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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8c0973f0807sm1195174785a.41.2025.12.23.17.20.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Dec 2025 17:20:08 -0800 (PST) Date: Tue, 23 Dec 2025 20:19:32 -0500 From: Gregory Price To: Bing Jiao Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, longman@redhat.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, david@kernel.org, zhengqi.arch@bytedance.com, lorenzo.stoakes@oracle.com, axelrasmussen@google.com, chenridong@huaweicloud.com, yuanchu@google.com, weixugc@google.com, cgroups@vger.kernel.org Subject: Re: [PATCH v3] mm/vmscan: fix demotion targets checks in reclaim/demotion Message-ID: References: <20251221233635.3761887-1-bingjiao@google.com> <20251223212032.665731-1-bingjiao@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251223212032.665731-1-bingjiao@google.com> On Tue, Dec 23, 2025 at 09:19:59PM +0000, Bing Jiao wrote: > -static inline bool cpuset_node_allowed(struct cgroup *cgroup, int nid) > +static inline nodemask_t cpuset_node_get_allowed(struct cgroup *cgroup) > { > - return true; > + return node_possible_map; ... > -static inline bool mem_cgroup_node_allowed(struct mem_cgroup *memcg, int nid) > +static inline nodemask_t mem_cgroup_node_get_allowed(struct mem_cgroup *memcg) > { > - return true; > + return node_possible_map; > } ... > -bool cpuset_node_allowed(struct cgroup *cgroup, int nid) > +nodemask_t cpuset_node_get_allowed(struct cgroup *cgroup) > { > + nodemask_t nodes = node_possible_map; ... > -bool mem_cgroup_node_allowed(struct mem_cgroup *memcg, int nid) > +nodemask_t mem_cgroup_node_get_allowed(struct mem_cgroup *memcg) > { > - return memcg ? cpuset_node_allowed(memcg->css.cgroup, nid) : true; > + if (memcg) > + return cpuset_node_get_allowed(memcg->css.cgroup); > + return node_possible_map; > } node_possible_map or node_states[N_MEMORY]? The latter seems more appropriate to me since node_possible_map will include offline nodes. > - allowed = node_isset(nid, cs->effective_mems); > + nodes_copy(nodes, cs->effective_mems); > css_put(css); > - return allowed; > + return nodes; > } I saw in vmscan you check for returning an empty nodemask, may want to at least add a comment to the function definition that says this needs to be checked. > diff --git a/mm/vmscan.c b/mm/vmscan.c > index a4b308a2f9ad..711a04baf258 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -345,18 +345,24 @@ static bool can_demote(int nid, struct scan_control *sc, > struct mem_cgroup *memcg) > { > int demotion_nid; > + struct pglist_data *pgdat = NODE_DATA(nid); > + nodemask_t allowed_mask, allowed_mems; Only other concern i have is the number of nodemasks being added to the stack. Should be <512 bytes, but I've run into situations where builds have screamed at me for adding one nodemask to the stack, let alone 3+. Have you run this through klp? ~Gregory