nvmet: Optionally use PCI P2P memory
Create a configfs attribute in each nvme-fabrics namespace to enable P2P memory use. The attribute may be enabled (with a boolean) or a specific P2P device may be given (with the device's PCI name). When enabled, the namespace will ensure the underlying block device supports P2P and is compatible with any specified P2P device. If no device was specified it will ensure there is compatible P2P memory somewhere in the system. Enabling a namespace with P2P memory will fail with EINVAL (and an appropriate dmesg error) if any of these conditions are not met. Once a controller is set up on a specific port, the P2P device to use for each namespace will be found and stored in a radix tree by namespace ID. When memory is allocated for a request, the tree is used to look up the P2P device to allocate memory against. If no device is in the tree (because no appropriate device was found), or if allocation of P2P memory fails, fall back to using regular memory. Signed-off-by: NStephen Bates <sbates@raithlin.com> Signed-off-by: NSteve Wise <swise@opengridcomputing.com> [hch: partial rewrite of the initial code] Signed-off-by: NChristoph Hellwig <hch@lst.de> Signed-off-by: NLogan Gunthorpe <logang@deltatee.com> Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
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