On Wed, Jun 12, 2019 at 3:29 AM Jan Kara <jack@xxxxxxx> wrote: > > On Fri 07-06-19 07:52:13, Ira Weiny wrote: > > On Fri, Jun 07, 2019 at 09:17:29AM -0300, Jason Gunthorpe wrote: > > > On Fri, Jun 07, 2019 at 12:36:36PM +0200, Jan Kara wrote: > > > > > > > Because the pins would be invisible to sysadmin from that point on. > > > > > > It is not invisible, it just shows up in a rdma specific kernel > > > interface. You have to use rdma netlink to see the kernel object > > > holding this pin. > > > > > > If this visibility is the main sticking point I suggest just enhancing > > > the existing MR reporting to include the file info for current GUP > > > pins and teaching lsof to collect information from there as well so it > > > is easy to use. > > > > > > If the ownership of the lease transfers to the MR, and we report that > > > ownership to userspace in a way lsof can find, then I think all the > > > concerns that have been raised are met, right? > > > > I was contemplating some new lsof feature yesterday. But what I don't > > think we want is sysadmins to have multiple tools for multiple > > subsystems. Or even have to teach lsof something new for every potential > > new subsystem user of GUP pins. > > Agreed. > > > I was thinking more along the lines of reporting files which have GUP > > pins on them directly somewhere (dare I say procfs?) and teaching lsof to > > report that information. That would cover any subsystem which does a > > longterm pin. > > So lsof already parses /proc/<pid>/maps to learn about files held open by > memory mappings. It could parse some other file as well I guess. The good > thing about that would be that then "longterm pin" structure would just hold > struct file reference. That would avoid any needs of special behavior on > file close (the file reference in the "longterm pin" structure would make > sure struct file and thus the lease stays around, we'd just need to make > explicit lease unlock block until the "longterm pin" structure is freed). > The bad thing is that it requires us to come up with a sane new proc > interface for reporting "longterm pins" and associated struct file. Also we > need to define what this interface shows if the pinned pages are in DRAM > (either page cache or anon) and not on NVDIMM. The anon vs shared detection case is important because a longterm pin might be blocking a memory-hot-unplug operation if it is pinning ZONE_MOVABLE memory, but I don't think we want DRAM vs NVDIMM to be an explicit concern of the interface. For the anon / cached case I expect it might be useful to put that communication under the memory-blocks sysfs interface. I.e. a list of pids that are pinning that memory-block from being hot-unplugged.
