Re: [PATCH] IB/iser: Remove support for FMR memory registration

[Jason Gunthorpe <jgg@mellanox.com>]

On Tue, May 12, 2020 at 01:09:02PM -0700, Bart Van Assche wrote:
> On 2020-05-12 10:16, Leon Romanovsky wrote:
> > On Tue, May 12, 2020 at 07:08:59PM +0300, Israel Rukshin wrote:
> >> FMR is not supported on most recent RDMA devices (that use fast memory
> >> registration mechanism). Also, FMR was recently removed from NFS/RDMA
> >> ULP.
> >>
> >> Signed-off-by: Israel Rukshin <israelr@mellanox.com>
> >> Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
> >>  drivers/infiniband/ulp/iser/iscsi_iser.h     |  79 +----------
> >>  drivers/infiniband/ulp/iser/iser_initiator.c |  19 ++-
> >>  drivers/infiniband/ulp/iser/iser_memory.c    | 188 ++-------------------------
> >>  drivers/infiniband/ulp/iser/iser_verbs.c     | 126 +++---------------
> >>  4 files changed, 40 insertions(+), 372 deletions(-)
> > 
> > Can we do an extra step and remove FMR from srp too?
> 
> Which HCA's will be affected by removing FMR support? Or in other words,
> when did (Mellanox) HCA's start supporting fast memory registration? I'm
> asking this because there is a tradition in the Linux kernel not to
> remove support for old hardware unless it is pretty sure that nobody is
> using that hardware anymore.

We haven't entirely been following that in RDMA.. More like when
people can't test any more it can go.

For FMR the support was dropped in newer HW so AFAIK, nobody tests
this and it just stands in the way of making FRWR work properly.

Do the ULPs stop working or do they just run slower with some regular
MR flow?

Jason