今天遇到一个问题，使用virsh edit <vm>命令调整了虚拟机的内存大小后， 保存退出，再次使用virsh edit <vm>命令查看虚拟机配置文件，发现内存又改回了先前的值。
我的原始配置文件是：
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<domain type='kvm'> <name>vm21</name> <uuid>81a67c14-ae40-4c86-8b1a-0b19dfb4575b</uuid> <memory unit='KiB'>2029144</memory> <currentMemory unit='KiB'>2029144</currentMemory> <memoryBacking> <hugepages> <page size='2048' unit='KiB'/> </hugepages> <access mode='shared'/> </memoryBacking> <vcpu placement='static' cpuset='8,10,12,14'>4</vcpu> <cputune> <vcpupin vcpu='0' cpuset='8'/> <vcpupin vcpu='1' cpuset='10'/> <vcpupin vcpu='2' cpuset='12'/> <vcpupin vcpu='3' cpuset='14'/> </cputune> <resource> <partition>/machine</partition> </resource> <os> <type arch='x86_64' machine='pc-i440fx-2.2'>hvm</type> <boot dev='hd'/> </os> <features> <acpi/> <apic/> </features> <cpu mode='host-passthrough' check='none'> <topology sockets='1' cores='4' threads='1'/> <numa> <cell id='0' cpus='0-3' memory='4194304' unit='KiB' memAccess='shared'/> </numa> </cpu> <clock offset='utc'> <timer name='rtc' tickpolicy='catchup'/> <timer name='pit' tickpolicy='delay'/> <timer name='hpet' present='no'/> </clock> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>destroy</on_crash> <pm> <suspend-to-mem enabled='no'/> <suspend-to-disk enabled='no'/> </pm> <devices> <emulator>/usr/local/bin/qemu-system-x86_64</emulator> <disk type='file' device='disk'> <driver name='qemu' type='qcow2'/> <source file='/data/vms/vm21.img'/> <target dev='vda' bus='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/> </disk> <disk type='file' device='cdrom'> <driver name='qemu' type='raw'/> <target dev='hda' bus='ide'/> <readonly/> <address type='drive' controller='0' bus='0' target='0' unit='0'/> </disk> <controller type='usb' index='0' model='ich9-ehci1'> <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x7'/> </controller> <controller type='usb' index='0' model='ich9-uhci1'> <master startport='0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0' multifunction='on'/> </controller> <controller type='usb' index='0' model='ich9-uhci2'> <master startport='2'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x1'/> </controller> <controller type='usb' index='0' model='ich9-uhci3'> <master startport='4'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x2'/> </controller> <controller type='pci' index='0' model='pci-root'/> <controller type='ide' index='0'> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/> </controller> <controller type='virtio-serial' index='0'> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/> </controller> <interface type='network'> <mac address='52:54:00:77:1d:e0'/> <source network='default'/> <model type='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/> </interface> <interface type='vhostuser'> <mac address='52:54:00:00:24:6b'/> <source type='unix' path='/tmp/vm21.sock' mode='server'/> <model type='virtio'/> <driver name='vhost' queues='4' rx_queue_size='1024' tx_queue_size='1024'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x09' function='0x0'/> </interface> <serial type='pty'> <target type='isa-serial' port='0'> <model name='isa-serial'/> </target> </serial> <console type='pty'> <target type='serial' port='0'/> </console> <channel type='unix'> <target type='virtio' name='org.qemu.guest_agent.0'/> <address type='virtio-serial' controller='0' bus='0' port='1'/> </channel> <input type='tablet' bus='usb'> <address type='usb' bus='0' port='1'/> </input> <input type='mouse' bus='ps2'/> <input type='keyboard' bus='ps2'/> <graphics type='vnc' port='-1' autoport='yes' listen='0.0.0.0'> <listen type='address' address='0.0.0.0'/> </graphics> <video> <model type='cirrus' vram='16384' heads='1' primary='yes'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/> </video> <memballoon model='virtio'> <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/> </memballoon> <rng model='virtio'> <backend model='random'>/dev/urandom</backend> <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/> </rng> </devices> </domain> |
我想把虚拟机内存改为2M，于是找到下面两行：
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<memory unit='KiB'>2029144</memory> <currentMemory unit='KiB'>2029144</currentMemory> |
将其修改为：
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<memory unit='KiB'>4194304</memory> <currentMemory unit='KiB'>4194304</currentMemory> |
保存退出，virsh显示一切OK：
| [root@t620 SourceCode]# virsh edit vm21 Domain vm21 XML configuration edited. |
但是再次查看VM21的XML配置文件，发现这两行又恢复为原值。
经过仔细观察，发现在文档中还有一处配置：
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<cpu mode='host-passthrough' check='none'> <topology sockets='1' cores='4' threads='1'/> <numa> <cell id='0' cpus='0-3' memory='2029144' unit='KiB' memAccess='shared'/> </numa> </cpu> |
同时修改这三处，问题解决。
根因： 虚拟机的XML文件要上下一致。上面定义2G内存，那么在CPU的设置中也需要用完这2G内存。否则，系统会自动恢复成自认为正确的值。
