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When either "cpuset" of <vcpu> is specified, or the "placement" of
<vcpu> is "auto", only setting the cpuset.mems might cause the guest
starting to fail. E.g. ("placement" of both <vcpu> and <numatune> is
"auto"):
1) Related XMLs
<vcpu placement='auto'>4</vcpu>
<numatune>
<memory mode='strict' placement='auto'/>
</numatune>
2) Host NUMA topology
% numactl --hardware
available: 8 nodes (0-7)
node 0 cpus: 0 4 8 12 16 20 24 28
node 0 size: 16374 MB
node 0 free: 11899 MB
node 1 cpus: 32 36 40 44 48 52 56 60
node 1 size: 16384 MB
node 1 free: 15318 MB
node 2 cpus: 2 6 10 14 18 22 26 30
node 2 size: 16384 MB
node 2 free: 15766 MB
node 3 cpus: 34 38 42 46 50 54 58 62
node 3 size: 16384 MB
node 3 free: 15347 MB
node 4 cpus: 3 7 11 15 19 23 27 31
node 4 size: 16384 MB
node 4 free: 15041 MB
node 5 cpus: 35 39 43 47 51 55 59 63
node 5 size: 16384 MB
node 5 free: 15202 MB
node 6 cpus: 1 5 9 13 17 21 25 29
node 6 size: 16384 MB
node 6 free: 15197 MB
node 7 cpus: 33 37 41 45 49 53 57 61
node 7 size: 16368 MB
node 7 free: 15669 MB
4) cpuset.cpus will be set as: (from debug log)
2013-05-09 16:50:17.296+0000: 417: debug : virCgroupSetValueStr:331 :
Set value '/sys/fs/cgroup/cpuset/libvirt/qemu/toy/cpuset.cpus'
to '0-63'
5) The advisory nodeset got from querying numad (from debug log)
2013-05-09 16:50:17.295+0000: 417: debug : qemuProcessStart:3614 :
Nodeset returned from numad: 1
6) cpuset.mems will be set as: (from debug log)
2013-05-09 16:50:17.296+0000: 417: debug : virCgroupSetValueStr:331 :
Set value '/sys/fs/cgroup/cpuset/libvirt/qemu/toy/cpuset.mems'
to '0-7'
I.E, the domain process's memory is restricted on the first NUMA node,
however, it can use all of the CPUs, which will likely cause the domain
process to fail to start because of the kernel fails to allocate
memory with the the memory policy as "strict".
% tail -n 20 /var/log/libvirt/qemu/toy.log
...
2013-05-09 05:53:32.972+0000: 7318: debug : virCommandHandshakeChild:377 :
Handshake with parent is done
char device redirected to /dev/pts/2 (label charserial0)
kvm_init_vcpu failed: Cannot allocate memory
...
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>