From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tom Talpey Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA Date: Thu, 7 Feb 2019 16:31:53 -0500 Message-ID: <93012d17-d3f9-76d5-e6e0-ea39198db5a9@talpey.com> References: <20190206175233.GN21860@bombadil.infradead.org> <47820c4d696aee41225854071ec73373a273fd4a.camel@redhat.com> <01000168c43d594c-7979fcf8-b9c1-4bda-b29a-500efe001d66-000000@email.amazonses.com> <20190206210356.GZ6173@dastard> <20190206220828.GJ12227@ziepe.ca> <0c868bc615a60c44d618fb0183fcbe0c418c7c83.camel@redhat.com> <20190207035258.GD6173@dastard> <20190207052310.GA22726@ziepe.ca> <6b260348-966a-bc95-162b-44ae8265cf03@talpey.com> <20190207165740.GB29531@iweiny-DESK2.sc.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190207165740.GB29531@iweiny-DESK2.sc.intel.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Ira Weiny Cc: Chuck Lever , Jason Gunthorpe , Dave Chinner , Doug Ledford , Christopher Lameter , Matthew Wilcox , Jan Kara , lsf-pc@lists.linux-foundation.org, linux-rdma , linux-mm@kvack.org, Linux Kernel Mailing List , John Hubbard , Jerome Glisse , Dan Williams , Michal Hocko List-Id: linux-rdma@vger.kernel.org On 2/7/2019 11:57 AM, Ira Weiny wrote: > On Thu, Feb 07, 2019 at 10:28:05AM -0500, Tom Talpey wrote: >> On 2/7/2019 10:04 AM, Chuck Lever wrote: >>> >>> >>>> On Feb 7, 2019, at 12:23 AM, Jason Gunthorpe wrote: >>>> >>>> On Thu, Feb 07, 2019 at 02:52:58PM +1100, Dave Chinner wrote: >>>> >>>>> Requiring ODP capable hardware and applications that control RDMA >>>>> access to use file leases and be able to cancel/recall client side >>>>> delegations (like NFS is already able to do!) seems like a pretty >>>> >>>> So, what happens on NFS if the revoke takes too long? >>> >>> NFS distinguishes between "recall" and "revoke". Dave used "recall" >>> here, it means that the server recalls the client's delegation. If >>> the client doesn't respond, the server revokes the delegation >>> unilaterally and other users are allowed to proceed. >> >> The SMB3 protocol has a similar "lease break" mechanism, btw. >> >> SMB3 "push mode" has long-expected to allow DAX mapping of files >> only when an exclusive lease is held by the requesting client. >> The server may recall the lease if the DAX mapping needs to change. >> >> Once local (MMU) and remote (RDMA) mappings are dropped, the >> client may re-request that the server reestablish them. No >> connection or process is terminated, and no data is silently lost. > > How long does one wait for these remote mappings to be dropped? The recall process depends on several things, but it certainly takes a network round trip. If recall fails, the file protocols allow the server to revoke. However, since this results in loss of data, it's a last resort. Tom.