On Mon, Nov 25, 2019 at 10:21 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > 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. > I didn't mean we must relcaim the protected pages in all cases, while I mean sometimes we should relcaim the protected pages. If the kernel can't make an educated guess, we can tell the kernel to do it, for example, to introduce a new controller file to tell the kernel whehter or not relcaim the protected pages if there're no proceses running. > > > 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. That may be a misconfiguration, but the kernel can do something before the admin notice it. Thanks Yafang
