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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Miaohe Lin , Naoya Horiguchi , Wei Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/4] mm/huge_memory: replace can_split_folio() with direct refcount calculation Date: Tue, 25 Nov 2025 10:41:53 -0500 X-Mailer: MailMate (2.0r6290) Message-ID: In-Reply-To: <5421c8d0-1151-48dc-8774-fd2e983735a5@kernel.org> References: <20251122025529.1562592-1-ziy@nvidia.com> <20251122025529.1562592-3-ziy@nvidia.com> <51675d77-9453-43cc-bfda-f21a2edfeace@nvidia.com> <5421c8d0-1151-48dc-8774-fd2e983735a5@kernel.org> Content-Type: text/plain Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: MN2PR15CA0025.namprd15.prod.outlook.com (2603:10b6:208:1b4::38) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB9473:EE_|CY3PR12MB9577:EE_ X-MS-Office365-Filtering-Correlation-Id: aaa8431b-b39d-4196-3329-08de2c39299b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016|7053199007; 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Open code it with >>> folio_expected_ref_count() !=3D folio_ref_count() - 1. For the extra_= pins >>> used by folio_ref_freeze(), add folio_cache_references() to calculate= it. >>> >>> Suggested-by: David Hildenbrand (Red Hat) >>> Signed-off-by: Zi Yan >>> --- >>> include/linux/huge_mm.h | 1 - >>> mm/huge_memory.c | 43 ++++++++++++++++----------------------= --- >>> mm/vmscan.c | 3 ++- >>> 3 files changed, 19 insertions(+), 28 deletions(-) >>> >>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >>> index 97686fb46e30..1ecaeccf39c9 100644 >>> --- a/include/linux/huge_mm.h >>> +++ b/include/linux/huge_mm.h >>> @@ -369,7 +369,6 @@ enum split_type { >>> SPLIT_TYPE_NON_UNIFORM, >>> }; >>> -bool can_split_folio(struct folio *folio, int caller_pins, int *pex= tra_pins); >>> int __split_huge_page_to_list_to_order(struct page *page, struct li= st_head *list, >>> unsigned int new_order); >>> int folio_split_unmapped(struct folio *folio, unsigned int new_orde= r); >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index c1f1055165dd..6c821c1c0ac3 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -3455,23 +3455,6 @@ static void lru_add_split_folio(struct folio *= folio, struct folio *new_folio, >>> } >>> } >>> -/* Racy check whether the huge page can be split */ >>> -bool can_split_folio(struct folio *folio, int caller_pins, int *pext= ra_pins) >>> -{ >>> - int extra_pins; >>> - >>> - /* Additional pins from page cache */ >>> - if (folio_test_anon(folio)) >>> - extra_pins =3D folio_test_swapcache(folio) ? >>> - folio_nr_pages(folio) : 0; >>> - else >>> - extra_pins =3D folio_nr_pages(folio); >>> - if (pextra_pins) >>> - *pextra_pins =3D extra_pins; >>> - return folio_mapcount(folio) =3D=3D folio_ref_count(folio) - extra_= pins - >>> - caller_pins; >>> -} >>> - >>> static bool page_range_has_hwpoisoned(struct page *page, long nr_pa= ges) >>> { >>> for (; nr_pages; page++, nr_pages--) >>> @@ -3776,17 +3759,26 @@ int folio_check_splittable(struct folio *foli= o, unsigned int new_order, >>> return 0; >>> } >>> +/* Number of folio references from the pagecache or the swapcache. = */ >>> +static unsigned int folio_cache_references(const struct folio *folio= ) >> >> folio_cache_ref_count? > > Yes, makes sense. > >> >>> +{ >>> + if (folio_test_anon(folio) && !folio_test_swapcache(folio)) >>> + return 0; >>> + return folio_nr_pages(folio); >>> +} >>> +> >> Does this belong to include/linux/mm.h with the other helpers? > > Not for now I think, in particular, as we require earlier !folio->mappi= ng checks to give a correct answer. Most people should be using folio_exp= ected_ref_count(). > Got it. Will use folio_cache_ref_count() in the next version. Best Regards, Yan, Zi