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Tue, 13 Jan 2026 00:15:35 -0800 (PST) From: Akinobu Mita To: akinobu.mita@gmail.com Cc: linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, david@kernel.org, mhocko@kernel.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, bingjiao@google.com, jonathan.cameron@huawei.com, pratyush.brahma@oss.qualcomm.com Subject: [PATCH v4 2/3] mm: numa_emu: add document for NUMA emulation Date: Tue, 13 Jan 2026 17:14:52 +0900 Message-ID: <20260113081453.8293-3-akinobu.mita@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260113081453.8293-1-akinobu.mita@gmail.com> References: <20260113081453.8293-1-akinobu.mita@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: xq1js86huw497o9g4bued6aeiwm5yomp X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 5A35CA000F X-HE-Tag: 1768292137-369784 X-HE-Meta: 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 JuDggxw7 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Add a document with a brief explanation of numa emulation and how to use the newly added "numa_emulation.adistance=" kernel cmdline parameter. Signed-off-by: Akinobu Mita Reviewed-by: Jonathan Cameron --- v4: - typo in abstruct distance value - add information about supported architectures in numa_emulation.rst v2: - added in v2 Documentation/mm/index.rst | 1 + Documentation/mm/numa_emulation.rst | 31 +++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+) create mode 100644 Documentation/mm/numa_emulation.rst diff --git a/Documentation/mm/index.rst b/Documentation/mm/index.rst index 7aa2a8886908..7d628edd6a17 100644 --- a/Documentation/mm/index.rst +++ b/Documentation/mm/index.rst @@ -24,6 +24,7 @@ see the :doc:`admin guide <../admin-guide/mm/index>`. page_cache shmfs oom + numa_emulation Unsorted Documentation ====================== diff --git a/Documentation/mm/numa_emulation.rst b/Documentation/mm/numa_emulation.rst new file mode 100644 index 000000000000..81f15ea68022 --- /dev/null +++ b/Documentation/mm/numa_emulation.rst @@ -0,0 +1,31 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============== +NUMA emulation +============== + +NUMA emulation is currently supported on x86, arm64, and risc-v architectures. +If CONFIG_NUMA_EMU is enabled, you can create fake NUMA nodes with +``numa=fake=`` kernel cmdline option. +See Documentation/admin-guide/kernel-parameters.txt and +Documentation/arch/x86/x86_64/fake-numa-for-cpusets.rst for more information. + + +Multiple Memory Tiers Creation +============================== + +The "numa_emulation.adistance=" kernel cmdline option allows you to set +the abstract distance for each NUMA node. + +For example, you can create two fake nodes, each in a different memory +tier by booting with "numa=fake=2 numa_emulation.adistance=576,704". +Here, the abstract distances of node0 and node1 are set to 576 and 704, +respectively. + +Each memory tier covers an abstract distance chunk size of 128. Thus, +nodes with abstract distances between 512 and 639 are classified into the +same memory tier, and nodes with abstract distances between 640 and 767 +are classified into the next slower memory tier. + +The abstract distance of fake nodes not specified in the parameter will be +the default DRAM abstract distance of 576. -- 2.43.0