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Date:   Thu, 1 Mar 2018 16:49:30 -0700
From:   Keith Busch <keith.busch@intel.com>
To:     Stephen Bates <sbates@raithlin.com>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>,
        Logan Gunthorpe <logang@deltatee.com>,
        Sagi Grimberg <sagi@grimberg.me>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        "linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
        "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
        "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Max Gurtovoy <maxg@mellanox.com>,
        Dan Williams <dan.j.williams@intel.com>,
        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Steve Wise <swise@opengridcomputing.com>
Subject: Re: [PATCH v2 10/10] nvmet: Optionally use PCI P2P memory
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On Thu, Mar 01, 2018 at 11:00:51PM +0000, Stephen  Bates wrote:
> 
> P2P is about offloading the memory and PCI subsystem of the host CPU
> and this is achieved no matter which p2p_dev is used.

Even within a device, memory attributes for its various regions may not be
the same. There's a meaningful difference between writing to an NVMe CMB
vs PMR, and a single device could have both. We don't want to lump these
all together without knowing which region you're allocating from, right?