On Wed 17-10-12 01:14:48, Sha Zhengju wrote: > On Tuesday, October 16, 2012, Michal Hocko <mhocko@xxxxxxx> wrote: [...] > > Could you be more specific about the motivation for this patch? Is it > > "let's be consistent with the global oom" or you have a real use case > > for this knob. > > > > In our environment(rhel6), we encounter a memcg oom 'deadlock' > problem. Simply speaking, suppose process A is selected to be killed > by memcg oom killer, but A is uninterruptible sleeping on a page > lock. What's worse, the exact page lock is holding by another memcg > process B which is trapped in mem_croup_oom_lock(proves to be a > livelock). Hmm, this is strange. How can you get down that road with the page lock held? Is it possible this is related to the issue fixed by: 1d65f86d (mm: preallocate page before lock_page() at filemap COW)? > Then A can not exit successfully to free the memory and both of them > can not moving on. > Indeed, we should dig into these locks to find the solution and > in fact the 37b23e05 (x86, mm: make pagefault killable) and > 7d9fdac(Memcg: make oom_lock 0 and 1 based other than counter) have > already solved the problem, but if oom_killing_allocating_task is > memcg aware, enabling this suicide oom behavior will be a simpler > workaround. What's more, enabling the sysctl can avoid other potential > oom problems to some extent. As I said, I am not against this but I really want to see a valid use case first. So far I haven't seen any because what you mention above is a clear bug which should be fixed. I can imagine the huge number of tasks in the group could be a problem as well but I would like to see what are those problems first. > > The primary motivation for oom_kill_allocating_tas AFAIU was to reduce > > search over huge tasklists and reduce task_lock holding times. I am not > > sure whether the original concern is still valid since 6b0c81b (mm, > > oom: reduce dependency on tasklist_lock) as the tasklist_lock usage has > > been reduced conciderably in favor of RCU read locks is taken but maybe > > even that can be too disruptive? > > David? > > > On the other hand, from the semantic meaning of oom_kill_allocating_task, > it implies to allow suicide-like oom, which has no obvious relationship > with performance problems(such as huge task lists or task_lock holding > time). I guess that suicide-like oom in fact means "kill the poor soul that happened to charge the last". I do not see any use case for this from top of my head (appart from the performance benefits of course). > So make the sysctl be consistent with global oom will be better or set > an individual option for memcg oom just as panic_on_oom does. -- 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>