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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D18DAC624A5 for ; Mon, 31 Aug 2026 08:04:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id F248C6B0088; Mon, 31 Aug 2026 04:04:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id ED5D86B008A; Mon, 31 Aug 2026 04:04:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DC4056B00A5; Mon, 31 Aug 2026 04:04:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id B23956B0088 for ; Mon, 31 Aug 2026 04:04:28 -0400 (EDT) Received: from smtpin16.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 5321E1603A6 for ; Mon, 31 Aug 2026 07:56:25 +0000 (UTC) X-FDA: 85160807130.16.AAD2B85 Received: from SA9PR02CU001.outbound.protection.outlook.com (mail-southcentralusazon11013015.outbound.protection.outlook.com [40.93.196.15]) by imf27.hostedemail.com (Postfix) with ESMTP id 54D2B4000D for ; Mon, 31 Aug 2026 07:56:22 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=biCVvgVA; spf=pass (imf27.hostedemail.com: domain of noren@nvidia.com designates 40.93.196.15 as permitted sender) smtp.mailfrom=noren@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=1788162982; 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: references:dkim-signature; bh=L40kmwh0RKeXeWwMJhkteXPJBYYOEQqyYjSI23MQaxY=; b=V6iZSqeQv2KBgWNYQaXsFccDVLEm2gNJMR8g7OVuJ6YIFJ3E3wuWRaUXzwRrKMCeutacmU ff3O/HpM9nlhMNWzKu91s2Wi/cml8NyCTcwLgURQ4Ub/pCt5tChhzcY3IdibKvwDV7H07K VODK/rX7V2Wsn/b62G+BSnzjSWTBweA= ARC-Seal: i=2; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=pass; t=1788162982; b=cdp7ywmmJ0IwUIOipDq3vZUUyvlFsfHAhBQdFnNKbRy4WOBdLLXyo1bjNd7IFLwIqZLiUw eVcW5HDrG05XRrWgS7URu8zGign6yv56kSwhSBfQO1+VpHy+4Dos0JVJK5FTnR7lEzMMYJ JflN6+WX3x9sThwVnnWT80K4ukcjkAQ= ARC-Authentication-Results: i=2; imf27.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=biCVvgVA; spf=pass (imf27.hostedemail.com: domain of noren@nvidia.com designates 40.93.196.15 as permitted sender) smtp.mailfrom=noren@nvidia.com; dmarc=pass (policy=reject) header.from=nvidia.com; arc=pass ("microsoft.com:s=arcselector10001:i=1") ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=qaS6M08fXz6iLWJM4KbaeB7xJOdBla4wUElRdnS/lsCv+Q/ZmLUN2qkDbjeBmfGV7OqT+SKq+lmsj9bbh6KeOEOQNF9Kyr2i8bracqfBFYcE2LwoZcSA/RK+oG4LhgxKlI5BMPK5tDf/NYEBLOhuYXY/Ws0J7x9Vps4fQysq2pbqgMa4/1w66J0fBNyu0V4YGuN1Jsa9mDwRvooMPbdPeB3TqUn7OZtDDempkdKaXa9Mx8v+6aKaG5MgcpPz4bQ0fWBMIbF1IRhCubt5LJZyALYhnTOCnJE4FAQo0V0iTfKY9Thm3tRN6Dd0fGrT/n/CiVjMSAqfNI13Gq/7mtKubw== 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=L40kmwh0RKeXeWwMJhkteXPJBYYOEQqyYjSI23MQaxY=; b=FWeF3m1ZMc0T2JuZJBUdtBOZSdOjGx8mTBMbASUe9x6RIn8D9Hw/CUh2f28eyEr1cY6uy62Tw0u64n4j8vhXwfcaMJxUNE/ivF5Mnmbf6l1uxHWG7gjNHIJjitn+r54m0xSBK0thMgDcaiajt17iqKOMh+5EQ3d4nYckFRVL+NwAC/SURvvATcl6zy2GkzU++NNIhzsJ3PQqH+gfIonHcZiQnwWDIOtAiMLAEUXlfS/QIEyVP1hv9Zb3hbB5ZYeom8BuFoJ6a0W7XlK91yStNg9ELn+Y+/B3PHNgnN8IHBrGd6mblfjbi1nFUhfF5dhA6WYngoP+3jI0e0m0kHRoUA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass (sender ip is 216.228.117.161) smtp.rcpttodomain=linux-foundation.org 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=L40kmwh0RKeXeWwMJhkteXPJBYYOEQqyYjSI23MQaxY=; b=biCVvgVAdMh5FUMrt/UAno8UmJ1Lo3iC8xMADNJ7+pAkN/cdAAhbdNCcjB22Bq3pUlM51lOOomyohJ4WCfPgjMF3OqPNRsKyOAQDGFjM2C9U1FRIuGN7qmQX3JpPGTCIK9IxNLp2zaLw6cHmHov+nAoFZKZMdmaN6eR7Er0kcrgzuvJxzt44KLUCxSztBdCm7rH3uuLrYUgFzz0+je4SKBl9rlSAxqTuDOQkaBMZ+4njQ/5rdEX2UO6vAU3iRUhmCxr9PZGg4E2L2GAZXRyBeYfdVzrTkALnr9RdLzI6isaD/DZxNkdJ1i0iuK7zB2UnfVdgPmQxmMQJkjW4V4fOoA== Received: from PH8PR20CA0024.namprd20.prod.outlook.com (2603:10b6:510:23c::19) by CY8PR12MB8266.namprd12.prod.outlook.com (2603:10b6:930:79::5) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.360.13; Mon, 31 Aug 2026 07:56:14 +0000 Received: from SA2PEPF000015CD.namprd03.prod.outlook.com (2603:10b6:510:23c:cafe::7b) by PH8PR20CA0024.outlook.office365.com (2603:10b6:510:23c::19) with Microsoft SMTP Server (version=TLS1_3, cipher=TLS_AES_256_GCM_SHA384) id 15.21.360.13 via Frontend Transport; Mon, 31 Aug 2026 07:56:14 +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 SA2PEPF000015CD.mail.protection.outlook.com (10.167.241.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.382.8 via Frontend Transport; Mon, 31 Aug 2026 07:56:14 +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 15.2.2562.46; Mon, 31 Aug 2026 00:55:55 -0700 Received: from rnnvmail205.nvidia.com (10.129.68.10) 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 15.2.2562.46; Mon, 31 Aug 2026 00:55:55 -0700 Received: from vdi.nvidia.com (10.127.8.14) by mail.nvidia.com (10.129.68.10) with Microsoft SMTP Server id 15.2.2562.46 via Frontend Transport; Mon, 31 Aug 2026 00:55:47 -0700 From: Nimrod Oren To: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Jonathan Corbet , Vlastimil Babka CC: "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Shuah Khan" , Randy Dunlap , "Zi Yan" , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Nirmoy Das , Dragos Tatulea , , , , Nimrod Oren Subject: [PATCH v2] mm/khugepaged: cap min_free_kbytes recommendation at 1 GiB Date: Mon, 31 Aug 2026 10:56:35 +0300 Message-ID: <20260831075635.2244437-1-noren@nvidia.com> X-Mailer: git-send-email 2.45.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SA2PEPF000015CD:EE_|CY8PR12MB8266:EE_ X-MS-Office365-Filtering-Correlation-Id: d8cc7507-67fe-47e7-a0ab-08df07355490 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|36860700016|1800799024|23010399003|376014|7416014|18002099003|56012099006|13003099007|6133799003|11063799006|10067099003; X-Microsoft-Antispam-Message-Info: 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 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)(82310400026)(36860700016)(1800799024)(23010399003)(376014)(7416014)(18002099003)(56012099006)(13003099007)(6133799003)(11063799006)(10067099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: vrnEFyhBEwVs+cDloI3aPzMT1oLZ8gyv7GYdYnTkJbUEHXqVYuR7cliUVHodBybZm1Ses2sHMUEmUGaFGaTyM5CvpuDF0NxCAyRgkBsg1T5/7zuyxiVjYUcipwxbQVt2q6ZkAyul7jjZLGyoPMTB10wPMVTmqDoY1FOc/lmboCPeBT80OLkXlFbmDlcc1WZ0eXqBx6Dm3YLrjo4prVslL7WzTcWW7sidxOkuvdJEDTKvYlX6sxykoFrDADTBT+NHOQaPDu4cvgfHSdvPVHJ1twmZ15kEwyQf9eMlJcSqZCRSy6JRIKVH/3Zz9IE4mEoOXJ75H4nDS4yF56zdsXqmUFTp/+Sd7MWoqKNuu8d/J67MPCqn0RBQMSxg/m5HE5yLnf8wLom5xQYq7zdSflLY8f7PkOrISZ5NAPSah+8tDv8U2bnS9jwn3nPVc1rk+a6p X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 31 Aug 2026 07:56:14.1804 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d8cc7507-67fe-47e7-a0ab-08df07355490 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: SA2PEPF000015CD.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR12MB8266 X-Stat-Signature: ekycfnoms6k14mhoygdwpemoguoq9umr X-Rspamd-Queue-Id: 54D2B4000D X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1788162982-602936 X-HE-Meta: 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 W1aF5gxy dJ/stfcm5eWuv25gncByAxC1kpPd0i+kziDDER5c+9JZ5vDIlfdfml88bPf4yeFh0J8CGVc/Y1f4RTG2cDhhOtpMhEWzXp2GGGRNPHH+Zt0+dgrnwFpAJ8MBN5rHUl57q6+n3/jBxOi+5QitXCp4Jwh9u9mZ5Xt50BKfN226bzXxsY5Lal60a3artlLRKiQ7NQIKCK52gJxngKg8fh/md/OnLyRNSL/yHgv/5dFeByveYwpMKGotKljukq2T1dqH+0J1QOK9a2hkROW8pg5amrNE+LKkmYAfNc2AgHe2MsAnx+X4c8QNvlBBJo8TWnd6ophmt0mi9DU03I//LlGDwCPjDMvQqpAiUQb8FAHBfAj6hQcRLIwqjHB0/zoBrifD46DA5rwstn/WHF8xTauswM/cYKg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: When THP is enabled, set_recommended_min_free_kbytes() may raise min_free_kbytes using a heuristic that scales with pageblock_nr_pages. With MIGRATE_PCPTYPES equal to 3, the formula accounts for 11 pageblocks for every eligible populated zone before capping the result at 5% of low memory. This is reasonable when a pageblock is 2 MiB, as on common 4 KiB page configurations, but scales poorly with larger base page sizes. With the default arm64 pageblock sizes, the contribution per eligible zone before the 5% cap is: 4 KiB pages: 2 MiB pageblock, 22 MiB per zone 16 KiB pages: 32 MiB pageblock, 352 MiB per zone 64 KiB pages: 512 MiB pageblock, 5.5 GiB per zone Consequently, min_free_kbytes can reach excessive and unwanted levels. Add an absolute 1 GiB cap to the recommendation, in addition to the existing percentage cap. This bounds the automatic recommendation to a sane value on systems with large pageblocks while preserving existing behavior for typical systems with 2 MiB pageblocks. Link: https://lore.kernel.org/r/20260716173504.760369-1-noren@nvidia.com/ Suggested-by: Lorenzo Stoakes (ARM) Signed-off-by: Nimrod Oren --- v2: * Use a named constant for the cap. * Drop explicit linux/sizes.h include. * Update min_free_kbytes documentation. v1: * Cap the final recommendation at 1 GiB as suggested by Lorenzo. https://lore.kernel.org/r/20260728202014.2517142-1-noren@nvidia.com/ RFC v1: https://lore.kernel.org/r/20260716173504.760369-1-noren@nvidia.com/ --- Documentation/admin-guide/sysctl/vm.rst | 8 ++++++++ mm/khugepaged.c | 7 ++++++- 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index 5b318d17aa4b..c0c925e6f504 100644 --- a/Documentation/admin-guide/sysctl/vm.rst +++ b/Documentation/admin-guide/sysctl/vm.rst @@ -539,6 +539,14 @@ watermark[WMARK_MIN] value for each lowmem zone in the system. Each lowmem zone gets a number of reserved free pages based proportionally on its size. +When Transparent Hugepage (THP) support is enabled through global or +per-size controls, the kernel may raise this value automatically to +help keep pageblocks free and reduce fragmentation for THP allocations. +The automatic recommendation cannot exceed 5% of low memory or 1 GiB, +whichever is lower. This limit applies only to the automatic +recommendation and does not constrain a higher value written by +userspace. + Some minimal amount of memory is needed to satisfy PF_MEMALLOC allocations; if you set this to lower than 1024KB, your system will become subtly broken, and prone to deadlock under high loads. diff --git a/mm/khugepaged.c b/mm/khugepaged.c index f49a6710933b..a8fc061d2488 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -101,6 +101,7 @@ static DEFINE_READ_MOSTLY_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS); static struct kmem_cache *mm_slot_cache __ro_after_init; +#define THP_MIN_FREE_MAX_PAGES (SZ_1G / PAGE_SIZE) #define KHUGEPAGED_MIN_MTHP_ORDER 2 struct collapse_control { @@ -3120,9 +3121,13 @@ void set_recommended_min_free_kbytes(void) recommended_min += pageblock_nr_pages * nr_zones * MIGRATE_PCPTYPES * MIGRATE_PCPTYPES; - /* don't ever allow to reserve more than 5% of the lowmem */ + /* + * Don't allow the THP recommendation to exceed 5% of lowmem or an + * absolute cap, whichever is smaller. + */ recommended_min = min(recommended_min, (unsigned long) nr_free_buffer_pages() / 20); + recommended_min = min(recommended_min, THP_MIN_FREE_MAX_PAGES); recommended_min <<= (PAGE_SHIFT-10); if (recommended_min > min_free_kbytes) { -- 2.45.0