Re: [Xen-devel] HVM guest max memory allocation

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Jul 24, 2015 at 06:04:53AM +0000, Hao, Xudong wrote:
> Hi, 
> 
> When creating HVM guest(no balloon driver), what's the max memory we
> could set? We can get the current system free memory by "xl info", but
> when configure the free memory to a HVM guest, it fail to boot up.
> Does Xen allocate additional memory when do VM creating? How many the
> additional memory burning per HVM by Xen?

Historically libxl will add some slack on top of the memory you ask for.

The extra memory for HVM at the moment is 2 MB. That means if you ask for
1024 MB for guest, libxl bumps that to 1026.

You also need to spare some memory for Xen itself to allocate internal
structures. I would say try to reduce the number for a few MBs.

Wei.

> 
> ==============================
> # xl cr xlexample_win.hvm 
> Parsing config from xlexample_win.hvm
> libxl: notice: libxl_numa.c:499:libxl__get_numa_candidate: NUMA placement 
> failed, performance might be affected
> xc: error: Could not allocate memory for HVM guest as we cannot claim memory! 
> (12 = Cannot allocate memory): Internal error
> libxl: error: libxl_dom.c:979:libxl__build_hvm: hvm building failed
> libxl: error: libxl_create.c:1163:domcreate_rebuild_done: cannot (re-)build 
> domain: -3
> libxl: error: libxl_dm.c:1667:kill_device_model: unable to find device model 
> pid in /local/domain/236/image/device-model-pid
> libxl: error: libxl.c:1620:libxl__destroy_domid: libxl__destroy_device_model 
> failed for 236
> 
> 
> ==============================
> # xl info
> ...
> free_memory            : 28036
> ...
> 
> ==============================
> xlexample_win.hvm configure file:
> builder = "hvm"
> name = "win8"
> memory = 28036
> vcpus=2
> vif = [ 'type=ioemu, mac=00:15:17:19:2D:35, bridge=xenbr0' ]
> disk = [ '/root/longtao/win8.qcow,qcow2,xvda,rw']
> device_model_override = '/usr/local/lib/xen/bin/qemu-system-i386'
> device_model_version = 'qemu-xen'
> sdl=0
> vnc=1
> stdvga=1
> hap=1
> usb=1
> usbdevice='tablet'
> hpet=1
> 
> 
> Best Regards,
> Xudong
> 
> 
> 
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