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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id ED04DC55171 for ; Sat, 1 Aug 2026 02:17:30 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4hBmmT02fxz2ygg; Sat, 01 Aug 2026 12:17:29 +1000 (AEST) Authentication-Results: lists.ozlabs.org; arc=pass smtp.remote-ip="2a01:111:f403:c110::3" arc.chain=microsoft.com ARC-Seal: i=2; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1785550648; cv=pass; b=GCdwf9QNli29vzj8Sj/9Fcx74pOUpfFJCiTp1z2W+Q8R+PbN7lED1ePwA6/rcqbE3dKHgme8Gnpqs8RsSqbmvFs2u/fAXAYjeBwnIuNxoTZlTpGsyZLZxT9xCGuyEHm+QdtFlQGxyX0cwfOqq0qPYyRea498V5XNYqtTwHhj4mGto/DeGQgZhgKVJwk9oWq6hiGB8R35YemoofEWK1mX1PBhG8J5tVqm4vYQZDLbfBGPeLpO4EFiJWeMcmFcDClsGspIzK1cIihTzj2tMhC38QAXr6dqFjTLV8A+ynVQofTGc/cGUQTAG8RqRJH46wAx6jlF+Th4FobUIuCCqGIVIA== ARC-Message-Signature: i=2; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1785550648; c=relaxed/relaxed; bh=Cu2PNoyPHXaPHHDe/kk5zDlt2W8gJm9Sv8bR1p8K1bM=; h=From:Date:Subject:Content-Type:Message-Id:References:In-Reply-To: To:Cc:MIME-Version; b=WN/uQePA/yAELA1q7eqQ1sbDa1wG/uUw5pjnlLVFMKCCkOxgzyVjzEVT/AYZY/xqbwWTw2u2tBvCYg7LwtJAcynigdB9lFC7Oray0zrNBgTBPorsvY1sK4lXvkTIaytS44T64llhDpbxH07a1n9GAPft+Ma3cBafbrPyYWX/kZKkc66pLNdN9PnGAfo/wZUOYI8mR81zbJu+0WI8o8V1MrjSP7jRBG+cC+LKEZjohetUBFQUEWzpgqNKMDmK6UAXfRJ0begNQoVgRLZXECrn8cYUkd1Lz+QH1kkkoJu9NgkdODZiHOdSEa+/RvrxSHSyvLi/WCY/I21pNAmuNvpBxA== ARC-Authentication-Results: i=2; lists.ozlabs.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; dkim=pass (2048-bit key; unprotected) header.d=Nvidia.com header.i=@Nvidia.com header.a=rsa-sha256 header.s=selector2 header.b=cqL2slsZ; dkim-atps=neutral; spf=pass (client-ip=2a01:111:f403:c110::3; helo=bn8pr05cu002.outbound.protection.outlook.com; envelope-from=ziy@nvidia.com; receiver=lists.ozlabs.org) smtp.mailfrom=nvidia.com Authentication-Results: lists.ozlabs.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=Nvidia.com header.i=@Nvidia.com header.a=rsa-sha256 header.s=selector2 header.b=cqL2slsZ; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nvidia.com (client-ip=2a01:111:f403:c110::3; helo=bn8pr05cu002.outbound.protection.outlook.com; envelope-from=ziy@nvidia.com; receiver=lists.ozlabs.org) Received: from BN8PR05CU002.outbound.protection.outlook.com (mail-eastus2azlp170110003.outbound.protection.outlook.com [IPv6:2a01:111:f403:c110::3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange secp256r1 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4hBmmR6wbHz2xF8 for ; Sat, 01 Aug 2026 12:17:27 +1000 (AEST) ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=hQltLXNeMPD1NXXjLvK+awgv9a3snayNMjtOfZwOrRkLksPmZlEFFtpDCMI9oKHzCzc/lZKeG8k2Ya/ZmlI424oMTuHGIKIxunVVC8oUS2PIN27nr+uCFBHeJvOykfMJg5aiAYNpokKqRj2X3FLPupCwIflXS2I86WstG27IUTDJ3Sos9LO93gTq+s6oSD04n2qn9Uk4vgFAZflS00+e8fpCuTY893+xicjVcFzl2/8YeIgn3wJGkvsSiwNJ5AWnILH6B4+nN5ijQ5jR9bMGw/2snkiSpNMxXJY5wH85DOyMkX1CxWL9y2G7FX2pB+MLpmKKTjbozblz+4u7z38BGg== 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=Cu2PNoyPHXaPHHDe/kk5zDlt2W8gJm9Sv8bR1p8K1bM=; b=a2KPswTbQxdVFxfCs2eT/0ZM8mprJs6zcE+7hEuPHZGHgrNqRMQRBGja8EEzl14LNORhCsnpS++lXcBgEnimmCafCIdcbOSugjroGkbob4jtoUPXgyOmvqvAmFeQlwcmYV5p4IkgHjoeSjlMF2p1u4AKpU9hrdfnsxDJxRBtbpIlCB+j1et6Ww+zt3ikj8YAdWhrdfOoCHuSJPFnKwRMok9nBnROB0bkUgbcmS3sMJXSwQuip+SMfhml6S3S1KYtp8DQuydIdqoJLOvOsb0pznpaKkiE6nEwOEl7vXae+BUkMSL+GZ7dyDeRIO5IdvN7i6j6oUGrvxJpk8KbT2yJ4w== 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=Cu2PNoyPHXaPHHDe/kk5zDlt2W8gJm9Sv8bR1p8K1bM=; b=cqL2slsZebnGMQ95nmBSWGj1jv94ONjMj7ucuvWuVaw+a6mtVNg3siAs/Psssbkh3EOvL9pyFoc1tmoWwL0IhcDTJYMW8MpWUIX+slGpwqZXxXK7spaJmlPqBzMLJQLzuBUUg4fhdNDdS0jEPHuO03x3xTcGWmZ1WD4TYQI1FsMZi3GF9xCLLxFNL/32w8eb98p+UHPgGTmxs6w0NkLqTfyfPz4Qvod95zWtUptmqwpDeg/aopLzLzNYgwv7L/6hICsudrmEd7f5kWQH3VBTNmLvJuk4GzNiX70jkG5hUi7m7wt8wXrofsMj3db2jnvXzcp7oO2tom3e9WskbrJkTw== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) by PH8PR12MB7373.namprd12.prod.outlook.com (2603:10b6:510:217::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.270.16; Sat, 1 Aug 2026 02:17:00 +0000 Received: from IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16]) by IA0PR12MB8374.namprd12.prod.outlook.com ([fe80::d85f:4c87:ae84:3f16%5]) with mapi id 15.21.0270.015; Sat, 1 Aug 2026 02:17:00 +0000 From: Zi Yan Date: Fri, 31 Jul 2026 22:13:30 -0400 Subject: [PATCH RFC 07/14] fs/erofs: mm/pagemap: add readahead_folio_reverse() to avoid folio->private Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260731-remove-pg_private-v1-7-142c97ba3562@nvidia.com> References: <20260731-remove-pg_private-v1-0-142c97ba3562@nvidia.com> In-Reply-To: <20260731-remove-pg_private-v1-0-142c97ba3562@nvidia.com> To: David Hildenbrand , "Matthew Wilcox (Oracle)" , Andrew Morton , Muchun Song , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Gregory Price , Ying Huang , Alistair Popple , Johannes Weiner , Qi Zheng , Shakeel Butt , Kairui Song Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Zi Yan , Gao Xiang , Chao Yu , Jan Kara , Yue Hu , Jeffle Xu , Sandeep Dhavale , Hongbo Li , Chunhai Guo , linux-erofs@lists.ozlabs.org, linux-fsdevel@vger.kernel.org X-Mailer: b4 0.14.3 X-ClientProxiedBy: IA4P220CA0002.NAMP220.PROD.OUTLOOK.COM (2603:10b6:208:558::13) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) X-Mailing-List: linux-erofs@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|PH8PR12MB7373:EE_ X-MS-Office365-Filtering-Correlation-Id: 5b718f75-4527-4ad5-4b46-08deef72f81f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|23010399003|366016|11063799006|56012099006|10067099003|18002099003|22082099003|921020; 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:IA0PR12MB8374.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(7416014)(376014)(1800799024)(23010399003)(366016)(11063799006)(56012099006)(10067099003)(18002099003)(22082099003)(921020);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?ZDEwOE5ITDhMdmFhQlFUaExGK0tGZEdlbUZFR2FtWmg2U1pMTkx1eUUxWGZ1?= =?utf-8?B?U1JnUTNpTDZYS005QnhJM1EvMFd1OFVWakowSEViN2wvclhpQVJuMUd5TC96?= =?utf-8?B?WWpxLzdScDdrUGN0a0hZZTlZL3NDcFBnZ29GazNsVTdkaHV1UnV4M3krbEx1?= =?utf-8?B?VGRFdll1VGoyajh6RnU5ZS80WlBLQUVxblovQ2RKNXRIWndndENpcE9wK1Fm?= =?utf-8?B?bzBLWWFVZFUwQWFnTGdqakd5dk5HdTNwQmxaYlZUMzB3UDlIdjBuNjk5YXQy?= =?utf-8?B?c0Q5TGxOSCsrQ0s3b083QXdQRjJodmFtdVB1RXREVzNOYjgzenFyb0MrUWwr?= =?utf-8?B?MTQ1d3NCNGtKUEZ5VXl5bklhYjdvR1Iwb2Z4bFdBTERHOFI3NVBLdkJER2hh?= =?utf-8?B?K01sRVNRRWVNK29sV0djWkhCdDZJVmw5Mmc5bnJPQlUxcUpiWFBOa3JleFNP?= =?utf-8?B?bDYvZXZveE9nZXlicEVhTWpYcnFseUw4ZnJCNFEzbmU5b1I0VlVNLy9pS3lG?= =?utf-8?B?TjRSMHJRQ3A2b1ljRUFYaE9yTDFDTzB2Ny9TZ3FHM2NxeDB3ZEVoOXJOaCt0?= =?utf-8?B?c2NaNFh2Y3NHT2ZFeEtPVmxSbzdzeXEvSUR2akppUmkzelJxYkxtRk1IYkky?= =?utf-8?B?VWFiWFV0ZUtqVFhGdmwxMmVFTEgvZWRTU0R1QXZJaHQrc0F2OW14R3Z6S3lP?= =?utf-8?B?Z2wzZ3FIc1M4U1FPSzlpS28vZWVCY3FQWk15N0xURXgvZEF0N3F5VmZqbXZ3?= =?utf-8?B?TmV2UjlIZXQ0R1VxOWVhM1hPa3VOQWQzYURUem9Edktpa2x0bWpSelJDYnlB?= =?utf-8?B?TzlXOWZPVmpzYzJwSjNtc2ZtQVl1eGlWMVZTSDVqSkpGVTZuUmYvbFY0dXRw?= =?utf-8?B?eGNxOGJOa2pXNFVTaW1IUWxCeDRTZmVnZk54WW1SaTFqQnNlcEJWcnlZRlBL?= =?utf-8?B?eHM2ZklPcG9oMUIvbnV2VlUrcGxkSHJwNVIrZGpNb05wYXNqWnRBcGNOMzRz?= =?utf-8?B?RGpxampUWEllSzZYR09qbTNaRERXZGZvSXc5Q3h1bEkzdVl4QTN3YWxIU3Nh?= =?utf-8?B?ZlVJVjI5ck9wUlpybUtkR0NaTFZSaC8zT1Z5OHlsQ0I4QW16a1NPNXlvSkxF?= =?utf-8?B?eXJxRlltejVRUitrRnEwYkZPdmZQVVhSMGJ3VWtMVVU0V0pvdnpvdzlJSTF4?= =?utf-8?B?S2hJQmRqWG5tWTQ3MXlZeE1McG92VDBheE9MV0llaVdLcno5SUVyRjU2S2gx?= =?utf-8?B?L3pjNDQ0QkxCK0Jub3ZMOW45T2RpdytsWEdrOVR4ZmJmdk5aZzF6d2pWWW5Y?= =?utf-8?B?SkR4czcwVWQ4d2J0UmpzSC9ReXZndFJvWElkUkFJMFcvb1JaR0xROEFCdi9h?= =?utf-8?B?V2xqelZuV3YxSlNMeHNFaGg4b3UrSGJlMmw2SGY1RVRCWWw0dFFBaHZVS0R4?= =?utf-8?B?cUVzTUpEaW9aYWZ2N0NNZFFyQ0VZSVhrbUw1ZkNuTm5hMlQ4clhSN003Szcr?= =?utf-8?B?VThCN3BqSURpV2M3KzB6ZVBhdTlVZ3dqaGxNLzBUdnJTajF1T1YyODE2aDR1?= =?utf-8?B?eGNpTUd6bkZUQzVrYTJvYVBLVWFFZVk5TUJkUGs0eUV6Mi9BZ3J6Ym5ZOHZq?= =?utf-8?B?eUZoOWtmMTNRcTFlWWZvV0tweWV4UGptYzhDOXdGUVFXamlrMDNaRXFpaTZJ?= =?utf-8?B?elhPbUpGbW9MbGdmNEt1Rk1DanFUYmxUcG9OOE81eVpWT0ZIYVp5cTI2MGdP?= =?utf-8?B?MmYwZ3hBWFp6WEM5YjRKK0NpbjBrRXNxL3JVN2R5dUx0YUF5cVc4d3ExdmE2?= =?utf-8?B?cTI2RnFJRXdROVhaMi9wWnBCQjFOOEtvOWl1MWx3WnU5VmZTdmNzRWFzWXdT?= =?utf-8?B?cmxCcElIazEvNDlxRm0vQ1FoTGFLRjNLaEx6NWo3WlFvSWdxRUtPb1ZBN1pt?= =?utf-8?B?ZlNjbnNWb2FFT3FrRE1MSjZUQkhlVmtJZG54TVYvY0JNUGtuY1Z6NUhzYnRQ?= =?utf-8?B?YmZ1WXRWcG5TVDQyS0lsdG1Nbkh3ZCtMd1JTVndSb2Y0YUc5VHlYMFZJRlla?= =?utf-8?B?ZU8yeTNmWWxnVUhHeGFJaWwxOFo5V2ljUGZ4TmVLSWhvSDExNDFLTDdsNUlp?= =?utf-8?B?dGVSdk1KaHFhOUZyMkFnTThTVllvYVY4OXZZaXZJMzMxMjRkSzF3OVNIODJl?= =?utf-8?B?bFBMNWUxV0dJa25vL3dYVWxQL3gwUlVuR1NHMnB3b0xOdUdncHIrR3ZMZy9X?= =?utf-8?B?L3UyRGZJbFppUWVYWEJoOHpUTHJ2SWNqaS9mRmw3NGtvc3lLYWNYVXVPeWs4?= =?utf-8?Q?Q8UZdz3YGAIPhFr/Bs?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 5b718f75-4527-4ad5-4b46-08deef72f81f X-MS-Exchange-CrossTenant-AuthSource: IA0PR12MB8374.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Aug 2026 02:17:00.1951 (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: due+TvJ9NIwYy7oj02SiKmUnCFUNpRJ6VtB8+179ZDHkHol703nFyxLh+tNAby6S X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH8PR12MB7373 erofs needs to traverse readahead folios in reverse order to achieve maximum performance by 1. reading all folios from readahead_folio(); 2. storing the prior folio pointer in folio->private; 3. traverse from the last folio to the first one. Add readahead_folio_reverse() to achieve the same function without using folio->private. It prepares for a future commit that replaces PG_private checks with !folio->private checks. After switching the checks, erofs's use of folio->private without bumping folio refcount can cause unexpected outcomes, e.g., in filemap_release_folio(), try_to_free_buffers() becomes reachable. No funtional change intended. Assisted-by: Claude:claude-opus-4-8 Assisted-by: Codex:gpt-5 Signed-off-by: Zi Yan To: Gao Xiang To: Chao Yu To: "Matthew Wilcox (Oracle)" To: Jan Kara Cc: Yue Hu Cc: Jeffle Xu Cc: Sandeep Dhavale Cc: Hongbo Li Cc: Chunhai Guo Cc: linux-erofs@lists.ozlabs.org Cc: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-mm@kvack.org --- fs/erofs/zdata.c | 11 ++--------- include/linux/pagemap.h | 31 +++++++++++++++++++++++++++++++ 2 files changed, 33 insertions(+), 9 deletions(-) diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c index 74520e9102596..b59f2745a8e72 100644 --- a/fs/erofs/zdata.c +++ b/fs/erofs/zdata.c @@ -1902,21 +1902,14 @@ static void z_erofs_readahead(struct readahead_control *rac) struct inode *realinode = erofs_real_inode(sharedinode, &need_iput); Z_EROFS_DEFINE_FRONTEND(f, realinode, sharedinode, readahead_pos(rac)); unsigned int nrpages = readahead_count(rac); - struct folio *head = NULL, *folio; + struct folio *folio; int err; trace_erofs_readahead(realinode, readahead_index(rac), nrpages, false); z_erofs_pcluster_readmore(&f, rac, true); - while ((folio = readahead_folio(rac))) { - folio->private = head; - head = folio; - } /* traverse in reverse order for best metadata I/O performance */ - while (head) { - folio = head; - head = folio_get_private(folio); - + while ((folio = readahead_folio_reverse(rac))) { err = z_erofs_scan_folio(&f, folio, true); if (err && err != -EINTR) erofs_err(realinode->i_sb, "readahead error at folio %lu @ nid %llu", diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 4e8b2b29f6d3e..90904a4d173b7 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -1549,6 +1549,37 @@ static inline struct folio *readahead_folio(struct readahead_control *ractl) return folio; } +/** + * readahead_folio_reverse - Get the next folio to read, from the tail. + * @ractl: The current readahead request. + * + * Like readahead_folio(), but walks the range back-to-front. The folio is + * returned locked with its refcount dropped; the caller unlocks it once I/O + * completes. Compound folios are returned once, at their head index. + * + * Context: The folio is locked. + * Return: A pointer to the next folio, or %NULL when done. + */ +static inline struct folio *readahead_folio_reverse(struct readahead_control *ractl) +{ + struct folio *folio; + + if (!ractl->_nr_pages) + return NULL; + + /* xa_load() follows sibling entries, so a tail index returns the head */ + folio = xa_load(&ractl->mapping->i_pages, + ractl->_index + ractl->_nr_pages - 1); + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); + + /* Shrink the window from the tail down to this folio's head index */ + ractl->_nr_pages = folio->index - ractl->_index; + ractl->_batch_count = 0; + + folio_put(folio); + return folio; +} + static inline unsigned int __readahead_batch(struct readahead_control *rac, struct page **array, unsigned int array_sz) { -- 2.53.0