Re: [PATCH V3 1/5] RDMA/core: Transport-independent access flags

["'Christoph Hellwig'" <hch@infradead.org>]

On Mon, Jul 13, 2015 at 10:57:48AM -0600, Jason Gunthorpe wrote:
> > Currently various drivers are using ib_get_dma_mr with remote flags
> > unfortunately, e.g. the SRP initiator driver uses it to optimize away
> > memory registrtions for single SGL entry requests.
> 
> Unconditionally? Ugh. Maybe we do need the warn_on :(

There is a "register_always" flag to always use real MRs, but it's
off by default:

	if (count == 1 && !register_always) {
		/*
		 * The midlayer only generated a single gather/scatter
		 * entry, or DMA mapping coalesced everything to a
		 * single entry. So a direct descriptor along with
		 * the DMA MR suffices.
		 */
		struct srp_direct_buf *buf = (void *) cmd->add_data;

		buf->va  = cpu_to_be64(ib_sg_dma_address(ibdev, scat));
                buf->key = cpu_to_be32(target->rkey);
		buf->len = cpu_to_be32(ib_sg_dma_len(ibdev, scat));

		req->nmdesc = 0;
		goto map_complete;
	}