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614f3c96d7
On some platforms, DMA mapping part of a page is more costly than copying bytes. Restore the pull-up code and use that when we think it's going to be faster. The heuristic for now is to pull-up when the size of the RPC message body fits in the buffer underlying the head iovec. Indeed, not involving the I/O MMU can help the RPC/RDMA transport scale better for tiny I/Os across more RDMA devices. This is because interaction with the I/O MMU is eliminated, as is handling a Send completion, for each of these small I/Os. Without the explicit unmapping, the NIC no longer needs to do a costly internal TLB shoot down for buffers that are just a handful of bytes. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>