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 830FD58F09F; Tue, 8 Sep 2026 16:56:54 +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=1788886616; cv=none; b=rMhrl1gmwTWbqB1QF+DtJcDH+nA12jyNlQrpNSg86Lhs9H+ojf3+0vgdG+zNEn7naE3CMYlJkxQUBk61YeCpnKp+3zaAgzjNUs0mWSsQ1PTH3arCoQzgirtC0D5uqGmgc9oG3EXiXy9mNIjvKli1Zl+Pkf0qzkTc5icRmFrQg1w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788886616; c=relaxed/simple; bh=kqxeMi4ArDzzKPZSPAYbFi0k/RQwHKztgs/wUmPdSsE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SiaKVIa1/W6fzgRHOfoPDtW5zPa2ZPL5HyZloauoJ03ccxGSsz//W3BOl5RXUj3Gek7MSQjuksjQQ8EkDcL4m98RXGw2xGsvp8n/4QHY273mfbaZgUn0ZoeYUtQxKOXJ5kyRaEbDfkZ0my1HwDFITLB+qureHR3iM/UBJtyM+xY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oaCiuBJH; 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="oaCiuBJH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5E39A1F00A3D; Tue, 8 Sep 2026 16:56:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788886614; bh=7HFhd4KDSfD7wKAluuKwUfaCYQwrDIt/d+mkB/YfLSk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=oaCiuBJHcKgdnJXHuF42Gzn0lhaqMVP/UkFfIBAUqBxb807yLavtvcGoPz6cRuN6G Gz9iTzi01MNzkULWuYzsM222rtvW8VlUZsqcufeVph6urpPk1fq7jq+DD1dw4nk/7o z5o9hGwvA0pLqg0VTxIpay5TpKTE2KrpHOap8FxcJCTa/boF8eOrk3WXzh2hSkhBvd mwvUhIhsgTgjsSXbJWaZcRSbTgrCrB/nPCczcKQokivuwdrYgXoEJj6JidRCMzOuNE C0XjaiTLaVLDiOD6roe2m8oNg3/4w7dtuyMQ2SjWxQoBAZRvpcNzsLJOKeXMuzgb3U N+I5lEnfyJ+xQ== Message-ID: <9395aac2-af01-42cf-92ea-4e3d5e7eec6d@kernel.org> Date: Tue, 8 Sep 2026 18:56:39 +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 09/14] mm/page-flags: check page/folio->private instead of PG_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, Steven Rostedt , Masami Hiramatsu , Jan Kara , Mathieu Desnoyers , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Axel Rasmussen , Yuanchu Xie , Wei Xu , linux-fsdevel@vger.kernel.org, linux-trace-kernel@vger.kernel.org References: <20260907-remove-pg_private-v3-0-6ae22f9d9272@nvidia.com> <20260907-remove-pg_private-v3-9-6ae22f9d9272@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-v3-9-6ae22f9d9272@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/8/26 04:56, Zi Yan wrote: > After the changes of the prior commits, page/folio->private != NULL is now > equivalent to checking PG_private. > > Stop checking PG_private on pages and folios and use page/folio->private > instead, except swapcache and hugetlb folios, because the former uses a > field (swp_entry_t swap) overlapping with ->private and the latter sets its > flags in ->private. Exclude swapcache and hugetlb when the code is meant to > check PG_private only. PG_swapcache and folio->swap.val cannot be set/clear > as a whole, so excluding swapcache with folio_test_swapcache() is not > reliable. Instead, use folio_test_swapbacked(), since PG_swapbacked is > stable when a folio is added to/removed from swapcache. > > folio_expected_ref_count() can be called without folio lock, so annotate > folio_test_private() with data_race() to avoid triggering race condition > checks. While at it, annotate folio->mapping too. Add data_race() > annotation for other lockless callers too. > > folio_set/clear_private() and Set/ClearPagePrivate() become no-ops. > PG_private is no longer checked at page free time. > > Remove KPF_PRIVATE since PG_private is no longer used. > > Assisted-by: Claude:claude-opus-4-8 > Assisted-by: Codex:gpt-5 > Signed-off-by: Zi Yan > To: Andrew Morton > To: David Hildenbrand > To: Steven Rostedt > To: Masami Hiramatsu > To: Lorenzo Stoakes > To: "Matthew Wilcox (Oracle)" > To: Jan Kara > To: Johannes Weiner > Cc: "Liam R. Howlett" > Cc: Vlastimil Babka > Cc: Mike Rapoport > Cc: Suren Baghdasaryan > Cc: Michal Hocko > Cc: Mathieu Desnoyers > Cc: Zi Yan > Cc: Baolin Wang > Cc: Nico Pache > Cc: Ryan Roberts > Cc: Dev Jain > Cc: Barry Song > Cc: Lance Yang > Cc: Usama Arif > Cc: Matthew Brost > Cc: Joshua Hahn > Cc: Rakie Kim > Cc: Byungchul Park > Cc: Gregory Price > Cc: Ying Huang > Cc: Alistair Popple > Cc: Qi Zheng > Cc: Shakeel Butt > Cc: Kairui Song > Cc: Axel Rasmussen > Cc: Yuanchu Xie > Cc: Wei Xu > Cc: linux-kernel@vger.kernel.org > Cc: linux-fsdevel@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: linux-trace-kernel@vger.kernel.org > --- [...] > /* !PageAnon && !swapper_space */ > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 40d3f1b48a74c..9348ebf9de882 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -978,7 +978,8 @@ static void folio_check_dirty_writeback(struct folio *folio, > *writeback = folio_test_writeback(folio); > > /* Verify dirty/writeback state if the filesystem supports it */ > - if (!folio_test_private(folio)) > + if (!(folio_test_private(folio) && !folio_test_swapbacked(folio) && > + !folio_test_hugetlb(folio))) Now that I read that check ... a fourth time? a fifth? I stopped counting :) Should we have a (in light of folio_attach_private()): static inline bool folio_has_attached_private(const struct folio *folio) { /* Careful, we might get called on unlocked folios. */ if (!data_race(folio->private)) return false; /* On some folios ->private is used for different purposes. */ return !folio_test_swapbacked(folio) && !folio_test_hugetlb(folio); } Of course, adding some nice documentation what having attached private means? -- Cheers, David