Messages in this thread | | | Subject | Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA | From | Tom Talpey <> | Date | Thu, 7 Feb 2019 16:31:53 -0500 |
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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 <jgg@ziepe.ca> 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.
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