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Date: Fri, 9 Apr 2021 20:29:43 +0800 From: Muchun Song <songmuchun@...edance.com> To: guro@...com, hannes@...xchg.org, mhocko@...nel.org, akpm@...ux-foundation.org, shakeelb@...gle.com, vdavydov.dev@...il.com Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, duanxiongchun@...edance.com, fam.zheng@...edance.com, bsingharora@...il.com, shy828301@...il.com, alex.shi@...ux.alibaba.com, Muchun Song <songmuchun@...edance.com> Subject: [RFC PATCH v2 02/18] 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. Signed-off-by: Muchun Song <songmuchun@...edance.com> Acked-by: Johannes Weiner <hannes@...xchg.org> --- mm/memcontrol.c | 21 ++++++++++----------- 1 file changed, 10 insertions(+), 11 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index f229de925aa5..9cbfff59b171 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -901,20 +901,19 @@ 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. + */ + 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
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