linux-kernel - Re: [PATCH v5 10/13] nvme-pci: Add support for P2P memory in requests

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Message-ID: <d5548f5d-59df-f38e-255d-59b46a17a219@deltatee.com>
Date:   Tue, 4 Sep 2018 09:47:07 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Jason Gunthorpe <jgg@...lanox.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-block@...r.kernel.org,
        Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH v5 10/13] nvme-pci: Add support for P2P memory in requests



On 04/09/18 09:16 AM, Jason Gunthorpe wrote:
>>  	if (iod->nents) {
>> -		dma_unmap_sg(dev->dev, iod->sg, iod->nents, dma_dir);
>> +		/* P2PDMA requests do not need to be unmapped */
>> +		if (!is_pci_p2pdma_page(sg_page(iod->sg)))
>> +			dma_unmap_sg(dev->dev, iod->sg, iod->nents, dma_dir);
> 
> This seems like a poor direction, if we add IOMMU hairpin support we
> will need unmapping.

It can always be added later. In any case, you'll have to convince
Christoph who requested the change; I'm not that invested in this decision.

Logan