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. >> Fix that by forcing the kernel threads to use init_mm as the active_mm >> if the previous active_mm is dying. >> >> The determination of a dying mm is based on the absence of an owning >> task. The selection of the owning task only happens with the CONFIG_MEMCG >> option. Without that, there is no simple way to determine the life span >> of a given mm. So it falls back to the old behavior. > Please don't. We really wont to remove mm->owner long term. OK, if that is the case, I will need to find an alternative way to determine if an mm is to be freed soon and perhaps set a flag to indicate that. Thanks, Longman
