Using Remote Invalidation With RPC-Over-RDMA Transport Protocols
draft-cel-nfsv4-reminv-design-03

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Network File System Version 4                                   C. Lever
Internet-Draft                                                    Oracle
Intended status: Informational                         September 9, 2016
Expires: March 13, 2017

    Using Remote Invalidation With RPC-Over-RDMA Transport Protocols
                    draft-cel-nfsv4-reminv-design-03

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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   This Internet-Draft will expire on March 13, 2017.

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Lever                    Expires March 13, 2017                 [Page 1]
Internet-Draft    Remote Invalidation And RPC-over-RDMA   September 2016

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  General Requirements  . . . . . . . . . . . . . . . . . . . .   4
   3.  Remote Invalidation In Operation  . . . . . . . . . . . . . .   6
   4.  Protocol Elements . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  16
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  17

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 a bulk data 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 on behalf of a remote peer.
   This act is referred to as "memory registration."  The RNIC uses this
   STag to steer data to and from the registered memory region.

   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 should be done before RPC
   applications 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
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