On Sat 06-02-16 14:54:24, Tetsuo Handa wrote: > Michal Hocko wrote: > > > But if we consider non system-wide OOM events, it is not very unlikely to hit > > > this race. This queue is useful for situations where memcg1 and memcg2 hit > > > memcg OOM at the same time and victim1 in memcg1 cannot terminate immediately. > > > > This can happen of course but the likelihood is _much_ smaller without > > the global OOM because the memcg OOM killer is invoked from a lockless > > context so the oom context cannot block the victim to proceed. > > Suppose mem_cgroup_out_of_memory() is called from a lockless context via > mem_cgroup_oom_synchronize() called from pagefault_out_of_memory(), that > "lockless" is talking about only current thread, doesn't it? Yes and you need the OOM context to sit on the same lock as the victim to form a deadlock. So while the victim might be blocked somewhere it is much less likely it would be deadlocked. > Since oom_kill_process() sets TIF_MEMDIE on first mm!=NULL thread of a > victim process, it is possible that non-first mm!=NULL thread triggers > pagefault_out_of_memory() and first mm!=NULL thread gets TIF_MEMDIE, > isn't it? I got lost here completely. Maybe it is your usage of thread terminology again. > Then, where is the guarantee that victim1 (first mm!=NULL thread in memcg1 > which got TIF_MEMDIE) is not waiting at down_read(&victim2->mm->mmap_sem) > when victim2 (first mm!=NULL thread in memcg2 which got TIF_MEMDIE) is > waiting at down_write(&victim2->mm->mmap_sem) All threads/processes sharing the same mm are in fact in the same memory cgroup. That is the reason we have owner in the task_struct > or both victim1 and victim2 > are waiting on a lock somewhere in memory reclaim path (e.g. > mutex_lock(&inode->i_mutex))? Such waiting has to make a forward progress at some point in time because the lock itself cannot be deadlocked by the memcg OOM context. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>