On Wed 23-01-19 14:05:28, Kirill Tkhai wrote: > 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?
Have a look at mem_cgroup_iter -- Michal Hocko SUSE Labs
