qemu-kvm如何mem 热插拔
linux内核已经实现了内存热插的支持，当一个linux系统不管运行在 物理环境 或者虚拟环境时只要宿主能提供内存热插拔机制，linux内核就能相应的增加或者减少内存。 目前已知的VMware已经可以做到内存热插。改变内存容量有两种方式：
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[*]401.1 purpose of memory hotplug
[*]41------------
[*]42Memory Hotplug allows users to increase/decrease the amount of memory.
[*]43Generally, there are two purposes.
[*]44
[*]45(A) For changing the amount of memory.
[*]46 This is to allow a feature like capacity on demand.
[*]47(B) For installing/removing DIMMs or NUMA-nodes physically.
[*]48 This is to exchange DIMMs/NUMA-nodes, reduce power consumption, etc.
[*]
前些天检查maillist时发现已经有人实现了DIMMs 方式更改内存大小。这种方式还没有并入mainline tree。
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[*]https://github.com/vliaskov/seabios/commits/memhp-v3-alt
[*]https://github.com/vliaskov/qemu-kvm/commits/memhp-v3-alt
可以测试下：
1）下载带有 dimm hotplug 功能的qemu-kvm：
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[*]git clone -bmemhp-v3-alt https://github.com/vliaskov/qemu-kvm/commits/memhp-v3-alt
配置编译:
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[*]$./configure --target-list="i386-softmmu x86_64-softmmu i386-linux-user x86_64-linux-user" --enable-kvm
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[*]$make
2）下载linux内核 linux-3.0.1.tar.bz2 做测试：（32bit）
linux memory hotplug 需要内核编译进如下选项：
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[*]- For all memory hotplug
[*] Memory model -> Sparse Memory(CONFIG_SPARSEMEM)
[*]location:
[*]Processor type and features
[*] Memory model (Sparse Memory)--->
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[*] Allow for memory hot-add (CONFIG_MEMORY_HOTPLUG)
[*]location:
[*]Power management and ACPI options
[*] ACPI (Advanced Configuration and Power Interface) Support
[*] Memory Hotplug
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[*]- To enable memory removal, the followings are also necessary
[*] Allow for memory hot remove (CONFIG_MEMORY_HOTREMOVE)
[*] Page Migration (CONFIG_MIGRATION)
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[*]- For ACPI memory hotplug, the followings are also necessary
[*] Memory hotplug (under ACPI Support menu) (CONFIG_ACPI_HOTPLUG_MEMORY)
[*] This option can be kernel module.
[*]
[*]- As a related configuration, if your box has a feature of NUMA-node hotplug
[*]via ACPI, then this option is necessary too.
[*] ACPI0004,PNP0A05 and PNP0A06 Container Driver (under ACPI Support menu)
[*] (CONFIG_ACPI_CONTAINER).
[*] This option can be kernel module too.
配置好之后就可以用make 了。
编译完成后将得到的bzImage文件拷贝出来。
3)制作启动所需固件：
当内存hotplugged之后，内核需要知道新增加上的内存并且制作内存管理表，生成sysfs文件来操作内存。
由于这需要固件的支持，而现有的qemu mainline 中包含的bios并不支持相应的功能，所以需要下载bios来重新编译：
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[*]git clone -b memhp-v3-alt https://github.com/vliaskov/seabios/commits/memhp-v3-alt
创建一个放固件的目录：bios 里面放的固件如下所示：（这些都是编译后qemu目录下的）
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[*].
[*]├── bios.bin
[*]├── keymaps
[*]│ ├── common
[*]│ ├── en-us
[*]│ └── modifiers
[*]├── kvmvapic.bin
[*]├── linuxboot.bin
[*]├── multiboot.bin
[*]├── optionrom
[*]│ ├── kvmvapic.bin
[*]│ ├── linuxboot.bin
[*]│ └── multiboot.bin
[*]├── ppc_rom.bin
[*]├── pxe-e1000.rom
[*]├── sgabios.bin
[*]├── slof.bin
[*]├── spapr-rtas.bin
[*]├── vgabios.bin
[*]├── vgabios-cirrus.bin
[*]├── vgabios-qxl.bin
[*]├── vgabios-stdvga.bin
[*]└── vgabios-vmware.bin
将编译好的固件 ./out/bios.bin替换上面的bios.bin。
4）制作文件系统busybox.img
可参考如下连接：
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[*]http://blog.iyunv.com/gudujianjsk/article/details/7655855
现在测试用的内核文件都得到了，用如下脚本开启测试：
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[*]./../qemu-kvm/i386-softmmu/qemu-system-i386 -enable-kvm -m 512 -kernel bzImage -L ./../bios -append "root=/dev/sda" -dimm id=dimm0,size=512M,node=0,populated=off -boot c -smp 1-hda busybox.img -monitor stdio -k en-us -vnc :2
启动后系统显示如下：
由于编译时配置将 CONFIG_ACPI_HOTPLUG_MEMORY 配置为内核模块了，所以这里需要首先加载一个内核模块：acpi_memhotplug.ko.
所有的sections都在sysfs下有它们的设备信息。每一个section都是在 /sys/devices/system/memory/目录下的内存块的一部分。
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[*]/sys/devices/system/memory/memoryXXX
在这里XXX就是内存ID。
在monitor中动态 增加dimm：
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[*]sae@lx15:/var/dbg/test-dimm/busybox$ sudo ./test-box.sh
[*]QEMU 1.2.50 monitor - type 'help' for more information
[*](qemu) device_add dimm,id=dimm0
此时在虚拟机中可见多了个memory1，其状态是offline：
此时新增加的内存还没有做好使用的准备。为了使用新增加的内存你需要把新增加的内存设置为online 状态
此时用free查看总计的内存数量：
测试完毕。
http://www.mjmwired.net/kernel/Documentation/memory-hotplug.txt
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