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 2E93C3F6C55; Mon, 14 Sep 2026 13:26:44 +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=1789392406; cv=none; b=mnWL2xckVb+VASo2gm2JQ7W/SJX8JIQxHWdO1jGsVHBSCjTaV8tozglzgKYMBHUtzJRFBLE5Af77tiuHTqg9zcXPd0G+1fnrqnFjoTXv6YCPpjwuyCT6j/bGUaPnTLjC6jquAoHltyGggYURwSvAn4fQIPgTF1Qio/UdbZFWweU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789392406; c=relaxed/simple; bh=HmzjIkuVxdHGaHtRTI9i57ZzwPB6ndCm/BZ1g0ko5YQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mEx3v/nakeK3puOfiLA3kbtgaS9NpabAg/ChZ6xHPbdOPu0IrtW/TN/XjwjR39dC19GH2fW/xKWqgcJCzZcI1fwqBkHUSdzqN9jqkFgEAB1pi4Li5HiCtdTRhS1UjjMCyHbLdiyx5BkpOBo1oXTkrz4kvJadcY4DnsRnoJyfYLU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LVfA7IiV; 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="LVfA7IiV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1DD861F000FF; Mon, 14 Sep 2026 13:26:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789392404; bh=YlYwFRzA7o/DVEj1e1cnP7ktHjtNeLhR3AAaGHH8Ug0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LVfA7IiVasTAzRSrRiQszUUtDWQYqay80S/mtUAUne2QZDkIdnbFlLxSzuw89mGL2 kzFDYBDe3UKTXgb2xTp5/yrZ00NOM8y1SB3368cKIYF98nTIPL2FKjONdAtxkxUEuv 5eGR1Q1I2RYvrXYTaGWW6KJWotvtq7YNnFqeRz7jffklbi9fqKi9Uzsn5YosJfcQLt j4p23sZ8KdrtPEGIdDa6u0v/vp3uWj7kUL0H9qWQdLZKrKbU5g6b59w8EXk5VIyasd 9ibkY0UkNJyk5bb+Zf2ReOn1IQYH8x1PxVPvY0Ce5u+/9OmmwJ3w6Dmb3gQHicSR3Y E1XcXKJKkRGJg== Message-ID: <37f9a01c-4f6f-429d-b221-73ceffd55369@kernel.org> Date: Mon, 14 Sep 2026 15:26:32 +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 v4 10/16] 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: <20260913-remove-pg_private-v4-0-848550f7574e@nvidia.com> <20260913-remove-pg_private-v4-10-848550f7574e@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: <20260913-remove-pg_private-v4-10-848550f7574e@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/14/26 04:24, 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. Add a helper, > folio_has_attached_private(), for this check. > > 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. Shouldn't we just move the data_race() into folio_has_attached_private() and document there, that it can be called without the folio lock as well? Having the data_race in multiple callers looks odd. > > folio_set/clear_private() and Set/ClearPagePrivate() become no-ops. > PG_private is no longer checked at page free time. You can mention here that we will clean this part up next, to remove these helpers entirely. [...] > } > > /* One reference per page table mapping. */ > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 462e89e055485..08988877331ba 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -577,7 +577,23 @@ FOLIO_FLAG(swapbacked, FOLIO_HEAD_PAGE) > * for its own purposes. > * - PG_private and PG_private_2 cause release_folio() and co to be invoked > */ > -PAGEFLAG(Private, private, PF_ANY) > + > +static __always_inline bool folio_test_private(const struct folio *folio) > +{ > + return folio->private; > +} > + > +static __always_inline int PagePrivate(const struct page *page) > +{ > + return !!page->private; > +} > + > +/* no-ops during transition */ > +static __always_inline void folio_set_private(struct folio *folio) { } > +static __always_inline void folio_clear_private(struct folio *folio) { } > +static __always_inline void SetPagePrivate(struct page *page) { } > +static __always_inline void ClearPagePrivate(struct page *page) { } > + > FOLIO_FLAG(private_2, FOLIO_HEAD_PAGE) > > /* owner_2 can be set on tail pages for anon memory */ > @@ -1169,7 +1185,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page) > */ > #define PAGE_FLAGS_CHECK_AT_FREE \ > (1UL << PG_lru | 1UL << PG_locked | \ > - 1UL << PG_private | 1UL << PG_private_2 | \ > + 1UL << PG_private_2 | \ > 1UL << PG_writeback | 1UL << PG_reserved | \ > 1UL << PG_active | \ > 1UL << PG_unevictable | __PG_MLOCKED | LRU_GEN_MASK) > @@ -1193,8 +1209,28 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page) > (0xffUL /* order */ | 1UL << PG_has_hwpoisoned | \ > 1UL << PG_large_rmappable | 1UL << PG_partially_mapped) > > -#define PAGE_FLAGS_PRIVATE \ > - (1UL << PG_private | 1UL << PG_private_2) > +/** > + * folio_has_attached_private - check if the folio has private data attached > + * @folio: The folio to check. > + * > + * Use this in code that may encounter swapcache or hugetlb folios but only > + * wants to detect attached private data. Swapcache stores swp_entry_t in > + * folio->swap, a union with folio->private, and hugetlb stores its own flags > + * in folio->private; both are excluded. This is an implementation detail that is irrelevant for callers. Move that above the actual checks in the code below. > + * > + * NOTE: For swapcache, folio->swap.val PG_swapcache are not set as a whole, > + * so folio_test_swapcache() is not reliable to exclude swapcache. > + * Use folio_test_swapbacked() instead, since it remains set when a folio is > + * added to/removed from swapcache. Dito, a caller of this function doesn't care. > + * > + * Return: true if folio->private is set and the folio is neither swapcache > + * nor hugetlb. Can we remove these implementation details here instead and talk about "true if the folio has private data attached" ? > + */ > +static inline bool folio_has_attached_private(const struct folio *folio) > +{ > + return folio_test_private(folio) && !folio_test_swapbacked(folio) && > + !folio_test_hugetlb(folio); > +} Apart from that LGTM. -- Cheers, David