Re: [PATCH v1 1/4] xprtrdma: Remove support for FMR memory registration

From: Jason Gunthorpe <jgg@ziepe.ca>
To: Chuck Lever <chuck.lever@oracle.com>
Cc: Bart Van Assche <bvanassche@acm.org>,
	linux-rdma <linux-rdma@vger.kernel.org>,
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
	Lijun Ou <oulijun@huawei.com>,
	umalhi@cisco.com, zhongjiang@huawei.com,
	venkata.s.dhanalakota@intel.com,
	Dennis Dalessandro <dennis.dalessandro@intel.com>
Subject: Re: [PATCH v1 1/4] xprtrdma: Remove support for FMR memory registration
Date: Mon, 19 Nov 2018 16:10:32 -0700	[thread overview]
Message-ID: <20181119231032.GO4890@ziepe.ca> (raw)
In-Reply-To: <1172062C-E8CB-4F37-905D-F40EC8D9270C@oracle.com>

On Mon, Nov 19, 2018 at 05:56:54PM -0500, Chuck Lever wrote:
> 
> 
> > On Nov 19, 2018, at 5:41 PM, Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > 
> > On Mon, Nov 19, 2018 at 08:16:37AM -0800, Bart Van Assche wrote:
> >> On Mon, 2018-11-19 at 10:45 -0500, Chuck Lever wrote:
> >>> FMR is not supported on most recent RDMA devices. It is also slower
> >>> and less secure than FRWR. As discussed during the RDMA BoF at LPC
> >>> 2018, it is time to remove support for FMR in the NFS/RDMA client
> >>> stack. NFS/RDMA server-side uses either local memory registration or
> >>> FRWR.  There is no change required there to deprecate FMR.
> >>> 
> >>> There are a few Infiniband/RoCE devices in the kernel tree that do
> >>> not support MEM_MGT_EXTENSIONS, and therefore will no longer support
> >>> client-side NFS/RDMA. These are:
> >>> 
> >>> - mthca
> >>> - qib
> > 
> > Ooh, qib was not in the list when we talked on this in plumbers. That
> > does change things. 
> > 
> > Dennis: Could qib be changed? HFI1 supports FRWR right?
> > 
> >>> - usnic
> >>> - hns (RoCE)
> >> 
> >> Can someone from Intel comment on how many of their customers rely on the qib
> >> driver?
> >> 
> >> Can someone from Cisco comment on how many of their customers rely on the usnic
> >> driver?
> > 
> > Ignore usnic, it is not a RDMA driver
> > 
> >> Can someone from Huawei comment on how many of their customers rely on the hns
> >> driver?
> > 
> > Nor was this, this is an actively used driver..
> > 
> > Could hns do FRWR? It is very disappointing that such a new driver
> > does not support FRWR.
> > 
> > I guess it is worth stating again that FMR is deprecated. People are
> > going to be disappointed if they try to submit new drivers that don't
> > support FRWR :(
> 
> My methodology was to search for whether each driver asserts
> IB_DEVICE_MEM_MGT_EXTENSIONS in device_cap_flags.

Drivers might be broken here, or we might need more flags.

Searching for FWMR shows hits in hns, which is encouraging...

Jason