On Mon 25-11-19 22:11:15, Yafang Shao wrote: > On Mon, Nov 25, 2019 at 8:45 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > On Mon 25-11-19 20:37:52, Yafang Shao wrote: > > > On Mon, Nov 25, 2019 at 8:31 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: [...] > > > > Again, what is a problem that you are trying to fix? > > > > > > When there's no processes running in a memcg, for example if they are > > > killed by OOM killer, we can't reclaim the file page cache protected > > > by memory.min of this memcg. These file page caches are useless in > > > this case. > > > That's what I'm trying to fix. > > > > Could you be more specific please? I would assume that the group oom > > configured memcg would either restart its workload when killed (that is > > why you want to kill the whole workload to restart it cleanly in many > > case) or simply tear down the memcg altogether. > > > > Yes, we always restart it automatically if these processes are exit > (no matter because of OOM or some other reason). > It is safe to do that if OOM happens, because OOM is always because of > anon pages leaked and the restart can free these anon pages. No this is an incorrect assumption. The OOM might happen for many different reasons. > But there may be some cases that we can't success to restart it, while > if that happens the protected pages will be never be reclaimed until > the admin reset it or make this memcg offline. If the workload cannot be restarted for whatever reason then you need an admin intervention and a proper cleanup. That would include resetting reclaim protection when in use. > When there're no processes, we don't need to protect the pages. You > can consider it as 'fault tolerance' . I have already tried to explain why this is a bold statement that doesn't really hold universally and that the kernel doesn't really have enough information to make an educated guess. > > In other words why do you care about the oom killer case so much? It is > > not different that handling a lingering memcg with the workload already > > finished. You simply have no way to know whether the reclaim protection > > is still required. Admin is supposed to either offline the memcg that is > > no longer used or drop the reclaim protection once it is not needed > > because that has some visible consequences on the overall system > > operation. > > Actually what I concern is the case that there's no process running > but memory protection coninues protecting the file pages. > OOM is just one case of them. This sounds like a misconfiguration which should be handled by an admin. -- Michal Hocko SUSE Labs
