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

["Hao, Xudong" <xudong.hao@xxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> Sent: Friday, July 24, 2015 3:29 PM
> To: Hao, Xudong
> Cc: xen-devel@xxxxxxxxxxxxx; Wu, Feng; wei.liu2@xxxxxxxxxx
> Subject: Re: [Xen-devel] HVM guest max memory allocation
> 
> 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.
> 

Wei, 

Thanks for your quick response, sorry I reply later as this mail missed by my 
outlook... 
OK, 2MB for tool stack per HVM.

> 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.
> 

Does different HVM configure get different memory consume of Xen itself? Can we 
calculate an accurate boundary memory for HVM?

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