When mm is NULL, we do not need to hold rcu lock and call css_tryget for
the root memcg. And we also do not need to check !mm in every loop of
while. So bail out early when !mm.
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
mm/memcontrol.c | 21 ++++++++++-----------
1 file changed, 10 insertions(+), 11 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d0c4f6e91e17..48e4c20bf115 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1029,20 +1029,19 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
if (mem_cgroup_disabled())
return NULL;
+ /*
+ * Page cache insertions can happen withou an
+ * actual mm context, e.g. during disk probing
+ * on boot, loopback IO, acct() writes etc.
+ */
+ if (unlikely(!mm))
+ return root_mem_cgroup;
+
rcu_read_lock();
do {
- /*
- * Page cache insertions can happen withou an
- * actual mm context, e.g. during disk probing
- * on boot, loopback IO, acct() writes etc.
- */
- if (unlikely(!mm))
+ memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
+ if (unlikely(!memcg))
memcg = root_mem_cgroup;
- else {
- memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
- if (unlikely(!memcg))
- memcg = root_mem_cgroup;
- }
} while (!css_tryget(&memcg->css));
rcu_read_unlock();
return memcg;
--
2.11.0
