Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA

From: Matthew Wilcox
Date: Wed Feb 06 2019 - 15:50:00 EST

On Wed, Feb 06, 2019 at 03:47:53PM -0500, Doug Ledford wrote:
> On Wed, 2019-02-06 at 12:41 -0800, Matthew Wilcox wrote:
> > On Wed, Feb 06, 2019 at 03:28:35PM -0500, Doug Ledford wrote:
> > > On Wed, 2019-02-06 at 12:20 -0800, Matthew Wilcox wrote:
> > > > Not hot-unplugging the RDMA device but hot-unplugging an NV-DIMM.

^^^ I think you missed this line ^^^

> You said "now that I think about it, there was a desire to support hot-
> unplug which also needed revoke". For us, hot unplug is done at the
> device level and means all connections must be torn down. So in the
> context of this argument, if people want revoke so DAX can migrate from
> one NV-DIMM to another, ok. But revoke does not help RDMA migrate.
> If, instead, you mean that you want to support hot unplug of an NV-DIMM
> that is currently the target of RDMA transfers, then I believe
> Christoph's answer on this is correct. It all boils down to which
> device you are talking about doing the hot unplug on.