On Wed, 23 Feb 2011, David Rientjes wrote: > On Wed, 23 Feb 2011, Andrew Morton wrote: > > > Your patch still stinks! > > > > If userspace can't handle a disabled oom-killer then userspace > > shouldn't have disabled the oom-killer. > > > > I agree, but userspace may not always be perfect especially on large > scale; we, in kernel land, can easily choose to ignore that but it's only > a problem because we're providing an interface where the memcg will > livelock without userspace intervention. The global oom killer doesn't > have this problem and for years it has even radically panicked the machine > instead of livelocking EVEN THOUGH other threads, those that are > OOM_DISABLE, may be getting work done. > > This is a memcg-specific issue because memory.oom_control has opened the > possibility up to livelock that userspace may have no way of correcting on > its own especially when it may be oom itself. The natural conclusion is > that you should never set memory.oom_control unless you can guarantee a > perfect userspace implementation that will never be unresponsive. At our > scale, we can't make that guarantee so memory.oom_control is not helpful > at all. > > If that's the case, then what else do we have at our disposal other than > memory.oom_delay_millisecs that allows us to increase a hard limit or kill > a job of lower priority other than setting memory thresholds and hoping > userspace will schedule and respond before the memcg is completely oom? > > > How do we fix this properly? > > > > A little birdie tells me that the offending userspace oom handler is > > running in a separate memcg and is not itself running out of memory. > > It depends on how you configure your memory controllers, but even if it is > running in a separate memcg how can you make the conclusion it isn't oom > in parallel? > > > The problem is that the userspace oom handler is also taking peeks into > > processes which are in the stressed memcg and is getting stuck on > > mmap_sem in the procfs reads. Correct? > > > > That's outside the scope of this feature and is a separate discussion; > this patch specifically addresses an issue where a userspace job scheduler > wants to take action when a memcg is oom before deferring to the kernel > and happens to become unresponsive for whatever reason. > > > It seems to me that such a userspace oom handler is correctly designed, > > and that we should be looking into the reasons why it is unreliable, > > and fixing them. Please tell us about this? > > > > The problem isn't specific to any one cause or implementation, we know > that userspace programs have bugs, they can stall forever in D-state, they > can be oom themselves, they get stuck waiting on a lock, etc etc. > Was there a response to this, or can this patch be merged? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>