The Use of Remote Invalidation with RPC-Over-RDMA Transport Protocols
draft-cel-nfsv4-reminv-design-00

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Network File System Version 4                                   C. Lever
Internet-Draft                                                    Oracle
Intended status: Informational                            August 3, 2016
Expires: February 4, 2017

 The Use of Remote Invalidation with RPC-Over-RDMA Transport Protocols
                    draft-cel-nfsv4-reminv-design-00

Abstract

   Remote Invalidation relieves requesters/initiators of some of the
   burden of preparing memory to be accessed remotely, thus reducing the
   latency of transactions that require the use of explicit RDMA
   operations.  This document considers how to introduce Remote
   Invalidation to RPC-over-RDMA transport protocols.

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Lever                   Expires February 4, 2017                [Page 1]
Internet-Draft   RPC-over-RDMA with Remote Invalidation      August 2016

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Remote Invalidation In Operation  . . . . . . . . . . . . . .   3
   3.  Protocol Elements . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Like other RDMA-enabled storage protocols, RPC-over-RDMA Version Two
   [I-D.cel-nfsv4-rpcrdma-version-two] employs a Read-Write transfer
   model when using explicit RDMA operations to transfer data.  This
   means an RPC-over-RDMA requester exposes regions of its memory to an
   RPC-over-RDMA responder, which then uses RDMA Read and Write
   operations to transfer bulk data payloads.

   In preparation for such a transfer, a requester asks its RNIC to
   assign a steering tag, or STag, to a region of memory containing the
   data to be moved.  At this time, access rights are granted that allow
   the RNIC to access or update that memory.  This act is referred to as
   memory "registration."  RNICs use STags to steer data to and from
   registered memory regions.

   When data movement is complete, each STag is dissociated from its
   memory region.  This act is referred to as memory "invalidation."  It
   prevents further responder access to that memory region by revoking
   its remote access rights.  Invalidation must be done before upper
   layers (ie, RPC consumers) on the requester are allowed access to
   memory that was involved in an explicit RDMA operation.

   Remote Invalidation is a technique by which an RDMA peer can request
   that a remote RNIC invalidate an STag associated with memory on that
   remote peer [RFC5042].  An RDMA consumer requests Remote Invalidation
   by posting an RDMA Send With Invalidate Work Request in place of an
   RDMA Send Work Request.  RDMA Send With Invalidate is similar to RDMA
   Send, but takes one additional argument: a single STag to be
   invalidated by the RNIC that receives the sent message.  An RDMA Send
   message is transmitted with additional header information that
   conveys the STag that is to be invalidated [RFC5040].

   The benefit of Remote Invalidation is that an extra Work Request,
   context switch, and interrupt to perform memory invalidation are not
   required by the requester as part of handling the completion of an

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