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From: Shakeel Butt To: Gregory Price 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: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 2A5751C0008 X-Stat-Signature: 7fdpdm69rgo81gikgoxtbnco1wpeqph4 X-Rspam-User: X-HE-Tag: 1745280659-827866 X-HE-Meta: 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 MC8qmy4A TSVoCYoNSIxTiITRx+xWVheOXVNOaCN05Xbesbl1BiBRH7uBlfIdcszpg6K8mV9X2Etq7I4LXT15SgR5KJRr0lcgOO2FHXR4rBlOXfoak3KgLzPhSWdixvb6WCxyAP8SWJDRQiSbH1HqCyKJ30n5yiyW2Sqw/Pgjof9ZP7C/B18JXFSKEVIuFtx9nLtSdHEIHhZDnPvTv9pqE3c04HEFLWj5KMMt/TN4+yCQNZrxhOgOUgFM= 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 07:58:44PM -0400, Gregory Price wrote: > On Mon, Apr 21, 2025 at 04:15:49PM -0700, Shakeel Butt wrote: > > On Mon, Apr 21, 2025 at 06:59:20PM -0400, Gregory Price wrote: > > > 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. > > > > For bitmaps smaller than 64 bits, it seems atomic and MAX_NUMNODES seems > > smaller than 64 in all the archs. > > Unfortunately, it's config-defined on (NODES_SHIFT) and the max is 1024. > > Is there an argument here for ignoring v1 and just doing the bit-check > without the lock? Is there an easy ifdef way for us to just return true > if it's v1? > It is !(cgroup_subsys_on_dfl(cpuset_cgrp_subsys)) and I see cpuset_v2() and is_in_v2_mode() in kernel/cgroup/cpuset.c.