Re: [PATCH v8 13/13] nvmet: Optionally use PCI P2P memory

[Keith Busch <keith.busch-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

On Thu, Sep 27, 2018 at 10:54:20AM -0600, Logan Gunthorpe wrote:
> We create a configfs attribute in each nvme-fabrics target port to
> enable p2p memory use. When enabled, the port will only then use the
> p2p memory if a p2p memory device can be found which is behind the
> same switch hierarchy as the RDMA port and all the block devices in
> use. If the user enabled it and no devices are found, then the system
> will silently fall back on using regular memory.
> 
> If appropriate, that port will allocate memory for the RDMA buffers
> for queues from the p2pmem device falling back to system memory should
> anything fail.
> 
> Ideally, we'd want to use an NVME CMB buffer as p2p memory. This would
> save an extra PCI transfer as the NVME card could just take the data
> out of it's own memory. However, at this time, only a limited number
> of cards with CMB buffers seem to be available.
> 
> Signed-off-by: Stephen Bates <sbates-pv7U853sEMVWk0Htik3J/w@public.gmane.org>
> Signed-off-by: Steve Wise <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>
> [hch: partial rewrite of the initial code]
> Signed-off-by: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
> Signed-off-by: Logan Gunthorpe <logang-OTvnGxWRz7hWk0Htik3J/w@public.gmane.org>

I haven't the necessary hardware to try this out, but looking forward
to it in the future. Looks good.

Reviewed-by: Keith Busch <keith.busch-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>