This post illustrates the steps about how to increase KVM guest memory. If the current KVM guest memory is the same as the memory limit, you can to increase the memory offline following the below steps:

1. Check the current memory status of the KVM guest:

[[email protected]]# virsh dumpxml kvm-guest | grep -i memory
<memory unit="KiB">8392704</memory>                   ### the maximum amount of memory that can be allocated to the VM
<currentMemory unit="KiB">8392704</currentMemory>     ### current Guest VM memory
[[email protected]]# virsh dominfo kvm-guest
Id: 12
Name: kvm-guest
UUID: 8f6fc48c-a6f4-429d-b77e-88a4b8d3d961
OS Type: hvm
State: running
CPU(s): 4
CPU time: 429.8s
Max memory: 8392704 KiB
Used memory: 8392704 KiB
Persistent: yes
Autostart: disable
Managed save: no
Security model: selinux
Security DOI: 0
Security label: system_u:system_r:svirt_t:s0:c339,c981 (enforcing)
[[email protected]]# virsh dominfo kvm-guest
Id: 12
Name: kvm-guest
UUID: 8f6fc48c-a6f4-429d-b77e-88a4b8d3d961
OS Type: hvm
State: running
CPU(s): 4
CPU time: 429.8s
Max memory: 8392704 KiB
Used memory: 8392704 KiB
Persistent: yes
Autostart: disable
Managed save: no
Security model: selinux
Security DOI: 0
Security label: system_u:system_r:svirt_t:s0:c339,c981 (enforcing)

2. Shutdown the Guest VM:

[[email protected]]# virsh list
Id Name State
----------------------------------------------------
12 kvm-guest running
[[email protected]]# virsh destroy kvm-guest
Domain kvm-guest destroyed
[[email protected]]# virsh list
Id Name State
----------------------------------------------------

3. Update the memory:

For example:

[[email protected]]# virsh edit kvm-guest
Domain kvm-guest XML configuration edited.

From:

<memory unit="KiB">8392704</memory>
<currentMemory unit="KiB">8392704</currentMemory>

To:

<memory unit="KiB">16777216</memory>
<currentMemory unit="KiB">16777216</currentMemory>

4. Boot the Guest VM:

[[email protected]]# virsh start kvm-guest
Domain kvm-guest started

5. Check if the memory has been increased:

From KVM host:

[[email protected]]# virsh dominfo kvm-guest
...
Name: kvm-guest
UUID: 8f6fc48c-a6f4-429d-b77e-88a4b8d3d961
Max memory: 16777216 KiB
Used memory: 16777216 KiB
...
[[email protected]]# virsh dumpxml kvm-guest |grep -i memo
<memory unit="KiB">16777216</memory>
<currentMemory unit="KiB">16777216</currentMemory>

From guest:

[[email protected] ~]# free -g
total used free shared buffers cached
Mem: 15 0 15 0 0 0
-/+ buffers/cache: 0 15
Swap: 3 0 3
How to Increase KVM Guest vCPU Resources