On 23.01.2019 14:02, Michal Hocko wrote: > On Wed 23-01-19 13:28:03, Kirill Tkhai wrote: >> On 22.01.2019 23:09, Yang Shi wrote: >>> In current implementation, both kswapd and direct reclaim has to iterate >>> all mem cgroups. It is not a problem before offline mem cgroups could >>> be iterated. But, currently with iterating offline mem cgroups, it >>> could be very time consuming. In our workloads, we saw over 400K mem >>> cgroups accumulated in some cases, only a few hundred are online memcgs. >>> Although kswapd could help out to reduce the number of memcgs, direct >>> reclaim still get hit with iterating a number of offline memcgs in some >>> cases. We experienced the responsiveness problems due to this >>> occassionally. >>> >>> Here just break the iteration once it reclaims enough pages as what >>> memcg direct reclaim does. This may hurt the fairness among memcgs >>> since direct reclaim may awlays do reclaim from same memcgs. But, it >>> sounds ok since direct reclaim just tries to reclaim SWAP_CLUSTER_MAX >>> pages and memcgs can be protected by min/low. >> >> In case of we stop after SWAP_CLUSTER_MAX pages are reclaimed; it's possible >> the following situation. Memcgs, which are closest to root_mem_cgroup, will >> become empty, and you will have to iterate over empty memcg hierarchy long time, >> just to find a not empty memcg. >> >> I'd suggest, we should not lose fairness. We may introduce >> mem_cgroup::last_reclaim_child parameter to save a child >> (or its id), where the last reclaim was interrupted. Then >> next reclaim should start from this child: > > Why is not our reclaim_cookie based caching sufficient? Hm, maybe I missed them. Do cookies already implement this functionality? Kirill
