From: Muchun Song <songmuchun@bytedance.com>
To: guro@fb.com, hannes@cmpxchg.org, mhocko@kernel.org,
akpm@linux-foundation.org, shakeelb@google.com,
vdavydov.dev@gmail.com
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
duanxiongchun@bytedance.com,
Muchun Song <songmuchun@bytedance.com>,
Michal Hocko <mhocko@suse.com>
Subject: [PATCH v3 2/8] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm
Date: Sat, 17 Apr 2021 12:35:32 +0800 [thread overview]
Message-ID: <20210417043538.9793-3-songmuchun@bytedance.com> (raw)
In-Reply-To: <20210417043538.9793-1-songmuchun@bytedance.com>
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@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
mm/memcontrol.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f229de925aa5..50e3cf1e263e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -901,20 +901,23 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
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;
--
2.11.0
next prev parent reply other threads:[~2021-04-17 4:38 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-17 4:35 [PATCH v3 0/8] memcontrol code cleanup and simplification Muchun Song
2021-04-17 4:35 ` [PATCH v3 1/8] mm: memcontrol: fix page charging in page replacement Muchun Song
2021-04-17 4:35 ` Muchun Song [this message]
2021-04-17 4:35 ` [PATCH v3 3/8] mm: memcontrol: remove the pgdata parameter of mem_cgroup_page_lruvec Muchun Song
2021-04-17 4:35 ` [PATCH v3 4/8] mm: memcontrol: simplify lruvec_holds_page_lru_lock Muchun Song
2021-04-17 4:35 ` [PATCH v3 5/8] mm: memcontrol: rename lruvec_holds_page_lru_lock to page_matches_lruvec Muchun Song
2021-04-17 4:35 ` [PATCH v3 6/8] mm: memcontrol: simplify the logic of objcg pinning memcg Muchun Song
2021-04-17 4:35 ` [PATCH v3 7/8] mm: memcontrol: move obj_cgroup_uncharge_pages() out of css_set_lock Muchun Song
2021-04-17 4:35 ` [PATCH v3 8/8] mm: vmscan: remove noinline_for_stack Muchun Song
2021-04-26 7:49 ` [PATCH v3 0/8] memcontrol code cleanup and simplification Muchun Song
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