From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 7693F21130057 for ; Tue, 25 Sep 2018 10:47:22 -0700 (PDT) Date: Tue, 25 Sep 2018 11:48:35 -0600 From: Keith Busch Subject: Re: [PATCH v7 10/13] nvme-pci: Add support for P2P memory in requests Message-ID: <20180925174835.GA12185@localhost.localdomain> References: <20180925162231.4354-1-logang@deltatee.com> <20180925162231.4354-11-logang@deltatee.com> <20180925171147.GB11822@localhost.localdomain> <3549a9bb-3604-1739-c008-4e1a95441333@deltatee.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <3549a9bb-3604-1739-c008-4e1a95441333@deltatee.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Logan Gunthorpe Cc: Jens Axboe , Alex Williamson , linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, =?iso-8859-1?B?Suly9G1l?= Glisse , Jason Gunthorpe , Christian =?iso-8859-1?Q?K=F6nig?= , Benjamin Herrenschmidt , Bjorn Helgaas , Max Gurtovoy , Christoph Hellwig List-ID: On Tue, Sep 25, 2018 at 11:41:44AM -0600, Logan Gunthorpe wrote: > Hey, > > On 2018-09-25 11:11 a.m., Keith Busch wrote: > > Sorry if this was already discussed. Is there a reason the following > > pattern is not pushed to the generic dma_map_sg_attrs? > > > > if (is_pci_p2pdma_page(sg_page(sg))) > > pci_p2pdma_map_sg(dev, sg, nents, dma_dir); > > > > Beyond that, series looks good. > > Yes, this has been discussed. It comes down to a few reasons: > > 1) Intrusiveness on other systems: ie. not needing to pay the cost for > every single dma_map_sg call > > 2) Consistency: we can add the check to dma_map_sg, but adding similar > functionality to dma_map_page, etc is difficult seeing it's hard for the > unmap operation to detect if a dma_addr_t was P2P memory to begin with. > > 3) Safety for developers trying to use P2P memory: Right now developers > must be careful with P2P pages and ensure they aren't mapped using other > means (ie dma_map_page). Having them check the drivers that are handling > the pages to ensure the appropriate map function is always used is and > that P2P pages aren't being mixed with regular pages is better than > developers relying on magic in dma_map_sg() and getting things wrong. > > That being said, I think in the future everyone would like to move in > that direction but it means we will have to solve some difficult > problems with the existing infrastructure. Gotchya, thanks for jogging my memory. _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm