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Wed, 12 Aug 2026 18:21:10 -0700 (PDT) Date: Wed, 12 Aug 2026 21:21:04 -0400 From: Gregory Price To: Pankaj Gupta 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, "Gupta, Pankaj" Subject: Re: [PATCH v5 00/36] Private Memory NUMA Nodes Message-ID: References: <20260720193431.3841992-1-gourry@gourry.net> 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 Wed, Aug 12, 2026 at 02:01:12PM +0200, Pankaj Gupta wrote: > > > > Bonus Configuration: HBM device memory tiering > > ============================================== > > echo 1 > dax0.0/private # make the node private > > echo 0 > dax0.0/adistance # highest tier > > echo 1 > dax0.0/reclaim # reclaim active > > echo 1 > dax0.0/demotion # may demote from the node > > echo 1 > dax0.0/user_numa # mbind() > > echo online_movable > dax0.0/state > > echo 1 > numa/demotion_enabled > > I am bit confused by the HBM device example being discovered as a DAX > device. Is it to > only to showcase the use-case? Or we see HBM device is actually > expected to be discovered as > DAX device with N_MEMORY_PRIVATE? > "actually expected to be" -> no. there's no requirement HBM be discovered and boudn to DAX, DAX is simply a convenient intermediary to memory-hotplug. This is at best a demonstration. A device driver could very well just call memory-hotplug directly, or its memory could be brought up as a private node via a boot paremeter (which I have sculpted for v7). The former is preferred, but there's a bit of a chicken/egg scenario for bootstrapping. Most of these UAPI extensions are going to be consolidated into a debugfs interface for testing purposes only in v7. I've been working on aggressive Linux Test Project test expansion to ensure there is no UAPI regressions. ~Gregory