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

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

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> Sent: Thursday, July 30, 2015 6:07 PM
> To: Hao, Xudong
> Cc: Wei Liu; xen-devel@xxxxxxxxxxxxx; Wu, Feng; George Dunlap
> Subject: Re: [Xen-devel] HVM guest max memory allocation
> 
> On Thu, Jul 30, 2015 at 06:21:06AM +0000, Hao, Xudong wrote:
> > > -----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?
> 
> That would be hard I think, because when you have different features
> enabled, Xen allocates different structures to keep track of guest
> state.
> 

I think so, thanks Wei.

> It is like a OS keeping track of the state of a process. It's hard to
> tell in Linux how many kernel objects are allocated for a particular
> process, no? It's also hard to tell how many tricks (which consumes
> memory) Linux has done to make things run fast.
> 
> The closely thing I can think of is the debug key H and m. With those you
> know how much actual memory is used. And, *if* Xen almost allocates all
> structures up front you can have a relatively close approximation of
> memory consumption.
> 
> George (CC'ed) might have some more ideas.
> 
> Wei.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel