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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id u5sm1592838qtg.57.2020.11.06.16.14.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Nov 2020 16:14:57 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kbBsf-0015Rr-2V; Fri, 06 Nov 2020 20:14:57 -0400 Date: Fri, 6 Nov 2020 20:14:57 -0400 From: Jason Gunthorpe To: Logan Gunthorpe Cc: linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, iommu@lists.linux-foundation.org, Stephen Bates , Christoph Hellwig , Dan Williams , Christian =?utf-8?B?S8O2bmln?= , Ira Weiny , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter Subject: Re: [RFC PATCH 14/15] PCI/P2PDMA: Introduce pci_mmap_p2pmem() Message-ID: <20201107001457.GB244516@ziepe.ca> References: <20201106172206.GS36674@ziepe.ca> <20201106174223.GU36674@ziepe.ca> <2c2d2815-165e-2ef9-60d6-3ace7ff3aaa5@deltatee.com> <20201106180922.GV36674@ziepe.ca> <09885400-36f8-bc1d-27f0-a8adcf6104d4@deltatee.com> <20201106193024.GW36674@ziepe.ca> <03032637-0826-da76-aec2-121902b1c166@deltatee.com> <20201106195341.GA244516@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 06, 2020 at 01:03:26PM -0700, Logan Gunthorpe wrote: > I don't think a function like that will work for the p2pmem use case. In > order to implement proper page freeing I expect I'll need a loop around > the allocator and vm_insert_mixed()... Something roughly like: > > for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) { > vaddr = pci_alloc_p2pmem(pdev, PAGE_SIZE); > ret = vmf_insert_mixed(vma, addr, > __pfn_to_pfn_t(virt_to_pfn(vaddr), PFN_DEV | PFN_MAP)); > } > > That way we can call pci_free_p2pmem() when a page's ref count goes to > zero. I suspect your use case will need to do something similar. Yes, but I would say the pci_alloc_p2pmem() layer should be able to free pages on a page-by-page basis so you don't have to do stuff like the above. There is often a lot of value in having physical contiguous addresses, so allocating page by page as well seems poor. Jason