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 5F007C79F82 for ; Tue, 8 Sep 2026 16:05:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7A67B6B00B3; Tue, 8 Sep 2026 12:05:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 77DDF6B00B4; Tue, 8 Sep 2026 12:05:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 693636B00B5; Tue, 8 Sep 2026 12:05:17 -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 40AA46B00B3 for ; Tue, 8 Sep 2026 12:05:17 -0400 (EDT) Received: from smtpin17.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id DD03716069E for ; Tue, 8 Sep 2026 16:05:15 +0000 (UTC) X-FDA: 85191069390.17.27D0882 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf18.hostedemail.com (Postfix) with ESMTP id 9CF751C0018 for ; Tue, 8 Sep 2026 16:05:13 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="fN/nuOR6"; spf=pass (imf18.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1788883513; 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=52DvIl2of7dUjq8RgKJMVXe+11DIg6SDkc/sKpreXrU=; b=Hpa3wYd8vBE2gQiswNtg04ZsD3Yl1VAMZ/HyTVjgkGNCfgBYoS6p9m+2sNun1k/GfL4Oal BE/jmOUpl5u0l5l25VHhqC9eXvQRCZC1/c6tefGpz37Mv8ypL+kxs2Dt0c9WZkfqmiCY8z aW8Dg6fqMzNtzZ4ZA3NNX9OlAgA48N8= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788883513; b=5Wb5BnmLsNbn3Sf/tMfMJXHqFg4H+/aDX1F8gJiU5+kMpDtMV/1ZhEpO7SxKUpmLkjTwdI p1fSs6AbcxO+hFLqS8ITHBZv5OEciOLmvBRNCmwNIcIn4oM4Mpod+fpor4Goo5zw3zxZwf D0KViCr8hreg0f6tIi9M7TfJWY35nsE= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="fN/nuOR6"; spf=pass (imf18.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id B071E42D6A; Tue, 8 Sep 2026 16:05:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AC82A1F00A3A; Tue, 8 Sep 2026 16:05:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788883512; bh=52DvIl2of7dUjq8RgKJMVXe+11DIg6SDkc/sKpreXrU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fN/nuOR6B2tJjVtren7fsjMrU4FFs7pugNQOxdQjZ1vubCKzB+NHQfxaosCEOrn4e 350jvM32cKifPJw5w9kgsYBaIoyqpsXrx1DPRvTMd0ZEn1P7n6kYQSNwOqliy3v6AD ucHf7W/RnXMjWGmyJcbaTs6ByEGnULj+CbAZYGc+LjmSxoCPZRYIwBT+gwCLYw+Q0L vvQCBgZdJY0Ly1Ly2T8rE9IGtstaXzuA+2zuV3x/xAlGByc6Z+a7yvZIBgEcK5WE0A Q3LA7xQ6JoJXOA6P5vGhbNaYXrbK6lrVpBM62Vf74KJDLC1cEb4j8/lZNgM33bult8 Xm9c0+WfPXM5g== Message-ID: Date: Tue, 8 Sep 2026 18:04:59 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 07/14] erofs: mm/pagemap: add readahead_folio_last() to avoid folio->private To: Zi Yan , "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, 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 References: <20260907-remove-pg_private-v3-0-6ae22f9d9272@nvidia.com> <20260907-remove-pg_private-v3-7-6ae22f9d9272@nvidia.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260907-remove-pg_private-v3-7-6ae22f9d9272@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 7oqam3r6et1gbsojgcr7q9795es1hdcf X-Rspam-User: X-Rspamd-Queue-Id: 9CF751C0018 X-Rspamd-Server: rspam03 X-HE-Tag: 1788883513-802672 X-HE-Meta: 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 TogObZuE 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/8/26 04:56, 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. > > Add readahead_folio_last() to achieve the same function without using > folio->private. __readahead_advance() helper shares readahead_control > adjustment code among __readahead_folio(), readahead_folio_last(), and > __readahead_batch() by checking new private member, _forward, of > readahead_control. > > 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. Ah, I was just about to ask. So it's really about folios never using folio->private manually (without the attach/detach). > > No functional 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 | 13 +++--------- > include/linux/pagemap.h | 56 ++++++++++++++++++++++++++++++++++++++++++------- > 2 files changed, 51 insertions(+), 18 deletions(-) > > diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c > index e1e25ca0d1904..78fd7d980e957 100644 > --- a/fs/erofs/zdata.c > +++ b/fs/erofs/zdata.c > @@ -1898,21 +1898,14 @@ 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); > > + /* traverse from last to first for best metadata I/O performance */ > + while ((folio = readahead_folio_last(rac))) { Intuitively, this should be called readahead_folio_reverse / readahead_folio_reversed, thinking of list_for_each_entry_reverse()? list_for_each_entry_reverse - iterate backwards over list of given type. or maybe readahead_folio_backwards (which matches the forward below) But I'm not a readahead expert :) > 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 939f3a5e973f6..2257df004305e 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -1415,6 +1415,7 @@ struct readahead_control { > bool dropbehind; > bool _workingset; > unsigned long _pflags; > + bool _forward; > }; > > #define DEFINE_READAHEAD(ractl, f, r, m, i) \ > @@ -1479,18 +1480,25 @@ void page_cache_async_readahead(struct address_space *mapping, > page_cache_async_ra(&ractl, folio, req_count); > } > > +static inline void __readahead_advance(struct readahead_control *rac) > +{ > + if (rac->_forward) > + rac->_index += rac->_batch_count; No expert, but shouldn't we decrement the _index somewhere in the other case? Or where is that done? A comment might help :) -- Cheers, David