The patch titled
Subject: mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm
has been removed from the -mm tree. Its filename was
mm-memcontrol-bail-out-early-when-mm-in-get_mem_cgroup_from_mm.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Subject: mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm
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.
Link: https://lkml.kernel.org/r/20210417043538.9793-3-songmuchun@xxxxxxxxxxxxx
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)
--- a/mm/memcontrol.c~mm-memcontrol-bail-out-early-when-mm-in-get_mem_cgroup_from_mm
+++ a/mm/memcontrol.c
@@ -919,20 +919,23 @@ struct mem_cgroup *get_mem_cgroup_from_m
if (mem_cgroup_disabled())
return NULL;
+ /*
+ * Page cache insertions can happen without an
+ * actual mm context, e.g. during disk probing
+ * on boot, loopback IO, acct() writes etc.
+ *
+ * No need to css_get on root memcg as the reference
+ * counting is disabled on the root level in the
+ * cgroup core. See CSS_NO_REF.
+ */
+ if (unlikely(!mm))
+ return root_mem_cgroup;
+
rcu_read_lock();
do {
- /*
- * Page cache insertions can happen without 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;
_
Patches currently in -mm which might be from songmuchun@xxxxxxxxxxxxx are
