# xen动态添加或移除guest内存或CPU
尝试给虚拟机 i-23gst39so 添加内存
```
[admin@r8mo02537.cloud.am5:/home/admin]
$sudo xm list | grep i-23gst39so
i-23gst39so.3048243.311136 1344 8192 4 r----- 1888.2
[admin@r8mo02537.cloud.am5:/home/admin]
$sudo virsh dumpxml i-23gst39so.3048243.311136 | grep -i memo
8388608
8388608
```
> 物理服务器 AY66N 10.154.177.160
检查配置
```
[admin@r8mo02537.cloud.am5:/home/admin]
$sudo virsh dominfo i-23gst39so.3048243.311136
Id: 1336
Name: i-23gst39so.3048243.311136
UUID: cede2fda-78f2-4806-b204-d86883dc37e1
OS Type: hvm
State: running
CPU(s): 4
CPU time: 128431.4s
Max memory: 8392704 kB
Used memory: 8392668 kB
Autostart: disable
```
设置内存
```
sudo virsh setmem i-23gst39so.3048243.311136 16384M
```
但是比较奇怪，但是发现没有生效
```
[admin@r8mo02537.cloud.am5:/home/admin]
$sudo virsh dominfo i-23gst39so.3048243.311136
Id: 1336
Name: i-23gst39so.3048243.311136
UUID: cede2fda-78f2-4806-b204-d86883dc37e1
OS Type: hvm
State: running
CPU(s): 4
CPU time: 129163.6s
Max memory: 8392704 kB
Used memory: 8392668 kB
Autostart: disable
```
原来这个是xen的系统，居然不能使用virsh来调整
改为xm
```
sudo xm mem-set i-23gst39so.3048243.311136 16384
```
但是报错
```
Error: memory_dynamic_max must be less than or equal to memory_static_max
Usage: xm mem-set
Set the current memory usage for a domain.
```
先设置DomU max memory
```
sudo xm mem-max i-23gst39so.3048243.311136 16384
```
然后再设置内存就不再报错
```
sudo xm mem-set i-23gst39so.3048243.311136 16384
```
检查发现显示内存已经扩容
```
$sudo xm list | grep i-23gst39so.3048243.311136
i-23gst39so.3048243.311136 1336 16384 4 r----- 131582.9
```
不过，虚拟机内部`cat /proc/meminfo`依然显示8G
```
[root@emr-header-1 proc]# cat /proc/meminfo
MemTotal: 8058056 kB
MemFree: 312760 kB
Buffers: 43488 kB
Cached: 3431344 kB
SwapCached: 0 kB
Active: 6166360 kB
Inactive: 1295604 kB
Active(anon): 4590644 kB
Inactive(anon): 873464 kB
Active(file): 1575716 kB
Inactive(file): 422140 kB
```
此时使用 `sudo virsh dominfo i-23gst39so.3048243.311136` 可以看到`Used memory` 依然是 8G
```
Id: 1344
Name: i-23gst39so.3048243.311136
UUID: cede2fda-78f2-4806-b204-d86883dc37e1
OS Type: hvm
State: running
CPU(s): 4
CPU time: 2194.3s
Max memory: 16777216 kB
Used memory: 8392668 kB
Autostart: disable
```
参考 [Xen VPS not reflecting the RAM upgrade using xm mem-set](http://serverfault.com/questions/546475/xen-vps-not-reflecting-the-ram-upgrade-using-xm-mem-set)
原来在虚拟机内部需要使用 [Linux Memory Hotplug](http://lhms.sourceforge.net/%20%22Linux%20Memory%20Hotplug) ，这个 [Linux Memory Hotplug](http://lhms.sourceforge.net/%20%22Linux%20Memory%20Hotplug) 提供了访问 `/sys/devices/system/memory` 的sysfs接口，这样可以通过写入 `/sys/devices/system/memory/memory[number]/state` 来激活或关闭模块。
[VMWare KB article](http://kb.vmware.com/selfservice/microsites/search.do?language=en_US\&cmd=displayKC\&externalId=1012764) 提供了设置步骤方法。
检查
```
grep line /sys/devices/system/memory/*/state
```
但是我发现都是`online`状态
```
/sys/devices/system/memory/memory0/state:online
/sys/devices/system/memory/memory10/state:online
...
/sys/devices/system/memory/memory8/state:online
/sys/devices/system/memory/memory9/state:online
```
[Changing a Domain's Memory Size Under Xen](https://blogs.oracle.com/rscott/entry/changing_a_domain_s_memory)
换一台测试虚拟机 houyiecsay-1423698772021.187469.48154 10.175.192.6 ，物理服务器是10.154.173.10
* 先检查虚拟机内存配置显示是512M
```
sudo xm list | grep houyiecsay-1423698772021.187469.48154
```
```
houyiecsay-1423698772021.187469.48154 829 512 1 -b---- 98701.3
```
```
sudo virsh dominfo houyiecsay-1423698772021.187469.48154
```
```
Id: 829
Name: houyiecsay-1423698772021.187469.48154
UUID: 24e3f190-a43f-4d73-a6d5-6b03a14610eb
OS Type: hvm
State: idle
CPU(s): 1
CPU time: 98700.5s
Max memory: 528384 kB
Used memory: 528348 kB
Autostart: disable
```
虚拟机内部检查
```
cat /proc/meminfo
```
```
MemTotal: 500472 kB
MemFree: 12456 kB
Buffers: 137420 kB
Cached: 112464 kB
```
* 设置内存改成1G
```
sudo xm mem-max houyiecsay-1423698772021.187469.48154 1024
sudo xm mem-set houyiecsay-1423698772021.187469.48154 1024
```
* 此时检查虚拟机内存可以看到
```
sudo virsh dominfo houyiecsay-1423698772021.187469.48154
```
显示内存最大1G，但是使用了512M
```
Max memory: 1048576 kB
Used memory: 528348 kB
```
检查了虚拟机内部sysfs接口的`/sys/devices/system/memory/memory*/state`，发现在物理服务器上调整虚拟机的内存都没有变化。究竟如何让虚拟机操作系统能刷新出内存配置的变化？
## 动态调整XEN虚拟机的CPU
在domU配置，你需要设置`maxvcpus`来设置允许的虚拟cpu数量，如果没有设置这个`maxvcpus`，则这个值默认和`vcpus`相等。
```
#vcpus - number of VCPUs to boot the system with.
vcpus = 2;
#maxvcpus - maximum number of VCPUs (total) that can be hot added later.
maxvcpus = 8;
```
> `maxvcpus`需要在domU创建的时候设置，运行状态的vm无法动态修改`maxvcpus`，所以要让虚拟机能够伸缩，建议提前设置好一些余量。
* 动态添加vcpu
```
sudo xm list | grep houyiecsay-1423698772021.187469.48154
```
显示是1个cpu
```
houyiecsay-1423698772021.187469.48154 829 1024 1 -b---- 98714.9
```
* 动态设置vcpu
```
sudo xm vcpu-set houyiecsay-1423698772021.187469.48154 4
```
显示报错
```
Error: Cannot set vcpus greater than max vcpus on running domain
Usage: xm vcpu-set
Set the number of active VCPUs for allowed for the domain.
```
也就是要先修改 `vcpumax`设置。这个设置似乎不能动态调整，要在虚拟机创建时即设置好。
## 参考
* [How to Hot Add/Remove Memory from a Xen Domain](http://backdrift.org/xen-memory-hot-add-and-remove)
* \[]
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