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Wong" , Trond Myklebust , Anna Schumaker , Jan Kara , David Hildenbrand , Logan Gunthorpe , , , , , , LKML , John Hubbard Subject: [PATCH v2 2/7] mm/gup: introduce pin_user_page() Date: Tue, 30 Aug 2022 21:18:38 -0700 Message-ID: <20220831041843.973026-3-jhubbard@nvidia.com> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220831041843.973026-1-jhubbard@nvidia.com> References: <20220831041843.973026-1-jhubbard@nvidia.com> MIME-Version: 1.0 X-NVConfidentiality: public X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 33d05557-4ac9-4362-9877-08da8b07ea09 X-MS-TrafficTypeDiagnostic: PH0PR12MB5402:EE_ 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:12.22.5.236;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:InfoNoRecords;CAT:NONE;SFS:(13230016)(4636009)(39860400002)(376002)(396003)(136003)(346002)(46966006)(36840700001)(40470700004)(70206006)(86362001)(82310400005)(6666004)(478600001)(107886003)(41300700001)(81166007)(26005)(336012)(82740400003)(40460700003)(40480700001)(186003)(356005)(83380400001)(47076005)(1076003)(426003)(5660300002)(2616005)(36860700001)(4326008)(8936002)(7416002)(8676002)(54906003)(2906002)(316002)(6916009)(36756003)(70586007)(36900700001);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 31 Aug 2022 04:18:53.2625 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 33d05557-4ac9-4362-9877-08da8b07ea09 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[12.22.5.236];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT082.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR12MB5402 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@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 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 | 50 ++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 51 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index 61c5dc37370e..c6c98d9c38ba 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1876,6 +1876,7 @@ 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 5abdaf487460..2c231dca39dd 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -3213,6 +3213,56 @@ 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 file-backed page that the + * caller already owns. + * + * @page: the page to be pinned. + * + * pin_user_page() elevates a page's refcount using FOLL_PIN rules. This means + * that the caller must release the page via unpin_user_page(). + * + * pin_user_page() is intended as a drop-in replacement for get_page(). This + * provides a way for callers to do a subsequent unpin_user_page() on the + * affected page. However, it is only intended for use by callers (file systems, + * block/bio) that have a file-backed page. Anonymous pages are not expected nor + * supported, and will generate a warning. + * + * pin_user_page() may also be thought of as 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(). + * + * IMPORTANT: 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); + + /* + * This function is only intended for file-backed callers, who already + * have a page reference. + */ + WARN_ON_ONCE(PageAnon(page)); + + /* + * 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