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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alistair Popple Subject: Re: [PATCH v3 1/7] mm: Add folio_split_unref helper Date: Fri, 09 Jan 2026 09:30:13 -0500 X-Mailer: MailMate (2.0r6290) Message-ID: In-Reply-To: <1319a24a-bcfc-47e5-a022-f5d00994acc9@kernel.org> References: <20260109085605.443316-1-francois.dugast@intel.com> <20260109085605.443316-2-francois.dugast@intel.com> <59fb1669-2908-4cab-b3c0-b97479da3fb9@kernel.org> <1319a24a-bcfc-47e5-a022-f5d00994acc9@kernel.org> Content-Type: text/plain Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: SJ0PR03CA0334.namprd03.prod.outlook.com (2603:10b6:a03:39c::9) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB9473:EE_|DS7PR12MB5838:EE_ X-MS-Office365-Filtering-Correlation-Id: 1ee3aaa2-a61a-4e19-489b-08de4f8b9de6 X-MS-Exchange-SenderADCheck: 1 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 bVbc2JUR eaRGN4+VhuQJvZF558s9edKYHjd9Vivza3oLjkBnVNdEhm3B2cFQJ13AYY0lJpt0vVwQrCGTd4ft4U1xNkq4PiORGudXtBkfjcMAQiVlSJUsybrEKb3N/AW3IgXWa5k0ak33l0x3v4hdl11TQpmL1FeSm43lw/aFrGQ99FrAT0B3xWkY7t/8Nh4iFY/oXlt1TzyJ6gECyZUK8fjsFG0frqt0Wr9bKoYcSPuhZRM/5uGzLEZaayjq8XIRDWQ3TV4AhPPbHKCOvn56lWG8q4u7CgFtaBF5fuhN1O2InFMKlcC92kIWod3sZ+Tzx8cK/FnakMFKZ+1Q/YvMQ8ULyRf7XYSxRJi/c0sFXFsXNyHIh9xJTNu5hiTg+7Bq/yOFEfSwcMQvJtgSLxxDWbO73Y2CR/tilIP5VtpWgzOaz/7sQfiP6MC5tdG6c/tCdfg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9 Jan 2026, at 8:26, David Hildenbrand (Red Hat) wrote: > On 1/9/26 14:19, David Hildenbrand (Red Hat) wrote: >> On 1/9/26 09:54, Francois Dugast wrote: >>> From: Matthew Brost >>> >>> Add folio_split_unref helper which splits an unreferenced folio >> >> split_unref reads like "split and unref". >> >> You probably want to call this something like "folio_split_frozen" ? >> >> The very definition of "frozen" is "refcount =3D 0 ", so you can simpl= ify >> the documentation. >> >> Are the folios you want to pass in there completely unused (-> free) o= r >> might they still be in use (e.g., migration entries point at them duri= ng >> folio split) >> >> So I am not sure yet if this should be "folio_split_frozen()" or >> "folio_split_freed()" or sth like that. >> >> I'm not CCed on the other patches in the series or the cover letter, s= o >> I don't see the context. >> > > Ah, I was CCed on #3 where we call this function on folios that are get= ting freed. > > In that case it would be acceptable to initialize folio->mapping (and f= olio->index?) of the split folios. Do we also have to initialize folio->f= lags, folio->private etc? > > See __split_huge_page_tail(). > > folio_split_freed() would likely be best, because then it is clearer th= at there is absolutely no state to copy from the large folio. Yes, basically, we do not have a reverse function of prep_compound_page()= and open codes the reverse process in free_pages_prepare(). For zone devices,= zone_device_page_init() calls prep_compound_page() to form a folio but free_zone_device_folio() never does the reverse. FS DAX has its own dax_folio_put() to do it. Alistair suggested to come up with a helper function for both FS DAX and free_zone_device_folio(). Maybe free_zone_device_folio_prepare() is better. And put it in mm/memrem= ap.c. > >> You should describe in this patch here in which context the function i= s >> supposed to be used in later commits. > > -- = > Cheers > > David Best Regards, Yan, Zi