linux-kernel - Re: [PATCH v2 10/10] nvmet: Optionally use PCI P2P memory

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Date:   Thu, 1 Mar 2018 16:49:30 -0700
From:   Keith Busch <keith.busch@...el.com>
To:     Stephen Bates <sbates@...thlin.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Logan Gunthorpe <logang@...tatee.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        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>,
        Steve Wise <swise@...ngridcomputing.com>
Subject: Re: [PATCH v2 10/10] nvmet: Optionally use PCI P2P memory

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?