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Wong" , Theodore Ts'o , Alexander Viro , Miklos Szeredi , Andrew Morton , Chaitanya Kulkarni CC: , , , , LKML , John Hubbard Subject: [RFC PATCH 1/7] mm/gup: introduce pin_user_page() Date: Fri, 25 Feb 2022 00:50:19 -0800 Message-ID: <20220225085025.3052894-2-jhubbard@nvidia.com> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220225085025.3052894-1-jhubbard@nvidia.com> References: <20220225085025.3052894-1-jhubbard@nvidia.com> MIME-Version: 1.0 X-NVConfidentiality: public X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 0c8acfe7-76ca-4054-9073-08d9f83be34a X-MS-TrafficTypeDiagnostic: BL1PR12MB5094:EE_ X-Microsoft-Antispam-PRVS: X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:12.22.5.235;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:mail.nvidia.com;PTR:InfoNoRecords;CAT:NONE;SFS:(13230001)(4636009)(46966006)(40470700004)(36840700001)(36756003)(8936002)(7416002)(356005)(921005)(81166007)(5660300002)(508600001)(86362001)(40460700003)(8676002)(70206006)(70586007)(47076005)(107886003)(1076003)(6636002)(2616005)(316002)(336012)(426003)(186003)(26005)(2906002)(6666004)(83380400001)(36860700001)(4326008)(82310400004)(54906003)(110136005)(36900700001);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Feb 2022 08:50:34.7990 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 0c8acfe7-76ca-4054-9073-08d9f83be34a X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[12.22.5.235];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT030.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5094 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org pin_user_page() is an externally-usable version of try_grab_page(), but with semantics that match get_page(), so that it can act as a drop-in replacement for get_page(). Specifically, pin_user_page() has a void return type. pin_user_page() elevates a page's refcount is using FOLL_PIN rules. This means that the caller must release the page via unpin_user_page(). Signed-off-by: John Hubbard --- include/linux/mm.h | 1 + mm/gup.c | 34 ++++++++++++++++++++++++++++++++++ 2 files changed, 35 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index 929488a47181..bb51f5487aef 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1914,6 +1914,7 @@ long pin_user_pages_remote(struct mm_struct *mm, long get_user_pages(unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas); +void pin_user_page(struct page *page); long pin_user_pages(unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas); diff --git a/mm/gup.c b/mm/gup.c index 5c3f6ede17eb..44446241c3a9 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -3034,6 +3034,40 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages, } EXPORT_SYMBOL(pin_user_pages); +/** + * pin_user_page() - apply a FOLL_PIN reference to a page () + * + * @page: the page to be pinned. + * + * Similar to get_user_pages(), in that the page's refcount is elevated using + * FOLL_PIN rules. + * + * IMPORTANT: That means that the caller must release the page via + * unpin_user_page(). + * + */ +void pin_user_page(struct page *page) +{ + struct folio *folio = page_folio(page); + + WARN_ON_ONCE(folio_ref_count(folio) <= 0); + + /* + * Similar to try_grab_page(): be sure to *also* + * increment the normal page refcount field at least once, + * so that the page really is pinned. + */ + if (folio_test_large(folio)) { + folio_ref_add(folio, 1); + atomic_add(1, folio_pincount_ptr(folio)); + } else { + folio_ref_add(folio, GUP_PIN_COUNTING_BIAS); + } + + node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, 1); +} +EXPORT_SYMBOL(pin_user_page); + /* * pin_user_pages_unlocked() is the FOLL_PIN variant of * get_user_pages_unlocked(). Behavior is the same, except that this one sets