On Tue 24-07-18 07:49:40, Tejun Heo wrote: > Hello, Michal. > > On Tue, Jul 24, 2018 at 04:43:51PM +0200, Michal Hocko wrote: [...] > > So IMHO the best option would be to simply inherit the group_oom to > > children. This would allow users to do their weird stuff but the default > > configuration would be consistent. > > Persistent config inheritance is a big no no. It really sucks because > it makes the inherited state sticky and there's no way of telling why > the current setting is the way it is without knowing the past > configurations of the hierarchy. We actually had a pretty bad > incident due to memcg swappiness inheritance recently (top level > cgroups would inherit sysctl swappiness during boot before sysctl > initialized them and then post-boot it isn't clear why the settings > are the way they're). > > Nothing in cgroup2 does persistent inheritance. If something explicit > is necessary, we do .effective so that the effective config is clearly > visible. > > > A more restrictive variant would be to disallow changing children to > > mismatch the parent oom_group == 1. This would have a slight advantage > > that those users would get back to us with their usecases and we can > > either loose the restriction or explain that what they are doing is > > questionable and help with a more appropriate configuration. > > That's a nack too because across delegation, from a child pov, it > isn't clear why it can't change configs and it's also easy to > introduce a situation where a child can lock its ancestors out of > chanding their configs. OK, fair points. I will keep thinking about this some more. I still cannot shake a bad feeling about the semantic and how poor users are going to scratch their heads what the heck is going on here. I will follow up in other email where we are discussing both options once I am able to sort this out myself. -- Michal Hocko SUSE Labs
