On Wed 21-03-18 21:20:12, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Wed 21-03-18 20:35:47, Tetsuo Handa wrote: > > > Michal Hocko wrote: > > > > On Wed 21-03-18 19:39:32, Tetsuo Handa wrote: > > > > > Tetsuo Handa wrote: > > > > > > Michal Hocko wrote: > > > > > > > > But since Michal is still worrying that adding a single synchronization > > > > > > > > point into the OOM path is risky (without showing a real life example > > > > > > > > where lock_killable() in the coldest OOM path hurts), changes made by > > > > > > > > this patch will be enabled only when oom_compat_mode=0 kernel command line > > > > > > > > parameter is specified so that users can test whether their workloads get > > > > > > > > hurt by this patch. > > > > > > > > > > > > > > > Nacked with passion. This is absolutely hideous. First of all there is > > > > > > > absolutely no need for the kernel command line. That is just trying to > > > > > > > dance around the fact that you are not able to argue for the change > > > > > > > and bring reasonable arguments on the table. We definitely do not want > > > > > > > two subtly different modes for the oom handling. Secondly, and repeatedly, > > > > > > > you are squashing multiple changes into a single patch. And finally this > > > > > > > is too big of a hammer for something that even doesn't solve the problem > > > > > > > for PREEMPTIVE kernels which are free to schedule regardless of the > > > > > > > sleep or the reclaim retry you are so passion about. > > > > > > > > > > > > So, where is your version? Offload to a kernel thread like the OOM reaper? > > > > > > Get rid of oom_lock? Just rejecting my proposal makes no progress. > > > > > > > > > > > Did you come up with some idea? > > > > > Even CONFIG_PREEMPT=y, as far as I tested, v2 patch significantly reduces stalls than now. > > > > > I believe there is no valid reason not to test my v2 patch at linux-next. > > > > > > > > There are and I've mentioned them in my review feedback. > > > > > > > Where? When I tried to disable preemption while oom_lock is held, > > > you suggested not to disable preemption. Thus, I followed your feedback. > > > Now, you again complain about preemption. > > > > > > When I tried to replace only mutex_trylock() with mutex_lock_killable() in v1, > > > you said we need followup changes. Thus, I added followup changes in v2. > > > > > > What are still missing? I can't understand what you are saying. > > > > http://lkml.kernel.org/r/20180302141000.GB12772@xxxxxxxxxxxxxx > > > > There are several points I really disliked. Ignoring them is not going > > to move this work forward. > > "And finally this is too big of a hammer for something that even doesn't solve > the problem for PREEMPTIVE kernels which are free to schedule regardless of the > sleep or the reclaim retry you are so passion about." is not a problem, for > preemption is there in the hope that preemption allows processes to do something > useful. But current code allows processes to simply waste CPU resources by > pointless direct reclaim and prevents the owner of oom_lock from making progress > (i.e. AB-BA deadlock). > > "Secondly, and repeatedly, you are squashing multiple changes into a single > patch." is a result of your feedback "This is not a solution without further > steps." While v2 patch will need to be split into multiple patches when merging, > you should give feedback based on what changes are missing. Doing multiple changes > into a single patch can be a reason not to merge but can not be a reason not to > test these changes. > > "We definitely do not want two subtly different modes for the oom handling." is > not there in v2 patch. > > If you say "you are not able to argue for the change and bring reasonable arguments > on the table.", please show us your arguments which is better than mine. Nothing can > justify current code (i.e. AB-BA deadlock). I'm asking your arguments by > "So, where is your version?" This is just a waste of time. I am off from this thread. My nack still holds and you should seriously reconsider the way you take the review feedback. -- Michal Hocko SUSE Labs
