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From: Shakeel Butt To: Waiman Long Cc: Gregory Price , 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: <7dtp6v5evpz5sdevwrexhwcdtl5enczssvuepkib2oiaexk3oo@ranij7pskrhe> References: <20250419053824.1601470-1-gourry@gourry.net> <20250419053824.1601470-3-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: agdajehtmmjf5n5is7r919pu79eefbtx X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 188BE180008 X-Rspam-User: X-HE-Tag: 1745257205-443147 X-HE-Meta: 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 Nx14zlUP Q/pH4UYPcsmjg+/SnMMOGwzqU0u80lmxEXhzFg8rGuvYH1tIE/e8U52lBQhGQV+GxS+fkiXzW5QyDCCOpBOfhZ12sVxqc4q1oWA6wWORGgSKSIBmcSK+WmU65Ap/sfje5qgGGDZwz5Trs0Nv2SDGoNwViseIlZNaiQN7W4SkIz98khu0dn+MRrTKy1vJ36Ow5aXtxEi6v1t7fhNNM3ghVko+DzP501rwcoSseMsDOfYesFkY= 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 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?