On Mon, Nov 26, 2012 at 09:08:48PM +0100, Michal Hocko wrote: > On Mon 26-11-12 14:29:41, Johannes Weiner wrote: > > On Mon, Nov 26, 2012 at 08:03:29PM +0100, Michal Hocko wrote: > > > On Mon 26-11-12 13:24:21, Johannes Weiner wrote: > > > > On Mon, Nov 26, 2012 at 07:04:44PM +0100, Michal Hocko wrote: > > > > > On Mon 26-11-12 12:46:22, Johannes Weiner wrote: > > > [...] > > > > > > I think global oom already handles this in a much better way: invoke > > > > > > the OOM killer, sleep for a second, then return to userspace to > > > > > > relinquish all kernel resources and locks. The only reason why we > > > > > > can't simply change from an endless retry loop is because we don't > > > > > > want to return VM_FAULT_OOM and invoke the global OOM killer. > > > > > > > > > > Exactly. > > > > > > > > > > > But maybe we can return a new VM_FAULT_OOM_HANDLED for memcg OOM and > > > > > > just restart the pagefault. Return -ENOMEM to the buffered IO syscall > > > > > > respectively. This way, the memcg OOM killer is invoked as it should > > > > > > but nobody gets stuck anywhere livelocking with the exiting task. > > > > > > > > > > Hmm, we would still have a problem with oom disabled (aka user space OOM > > > > > killer), right? All processes but those in mem_cgroup_handle_oom are > > > > > risky to be killed. > > > > > > > > Could we still let everybody get stuck in there when the OOM killer is > > > > disabled and let userspace take care of it? > > > > > > I am not sure what exactly you mean by "userspace take care of it" but > > > if those processes are stuck and holding the lock then it is usually > > > hard to find that out. Well if somebody is familiar with internal then > > > it is doable but this makes the interface really unusable for regular > > > usage. > > > > If oom_kill_disable is set, then all processes get stuck all the way > > down in the charge stack. Whatever resource they pin, you may > > deadlock on if you try to touch it while handling the problem from > > userspace. > > OK, I guess I am getting what you are trying to say. So what you are > suggesting is to just let mem_cgroup_out_of_memory send the signal and > move on without retry (or with few charge retries without further OOM > killing) and fail the charge with your new FAULT_OOM_HANDLED (resp. > something like FAULT_RETRY) error code resp. ENOMEM depending on the > caller. OOM disabled case would be "you are on your own" because this > has been dangerous anyway. Correct? Yes. > I do agree that the current endless retry loop is far from being ideal > and can see some updates but I am quite nervous about any potential > regressions in this area (e.g. too aggressive OOM etc...). I have to > think about it some more. Agreed on all points. Maybe we can keep a couple of the oom retry iterations or something like that, which is still much more than what global does and I don't think the global OOM killer is overly eager. Testing will show more. > Anyway if you have some more specific ideas I would be happy to review > patches. Okay, I just wanted to check back with you before going down this path. What are we going to do short term, though? Do you want to push the disable-oom-for-pagecache for now or should we put the VM_FAULT_OOM_HANDLED fix in the next version and do stable backports? This issue has been around for a while so frankly I don't think it's urgent enough to rush things. -- 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>