From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from MW6PR02CU001.outbound.protection.outlook.com (mail-westus2azon11012032.outbound.protection.outlook.com [52.101.48.32]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 39E213911C0; Mon, 3 Aug 2026 16:56:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.48.32 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785776205; cv=fail; b=Bfd683Js1lrDPR2XB87y+fJ+nRuDoeGSeE9XocIkjleUq8wLUz7iugWdBpoHs+W+hxmTZuXj4lIHXTkBt5ZKGJkbOWFSIvgJLdgdgP9xU9j5+VuzFy+VU0OtxMe2td1P4dBRwJGRt023ATHVDI4+5WcNpIXZ8RtVaj6dWxMXjNI= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785776205; c=relaxed/simple; bh=jInUMGAZ8t5uTaq+0sr8CZ35NWhmyqthM5KC3F8nIc0=; h=Content-Type:Date:Message-Id:To:From:Subject:Cc:References: In-Reply-To:MIME-Version; b=UYS1P8vKIH1cVzuuP4+XAvwa9X6ziCjNEHPCsjVY8LZ4Y7Rb6RwSiSgsBP0jvR4yvI2724XgArF2lH98yqSfxso7LUqlItAeCz8PPfiFy4Q6rJLCrXm+YQkpJgEhpGGkrc0Ly8tkGtFIHTx5fiCnq1ZWBUtLgWJWsGtxKq5SgCI= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; spf=fail smtp.mailfrom=nvidia.com; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b=WmnTFywc; arc=fail smtp.client-ip=52.101.48.32 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nvidia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b="WmnTFywc" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=nZ1aJIeCeXj87wJpD8o26XuofOQQT7aY6ORXc+WqCGuRqLuwK1gqhgZv2R8kzDHxroJpnlK/biTNoh7nRwheDS9DHnahYZyMjDlt0gay9T7k+pHRT8ULs+Dj0x+20k+XoKzLVSO5CttRMLrxf/EqXI2uc3IytQ4jzz9eI4OMC/2LNHUqape2e+YBKN9zlA7SvZ1wU6G6YiqppqnGtFCdKCnFQnEXegW9Pga9W1GH+W26LUClKkMn/YbuYG/a9c4LFwDBJ3aHbfF82LH59EGTPYD5qgemi73lheWMKgEpV19vi3jVgognko1CfzoJrQhWyFldvQyLXntogVNb+HWdiQ== 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=FRnY5tNaG/4K6dlwwkSnxbPqAghp1PbId++hkByIeAc=; b=Kb8tVH++MK18ENDM0CLQnPrp4HgyAWFmQQuDpiI/+5DyCXTTsuvGFgDjbb2cZNlh3Kf3Ddxt2qfQowrMZucfsiKjogT06qCsf6c2T5Te759rHkY9XXmQtPyoTlNtPxTPasQGbFAMZc06h1CF4A0FMSitSGRBi/aIi3VRhvwFo7BIxFePBrW8skmF+7nAONgls0straQHK8VBpScpPiSEiiiMtEZNNP/YCvD1bov+Il4t751fFvauYCe3oFv4v3R8EE5dKJQHmh/TNRjUgDy+hoAmFPGB85fYado1PUUFyZat6xNHsXSWcfqd/qmAmULIoIarxcUqmRIk8JgoK2qtKA== 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=FRnY5tNaG/4K6dlwwkSnxbPqAghp1PbId++hkByIeAc=; b=WmnTFywc3df5N500P8K1ExxnDjZazTSOIIQrbb8g7DzLXy6VmLkRTHUDWXe7LPT41RjX+lTw9Tw0el95Pr1efsi2NcoC+7EyoDzDAZ8ALVc7XgaZWfE9cyKkum7vMkLXHKvlmfDTw1fscJhqeDkoklFk/rY9A3Xq6x8clRgyADP0aynIfE6EgB+En6Srhq0QjoEZJTF3r+298Y1ZMUvv5oG1qsA2U9nGK7ARjsN3ltl6M9whjyBafTnO7iGwVo4bTbS3M6pzo9mW2ganTmnAqyx6P+wvBRc6FrXLDGUlKovXBIeK8fPMLDxTr8Qt4JuvIJXmqxVE/6oQlFWzB/+8iA== 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 SN7PR12MB8790.namprd12.prod.outlook.com (2603:10b6:806:34b::7) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.270.18; Mon, 3 Aug 2026 16:56:38 +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 15.21.0270.017; Mon, 3 Aug 2026 16:56:38 +0000 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 03 Aug 2026 12:56:36 -0400 Message-Id: To: "Jan Kara" From: "Zi Yan" Subject: Re: [PATCH RFC 07/14] fs/erofs: mm/pagemap: add readahead_folio_reverse() to avoid folio->private Cc: "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" , , , "Gao Xiang" , "Chao Yu" , "Yue Hu" , "Jeffle Xu" , "Sandeep Dhavale" , "Hongbo Li" , "Chunhai Guo" , , X-Mailer: aerc 0.21.0 References: <20260731-remove-pg_private-v1-0-142c97ba3562@nvidia.com> <20260731-remove-pg_private-v1-7-142c97ba3562@nvidia.com> <332rknj4vo3cfhvfhhlf6pvg37s3lbrnzbbnv4swa6gctsiu6a@ndotgokvnglc> In-Reply-To: <332rknj4vo3cfhvfhhlf6pvg37s3lbrnzbbnv4swa6gctsiu6a@ndotgokvnglc> X-ClientProxiedBy: MN2PR15CA0059.namprd15.prod.outlook.com (2603:10b6:208:237::28) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|SN7PR12MB8790:EE_ X-MS-Office365-Filtering-Correlation-Id: cfadc822-731c-4681-de73-08def1802edd X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|23010399003|376014|7416014|1800799024|6133799003|56012099006|11063799006|10067099003|4143699003|22082099003|18002099003; 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)(366016)(23010399003)(376014)(7416014)(1800799024)(6133799003)(56012099006)(11063799006)(10067099003)(4143699003)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?SVljM2IxZzlnbjRPdjFLN2ZQbHN6QldmMlV2NGZDNXdYNEdvSkJSRUVITmo0?= =?utf-8?B?akRoN3BwZzlqOHEzN0J3NE5aVlBoVjdRWElucTEycVVsWUQwWVVOQmdQaERu?= =?utf-8?B?K0dTMEFDamdLWnE4K3FYSm4zMDFHank3SlpxNkNjb3Q5bjZ4cUNkVVdGRW4z?= =?utf-8?B?Um1yNWlzODZtaXM5NjdsNFZwRVdlK3IxV0RmSzlXUmxqdlNpL05hczRZQ1gz?= =?utf-8?B?Nm0xQ0p2cEIrS3QxaDE2REFZWE9HaXdTVC8wTlgxcFhiMVpSWnZXL1FwTkJ4?= =?utf-8?B?Ni9kUnhEZkxZWGFyRGpjMU40TUc3SDhYd2JJY0t2NkovVUU1M3RUSTVXNU5y?= =?utf-8?B?cUY1Y0JRZjZ5ZFBrY29TTnFiNlpvMVVQNDQ5UWJ3cERlSHZFamI5NjVGRVp6?= =?utf-8?B?Mk5qdkJReENkVENnejNtLzdRdUJTWUxZbjlVVXFMNjYyaUE0YmwxY2c2UVNI?= =?utf-8?B?cUk0aEF2Q3JGeWQrRWkrK1ZCcm1lVXdKRnlYWjhQQ3MrbTA5WENmbnl3Zno4?= =?utf-8?B?UmJWVTN4UjJHTWxOMFoxQzg5R1BSVHk0NlhHWC91L3NtbjJjVlYyalhJNEpp?= =?utf-8?B?cDNuaGZnYjBlYUN4anoyeGRGRUdHdVlRNU1RMDJHTG9IVndjMkttU1BSMDlp?= =?utf-8?B?K0MxeEE2emNIa29UTlR5VzF4ZkE1R2VvdUxDa2Q2VHR5b2RvNjNpQkoxbUhO?= =?utf-8?B?SWFLQStxOVhhR2ZxSnJ0clh5eHFSc1NweUplK3N6bDZDRTRPYUxXcitwYTcw?= =?utf-8?B?aUl2azhwQldEWi8yOFJDYmF2ZjJsVFpzRlQ3Z25BWUJXQ2R3eTdOaEN1U0xu?= =?utf-8?B?TTMvNEJnMHI2OTc1enFCdFlqTmJBRW55QVRzZXA1NDdyeUhKNyt0UnZjMUkv?= =?utf-8?B?SkxZaXo0ZTJacGkvZmtSUUVuTzhPOXFRTCtDbW9YVG5YRlF0QSsrWUYvaDUv?= =?utf-8?B?akFydmx4MmY0anV2ZnZEZzZjNTJaMG16VmdmbkNlNzhGY2lhTXI2aTIrN2FP?= =?utf-8?B?NGgwbWtLeFBhZENZQ1RXTy9ESHVMcDExM0V4a2NLdmpyU294aTlKV2dNaHZC?= =?utf-8?B?OXJLZE1HSVFLVlpvajByeVd2WjFqNEpRdjI5aVc4YVgwUFlpeWIyRjgvdUlx?= =?utf-8?B?UDI2b25ONXhUaWNKMjE5Rm5kdzNjSEt6dWdqK0gzUDhucGFhQlJIRHJGN0hN?= =?utf-8?B?cUIzcXV4OFpCM1Q3MjUySW5XY01IZk9pU056Vm5Ra0ZkRW9WNU1hZzJHVXFz?= =?utf-8?B?TVhKT2NxcE9pMkpwSVBpcUN6SFRyRGdVemVEa3dnVUFIam9yZUJOaG5lRjVN?= =?utf-8?B?TU5YU2dCdTJPRFNiRVRZL1hiSU9lNTEySk5iMlF2M2FaRkFMdk41c2pqaGRi?= =?utf-8?B?S1EvMTVYYXBySzVtdHJjRjBVQzB4dktpNGcwajV1ajVsdHRVWm5kU1FjNUlH?= =?utf-8?B?REJQbit3K1RpQy9NeXN2OHBmMjdTTERmTUlOUmZMdjAwLzRIbUxUbzNMN09P?= =?utf-8?B?R1owcVpxRzAxUmdzQXJFa1ZVZGV6NWZ4ZzRhbHFVR0lwM3pHMXh0cGFFNFFn?= =?utf-8?B?UUk1elBkbE54cU1CYkdNYlNXYjFoYXhlcW83Z1E2RjFYd0RDNTJRbUxYYm5m?= =?utf-8?B?SFZzc0RtNEVTNDJzUDNOdjB4WVRRSXVYZkpMWDRQR2tXVTNuWlVWODNoOEJ0?= =?utf-8?B?QnlwRXRNNVlTcGdDZlFRbDNiOVBoeXpjMDg5bFUyd3hBYnRwelBxcWJ3WHVR?= =?utf-8?B?SG0vY3RCVzhsU08ya0k3aWIvMlNvWEhqTDdTVTZYSXpLRWpZbmhBZWsrMVJo?= =?utf-8?B?T2xES2tyVnQwb3p5anhOR25JdlYvSUlDaWl2K0dZTWcrQVdMb1VCNGJXdkhO?= =?utf-8?B?RG16RFVWVDc4N0U1NnFUU2hMdjBFeG1mWmJadHVNaTc5blVKU0VWMHl3d29x?= =?utf-8?B?N3NNUWJqUUVhU2JzMytiSXhDeHBoM2JSS2xpZC95YUcwelBmeUtHY3Rrdjl6?= =?utf-8?B?TDBoaDhWc1NGZ3dwWUxFQWdqeEFONUxReXlRVWZkNEFBYVlCbzRtQ09EazVC?= =?utf-8?B?bVRLcDVuL054K1d5SUpRYlUrd0hxTC9pQXE3NmJVNWJyWnl6OU5TdUZ1TlRO?= =?utf-8?B?eVBTVkF2WEoxYmRYdWdsOGdSVFZyTjF2V1NweWt6RVVDVzBMQkpId1ROVHlC?= =?utf-8?B?V3RvTVV1bzdKc2tMUU8yWThmcU94MDkzWjZjWVN6bnc3VlVRbDc5WXh0YkN0?= =?utf-8?B?d00rSW5DODV4WnJyTXlaTDZoYWgyMk5tVDJrcnBGc2l4UUVJNC9pQ0QrUGFs?= =?utf-8?Q?ppWjsqrSQ8k/SVEWFw?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: cfadc822-731c-4681-de73-08def1802edd X-MS-Exchange-CrossTenant-AuthSource: IA0PR12MB8374.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Aug 2026 16:56:37.9461 (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: cY3UY38o0uSrCwJe2Tz34p6FyT+o54RkwEgtEasnGWb9mBI+w8HTpIo2q6nHT/tX X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB8790 On Mon Aug 3, 2026 at 5:54 AM EDT, Jan Kara wrote: > On Fri 31-07-26 22:13:30, Zi Yan wrote: >> 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. >>=20 >> Add readahead_folio_reverse() to achieve the same function without using >> folio->private. >>=20 >> 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() become= s >> reachable. >>=20 >> No funtional change intended. >>=20 >> 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 > > One comment regarding the generic infrastructure below. > >> 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(struc= t readahead_control *ractl) >> return folio; >> } >> =20 >> +/** >> + * 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 onc= e 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_co= ntrol *ractl) >> +{ >> + struct folio *folio; >> + >> + if (!ractl->_nr_pages) >> + return NULL; >> + >> + /* xa_load() follows sibling entries, so a tail index returns the head= */ >> + folio =3D 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 =3D folio->index - ractl->_index; >> + ractl->_batch_count =3D 0; > > Thanks for the patch! Currently there's the invariant that the returned > folio is still inside the _index .. _index+_nr_pages range. I think when = we > are providing a generic helper, we should keep that to make code more > robust for the future when more people start using it. Definitely. > > What I'd suggest doing is add bool in struct readahead_control telling > whether the last folio (batch) was taken from the head or tail of the > range, advance _nr_pages and _index accordingly in the functions returnin= g > folios (probably hide this in a helper function __readahead_advance() > because it will be used in 3 places) and maybe call this new function > readahead_folio_last() instead of _reverse() (but I have only a slight > preference here so .._reverse() is ok with me if other people prefer it). The below is what I come up with. I did not add a bool to readahead_control, since I think that is the decision of caller of __readahead_advance(). But let me know if you disagree. diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c index b59f2745a8e72..23f423c22ac8c 100644 --- a/fs/erofs/zdata.c +++ b/fs/erofs/zdata.c @@ -1908,8 +1908,8 @@ static void z_erofs_readahead(struct readahead_contro= l *rac) trace_erofs_readahead(realinode, readahead_index(rac), nrpages, false); z_erofs_pcluster_readmore(&f, rac, true); =20 - /* traverse in reverse order for best metadata I/O performance */ - while ((folio =3D readahead_folio_reverse(rac))) { + /* traverse from last to first for best metadata I/O performance */ + while ((folio =3D readahead_folio_last(rac))) { err =3D z_erofs_scan_folio(&f, folio, true); if (err && err !=3D -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 5ca5aa365f319..2cc3de5594518 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -1510,13 +1510,21 @@ void page_cache_async_readahead(struct address_spac= e *mapping, page_cache_async_ra(&ractl, folio, req_count); } =20 +static inline void __readahead_advance(struct readahead_control *rac, + bool read_from_head) +{ + if (read_from_head) + rac->_index +=3D rac->_batch_count; + + rac->_nr_pages -=3D rac->_batch_count; +} + static inline struct folio *__readahead_folio(struct readahead_control *ra= ctl) { - struct folio *folio; + struct folio *folio =3D NULL; =20 BUG_ON(ractl->_batch_count > ractl->_nr_pages); - ractl->_nr_pages -=3D ractl->_batch_count; - ractl->_index +=3D ractl->_batch_count; + __readahead_advance(ractl, /* read_from_head=3D */ true); =20 if (!ractl->_nr_pages) { ractl->_batch_count =3D 0; @@ -1548,7 +1556,7 @@ static inline struct folio *readahead_folio(struct re= adahead_control *ractl) } =20 /** - * readahead_folio_reverse - Get the next folio to read, from the tail. + * readahead_folio_last - 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 @@ -1558,21 +1566,24 @@ static inline struct folio *readahead_folio(struct = readahead_control *ractl) * 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_contr= ol *ractl) +static inline struct folio *readahead_folio_last(struct readahead_control = *ractl) { struct folio *folio; =20 - if (!ractl->_nr_pages) + /* Shrink the window from the tail down to this folio's head index */ + __readahead_advance(ractl, /* read_from_head=3D */ false); + + if (!ractl->_nr_pages) { + ractl->_batch_count =3D 0; return NULL; + } =20 /* xa_load() follows sibling entries, so a tail index returns the head */ folio =3D xa_load(&ractl->mapping->i_pages, ractl->_index + ractl->_nr_pages - 1); VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); =20 - /* Shrink the window from the tail down to this folio's head index */ - ractl->_nr_pages =3D folio->index - ractl->_index; - ractl->_batch_count =3D 0; + ractl->_batch_count =3D folio_nr_pages(folio); =20 folio_put(folio); return folio; @@ -1583,11 +1594,10 @@ static inline unsigned int __readahead_batch(struct= readahead_control *rac, { unsigned int i =3D 0; XA_STATE(xas, &rac->mapping->i_pages, 0); - struct folio *folio; + struct folio *folio =3D NULL; =20 BUG_ON(rac->_batch_count > rac->_nr_pages); - rac->_nr_pages -=3D rac->_batch_count; - rac->_index +=3D rac->_batch_count; + __readahead_advance(rac, /* read_from_head=3D */ true); rac->_batch_count =3D 0; =20 xas_set(&xas, rac->_index); --=20 Best Regards, Yan, Zi