mm/memcontrol.c: remove the redundant updating of stats_flush_threshold

Remove the redundant updating of stats_flush_threshold.  If the global var
stats_flush_threshold has exceeded the trigger value for
__mem_cgroup_flush_stats, further increment is unnecessary.

Apply the patch and test the pts/hackbench-1.0.0 Count:4 (160 threads).

Score gain: 1.95x
Reduce CPU cycles in __mod_memcg_lruvec_state (44.88% -> 0.12%)

CPU: ICX 8380 x 2 sockets
Core number: 40 x 2 physical cores
Benchmark: pts/hackbench-1.0.0 Count:4 (160 threads)

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Jiebin Sun <[email protected]>
Acked-by: Shakeel Butt <[email protected]>
Reviewed-by: Roman Gushchin <[email protected]>
Reviewed-by: Tim Chen <[email protected]>
Acked-by: Muchun Song <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Amadeusz Sawiski <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 8 insertions, 1 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2b831cc48c7d..c65751ab4516 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -626,7 +626,14 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val)
 
 	x = __this_cpu_add_return(stats_updates, abs(val));
 	if (x > MEMCG_CHARGE_BATCH) {
-		atomic_add(x / MEMCG_CHARGE_BATCH, &stats_flush_threshold);
+		/*
+		 * If stats_flush_threshold exceeds the threshold
+		 * (>num_online_cpus()), cgroup stats update will be triggered
+		 * in __mem_cgroup_flush_stats(). Increasing this var further
+		 * is redundant and simply adds overhead in atomic update.
+		 */
+		if (atomic_read(&stats_flush_threshold) <= num_online_cpus())
+			atomic_add(x / MEMCG_CHARGE_BATCH, &stats_flush_threshold);
 		__this_cpu_write(stats_updates, 0);
 	}
 }