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 27776C88E50 for ; Mon, 14 Sep 2026 13:26:49 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 299F96B008C; Mon, 14 Sep 2026 09:26:48 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 24AF56B0096; Mon, 14 Sep 2026 09:26:48 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 13A7F6B0099; Mon, 14 Sep 2026 09:26:48 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id E66B46B008C for ; Mon, 14 Sep 2026 09:26:47 -0400 (EDT) Received: from smtpin29.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 7143C140143 for ; Mon, 14 Sep 2026 13:26:47 +0000 (UTC) X-FDA: 85212442854.29.F649BED Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf06.hostedemail.com (Postfix) with ESMTP id 96F0F180015 for ; Mon, 14 Sep 2026 13:26:45 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=LVfA7IiV; spf=pass (imf06.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=1789392405; 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=YlYwFRzA7o/DVEj1e1cnP7ktHjtNeLhR3AAaGHH8Ug0=; b=Tm1mdpF8AiXlfDbnUREt/IHkIMfc47399sSaI2Z20X0icxdndxjR+aRvDwJIIFJIapjFCW XXxoBidY2t/f+rTtZNFsnb/vw/oMLWKJR0kmvTSSNL4gsAZvDg2QBHmN9DbDrpefyROlc0 EcQQO1JSs5CxFi8nIw8tfNKD+q8YidU= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789392405; b=hW5t8hQu7U6YGKMi0s4hbi6vrB7iLSc7PPDL5p7taKUFYrF5+fkjW+9pJBLz0cfXMcWllT VdHjhwtd+N83CFbemTnBEFAt0s9J8XKs6or68J48bJ6L8OZ6JZMCntgLDWESriYjWRi5AQ tIFBdoCyPZVn4+VP7N7U1pFj9dmQqIc= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=LVfA7IiV; spf=pass (imf06.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 DADA341FFD; Mon, 14 Sep 2026 13:26:44 +0000 (UTC) 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 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 X-Stat-Signature: knkn9zhn1q13j83m5agscnj1buncct1a X-Rspam-User: X-Rspamd-Queue-Id: 96F0F180015 X-Rspamd-Server: rspam03 X-HE-Tag: 1789392405-442775 X-HE-Meta: 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 yifEftKW XVXak+qYD+//eeBZgGj2w54RrT5dItetyxBm2Blqs7mVwvcFrIrFJqkEOxJF5yqAPORpC41WB2OvHL2/IIXrVqXv/Besbox2rcQegnFh18Y3lEIbfawtGll3imOcOwuN+aFXD9BG3oJrYrLqRDmYZbCS7co9vQaARAT8gMSzkMFA6dIamY5jqk+3ilJdQ4z0aHumZtAXJS1kaiMfEv00YIjXi81Dd+Yy/7cLZ0WUrwznC585/3pXwUKIAQjKxGYiIRMfv1HOi5YyydlC2okVRk/O/29Mv+HEyJvTYUG2oDubLIjdEBxcZ5MfwlCXezitJNCtkx8FoSQq8KSS8dc2n4lzZAkwhfr9erLeHCEAwHRzBcjmJSagAAohFzHryrVajprnn Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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