Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758858AbdDSBXF (ORCPT ); Tue, 18 Apr 2017 21:23:05 -0400 Received: from gate.crashing.org ([63.228.1.57]:43298 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755254AbdDSBXD (ORCPT ); Tue, 18 Apr 2017 21:23:03 -0400 Message-ID: <1492564910.25766.125.camel@kernel.crashing.org> Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory From: Benjamin Herrenschmidt To: Jason Gunthorpe , Dan Williams Cc: Logan Gunthorpe , Bjorn Helgaas , Christoph Hellwig , Sagi Grimberg , "James E.J. Bottomley" , "Martin K. Petersen" , Jens Axboe , Steve Wise , Stephen Bates , Max Gurtovoy , Keith Busch , linux-pci@vger.kernel.org, linux-scsi , linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, linux-nvdimm , "linux-kernel@vger.kernel.org" , Jerome Glisse Date: Wed, 19 Apr 2017 11:21:50 +1000 In-Reply-To: <20170418212258.GA26838@obsidianresearch.com> References: <1492381396.25766.43.camel@kernel.crashing.org> <20170418164557.GA7181@obsidianresearch.com> <20170418190138.GH7181@obsidianresearch.com> <20170418210339.GA24257@obsidianresearch.com> <20170418212258.GA26838@obsidianresearch.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-1.fc25) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 726 Lines: 20 On Tue, 2017-04-18 at 15:22 -0600, Jason Gunthorpe wrote: > On Tue, Apr 18, 2017 at 02:11:33PM -0700, Dan Williams wrote: > > > I think this opens an even bigger can of worms.. > > > > No, I don't think it does. You'd only shim when the target page is > > backed by a device, not host memory, and you can figure this out by > > a > > is_zone_device_page()-style lookup. > > The bigger can of worms is how do you meaningfully stack dma_ops. > > What does the p2p provider do when it detects a p2p page? Yeah I think we don't really want to stack dma_ops... thinking more about it. As I just wrote, it looks like we might need a more specialised hook in the devmap to be used by the main dma_op, on a per-page basis. Ben.