On Fri 24-04-20 09:44:38, Johannes Weiner wrote: > On Fri, Apr 24, 2020 at 09:14:52AM -0400, Johannes Weiner wrote: > > However, mem_cgroup_protected() never expected anybody to look at the > > effective protection values when it indicated that the cgroup is above > > its protection. As a result, a query during limit reclaim may return > > stale protection values that were calculated by a previous reclaim > > cycle in which the cgroup did have siblings. > > Btw, I think there is opportunity to make this a bit less error prone. > > We have a mem_cgroup_protected() that returns yes or no, essentially, > but protection isn't a binary state anymore. > > It's also been a bit iffy that it looks like a simple predicate > function, but it indeed needs to run procedurally for each cgroup in > order for the calculations throughout the tree to be correct. > > It might be better to have a > > mem_cgroup_calculate_protection() > > that runs for every cgroup we visit and sets up the internal state; > then have more self-explanatory query functions on top of that: > > mem_cgroup_below_min() > mem_cgroup_below_low() > mem_cgroup_protection() > > What do you guys think? Fully agreed. I have to say that I have considered the predicate with side effects really confusing. -- Michal Hocko SUSE Labs
