79 lines
3.2 KiB
ReStructuredText
79 lines
3.2 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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=====================
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Fake NUMA For CPUSets
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=====================
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:Author: David Rientjes <rientjes@cs.washington.edu>
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Using numa=fake and CPUSets for Resource Management
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This document describes how the numa=fake x86_64 command-line option can be used
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in conjunction with cpusets for coarse memory management. Using this feature,
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you can create fake NUMA nodes that represent contiguous chunks of memory and
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assign them to cpusets and their attached tasks. This is a way of limiting the
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amount of system memory that are available to a certain class of tasks.
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For more information on the features of cpusets, see
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Documentation/cgroup-v1/cpusets.txt.
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There are a number of different configurations you can use for your needs. For
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more information on the numa=fake command line option and its various ways of
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configuring fake nodes, see Documentation/x86/x86_64/boot-options.txt.
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For the purposes of this introduction, we'll assume a very primitive NUMA
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emulation setup of "numa=fake=4*512,". This will split our system memory into
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four equal chunks of 512M each that we can now use to assign to cpusets. As
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you become more familiar with using this combination for resource control,
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you'll determine a better setup to minimize the number of nodes you have to deal
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with.
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A machine may be split as follows with "numa=fake=4*512," as reported by dmesg::
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Faking node 0 at 0000000000000000-0000000020000000 (512MB)
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Faking node 1 at 0000000020000000-0000000040000000 (512MB)
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Faking node 2 at 0000000040000000-0000000060000000 (512MB)
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Faking node 3 at 0000000060000000-0000000080000000 (512MB)
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...
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On node 0 totalpages: 130975
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On node 1 totalpages: 131072
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On node 2 totalpages: 131072
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On node 3 totalpages: 131072
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Now following the instructions for mounting the cpusets filesystem from
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Documentation/cgroup-v1/cpusets.txt, you can assign fake nodes (i.e. contiguous memory
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address spaces) to individual cpusets::
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[root@xroads /]# mkdir exampleset
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[root@xroads /]# mount -t cpuset none exampleset
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[root@xroads /]# mkdir exampleset/ddset
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[root@xroads /]# cd exampleset/ddset
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[root@xroads /exampleset/ddset]# echo 0-1 > cpus
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[root@xroads /exampleset/ddset]# echo 0-1 > mems
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Now this cpuset, 'ddset', will only allowed access to fake nodes 0 and 1 for
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memory allocations (1G).
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You can now assign tasks to these cpusets to limit the memory resources
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available to them according to the fake nodes assigned as mems::
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[root@xroads /exampleset/ddset]# echo $$ > tasks
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[root@xroads /exampleset/ddset]# dd if=/dev/zero of=tmp bs=1024 count=1G
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[1] 13425
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Notice the difference between the system memory usage as reported by
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/proc/meminfo between the restricted cpuset case above and the unrestricted
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case (i.e. running the same 'dd' command without assigning it to a fake NUMA
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cpuset):
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======== ============ ==========
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Name Unrestricted Restricted
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======== ============ ==========
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MemTotal 3091900 kB 3091900 kB
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MemFree 42113 kB 1513236 kB
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======== ============ ==========
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This allows for coarse memory management for the tasks you assign to particular
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cpusets. Since cpusets can form a hierarchy, you can create some pretty
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interesting combinations of use-cases for various classes of tasks for your
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memory management needs.
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