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[34.125.132.248]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a2f3c87845sm214750925ad.39.2025.12.26.10.58.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Dec 2025 10:58:47 -0800 (PST) Date: Fri, 26 Dec 2025 18:58:42 +0000 From: Bing Jiao To: Chen Ridong Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, gourry@gourry.net, 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, 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> <646ee1fa-edd1-4588-9720-c3c1df8ebce5@huaweicloud.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: <646ee1fa-edd1-4588-9720-c3c1df8ebce5@huaweicloud.com> On Wed, Dec 24, 2025 at 09:49:38AM +0800, Chen Ridong wrote: > > +nodemask_t cpuset_node_get_allowed(struct cgroup *cgroup) > > { > > Could we define it as: > > void cpuset_node_get_allowed(struct cgroup *cgroup, nodemask_t *node) > > to align with the naming style of node_get_allowed_targets? > > > -bool mem_cgroup_node_allowed(struct mem_cgroup *memcg, int nid) > > +nodemask_t mem_cgroup_node_get_allowed(struct mem_cgroup *memcg) > > void mem_cgroup_node_get_allowed(struct mem_cgroup *memcg, nodemask_t *node) Thanks for the suggestion. Pass a pointer is better. Also, Gregory mentioned that the stack size may be an issue if systems have many nodes. Do you think it is better to use mem_cgroup_node_filter_allowed() to keep the stack size smaller? > > - demotion_nid = next_demotion_node(nid); > > - if (demotion_nid == NUMA_NO_NODE) > > + node_get_allowed_targets(pgdat, &allowed_mask); > > + if (nodes_empty(allowed_mask)) > > + return false; This is a fast-fail path. When the queried node is the farthest node, allowed_mask will be empty. Thus, I would like to keep this check before mem_cgroup_node_get_allowed(). > > + > > + allowed_mems = mem_cgroup_node_get_allowed(memcg); > > + nodes_and(allowed_mask, allowed_mask, allowed_mems); > > + if (nodes_empty(allowed_mask)) > > return false; > > > node_get_allowed_targets(pgdat, &allowed_mask); > mem_cgroup_node_get_allowed(memcg, allowed_mems); > if (!nodes_intersects(allowed_mask, allowed_mems)) > return false; > > Would it look better? Yes, nodes_intersects() is better than logic-and. Will update in v3. Best, Bing