On Mon 03-12-18 23:20:31, Xunlei Pang wrote: > On 2018/12/3 下午7:56, Michal Hocko wrote: > > On Mon 03-12-18 16:01:18, Xunlei Pang wrote: > >> There may be cgroup memory overcommitment, it will become > >> even common in the future. > >> > >> Let's enable kswapd to reclaim low-protected memory in case > >> of memory pressure, to mitigate the global direct reclaim > >> pressures which could cause jitters to the response time of > >> lantency-sensitive groups. > > > > Please be more descriptive about the problem you are trying to handle > > here. I haven't actually read the patch but let me emphasise that the > > low limit protection is important isolation tool. And allowing kswapd to > > reclaim protected memcgs is going to break the semantic as it has been > > introduced and designed. > > We have two types of memcgs: online groups(important business) > and offline groups(unimportant business). Online groups are > all configured with MAX low protection, while offline groups > are not at all protected(with default 0 low). > > When offline groups are overcommitted, the global memory pressure > suffers. This will cause the memory allocations from online groups > constantly go to the slow global direct reclaim in order to reclaim > online's page caches, as kswap is not able to reclaim low-protection > memory. low is not hard limit, it's reasonable to be reclaimed by > kswapd if there's no other reclaimable memory. I am sorry I still do not follow. What role do offline cgroups play. Those are certainly not low mem protected because mem_cgroup_css_offline will reset them to 0. -- Michal Hocko SUSE Labs
