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https://bugzilla.redhat.com/show_bug.cgi?id=1198645 Once upon a time, there was a little domain. And the domain was pinned onto a NUMA node and hasn't fully allocated its memory: <memory unit='KiB'>2355200</memory> <currentMemory unit='KiB'>1048576</currentMemory> <numatune> <memory mode='strict' nodeset='0'/> </numatune> Oh little me, said the domain, what will I do with so little memory. If I only had a few megabytes more. But the old admin noticed the whimpering, barely audible to untrained human ear. And good admin he was, he gave the domain yet more memory. But the old NUMA topology witch forbade to allocate more memory on the node zero. So he decided to allocate it on a different node: virsh # numatune little_domain --nodeset 0-1 virsh # setmem little_domain 2355200 The little domain was happy. For a while. Until bad, sharp teeth shaped creature came. Every process in the system was afraid of him. The OOM Killer they called him. Oh no, he's after the little domain. There's no escape. Do you kids know why? Because when the little domain was born, her father, Libvirt, called numa_set_membind(). So even if the admin allowed her to allocate memory from other nodes in the cgroups, the membind() forbid it. So what's the lesson? Libvirt should rely on cgroups, whenever possible and use numa_set_membind() as the last ditch effort. Signed-off-by: Michal Privoznik <mprivozn@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>