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[67.212.218.66]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c9282cca4esm232635685a.50.2025.04.19.17.14.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 19 Apr 2025 17:14:31 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: Date: Sat, 19 Apr 2025 20:14:29 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/2] vmscan,cgroup: apply mems_effective to reclaim To: Shakeel Butt , Gregory Price 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, muchun.song@linux.dev, tj@kernel.org, mkoutny@suse.com, akpm@linux-foundation.org References: <20250419053824.1601470-1-gourry@gourry.net> <20250419053824.1601470-3-gourry@gourry.net> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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. Cheers, Longman > >> + /* On v1 effective_mems may be empty, simply allow */ >> + allowed = node_isset(nid, cs->effective_mems) || >> + nodes_empty(cs->effective_mems); >> + spin_unlock_irqrestore(&callback_lock, flags); >> + css_put(css); >> + return allowed; >> +}