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Subject[PATCH 3/4] mm: memcontrol: bail out early when id is zero
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The memcg ID cannot be zero, but we can pass zero to mem_cgroup_from_id,
so idr_find() is pointless and wastes CPU cycles.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
mm/memcontrol.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a3f26522765a..68ed4b297c13 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5173,6 +5173,9 @@ static inline void mem_cgroup_id_put(struct mem_cgroup *memcg)
struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
{
WARN_ON_ONCE(!rcu_read_lock_held());
+ /* The memcg ID cannot be zero. */
+ if (id == 0)
+ return NULL;
return idr_find(&mem_cgroup_idr, id);
}

--
2.11.0
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