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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" From: "Zi Yan" Subject: Re: [PATCH v4 05/16] mm/hugetlb: use direct assignment instead of folio_change_private() Cc: , , "Oscar Salvador" X-Mailer: aerc 0.22.0 References: <20260913-remove-pg_private-v4-0-848550f7574e@nvidia.com> <20260913-remove-pg_private-v4-5-848550f7574e@nvidia.com> In-Reply-To: X-ClientProxiedBy: YQZPR01CA0168.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:8c::27) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|CH2PR12MB4261:EE_ X-MS-Office365-Filtering-Correlation-Id: d429d0f7-c941-4016-58a1-08df1525ffea X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|366016|1800799024|23010399003|10067099003|56012099006|4143699003|11063799006|22082099003|18002099003|921020; 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Change it to direct assignment to a= void >>> semantic confusion. >>> >>> It prepares for a future commit that remove PG_private. >>> >>> No functional change intended. >>> >>> Assisted-by: LLM >>> To: Muchun Song >>> To: Oscar Salvador >>> To: Andrew Morton >>> Cc: David Hildenbrand >>> Cc: linux-mm@kvack.org >>> Cc: linux-kernel@vger.kernel.org >>> Acked-by: Usama Arif >>> Reviewed-by: Gregory Price (Meta) >>> Signed-off-by: Zi Yan >>> --- >>> mm/hugetlb.c | 7 ++----- >>> 1 file changed, 2 insertions(+), 5 deletions(-) >>> >>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>> index d3a0650ff6905..8d551cdaef9db 100644 >>> --- a/mm/hugetlb.c >>> +++ b/mm/hugetlb.c >>> @@ -1446,11 +1446,8 @@ void add_hugetlb_folio(struct hstate *h, struct = folio *folio, >>> } >>> >>> __folio_set_hugetlb(folio); >>> - folio_change_private(folio, NULL); >>> - /* >>> - * We have to set hugetlb_vmemmap_optimized again as above >>> - * folio_change_private(folio, NULL) cleared it. >>> - */ >>> + /* Clear all folio->private flags except hugetlb_vmemmap_optimized. *= / >>> + folio->private =3D NULL; >>> folio_set_hugetlb_vmemmap_optimized(folio); >>> >>=20 >> Sashiko[1] said when a CMA hugetlb folio is freed but fails vmemmap rest= ore, >> add_hugetlb_folio() clears HPG_cma. It either bypasses >> hugetlb_cma_free_frozen_folio() due to the missing HPG_cma flag, or >> skips cma_release() and causes a CMA memory leak if it is free directly >> to buddy allocator. Sashiko also asked if HPG_temporary should be preser= ved >> as well HPG_cma. >>=20 >> Answer: >>=20 >> Missing HPG_cma is a real issue. It can be fixed by checking >> folio_test_hugetlb_cma(folio) at the beginning of add_hugetlb_folio() an= d >> setting HPG_cma after folio->private is assigned to NULL. > > > Maybe we should just simply only clear flags we actually want to clear ..= . And it turns out to be a clean result (see below). add_hugetlb_folio() adds a hugetlb folio back to freelist, so prior operations like remove_hugetlb_folio() should clear hugetlb flags, like HPG_freed, HPG_restore_reserve, HPG_migratible. HPG_temporary is only set in one callsite in free_huge_folio() and is cleared before the folio is passed to add_hugetlb_folio() via update_and_free_hugetlb_folio(). HPG_raw_hwp_unreliable probably can stay, since it preserves poison information. The remaining HPG_cma and HPG_vmemmap_optimized are the two we want to preserve. Muchun, maybe you can chime in about the patch below. It can be a follow-up patch after this series. Thanks. diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 8d551cdaef9db..bc772954e5685 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1446,9 +1446,6 @@ void add_hugetlb_folio(struct hstate *h, struct folio= *folio, } =20 __folio_set_hugetlb(folio); - /* Clear all folio->private flags except hugetlb_vmemmap_optimized. */ - folio->private =3D NULL; - folio_set_hugetlb_vmemmap_optimized(folio); =20 arch_clear_hugetlb_flags(folio); enqueue_hugetlb_folio(h, folio); @@ -1736,6 +1733,7 @@ void free_huge_folio(struct folio *folio) h->resv_huge_pages++; =20 if (folio_test_hugetlb_temporary(folio)) { + folio_clear_hugetlb_temporary(folio); remove_hugetlb_folio(h, folio, false); spin_unlock_irqrestore(&hugetlb_lock, flags); update_and_free_hugetlb_folio(h, folio, true); --=20 Best Regards, Yan, Zi