On 2018/12/4 AM 1:22, Michal Hocko wrote: > 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. > Oh, I meant "offline groups" to be "offline-business groups", memcgs refered to here are all "online state" from kernel's perspective.
