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Subject[8/8, v5] NUMA Hotplug Emulator: documentation
From: Shaohui Zheng <>

add a text file Documentation/x86/x86_64/numa_hotplug_emulator.txt
to explain the usage for the hotplug emulator.

Reviewed-By: Randy Dunlap <>
Signed-off-by: Haicheng Li <>
Signed-off-by: Shaohui Zheng <>
Index: linux-hpe4/Documentation/x86/x86_64/numa_hotplug_emulator.txt
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-hpe4/Documentation/x86/x86_64/numa_hotplug_emulator.txt 2010-11-29 16:07:34.439066001 +0800
@@ -0,0 +1,103 @@
+NUMA Hotplug Emulator for x86_64
+NUMA hotplug emulator is able to emulate NUMA Node Hotplug
+thru a pure software way. It intends to help people easily debug
+and test node/CPU/memory hotplug related stuff on a
+none-NUMA-hotplug-support machine, even a UMA machine and virtual
+1) Node hotplug emulation:
+Adds a numa=possible=<N> command line option to set an additional N nodes
+as being possible for memory hotplug. This set of possible nodes
+controls nr_node_ids and the sizes of several dynamically allocated node
+This allows memory hotplug to create new nodes for newly added memory
+rather than binding it to existing nodes.
+For emulation on x86, it would be possible to set aside memory for hotplugged
+nodes (say, anything above 2G) and to add an additional four nodes as being
+possible on boot with
+ mem=2G numa=possible=4
+and then creating a new 128M node at runtime:
+ # echo 128M@0x80000000 > /sys/kernel/debug/node/add_node
+ On node 1 totalpages: 0
+ init_memory_mapping: 0000000080000000-0000000088000000
+ 0080000000 - 0088000000 page 2M
+Once the new node has been added, its memory can be onlined. If this
+memory represents memory section 16, for example:
+ # echo online > /sys/devices/system/memory/memory16/state
+ Built 2 zonelists in Node order, mobility grouping on. Total pages: 514846
+ Policy zone: Normal
+ [ The memory section(s) mapped to a particular node are visible via
+ /sys/devices/system/node/node1, in this example. ]
+2) CPU hotplug emulation:
+The emulator reserve CPUs throu grub parameter, the reserved CPUs can be
+hot-add/hot-remove in software method, it emulates the process of physical
+cpu hotplug.
+When hotplugging a CPU with emulator, we are using a logical CPU to emulate the CPU
+socket hotplug process. For the CPU supported SMT, some logical CPUs are in the
+same socket, but it may located in different NUMA node after we have emulator.
+We put the logical CPU into a fake CPU socket, and assign it a unique
+phys_proc_id. For the fake socket, we put one logical CPU in only.
+ - to hide CPUs
+ - Using boot option "maxcpus=N" hide CPUs
+ N is the number of CPUs to initialize; the reset will be hidden.
+ - Using boot option "cpu_hpe=on" to enable CPU hotplug emulation
+ when cpu_hpe is enabled, the rest CPUs will not be initialized
+ - to hot-add CPU to node
+ $ echo nid > cpu/probe
+ - to hot-remove CPU
+ $ echo nid > cpu/release
+3) Memory hotplug emulation:
+The emulator reserves memory before OS boots, the reserved memory region is
+removed from e820 table, and they can be hot-added via the probe interface.
+this interface was extended to support adding memory to the specified node. It
+maintains backwards compatibility.
+The difficulty of Memory Release is well-known, we have no plan for it until now.
+ - reserve memory thru a kernel boot paramter
+ mem=1024m
+ - add a memory section to node 3
+ $ echo 0x40000000,3 > memory/probe
+ OR
+ $ echo 1024m,3 > memory/probe
+ OR
+ $ echo "physical_address=0x40000000 numa_node=3" > memory/probe
+4) Script for hotplug testing
+These scripts provides convenience when we hot-add memory/cpu in batch.
+- Online all memory sections:
+for m in /sys/devices/system/memory/memory*;
+ echo online > $m/state;
+- CPU Online:
+for c in /sys/devices/system/cpu/cpu*;
+ echo 1 > $c/online;
+- Haicheng Li <>
+- Shaohui Zheng <>
+ Nov 2010
Thanks & Regards,

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