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Sun, 22 Sep 2024 01:00:54 +0000 Date: Sun, 22 Sep 2024 03:00:50 +0200 From: Dan Williams To: Alistair Popple , , CC: Alistair Popple , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH 02/12] pci/p2pdma: Don't initialise page refcount to one Message-ID: <66ef6c41eeb4f_10422294fb@dwillia2-mobl3.amr.corp.intel.com.notmuch> References: <4f8326d9d9e81f1cb893c2bd6f17878b138cf93d.1725941415.git-series.apopple@nvidia.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <4f8326d9d9e81f1cb893c2bd6f17878b138cf93d.1725941415.git-series.apopple@nvidia.com> X-ClientProxiedBy: MW4PR03CA0042.namprd03.prod.outlook.com (2603:10b6:303:8e::17) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|DM3PR11MB8684:EE_ X-MS-Office365-Filtering-Correlation-Id: 1a4258af-e9e9-4249-a679-08dcdaa20290 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|7416014|376014; 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This is currently > the case for MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_COHERENT pages > but not MEMORY_DEVICE_PCI_P2PDMA pages so fix that up. > > Signed-off-by: Alistair Popple > --- > drivers/pci/p2pdma.c | 6 ++++++ > mm/memremap.c | 17 +++++++++++++---- > mm/mm_init.c | 22 ++++++++++++++++++---- > 3 files changed, 37 insertions(+), 8 deletions(-) > > diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c > index 4f47a13..210b9f4 100644 > --- a/drivers/pci/p2pdma.c > +++ b/drivers/pci/p2pdma.c > @@ -129,6 +129,12 @@ static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj, > } > > /* > + * Initialise the refcount for the freshly allocated page. As we have > + * just allocated the page no one else should be using it. > + */ > + set_page_count(virt_to_page(kaddr), 1); Perhaps VM_WARN_ONCE to back up that assumption? I also notice that there are multiple virt_to_page() lookups in this routine, so maybe time for a local @page variable. > + > + /* > * vm_insert_page() can sleep, so a reference is taken to mapping > * such that rcu_read_unlock() can be done before inserting the > * pages > diff --git a/mm/memremap.c b/mm/memremap.c > index 40d4547..07bbe0e 100644 > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -488,15 +488,24 @@ void free_zone_device_folio(struct folio *folio) > folio->mapping = NULL; > folio->page.pgmap->ops->page_free(folio_page(folio, 0)); > > - if (folio->page.pgmap->type != MEMORY_DEVICE_PRIVATE && > - folio->page.pgmap->type != MEMORY_DEVICE_COHERENT) > + switch (folio->page.pgmap->type) { > + case MEMORY_DEVICE_PRIVATE: > + case MEMORY_DEVICE_COHERENT: > + put_dev_pagemap(folio->page.pgmap); > + break; > + > + case MEMORY_DEVICE_FS_DAX: > + case MEMORY_DEVICE_GENERIC: > /* > * Reset the refcount to 1 to prepare for handing out the page > * again. > */ > folio_set_count(folio, 1); > - else > - put_dev_pagemap(folio->page.pgmap); > + break; > + > + case MEMORY_DEVICE_PCI_P2PDMA: > + break; A follow on cleanup is that either all implementations should be put_dev_pagemap(), or none of them. Put the onus on the implementation to track how many pages it has handed out in the implementation allocator. > + } > } > > void zone_device_page_init(struct page *page) > diff --git a/mm/mm_init.c b/mm/mm_init.c > index 4ba5607..0489820 100644 > --- a/mm/mm_init.c > +++ b/mm/mm_init.c > @@ -1015,12 +1015,26 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn, > } > > /* > - * ZONE_DEVICE pages are released directly to the driver page allocator > - * which will set the page count to 1 when allocating the page. > + * ZONE_DEVICE pages other than MEMORY_TYPE_GENERIC and > + * MEMORY_TYPE_FS_DAX pages are released directly to the driver page > + * allocator which will set the page count to 1 when allocating the > + * page. > + * > + * MEMORY_TYPE_GENERIC and MEMORY_TYPE_FS_DAX pages automatically have > + * their refcount reset to one whenever they are freed (ie. after > + * their refcount drops to 0). I'll send some follow on patches to clean up device-dax. For this one: Reviewed-by: Dan Williams