Re: [PATCH v5 13/13] nvmet: Optionally use PCI P2P memory

From: Sagi Grimberg <sagi@grimberg.me>
To: Logan Gunthorpe <logang@deltatee.com>,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org,
	linux-nvdimm@lists.01.org, linux-block@vger.kernel.org
Cc: "Christian König" <christian.koenig@amd.com>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Steve Wise" <swise@opengridcomputing.com>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Jason Gunthorpe" <jgg@mellanox.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Max Gurtovoy" <maxg@mellanox.com>,
	"Christoph Hellwig" <hch@lst.de>
Subject: Re: [PATCH v5 13/13] nvmet: Optionally use PCI P2P memory
Date: Thu, 30 Aug 2018 17:25:09 -0700	[thread overview]
Message-ID: <ecbb669a-2e84-1333-7e0d-1560cf014750@grimberg.me> (raw)
In-Reply-To: <20180830185352.3369-14-logang@deltatee.com>

> +/*
> + * If allow_p2pmem is set, we will try to use P2P memory for the SGL lists for
> + * Ι/O commands. This requires the PCI p2p device to be compatible with the
> + * backing device for every namespace on this controller.
> + */
> +static void nvmet_setup_p2pmem(struct nvmet_ctrl *ctrl, struct nvmet_req *req)
> +{
> +	struct nvmet_ns *ns;
> +	int ret;
> +
> +	if (!req->port->use_p2pmem || !req->p2p_client)
> +		return;
> +
> +	mutex_lock(&ctrl->subsys->lock);
> +
> +	ret = pci_p2pdma_add_client(&ctrl->p2p_clients, req->p2p_client);
> +	if (ret) {
> +		pr_err("failed adding peer-to-peer DMA client %s: %d\n",
> +		       dev_name(req->p2p_client), ret);
> +		goto free_devices;
> +	}
> +
> +	list_for_each_entry_rcu(ns, &ctrl->subsys->namespaces, dev_link) {
> +		ret = nvmet_p2pdma_add_client(ctrl, ns);
> +		if (ret)
> +			goto free_devices;
> +	}
> +
> +	if (req->port->p2p_dev) {
> +		if (!pci_p2pdma_assign_provider(req->port->p2p_dev,
> +						&ctrl->p2p_clients)) {
> +			pr_info("peer-to-peer memory on %s is not supported\n",
> +				pci_name(req->port->p2p_dev));
> +			goto free_devices;
> +		}
> +		ctrl->p2p_dev = pci_dev_get(req->port->p2p_dev);
> +	} else {

When is port->p2p_dev == NULL? a little more documentation would help 
here...
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