# 八：如何在线添加/移除虚拟机的内存
如果应用／DB需要更多内存，则需要调整VM的内存限制。KVM支持在配置了VM最大内存限制范围内动态调整内存。VM配置包涵2部分：
* 最大限制
* 当前分配
任何时候，你不能使用`virsh setmem`命令动态分配超过最大内存的量，而是需要关闭guest来调整VM最大内存限制。
检查VM的内存限制和当前分配内存
```
[root@UA-HA ~]# virsh dumpxml UAKVM2|grep -i memo
2621440
1048576
```
以上配置
分配给VM的内存：1GB(Current Memory Unit) 最大内存限制：2.5GB(Memory Unit)
注意：VM虚拟机只能看见"currentMemory Unit"值
## 调整运行中VM的RAM/Memory
* 登陆到KVM虚拟机中查看分配和使用的内存
```
[root@UA-KVM1 ~]# free -m
total used free shared buff/cache available
Mem: 1001 78 780 6 141 787
Swap: 411 0 411
[root@UA-KVM1 ~]#
```
* 使用root登陆到KVM主机
* 列出KVM虚拟机查看domain配置
```
[root@UA-HA ~]# virsh dominfo UAKVM2
Id: 34
Name: UAKVM2
UUID: 6013be3b-08f9-4827-83fb-390bd5a86de6
OS Type: hvm
State: running
CPU(s): 1
CPU time: 318.4s
Max memory: 2621440 KiB
Used memory: 1048576 KiB
Persistent: yes
Autostart: disable
Managed save: no
Security model: selinux
Security DOI: 0
Security label: system_u:system_r:svirt_t:s0:c361,c741 (permissive)
[root@UA-HA ~]#
```
* 缩减内存到 512M
```
[root@UA-HA ~]# virsh setmem UAKVM2 512M
[root@UA-HA ~]# virsh dominfo UAKVM2
Id: 34
Name: UAKVM2
UUID: 6013be3b-08f9-4827-83fb-390bd5a86de6
OS Type: hvm
State: running
CPU(s): 1
CPU time: 320.2s
Max memory: 2621440 KiB
Used memory: 524288 KiB
Persistent: yes
Autostart: disable
Managed save: no
Security model: selinux
Security DOI: 0
Security label: system_u:system_r:svirt_t:s0:c361,c741 (permissive)
[root@UA-HA ~]#
```
检查 KVM guest
```
[root@UA-KVM1 ~]# free -m
total used free shared buff/cache available
Mem: 479 78 259 6 141 266
Swap: 411 0 411
[root@UA-KVM1 ~]#
```
也可以增加虚拟机内存
```
[root@UA-HA ~]# virsh setmem UAKVM2 2048M
[root@UA-HA ~]# virsh dominfo UAKVM2
Id: 36
Name: UAKVM2
UUID: 6013be3b-08f9-4827-83fb-390bd5a86de6
OS Type: hvm
State: running
CPU(s): 1
CPU time: 56.0s
Max memory: 2621440 KiB
Used memory: 2097152 KiB
Persistent: yes
Autostart: disable
Managed save: no
Security model: selinux
Security DOI: 0
Security label: system_u:system_r:svirt_t:s0:c305,c827 (permissive)
[root@UA-HA ~]#
```
* 需要编辑VM配置来避免VM关闭和启动配置丢失
```
[root@UA-HA ~]# virsh setmem UAKVM2 2048M --config
```
或者
```
[root@UA-HA ~]# virsh edit UAKVM2
```
## 增加VM的内存限制
如果尝试配置超过VM内存限制的内存分配，则会遇到以下报错：`error: invalid argument: cannot set memory higher than max memory`。这不是BUG，而是因为`virsh setmem`不能分配超过内存限制的使用内存。
* 要增加内存限制，必须首先停止VM
```
[root@UA-HA ~]# virsh shutdown UAKVM2
[root@UA-HA ~]# virsh list --all
Id Name State
----------------------------------------------------
- UAKVM2 shut off
[root@UA-HA ~]#
```
* 增加VM内存限制
```
[root@UA-HA ~]# virsh setmaxmem UAKVM2 4G
```
* 启动VM
```
[root@UA-HA ~]# virsh start UAKVM2
[root@UA-HA ~]# virsh list --all
Id Name State
----------------------------------------------------
37 UAKVM2 running
[root@UA-HA ~]#
```
* 登陆到guest虚拟机中检查当前内存大小
```
[root@UA-KVM1 ~]# free -m
total used free shared buff/cache available
Mem: 719 90 502 8 126 473
Swap: 411 0 411
[root@UA-KVM1 ~]#
```
* 此时可以将分配内存调整到3G
```
[root@UA-HA ~]# virsh setmem UAKVM2 3G
[root@UA-HA ~]#
```
* 然后在guest中检查内存分配
```
[root@UA-KVM1 ~]# free -m
total used free shared buff/cache available
Mem: 2767 90 2544 8 132 2518
Swap: 411 0 411
[root@UA-KVM1 ~]#
```
* 更新VM配置（这样重启后不会丢失配置）
```
[root@UA-HA ~]# virsh setmem UAKVM2 3G --config
```
或者直接编辑VM XML文件的currentMemory值到3GB
```
[root@UA-HA ~]# virsh edit UAKVM2
```
```
4194304
3145728
```
至此已经成功分配了KVM虚拟机内核和调整了VM的最大内存限制。
## 系列教程编译
本系列教程根据 [UnixArena Linux KVM](http://www.unixarena.com/category/redhat-linux/linux-kvm) 系列教程编译，共分以下文章：
* [一：基于内核的虚拟机（KVM）概览](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/kernel_based_virtual_machine_kvm_overview/README.md)
* [二：Redhat企业Linux安装KVM](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/redhat_enterprise_linux_kvm_installation/README.md)
* [三：RHEL 7.2 配置KVM主机](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/rhel_7_2_configuring_kvm_hosts/README.md)
* [四：使用命令行启动第一个KVM实例](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/launch_the_first_kvm_instance_using_cli/README.md)
* [五：使用Virt-Manger(VMM)部署KVM实例](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/deploy_kvm_instance_using_virt_manger_vmm_gui/README.md)
* [六：如何克隆一个KVM虚拟机并重置该虚拟机](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/how_to_clone_a_kvm_virtual_machines_and_reset_the_vm/README.md)
* [七：如何在线添加/更改虚拟磁盘](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/how_to_add_resize_virtual_disk_on_fly/README.md)
* [八：如何在线添加/移除虚拟机的内存](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/how_to_add_remove_memory_to_guest_on_fly/README.md)
* [九：如何在线添加/移除虚拟机的vCPU](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/how_to_add_remove_vcpu_to_guest_on_fly/README.md)
* [十：更改libvirt虚拟机镜像存储路径](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/change_libvirt_vm_image_store_path/README.md)
* [十一：实现Linux KVM在线迁移](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/perform_live_migration_on_linux_kvm/README.md)
* [十二：RHEL7 Pacemaker - 配置高可用KVM虚拟机](https://github.com/huataihuang/cloud-atlas-draft/tree/6f3204fffc11cf006abd394631e2598d98b415c3/virtual/kvm/startup/rhel_7_pacemaker_configuring_ha_kvm_guest/README.md)
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