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[34.125.132.248]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a2f3c828dbsm208456505ad.22.2025.12.26.10.48.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Dec 2025 10:48:25 -0800 (PST) Date: Fri, 26 Dec 2025 18:48:20 +0000 From: Bing Jiao To: Gregory Price 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: On Tue, Dec 23, 2025 at 08:19:32PM -0500, Gregory Price wrote: > On Tue, Dec 23, 2025 at 09:19:59PM +0000, Bing Jiao wrote: > > -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. Yes, I agree that node_states[N_MEMORY] would be better. > > - 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. Will add a comment to say that it may return an empty nodemask. > > 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+. While having 3+ nodemasks presents a risk, utilizing two nodemasks should be acceptable. Given that the maximum number of nodes is 1024 (2^10), two nodemasks would require 256 bytes, which should be okay. Otherwise, we can keep to use mem_node_filter_allowed(). Only update it to return a nodemask when subsequent features need. > Have you run this through klp? I have not run it through klp. Will do it then. Thanks, Bing