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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-930f6a6c1efsm160195685a.38.2026.07.22.06.19.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jul 2026 06:19:28 -0700 (PDT) Date: Wed, 22 Jul 2026 09:19:23 -0400 From: Gregory Price To: Richard Cheng Cc: linux-mm@kvack.org, Zhigang.Luo@amd.com, arun.george@samsung.com, balbirs@nvidia.com, brendan.jackman@linux.dev, yuzenghui@huawei.com, apopple@nvidia.com, alucerop@amd.com, matthew.brost@intel.com, akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, skhan@linuxfoundation.org, gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, djbw@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, alison.schofield@intel.com, osandov@osandov.com, jannh@google.com, pfalcato@suse.de, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, pbonzini@redhat.com, osalvador@suse.de, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, kasong@tencent.com, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, yury.norov@gmail.com, linux@rasmusvillemoes.dk, longman@redhat.com, ridong.chen@linux.dev, tj@kernel.org, mkoutny@suse.com, sj@kernel.org, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, lance.yang@linux.dev, usama.arif@linux.dev, xu.xin16@zte.com.cn, chengming.zhou@linux.dev, roman.gushchin@linux.dev, muchun.song@linux.dev, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, driver-core@lists.linux.dev, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-debuggers@vger.kernel.org, linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, cgroups@vger.kernel.org, damon@lists.linux.dev, linux-kselftest@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v5 05/36] mm: add ZONELIST_PRIVATE(_NOFALLBACK) for N_MEMORY_PRIVATE nodes. Message-ID: References: <20260720193431.3841992-1-gourry@gourry.net> <20260720193431.3841992-6-gourry@gourry.net> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Jul 22, 2026 at 09:00:51PM +0800, Richard Cheng wrote: > On Mon, Jul 20, 2026 at 03:33:59PM +0800, Gregory Price wrote: > > static void build_zonelists(pg_data_t *pgdat) > > { > > static int node_order[MAX_NUMNODES]; > > + nodemask_t tier_nodes; > > int local_node = pgdat->node_id; > > int node, nr_nodes = 0; > > > > memset(node_order, 0, sizeof(node_order)); > > > > + /* > > + * Zonelists: FALLBACK, NOFALLBACK, PRIVATE > > + * > > + * FALLBACK: Allocation order for all nodes. Private nodes have lists > > + * but never appear as an entry in any list. Allocations > > + * targeting a private node w/ FALLBACK land on N_MEMORY. > > + * > > + * NOFALLBACK: A list for each node containing only itself. > > + * Allocations targeting a private node w/ NOFALLBACK > > + * will always fail (their NOFALLBACK is empty) > > + * > > + * PRIVATE: (N_MEMORY | N_MEMORY_PRIVATE) - allows access to > > + * private nodes, and falls back to normal memory unless > > + * __GFP_THISNODE otherwise constrains it. > > + */ > > + > > build_node_zonelist(pgdat, &node_states[N_MEMORY], ZONELIST_FALLBACK, > > true, node_order, &nr_nodes); > > build_thisnode_zonelists(pgdat); > > @@ -5912,6 +5957,10 @@ static void build_zonelists(pg_data_t *pgdat) > > for (node = 0; node < nr_nodes; node++) > > pr_cont("%d ", node_order[node]); > > pr_cont("\n"); > > + > > + nodes_or(tier_nodes, node_states[N_MEMORY], node_states[N_MEMORY_PRIVATE]); > > Hi Gregory, > > A question about this part, if my understanding is right, > ZONELIST_PRIVATE contains all private nodes, should we use some explicit target > nodemask here to make sure only the targeting owner's private node can be touched? > > Otherwise it might fall back into a different owner's private node. > > --Richard > Zonelists and the constructors here is a bit difficult to understand, and I see I actually did a poor job of explaining what's going on in the comments here. I will fix that up in v6. Lets say we have the following nodes: N_MEMORY : 0 1 N_MEMORY_PRIVATE : 2 3 The following zonelists would exist: ZONELIST_FALLBACK[0] = {0,1} ZONELIST_FALLBACK[1] = {1,0} ZONELIST_FALLBACK[2] = {0,1} ZONELIST_FALLBACK[3] = {0,1} ZONELIST_NOFALLBACK[0] = {0} ZONELIST_NOFALLBACK[1] = {1} ZONELIST_NOFALLBACK[2] = {} ZONELIST_NOFALLBACK[3] = {} ZONELIST_PRIVATE[0] = {0,1} ZONELIST_PRIVATE[1] = {1,0} ZONELIST_PRIVATE[2] = {2,0,1} <- no fallback to 3 ZONELIST_PRIVATE[3] = {3,0,1} <- no fallback to 2 ZONELIST_PRIVATE_NOFALLBACK[0] = {0} ZONELIST_PRIVATE_NOFALLBACK[1] = {1} ZONELIST_PRIVATE_NOFALLBACK[2] = {2} <- __GFP_THISNODE ZONELIST_PRIVATE_NOFALLBACK[3] = {3} <- __GFP_THISNODE In the current design, we actually can never fallback to another private node, and instead if you wanted to - for example - interleave across said nodes you'd have to do so manually. I think it's reasonable to later extend zonelist construction to support such a think like: ZONELIST_PRIVATE[2] = {2,0,1,3} Later if such a need arises, but I would say wait for the use case. ~Gregory