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Fri, 02 Apr 2021 08:08:40 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::1:8ca7]) by smtp.gmail.com with ESMTPSA id 75sm7322604qkd.114.2021.04.02.08.08.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Apr 2021 08:08:39 -0700 (PDT) Date: Fri, 2 Apr 2021 11:08:38 -0400 From: Johannes Weiner To: Muchun Song Cc: guro@fb.com, mhocko@kernel.org, akpm@linux-foundation.org, shakeelb@google.com, vdavydov.dev@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, duanxiongchun@bytedance.com Subject: Re: [RFC PATCH 02/15] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm Message-ID: References: <20210330101531.82752-1-songmuchun@bytedance.com> <20210330101531.82752-3-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210330101531.82752-3-songmuchun@bytedance.com> X-Rspamd-Queue-Id: 0FAE66000117 X-Stat-Signature: uu79xhnfg13ps6qoqk4sgsyc7f5azhyt X-Rspamd-Server: rspam02 Received-SPF: none (cmpxchg.org>: No applicable sender policy available) receiver=imf09; identity=mailfrom; envelope-from=""; helo=mail-qv1-f54.google.com; client-ip=209.85.219.54 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617376119-600493 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: On Tue, Mar 30, 2021 at 06:15:18PM +0800, Muchun Song wrote: > 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 Good observation. Acked-by: Johannes Weiner