Improving the Performance and Reliability of RPC Replies on RPC-over-RDMA Transports
draft-cel-nfsv4-rpcrdma-reliable-reply-02

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Network File System Version 4                                   C. Lever
Internet-Draft                                                    Oracle
Intended status: Experimental                            January 9, 2018
Expires: July 13, 2018

 Improving the Performance and Reliability of RPC Replies on RPC-over-
                            RDMA Transports
               draft-cel-nfsv4-rpcrdma-reliable-reply-02

Abstract

   RPC transports such as RPC-over-RDMA Version One require reply
   buffers to be in place before an RPC Call is sent.  However, Upper
   Layer Protocols sometimes have difficulty estimating the expected
   maximum size of RPC replies.  This introduces the risk that an RPC
   Reply message can overrun reply resources provided by the requester,
   preventing delivery of the message, through no fault of the
   requester.  This document describes a mechanism that eliminates the
   need for pre-allocation of reply resources for unpredictably large
   replies.

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Lever                     Expires July 13, 2018                 [Page 1]
Internet-Draft        RPC-Over-RDMA Reliable Reply          January 2018

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Reply Chunk Overrun . . . . . . . . . . . . . . . . . . .   4
     3.2.  Reply Size Calculation  . . . . . . . . . . . . . . . . .   4
     3.3.  Requester Registration Costs  . . . . . . . . . . . . . .   5
     3.4.  Denial of Service . . . . . . . . . . . . . . . . . . . .   5
     3.5.  Estimating Transport Header Size  . . . . . . . . . . . .   6
   4.  Responder-Provided Read Chunks  . . . . . . . . . . . . . . .   6
     4.1.  Specification . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Analysis  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Benefits  . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.2.  Costs . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     5.3.  Selecting a Reply Mechanism . . . . . . . . . . . . . . .  11
     5.4.  Implementation Complexity . . . . . . . . . . . . . . . .  12
     5.5.  Alternatives  . . . . . . . . . . . . . . . . . . . . . .  13
   6.  Interoperation Considerations . . . . . . . . . . . . . . . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  16
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   One way in which RPC-over-RDMA Version One improves transport
   efficiency is by ensuring resources for RPC replies are available in
   advance of each RPC transaction [RFC8166].  These resources are
   typically provisioned before a requester sends each RPC Call message.
   They are provided to the responder to use for transmiting the
   associated RPC Reply message back to the requester.

   In particular, when the Payload Stream of an RPC Reply message is
   expected to be large, the requester allocates and registers a Reply
   chunk.  The responder transfers the RPC Reply message's Payload
   stream directly into the requester memory associated with that chunk,
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