On Wed 08-06-16 06:49:24, Tetsuo Handa wrote: > Michal Hocko wrote: > > OK, so you are arming the timer for each mark_oom_victim regardless > > of the oom context. This means that you have replaced one potential > > lockup by other potential livelocks. Tasks from different oom domains > > might interfere here... > > > > Also this code doesn't even seem easier. It is surely less lines of > > code but it is really hard to realize how would the timer behave for > > different oom contexts. > > If you worry about interference, we can use per signal_struct timestamp. > I used per task_struct timestamp in my earlier versions (where per > task_struct TIF_MEMDIE check was used instead of per signal_struct > oom_victims). This would allow pre-mature new victim selection for very large victims (note that exit_mmap can take a while depending on the mm size). It also pushed the timeout heuristic for everybody which will sooner or later open a question why is this $NUMBER rathen than $NUMBER+$FOO. [...] > But expiring timeout by sleeping inside oom_kill_process() prevents other > threads which are OOM-killed from obtaining TIF_MEMDIE, for anybody needs > to wait for oom_lock in order to obtain TIF_MEMDIE. True, but please note that this will happen only for the _unlikely_ case when the mm is shared with kthread or init. All other cases would rely on the oom_reaper which has a feedback mechanism to tell the oom killer to move on if something bad is going on. > Unless you set TIF_MEMDIE to all OOM-killed threads from > oom_kill_process() or allow the caller context to use > ALLOC_NO_WATERMARKS by checking whether current was already OOM-killed > rather than TIF_MEMDIE, attempt to expiring timeout by sleeping inside > oom_kill_process() is useless. Well this is a rather strong statement for a highly unlikely corner case, don't you think? I do not mind fortifying this class of cases some more if we ever find out they are a real problem but I would rather make sure they cannot lockup at this stage rather than optimize for them. To be honest I would rather explore ways to handle kthread case (which is the only real one IMHO from the two) gracefully and made them a nonissue - e.g. enforce EFAULT on a dead mm during the kthread page fault or something similar. -- 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>