Michal Hocko wrote: > On Sat 08-07-17 13:59:54, Tetsuo Handa wrote: > [...] > > Quoting from http://lkml.kernel.org/r/20170705081956.GA14538@xxxxxxxxxxxxxx : > > Michal Hocko wrote: > > > On Sat 01-07-17 20:43:56, Tetsuo Handa wrote: > > > > You are rejecting serialization under OOM without giving a chance to test > > > > side effects of serialization under OOM at linux-next.git. I call such attitude > > > > "speculation" which you never accept. > > > > > > No I am rejecting abusing the lock for purpose it is not aimed for. > > > > Then, why adding a new lock (not oom_lock but warn_alloc_lock) is not acceptable? > > Since warn_alloc_lock is aimed for avoiding messages by warn_alloc() getting > > jumbled, there should be no reason you reject this lock. > > > > If you don't like locks, can you instead accept below one? > > No, seriously! Just think about what you are proposing. You are stalling > and now you will stall _random_ tasks even more. Some of them for > unbound amount of time because of inherent unfairness of cmpxchg. The cause of stall when oom_lock is already held is that threads which failed to hold oom_lock continue almost busy looping; schedule_timeout_uninterruptible(1) is not sufficient when there are multiple threads doing the same thing, for direct reclaim/compaction consumes a lot of CPU time. What makes this situation worse is, since warn_alloc() periodically appends to printk() buffer, the thread inside the OOM killer with oom_lock held can stall forever due to cond_resched() from console_unlock() from printk(). Below change significantly reduces possibility of falling into printk() v.s. oom_lock lockup problem, for the thread inside the OOM killer with oom_lock held no longer blocks inside printk(). Though there still remains possibility of sleeping for unexpectedly long at schedule_timeout_killable(1) with the oom_lock held. --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -1051,8 +1051,10 @@ bool out_of_memory(struct oom_control *oc) panic("Out of memory and no killable processes...\n"); } if (oc->chosen && oc->chosen != (void *)-1UL) { + preempt_disable(); oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" : "Memory cgroup out of memory"); + preempt_enable_no_resched(); /* * Give the killed process a good chance to exit before trying * to allocate memory again. I wish we could agree with applying this patch until printk-kthread can work reliably... > > If there is a _real_ problem it should be debugged and fixed. If this > is a limitation of what printk can handle then we should think how to > throttle it even more (e.g. does it make much sense to dump_stack when > it hasn't changed since the last time?). If this is about dump_stack > taking too long then we should look into it but we definitely should add > a more on top. The real problem is lack of CPU time for reclaiming memory when allocating threads failed to hold oom_lock. And you are refusing to allow allocating threads give CPU time to the thread holding oom_lock. -- 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>
