On 12/18/20 2:20 AM, Dmitry Kadashev wrote: > On Thu, Dec 17, 2020 at 8:43 PM Victor Stewart <v@nametag.social> wrote: >> >> On Thu, Dec 17, 2020 at 11:12 AM Dmitry Kadashev <dkadashev@xxxxxxxxx> wrote: >>> >>> On Thu, Dec 17, 2020 at 5:38 PM Josef <josef.grieb@xxxxxxxxx> wrote: >>>> >>>>>> That is curious. This ticket mentions Shmem though, and in our case it does >>>> > not look suspicious at all. E.g. on a box that has the problem at the moment: >>>> > Shmem: 41856 kB. The box has 256GB of RAM. >>>> > >>>> > But I'd (given my lack of knowledge) expect the issues to be related anyway. >>>> >>>> what about mapped? mapped is pretty high 1GB on my machine, I'm still >>>> reproduce that in C...however the user process is killed but not the >>>> io_wq_worker kernel processes, that's also the reason why the server >>>> socket still listening(even if the user process is killed), the bug >>>> only occurs(in netty) with a high number of operations and using >>>> eventfd_write to unblock io_uring_enter(IORING_ENTER_GETEVENTS) >>>> >>>> (tested on kernel 5.9 and 5.10) >>> >>> Stats from another box with this problem (still 256G of RAM): >>> >>> Mlocked: 17096 kB >>> Mapped: 171480 kB >>> Shmem: 41880 kB >>> >>> Does not look suspicious at a glance. Number of io_wq* processes is 23-31. >>> >>> Uptime is 27 days, 24 rings per process, process was restarted 4 times, 3 out of >>> these four the old instance was killed with SIGKILL. On the last process start >>> 18 rings failed to initialize, but after that 6 more were initialized >>> successfully. It was before the old instance was killed. Maybe it's related to >>> the load and number of io-wq processes, e.g. some of them exited and a few more >>> rings were initialized successfully. >> >> have you tried using IORING_SETUP_ATTACH_WQ? >> >> https://lkml.org/lkml/2020/1/27/763 > > No, I have not, but while using that might help to slow down progression of the > issue, it won't fix it - at least if I understand correctly. The problem is not > that those rings can't be created at all - there is no problem with that on a > freshly booted box, but rather that after some (potentially abrupt) owning > process terminations under load kernel gets into a state where - eventually - no > new rings can be created at all. Not a single one. In the above example the > issue just haven't progressed far enough yet. > > In other words, there seems to be a leak / accounting problem in the io_uring > code that is triggered by abrupt process termination under load (just no > io_uring_queue_exit?) - this is not a usage problem. Right, I don't think that's related at all. Might be a good idea in general depending on your use case, but it won't really have any bearing on the particular issue at hand. -- Jens Axboe
