On Wed, Feb 13, 2019 at 11:00:06PM -0700, Jason Gunthorpe wrote: > On Wed, Feb 13, 2019 at 05:53:14PM -0800, Ira Weiny wrote: > > On Mon, Feb 11, 2019 at 03:54:47PM -0700, Jason Gunthorpe wrote: > > > On Mon, Feb 11, 2019 at 05:44:32PM -0500, Daniel Jordan wrote: > > > > > > > All five of these places, and probably some of Davidlohr's conversions, > > > > probably want to be collapsed into a common helper in the core mm for > > > > accounting pinned pages. I tried, and there are several details that > > > > likely need discussion, so this can be done as a follow-on. > > > > > > I've wondered the same.. > > > > I'm really thinking this would be a nice way to ensure it gets cleaned up and > > does not happen again. > > > > Also, by moving it to the core we could better manage any user visible changes. > > > > From a high level, pinned is a subset of locked so it seems like we need a 2 > > sets of helpers. > > > > try_increment_locked_vm(...) > > decrement_locked_vm(...) > > > > try_increment_pinned_vm(...) > > decrement_pinned_vm(...) > > > > Where try_increment_pinned_vm() also increments locked_vm... Of course this > > may end up reverting the improvement of Davidlohr Bueso's atomic work... :-( > > > > Furthermore it would seem better (although I don't know if at all possible) if > > this were accounted for in core calls which tracked them based on how the pages > > are being used so that drivers can't call try_increment_locked_vm() and then > > pin the pages... Thus getting the account wrong vs what actually happened. > > > > And then in the end we can go back to locked_vm being the value checked against > > RLIMIT_MEMLOCK. > > Someone would need to understand the bug that was fixed by splitting > them. > My suggestion above assumes that splitting them is required/correct. To be fair I've not dug into if this is true or not, but I trust Christopher. What I have found is this commit: bc3e53f682d9 mm: distinguish between mlocked and pinned pages I think that commit introduced the bug (for IB) which at the time may have been "ok" because many users of IB at the time were HPC/MPI users and I don't think MPI does a lot of _separate_ mlock operations so the count of locked_vm was probably negligible. Alternatively, the clusters I've worked on in the past had compute nodes set with RLIMIT_MEMLOCK to 'unlimited' whilst running MPI applications on compute nodes of a cluster... :-/ I think what Christopher did was probably ok for the internal tracking but we _should_ have had something which summed the 2 for RLIMIT_MEMLOCK checking at that time to be 100% correct? Christopher do you remember why you did not do that? [1] http://lkml.kernel.org/r/20130524140114.GK23650@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx > > I think it had to do with double accounting pinned and mlocked pages > and thus delivering a lower than expected limit to userspace. > > vfio has this bug, RDMA does not. RDMA has a bug where it can > overallocate locked memory, vfio doesn't. Wouldn't vfio also be able to overallocate if the user had RDMA pinned pages? I think the problem is that if the user calls mlock on a large range then both vfio and RDMA could potentially overallocate even with this fix. This was your initial email to Daniel, I think... And Alex's concern. > > Really unclear how to fix this. The pinned/locked split with two > buckets may be the right way. Are you suggesting that we have 2 user limits? Ira > > Jason
