memcg: do not modify rstat tree for zero updates

In some situations, we may end up calling memcg_rstat_updated() with a
value of 0, which means the stat was not actually updated.  An example is
if we fail to reclaim any pages in shrink_folio_list().

Do not add the cgroup to the rstat updated tree in this case, to avoid
unnecessarily flushing it.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Yosry Ahmed <[email protected]>
Acked-by: Shakeel Butt <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Reviewed-by: Michal Koutný <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Josef Bacik <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Vasily Averin <[email protected]>
Cc: Zefan Li <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 3 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e9e79ceb9a11..3d040a5fa7a3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -619,6 +619,9 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val)
 {
 	unsigned int x;
 
+	if (!val)
+		return;
+
 	cgroup_rstat_updated(memcg->css.cgroup, smp_processor_id());
 
 	x = __this_cpu_add_return(stats_updates, abs(val));