Hello, On Fri, Apr 17, 2020 at 10:51:10AM -0700, Shakeel Butt wrote: > > Can you please elaborate concrete scenarios? I'm having a hard time seeing > > differences from page cache. > > Oh I was talking about the global reclaim here. In global reclaim, any > task can be throttled (throttle_direct_reclaim()). Memory freed by > using the CPU of high priority low latency jobs can be stolen by low > priority batch jobs. I'm still having a hard time following this thread of discussion, most likely because my knoweldge of mm is fleeting at best. Can you please ELI5 why the above is specifically relevant to this discussion? I'm gonna list two things that come to my mind just in case that'd help reducing the back and forth. * With protection based configurations, protected cgroups wouldn't usually go into direct reclaim themselves all that much. * We do have holes in accounting CPU cycles used by reclaim to the orgins, which, for example, prevents making memory.high reclaim async and lets memory pressure contaminate cpu isolation possibly to a significant degree on lower core count machines in some scenarios, but that's a separate issue we need to address in the future. > > cgroup A has memory.low protection and no other restrictions. cgroup B has > > no protection and has access to swap. When B's memory starts bloating and > > gets the system under memory contention, it'll start consuming swap until it > > can't. When swap becomes depleted for B, there's nothing holding it back and > > B will start eating into A's protection. > > > > In this example does 'B' have memory.high and memory.max set and by A B doesn't have anything set. > having no other restrictions, I am assuming you meant unlimited high > and max for A? Can 'A' use memory.min? Sure, it can but 1. the purpose of the example is illustrating the imcompleteness of the existing mechanism 2. there's a big difference between letting the machine hit the wall and waiting for the kernel OOM to trigger and being able to monitor the situation as it gradually develops and respond to it, which is the whole point of the low/high mechanisms. Thanks. -- tejun
