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xen-devel
Re: [Xen-devel] Xen Hypervisor's memory get roughly less 700MB(even 1400
On Wed, 1 Dec 2010, Jeremy Fitzhardinge wrote:
> On 12/01/2010 12:00 AM, benian wrote:
> >
> > Hi,
> >
> > I am using Xen 4.0.1-6 and fedora2.6.32.23-170.xendom0.fc12.x86_64
> >
> >
> >
> > When I try to set the a fix value for memory on grub
> >
> >
> >
> > For example
> >
> >
> >
> > title Xen_Fedora (2.6.32.23-170.xendom0.fc12.x86_64)
> >
> > root (hd0,0)
> >
> > kernel /xen-4.0.1.gz dom0_mem=5120M
> >
> >
> >
> > I found that when I set dom0_mem<=3GB, the system memory report by
> > “free” “xm list” “xl list” and “xentop” are both approximately conform
> > with the setting in grub.
> >
> > But when dom_mem>=4GB(roughly), the system memory is obviously
> > different from the grub.
> >
>
> Yes, that's expected. The BIOS reserves a chunk of address space
> between 3-4G to map PCI devices into. Since dom0 needs to get access to
> those devices, we free the Xen-supplied memory in that range back to the
> hypervisor. You should see that reflected in the free memory output of
> "xl info".
>
> In recent versions of xen/stable-2.6.32.x you can balloon dom0 back up
> again to its full size with "xl mem-set 0 <size>", but I don't think
> that's implemented in the version you're using.
>
> > “xm list”
> >
> > Name ID Mem VCPUs State Time(s)
> >
> > Domain-0 0 * 4384* 8 r----- 136.8
> >
> >
> >
> >
> >
> >
> >
> > “xl list”
> >
> > Name ID Mem VCPUs State Time(s)
> >
> > Domain-0 0 *3648* 8 r-- 139.8
> >
>
> That's just strange: xl and xm should show the same results here.
I am sure that libxl is doing the right thing; my guess would be that
the difference is due to xend printing max_pages instead of tot_pages.
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