On Mon, Jul 29, 2019 at 10:51:51AM -0400, Waiman Long wrote: > On 7/29/19 4:52 AM, Peter Zijlstra wrote: > > On Sat, Jul 27, 2019 at 01:10:47PM -0400, 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. > > Sure, but this has been so 'forever', why is it a problem now? > > I ran into this probem when running a test program that keeps on > allocating and touch memory and it eventually fails as the swap space is > full. After the failure, I could not rerun the test program again > because the swap space remained full. I finally track it down to the > fact that the mm stayed on as active_mm of kernel threads. I have to > make sure that all the idle cpus get a user task to run to bump the > dying mm off the active_mm of those cpus, but this is just a workaround, > not a solution to this problem. The 'sad' part is that x86 already switches to init_mm on idle and we only keep the active_mm around for 'stupid'. Rik and Andy were working on getting that 'fixed' a while ago, not sure where that went.
