linux-kernel - [PATCH v4 2/3] mm: numa_emu: add document for NUMA emulation

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Message-ID: <20260113081453.8293-3-akinobu.mita@gmail.com>
Date: Tue, 13 Jan 2026 17:14:52 +0900
From: Akinobu Mita <akinobu.mita@...il.com>
To: akinobu.mita@...il.com
Cc: linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
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Subject: [PATCH v4 2/3] mm: numa_emu: add document for NUMA emulation

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 <akinobu.mita@...il.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
---
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