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51 lines
2.1 KiB
Plaintext
51 lines
2.1 KiB
Plaintext
// Module included in the following assemblies:
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//
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// * virt/virtual_machines/advanced_vm_management/virt-managing-guest-memory.adoc
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:_content-type: PROCEDURE
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[id="virt-configuring-guest-memory-overcommitment_{context}"]
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= Configuring guest memory overcommitment
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If your virtual workload requires more memory than available, you can use memory overcommitment to allocate all or most of the host's memory to your virtual machine instances (VMIs). Enabling memory overcommitment means that you can maximize resources that are normally reserved for the host.
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For example, if the host has 32 GB RAM, you can use memory overcommitment to fit 8 virtual machines (VMs) with 4 GB RAM each. This allocation works under the assumption that the virtual machines will not use all of their memory at the same time.
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[IMPORTANT]
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====
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Memory overcommitment increases the potential for virtual machine processes to be killed due to memory pressure (OOM killed).
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The potential for a VM to be OOM killed varies based on your specific configuration, node memory, available swap space, virtual machine memory consumption, the use of kernel same-page merging (KSM), and other factors.
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====
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.Procedure
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. To explicitly tell the virtual machine instance that it has more memory available than was requested from the cluster, edit the virtual machine configuration file and set `spec.domain.memory.guest` to a higher value than `spec.domain.resources.requests.memory`. This process is called memory overcommitment.
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+
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In this example, `1024M` is requested from the cluster, but the virtual machine instance is told that it has `2048M` available. As long as there is enough free memory available on the node, the virtual machine instance will consume up to 2048M.
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+
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[source,yaml]
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----
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kind: VirtualMachine
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spec:
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template:
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domain:
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resources:
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requests:
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memory: 1024M
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memory:
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guest: 2048M
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----
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[NOTE]
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====
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The same eviction rules as those for pods apply to the virtual machine instance if the node is under memory pressure.
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====
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. Create the virtual machine:
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[source,terminal]
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----
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$ oc create -f <file_name>.yaml
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---- |