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: > > On Wed, Feb 06, 2019 at 03:16:02PM -0500, Doug Ledford wrote: > > > On Wed, 2019-02-06 at 11:40 -0800, Matthew Wilcox wrote: > > > > On Wed, Feb 06, 2019 at 07:16:21PM +0000, Christopher Lameter wrote: > > > > > though? If we only allow this use case then we may not have to worry about > > > > > long term GUP because DAX mapped files will stay in the physical location > > > > > regardless. > > > > > > > > ... except for truncate. And now that I think about it, there was a > > > > desire to support hot-unplug which also needed revoke. > > > > > > We already support hot unplug of RDMA devices. But it is extreme. How > > > does hot unplug deal with a program running from the device (something > > > that would have returned ETXTBSY)? > > > > Not hot-unplugging the RDMA device but hot-unplugging an NV-DIMM. > > > > It's straightforward to migrate text pages from one DIMM to another; > > you remove the PTEs from the CPU's page tables, copy the data over and > > pagefaults put the new PTEs in place. We don't have a way to do similar > > things to an RDMA device, do we? > > We don't have a means of migration except in the narrowly scoped sense > of queue pair migration as defined by the IBTA and implemented on some > dual port IB cards. This narrowly scoped migration even still involves > notification of the app. > > Since there's no guarantee that any other port can connect to the same > machine as any port that's going away, it would always be a > disconnect/reconnect sequence in the app to support this, not an under > the covers migration. I don't understand you. We're not talking about migrating from one IB card to another, we're talking about changing the addresses that an STag refers to.
