On 7/29/19 2:58 PM, Michal Hocko wrote: > On Mon 29-07-19 11:27:35, Waiman Long wrote: >> On 7/29/19 5:12 AM, Michal Hocko wrote: >>> On Sat 27-07-19 13:10:47, Waiman Long wrote: >>>> It was found that a dying mm_struct where the owning task has exited >>>> can stay on as active_mm of kernel threads as long as no other user >>>> tasks run on those CPUs that use it as active_mm. This prolongs the >>>> life time of dying mm holding up memory and other resources like swap >>>> space that cannot be freed. >>> IIRC use_mm doesn't pin the address space. It only pins the mm_struct >>> itself. So what exactly is the problem here? >> As explained in my response to Peter, I found that resource like swap >> space were depleted even after the exit of the offending program in a >> mostly idle system. This patch is to make sure that those resources get >> freed after program exit ASAP. > Could you elaborate more? How can a mm counter (do not confuse with > mm_users) prevent address space to be torn down on exit? Many of the resources tied to mm_struct are indeed freed when mm_users becomes 0 including swap space reservation, I think. I was testing a mm patch and it did have a missing mmput bug that cause mm_users not going to 0. I fixed the bug, and with sched patch to speed up the release the mm_struct, every was fine. I didn't realize that fixing the mm bug is enough to free the swap space. Still there are some resources not being free when the mm_count is non-zero. It is certainly less serious than what I have thought. Sorry for the confusion. Cheers, Longman
