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Tsirkin" , Jason Wang , Xuan Zhuo , =?utf-8?q?Eugenio_P=C3=A9rez?= , Alexander Viro , Christian Brauner , Jan Kara , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Matthew Wilcox (Oracle)" , Minchan Kim , Sergey Senozhatsky , Brendan Jackman , Johannes Weiner , Jason Gunthorpe , John Hubbard , Peter Xu , Xu Xin , Chengming Zhou , Miaohe Lin , Naoya Horiguchi , Oscar Salvador , Rik van Riel , Harry Yoo , Qi Zheng , Shakeel Butt Subject: Re: [PATCH RFC 04/29] mm/page_alloc: allow for making page types sticky until freed Date: Mon, 23 Jun 2025 11:28:38 -0400 X-Mailer: MailMate (2.0r6265) Message-ID: <9FD54B0C-FCC1-4657-8EBD-7EA81D8D2BC6@nvidia.com> In-Reply-To: <18ef9192-168f-4d07-a29a-952f2ce3a4f0@redhat.com> References: <20250618174014.1168640-1-david@redhat.com> <20250618174014.1168640-5-david@redhat.com> <18ef9192-168f-4d07-a29a-952f2ce3a4f0@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: BN8PR04CA0048.namprd04.prod.outlook.com (2603:10b6:408:d4::22) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB9473:EE_|IA0PPF64A94D5DF:EE_ X-MS-Office365-Filtering-Correlation-Id: cf7d0373-8ca0-4bce-6fb3-08ddb26aa2c5 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014|7053199007; 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>>>> page->mapping = NULL; >>>> } >>>> + if (unlikely(page_has_type(page))) >>>> + page->page_type = UINT_MAX; >>>> + >>>> if (is_check_pages_enabled()) { >>>> if (free_page_is_bad(page)) >>>> bad++; >>>> -- >>>> 2.49.0 >>> >>> How does this preserve page type? Isn’t page->page_type = UINT_MAX clearing >>> page_type? >> >> OK, next patch explains it. free_pages_prepare() clears page_type, >> so that caller does not need to. >> >> I think the message is better to be >> >> mm/page_alloc: clear page_type at page free time >> >> page_type is no longer needed to be cleared before a page is freed, as >> page free code does that. >> >> With this change, we can reliably identify typed folios even though >> they might be in the process of getting freed, which will come in handy >> in migration code (at least in the transition phase). > > > I'll change it to > > mm/page_alloc: let page freeing clear any set page type > Currently, any user of page types must clear that type before freeing > a page back to the buddy, otherwise we'll run into mapcount related > sanity checks (because the page type currently overlays the page > mapcount). > Let's allow for not clearing the page type by page type users by letting > the buddy handle it instead. > We'll focus on having a page type set on the first page of a larger > allocation only. > With this change, we can reliably identify typed folios even though > they might be in the process of getting freed, which will come in handy > in migration code (at least in the transition phase). Thanks. Reviewed-by: Zi Yan -- Best Regards, Yan, Zi