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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-47ae9c4d68csm48905001cf.47.2025.04.21.15.59.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Apr 2025 15:59:22 -0700 (PDT) Date: Mon, 21 Apr 2025 18:59:20 -0400 From: Gregory Price To: Shakeel Butt Cc: Waiman Long , 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, muchun.song@linux.dev, tj@kernel.org, mkoutny@suse.com, akpm@linux-foundation.org Subject: Re: [PATCH v3 2/2] vmscan,cgroup: apply mems_effective to reclaim Message-ID: References: <20250419053824.1601470-1-gourry@gourry.net> <20250419053824.1601470-3-gourry@gourry.net> <7dtp6v5evpz5sdevwrexhwcdtl5enczssvuepkib2oiaexk3oo@ranij7pskrhe> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7dtp6v5evpz5sdevwrexhwcdtl5enczssvuepkib2oiaexk3oo@ranij7pskrhe> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 27EC280005 X-Stat-Signature: o7hf9k9pj3tjxzsnf8p3jbq5h9wk7n35 X-HE-Tag: 1745276364-731941 X-HE-Meta: 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 9LFRyODv UuDp0gydjrjdYzxoOWSFIyE39ms2o0J2hxdj3RGjLYaVxewm4vvofdv09b8rEgYyHNNwvq61mJirZUfXlCv6KfdxsWpNGIaZ/sxyjE5go6iZF6MuvxTUawdkFKEbWCjJ4nu7T/0EO5GykZBV/vEqJ30H7hz/ceUu8UlgzKMPS4deRaf6ZnoHAWY1ss9xA009a/A50J8BtwInin/VrTdOQSPmo4qrtM4FwiL4RNp+nmLtehjsY/5Of9FEysY2NwvX0hRVmJxuYQR/keVfwXoJrFcT7PB71D/zAkQkQDQ0M5nbR95tgUmvpOMPyoh9PD9/vf9Cn2WMyNTC+HuabGL8WgtGEnlfd3e3n5o2lQHacGj7TcT++5hyZUsPEyQ== 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 10:39:58AM -0700, Shakeel Butt wrote: > On Sat, Apr 19, 2025 at 08:14:29PM -0400, Waiman Long wrote: > > > > On 4/19/25 2:48 PM, Shakeel Butt wrote: > > > On Sat, Apr 19, 2025 at 01:38:24AM -0400, Gregory Price wrote: > > > > +bool cpuset_node_allowed(struct cgroup *cgroup, int nid) > > > > +{ > > > > + struct cgroup_subsys_state *css; > > > > + unsigned long flags; > > > > + struct cpuset *cs; > > > > + bool allowed; > > > > + > > > > + css = cgroup_get_e_css(cgroup, &cpuset_cgrp_subsys); > > > > + if (!css) > > > > + return true; > > > > + > > > > + cs = container_of(css, struct cpuset, css); > > > > + spin_lock_irqsave(&callback_lock, flags); > > > Do we really need callback_lock here? We are not modifying and I am > > > wondering if simple rcu read lock is enough here (similar to > > > update_nodemasks_hier() where parent's effective_mems is accessed within > > > rcu read lock). > > > > The callback_lock is required to ensure the stability of the effective_mems > > which may be in the process of being changed if not taken. > > Stability in what sense? effective_mems will not get freed under us > here or is there a chance for corrupted read here? node_isset() and > nodes_empty() seems atomic. What's the worst that can happen without > callback_lock? Fairly sure nodes_empty is not atomic, it's a bitmap search. ~Gregory