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/20230330191801.1967435-9-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Michal Koutný <mkoutny@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vasily Averin <vasily.averin@linux.dev>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e9e79ceb9a11a1f2daba3aa780e6e8841062c09c..3d040a5fa7a35332be2e850a1cc10ab460bdf580 100644 (file)
--- 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));