Re: [Xen-devel] xm mem-set for HVM Domain

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Sun, 26 Sep 2010, Andrew Lyon wrote:
> On Sat, Sep 25, 2010 at 7:41 AM, cendhu <cendhu@xxxxxxxxx> wrote:
> > HI,
> > ???? ?? I have an ubuntu 10.04 with xen kernel 2.6.32.11 as Dom0. xm mem-set
> > does not seem to have any effect on the HVM domains.
> > Xen Version : 4.0.1
> > HVM : Ubuntu 10.04
> > I have allocated 512MB to dom0 and 2048MB to HVM.
> > $xm list
> > Name ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ??ID ?? Mem 
> > VCPUs ?? ?? ??State
> > Time(s)
> > Domain-0 ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? 0 ?? 512 ?? 
> > ?? 1 ?? ?? r-----
> > ??358.8
> > lucid_hvm ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ??1 ??2048 ?? 
> > ?? 1 ?? ?? -b----
> > ??5.9
> > The output of free command in the HVM
> > $free -m
> > ???? ?? ?? ?? ?? ?? total ?? ?? ?? used ?? ?? ?? free ?? ?? shared ?? 
> > ??buffers ?? ?? cached
> > Mem: ?? ?? ?? ?? ??2012 ?? ?? ?? ??153 ?? ?? ?? 1858 ?? ?? ?? ?? ??0 ?? ?? 
> > ?? ?? 24 ?? ?? ?? ?? 74
> > -/+ buffers/cache: ?? ?? ?? ?? 55 ?? ?? ?? 1957
> > Swap: ?? ?? ?? ?? ??228 ?? ?? ?? ?? ??0 ?? ?? ?? ??228
> > Using xm mem-set, i tried to allocate 1024MB to the HVM
> > $xm mem-set lucid_hvm 1024
> > $xm list
> > Name ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ??ID ?? Mem 
> > VCPUs ?? ?? ??State
> > Time(s)
> > Domain-0 ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? 0 ?? 512 ?? 
> > ?? 1 ?? ?? r-----
> > ??363.1
> > lucid_hvm ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ??1 ??1024 ?? 
> > ?? 1 ?? ?? -b----
> > ??7.2
> > ??xm list shows that only 1024MB of physical memory is allocated to the HVM.
> > but, the output of free command in the HVM
> > $ free -m
> > ???? ?? ?? ?? ?? ?? total ?? ?? ?? used ?? ?? ?? free ?? ?? shared ?? 
> > ??buffers ?? ?? cached
> > Mem: ?? ?? ?? ?? ??2012 ?? ?? ?? ??154 ?? ?? ?? 1858 ?? ?? ?? ?? ??0 ?? ?? 
> > ?? ?? 24 ?? ?? ?? ?? 74
> > -/+ buffers/cache: ?? ?? ?? ?? 55 ?? ?? ?? 1957
> > Swap: ?? ?? ?? ?? ??228 ?? ?? ?? ?? ??0 ?? ?? ?? ??228
> > No change in allocated memory. But, xm mem-set works perfectly with paraVM.
> > I migrated HVM to another machine and checked the amount of data transferred
> > which is 2048MB.
> >
> >
> >
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >
> >
> 
> I noticed the same thing a few days ago, I think that the mem-set
> command should only work if there is a balloon driver running inside
> the hvm domU which can "take away" the memory from the OS and return
> it back to Xen, I don't understand why the command succeeds without a
> balloon driver but your tests seem to show that it doesn't actually
> work as migration moves the original amount of memory.
> 
> I will investigate this further tomorrow.
> 
 
Yes, xm/xl mem-set only has an effect if there is a balloon driver
running in the guest.
The command succeeds anyway because all mem-set does is writing a value
to xenstore, nothing is guaranteed to happen after that.
However if you install a pv on hvm kernel in the guest, you should see
the memory being given back to xen, you can download the latest pv on
hvm branch from here:

git://xenbits.xen.org/people/sstabellini/linux-pvhvm.git 2.6.35-rc5-pvhvm-v7

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel