On Tue, Nov 23, 2021 at 11:04:04PM +0100, Vlastimil Babka wrote: > On 11/23/21 18:00, Jason Gunthorpe wrote: > > > >> believe what you say and I trust your experience :) So could as well be > >> that on such a "special" (or not so special) systems there should be a > >> way to restrict it to privileged users only. > > > > At this point RDMA is about as "special" as people running large > > ZONE_MOVABLE systems, and the two are going to start colliding > > heavily. The RDMA VFIO migration driver should be merged soon which > > makes VMs using this stuff finally practical. > > How does that work, I see the word migration, so does it cause pages to Sorry I mean what is often called "VM live migration". Typically that cannot be done if a PCI device is assigned to the VM as suspending and the migrating a PCI device to another server is complicated. With forthcoming hardware mlx5 can do this and thus the entire RDMA stack becomes practically usable and performant within a VM. > be migrated out of ZONE_MOVABLE before they are pinned? GUP already does this automatically for FOLL_LONGTERM. > Similarly for io-uring we could be migrating pages to be pinned so that > the end up consolidated close together, and prevent pathologic > situations like in David's reproducer. It is an interesting idea to have GUP do some kind of THP preserving migration. Jason
