From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 C795E577E39; Wed, 9 Sep 2026 14:10:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788963020; cv=none; b=LVBhg/R38Slzflao+mQkSk6gDq931+6wfgxMq05HVGmSHxM/nBsw8CYxCG2TSWyhbrw0joGCrhw5W6SK1Ywu0lNgAIPCQJczsywFwIKwHx+gNDUpc+28CSKEXx5Thy5mkwKNgczlLOWy3dJqwvP5GGw39KIdOVfrwrNaJc9Ml3c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788963020; c=relaxed/simple; bh=0x/6GcnpfRPjncZsYn7x803r/RT3vtWvc1b3ROhMRhU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZEFk+IEfiJiK1wH+Ns/GVI3XoSjJTjJCeCxjeEZEpU3F7U6NtVfejsRXqxGWR/WDUsU14eIB6PSKTn1E25Bb6tx0rowH27OYexDtQtZpFs3VjjQUK9ARjqunxutVijpedQUMSpyAWaSAis2FHuCo6aaYUr6ZWwILfS9kkJlk4r0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nBABSYKc; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nBABSYKc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65B391F00A3A; Wed, 9 Sep 2026 14:10:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788963018; bh=pOXZ86V7gEk1w7Bapk1GcuFyX4Hl3hOcDoOjdyQuqEY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=nBABSYKchY7wcnJtyWy+cEItvh9ka1L52TnNXwFAU4EET/ki8hhcXOhw+Pd8Wt3YY mNiN5x0pVLb+FQon788ytN5uc1wRvO0WO9aiypMyHCm/osQKYAe0lqcKij3KdPog62 duGllUAgxZloduF66dypFkpugBAimsXFAqzRVoHobcM8q69o0S9gyk4PKB6GWudvch x/migNK60lqqxslKNKOHXLOfooWB9OWgVRzjuvg8NB1JtyWhGl/4v+31Pl7ytIh9CG yD7Lm4Dfon72msbCyIxhMgJnCyYiCbyqeaT4mTsMJYIpxw3QBQy7UuLJ9VfjHSsfIB uPFy+2LGFiZoQ== Message-ID: <30e544c3-eada-4f08-8971-aa07d6b38ffb@kernel.org> Date: Wed, 9 Sep 2026 16:10:06 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/8/26 19:05, Zi Yan wrote: > On Tue Sep 8, 2026 at 12:04 PM EDT, David Hildenbrand (Arm) wrote: >> 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 :) > > Jan suggested the name[1]. It can be readahead_folio_reverse() if you > prefer it, like Jan said. > > [1] https://lore.kernel.org/all/332rknj4vo3cfhvfhhlf6pvg37s3lbrnzbbnv4swa6gctsiu6a@ndotgokvnglc/ Heh, to me _reverse() is clearer; whatever people prefer. Acked-by: David Hildenbrand (Arm) -- Cheers, David