On Tue 24-04-18 17:08:15, Michal Hocko wrote: > On Tue 24-04-18 14:07:52, David Rientjes wrote: > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > > > > My patch has passed intensive testing on both x86 and powerpc, so I'll ask > > > > > > that it's pushed for 4.17-rc3. Many thanks to Tetsuo for the suggestion > > > > > > on calling __oom_reap_task_mm() from exit_mmap(). > > > > > > > > > > Yeah, but your patch does have a problem with blockable mmu notifiers > > > > > IIUC. > > > > > > > > What on earth are you talking about? exit_mmap() does > > > > mmu_notifier_release(). There are no blockable mmu notifiers. > > > > > > MMF_OOM_SKIP - remember? The thing that guarantees a forward progress. > > > So we cannot really depend on setting MMF_OOM_SKIP if a > > > mmu_notifier_release blocks for an excessive/unbounded amount of time. > > > > > > > If the thread is blocked in exit_mmap() because of mmu_notifier_release() > > then the oom reaper will eventually grab mm->mmap_sem (nothing holding it > > in exit_mmap()), return true, and oom_reap_task() will set MMF_OOM_SKIP. > > This is unchanged with the patch and is a completely separate issue. > > I must be missing something or we are talking past each other. Ohh. Ok, so _I_ was missing that mm_has_notifiers is false after mmu_notifier_release. So we cannot block at that time. Then we are good. Sorry about the confusion! -- Michal Hocko SUSE Labs
