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emacs 29.1 From: Alistair Popple To: Christoph Hellwig Cc: dan.j.williams@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, logang@deltatee.com, bhelgaas@google.com, jack@suse.cz, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, mpe@ellerman.id.au, npiggin@gmail.com, dave.hansen@linux.intel.com, ira.weiny@intel.com, willy@infradead.org, djwong@kernel.org, tytso@mit.edu, linmiaohe@huawei.com, david@redhat.com, peterx@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, david@fromorbit.com Subject: Re: [PATCH 10/13] fs/dax: Properly refcount fs dax pages Date: Fri, 06 Sep 2024 16:00:38 +1000 In-reply-to: <20240627054455.GF14837@lst.de> Message-ID: <87wmjpb9g6.fsf@nvdebian.thelocal> Content-Type: text/plain X-ClientProxiedBy: SY5PR01CA0085.ausprd01.prod.outlook.com (2603:10c6:10:1f5::12) To DS0PR12MB7726.namprd12.prod.outlook.com (2603:10b6:8:130::6) 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: DS0PR12MB7726:EE_|SA0PR12MB4495:EE_ X-MS-Office365-Filtering-Correlation-Id: d081438c-657d-4fc3-63dd-08dcce3a5e92 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016; 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>> } >> >> - pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP); >> + pfn = phys_to_pfn_t(phys, 0); >> >> dax_set_mapping(vmf, pfn, fault_size); >> >> - return vmf_insert_mixed(vmf->vma, vmf->address, pfn); >> + return dax_insert_pfn(vmf->vma, vmf->address, pfn, vmf->flags & FAULT_FLAG_WRITE); > > Plenty overly long lines here and later. > > Q: hould dax_insert_pfn take a vm_fault structure instead of the vma? > Or are the potential use cases that aren't from the fault path? Nope, good idea. I will update it to take a vm_fault struct for the next version. > similar instead of the bool write passing the fault flags might actually > make things more readable than the bool. > > Also at least currently it seems like there are no modular users despite > the export, or am I missing something? It gets used in drivers/dax/device.c which I think is built into device_dax.ko: obj-$(CONFIG_DEV_DAX) += device_dax.o ... device_dax-y := device.o >> { >> + /* >> + * Make sure we flush any cached data to the page now that it's free. >> + */ >> + if (PageDirty(page)) >> + dax_flush(NULL, page_address(page), page_size(page)); >> + > > Adding the magic dax_dev == NULL case to dax_flush and going through it > vs just calling arch_wb_cache_pmem directly here seems odd. > > But I also don't quite understand how it is related to the rest > of the patch anyway. Yeah, that should be unnecessary as it gets called elsewhere as needed so will remove it. >> if (!pmd_present(*pmd)) >> goto out; >> diff --git a/mm/mm_init.c b/mm/mm_init.c >> index b7e1599..f11ee0d 100644 >> --- a/mm/mm_init.c >> +++ b/mm/mm_init.c >> @@ -1016,7 +1016,8 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn, >> */ >> if (pgmap->type == MEMORY_DEVICE_PRIVATE || >> pgmap->type == MEMORY_DEVICE_COHERENT || >> - pgmap->type == MEMORY_DEVICE_PCI_P2PDMA) >> + pgmap->type == MEMORY_DEVICE_PCI_P2PDMA || >> + pgmap->type == MEMORY_DEVICE_FS_DAX) >> set_page_count(page, 0); >> } > > So we'll skip this for MEMORY_DEVICE_GENERIC only. Does anyone remember > if that's actively harmful or just not needed? If the latter it might > be simpler to just set the page count unconditionally here. Yeah I'm not sure but the switch statement you suggested at least makes this much clearer. Once I get this series finished I can chase down the MEMORY_DEVICE_GENERIC differences. I suspect we can just do it unconditionally.