CCing Yosry, Muchun & Johannes On Tue, Jul 12, 2022 at 2:52 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Tue 12-07-22 16:39:48, Yafang Shao wrote: > > On Tue, Jul 12, 2022 at 3:40 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > [...] > > > > Roman already sent reparenting fix: > > > > https://patchwork.kernel.org/project/netdevbpf/patch/20220711162827.184743-1-roman.gushchin@xxxxxxxxx/ > > > > > > Reparenting is nice but not a silver bullet. Consider a shallow > > > hierarchy where the charging happens in the first level under the root > > > memcg. Reparenting to the root is just pushing everything under the > > > system resources category. > > > > > > > Agreed. That's why I don't like reparenting. > > Reparenting just reparent the charged pages and then redirect the new > > charge, but can't reparents the 'limit' of the original memcg. > > So it is a risk if the original memcg is still being charged. We have > > to forbid the destruction of the original memcg. > > yes, I was toying with an idea like that. I guess we really want a > measure to keep cgroups around if they are bound to a resource which is > sticky itself. I am not sure how many other resources like BPF (aka > module like) we already do charge for memcg but considering the > potential memory consumption just reparenting will not help in general > case I am afraid. Another very obvious example is the filesystem shared between multiple jobs. We had a similar discussion [1] on LRU reparenting patch series. For this use-case internally we have a memcg= mount option where the given memcg is the common ancestor (think of pod in k8s environment) of the jobs who are sharing the filesystem. [1] https://lore.kernel.org/all/20210330101531.82752-1-songmuchun@xxxxxxxxxxxxx/
