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? -- Michal Hocko SUSE Labs
