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Mon, 12 Apr 2021 23:57:57 -0700 (PDT) Received: from localhost.localdomain ([139.177.225.241]) by smtp.gmail.com with ESMTPSA id 78sm11508562pfu.40.2021.04.12.23.57.53 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 12 Apr 2021 23:57:57 -0700 (PDT) From: Muchun Song 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, fam.zheng@bytedance.com, Muchun Song Subject: [PATCH 5/7] mm: memcontrol: simplify the logic of objcg pinning memcg Date: Tue, 13 Apr 2021 14:51:51 +0800 Message-Id: <20210413065153.63431-6-songmuchun@bytedance.com> X-Mailer: git-send-email 2.21.0 (Apple Git-122) In-Reply-To: <20210413065153.63431-1-songmuchun@bytedance.com> References: <20210413065153.63431-1-songmuchun@bytedance.com> MIME-Version: 1.0 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 18470200025D X-Stat-Signature: zz9fbjcjks8grx4rge39ncjpc31t1noh Received-SPF: none (bytedance.com>: No applicable sender policy available) receiver=imf18; identity=mailfrom; envelope-from=""; helo=mail-pj1-f54.google.com; client-ip=209.85.216.54 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618297078-259698 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The obj_cgroup_release() and memcg_reparent_objcgs() are serialized by the css_set_lock. We do not need to care about objcg->memcg being released in the process of obj_cgroup_release(). So there is no need to pin memcg before releasing objcg. Remove those pinning logic to simplfy the code. There are only two places that modifies the objcg->memcg. One is the initialization to objcg->memcg in the memcg_online_kmem(), another is objcgs reparenting in the memcg_reparent_objcgs(). It is also impossible for the two to run in parallel. So xchg() is unnecessary and it is enough to use WRITE_ONCE(). Signed-off-by: Muchun Song Acked-by: Johannes Weiner --- mm/memcontrol.c | 20 ++++++-------------- 1 file changed, 6 insertions(+), 14 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 1f807448233e..42d8c0f4ab1d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -261,7 +261,6 @@ static void obj_cgroup_uncharge_pages(struct obj_cgro= up *objcg, static void obj_cgroup_release(struct percpu_ref *ref) { struct obj_cgroup *objcg =3D container_of(ref, struct obj_cgroup, refcn= t); - struct mem_cgroup *memcg; unsigned int nr_bytes; unsigned int nr_pages; unsigned long flags; @@ -291,11 +290,9 @@ static void obj_cgroup_release(struct percpu_ref *re= f) nr_pages =3D nr_bytes >> PAGE_SHIFT; =20 spin_lock_irqsave(&css_set_lock, flags); - memcg =3D obj_cgroup_memcg(objcg); if (nr_pages) obj_cgroup_uncharge_pages(objcg, nr_pages); list_del(&objcg->list); - mem_cgroup_put(memcg); spin_unlock_irqrestore(&css_set_lock, flags); =20 percpu_ref_exit(ref); @@ -330,17 +327,12 @@ static void memcg_reparent_objcgs(struct mem_cgroup= *memcg, =20 spin_lock_irq(&css_set_lock); =20 - /* Move active objcg to the parent's list */ - xchg(&objcg->memcg, parent); - css_get(&parent->css); - list_add(&objcg->list, &parent->objcg_list); - - /* Move already reparented objcgs to the parent's list */ - list_for_each_entry(iter, &memcg->objcg_list, list) { - css_get(&parent->css); - xchg(&iter->memcg, parent); - css_put(&memcg->css); - } + /* 1) Ready to reparent active objcg. */ + list_add(&objcg->list, &memcg->objcg_list); + /* 2) Reparent active objcg and already reparented objcgs to parent. */ + list_for_each_entry(iter, &memcg->objcg_list, list) + WRITE_ONCE(iter->memcg, parent); + /* 3) Move already reparented objcgs to the parent's list */ list_splice(&memcg->objcg_list, &parent->objcg_list); =20 spin_unlock_irq(&css_set_lock); --=20 2.11.0