On 2018/08/08 5:19, Johannes Weiner wrote: > On Tue, Aug 07, 2018 at 07:15:11PM +0900, Tetsuo Handa wrote: >> On 2018/08/07 16:25, Michal Hocko wrote: >>> @@ -1703,7 +1703,8 @@ static enum oom_status mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int >>> return OOM_ASYNC; >>> } >>> >>> - if (mem_cgroup_out_of_memory(memcg, mask, order)) >>> + if (mem_cgroup_out_of_memory(memcg, mask, order) || >>> + tsk_is_oom_victim(current)) >>> return OOM_SUCCESS; >>> >>> WARN(1,"Memory cgroup charge failed because of no reclaimable memory! " >>> >> >> I don't think this patch is appropriate. This patch only avoids hitting WARN(1). >> This patch does not address the root cause: >> >> The task_will_free_mem(current) test in out_of_memory() is returning false >> because test_bit(MMF_OOM_SKIP, &mm->flags) test in task_will_free_mem() is >> returning false because MMF_OOM_SKIP was already set by the OOM reaper. The OOM >> killer does not need to start selecting next OOM victim until "current thread >> completes __mmput()" or "it fails to complete __mmput() within reasonable >> period". > > I don't see why it matters whether the OOM victim exits or not, unless > you count the memory consumed by struct task_struct. We are not counting memory consumed by struct task_struct. But David is counting memory released between set_bit(MMF_OOM_SKIP, &mm->flags) and completion of exit_mmap(). > >> According to https://syzkaller.appspot.com/text?tag=CrashLog&x=15a1c770400000 , >> PID=23767 selected PID=23766 as an OOM victim and the OOM reaper set MMF_OOM_SKIP >> before PID=23766 unnecessarily selects PID=23767 as next OOM victim. >> At uptime = 366.550949, out_of_memory() should have returned true without selecting >> next OOM victim because tsk_is_oom_victim(current) == true. > > The code works just fine. We have to kill tasks until we a) free > enough memory or b) run out of tasks or c) kill current. When one of > these outcomes is reached, we allow the charge and return. > > The only problem here is a warning in the wrong place. > If forced charge contained a bug, removing this WARN(1) deprives users of chance to know that something is going wrong.
