| Message ID | 1548799877-10949-1-git-send-email-yang.shi@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC,v2] mm: vmscan: do not iterate all mem cgroups for global direct reclaim | expand |
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@cmpxchg.org> > Cc: Michal Hocko <mhocko@suse.com> > Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> Looks sane to me, thanks Yang. Acked-by: Johannes Weiner <hannes@cmpxchg.org>
On Wed 30-01-19 06:11:17, 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@cmpxchg.org> > Cc: Michal Hocko <mhocko@suse.com> > Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> Acked-by: Michal Hocko <mhocko@suse.com> > --- > v2: Added some test data in the commit log > Updated commit log about iterator cookie could maintain fairness > Dropped !global_reclaim() since !current_is_kswapd() is good enough > > mm/vmscan.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index a714c4f..5e35796 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2764,16 +2764,15 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) > sc->nr_reclaimed - reclaimed); > > /* > - * Direct reclaim and kswapd have to scan all memory > - * cgroups to fulfill the overall scan target for the > - * node. > + * Kswapd have to scan all memory cgroups to fulfill > + * the overall scan target for the node. > * > * Limit reclaim, on the other hand, only cares about > * nr_to_reclaim pages to be reclaimed and it will > * retry with decreasing priority if one round over the > * whole hierarchy is not sufficient. > */ > - if (!global_reclaim(sc) && > + if (!current_is_kswapd() && > sc->nr_reclaimed >= sc->nr_to_reclaim) { > mem_cgroup_iter_break(root, memcg); > break; > -- > 1.8.3.1 >
diff --git a/mm/vmscan.c b/mm/vmscan.c index a714c4f..5e35796 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2764,16 +2764,15 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) sc->nr_reclaimed - reclaimed); /* - * Direct reclaim and kswapd have to scan all memory - * cgroups to fulfill the overall scan target for the - * node. + * Kswapd have to scan all memory cgroups to fulfill + * the overall scan target for the node. * * Limit reclaim, on the other hand, only cares about * nr_to_reclaim pages to be reclaimed and it will * retry with decreasing priority if one round over the * whole hierarchy is not sufficient. */ - if (!global_reclaim(sc) && + if (!current_is_kswapd() && sc->nr_reclaimed >= sc->nr_to_reclaim) { mem_cgroup_iter_break(root, memcg); break;
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@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.com> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> --- v2: Added some test data in the commit log Updated commit log about iterator cookie could maintain fairness Dropped !global_reclaim() since !current_is_kswapd() is good enough mm/vmscan.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)