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