-4. At that point, we should just notice that it is already >> an aligned order-4 folio and bypass collapse. Of course we may have already >> chosen to collapse it into a higher order, but we should definitely not get to a >> lower order before we notice it. >> >> Hmm... I guess if the sysfs thp settings have been changed then things could get >> spicy... if order-8 was previously enabled and we have an order-8 folio, then it >> get's disabled and khugepaged is scanning for order-4 (which is still enabled) >> then hits the order-8; what's the expected policy? rework into 2 order-4 folios >> or leave it as as single order-8? > > Exactly, sorry, I should have made it clear in the patch description that I am > handling the following scenario: there is a long running system on which we are > using order-8 folios, and now we decide to downgrade to order-4. Will it be a > good idea to take the pain of splitting order-8 to 16 order-4 folios? This should > be a rare situation in the first place, so I have currently decided to ignore the > folios set up by the previous sysfs setting and only focus on collapsing fresh memory. > > Thinking again, a sys-admin deciding to downgrade order of folios, should do that in > the hopes of reducing internal fragmentation or increasing swap speed etc, so it makes > sense to shatter large folios....maybe we can have a sysfs tunable for this? Maybe we should not support it (at runtime) at all. We are trying to build systems that don't require incredibly detailed sysadmin involvement, and this level of tweaking qualifies, thoroughly, as "incredibly detailed sysadmin micromanagement", imho. Apologies for not having gone through the series in detail yet, but this point jumped out at me. thanks, -- John Hubbard