On Wed, Jan 30, 2019 at 06:11:17AM +0800, 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. > > A simple test with pref shows it may take around 220ms to iterate 8K memcgs > in direct reclaim: > dd 13873 [011] 578.542919: vmscan:mm_vmscan_direct_reclaim_begin > dd 13873 [011] 578.758689: vmscan:mm_vmscan_direct_reclaim_end > So for 400K, it may take around 11 seconds to iterate all memcgs. > > Here just break the iteration once it reclaims enough pages as what > memcg direct reclaim does. This may hurt the fairness among memcgs. But > the cached iterator cookie could help to achieve the fairness more or > less. > > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> Looks sane to me, thanks Yang. Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
