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 1Using numa=fake and CPUSets for Resource Management
 2Written by David Rientjes <>
 4This document describes how the numa=fake x86_64 command-line option can be used
 5in conjunction with cpusets for coarse memory management.  Using this feature,
 6you can create fake NUMA nodes that represent contiguous chunks of memory and
 7assign them to cpusets and their attached tasks.  This is a way of limiting the
 8amount of system memory that are available to a certain class of tasks.
10For more information on the features of cpusets, see
12There are a number of different configurations you can use for your needs.  For
13more information on the numa=fake command line option and its various ways of
14configuring fake nodes, see Documentation/x86/x86_64/boot-options.txt.
16For the purposes of this introduction, we'll assume a very primitive NUMA
17emulation setup of "numa=fake=4*512,".  This will split our system memory into
18four equal chunks of 512M each that we can now use to assign to cpusets.  As
19you become more familiar with using this combination for resource control,
20you'll determine a better setup to minimize the number of nodes you have to deal
23A machine may be split as follows with "numa=fake=4*512," as reported by dmesg:
25	Faking node 0 at 0000000000000000-0000000020000000 (512MB)
26	Faking node 1 at 0000000020000000-0000000040000000 (512MB)
27	Faking node 2 at 0000000040000000-0000000060000000 (512MB)
28	Faking node 3 at 0000000060000000-0000000080000000 (512MB)
29	...
30	On node 0 totalpages: 130975
31	On node 1 totalpages: 131072
32	On node 2 totalpages: 131072
33	On node 3 totalpages: 131072
35Now following the instructions for mounting the cpusets filesystem from
36Documentation/cgroups/cpusets.txt, you can assign fake nodes (i.e. contiguous memory
37address spaces) to individual cpusets:
39	[root@xroads /]# mkdir exampleset
40	[root@xroads /]# mount -t cpuset none exampleset
41	[root@xroads /]# mkdir exampleset/ddset
42	[root@xroads /]# cd exampleset/ddset
43	[root@xroads /exampleset/ddset]# echo 0-1 > cpus
44	[root@xroads /exampleset/ddset]# echo 0-1 > mems
46Now this cpuset, 'ddset', will only allowed access to fake nodes 0 and 1 for
47memory allocations (1G).
49You can now assign tasks to these cpusets to limit the memory resources
50available to them according to the fake nodes assigned as mems:
52	[root@xroads /exampleset/ddset]# echo $$ > tasks
53	[root@xroads /exampleset/ddset]# dd if=/dev/zero of=tmp bs=1024 count=1G
54	[1] 13425
56Notice the difference between the system memory usage as reported by
57/proc/meminfo between the restricted cpuset case above and the unrestricted
58case (i.e. running the same 'dd' command without assigning it to a fake NUMA
60				Unrestricted	Restricted
61	MemTotal:		3091900 kB	3091900 kB
62	MemFree:		  42113 kB	1513236 kB
64This allows for coarse memory management for the tasks you assign to particular
65cpusets.  Since cpusets can form a hierarchy, you can create some pretty
66interesting combinations of use-cases for various classes of tasks for your
67memory management needs.