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? 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. Anyway if you have some more specific ideas I would be happy to review patches. [...] Thanks -- 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>