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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c925b6e198sm500347285a.103.2025.04.21.21.07.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Apr 2025 21:07:09 -0700 (PDT) Date: Tue, 22 Apr 2025 00:07:08 -0400 From: Gregory Price To: Waiman Long Cc: linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, tj@kernel.org, mkoutny@suse.com, akpm@linux-foundation.org Subject: Re: [PATCH v4 2/2] vmscan,cgroup: apply mems_effective to reclaim Message-ID: References: <20250422012616.1883287-1-gourry@gourry.net> <20250422012616.1883287-3-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: tkotzmedp7unehqixpjhfba4jssifr4c X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 4E6DE1C000B X-Rspam-User: X-HE-Tag: 1745294831-333801 X-HE-Meta: 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 LpkGMIko 6FOcdB9zzVH28bxGJITMGal7gUOGVdU/pm2rMn09NRp/lJESBTkSHEwzI4orTt6CqgkghjnzeUCZhBG6hsbVOj+Ehfucm+e4BCERp4/058T/oAfHgIwxitsjUM9LO2+XaFxGCRGM/QyDCLB9rWImkJ+EWj2vHCq0+xhwS65gmxH0cgXoi6X8AkooN2Ak7IHMSi0ASTahFdDu3MOgnylpjPrmnqTI/0yJoX2EWT89nZhT0dlpq+EdPVMlZNpF/i2Vkj6Q88sbzDlmfc0fzL7YEQ3IyiGgKxYGeq1EznfCOth+Me3o7Qf2jV1PzLuAr2r/uSwQk5dhoW7iu4YSFW/4VOwTN6kM4fAzkScKqr5j9YTH7f/IAsMR91FIXBA== 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: List-Subscribe: List-Unsubscribe: On Mon, Apr 21, 2025 at 10:02:22PM -0400, Waiman Long wrote: > > +bool cpuset_node_allowed(struct cgroup *cgroup, int nid) > > +{ > > + struct cgroup_subsys_state *css; > > + struct cpuset *cs; > > + bool allowed; > > + > > + /* > > + * In v1, mem_cgroup and cpuset are unlikely in the same hierarchy > > + * and mems_allowed is likely to be empty even if we could get to it, > > + * so return true to avoid taking a global lock on the empty check. > > + */ > > + if (!cpuset_v2()) > > + return true; > > + > > + css = cgroup_get_e_css(cgroup, &cpuset_cgrp_subsys); > > + if (!css) > > + return true; > > + > > + cs = container_of(css, struct cpuset, css); > > + rcu_read_lock(); > > Sorry, I missed the fact that cgroup_get_e_css() will take a reference to > the css and so it won't go away. In that case, rcu_read_lock() isn't really > needed. However, I do want a comment to say that accessing effective_mems > should normally requrie taking either a cpuset_mutex or callback_lock, but > is skipped in this case to avoid taking a global lock in the reclaim path at > the expense that the result may be inaccurate in some rare cases. > I'll add a differential patch here. ~Gregory